Candidate Progenitor of the Type Ib SN 2010O in NGC 3690

ATel #2422; Howard E. Bond (1), A. Aloisi (1), K. Garmany (2), B. James (1), J. Newton (3), T. Puckett (3), J. Smolinski (4), S. T. Sohn (1), T. Spuck (5). (1) Space Telescope Science Institute, (2) Kitt Peak National Observatory, (3) Puckett Supernova Search, (4) Michigan State University, (5) Oil City High School, PA
on 5 Feb 2010; 01:35 UT
Credential Certification: Howard E. Bond (bond@stsci.edu)

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SN 2010O in the galaxy NGC 3690 was discovered on 2010 Jan 24 UT by Newton & Puckett (CBET 2144) at magnitude 15.6. NGC 3690 is interacting with IC 694; the pair is cataloged as Arp 299, lying at a distance of about 45 Mpc. Arp 299 is undergoing intense star formation and has produced 7 other known SNe, from 1990 to 2010.

Mattila et al. (CBET 2149) obtained spectra on 2010 Jan 28 and classified SN 2010O as a Type Ib SN near maximum light. The outbursts of SNe Ib and Ic are due to core collapses of H-deficient stars, but their exact origin remains uncertain: no progenitor star of a SN Ib or Ic has yet been detected in high-spatial-resolution pre-explosion images (cf. the review by Smartt 2009, ARAA, 47, 63). The leading suggestions are that the progenitors are massive Wolf-Rayet stars, or lower-mass stars that have lost their H envelopes through interactions in binary systems.

There are extensive multiwavelength pre-explosion images of NGC 3690 in the Hubble Space Telescope (HST) archive, covering the UV through near-IR. Here we give a preliminary discussion of our search for a progenitor of SN 2010O.

New images showing SN 2010O were obtained on 2010 Jan 26 and 31 by Smolinski, Garmany, & Spuck, using the WIYN 0.9m telescope at Kitt Peak. We selected the best frame, a 300-s R-band exposure, for comparison with pre-explosion HST images obtained with the Wide Field Channel of the Advanced Camera for Surveys (ACS) on 2006 Mar 19 (HST program 10592, PI A. Evans). The ACS exposures were 1425 s in B (F435W filter) and 830 s in I (F814W).

There are insufficient stars in common between the 0.9m and HST images, so we instead first astrometrically registered the 0.9m frame with the SDSS image of the field, and then registered the SDSS image with the archival HST images. We were thus able to localize SN 2010O in the HST images to within a few pixels (seeSN2010O/SN2010O.png"> http://www.stsci.edu/~tsohn/SN2010O/SN2010O.png for figures). Lying within ~0".2 of the SN position is a bright, blue, slightly resolved object, most probably a stellar cluster. Correcting for a reddening of E(B-V)=0.6 (Mattila et al.), this object has a B magnitude of ~19.2 (corresponding to an absolute magnitude of about -14) and an unreddened B-I color of -0.25. The very blue intrinsic color suggests that the pre-explosion object is a cluster with an age of <5 Myr, whose evolved stars would thus be quite massive. It would be important to obtain more accurate astrometry of the SN while it is still luminous, in order to establish its connection to this cluster more firmly.