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Astrometry and possible progenitor of SN 2008bk in NGC 7793

ATel #1448; W. Li (UC Berkeley), S. D. Van Dyk (Spitzer), A. V. Filippenko, R. J. Foley (UC Berkeley), G. Pignata, M. Hamuy, J. Moza (Universidad de Chile), D. Reichart, K. Ivarsen, A. Crain, D. Foster, M. Nysewander, A. LaCluyze (University of North Carolina at Chapel Hill)
on 30 Mar 2008; 20:37 UT
Credential Certification: Weidong Li (weidong@astron.berkeley.edu)

Subjects: Optical, Star, Supernovae, Transient, Variables

Referred to by ATel #: 1455, 1464, 1465

We have analyzed the discovery images of SN 2008bk in NGC 7793 taken by Berto Monard (c.f. CBET 1315) and also images taken with the 0.41-m "PROMPT 2" telescope at CTIO on Mar 28.41 UT. Using half a dozen stars for an astrometric solution, we derive the following precise position for the SN:

  • R. A. = 23h57m50s.42
  • Decl. = -32d33'21".5 (equinox 2000.0)
  • which is 9".2 east and 126".4 north of the nucleus of NGC 7793.

    We further apply our astrometric solution to deep archival ground-based images taken with the Very Large Telescopes (VLT). Within the uncertainty of the solution (0".2 error radius), we identified a single point source on an I-band image taken on Sep 16, 2001 UT, which we propose as the possible progenitor for SN 2008bk. The source is not detected in the B and V band images, so it is a red source (likely a red supergiant star). The possible progenitor of SN 2008bk also resides in a cluster of bright blue and red supergiant stars. Based on the environment of SN 2008bk and its possible progenitor identification, we postulate that SN 2008bk is a core collapse (likely a Type II) event. Further analysis on the astrometry and photometry of the progenitor star is ongoing. A finder chart for the possible progenitor can be found at http://astro.berkeley.edu/~weidong/sn2008bk.vlt-prog.gif