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SN 2011dh and the progenitors of Type IIb supernovae
Stockholm University, Faculty of Science, Department of Astronomy. (Supernovae group)ORCID iD: 0000-0002-6209-6015
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Core-collapse supernovae (SNe) are the observed events following the collapse of the core of evolved massive stars. The gravitational energy released creates a powerful shock that disrupts the star and ejects the heated material into the surrounding circumstellar medium. The observed properties depend on the mass lost by the star, e.g. through stellar winds or mass transfer in binary systems, and the subject of this thesis is the class of Type IIb SNe, which are thought to have lost most, but not all of their hydrogen envelopes. A quite unique set of observations has recently been obtained for the Type IIb SN 2011dh, which was followed to more than a thousand days after the explosion, and observed by several groups at a wide range of wavelengths. In this work, the bulk portion of the ultraviolet to mid-infrared observations, as well as pre-explosion images of the progenitor star, are presented, discussed, and analysed. Lightcurve and spectral modelling of the SN observations, presented in this and related works, all suggest a progenitor of modest initial mass (<15 solar masses) with an extended and low-mass hydrogen envelope, consistent with what is found from the pre-explosion observations. Although mass-loss rates for single stars are uncertain, they are likely too weak to expel the hydrogen envelope for stars in this mass range. Therefore, an appealing alternative is mass-loss by Roche-lobe overflow in a binary system, as was likely the case for the Type IIb SN 1993J. Post-explosion observations have revealed a blue compact companion star blended with the fading SN 1993J, and a similar result has been claimed for SN 2011dh. The fact that some SNe arise from binary systems is not surprising given the large binary fraction observed for massive stars, and in this work, a grid of hydrodynamical SN models is used to infer modest initial masses (<15 solar masses) for most Type IIb SNe documented in the literature, suggesting that binary systems actually dominate the production of Type IIb SNe.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University , 2015.
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-115811ISBN: 978-91-7649-165-2 (print)OAI: oai:DiVA.org:su-115811DiVA, id: diva2:800078
Public defence
2015-05-27, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Accepted. Paper 4: Submitted.

Available from: 2015-05-05 Created: 2015-04-01 Last updated: 2020-02-03Bibliographically approved
List of papers
1. THE YELLOW SUPERGIANT PROGENITOR OF THE TYPE II SUPERNOVA 2011dh IN M51
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2011 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 739, no 2, article id L37Article in journal (Refereed) Published
Abstract [en]

We present the detection of the putative progenitor of the Type IIb SN 2011dh in archival pre-explosion Hubble Space Telescope images. Using post-explosion Adaptive Optics imaging with Gemini NIRI+ALTAIR, the position of the supernova (SN) in the pre-explosion images was determined to within 23 mas. The progenitor candidate is consistent with an F8 supergiant star (logL/L(circle dot) = 4.92 +/- 0.20 and T(eff) = 6000 +/- 280 K). Through comparison with stellar evolution tracks, this corresponds to a single star at the end of core C-burning with an initial mass of M(ZAMS) = 13 +/- 3 M(circle dot). The possibility of the progenitor source being a cluster is rejected, on the basis of: (1) the source not being spatially extended, (2) the absence of excess H alpha emission, and (3) the poor fit to synthetic cluster spectral energy distributions (SEDs). It is unclear if a binary companion is contributing to the observed SED, although given the excellent correspondence of the observed photometry to a single star SED we suggest that the companion does not contribute significantly. Early photometric and spectroscopic observations show fast evolution similar to the transitional Type IIb SN 2008ax and suggest that a large amount of the progenitor's hydrogen envelope was removed before explosion. Late-time observations will reveal if the yellow supergiant or the putative companion star were responsible for this SN explosion.

Keywords
supernovae: general, supernovae: individual (2011dh)
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-66550 (URN)10.1088/2041-8205/739/2/L37 (DOI)000294997600003 ()
Note

authorCount :14

Available from: 2011-12-21 Created: 2011-12-20 Last updated: 2019-12-16Bibliographically approved
2. Optical and near-infrared observations of SN 2011dh-The first 100 days
Open this publication in new window or tab >>Optical and near-infrared observations of SN 2011dh-The first 100 days
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2014 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 562, p. A17-, article id A17Article in journal (Refereed) Published
Abstract [en]

We present optical and near-infrared (NIR) photometry and spectroscopy of the Type IIb supernova (SN) 2011dh for the first 100 days. We complement our extensive dataset with Swift ultra-violet (UV) and Spitzer mid-infrared (MIR) data to build a UV to MIR bolometric lightcurve using both photometric and spectroscopic data. Hydrodynamical modelling of the SN based on this bolometric lightcurve have been presented in Bersten et al. (2012, ApJ, 757, 31). We find that the absorption minimum for the hydrogen lines is never seen below similar to 11 000 km s(-1) but approaches this value as the lines get weaker. This suggests that the interface between the helium core and hydrogen rich envelope is located near this velocity in agreement with the Bersten et al. (2012) He4R270 ejecta model. Spectral modelling of the hydrogen lines using this ejecta model supports the conclusion and we find a hydrogen mass of 0.01-0.04 M-circle dot to be consistent with the observed spectral evolution. We estimate that the photosphere reaches the helium core at 5-7 days whereas the helium lines appear between similar to 10 and similar to 15 days, close to the photosphere and then move outward in velocity until similar to 40 days. This suggests that increasing non-thermal excitation due to decreasing optical depth for the gamma-rays is driving the early evolution of these lines. The Spitzer 4.5 mu m band shows a significant flux excess, which we attribute to CO fundamental band emission or a thermal dust echo although further work using late time data is needed. The distance and in particular the extinction, where we use spectral modelling to put further constraints, is discussed in some detail as well as the sensitivity of the hydrodynamical modelling to errors in these quantities. We also provide and discuss pre- and post-explosion observations of the SN site which shows a reduction by similar to 75 percent in flux at the position of the yellow supergiant coincident with SN 2011dh. The B, V and r band decline rates of 0.0073, 0.0090 and 0.0053 mag day(-1) respectively are consistent with the remaining flux being emitted by the SN. Hence we find that the star was indeed the progenitor of SN 2011dh as previously suggested by Maund et al. (2011, ApJ, 739, L37) and which is also consistent with the results from the hydrodynamical modelling.

Keywords
supernovae: general, supernovae: individual: SN 2011dh, galaxies: clusters: individual: M51
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-102984 (URN)10.1051/0004-6361/201321850 (DOI)000332161800029 ()
Note

AuthorCount:29;

Available from: 2014-04-25 Created: 2014-04-25 Last updated: 2019-12-16Bibliographically approved
3. The Type IIb SN 2011dh: Two years of observations and modelling of the lightcurves
Open this publication in new window or tab >>The Type IIb SN 2011dh: Two years of observations and modelling of the lightcurves
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2015 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 580, article id A142Article in journal (Refereed) Published
Abstract [en]

We present optical and near-infrared (NIR) photometry and spectroscopy as well as modelling of the lightcurves of the Type IIb supernova (SN) 2011dh. Our extensive dataset, for which we present the observations obtained after day 100, spans two years, and complemented with Spitzer mid-infrared (MIR) data, we use it to build an optical-to-MIR bolometric lightcurve between days 3 and 732. To model the bolometric lightcurve before day 400 we use a grid of hydrodynamical SN models, which allows us to determine the errors in the derived quantities, and a bolometric correction determined with steady-state non-local thermodynamic equilibrium (NLTE) modelling. Using this method we find a helium core mass of 3.1+0.7-0.4 M for SN 2011dh, consistent within error bars with previous results obtained using the bolometric lightcurve before day 80. We compute bolometric and broad-band lightcurves between days 100 and 500 from spectral steady-state NLTE models, presented and discussed in a companion paper. The preferred 12 M (initial mass) model, previously found to agree well with the observed spectra, shows a good overall agreement with the observed lightcurves, although some discrepancies exist. Time-dependent NLTE modelling shows that after day ~600 a steady-state assumption is no longer valid. The radioactive energy deposition in this phase is likely dominated by the positrons emitted in the decay of 56Co, but seems insufficient to reproduce the lightcurves, and what energy source is dominating the emitted flux is unclear. We find an excess in the K and the MIR bands developing between days 100 and 250, during which an increase in the optical decline rate is also observed. A local origin of the excess is suggested by the depth of the He I 20 581 Å absorption. Steady-state NLTE models with a modest dust opacity in the core (τ = 0.44), turned on during this period, reproduce the observed behaviour, but an additional excess in the Spitzer 4.5 μm band remains. Carbon-monoxide (CO) first-overtone band emission is detected at day 206, and possibly at day 89, and assuming the additional excess to bedominated by CO fundamental band emission, we find fundamental to first-overtone band ratios considerably higher than observed in SN 1987A. The profiles of the [O I] 6300 Å and Mg I] 4571 Å lines show a remarkable similarity, suggesting that these lines originate from a common nuclear burning zone (O/Ne/Mg), and using small scale fluctuations in the line profiles we estimate a filling factor of ≲0.07 for the emitting material. This paper concludes our extensive observational and modelling work on SN 2011dh. The results from hydrodynamical modelling, steady-state NLTE modelling, and stellar evolutionary progenitor analysis are all consistent, and suggest an initial mass of ~12 M for the progenitor.

Keywords
supernovae: individual: SN 2008ax / supernovae: individual: SN 2011dh / galaxies: individual: M 51 / supernovae: general / supernovae: individual: SN 1993J
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-116255 (URN)10.1051/0004-6361/201424592 (DOI)000360020200142 ()
Available from: 2015-04-16 Created: 2015-04-16 Last updated: 2019-12-17Bibliographically approved
4. Hydrodynamical modelling of Type IIb SNe
Open this publication in new window or tab >>Hydrodynamical modelling of Type IIb SNe
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(English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed) Submitted
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-116253 (URN)
Available from: 2015-04-16 Created: 2015-04-16 Last updated: 2019-12-16Bibliographically approved

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