Professor Stephen Smartt CBE FRS MRIA

Abstract:

We present optical and infrared monitoring data of SN2012hn collected by the Public European Southern Observatory Spectroscopic Survey for Transient Objects. We show that SN 2012hn has a faint peak magnitude (MR ~ -15.65) and shows no hydrogen and no clear evidence for helium in its spectral evolution. Instead, we detect prominent Ca II lines at all epochs, which relates this transient to previously described 'Ca-rich' or 'gap' transients. However, the photospheric spectra (from -3 to +32 d with respect to peak) of SN 2012hn show a series of absorption lines which are unique and a red continuum that is likely intrinsic rather than due to extinction. Lines of Ti II and Cr II are visible. Thismay be a temperature effect,which could also explain the red photospheric colour. A nebular spectrum at +150 d shows prominent Ca II, OI, CI and possibly MgI lines which appear similar in strength to those displayed by core-collapse supernovae (SNe). To add to the puzzle, SN 2012hn is located at a projected distance of 6 kpc from an E/S0 host and is not close to any obvious star-forming region. Overall SN 2012hn resembles a group of faint H-poor SNe that have been discovered recently and for which a convincing and consistent physical explanation is still missing. They all appear to explode preferentially in remote locations offset from a massive host galaxy with deep limits on any dwarf host galaxies, favouring old progenitor systems. SN 2012hn adds heterogeneity to this sample of objects.We discuss potential explosion channels including He-shell detonations and double detonations of white dwarfs as well as peculiar core-collapse SNe. © 2013 The Authors.

Abstract:

We present optical and near-infrared (NIR) photometry and NIR spectroscopy of SN 2004am, the only optically detected supernova (SN) in M82. These demonstrate that SN 2004am was a highly reddened Type II-P SN similar to the low-luminosity Type II-P events such as SNe 1997D and 2005cs.We show that SN 2004am was located coincident with the obscured super star cluster M82-L, and from the cluster age infer a progenitor mass of 12+7 -3M. In addition to this, we present a high spatial resolution Gemini-North Telescope K-band adaptive optics image of the site of SN 2008iz and a second transient of uncertain nature, both detected so far only at radio wavelengths. Using image subtraction techniques together with archival datafrom the Hubble Space Telescope, we are able to recover a NIR transient source coincident with both objects. We find the likely extinction towards SN 2008iz to be not more than AV~10. The nature of the second transient remains elusive and we regard an extremely bright microquasar in M82 as the most plausible scenario. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.