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THE ASTRONOMER Electronic Circular No 3145      2016 Feb 20 17.19UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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SN 2016adj IN NGC 5128: PROGENITOR
D. Schuyler Van Dyk (IPAC/Caltech) et. al. report further on this object
(ATEL 8693) the identification of the progenitor star of the Type IIb SN
2016adj in archival Hubble Space Telescope (HST) WFC3/UVIS image data
obtained in 2010 July and near-infrared JHKs images obtained in 2008 July
with the NAOS+CONICA (NACO) instrument on the ESO VLT UT4-Yepun.

They acquired a co-added image of the SN on 2016 February 13 UT in z'-band
with the Magellan 6.5-m Clay AO system and registered it to the WFC3 image
mosaic in F814W (~I-band), using 14 stars in common, to ~0.19 UVIS pixel or
~8 mas. A star with brightness at F814W of magnitude 23.1 is near to this
position (at ~5 sigma) in the HST image. They tentatively assign this star
as the candidate progenitor, which also has apparent counterparts in the
JHKs images. 

The star does not appear to be detected in any WFC3 data shortward of F814W.
>From its brightness in this band alone, adjusting to an assumed reddening to
the SN (and to the progenitor) of E(B-V)~1 mag (ATel #8657) and a distance
modulus of 27.67 mag, they find that the star would be less luminous (at M_I
~ -6.4 mag) than the progenitors of the SNe IIb 1993J (e.g, Aldering et al.
1994, AJ, 107, 662) and 2013df (Van Dyk et al. 2014, AJ, 147, 37) and more
consistent with the luminosity of the progenitor of SN 2008ax (Folatelli et
al. 2015, ApJ, 811, 147), implying that SN 2016adj may be a 'compact',
rather than 'extended', SN IIb. They also measure preliminary JHKs
photometry for the star of 24.5, 24.5, and 24.2 mag (with a ~1 mag
uncertainty in Ks), respectively, which is odd, given the I-band brightness,
but could imply that the star was varying significantly in the years before
explosion. Further analysis is ongoing.

Editor: A number of different supernova types have been quoted in the very
substantial amount of literature which has accumulated since its discovery.

Guy M Hurst