A Search for the Progenitor of Supernova PTF12os (PSN J14595904+0153251)

ATel #3884; Schuyler D. Van Dyk (Spitzer Science Center/Caltech), Avishay Gal-Yam, Iair Arcavi (Weizmann Institute), Mansi M. Kasliwal (Carnegie/Princeton), and Assaf Horesh (Caltech), PTF collaboration
on 25 Jan 2012; 01:41 UT
Credential Certification: Schuyler D. Van Dyk (vandyk@ipac.caltech.edu)

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Schuyler D. Van Dyk (Spitzer Science Center/Caltech), Avishay Gal-Yam, Iair Arcavi (Weizmann Institute), Mansi M. Kasliwal (OCIW/Princeton), and Assaf Horesh (Caltech), on behalf of the larger PTF collaboration, report their attempt to identify the progenitor of the Type IIb supernova PTF12os, aka PSN J14595904+0153251, in archival Hubble Space Telescope (HST) ACS/WFC F435W, F555W, and F814W images from 2005 March 10 UT (PI: Smartt). We have astrometrically matched a B-band image (with 0.87" seeing) from 2012 January 18 UT obtained with the IMACS camera on the Magellan Baade 6.5 m telescope at Las Campanas Observatory, Chile, with the ACS F435W image, using 10 fiducial stars in common. The SN position has been located on the ACS image with an uncertainty of 0.57 WFC pixel, or 0.028". This is within 1 WFC pixel, to the southwest, of a candidate source detected in all three ACS bands. The site of PTF12os lies approximately 2.2" southeast of the position of the Type II SN 2004dg in this same host galaxy. Preliminary photometry of the ACS images using Dolphot (Dolphin 2000, PASP, 112, 1383) results in a brightness for the object of B=23.30, V=23.04, and I=22.53 (uncertainties are all 0.012 mag or smaller). Assuming the average value of the distance modulus to the host, NGC 5608, from the NASA/IPAC Extragalactic Database (NED), 32.01 mag, and also assuming only the Galactic foreground extinction at V-band from Schlegel, Finkbeiner, & Davis (1998, ApJ, 500, 525), 0.17 mag, this object had V absolute magnitude of -9.1 and absolute colors (B-V)_0=0.21 and (V-I)_0=0.44 (consistent with an early F spectral type). This could be a highly-luminous supergiant star, or, alternatively, a compact star cluster. Evidence exists from the strength of the Na I D lines in follow-up spectra (ATel 3881) that the extinction to the SN could, in fact, be higher, implying that the source is even more luminous and bluer. We tentatively identify this source as a candidate for the progenitor, although given the offset of the SN position from the object's centroid, the host galaxy distance, and the inferred higher extinction, it is quite possible that the progenitor has not been detected. Higher-resolution imaging is pending for candidate confirmation, and further analysis is ongoing.