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Observations of rare supernovae and their environments
Stockholm University, Faculty of Science, Department of Astronomy.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Supernovae (SNe) are the final stage in the life of massive stars. Their explosion unbinds the progenitor star revealing its inner layers. The SN ejecta interact with the circumstellar material (CSM), providing further information on the progenitor star.

In this work we present the study of rare SN subtypes, aiming to investigate their observational and physical properties and those of their progenitor stars.These studies include the analysis of SN samples as well as that of single objects.Two main SN classes are discussed: radioactively-powered events and SNe interacting with their CSM.

Within the first group, we investigated the rare (~1% of core-collapse SNe) family of SN 1987A-like events. These SNe are found to be the explosion of compact, hydrogen-rich blue supergiant (BSG) stars, and to occur mainly in moderately low metallicity environs. We also studied a sample of 20 stripped-envelope (SE) SNe, which are also powered by the decay of radioactive 56Ni. These SNe are the result of the core-collapse of massive, hydrogen or even helium-poor stars stripped of their outer envelopes by line-driven winds and/or by the accretion onto companion stars.We investigated the differences among the early-time light curves of the subtypes forming the SE SN group (IIb, Ib, Ic, Ic-BL) and found that in all of them the 56Ni is strongly mixed out in the ejecta. This result suggests that the difference between helium-poor and helium-rich SNe is due to an actual lack of helium in SNe Ic and Ic-BL rather than to a different degree of 56Ni mixing.

Our work on CSM-interacting SNe include the study of a sample of SNe IIn, i.e. core-collapse SNe interacting with hydrogen-rich CSM, and the analysis of SN 2008J, a particularly rare event which we interpreted as the interaction of a thermonuclear SN Ia with a thick hydrogen-rich CSM. Spectral analysis of the SN IIn sample suggests that these SNe are likely to be the explosion of luminous blue variable stars (LBVs), although other channels are not excluded.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University , 2014. , 80 p.
Keyword [en]
Supernova, stellar evolution, metallicity, circumstellar interaction
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-108286ISBN: 978-91-7649-030-3 (print)OAI: oai:DiVA.org:su-108286DiVA: diva2:756549
Public defence
2014-12-19, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Submitted.

Available from: 2014-11-27 Created: 2014-10-17 Last updated: 2014-11-20Bibliographically approved
List of papers
1. The Type II supernovae 2006V and 2006au: two SN 1987A-like events
Open this publication in new window or tab >>The Type II supernovae 2006V and 2006au: two SN 1987A-like events
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2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 537, 140- p.Article in journal (Refereed) Published
Abstract [en]

Context. Supernova 1987A revealed that a blue supergiant (BSG) star can end its life as a core-collapse supernova (SN). SN 1987A and other similar objects exhibit properties that distinguish them from ordinary Type II Plateau (IIP) SNe, whose progenitors are believed to be red supergiants (RSGs). Similarities among 1987A-like events include a long rise to maximum, early luminosity fainter than that of normal Type IIP SNe, and radioactivity acting as the primary source powering the light curves. Aims: We present and analyze two SNe monitored by the Carnegie Supernova Project that are reminiscent of SN 1987A. Methods: Optical and near-infrared (NIR) light curves, and optical spectroscopy of SNe 2006V and 2006au are presented. These observations are compared to those of SN 1987A, and are used to estimate properties of their progenitors. Results: Both objects exhibit a slow rise to maximum and light curve evolution similar to that of SN 1987A. At the earliest epochs, SN 2006au also displays an initial dip which we interpret as the signature of the adiabatic cooling phase that ensues shock break-out. SNe 2006V and 2006au are both found to be bluer, hotter and brighter than SN 1987A. Spectra of SNe 2006V and 2006au are similar to those of SN 1987A and other normal Type II objects, although both consistently exhibit expansion velocities higher than SN 1987A. Semi-analytic models are fit to the UVOIR light curve of each object from which physical properties of the progenitors are estimated. This yields ejecta mass estimates of Mej ≈ 20 M&sun;, explosion energies of E ≈ 2-3 × 1051 erg s-1, and progenitor radii of R ≈ 75-100 R&sun; for both SNe. Conclusions: The progenitors of SNe 2006V and 2006au were most likely BSGs with a larger explosion energy as compared to that of SN 1987A. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (ESO Programme 076.A-0156). This paper includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory, Chile.Tables 1-6 are available in electronic form at http://www.aanda.org

Keyword
supernovae: general, supernovae: individual: SN 2006V, supernovae: individual: SN 2006au, supernovae: individual: SN 1987A
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-83518 (URN)10.1051/0004-6361/201118091 (DOI)
Available from: 2012-12-12 Created: 2012-12-12 Last updated: 2017-12-07Bibliographically approved
2. Supernova 2008J: early time observations of a heavily reddened SN 2002ic-like transient
Open this publication in new window or tab >>Supernova 2008J: early time observations of a heavily reddened SN 2002ic-like transient
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2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 545, L7- p.Article in journal (Refereed) Published
Abstract [en]

Aims: We provide additional observational evidence that some Type Ia supernovae (SNe Ia) show signatures of circumstellar interaction (CSI) with hydrogen-rich material. Methods: Early phase optical and near-infrared (NIR) light curves and spectroscopy of SN 2008J obtained by the Carnegie Supernova Project are studied and compared to those of SNe 2002ic and 2005gj. Our NIR spectrum is the first obtained for a 2002ic-like object extending up to 2.2 μm. A published high-resolution spectrum is used to provide insight on the circumstellar material (CSM). Results: SN 2008J is found to be affected by AV ~ 1.9 mag of extinction and to closely resemble SN 2002ic. Spectral and color comparison to SNe 2002ic and 2005gj suggests RV < 3.1. Spectral decomposition reveals the underlying SN emission matches a 1991T-like event and, since SN 2008J is as luminous as SN 2005gj (Vmax = -20.3 mag), we conclude that their CSI emissions are similarly robust. The high-resolution spectrum reveals narrow emission lines produced from un-shocked gas characterized by a wind velocity of ~50 km s-1. We conclude that SN 2008J best matches an explosion of a SN Ia that interacts with its CSM. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (ESO Programme 080.A-0516).Figure 4 and Tables 1-6 are available in electronic form at http://www.aanda.org

Keyword
supernovae: general, supernovae: individual: SN 2008J
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-83517 (URN)10.1051/0004-6361/201220105 (DOI)000309254900163 ()
Available from: 2012-12-12 Created: 2012-12-12 Last updated: 2017-12-07Bibliographically approved
3. Carnegie Supernova Project: Observations of Type IIn supernovae
Open this publication in new window or tab >>Carnegie Supernova Project: Observations of Type IIn supernovae
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2013 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 555, A10- p.Article in journal (Refereed) Published
Abstract [en]

Aims. The observational diversity displayed by various Type IIn supernovae (SNe IIn) is explored and quantified. In doing so, a more coherent picture ascribing the variety of observed SNe IIn types to particular progenitor scenarios is sought. Methods. Carnegie Supernova Project (CSP) optical and near-infrared light curves and visual-wavelength spectroscopy of the Type IIn SNe 2005kj, 2006aa, 2006bo, 2006qq, and 2008fq are presented. Combined with previously published observations of the Type IIn SNe 2005ip and 2006jd, the full CSP sample is used to derive physical parameters that describe the nature of the interaction between the expanding SN ejecta and the circumstellar material (CSM). Results. For each SN of our sample, we find counterparts, identifying objects similar to SNe 1994W (SN 2006bo), 1998S (SN 2008fq), and 1988Z (SN 2006qq). We present the unprecedented initial u-band plateau of SN 2006aa, and its peculiar late-time luminosity and temperature evolution. For each SN, mass-loss rates of 10(-4)-10(-2) M-circle dot yr(-1) are derived, assuming the CSM was formed by steady winds. Typically wind velocities of a few hundred km s(-1) are also computed. Conclusions. The CSP SN IIn sample seems to be divided into subcategories rather than to have exhibited a continuum of observational properties. The wind and mass-loss parameters would favor a luminous blue variable progenitor scenario. However, the assumptions made to derive those parameters strongly influence the results, and therefore, other progenitor channels behind SNe IIn cannot be excluded at this time.

Keyword
supernovae: general, stars: winds, outflows, stars: massive
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-93583 (URN)10.1051/0004-6361/201321180 (DOI)000322008600010 ()
Note

AuthorCount:19;

Funding Agencies:

Instrument Centre for Danish Astrophysics (IDA)

NSF AST-0306969,  AST-0607438,  AST-1008343 

Swedish Research Council  

CONICYT through FONDECYT 3110142 

Millennium Center for Supernova Science P10-064-F

National Aeronautics and Space Administration  

Available from: 2013-09-10 Created: 2013-09-10 Last updated: 2017-12-06Bibliographically approved
4. A metallicity study of 1987A-like supernova host galaxies
Open this publication in new window or tab >>A metallicity study of 1987A-like supernova host galaxies
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2013 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 558, UNSP A143Article in journal (Refereed) Published
Abstract [en]

Context. The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A has long been debated, along with the role that its sub-solar metallicity played. We now have a sample of SN 1987A-like events that arise from the rare core collapse (CC) of massive (similar to 20 M-circle dot) and compact (less than or similar to 100 R-circle dot) BSGs. Aims. The metallicity of the explosion sites of the known BSG SNe is investigated, as well as the association of BSG SNe to star-forming regions. Methods. Both indirect and direct metallicity measurements of 13 BSG SN host galaxies are presented, and compared to those of other CC SN types. Indirect measurements are based on the known luminosity-metallicity relation and on published metallicity gradients of spiral galaxies. In order to provide direct metallicity measurements based on strong line diagnostics, we obtained spectra of each BSG SN host galaxy both at the exact SN explosion sites and at the positions of other H II regions. We also observed these hosts with narrow H alpha and broad R-band filters in order to produce continuum-subtracted H alpha images. This allows us to measure the degree of association between BSG SNe and star-forming regions, and to compare it to that of other SN types. Results. BSG SNe are found to explode either in low-luminosity galaxies or at large distances from the nuclei of luminous hosts. Therefore, their indirectly measured metallicities are typically lower than those of SNe IIP and Ibc. This result is confirmed by the direct metallicity estimates, which show slightly sub-solar oxygen abundances (12 + log (O/H) similar to 8.3-8.4 dex) for the local environments of BSG SNe, similar to that of the Large Magellanic Cloud (LMC), where SN 1987A exploded. However, we also note that two objects of our sample (SNe 1998A and 2004em) were found at near solar metallicity. SNe IIb have a metallicity distribution similar to that of our BSG SNe. Finally, we find that the degree of association to star-forming regions is similar among BSG SNe, SNe IIP and IIn. Conclusions. Our results suggest that LMC metal abundances play a role in the formation of some 1987A-like SNe. This would naturally fit in a single star scenario for the progenitors. However, the existence of two events at nearly solar metallicity suggests that also other channels, e.g. binarity, contribute to produce BSG SNe.

Keyword
supernovae: general, stars: evolution, galaxies: abundances
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-98317 (URN)10.1051/0004-6361/201322276 (DOI)000326574000143 ()
Note

AuthorCount:9;

Available from: 2014-01-03 Created: 2014-01-03 Last updated: 2017-12-06Bibliographically approved
5. Early-time light curves of Type Ib/c supernovae from the SDSS-II Supernova Survey
Open this publication in new window or tab >>Early-time light curves of Type Ib/c supernovae from the SDSS-II Supernova Survey
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2015 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 574, A60Article in journal (Refereed) Published
Abstract [en]

Context. Type Ib/c supernovae (SNe Ib/c) have been investigated in several single-object studies; however, there is still a paucity of works concerning larger, homogeneous samples of these hydrogen-poor transients, in particular regarding the premaximum phase of their light curves.

Aims. In this paper we present and analyze the early-time optical light curves (LCs, ugriz) of 20 SNe Ib/c from the Sloan Digital Sky Survey (SDSS) SN survey II, aiming to study their observational and physical properties, as well as to derive their progenitor parameters.

Methods. High-cadence, multiband LCs are fitted with a functional model and the best-fit parameters are compared among the SN types. Bolometric LCs (BLCs) are constructed for the entire sample. We also computed the black-body (BB) temperature (TBB) and photospheric radius (Rph) evolution for each SN via BB fits on the spectral energy distributions. In addition, the bolometric properties are compared to both hydrodynamical and analytical model expectations.

Results. Complementing our sample with literature data, we find that SNe Ic and Ic-BL (broad-line) have shorter rise times than those of SNe Ib and IIb. The decline rate parameter, Δm15, is similar among the different subtypes. SNe Ic appear brighter and bluer than SNe Ib, but this difference vanishes if we consider host galaxy extinction corrections based on colors. Templates for SN Ib/c LCs are presented. Our SNe have typical TBB of ~10 000 K at the peak and Rph of ~1015 cm. Analysis of the BLCs of SNe Ib and Ic gives typical ejecta masses Mej≈ 3.6−5.7  M, energies EK≈ 1.5−1.7×1051 erg, and M(56Ni) ≈ 0.3  M. Higher values for EK and M(56Ni) are estimated for SNe Ic-BL (Mej≈ 5.4  MEK≈ 10.7×1051 erg, M(56Ni) ≈ 1.1  M). For the majority of SNe Ic and Ic-BL, we can put strong limits (<2−4 days) on the duration of the expected early-time plateau. Less stringent limits can be placed on the duration of the plateau for the sample of SNe Ib. In the single case of SN Ib 2006lc, a >5.9 days plateau seems to be detected. The rising part of the BLCs is reproduced by power laws with index <2. For two events (SN 2005hm and SN 2007qx), we find signatures of a possible shock break-out cooling tail.

Conclusions. Based on the limits for the plateau length and on the slow rise of the BLCs, we find that in most of our SNe Ic and Ic-BL the 56Ni is mixed out to the outer layers, suggesting that SN Ic progenitors are de facto helium poor. The derived progenitor parameters (56Ni, EKMej) are consistent with previous works.

Keyword
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Solar and Stellar Astrophysics
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-108294 (URN)10.1051/0004-6361/201423915 (DOI)000349467000060 ()
Available from: 2014-10-17 Created: 2014-10-17 Last updated: 2017-12-05Bibliographically approved

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