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The Massive Progenitor Of The Type II-L SN2009hd In M66

31/10/2011

There are two main classes of supernovae (SNe): Type Ia accretion event supernovae, usually associated with binary star systems and degenerate stars, and core-collapse supernovae (CC-SNe)* of massive stars. The Type II core-collapse event, for lack of complication, is a result of the collapse of the degenerate Iron core of a massive star when it reaches the Chandrasekhar limit (Gilmore 2004).

N.B.* This ‘type’ (which also includes Type Ib and Ic) can be sub-allocated either linear (L) or plateau (P) which are features attributed to their light curves.

Type II-Linear supernovae (SNe II-L) are among the least common and, therefore, most poorly studied subclasses of CC-SNe. They represent 6.4–10% of all CC-SNe (Smith et al. 2011; Li et al. 2011). The spectra of SNe II-L are similar to those of the much more common SNe II-Plateau (II-P), but SNe II-L are distinguished by the shapes of their light curves. While light curves of SNe II-P exhibit a relatively constant plateau for approximately 100 days after an initial peak in the first few days, the light curves of SNe II-L instead show a linear decline commencing just after the initial peak (e.g. Barbon, Ciatti & Rosino 1979).

A recent discovery of a Type II CC-SNe was made by Monard (2009) in July 2009: 2009hd, which was subsequently designated as a ‘reddened’ Type II SNe (Kasliwal, Sahu & Anupama 2009) and, now, perhaps wrongly as a Type II-P SNe by Kasliwal, Sahu & Anupama (2009). A recent paper by Filippenko et al. 2011 has now challenged the orginal Kasliwal, Sahu, & Anupama Type II-P designation, stating that it is, from their analysis, a Type II-L SNe.

After this re-designation from a Type II-P to a Type II-L Fillipenko et al. (2011) went on to constrain the properties (luminosity, mass and effective temperature) of the progenitor star for SN 2009hd.

Fillipenko et al. (2011) found that the inferred properties are certainly consistent with a red supergiant (RSG), the constraints also allow for the possibility that the star is more yellow than red. A yellow colour may indicate that it exploded in a post-RSG evolutionary state, or perhaps it is an RSG in a binary system with a bluish companion. The progenitor may have evolved back to the blue phase after reaching the RSG stage, for example, because it has lost mass (Meynet et al. 2011) perhaps through pulsationally induced and enhanced mass loss (Yoon & Cantiello 2010).

Fillipenko et al. (2011) then analysed the hydrogen lines and found them to be weak, possibly indicating that the SNe progenitor exploded with a low-mass outer hydrogen envelope which is consistent with mass loss via huge stellar winds.

Through comparison with high-mass stellar evolutionary tracks at solar metallicity they were are able to, all be it conservatively, constrain the initial mass of the progenitor to  This limit to the initial mass estimate for the SN2009hd progenitor is consistent with the range in mass found for the SN II-L 2009kr (Elias-Rosa et al. 2010) and SN2008cn (Elias-Rosa et al. 2009).

Ultimately, a very-late-time set of multi-band images of the SN 2009hd field should be obtained with HST and the Wide Field Camera 3 (WFC3) many years later, when the SN has greatly faded, as has been done for the SN IIn 2005gl (Gal-Yam & Leonard 2009) and for the SN IIb 1993J and SN II-P 2003gd (Maund & Smartt 2009), to better distinguish the constituents of the SN 2009hd environment and help decipher the true nature of the progenitor star.

Journal References:

  • Filippenko, A.V.; Elias-Rosa, N. et al. (2011) The Massive Progenitor Of The Possible Type II-Linear Supernova 2009hd In Messier 66. The Astrophysical Journal, 742 (1) Article I.D.: 6.
  • Elias-Rosa, N. et al. (2010) The Massive Progenitor Of The Type II-Linear Supernova 2009krThe Astrophysical Journal: Letters, 714 (2) pp. L254-L259.
  • Berger, E.; Foley, R.; Covarrubias, R. (2009) SN2009hd Is A Highly-reddened Type II-P SupernovaThe Astronomer’s Telegram, #2118.
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