Hydrogen and helium traces in type Ib-c supernovae

Free access article

Issue		A&A Volume 450, Number 1, April IV 2006


Page(s)		305 - 330
Section		Stellar structure and evolution
DOI		http://dx.doi.org/10.1051/0004-6361:20054366

A&A 450, 305-330 (2006)
DOI: 10.1051/0004-6361:20054366

Hydrogen and helium traces in type Ib-c supernovae

A. Elmhamdi^{1, 2, 3}, I. J. Danziger³, D. Branch⁴, B. Leibundgut⁵, E. Baron⁴ and R. P. Kirshner⁶

¹ ICTP-International Center for Theoretical Physics, Strada Costiera 11, 34014 Trieste, Italy
e-mail: elmhamdi@ts.astro.it; elmhamdi@sissa.it
² INAF-Osservatorio Astronomico di Callurania, via Mentore Maggini, 64100 Teramo, Italy
³ INAF-Osservatorio Astronomico di Trieste, via G.B.Tiepolo 11, 34131 Trieste, Italy
⁴ Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019, USA
⁵ European Southern Observatory, Karl-Schwarzschild-Strasse 2. 85478, Garching, Germany
⁶ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

(Received 17 October 2005 / Accepted 29 December 2005 )

Abstract
Aims.To investigate the spectroscopic properties of a selected optical photospheric spectra of core collapse supernovae (CCSNe). Special attention is devoted to traces of hydrogen at early phases. The impact on the physics and nature of their progenitors is emphasized.
Methods.The CCSNe-sample spectra are analyzed with the parameterized supernova synthetic spectrum code "SYNOW" adopting some simplifying approximations.
Results.The generated spectra are found to match the observed ones reasonably well, including a list of only 23 candidate ions. Guided by SN Ib 1990I, the observed trough near 6300 Å is attributed to H $\alpha$ in almost all type Ib events, although in some objects it becomes too weak to be discernible, especially at later phases. Alternative line identifications are discussed. Differences in the way hydrogen manifests its presence within CCSNe are highlighted. In type Ib SNe, the H $\alpha$ contrast velocity (i.e. line velocity minus the photospheric velocity) seems to increase with time at early epochs, reaching values as high as 8000 km s^-1 around 15-20 days after maximum and then remains almost constant. The derived photospheric velocities, indicate a lower velocity for type II SNe 1987A and 1999em as compared to SN Ic 1994I and SN IIb 1993J, while type Ib events display a somewhat larger variation. The scatter, around day 20, is measured to be ~5000 km s^-1. Following two simple approaches, rough estimates of ejecta and hydrogen masses are given. A mass of hydrogen of approximately 0.02 $M_\odot$ is obtained for SN 1990I, while SNe 1983N and 2000H ejected ~0.008 $M_\odot$ and ~0.08 $M_\odot$ of hydrogen, respectively. SN 1993J has a higher hydrogen mass, ~0.7 $M_\odot$ with a large uncertainty. A low mass and thin hydrogen layer with very high ejection velocities above the helium shell, is thus the most likely scenario for type Ib SNe. Some interesting and curious issues relating to oxygen lines suggest future investigations.

Key words: stars: supernovae: general -- line: identification -- line: profiles

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