Professor Stephen Smartt CBE FRS MRIA

Abstract:

We present the first near-infrared Hubble diagram for Type II-P supernovae (SNe), to further explore their value as distance indicators. We use a modified version of the standardized candle method, which relies on the tight correlation between the absolute magnitudes of Type II-P SNe and their expansion velocities during the plateau phase. Although our sample contains only 12 II-P SNe and they are necessarily local (z < 0.02), we demonstrate using near-infrared JHK photometry that it may be possible to reduce the scatter in the Hubble diagram to 0.1-0.15 mag. While this is potentially similar to the dispersion seen for Type Ia SNe, we caution that this needs to be confirmed with a larger sample of II-P SNe in the Hubble flow. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

We identify a source coincident with SN 2009kr in Hubble Space Telescope pre-explosion images. The object appears to be a single point source with an intrinsic color V - I = 1.1 ± 0.25 and MV = -7.6 ± 0.6. If this is a single star, it would be a yellow supergiant of log L/L 5.1 and a mass of 15⁺⁵ -4 M. The spatial resolution does not allow us yet to definitively determine if the progenitor object is a single star, a binary system, or a compact cluster. We show that the early light curve is similar to a Type IIL SN, but the prominent Hα P-Cygni profiles and the signature of the end of a recombination phase are reminiscent of a Type IIP. The evolution of the expanding ejecta will play an important role in understanding the progenitor object. © 2010. The American Astronomical Society. All rights reserved.

Abstract:

We present new optical and near-infrared (NIR) photometry and spectroscopy of the Type IIP supernova (SN), SN 2004et. In combination with already published data, this provides one of the most complete studies of optical and NIR data for any Type IIP SN from just after explosion to +500 d. The contribution of the NIR flux to the bolometric light curve is estimated to increase from 15 per cent at explosion to around 50 per cent at the end of the plateau and then declines to 40 per cent at 300 d. SN 2004et is one of the most luminous IIP SNe which has been well studied and characterized, and with a luminosity of log L= 42.3 erg s^-1 and a ⁵⁶Ni mass of 0.06 ± 0.04 M⊙, it is two times brighter than SN 1999em. We provide parametrized bolometric corrections as a function of time since explosion for SN 2004et and three other IIP SNe that have extensive optical and NIR data. These can be used as templates for future events in optical and NIR surveys without full wavelength coverage. We compare the physical parameters of SN 2004et with those of other well-studied IIP SNe and find that the kinetic energies span a range of 10⁵⁰-10⁵¹ erg. We compare the ejected masses calculated from hydrodynamic models with the progenitor masses and limits derived from pre-discovery images. Some of the ejected mass estimates are significantly higher than the progenitor mass estimates, with SN 2004et showing perhaps the most serious mass discrepancy. With the current models, it appears difficult to reconcile 100 d plateau lengths and high expansion velocities with the low ejected masses of 5-6 M⊙ implied from 7-8 M⊙ progenitors. The nebular phase is studied using very late-time Hubble Space Telescope photometry, along with optical and NIR spectroscopy. The light curve shows a clear flattening at 600 d in the optical and the NIR, which is likely due to the ejecta impacting on circumstellar material. We further show that the [O i] 6300, 6364 Å line strengths in the nebular spectra of four Type IIP SNe imply ejected oxygen masses of 0.5-1.5 M⊙. © 2010 The Authors. Journal compilation © 2010 RAS.