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ASASSN-16oe: A Very Bright, Unusual Transient Near the Galactic Plane

ATel #9860; J. Strader, L. Chomiuk (MSU), K. Z. Stanek, J. S. Brown, T. W.-S. Holoien, C. S. Kochanek, J. Shields, T. A. Thompson (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong, S. Bose, Ping Chen (KIAA-PKU), J. Brimacombe (Coral Towers Observatory)
on 14 Dec 2016; 20:39 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

Subjects: Optical, Transient

Referred to by ATel #: 9879

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the quadruple 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered a new transient source, of unknown nature, close to the Galactic plane

ASASSN-16oe was discovered in images obtained on UT 2016-11-30.35 at V~13.3 mag, and the outburst is detected in several epochs before and after (light curve plot). This object is not in outburst in images taken on UT 2016-08-21.97 and before (the field containing this transient only recently became observable from behind the Sun, which is why there is a gap in our observations.) ASAS-SN has been observing this region of the sky since 2016-02-09.

At the position of the transient Vizier reports a red match, 1.3" away, with photographic USNO magnitudes B=17.4, R=15.7, and also a Gaia DR1 match with G=15.9. We obtained a revised position of RA=12:46:20.147, DEC=-58:53:38.87 from the spectroscopy acquisition images, which matches the Gaia object position to 0.04". vsnet-alert 20448 reports observations in three bands by J. Hambsch, stating that the "object is red (B-V = +0.8) and is likely a reddened nova."

Given these observations, we obtained a spectrum (covering 380-780 nm) with the Goodman spectrograph on the SOAR telescope on UT 2016-12-12.29. The spectrum shows absorption lines characteristic of an F star, with Balmer and some metal lines. No emission lines or broad absorption lines are apparent, hence this source is not a nova or a dwarf nova. Given its location and light curve, ASASSN-16oe might be a disk microlensing event.

The position of ASASSN-16oe is approximately 4 degrees away from the Galactic plane (l=302.268, b=3.97). Properties of the new source and photometry are summarized in the tables below:

Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. V mag 
ASASSN-16oe  12:46:20.147  -58:53:38.87      2016-11-30.35     13.3 
Obs. UT Date     V mag  sig_V 
2016-08-21.97    15.8   0.20 
2016-11-29.35    13.4   0.03 
2016-11-30.35    13.3   0.02 
2016-12-07.36    13.4   0.03 
2016-12-08.34    13.5   0.02 
2016-12-10.34    13.7   0.02 
2016-12-13.36    14.0   0.07 
Follow-up observations are encouraged.

We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is supported by NSF grant AST-1515927, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and the Mt. Cuba Astronomical Foundation.

ASAS-SN Light Curve of ASASSN-16oe