Revised Phase II -- the only change is to visit 2, in which the F555W and F675W exposures were changed to all use F606W. Recent data suggests SN 2005hk has faded much more rapidly than it had been in the V-band. The change to the observations will allow us to go significantly deeper, without substantially affecting our ability to constrain the SN SED. ----- Attempting Submission 1 (Fri May 11 16:06:28 GMT 2007) ----- ----- Attempting Submission 2 (Thu Jun 14 18:26:49 GMT 2007) ----- Revised version of ACS proposal ID #670 Assigned ID: 1250 ----- Attempting Submission 1 (Fri Feb 09 05:57:28 PST 2007) ----- Late-Time Photometry of SN 2005hk: A New Kind of Type Ia Supernova Our lack of understanding of Type Ia supernova (SN Ia) explosions limits our confidence in their use for cosmology. While there is broad agreement that these objects represent the explosions of white dwarfs, the details of the explosion mechanism are not well-understood. Recent observations have detected a previously unacknowledged variant class of SNe Ia whose photometric and spectroscopic peculiarities make them quite distinct from normal SNe Ia. These objects represent a challenge for thermonuclear supernova models, as a complete theory of exploding white dwarfs must allow for their existence. A particularly well-studied example of this class of objects is the recent SN 2005hk, whose properties in some respects resemble those of models which invoke a subsonic burning front, called a deflagration. We propose to test SN Ia models by obtaining late-time photometry for this extreme SN Ia using WFPC2 and NICMOS on HST. We will accurately measure the late-time photometric decline rate and spectral energy distribution (SED). These observations will allow us to test whether the ejecta contain the large amount of oxygen predicted by certain models, the efficiency of energy deposition by gamma rays and positrons, and possibly detect major evolution of the SED expected due to a change in the dominant cooling mechanism of the ejecta.
We will observe SN 2005hk with WFPC2 in F555W, F675W, and F814W. To image SN 2005hk, we will use the PC with a standard dither pattern, providing a well-sampled point-spread function and the best photometry. In addition we will follow the recommendation to mitigate CTE losses by placing the SN at position (150,150), nearer to the readout electronics than the default aperture. Other point sources throughout the field will be used to firmly establish the astrometry and precise location of SN 2005hk. Based on extrapolations of the current data and inferences from other SNe Ia, we anticipate SN 2005hk to have V ~ 25, R ~ 24.5, and I ~ 23.5, at the epoch of observation, with an uncertainty of about 1 mag. To meaningfully constrain models, we must achieve S/N >= 10 in all bands, even in the pessimistic case (1 mag below the prediction). Based on the WFPC2 exposure time calculator and including overheads, this requires a total of 4 orbits. We will also observe SN 2005hk with NICMOS in F110W and F160W. During the observation window, we predict J ~ 23.5, and H ~ 23, for the supernova. We have chosen the NIC2 detector to get the best balance of high sensitivity and angular resolution to resolve the PSF, and will use a standard dither pattern. With 2 orbits in F110W and 3 orbits in F160W, we will again ensure S/N >= 10 even if the SN flux is low by as much as 1 mag. UPDATE: Recent data show that SN 2005hk has faded faster in the optical than its previous decline rate would have predicted. We thus intend to go deeper in our observations by replacing the V (F555W) and R (F675W) exposures with images in the more efficient F606W passband (effectively V+R). This change will still allow us to constrain the SN SED in the optical region. HOT STARS 12 false 0.0 false false false false false false SUPPORTED EXT-STAR SUPERNOVA TYPE IA This object was generated by the targetselector and retrieved from the NED database. 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