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  • 1.
    Eriksson, Simon
    Stockholm University, Faculty of Science, Department of Astronomy.
    A Photometric Variability Study Using Brown Dwarfs As Giant Planet Analogues: Investigating rotation periods and cloud structure2016Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
  • 2.
    Eriksson, Simon C.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Calissendorff, Per
    Stockholm University, Faculty of Science, Department of Astronomy.
    Detection of new strongly variable brown dwarfs in the L/T transition2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 629, article id A145Article in journal (Refereed)
    Abstract [en]

    Context. Brown dwarfs in the spectral range L9-T3.5, within the so called L/T transition, have been shown to be variable at higher amplitudes and with greater frequency than other field dwarfs. This strong variability allows for the probing of their atmospheric structure in 3D through multi-wavelength observations for studying the underlying physical mechanisms responsible for the variability. The few known strongly variable dwarfs in this range have been extensively studied. Now, more variables such as these need to be discovered and studied to better constrain atmospheric models. This is also critical to better understand giant exoplanets and to shed light on a number of possible correlations between brown dwarf characteristics and variability.

    Aims. Previous studies suggest an occurrence rate for strong variability (peak-to-peak amplitudes >2%) of up to similar to 39% among brown dwarfs within the L/T transition. In this work, we aim to discover new strong variables in this spectral range by targeting ten previously unsurveyed brown dwarfs.

    Methods. We used the NOTCam at the Nordic Optical Telescope to observe 11 targets, with spectral types ranging from L9.5 to T3.5, in the J-band during October 2017 and September 2018. Using differential aperture photometry, we then analysed the light curves for significant variability using Lomb-Scargle periodogram algorithms and least squares fitting.

    Results. We report first discoveries of strong and significant variability in four out of the ten targets (false alarm probability <0.1%), measuring peak-to-peak amplitudes up to 10.7 +/- 0.4% in J for the T1 dwarf 2MASS J22153705+2110554, for which we observe significant light curve evolution between the 2017 and 2018 epochs. We also report a marginally significant detection of strong variability, and confirm that the well known 2MASS J01365662+0933473 is still strongly variable three years after the last reported epoch. Finally, we present an extensive multi-epoch catalogue of strong variables reported in the literature and discuss possible correlations that are identifiable from the catalogue.

    Conclusions. We significantly add to the number of known strong variables, and through Poisson statistics infer an occurrence rate for strong variability among L9-T3.5 brown dwarfs of 40(-19)(+32)%, which is in agreement with previous estimates. The new variables identified in this work are also excellently suited for extensive multi-wavelength observations dedicated to probing the 3D structure of brown dwarf atmospheres.

  • 3.
    Janson, Markus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    André, Damien
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bonnefoy, Mickaël
    Delorme, Philippe
    Reffert, Sabine
    Desidera, Silvano
    Langlois, Maud
    Chauvin, Gaël
    Gratton, Raffaele
    Bohn, Alexander J.
    Eriksson, Simon C.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Marleau, Gabriel-Dominique
    Mamajek, Eric E.
    Vigan, Arthur
    Carson, Joseph C.
    The B-Star Exoplanet Abundance Study: a co-moving 16-25 M-Jup companion to the young binary system HIP 790982019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 626, article id A99Article in journal (Refereed)
    Abstract [en]

    Wide low-mass substellar companions are known to be very rare among low-mass stars, but appear to become increasingly common with increasing stellar mass. However, B-type stars, which are the most massive stars within similar to 150 pc of the Sun, have not yet been examined to the same extent as AFGKM-type stars in that regard. In order to address this issue, we launched the ongoing B-star Exoplanet Abundance Study (BEAST) to examine the frequency and properties of planets, brown dwarfs, and disks around B-type stars in the Scorpius-Centaurus (Sco-Cen) association; we also analyzed archival data of B-type stars in Sco-Cen. During this process, we identified a candidate substellar companion to the B9-type spectroscopic binary HIP 79098 AB, which we refer to as HIP 79098 (AB)b. The candidate had been previously reported in the literature, but was classified as a background contaminant on the basis of its peculiar colors. Here we demonstrate that the colors of HIP 79098 (AB)b are consistent with several recently discovered young and low-mass brown dwarfs, including other companions to stars in Sco-Cen. Furthermore, we show unambiguous common proper motion over a 15-yr baseline, robustly identifying HIP 79098 (AB)b as a bona fide substellar circumbinary companion at a 345 +/- 6 AU projected separation to the B9-type stellar pair. With a model-dependent mass of 16-25 M-Jup yielding a mass ratio of <1%, HIP 79098 (AB)b joins a growing number of substellar companions with planet-like mass ratios around massive stars. Our observations underline the importance of common proper motion analysis in the identification of physical companionship, and imply that additional companions could potentially remain hidden in the archives of purely photometric surveys.

  • 4. Vos, Johanna M.
    et al.
    Biller, Beth A.
    Bonavita, Mariangela
    Eriksson, Simon
    Stockholm University, Faculty of Science, Department of Astronomy.
    Liu, Michael C.
    Best, William M. J.
    Metchev, Stanimir
    Radigan, Jacqueline
    Allers, Katelyn N.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Buenzli, Esther
    Dupuy, Trent J.
    Bonnefoy, Mickael
    Manjavacas, Elena
    Brandner, Wolfgang
    Crossfield, Ian
    Deacon, Niall
    Henning, Thomas
    Homeier, Derek
    Kopytova, Taisiya
    Schlieder, Joshua
    A search for variability in exoplanet analogues and low-gravity brown dwarfs2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 483, no 1, p. 480-502Article in journal (Refereed)
    Abstract [en]

    We report the results of a J-band survey for photometric variability in a sample of young, low-gravity objects using the New Technology Telescope (NTT) and the United Kingdom Infrared Telescope (UKIRT). Surface gravity is a key parameter in the atmospheric properties of brown dwarfs and this is the first large survey that aims to test the gravity dependence of variability properties. We do a full analysis of the spectral signatures of youth and assess the group membership probability of each target using membership tools from the literature. This results in a 30 object sample of young low-gravity brown dwarfs. Since we are lacking in objects with spectral types later than L9, we focus our statistical analysis on the L0-L8.5 objects. We find that the variability occurrence rate of L0-L8.5 low-gravity brown dwarfs in this survey is 30(-8)(+16) per cent. We reanalyse the results of Radigan (2014) and find that the field dwarfs with spectral types L0-L8.5 have a variability occurrence rate of 11(-4)(+13) per cent. We determine a probability of 98 per cent that the samples are drawn from different distributions. This is the first quantitative indication that the low-gravity objects are more likely to be variable than the field dwarf population. Furthermore, we present follow-up J(S) and K-S observations of the young, planetary-mass variable object PSO 318.5-22 over three consecutive nights. We find no evidence of phase shifts between the J(S) and K-S bands and find higher J(S) amplitudes. We use the J(S) light curves to measure a rotational period of 8.45 +/- 0.05 h for PSO 318.5-22.

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