Constraints on the Progenitor of SN 2013ai (=PSN J06161835-2122329) in NGC 2207
ATel #4862; Dan Milisavljevic, Alicia Soderberg, Ryan Foley, Ryan Chornock, Wen-fei Fong, Peter Williams, Edo Berger, Maria Drout, Raffaella Margutti, (Harvard University); and Schuyler D. Van Dyk (Spitzer Science Center/Caltech)
on 6 Mar 2013; 05:06 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: D. Milisavljevic (dmilisav@cfa.harvard.edu)
Subjects: Optical, Ultra-Violet, Supernovae
Referred to by ATel #: 4901
We report preliminary analysis of archival Hubble Space Telescope
(HST) images in an attempt to identify the progenitor star of the
recently discovered and confirmed Type II supernova SN 2013ai (= PSN
J06161835-2122329; CBET 3431, ATel #4849, ATel #4851).
We retrieved archival HST images of the field surrounding the SN from
the Hubble Legacy Archive and the Mikulski Archive for Space
Telescopes. Images were originally obtained with the Wide Field
Planetary Camera 2 (WFPC2) with filters F336W, F439W, F555W, and F814W
on 1996-05-25 under program GO 6483 (PI: D. Elmegreen).
Two short r-band exposures of the SN were obtained with the 4m Blanco
Telescope at Cerro Tololo Inter-American Observatory using the Dark
Energy Camera (DECam) on 2013-03-04 UT (during program 2013A-0214; PI
Berger) under 1" seeing conditions. We astrometrically registered the
images using five fiducial stars common to both HST and DECam images
and the IRAF/PYRAF software applications geomap and geotran. The
alignment was good to 1-sigma errors of 0.75 pixel (0.1 arcsec) in x
(east-west) and 2.0 pixel (0.2 arcsec) in y (north-south).
A relatively bright, blue source is located close to the SN, and we
used the package Dolphot v2.0 (Dolphin 2000, PASP, 112, 1383) to
conduct photometry on the available images. Assuming a distance to the
host galaxy NGC 2207 of 26.5 Mpc and Galactic extinction of A_v =
0.237 mag (retrieved from NED), the absolute extinction-corrected
magnitudes of the blue source are approximately M_U = -9.6 mag, M_B =
-8.5 mag, M_V = -9.0 mag, and M_I = -9.7 mag. This source is likely a
tight stellar cluster, but the data do not rule out a single, massive,
luminous progenitor.
We note that within the 3-sigma error ellipse is a much fainter red
source that is weakly visible in the F555W image and clearly detected
in the F814W image. It lies 0.24 arcsec west and 0.54 arcsec north of
the blue source. The estimated extinction-corrected absolute magnitude
is M_I = -7.9 mag, which places it in the plausible range of a red
supergiant.
Multi-wavelength follow-up observations of this SN are in progress,
and further studies of the progenitor are ongoing.
Aligned DECam and HST images of SN 2013ai and its candidate progenitor system