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SN 2008S: an electron-capture SN from a super-AGB progenitor?

Botticella, M. T. and Pastorello, A. and Smartt, S. J. and Meikle, W. P. S. and Benetti, S. and Kotak, R. and Cappellaro, E. and Crockett, R. M. and Mattila, S. and Sereno, M. and Patat, F. and Tsvetkov, D. and van Loon, J. Th. and Abraham, D. and Agnoletto, I. and Arbour, R. and Benn, C. and Di Rico, G. and Elias-Rosa, N. and Gorshanov, D. L. and Harutyunyan, A. and Hunter, D. and Lorenzi, V. and Keenan, F. P. and Maguire, K. and Mendez, J. and Mobberley, M. and Navasardyan, H. and Ries, C. and Stanishev, V. and Taubenberger, S. and Trundle, C. and Turatto, M. and Volkov, I. M. (2009) SN 2008S: an electron-capture SN from a super-AGB progenitor? Monthly Notices of the Royal Astronomical Society, 398 (3). pp. 1041-1068. ISSN 0035-8711. https://resolver.caltech.edu/CaltechAUTHORS:20091002-112058214

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Abstract

We present comprehensive photometric and spectroscopic observations of the faint transient SN 2008S discovered in the nearby galaxy NGC 6946. SN 2008S exhibited slow photometric evolution and almost no spectral variability during the first nine months, implying a long photon diffusion time and a high-density circumstellar medium. Its bolometric luminosity (≃10^(41) erg s^(−)1 at peak) is low with respect to most core-collapse supernovae but is comparable to the faintest Type II-P events. Our quasi-bolometric light curve extends to 300 d and shows a tail phase decay rate consistent with that of ^(56)Co. We propose that this is evidence for an explosion and formation of ^(56)Ni (0.0014 ± 0.0003 M_⊙). Spectra of SN 2008S show intense emission lines of Hα, [Ca ii] doublet and Ca ii near-infrared (NIR) triplet, all without obvious P-Cygni absorption troughs. The large mid-infrared (MIR) flux detected shortly after explosion can be explained by a light echo from pre-existing dust. The late NIR flux excess is plausibly due to a combination of warm newly formed ejecta dust together with shock-heated dust in the circumstellar environment. We reassess the progenitor object detected previously in Spitzer archive images, supplementing this discussion with a model of the MIR spectral energy distribution. This supports the idea of a dusty, optically thick shell around SN 2008S with an inner radius of nearly 90 au and outer radius of 450 au, and an inferred heating source of 3000 K. The luminosity of the central star is L ≃ 10^(4.6) L_⊙ . All the nearby progenitor dust was likely evaporated in the explosion leaving only the much older dust lying further out in the circumstellar environment. The combination of our long-term multiwavelength monitoring data and the evidence from the progenitor analysis leads us to support the scenario of a weak electron-capture supernova explosion in a super-asymptotic giant branch progenitor star (of initial mass 6–8 M_⊙ ) embedded within a thick circumstellar gaseous envelope. We suggest that all of main properties of the electron-capture SN phenomenon are observed in SN 2008S and future observations may allow a definitive answer.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1111/j.1365-2966.2009.15082.xDOIUNSPECIFIED
http://www3.interscience.wiley.com/journal/122547063/abstract?CRETRY=1&SRETRY=0PublisherUNSPECIFIED
Additional Information:© 2009 RAS. Accepted 2009 May 7; received 2009 May 7; in original form 2009 March 8. We would like to thank the referee, P. Bouchet, and J. Danziger for helpful discussions and F. Sabbadin for his suggestions on the evolution of line profiles. This work, conducted as part of the award ‘Understanding the Lives of Massive Stars from Birth to Supernovae’ (S.J. Smartt), done under the European Heads of Research Councils and European Science Foundation EURYI (European Young Investigator) Awards scheme, was supported by funds from the Participating Organisations of EURYI and the EC Sixth Framework Programme. SM acknowledges financial support from Academy of Finland (project 8120503), DT acknowledges financial support from the Program of Support for Leading Scientific Schools of Russian Federation (project NSh.433.2008.2), VS acknowledges financial support from the Fundac¸ ˜ao para a Ciˆencia e a Tecnologia and IMV acknowledges financial support from SAI scholarship. FPK is grateful to AWE Aldermaston for the award of a William Penney Fellowship. This work is based on observations collected at WHT (La Palma), NOT (La Palma), INT (La Palma), TNG (La Palma), Copernico 1.82 m telescope, the 2.2 m Telescope (Calar Alto). The WHT and INT are operated by the Isaac Newton Group; the NOT is operated jointly by Denmark, Finland, Iceland, Norway and Sweden; the Liverpool Telescope is operated by the Astrophysics Research Institute of Liverpool John Moores University and the TNG is operated by the Fundazione Galileo Galilei – National Institute for Astrophysics (INAF), Fundacion Canaria on the island of La Palma in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The 1.82 m telescope is operated by the Osservatorio di Padova INAF. The 2.2 m telescope is operated jointly by the Max-Planck- Institut fur Astronomie (MPIA) in Heidelberg, Germany, and the Instituto de Astrofisica de Andalucia (CSIC) inGranada/Spain in the Centro Astronomico Hispano Aleman at Calar Alto.We are grateful to the support astronomers at these telescopes for performing the follow up observations of SN 2008S in particular to P. Rodriguez Gil at Isaac Newton Group of Telescopes, V.P. Goranskij at SAO and T.R. Irsmambetova at SAI Crimean laboratory. Moreover, we are grateful to U. Hopp for arranging the observations at the Wendelstein Observatory, to M. Dolci and E. Di Carlo for arranging observations at Osservatorio di Campo Imperatore and to S. D. Van Dyk and J. Mauerhan for observations at Palomar 5 m telescope. We thank the members of the LBT partnership who contributed to the Science Demonstration Time observation and J. Knapen for the images of the Bok telescope. This work is based in part on archival data obtained with the Spitzer Space Telescope and made use of the NASA/IPAC Extragalactic Data base (NED), which are operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with National Aeronautics and Space Administration. Support for this work was provided by an award issued by JPL/Caltech. We also exploited data products from the 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.We acknowledge the usage of the HYPERLEDA data base (http://leda.univ-lyon1.fr).
Funders:
Funding AgencyGrant Number
European Heads of Research CouncilsUNSPECIFIED
European Science Foundation EURYI (European Young Investigator) Awards schemeUNSPECIFIED
EC Sixth Framework ProgrammeUNSPECIFIED
Academy of Finlandproject 8120503
Program of Support for Leading Scientific Schools of Russian Federationproject NSh.433.2008.2
Fundação para a Ciência e a TechnologiaUNSPECIFIED
SAI ScholarshipUNSPECIFIED
Willam Penney FellowshipUNSPECIFIED
Subject Keywords:stars: AGB and post-AGB; stars: general; supernovae: general; supernovae: individual: SN 2008S; supernovae: individual: NGC300 OT2008-1; supernovae: individual: M85 OT2006-1
Issue or Number:3
Record Number:CaltechAUTHORS:20091002-112058214
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20091002-112058214
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16169
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:05 Oct 2009 16:59
Last Modified:03 Oct 2019 01:08

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