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  • 1. Alonso, R.
    et al.
    Florén, Hans Gustav Axel
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Walton, N. A.
    No random transits in CHEOPS observations of HD 1391392023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 680, article id A78Article in journal (Refereed)
    Abstract [en]

    Context. The star HD 139139 (a.k.a. 'the Random Transiter') is a star that exhibited enigmatic transit-like features with no apparent periodicity in K2 data. The shallow depth of the events (similar to 200 ppm - equivalent to transiting objects with radii of similar to 1.5 R-circle plus in front of a Sun-like star) and their non-periodicity constitute a challenge for the photometric follow-up of this star. Aims. The goal of this study is to confirm with independent measurements the presence of shallow, non-periodic transit-like features on this object. Methods. We performed observations with CHEOPS for a total accumulated time of 12.75 days, distributed in visits of roughly 20 h in two observing campaigns in years 2021 and 2022. The precision of the data is sufficient to detect 150 ppm features with durations longer than 1.5 h. We used the duration and times of the events seen in the K2 curve to estimate how many events should have been detected in our campaigns, under the assumption that their behaviour during the CHEOPS observations would be the same as in the K2 data of 2017. Results. We do not detect events with depths larger than 150 ppm in our data set. If the frequency, depth, and duration of the events were the same as in the K2 campaign, we estimate the probability of having missed all events due to our limited observing window would be 4.8%. Conclusions. We suggest three different scenarios to explain our results : 1) Our observing window was not long enough, and the events were missed with the estimated 4.8% probability. 2) The events recorded in the K2 observations were time critical, and the mechanism producing them was either not active in the 2021 and 2022 campaigns or created shallower events under our detectability level. 3) The enigmatic events in the K2 data are the result of an unidentified and infrequent instrumental noise in the original data set or its data treatment.

  • 2. Biver, Nicolas
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Radio observations of Comet 9P/Tempel 1 before and after Deep Impact2007In: Icarus (Supplement), Vol. 191, no 2, p. 494-512Article in journal (Refereed)
  • 3. Biver, Nicolas
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Radio observations of Comet 9P/Tempel 1 before and after Deep Impact2007In: Icarus, Vol. 187, no 1, p. 253-271Article in journal (Refereed)
  • 4. Biver, Nicolas
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Submillimetre observations of comets with Odin: 2001 20052007In: Planetary and Space Science, Vol. 55, no 9, p. 1058-1068Article in journal (Refereed)
    Abstract [en]

    The Odin satellite, launched in February 2001, is equipped with a 1.1-m submillimetre telescope. Odin was used to observe the 557 GHz line of water with high spectral resolution in 12 comets between 2001 and 2005. Line shapes and spatial mapping provide information on the anisotropy of the outgassing and constraints on water excitation, enabling accurate measurements of the water production rate. Five comets were regularly observed over periods of more than one month to monitor the variation of their water outgassing rate with heliocentric distance. Observing campaigns have been generally coordinated with ground-based observations of molecular lines at Nançay, CSO or IRAM 30-m telescopes to obtain molecular abundances relative to water. Thanks to Odin's frequency coverage, it was also possible to detect the H218O 548 GHz line, first in comet 153P/Ikeya Zhang in April 2002 [Lecacheux, A., Biver, N., Crovisier, J. et al., 2003, Observations of water in comets with Odin. Astron. Astrophys. 402, L55 L58.] and then in comets C/2002 T7 (LINEAR), C/2001 Q4 (NEAT) and C/2004 Q2 (Machholz). The 16O/18O isotopic ratio (≈450) is consistent with the terrestrial value. Ammonia has been searched for in three comets through its J=1 0 line at 572 GHz and was tentatively detected in C/2001 Q4 and C/2002 T7. The derived abundances of NH3 relative to water are 0.5% and 0.3%, respectively, similar to values obtained in other comets with different techniques.

  • 5. Bonfanti, A.
    et al.
    Florén, Hans Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Walton, N. A.
    TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, article id L8Article in journal (Refereed)
    Abstract [en]

    Context. TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by ∼2σ.

    Aims. Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope.

    Methods. We fit a skew normal function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo scheme to simultaneously detrend the light curves and the RV time series.

    Results. We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of Mb = 20.4−2.5+2.6 M (∼12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of Rb = 3.490−0.064+0.070 R (∼1.9%). Our mass and radius measurements imply a mean density of ρb = 2.65−0.35+0.37 g cm−3 (∼14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of 0.41−0.20+0.34 M and a thickness of 1.05−0.29+0.30 R.

    Conclusions. Our RV extraction combined with the breakpoint technique has played a key role in the optimal removal of stellar activity from the HARPS time series, enabling us to solve the tension in the planetary mass values published so far for TOI-1055 b.

  • 6.
    Brandeker, Alexis
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans Gustav Axel
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    The HD 93963 A transiting system: A 1.04d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 667, article id A1Article in journal (Refereed)
    Abstract [en]

    We present the discovery of two small planets transiting HD 93963A (TOI-1797), a GOV star (M* = 1.109 ± 0.043MR* = 1.043 ± 0.009 R) in a visual binary system. We combined TESS and CHEOPS space-borne photometry with MuSCAT 2 ground-based photometry, ‘Alopeke and PHARO high-resolution imaging, TRES and FIES reconnaissance spectroscopy, and SOPHIE radial velocity measurements. We validated and spectroscopically confirmed the outer transiting planet HD 93963 A c, a sub-Neptune with an orbital period of Pc ≈ 3.65 d that was reported to be a TESS object of interest (TOI) shortly after the release of Sector 22 data. HD 93963 A c has amass of Mc = 19.2 ± 4.1 M and a radius of Rc = 3.228 ± 0.059 R, implying a mean density of ρc = 3.1 ± 0.7 g cm-3. The inner object, HD 93963 A b, is a validated 1.04 d ultra-short period (USP) transiting super-Earth that we discovered in the TESS light curve and that was not listed as a TOI, owing to the low significance of its signal (TESS signal-to-noise ratio ≈6.7, TESS + CHEOPS combined transit depth Db = 141.5−8.3+8.5 ppm). We intensively monitored the star with CHEOPS by performing nine transit observations to confirm the presence of the inner planet and validate the system. HD 93963 A b is the first small (Rb = 1.35 ± 0.042 R) USP planet discovered and validated by TESS and CHEOPS. Unlike planet c, HD 93963 Ab is not significantly detected in our radial velocities (Mb = 7.8 ± 3.2 M). The two planets are on either side of the radius valley, implying that they could have undergone completely different evolution processes. We also discovered a linear trend in our Doppler measurements, suggesting the possible presence of a long-period outer planet. With a V-band magnitude of 9.2, HD 93963 A is among the brightest stars known to host a USP planet, making it one of the most favourable targets for precise mass measurement via Doppler spectroscopy and an important laboratory to test formation, evolution, and migration models of planetary systems hosting ultra-short period planets.

  • 7. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Friis, M.
    Jackson, M.
    Kamae, T.
    Kataoka, J.
    Kawano, T.
    Kiss, M.
    Mikhalev, V
    Mizuno, T.
    Ohashi, N.
    Stana, T.
    Tajima, H.
    Takahashi, H.
    Uchida, N.
    Pearce, M.
    Accretion geometry of the black-hole binary Cygnus X-1 from X-ray polarimetry2018In: Nature Astronomy, E-ISSN 2397-3366, Vol. 2, no 8, p. 652-655Article in journal (Refereed)
    Abstract [en]

    Black hole binary (BHB) systems comprise a stellar-mass black hole and a closely orbiting companion star. Matter is transferred from the companion to the black hole, forming an accretion disk, corona and jet structures. The resulting release of gravitational energy leads to the emission of X-rays(1). The radiation is affected by special/general relativistic effects, and can serve as a probe for the properties of the black hole and surrounding environment, if the accretion geometry is properly identified. Two competing models describe the disk-corona geometry for the hard spectral state of BHBs, based on spectral and timing measurements(2,3). Measuring the polarization of hard X-rays reflected from the disk allows the geometry to be determined. The extent of the corona differs between the two models, affecting the strength of the relativistic effects (such as enhancement of the polarization fraction and rotation of the polarization angle). Here, we report observational results on the linear polarization of hard X-ray emission (19-181 keV) from a BHB, Cygnus X-1(4), in the hard state. The low polarization fraction, <8.6% (upper limit at a 90% confidence level), and the alignment of the polarization angle with the jet axis show that the dominant emission is not influenced by strong gravity. When considered together with existing spectral and timing data, our result reveals that the accretion corona is either an extended structure, or is located far from the black hole in the hard state of Cygnus X-1.

  • 8. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Friis, M.
    Jackson, M.
    Kamae, T.
    Kataoka, J.
    Kawano, T.
    Kiss, M.
    Mikhalev, V.
    Mizuno, T.
    Ohashi, N.
    Stana, T.
    Tajima, H.
    Takahashi, H.
    Uchida, N.
    Pearce, M.
    Shedding new light on the Crab with polarized X-rays2017In: Scientific Reports, E-ISSN 2045-2322, Vol. 7, article id 7816Article in journal (Refereed)
    Abstract [en]

    Strong magnetic fields, synchrotron emission, and Compton scattering are omnipresent in compact celestial X-ray sources. Emissions in the X-ray energy band are consequently expected to be linearly polarized. X-ray polarimetry provides a unique diagnostic to study the location and fundamental mechanisms behind emission processes. The polarization of emissions from a bright celestial X-ray source, the Crab, is reported here for the first time in the hard X-ray band (similar to 20-160 keV). The Crab is a complex system consisting of a central pulsar, a diffuse pulsar wind nebula, as well as structures in the inner nebula including a jet and torus. Measurements are made by a purpose-built and calibrated polarimeter, PoGO+. The polarization vector is found to be aligned with the spin axis of the pulsar for a polarization fraction, PF = (20.9 +/- 5.0)%. This is higher than that of the optical diffuse nebula, implying a more compact emission site, though not as compact as, e.g., the synchrotron knot. Contrary to measurements at higher energies, no significant temporal evolution of phase-integrated polarisation parameters is observed. The polarization parameters for the pulsar itself are measured for the first time in the X-ray energy band and are consistent with observations at optical wavelengths.

  • 9. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Friis, M.
    Jackson, M.
    Kamae, T.
    Kataoka, J.
    Kawano, T.
    Kiss, M.
    Mikhalev, V.
    Mizuno, T.
    Tajima, H.
    Takahashi, H.
    Uchida, N.
    Pearce, M.
    The PoGO plus view on Crab off-pulse hard X-ray polarization2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 477, no 1, p. l45-L49Article in journal (Refereed)
    Abstract [en]

    The linear polarization fraction (PF) and angle of the hard X-ray emission from the Crab provide unique insight into high-energy radiation mechanisms, complementing the usual imaging, timing, and spectroscopic approaches. Results have recently been presented by two missions operating in partially overlapping energy bands, PoGO+ (18-160 keV) and AstroSat CZTI (100-380 keV). We previously reported PoGO+ results on the polarization parameters integrated across the light curve and for the entire nebula-dominated off-pulse region. We now introduce finer phase binning, in light of the AstroSat CZTI claim that the PF varies across the off-pulse region. Since both missions are operating in a regime where errors on the reconstructed polarization parameters are non-Gaussian, we adopt a Bayesian approach to compare results from each mission. We find no statistically significant variation in off-pulse polarization parameters, neither when considering the mission data separately nor when they are combined. This supports expectations from standard high-energy emission models.

  • 10. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Jackson, M.
    Kamae, T.
    Kawano, T.
    Kiss, M.
    Kole, M.
    Mikhalev, V.
    Moretti, E.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Rydström, S.
    Takahashi, H.
    Iyudin, A.
    Arimoto, M.
    Fukazawa, Y.
    Kataoka, J.
    Kawai, N.
    Mizuno, T.
    Ryde, F.
    Tajima, H.
    Takahashi, T.
    Pearce, M.
    Observation of polarized hard X-ray emission from the Crab by the PoGOLite Pathfinder2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 456, no 1, p. l84-L88Article in journal (Refereed)
    Abstract [en]

    We have measured the linear polarization of hard X-ray emission from the Crab in a previously unexplored energy interval, 20-120 keV. The introduction of two new observational parameters, the polarization fraction and angle stands to disentangle geometrical and physical effects, thereby providing information on the pulsar wind geometry and magnetic field environment. Measurements are conducted using the PoGOLite Pathfinder - a balloon-borne polarimeter. Polarization is determined by measuring the azimuthal Compton scattering angle of incident X-rays in an array of plastic scintillators housed in an anticoincidence well. The polarimetric response has been characterized prior to flight using both polarized and unpolarized calibration sources. We address possible systematic effects through observations of a background field. The measured polarization fraction for the integrated Crab light curve is 18.4(-10.6)(+9.8) per cent, corresponding to an upper limit (99 per cent credibility) of 42.4 per cent, for a polarization angle of (149.2 +/- 16.0)degrees.

  • 11. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Jackson, M.
    Kamae, T.
    Kawano, T.
    Kiss, M.
    Kole, M.
    Mikhalev, V.
    Moretti, E.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Rydström, S.
    Takahashi, H.
    Lind, J.
    Strömberg, J. -E.
    Welin, O.
    Iyudin, A.
    Shifrin, D.
    Pearce, M.
    The design and flight performance of the PoGOLite Pathfinder balloon-borne hard X-ray polarimeter2016In: Experimental astronomy, ISSN 0922-6435, E-ISSN 1572-9508, Vol. 41, no 1, p. 17-41Article in journal (Refereed)
    Abstract [en]

    In the 50 years since the advent of X-ray astronomy there have been many scientific advances due to the development of new experimental techniques for detecting and characterising X-rays. Observations of X-ray polarisation have, however, not undergone a similar development. This is a shortcoming since a plethora of open questions related to the nature of X-ray sources could be resolved through measurements of the linear polarisation of emitted X-rays. The PoGOLite Pathfinder is a balloon-borne hard X-ray polarimeter operating in the 25-240 keV energy band from a stabilised observation platform. Polarisation is determined using coincident energy deposits in a segmented array of plastic scintillators surrounded by a BGO anticoincidence system and a polyethylene neutron shield. The PoGOLite Pathfinder was launched from the SSC Esrange Space Centre in July 2013. A near-circumpolar flight was achieved with a duration of approximately two weeks. The flight performance of the Pathfinder design is discussed for the three Crab observations conducted. The signal-to-background ratio for the observations is shown to be 0.25 +/- 0.03 and the Minimum Detectable Polarisation (99 % C.L.) is (28.4 +/- 2.2) %. A strategy for the continuation of the PoGOLite programme is outlined based on experience gained during the 2013 maiden flight.

  • 12. Chauvin, Maxime
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Jackson, Miranda
    Kamae, Tuneyoshi
    Kataoka, Jun
    Kiss, Mózsi
    Mikhalev, Victor
    Mizuno, Tsunefumi
    Takahashi, Hiromitsu
    Uchida, Nagomi
    Pearce, Mark
    PoGO plus polarimetric constraint on the synchrotron jet emission of Cygnus X-12019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 483, no 1, p. l138-L143Article in journal (Refereed)
    Abstract [en]

    We report a polarimetric constraint on the hard X-ray synchrotron jet emission from the Cygnus X-1 black hole binary system. The observational data were obtained using the PoGO+ hard X-ray polarimeter in 2016 July, when Cygnus X-1 was in the hard state. We have previously reported that emission from an extended corona with a low polarization fraction is dominating, and that the polarization angle is perpendicular to the disc surface. In the soft gamma-ray regime, a highly polarized synchrotron jet is reported with INTEGRAL observations. To constrain the polarization fraction and flux of such a jet component in the hard X-ray regime, we now extend analyses through vector calculations in the Stokes QU plane, where the dominant corona emission and the jet component are considered simultaneously. The presence of another emission component with different polarization angle could partly cancel out the net polarization. The 90 per cent upper limit of the polarization fraction for the additional synchrotron jet component is estimated as <10 per cent, <5 per cent, and <5 per cent for polarization angle perpendicular to the disc surface, parallel to the surface, and aligned with the emission reported by INTEGRAL data, respectively. From the 20-180 keV total flux of 2.6 x 10(-8) erg s(-1) cm(-2), the upper limit of the polarized flux is estimated as <3 x 10(-9) erg s(-1) cm(-2).

  • 13. Djupvik, A. A.
    et al.
    André, Philippe
    Bontemps, Sylvain
    Motte, F.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Gålfalk, Magnus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G62006In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 458, no 3, p. 789-803Article in journal (Refereed)
    Abstract [en]

    Aims.The aim of this paper is to characterise the star formation activity in the poorly studied embedded cluster Serpens/G3-G6, located ~45 arcmin (3 pc) to the south of the Serpens Cloud Core, and to determine the luminosity and mass functions of its population of Young Stellar Objects (YSOs).

    Methods: .Multi-wavelength broadband photometry was obtained to sample the near and mid-IR spectral energy distributions to separate YSOs from field stars and classify the YSO evolutionary stage. ISOCAM mapping in the two filters LW2 (5-8.5 μm) and LW3 (12-18 μm) of a 19 arcmin × 16 arcmin field was combined with JHKS data from 2MASS, KS data from Arnica/NOT, and L arcmin data from SIRCA/NOT. Continuum emission at 1.3 mm (IRAM) and 3.6 cm (VLA) was mapped to study the cloud structure and the coldest/youngest sources. Deep narrow band imaging at the 2.12 μm S(1) line of H2 from NOTCam/NOT was obtained to search for signs of bipolar outflows.

    Results: .We have strong evidence for a stellar population of 31 Class II sources, 5 flat-spectrum sources, 5 Class I sources, and two Class 0 sources. Our method does not sample the Class III sources. The cloud is composed of two main dense clumps aligned along a ridge over ~0.5 pc plus a starless core coinciding with absorption features seen in the ISOCAM maps. We find two S-shaped bipolar collimated flows embedded in the NE clump, and propose the two driving sources to be a Class 0 candidate (MMS3) and a double Class I (MMS2). For the Class II population we find a best age of ~2 Myr and compatibility with recent Initial Mass Functions (IMFs) by comparing the observed Class II luminosity function (LF), which is complete to 0.08 Lȯ, to various model LFs with different star formation scenarios and input IMFs.

  • 14. Ehrenreich, D.
    et al.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Walton, N. A.
    A full transit of v2 Lupi d and the search for an exomoon in its Hill sphere with CHEOPS2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, article id A154Article in journal (Refereed)
    Abstract [en]

    The planetary system around the naked-eye star v2 Lupi (HD 136352; TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6 Earth masses (M). The TESS and CHEOPS missions revealed that all three planets are transiting and have radii straddling the radius gap separating volatile-rich and volatile-poor super-earths. Only a partial transit of planet d had been covered so we re-observed an inferior conjunction of the long-period 8.6 M exoplanet v2 Lup d with the CHEOPS space telescope. We confirmed its transiting nature by covering its whole 9.1 h transit for the first time. We refined the planet transit ephemeris to P = 107.1361−0.0022+0.0019 days and Tc = 2459009.7759−0.0096+0.0101 BJDTDB, improving by ~40 times on the previously reported transit timing uncertainty. This refined ephemeris will enable further follow-up of this outstanding long-period transiting planet to search for atmospheric signatures or explore the planet’s Hill sphere in search for an exomoon. In fact, the CHEOPS observations also cover the transit of a large fraction of the planet’s Hill sphere, which is as large as the Earth’s, opening the tantalising possibility of catching transiting exomoons. We conducted a search for exomoon signals in this single-epoch light curve but found no conclusive photometric signature of additional transiting bodies larger than Mars. Yet, only a sustained follow-up of v2 Lup d transits will warrant a comprehensive search for a moon around this outstanding exoplanet.

  • 15.
    Florén, Hans Gustav Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    The planetary system around HD 190622 (TOI-1054) Measuring the gas content of low-mass planets orbiting F-stars2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 675, article id A183Article in journal (Refereed)
    Abstract [en]

    Context. Giant planets are known to dominate the long-term stability of planetary systems due to their prevailing gravitational interactions, but they are also thought to play an important role in planet formation. Observational constraints improve our understanding of planetary formation processes such as the delivery of volatile-rich planetesimals from beyond the ice line into the inner planetary system. Additional constraints may come from studies of the atmosphere, but almost all such studies of the atmosphere investigate the detection of certain species, and abundances are not routinely quantitatively measured.

    Aims. Accurate measurements of planetary bulk parameters – that is, mass and density – provide constraints on the inner structure and chemical composition of transiting planets. This information provides insight into properties such as the amounts of volatile species, which in turn can be related to formation and evolution processes.

    Methods. The Transiting Exoplanet Survey Satellite (TESS) reported a planetary candidate around HD 190622 (TOI-1054), which was subsequently validated and found to merit further characterization with photometric and spectroscopic facilities. The KESPRINT collaboration used data from the High Accuracy Radial Velocity Planet Searcher (HARPS) to independently confirm the planetary candidate, securing its mass, and revealing the presence of an outer giant planet in the system. The CHEOPS consortium invested telescope time in the transiting target in order to reduce the uncertainty on the radius, improving the characterization of the planet.

    Results. We present the discovery and characterization of the planetary system around HD 190622 (TOI-1054). This system hosts one transiting planet, which is smaller than Neptune (3.087-0.053+0.058REarth, 7.7 ± 1.0 MEarth) but has a similar bulk density (1.43 ± 0.21 g cm−3) and an orbital period of 16 days; and a giant planet, not known to be transiting, with a minimum mass of 227.0 ± 6.7 MEarth in an orbit with a period of 315 days.

    Conclusions. Our measurements constrain the structure and composition of the transiting planet. HD 190622b has singular properties among the known population of transiting planets, which we discuss in detail. Among the sub-Neptune-sized planets known today, this planet stands out because of its large gas content.

  • 16.
    Florén, Hans Gustav Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    A CHEOPS-enhanced view of the HD 3167 system2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 668, article id A31Article in journal (Refereed)
    Abstract [en]

    Much remains to be understood about the nature of exoplanets smaller than Neptune, most of which have been discovered in compact multi-planet systems. With its inner ultra-short period planet b aligned with the star and two larger outer planets d-c on polar orbits, the multi-planet system HD 3167 features a peculiar architecture and offers the possibility to investigate both dynamical and atmospheric evolution processes. To this purpose we combined multiple datasets of transit photometry and radial velocimetry (RV) to revise the properties of the system and inform models of its planets. This effort was spearheaded by CHEOPS observations of HD 3167b, which appear inconsistent with a purely rocky composition despite its extreme irradiation. Overall the precision on the planetary orbital periods are improved by an order of magnitude, and the uncertainties on the densities of the transiting planets b and c are decreased by a factor of 3. Internal structure and atmospheric simulations draw a contrasting picture between HD 3167d, likely a rocky super-Earth that lost its atmosphere through photo-evaporation, and HD 3167c, a mini-Neptune that kept a substantial primordial gaseous envelope. We detect a fourth, more massive planet on a larger orbit, likely coplanar with HD 3167d-c. Dynamical simulations indeed show that the outer planetary system d-c-e was tilted, as a whole, early in the system history, when HD 3167b was still dominated by the star influence and maintained its aligned orbit. RV data and direct imaging rule out that the companion that could be responsible for the present-day architecture is still bound to the HD 3167 system. Similar global studies of multi-planet systems will tell how many share the peculiar properties of the HD 3167 system, which remains a target of choice for follow-up observations and simulations.

  • 17.
    Florén, Hans Gustav Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Characterization of the HD 108236 system with CHEOPS and TESS Confirmation of a fifth transiting planet2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 668, article id A117Article in journal (Refereed)
    Abstract [en]

    Context. The HD 108236 system was first announced with the detection of four small planets based on TESS data. Shortly after, the transit of an additional planet with a period of 29.54 d was serendipitously detected by CHEOPS. In this way, HD 108236 (V = 9.2) became one of the brightest stars known to host five small transiting planets (Rp < 3 R).

    Aims. We characterize the planetary system by using all the data available from CHEOPS and TESS space missions. We use the flexible pointing capabilities of CHEOPS to follow up the transits of all the planets in the system, including the fifth transiting body.

    Methods. After updating the host star parameters by using the results from Gaia eDR3, we analyzed 16 and 43 transits observed by CHEOPS and TESS, respectively, to derive the planets’ physical and orbital parameters. We carried out a timing analysis of the transits of each of the planets of HD 108236 to search for the presence of transit timing variations.

    Results. We derived improved values for the radius and mass of the host star (R = 0.876 ± 0.007 R0 and M = 0.867-0.046+0.047M⊙). We confirm the presence of the fifth transiting planet f in a 29.54 d orbit. Thus, the HD 108236 system consists of five planets of Rb = 1.587±0.028, Rc = 2.122±0.025, Rd = 2.629 ± 0.031, Re = 3.008 ± 0.032, and Rf = 1.89 ± 0.04 [R]. We refine the transit ephemeris for each planet and find no significant transit timing variations for planets c, d, and e. For planets b and f, instead, we measure significant deviations on their transit times (up to 22 and 28 min, respectively) with a non-negligible dispersion of 9.6 and 12.6 min in their time residuals.

    Conclusions. We confirm the presence of planet f and find no significant evidence for a potential transiting planet in a 10.9 d orbital period, as previously suggested. Further monitoring of the transits, particularly for planets b and f, would confirm the presence of the observed transit time variations. HD 108236 thus becomes a key multi-planetary system for the study of formation and evolution processes. The reported precise results on the planetary radii – together with a profuse RV monitoring – will allow for an accurate characterization of the internal structure of these planets.

  • 18.
    Florén, Hans Gustav Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Discovery of TOI-1260d and the characterization of the multiplanet system2023In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 519, no 1, p. 1437-1451Article in journal (Refereed)
    Abstract [en]

    We report the discovery of a third planet transiting the star TOI-1260, previously known to host two transiting sub-Neptune planets with orbital periods of 3.127 and 7.493 d, respectively. The nature of the third transiting planet with a 16.6-d orbit is supported by ground-based follow-up observations, including time-series photometry, high-angular resolution images, spectroscopy, and archival imagery. Precise photometric monitoring with CHEOPS allows to improve the constraints on the parameters of the system, improving our knowledge on their composition. The improved radii of TOI-1260b and TOI-1260c are 2.36±0.06R⊕2.36±0.06R⊕⁠, 2.82±0.08R⊕2.82±0.08R⊕⁠, respectively while the newly discovered third planet has a radius of 3.09±0.09R⊕3.09±0.09R⊕⁠. The radius uncertainties are in the range of 3 per cent, allowing a precise interpretation of the interior structure of the three planets. Our planet interior composition model suggests that all three planets in the TOI-1260 system contains some fraction of gas. The innermost planet TOI-1260b has most likely lost all of its primordial hydrogen-dominated envelope. Planets c and d were also likely to have experienced significant loss of atmospheric through escape, but to a lesser extent compared to planet b.

  • 19.
    Florén, Hans Gustav Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Examining the orbital decay targets KELT-9 b, KELT-16 b, and WASP-4 b, and the transit-timing variations of HD 97658 b2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 669, article id A124Article in journal (Refereed)
    Abstract [en]

    Context. Tidal orbital decay is suspected to occur for hot Jupiters in particular, with the only observationally confirmed case of this being WASP-12b. By examining this effect, information on the properties of the host star can be obtained using the so-called stellar modified tidal quality factor Q*, which describes the efficiency with which the kinetic energy of the planet is dissipated within the star. This can provide information about the interior of the star.

    Aims. In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16, and WASP-4 systems in order to find evidence for or against the presence of tidal orbital decay. With this, we want to constrain the Q* value for each star. In addition, we aim to test the existence of the transit timing variations (TTVs) in the HD 97658 system, which previously favoured a quadratic trend with increasing orbital period.

    Methods. Making use of newly acquired photometric observations from CHEOPS (CHaracterising ExOplanet Satellite) and TESS (Transiting Exoplanet Survey Satellite), combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models to the data, namely a constant-period model, an orbital-decay model, and an apsidal-precession model.

    Results. We find that the KELT-9 system is best described by an apsidal-precession model for now, with an orbital decay trend at over 2 σ being a possible solution as well. A Keplerian orbit model with a constant orbital period provides the best fit to the transit timings of KELT-16 b because of the scatter and scale of their error bars. The WASP-4 system is best represented by an orbital decay model at a 5 σ significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find no conclusive evidence for a previously suspected strong quadratic trend in the data.

  • 20. Fridlund, M.
    et al.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans Gustav Axel
    Stockholm University, Faculty of Science, Department of Astronomy.
    Walton, N. A.
    Planets observed with CHEOPS: Two super-Earths orbiting the red dwarf star TOI-7762024In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 684, article id A12Article in journal (Refereed)
    Abstract [en]

    Context. M-dwarf stars are the most common of potential exoplanet host stars in the Galaxy. It is therefore very important to understand planetary systems orbiting such stars and to determine the physical parameters of such planets with high precision. Also with the launch of the James Webb Space Telescope (JWST) the observation of atmospheric parameters of planets orbiting these stars has begun. It is therefore required to determine properties of potential targets.

    Aims. Two planets around the red dwarf TOI-776 were detected by TESS. The objective of our study was to use transit observations obtained by the CHEOPS space mission to improve the current precision of the planetary radii, as well as additional radial velocity (RV) data in order to improve mass estimates of the two planets. Using these quantities, we wanted to derive the bulk densities of those planets, improving the precision in earlier results, and use this information to put them in context of other exoplanetary systems involving very low mass stars.

    Methods. Utilizing new transit data from the CHEOPS satellite and its photometric telescope, we obtained very high precision planetary transit measurements. Interpretation of these provides updated planetary radii, along with other system parameters. A concurrent ESO large observing program using the high precision spectrograph HARPS has doubled the available radial velocity data. Calculating the power spectrum of a number of stellar activity indices we update the previously estimated stellar rotation period to a lower value.

    Results. The CHEOPS data provide precise transit depths of 909 and 1177 ppm translating into radii of Rb = R and Rc = R, respectively. Our interpretation of the radial velocities and activity indicator time series data estimates a stellar rotation period for this early M dwarf of ~21.1 days. A further multi-dimensional Gaussian process approach confirm this new estimate. By performing a Skew-Normal (SN) fit onto the Cross Correlation Functions we extracted the RV data and the activity indicators to estimate the planetary masses, obtaining Mb = M and Mc = M.

    Conclusions. We improve the precision in planetary radius for TOI-776 b and c by a factor of more than two. Our data and modelling give us parameters of both bodies consistent with mini-Neptunes, albeit with a relatively high density. The stellar activity of TOI-776 is found to have increased by a factor larger than 2 since the last set of observations.

  • 21. Hjalmarson, Å.
    et al.
    Frisk, U.
    Olberg, M.
    Bergman, P.
    Bernath, P.
    Biver, N.
    Black, J. H.
    Booth, R. S.
    Buat, V.
    Crovisier, J.
    Curry, C. L.
    Dahlgren, M.
    Encrenaz, P. J.
    Falgarone, E.
    Feldman, P. A.
    Fich, M.
    Florén, H. G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fredrixon, M.
    Gerin, M.
    Gregersen, E. M.
    Hagström, M.
    Harju, J.
    Hasegawa, T.
    Horellou, C.
    Johansson, L. E. B.
    Kyrölä, E.
    Kwok, S.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lecacheux, A.
    Liljeström, T.
    Lindqvist, M.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Llewellyn, E. J.
    Mattila, K.
    Mégie, G.
    Mitchell, G. F.
    Murtagh, D.
    Nyman, L.-Å.
    Nordh, H. L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, A. O. H.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Persson, G.
    Plume, R.
    Rickman, H.
    Ristorcelli, I.
    Rydbeck, G.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    von Schéele, F.
    Serra, G.
    Torchinsky, S.
    Tothill, N. F.
    Volk, K.
    Wiklind, T.
    Wilson, C. D.
    Winnberg, A.
    Witt, G.
    Highlights from the first year of Odin observations2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L39-L46Article in journal (Refereed)
    Abstract [en]

    Key Odin operational and instrumental features and highlights from our sub-millimetre and millimetre wave observations of H2O, H218O, NH3, 15NH3 and O2 are presented, with some insights into accompanying Odin Letters in this A&A issue. We focus on new results where Odin's high angular resolution, high frequency resolution, large spectrometer bandwidths, high sensitivity or/and frequency tuning capability are crucial: H2O mapping of the Orion KL, W3, DR21, S140 regions, and four comets; H2O observations of Galactic Centre sources, of shock enhanced H2O towards the SNR IC443, and of the candidate infall source IRAS 16293-2422; H218O detections in Orion KL and in comet Ikeya-Zhang; sub-mm detections of NH3 in Orion KL (outflow, ambient cloud and bar) and ρ Oph, and very recently, of 15NH3 in~Orion KL. Simultaneous sensitive searches for the 119 GHz line of O2 have resulted in very low abundance limits, which are difficult to accomodate in chemical models. We also demonstrate, by means of a quantitative comparison of Orion KL H2O results, that the Odin and SWAS observational data sets are very consistently calibrated. Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes), and the Centre National d'études Spatiales (CNES, France). The Swedish Space Corporation (SSC) has been the prime industrial contractor, and is also responsible for the satellite operation from its Odin Mission Control Centre at SSC in Solna and its Odin Control Centre at ESRANGE near Kiruna in northern Sweden. See also the SNSB Odin web page: http://www.snsb.se/eng_odin_intro.shtml

  • 22. Hjalmarson, Åke
    et al.
    Bergman, Per
    Biver, Nicolas
    Florén, H.-G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, Urban
    Hasegawa, Tatsuhiko
    Justtanont, Kay
    Stockholm University, Faculty of Science, Department of Astronomy.
    Larsson, Bengt
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundin, Stefan
    Olberg, Michael
    Olofsson, Henrik
    Persson, Glenn
    Rydbeck, Gustaf
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    The Odin Team,
    Recent astronomy highlights from the Odin satellite2005In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 36, p. 1031-1047Article in journal (Refereed)
    Abstract [en]

    Astronomy highlights, mainly from the third year of Odin observations time shared 50/50% with aeronomy are presented: the very low O2 abundance limits achieved, the highly pressure broadened absorption lines of H2O, H218O, and CO (5 → 4) in the atmosphere of Mars, the high precision H2O and H218O observations of comets, the detections of NH3 and H2O around the C-rich star IRC+10216 (CW Leo) and of H2O around the O-rich star W Hya, NH3 and H2O observations of infall/outflow interactions, observations of H2O, H218O, H217O as well as NH3 and 15NH3 in multiple absorptions towards Sgr B2, and in emission towards Orion KL, the H2O detection of several new outflows in the DR21 W75S region. We also discuss the results of deconvolution of high S/N H2O, CO and 13CO (5 → 4) maps of the Orion KL region to 40″ resolution (the beam size of the Herschel telescope) and the first results from our ongoing “spectral scan” of Orion KL in bands around 555 and 570 GHz. Finally, a search for primordial molecules is presented.

  • 23. Hjalmarson, Åke
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    On the progress in Odin’s hunt for molecules2007In: Advances in Space Research, Vol. 40, no 5, p. 630-638Article in journal (Refereed)
  • 24. Kiss, M.
    et al.
    Larsson, Stefan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Bettolo, C.
    Bogaert, G.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Fukazawa, Y.
    Gunji, S.
    Hjalmarsdotter, Linnea
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Kamae, T.
    Kanai, Y.
    Kataoka, J.
    Kawai, N.
    Klamra, W.
    Kurita, K.
    Madejski, G.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Pearce, Mark
    Ryde, Felix
    Rydström, S.
    Tajima, H.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Ueno, M.
    Umeki, Y.
    Varner, G.
    Yoshida, H.
    The PoGOLite balloon-borne soft gamma-ray polarimeter2008In: COOL DISCS, HOT FLOWS: The Varying Faces of Accreting Compact Objects, 2008, p. 225-232Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Linearly polarized radiation in the hard X-ray/soft gamma-ray band is expected from a large variety of astronomical sources. We discuss the importance of polarimetric studies for several classes of sources-pulsars, accreting black holes, magnetic neutron stars and jets from active galaxies-and then describe PoGOLite, a balloon-borne instrument which is currently under construction and will be able to measure the polarization of electromagnetic radiation from such extra-solar objects in the energy range 25-80 keV.

  • 25. Lacedelli, G.
    et al.
    Wilson, T. G.
    Malavolta, L.
    Hooton, M. J.
    Collier Cameron, A.
    Alibert, Y.
    Mortier, A.
    Bonfanti, A.
    Haywood, R. D.
    Hoyer, S.
    Piotto, G.
    Bekkelien, A.
    Vanderburg, A. M.
    Benz, W.
    Dumusque, X.
    Deline, A.
    Lopez-Morales, M.
    Borsato, L.
    Rice, K.
    Fossati, L.
    Latham, D. W.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Poretti, E.
    Sousa, S. G.
    Sozzetti, A.
    Salmon, S.
    Burke, C. J.
    Van Grootel, V.
    Fausnaugh, M. M.
    Adibekyan, V.
    Huang, C. X.
    Osborn, H. P.
    Mustill, A. J.
    Palle, E.
    Bourrier, V.
    Nascimbeni, V.
    Alonso, R.
    Anglada, G.
    Barczy, T.
    Barrado y Navascues, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Billot, N.
    Bonfils, X.
    Broeg, C.
    Buchhave, L. A.
    Cabrera, J.
    Charnoz, S.
    Cosentino, R.
    Csizmadia, Sz.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    Demangeon, O.
    Demory, B.-O.
    Ehrenreich, D.
    Erikson, A.
    Esparza-Borges, E.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fortier, A.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Ghedina, A.
    Gillon, M.
    Gudel, M.
    Guterman, P.
    Harutyunyan, A.
    Heng, K.
    Isaak, K. G.
    Jenkins, J. M.
    Kiss, L.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Marafatto, L.
    Martinez Fiorenzano, A. F.
    Maxted, P. F. L.
    Mayor, M.
    Micela, G.
    Molinari, E.
    Murgas, F.
    Narita, N.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ottensamer, R.
    Pagano, I.
    Pasetti, A.
    Pedani, M.
    Pepe, F. A.
    Peter, G.
    Phillips, D. F.
    Pollacco, D.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Ratti, F.
    Rauer, H.
    Ribas, I.
    Santos, N. C.
    Sasselov, D.
    Scandariato, G.
    Seager, S.
    Segransan, D.
    Serrano, L. M.
    Simon, A. E.
    Smith, A. M. S.
    Steinberger, M.
    Steller, M.
    Szabo, Gy.
    Thomas, N.
    Twicken, J. D.
    Udry, S.
    Walton, N.
    Winn, J. N.
    Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N, and TESS2022In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 511, no 3, p. 4551-4571Article in journal (Refereed)
    Abstract [en]

    We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data withTESS and CHEOPS photometry, and a new set of 62 HARPS-N radial velocities (RVs). Our joint analysis confirms the presenceof four transiting planets, namely TOI-561 b (P = 0.45 d, R = 1.42 R⊕, M = 2.0 M⊕), c (P = 10.78 d, R = 2.91 R⊕, M =5.4 M⊕), d (P = 25.7 d, R = 2.82 R⊕, M = 13.2 M⊕), and e (P = 77 d, R = 2.55 R⊕, M = 12.6 R⊕). Moreover, we identifyan additional, long-period signal (>450 d) in the RVs, which could be due to either an external planetary companion or tostellar magnetic activity. The precise masses and radii obtained for the four planets allowed us to conduct interior structure andatmospheric escape modelling. TOI-561 b is confirmed to be the lowest density (ρb = 3.8 ± 0.5 g cm−3) ultra-short period(USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellarmetallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certainamount of water. In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in addition to a possibly large water layer.The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets b and c having experiencedsignificant gas loss, and planets d and e showing an atmospheric content consistent with the original one. The uniqueness ofthe USP planet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealingtarget for follow-up studies.

  • 26.
    Larsson, B.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bergman, P.
    Bernath, P.
    Black, J. H.
    Booth, R. S.
    Buat, V.
    Curry, C. L.
    Encrenaz, P.
    Falgarone, E.
    Feldman, P.
    Fich, M.
    Florén, H. G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Gerin, M.
    Gregersen, E. M.
    Harju, J.
    Hasegawa, T.
    Johansson, L. E. B.
    Kwok, S.
    Lecacheux, A.
    Liljeström, T.
    Mattila, K.
    Mitchell, G. F.
    Nordh, L. H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olberg, M.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Plume, R.
    Ristorcelli, I.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Schéele, F. v.
    Tothill, N. F. H.
    Volk, K.
    Wilson, C. D.
    Hjalmarson, Å.
    First NH3 detection of the Orion Bar2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L69-L72Article in journal (Refereed)
    Abstract [en]

    Odin has successfully observed three regions in the Orion A cloud, i.e. Ori KL, Ori S and the Orion Bar, in the 572.5 GHz rotational ground state line of ammonia, ortho-NH3 (J,K) = (1,0) -> (0,0), and the result for the Orion Bar represents the first detection in an ammonia line. Several velocity components are present in the data. Specifically, the observed line profile from the Orion Bar can be decomposed into two components, which are in agreement with observations in high-J CO lines by Wilson et al. (\cite{wilson01}). Using the source model for the Orion Bar by these authors, our Odin observation implies a total ammonia abundance of NH3/H2 = 5x 10-9. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation has been the industrial prime contractor.

  • 27.
    Larsson, Bengt
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Liseau, Rene
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, Laurent
    Bergman, Per
    Bernath, Peter
    Biver, Nicolas
    Black, John
    Booth, Roy
    Buat, Veronique
    Crovisier, Jacques
    Curry, Charles
    Dahlgren, Magnus
    Encrenaz, Pierre
    Falgarone, Edith
    Feldman, Paul
    Fish, Michel
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fredrixon,
    Frisk, Urban
    Gahm, Gösta
    Stockholm University, Faculty of Science, Department of Astronomy.
    Gerin, Maryvonne
    Hagström, Magne
    Harju, Jorma
    Hasegawa, Tatsuhiko
    Hjalmarsson, Åke
    Johansson, Lars
    Justtanout, Kay
    Stockholm University, Faculty of Science, Department of Astronomy.
    Klotz, Alain
    Kytölä, Erikii
    Kwok, Sun
    Lecacheux, Alain
    Liljeström, Tarja
    Llewellyn, Edward
    Lundin, Stefan
    Mégie, Gérard
    Mitchell, Gary
    Murtagh, Donal
    Nordh, Lennart
    Nyman, Lars-Åke
    Olberg, Michael
    Olofsson, Henrik
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Hans
    Stockholm University, Faculty of Science, Department of Astronomy.
    Persson, Glen
    Plume, Rene
    Rickman, Hans
    Ristorcelli, Isabelle
    Rydbeck, Gustaf
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    von Scheele, Fredrik
    Serra, Guy
    Torchinsky, Steve
    Tothill, Nick
    Volk, Kevin
    Wiklind, Tommy
    Wilson, Christine
    Winnberg, Anders
    Witt, George
    Department of Meteorology.
    Molecular oxygen in the rho Ophiuchi cloud2007In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 466, no 3, p. 5-Article in journal (Refereed)
    Abstract [en]

    Context: Molecular oxygen, O2, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission.

    Aims: The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods: The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core ρ Oph A was observed with Odin for 34 days during several observing runs.

    Results: We detect a spectral line at v_LSR =+3.5 km s-1 with Δ v_FWHM=1.5 km s-1, parameters which are also common to other species associated with ρ Oph A. This feature is identified as the O2 (NJ = 11 - 1_0) transition at 118 750.343 MHz.

    Conclusions: The abundance of molecular oxygen, relative to H{2} , is 5 × 10-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.

    Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Étude Spatiale (CNES). The Swedish Space Corporation has been the industrial prime contractor and also is operating the satellite. Appendix A is only available in electronic form at http://www.aanda.org

  • 28.
    Liseau, R.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, A.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bergman, P.
    Bernath, P.
    Black, J. H.
    Booth, R.
    Buat, V.
    Curry, C.
    Encrenaz, P.
    Falgarone, E.
    Feldman, P.
    Fich, M.
    Florén, H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Gerin, M.
    Gregersen, E.
    Harju, J.
    Hasegawa, T.
    Hjalmarson, Å.
    Johansson, L.
    Kwok, S.
    Lecacheux, A.
    Liljeström, T.
    Mattila, K.
    Mitchell, G.
    Nordh, L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olberg, M.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Plume, R.
    Ristorcelli, I.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Schéele, F. v.
    Serra, G.
    Tothill, N.
    Volk, K.
    Wilson, C.
    First detection of NH3 (10 -> 00) from a low mass cloud core. On the low ammonia abundance of the rho Oph A core2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L73-L76Article in journal (Refereed)
    Abstract [en]

    Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (JK = 10 -> 00). The interpretation of this result makes use of complementary molecular line data obtained from the ground (C17O and CH3OH) as part of the Odin preparatory work. Comparison of these observations with theoretical model calculations of line excitation and transfer yields a quite ordinary abundance of methanol, X(CH3OH)= 3 x 10-9. Unless NH3 is not entirely segregated from C17O and CH3OH, ammonia is found to be significantly underabundant with respect to typical dense core values, viz. X(NH3) = 8 x 10-10. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation has been the industrial prime contractor. and based on observations collected with the Swedish ESO Submillimeter Telescope, SEST, in La Silla, Chile.

  • 29. Maercker, M.
    et al.
    Ramstedt, S.
    Leal-Ferreira, M. L.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Floren, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    The detached dust shells around the carbon AGB stars R Sculptoris and V644 Scorpii2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 570, p. A101-Article in journal (Refereed)
    Abstract [en]

    Context. The morphology of the circumstellar envelopes (CSE) around asymptotic giant branch (AGB) stars gives information on the mass-loss process from the star, its evolution and wind, and on the effect of binary interaction. However, determining the distribution of dust in the circumstellar envelopes is difficult. Observations of polarised, dust-scattered stellar light in the optical have produced images with high-spatial resolution of the envelopes around evolved stars. For sources with detached shells in particular, this method has proven extremely successful. Detached shells are believed to be created during a thermal pulse, and studying them can constrain the time scales and physical properties of one of the main drivers of late stellar evolution. Aims. We aim at determining the morphology of the detached shells around the carbon AGB stars R Scl and V644 Sco. In particular, we attempt to constrain the radii and widths of the detached dust shells around the stars and compare them to observations of the detached gas shells. Methods. We observed the polarised, dust-scattered stellar light around the carbon AGB stars R Scl and V644 Sco using the PolCor instrument mounted on the ESO 3.6 m telescope. Observations were done with a coronographic mask to block out the direct stellar light. The polarised images clearly show the detached shells around R Scl and V644 Sco. Using a dust radiative transfer code to model the dust-scattered polarised light, we constrained the radii and widths of the shells. Results. We determine radii of 19 ''.5 and 9 ''.4 for the detached dust shells around R Scl and V644 Sco, respectively. Both shells have an overall spherical symmetry and widths of approximate to 2 ''. For R Scl, we can compare the observed dust emission directly with high spatialresolution maps of CO(3-2) emission from the shell observed with ALMA. We find that the dust and gas coincide almost exactly, indicating a common evolution. The data presented here for R Scl are the most detailed observations of the entire dusty detached shell to date. For V644 Sco, these are the first direct measurements of the detached shell. Also here we find that the dust most likely coincides with the gas shell. Conclusions. The observations are consistent with a scenario where the detached shells are created during a thermal pulse. The determined radii and widths will constrain hydrodynamical models describing the pre-pulse mass loss, the thermal pulse, and postpulse evolution of the star.

  • 30. Maxted, P. F. L.
    et al.
    Ehrenreich, D.
    Wilson, T. G.
    Alibert, Y.
    Collier Cameron, A.
    Hoyer, S.
    Sousa, S. G.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bekkelien, A.
    Deline, A.
    Delrez, L.
    Bonfanti, A.
    Borsato, L.
    Alonso, R.
    Anglada Escudé, G.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Billot, N.
    Biondi, F.
    Bonfils, X.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Broeg, C.
    Bárczy, T.
    Cabrera, J.
    Charnoz, S.
    Corral Van Damme, C.
    Csizmadia, Sz
    Davies, M. B.
    Deleuil, M.
    Demangeon, O. D. S.
    Demory, B.-O.
    Erikson, A.
    Florén, Hans Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Gillon, M.
    Guedel, M.
    Guterman, P.
    Heng, K.
    Isaak, K. G.
    Kiss, L.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Nascimbeni, V.
    Ottensamer, R.
    Pagano, I.
    Pallé, E.
    Peter, G.
    Piotto, G.
    Pollacco, D.
    Pozuelos, F. J.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Reimers, C.
    Ribas, I.
    Salmon, S.
    Santos, N. C.
    Scandariato, G.
    Simon, A. E.
    Smith, A. M. S.
    Steller, M.
    Swayne, M.
    Szabó, Gy. M.
    Ségransan, D.
    Thomas, N.
    Udry, S.
    Van Grootel, V.
    Walton, N. A.
    Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using pycheops2022In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 514, no 1, p. 77-104Article in journal (Refereed)
    Abstract [en]

    CHEOPS (CHaracterising ExOPlanet Satellite) is an ESA S-class mission that observes bright stars at high cadence from low-Earth orbit. The main aim of the mission is to characterize exoplanets that transit nearby stars using ultrahigh precision photometry. Here, we report the analysis of transits observed by CHEOPS during its Early Science observing programme for four well-known exoplanets: GJ 436 b, HD 106315 b, HD 97658 b, and GJ 1132 b. The analysis is done using pycheops, an open-source software package we have developed to easily and efficiently analyse CHEOPS light-curve data using state-of-the-art techniques that are fully described herein. We show that the precision of the transit parameters measured using CHEOPS is comparable to that from larger space telescopes such as Spitzer Space Telescope and Kepler. We use the updated planet parameters from our analysis to derive new constraints on the internal structure of these four exoplanets.

  • 31. Meech, K.J.
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    EPOXI: Comet 103P/Hartley 2 Observations from a Worldwide Campaign2011In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 734, no L1, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was ~16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production.

  • 32. Morgado, B. E.
    et al.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    de Wit, J.
    A dense ring of the trans-Neptunian object Quaoar outside its Roche limit2023In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 614, no 7947, p. 239-243Article in journal (Refereed)
    Abstract [en]

    In our efforts to characterize Quaoar’s shape and search for putative material around it, we have predicted and observed several stellar occultations by this body. Following a report from Australia of a Neptune-like ring detected during a 2021 occultation and independently suspected in 2019, we have identified secondary events in previous occultations observed between 2018 and 2020. They are consistent with a circular ring centred on the body, with two possible mirror solutions for the ring orientation. Both solutions have radii close to 4,100 km, or roughly 7.4 Quaoar radii. One solution has a ring pole that presents a large mismatch with Weywot’s orbital pole, whereas the other solution is consistent with a ring coplanar with Weywot’s orbit. This is our preferred solution, as a primordial collisional system surrounding Quaoar is expected to settle in a disc that subsequently forms both the ring and Weywot.

  • 33. Morgado, B. E.
    et al.
    Bruno, G.
    Gomes-Júnior, A. R.
    Pagano, I
    Sicardy, B.
    Fortier, A.
    Desmars, J.
    Maxted, P. F. L.
    Braga-Ribas, F.
    Queloz, D.
    Sousa, S. G.
    Ortiz, J. L.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Cameron, A. Collier
    Pereira, C. L.
    Florén, Hans Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hara, N.
    Souami, D.
    Isaak, K. G.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm Univ, Alballova Univ Ctr, Dept Astron, S-10691 Stockholm, Sweden.
    Santos-Sanz, P.
    Wilson, T. G.
    Broughton, J.
    Alibert, Y.
    Alonso, R.
    Anglada, G.
    Bárczy, T.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Billot, N.
    Bonfils, X.
    Broeg, C.
    Cabrera, J.
    Charnoz, S.
    Csizmadia, S.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    Demangeon, O. D. S.
    Demory, B. O.
    Ehrenreich, D.
    Erikson, A.
    Fossati, L.
    Fridlund, M.
    Gandolfi, D.
    Gillon, M.
    Güdel, M.
    Heng, K.
    Hoyer, S.
    Kiss, L. L.
    Laskar, J.
    des Etangs, A. Lecavelier
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Marafatto, L.
    Nascimbeni, V
    Ottensamer, R.
    Pallé, E.
    Peter, G.
    Piazza, D.
    Piotto, G.
    Pollacco, D.
    Ragazzoni, R.
    Rando, N.
    Ratti, F.
    Rauer, H.
    Reimers, C.
    Ribas, I
    Santos, N. C.
    Scandariato, G.
    Ségransan, D.
    Simon, A. E.
    Smith, A. M. S.
    Steller, M.
    Szabó, G. M.
    Thomas, N.
    Udry, S.
    Van Grootel, V.
    Walton, N. A.
    Westerdorff, K.
    A stellar occultation by the transneptunian object (50000) Quaoar observed by CHEOPS2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 664, article id L15Article in journal (Refereed)
    Abstract [en]

    Context. Stellar occultation is a powerful technique that allows the determination of some physical parameters of the occulting object. The result depends on the photometric accuracy, the temporal resolution, and the number of chords obtained. Space telescopes can achieve high photometric accuracy as they are not affected by atmospheric scintillation.

    Aims. Using ESA’s CHEOPS space telescope, we observed a stellar occultation by the transneptunian object (50000) Quaoar. We compare the obtained chord with previous occultations by this object and determine its astrometry with sub-milliarcsecond precision. Also, we determine upper limits to the presence of a global methane atmosphere on the occulting body.

    Methods. We predicted and observed a stellar occultation by Quaoar using the CHEOPS space telescope. We measured the occultation light curve from this dataset and determined the dis- and reappearance of the star behind the occulting body. Furthermore, a ground-based telescope in Australia was used to constrain Quaoar’s limb. Combined with results from previous works, these measurements allowed us to obtain a precise position of Quaoar at the occultation time.

    Results. We present the results obtained from the first stellar occultation by a transneptunian object using a space telescope orbiting Earth; it was the occultation by Quaoar observed on 2020 June 11. We used the CHEOPS light curve to obtain a surface pressure upper limit of 85 nbar for the detection of a global methane atmosphere. Also, combining this observation with a ground-based observation, we fitted Quaoar’s limb to determine its astrometric position with an uncertainty below 1.0 mas.

    Conclusions. This observation is the first of its kind, and it shall be considered as a proof of concept of stellar occultation observations of transneptunian objects with space telescopes orbiting Earth. Moreover, it shows significant prospects for the James Webb Space Telescope.

  • 34. Morris, B. M.
    et al.
    Delrez, L.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Cameron, A. C.
    Simon, A. E.
    Futyan, D.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hoyer, S.
    Fortier, A.
    Demory, B-O
    Lendl, M.
    Wilson, T. G.
    Oshagh, M.
    Heng, K.
    Ehrenreich, D.
    Sulis, S.
    Alibert, Y.
    Alonso, R.
    Anglada Escudé, G.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Bekkelien, A.
    Benz, W.
    Bergomi, M.
    Billot, N.
    Bonfils, X.
    Bourrier, V
    Broeg, C.
    Barczy, T.
    Cabrera, J.
    Charnoz, S.
    Davies, M. B.
    De Miguel Ferreras, D.
    Deleuil, M.
    Deline, A.
    Demangeon, O. D. S.
    Erikson, A.
    Florén, Hans Gustav Axel
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fossati, L.
    Fridlund, M.
    Gandolfi, D.
    Muñoz, A. García
    Gillon, M.
    Guedel, M.
    Guterman, P.
    Isaak, K.
    Kiss, L.
    Laskar, J.
    des Etangs, A. Lecavelier
    Lieder, M.
    Lovis, C.
    Magrin, D.
    Maxted, P. F. L.
    Nascimbeni, V
    Ottensamer, R.
    Pagano, I
    Pallé, E.
    Peter, G.
    Piotto, G.
    Pizarro Rubio, A.
    Pollacco, D.
    Pozuelos, F. J.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I
    Santos, N. C.
    Scandariato, G.
    Smith, A. M. S.
    Sousa, S. G.
    Steller, M.
    Szabó, Gy M.
    Ségransan, D.
    Thomas, N.
    Udry, S.
    Ulmer, B.
    Van Grootel, V.
    Walton, N. A.
    CHEOPS precision phase curve of the Super-Earth 55 Cancri e2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 653, article id A173Article in journal (Refereed)
    Abstract [en]

    Context. 55 Cnc e is a transiting super-Earth (radius 1.88 R and mass 8 M) orbiting a G8V host star on a 17-h orbit. Spitzer observations of the planet’s phase curve at 4.5 μm revealed a time-varying occultation depth, and MOST optical observations are consistent with a time-varying phase curve amplitude and phase offset of maximum light. Both broadband and high-resolution spectroscopic analyses are consistent with either a high mean molecular weight atmosphere or no atmosphere for planet e. A long-term photometric monitoring campaign on an independent optical telescope is needed to probe the variability in this system.

    Aims. We seek to measure the phase variations of 55 Cnc e with a broadband optical filter with the 30 cm effective aperture space telescope CHEOPS and explore how the precision photometry narrows down the range of possible scenarios.

    Methods. We observed 55 Cnc for 1.6 orbital phases in March of 2020. We designed a phase curve detrending toolkit for CHEOPS photometry which allowed us to study the underlying flux variations in the 55 Cnc system.

    Results. We detected a phase variation with a full-amplitude of 72 ± 7 ppm, but did not detect a significant secondary eclipse of the planet. The shape of the phase variation resembles that of a piecewise-Lambertian; however, the non-detection of the planetary secondary eclipse, and the large amplitude of the variations exclude reflection from the planetary surface as a possible origin of the observed phase variations. They are also likely incompatible with magnetospheric interactions between the star and planet, but may imply that circumplanetary or circumstellar material modulate the flux of the system.

    Conclusions. This year, further precision photometry of 55 Cnc from CHEOPS will measure variations in the phase curve amplitude and shape over time.

  • 35. Olofsson, A. O. H.
    et al.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hjalmarson, Å.
    Bergman, P.
    Black, J. H.
    Booth, R. S.
    Buat, V.
    Curry, C. L.
    Encrenaz, P. J.
    Falgarone, E.
    Feldman, P.
    Fich, M.
    Florén, H. G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Gerin, M.
    Gregersen, E. M.
    Harju, J.
    Hasegawa, T.
    Johansson, L. E. B.
    Kwok, S.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lecacheux, A.
    Liljeström, T.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mattila, K.
    Mitchell, G. F.
    Nordh, H. L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olberg, M.
    Olofsson, H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Plume, R.
    Ristorcelli, I.
    Rydbeck, G.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    von Schéele, F.
    Serra, G.
    Tothill, N. F.
    Volk, K.
    Wilson, C. D.
    Odin water mapping in the Orion KL region2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L47-L54Article in journal (Refereed)
    Abstract [en]

    New results from water mapping observations of the Orion KL region using the submm/mm wave satellite Odin (2.1\arcmin beam size at 557 GHz), are presented. The ortho-H2O \jkktrans{1}{1}{0}{1}{0}{1} ground state transition was observed in a 7arcminx 7arcmin rectangular grid with a spacing of 1\arcmin, while the same line of H218O was measured in two positions, Orion KL itself and 2\arcmin south of Orion KL. In the main water species, the KL molecular outflow is largely resolved from the ambient cloud and it is found to have an extension of 60\arcsec-110\arcsec. The H2O outflow profile exhibits a rather striking absorption-like asymmetry at the line centre. Self-absorption in the near (or ``blue'') part of the outflow (and possibly in foreground quiescent halo gas) is tentatively suggested to play a role here. We argue that the dominant part of the KL H218O outflow emission emanates from the compact (size ~ 15\arcsec) low-velocity flow and here estimate an H2O abundance of circa 10-5 compared to all H2 in the flow - an order of magnitude below earlier estimates of the H2O abundance in the shocked gas of the high-velocity flow. The narrow ambient cloud lines show weak velocity trends, both in the N-S and E-W directions. H218O is detected for the first time in the southern position at a level of ~ 0.15 K and we here estimate an H2O abundance of (1-8) x 10-8. Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes), and the Centre National d'Études Spatiales (CNES, France). The Swedish Space Corporation (SSC) was the industrial prime contractor and is also responsible for the satellite operation.

  • 36.
    Olofsson, Göran
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Nilsson, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Djupvik, A.
    Aberasturi, M.
    Polarimetric coronagraphy of BD+31 degrees 6432012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 544, p. A43-Article in journal (Refereed)
    Abstract [en]

    Context. The binary B5V star BD+ 31 degrees 643 exhibits a disk-like structure detected at optical wavelengths. Even though the feature is well centered on the star, it has been argued, based on Spitzer observations, that the feature is a filament not directly associated to the binary star. Aims. The purpose of the present paper is to investigate whether polarization imaging may provide evidence either for or against the disk hypothesis. In addition, we aim at clarifying whether there might be any additional close companion to the binary star. Methods. We used the coronagraph PolCor in its polarization mode in combination with an EMCCD camera allowing short unit exposure times. As a result of shift-and-add and frame selection, the spatial resolution is improved compared to traditional CCD imaging. In order to possibly reveal an additional stellar companion, we used high resolution spectroscopy in the optical and high spatial resolution imaging in the near-IR. Results. The disk/filament is much better seen in polarization; it is narrow and a line drawn along the ridge passes within a second of arc from the star. The degree of polarization is high (approximate to 50% after correction for the extended component of the reflection nebula) which means that the disk/filament must be approximately at the same distance as the star. Although we confirm that the feature is much brighter south-east than north-west of the star, the evidence that the feature is physically connected to the star is strengthened and suggests that we are witnessing the destruction process of an accretion disk. Our spectroscopy shows that at least one of the stars is a spectroscopic binary. We were, however, not able to spatially resolve any stellar component in addition to the two well separated stars.

  • 37.
    Olofsson, Göran
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Nilsson, Ricky
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Djupvik, Amanda
    Aberasturi, M.
    Polarimetric coronagraphy of BD+31°643Article in journal (Refereed)
  • 38. Osborn, H. P.
    et al.
    Florén, Hans Gustav Axel
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Winn, J. N.
    Two warm Neptunes transiting HIP 9618 revealed by TESS and Cheops2023In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 523, no 2, p. 3069-3089Article in journal (Refereed)
    Abstract [en]

    HIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright (G = 9.0 mag) solar analogue. TESS photometry revealed the star to have two candidate planets with radii of 3.9 +/- 0.044 R-circle plus (HIP 9618 b) and 3.343 +/- 0.039 R-circle plus (HIP 9618 c). While the 20.77291 d period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-d gap in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d. High-resolution spectroscopy with HARPS-N, SOPHIE, and CAFE revealed a mass of 10.0 +/- 3.1M(circle plus) for HIP 9618 b, which, according to our interior structure models, corresponds to a 6.8 +/- 1.4 per cent gas fraction. HIP 9618 c appears to have a lower mass than HIP 9618 b, with a 3-sigma upper limit of <18M(circle plus). Follow-up and archival RV measurements also reveal a clear long-term trend which, when combined with imaging and astrometric information, reveal a low-mass companion (0.08(-0.05)(+0.12) M-circle dot) orbiting at 26.0(-11.0)(+19.0) au. This detection makes HIP 9618 one of only five bright (K < 8 mag) transiting multiplanet systems known to host a planet with P > 50 d, opening the door for the atmospheric characterization of warm (T-eq < 750 K) sub-Neptunes.

  • 39. Pagani, L.
    et al.
    Olofsson, A. O. H.
    Bergman, P.
    Bernath, P.
    Black, J. H.
    Booth, R. S.
    Buat, V.
    Crovisier, J.
    Curry, C. L.
    Encrenaz, P. J.
    Falgarone, E.
    Feldman, P. A.
    Fich, M.
    Floren, H. G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Gerin, M.
    Gregersen, E. M.
    Harju, J.
    Hasegawa, T.
    Hjalmarson, Å.
    Johansson, L. E. B.
    Kwok, S.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lecacheux, A.
    Liljeström, T.
    Lindqvist, M.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mattila, K.
    Mitchell, G. F.
    Nordh, L. H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olberg, M.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ristorcelli, I.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    von Scheele, F.
    Serra, G.
    Tothill, N. F.
    Volk, K.
    Wiklind, T.
    Wilson, C. D.
    Low upper limits on the O2 abundance from the Odin satellite2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L77-L81Article in journal (Refereed)
    Abstract [en]

    For the first time, a search has been conducted in our Galaxy for the 119 GHz transition connecting to the ground state of O2, using the Odin satellite. Equipped with a sensitive 3 mm receiver (Tsys(SSB) = 600 K), Odin has reached unprecedented upper limits on the abundance of O2, especially in cold dark clouds where the excited state levels involved in the 487 GHz transition are not expected to be significantly populated. Here we report upper limits for a dozen sources. In cold dark clouds we improve upon the published SWAS upper limits by more than an order of magnitude, reaching N(O2)/N(H2) <= 10-7 in half of the sources. While standard chemical models are definitively ruled out by these new limits, our results are compatible with several recent studies that derive lower O2 abundances. Goldsmith et al. (\cite{SWAS2002}) recently reported a SWAS tentative detection of the 487 GHz transition of O2 in an outflow wing towards rho Oph A in a combination of 7 beams covering approximately 10arcmin x 14arcmin . In a brief (1.3 hour integration time) and partial covering of the SWAS region (~65% if we exclude their central position), we did not detect the corresponding 119 GHz line. Our 3 sigma upper limit on the O2 column density is 7.3x 1015 cm-2. We presently cannot exclude the possibility that the SWAS signal lies mostly outside of the 9\arcmin Odin beam and has escaped our sensitive detector. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation was the industrial prime contractor and is operating Odin.

  • 40.
    Sandqvist, Aa.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bergman, P.
    Black, J. H.
    Booth, R.
    Buat, V.
    Curry, C. L.
    Encrenaz, P.
    Falgarone, E.
    Feldman, P.
    Fich, M.
    Floren, H. G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Gerin, M.
    Gregersen, E. M.
    Harju, J.
    Hasegawa, T.
    Hjalmarson, Å.
    Johansson, L. E. B.
    Kwok, S.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lecacheux, A.
    Liljeström, T.
    Lindqvist, M.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mattila, K.
    Mitchell, G. F.
    Nordh, L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olberg, M.
    Olofsson, A. O. H.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Plume, R.
    Ristorcelli, I.
    Schéele, F. v.
    Serra, G.
    Tothill, N. F. H.
    Volk, K.
    Wilson, C. D.
    Winnberg, A.
    Odin observations of H2O in the Galactic Centre2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L63-L67Article in journal (Refereed)
    Abstract [en]

    The Odin satellite has been used to detect emission and absorption in the 557-GHz H216O line in the Galactic Centre towards the Sgr Astar Circumnuclear Disk (CND), and the Sgr A +20 km s-1 and +50 km s-1 molecular clouds. Strong broad H2O emission lines have been detected in all three objects. Narrow H2O absorption lines are present at all three positions and originate along the lines of sight in the 3-kpc Spiral Arm, the -30 km s-1 Spiral Arm and the Local Sgr Spiral Arm. Broad H2O absorption lines near -130 km s-1 are also observed, originating in the Expanding Molecular Ring. A new molecular feature (the ``High Positive Velocity Gas'' - HPVG) has been identified in the positive velocity range of ~+120 to +220 km s-1, seen definitely in absorption against the stronger dust continuum emission from the +20 km s-1 and +50 km s-1 clouds and possibly in emission towards the position of Sgr Astar CND. The 548-GHz H218O isotope line towards the CND is not detected at the 0.02 K (rms) level. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation was the industrial prime contractor and is also responsible for the satellite operation.

  • 41. Sicardy, B.
    et al.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans Gustav Axel
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Kate, A.
    Constraints on the evolution of the Triton atmosphere from occultations: 1989-20222024In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, article id L24Article in journal (Refereed)
    Abstract [en]

    Context. In about 2000, the south pole of Triton experienced an extreme summer solstice that occurs every ∼650 years, when the subsolar latitude reached about 50°S. Bracketing this epoch, a few occultations probed the Triton atmosphere in 1989, 1995, 1997, 2008, and 2017. A recent ground-based stellar occultation observed on 6 October 2022 provides a new measurement of the atmospheric pressure on Triton. This is presented here.

    Aims. The goal is to constrain the volatile transport models (VTMs) of the Triton atmosphere. The atmosphere is basically in vapor pressure equilibrium with the nitrogen ice at its surface.

    Methods. Fits to the occultation light curves yield the atmospheric pressure of Triton at the reference radius 1400 km, from which the surface pressure is deduced.

    Results. The fits provide a pressure p1400 = 1.211 ± 0.039 μbar at radius 1400 km (47 km altitude), from which a surface pressure of psurf = 14.54 ± 0.47 μbar is deduced (1σ error bars). To within the error bars, this is identical to the pressure derived from the previous occultation of 5 October 2017, p1400 = 1.18 ± 0.03 μbar and psurf = 14.1 ± 0.4 μbar, respectively. Based on recent models of the volatile cycles of Triton, the overall evolution of the surface pressure over the last 30 years is consistent with N2 condensation taking place in the northern hemisphere. However, models typically predict a steady decrease in the surface pressure for the period 2005-2060, which is not confirmed by this observation. Complex surface-atmosphere interactions, such as ice albedo runaway and formation of local N2 frosts in the equatorial regions of Triton, could explain the relatively constant pressure between 2017 and 2022.

  • 42. Swayne, M.
    et al.
    Maxted, P. F. L.
    Triaud, A. H. M. J.
    Sousa, S. G.
    Broeg, C.
    Florén, Hans Gustav Axel
    Stockholm University, Faculty of Science, Department of Astronomy.
    Guterman, P.
    Simon, A. E.
    Boisse, I.
    Bonfanti, A.
    Martin, D.
    Santerne, A.
    Salmon, S.
    Standing, M. R.
    Van Grootel, V.
    Wilson, T. G.
    Alibert, Y.
    Alonso, R.
    Anglada Escudé, G.
    Asquier, J.
    Bárczy, T.
    Barrado, D.
    Barros, S. C. C.
    Battley, M.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Bekkelien, A.
    Benz, W.
    Billot, N.
    Bonfils, X.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Busch, M.-D.
    Cabrera, J.
    Charnoz, S.
    Collier Cameron, A.
    Csizmadia, Sz.
    Davies, M. B.
    Deleuil, M.
    Deline, A.
    Delrez, L.
    Demangeon, O. D. S.
    Demory, B.-O.
    Dransfield, G.
    Ehrenreich, D.
    Erikson, A.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Gillon, M.
    Guedel, M.
    Hébrard, G.
    Heidari, N.
    Hellier, C.
    Heng, K.
    Hobson, M.
    Hoyer, S.
    Isaak, K. G.
    Kiss, L.
    Kunovac Hodžić, V.
    Lalitha, S.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Marafatto, L.
    McCormac, J.
    Miller, N.
    Nascimbeni, V.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ottensamer, R.
    Pagano, I.
    Pallé, E.
    Peter, G.
    Piotto, G.
    Pollacco, D.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I.
    Santos, N. C.
    Scandariato, G.
    Ségransan, D.
    Smith, A. M. S.
    Steinberger, M.
    Steller, M.
    Szabó, Gy. M.
    Thomas, N.
    Udry, S.
    Walter, I.
    Walton, N. A.
    Willett, E.
    The EBLM project – VIII. First results for M-dwarf mass, radius, and effective temperature measurements using CHEOPS light curves 2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 506, no 1, p. 306-322Article in journal (Refereed)
    Abstract [en]

    The accuracy of theoretical mass, radius, and effective temperature values for M-dwarf stars is an active topic of debate. Differences between observed and theoretical values have raised the possibility that current theoretical stellar structure and evolution models are inaccurate towards the low-mass end of the main sequence. To explore this issue, we use the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions. We use these light curves combined with the spectroscopic orbit for the solar-type companion to measure the mass, radius, and effective temperature of the M-dwarf star. Here, we present the analysis of three eclipsing binaries. We use the PYCHEOPS data analysis software to fit the observed transit and eclipse events of each system. Two of our systems were also observed by the TESS satellite – we similarly analyse these light curves for comparison. We find consistent results between CHEOPS and TESS, presenting three stellar radii and two stellar effective temperature values of low-mass stellar objects. These initial results from our on-going observing programme with CHEOPS show that we can expect to have ∼24 new mass, radius, and effective temperature measurements for very low-mass stars within the next few years.

  • 43. Wilson, C. D.
    et al.
    Mason, A.
    Gregersen, E.
    Olofsson, A. O. H.
    Bergman, P.
    Booth, R.
    Boudet, N.
    Buat, V.
    Curry, C. L.
    Encrenaz, P.
    Falgarone, E.
    Feldman, P.
    Fich, M.
    Floren, H. G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Gerin, M.
    Harju, J.
    Hasegawa, T.
    Hjalmarson, Å.
    Juvela, M.
    Kwok, S.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lecacheux, A.
    Liljestrom, T.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mattila, K.
    Mitchell, G.
    Nordh, L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olberg, M.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Plume, R.
    Ristorcelli, I.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Serra, G.
    Tothill, N.
    Volk, K.
    von Scheele, F.
    Submillimeter emission from water in the W3 region2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L59-L62Article in journal (Refereed)
    Abstract [en]

    Using the Odin satellite, we have mapped the submillimeter emission from the 110-101 transition of ortho-water in the W3 star-forming region. A 5arcminx 5arcmin map of the W3 IRS4 and W3 IRS5 region reveals strong water lines at half the positions in the map. The relative strength of the Odin lines compared to previous observations by SWAS suggests that we are seeing water emission from an extended region. Across much of the map the lines are double-peaked, with an absorption feature at -39 km s-1; however, some positions in the map show a single strong line at -43 km s-1. We interpret the double-peaked lines as arising from optically thick, self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted lines originate in emission near W3 IRS4. In this model, the unusual appearance of the spectral lines across the map results from a coincidental agreement in velocity between the emission near W3 IRS4 and the blue peak of the more complex lines near W3 IRS5. The strength of the water lines near W3 IRS4 suggests we may be seeing water emission enhanced in a photon-dominated region. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes), and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation was the industrial prime contractor and is also responsible for the satellite operation.

  • 44. Wilson, Thomas G.
    et al.
    Goffo, Elisa
    Alibert, Yann
    Gandolfi, Davide
    Bonfanti, Andrea
    Persson, Carina M.
    Collier Cameron, Andrew
    Fridlund, Malcolm
    Fossati, Luca
    Korth, Judith
    Benz, Willy
    Deline, Adrien
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Guterman, Pascal
    Adibekyan, Vardan
    Hooton, Matthew J.
    Hoyer, Sergio
    Leleu, Adrien
    Mustill, Alexander James
    Salmon, Sebastien
    Sousa, Sergio G.
    Suarez, Olga
    Abe, Lyu
    Agabi, Abdelkrim
    Alonso, Roi
    Anglada, Guillem
    Asquier, Joel
    Barczy, Tamas
    Barrado Navascues, David
    Barros, Susana C. C.
    Baumjohann, Wolfgang
    Beck, Mathias
    Beck, Thomas
    Billot, Nicolas
    Bonfils, Xavier
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Broeg, Christopher
    Bryant, Edward M.
    Burleigh, Matthew R.
    Buttu, Marco
    Cabrera, Juan
    Charnoz, Sebastien
    Ciardi, David R.
    Cloutier, Ryan
    Cochran, William D.
    Collins, Karen A.
    Colon, Knicole D.
    Crouzet, Nicolas
    Csizmadia, Szilard
    Davies, Melvyn B.
    Deleuil, Magali
    Delrez, Laetitia
    Demangeon, Olivier
    Demory, Brice-Olivier
    Dragomir, Diana
    Dransfield, Georgina
    Ehrenreich, David
    Erikson, Anders
    Fortier, Andrea
    Gan, Tianjun
    Gill, Samuel
    Gillon, Michael
    Gnilka, Crystal L.
    Grieves, Nolan
    Grziwa, Sascha
    Gudel, Manuel
    Guillot, Tristan
    Haldemann, Jonas
    Heng, Kevin
    Horne, Keith
    Howell, Steve B.
    Isaak, Kate G.
    Jenkins, Jon M.
    Jensen, Eric L. N.
    Kiss, Laszlo
    Lacedelli, Gaia
    Lam, Kristine
    Laskar, Jacques
    Latham, David W.
    Lecavelier des Etangs, Alain
    Lendl, Monika
    Lester, Kathryn
    Levine, Alan M.
    Livingston, John
    Lovis, Christophe
    Luque, Rafael
    Magrin, Demetrio
    Marie-Sainte, Wenceslas
    Maxted, Pierre F. L.
    Mayo, Andrew W.
    McLean, Brian
    Mecina, Marko
    Mekarnia, Djamel
    Nascimbeni, Valerio
    Nielsen, Louise D.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Osborn, Hugh P.
    Osborne, Hannah L. M.
    Ottensamer, Roland
    Pagano, Isabella
    Palle, Enric
    Peter, Gisbert
    Piotto, Giampaolo
    Pollacco, Don
    Queloz, Didier
    Ragazzoni, Roberto
    Rando, Nicola
    Rauer, Heike
    Redfield, Seth
    Ribas, Ignasi
    Ricker, George R.
    Rieder, Martin
    Santos, Nuno C.
    Scandariato, Gaetano
    Schmider, Francois-Xavier
    Schwarz, Richard P.
    Scott, Nicholas J.
    Seager, Sara
    Segransan, Damien
    Serrano, Luisa Maria
    Simon, Attila E.
    Smith, Alexis M. S.
    Steller, Manfred
    Stockdale, Chris
    Szabo, Gyula
    Thomas, Nicolas
    Ting, Eric B.
    Triaud, Amaury H. M. J.
    Udry, Stephane
    Van Eylen, Vincent
    Van Grootel, Valerie
    Vanderspek, Roland K.
    Viotto, Valentina
    Walton, Nicholas
    Winn, Joshua N.
    A pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 characterized with CHEOPS2022In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 511, no 1, p. 1043-1071Article in journal (Refereed)
    Abstract [en]

    We report the discovery and characterization of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in the Transiting Exoplanet Survey Satellite (TESS) photometry. To characterize the system, we performed and retrieved the CHaracterising ExOPlanets Satellite (CHEOPS), TESS, and ground-based photometry, the High Accuracy Radial velocity Planet Searcher (HARPS) high-resolution spectroscopy, and Gemini speckle imaging. We characterize the host star and determine Teff,⋆=4734±67K⁠, R⋆=0.726±0.007R⊙⁠, and M⋆=0.748±0.032M⊙⁠. We present a novel detrending method based on point spread function shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of Pb = 6.44387 ± 0.00003 d, a radius of Rb = 2.59 ± 0.04 R⊕, and a mass of Mb=13.5+1.7−1.8 M⊕, whilst TOI-1064 c has an orbital period of Pc=12.22657+0.00005−0.00004 d, a radius of Rc = 2.65 ± 0.04 R⊕, and a 3σ upper mass limit of 8.5 M⊕. From the high-precision photometry we obtain radius uncertainties of ∼1.6 per cent, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterized sub-Neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further radial velocities are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of mass–radius space, and it allow us to identify a trend in bulk density–stellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets.

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