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Limits on the Progenitor of the NGC 300 Luminous Transient from Pre-eruption HST Data

ATel #1544; Edo Berger and Alicia Soderberg (Princeton University)
on 27 May 2008; 03:24 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Edo Berger (eberger@astro.princeton.edu)

Subjects: Optical, Transient

Referred to by ATel #: 1550, 2406

We obtained an image of the luminous transient in NGC 300 (IAUC # 8946 ) using LDSS3 mounted on the Magellan/Clay 6.5m telescope on 2008 May 23.41 UT. Astrometry relative to the Naval Observatory Merged Astrometric Dataset (NOMAD) indicates a position of RA = 00:54:34.552, DEC = -37:38:31.79 (J2000) with an uncertainty of 0.25" in each coordinate. We note that this position is offset by 4.7"E and 3.2"S from the position provided by Monard (IAUC # 8946 ). We further obtained from the Hubble Space Telescope archive ACS/WFC images of NGC 300 taken on 2006 November 8 UT as part of program 10915 (PI: Delcanton). Observations are available in the F475W (1488 sec), F606W (1515 sec), and F814W (1542 sec) filters. The astrometric tie between the LDSS3 image and the HST images has an rms of 30 mas in each coordinate. We do not detect an obvious progenitor in any of the HST images within a 3-sigma circle of 90 mas radius. The 5-sigma limits in the three filters are 28.1 mag (F475W), 27.8 mag (F606W), and 27.3 mag (F814W). Using a distance modulus to NGC 300 of 26.4 mag, we place the following absolute magnitude limits on the progenitor: +1.7 mag (F475W), +1.4 mag (F606W), and +0.9 mag (F814W). These limits effectively rule out a giant (or supergiant) star origin, or an LBV. However, they are in good agreement with the F main sequence star progenitor of V838 Mon, or with any main sequence star with spectral type later than F. The limits on the progenitor continue to support the non-supernova nature of the transient, and a possible similarity to V838 Mon. We note that the nearest point source is located 0.2" (or 1.8 pc) away from the position of the transient. A figure showing the location of the transient on the HST pre-eruption images is available at: http://www.astro.princeton.edu/~eberger/ngc300_hst.gif