(cba:news) A W UMa joining the CV club?

[Joe Patterson]

Definitely worth tracking with time-series photometry!  Right away, 
while the "outburst" (?) is ongoing.

joe


-------- Forwarded Message --------
Subject: ATel  9112
Date: Sat,  4 Jun 2016 03:01:42 -0400 (EDT)
From: atel at astronomerstelegram.org
To: jop at astro.columbia.edu

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The Astronomer's Telegram 
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Posted: Within the last 24 hours
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ATEL #9112							     ATEL #9112

Title:	CRTS discovery of an outburst from a short period binary system
Author:	A. J. Drake, S. G. Djorgovski, A. A. Mahabal, M. J. Graham,
		C. Donalek,  R. Williams (Caltech); M. Catelan (PUC Chile); E. 
Christensen,
		 S. M. Larson (LPL/UA)
Queries:	ajd at cacr.caltech.edu
Posted:	4 Jun 2016; 03:25 UT
Subjects:Optical, Request for Observations, Binary, Star, Transient,
		Variables

Here we report the discovery of an outburst from known short period binary
system 2MASS_J16211735+4412541. On 2016-06-03.45 UT, 2MASS_J162117 was 
detected
by CRTS as a transient event (<a 
href=http://nesssi.cacr.caltech.edu/catalina/20160603/1606031430654136549.html>
CSS160603:162117+441254</a>) with V_CSS=13.3. This system has  an 
average magnitude of V_CSS=15.0 and an amplitude of 0.5 mags based on
359 prior observations taken between 2005-05-17 to 2016-05-14. No prior 
outbursts
have been observed.
This system was previously identified as a contact eclipsing binary (WUMa)

by Palaversa et al. (2013, AJ, 146, 101), Lohr et al. (2013, A&A 549, 86)

and Drake et al. (2014a, ApJS, 213, 9) with a period of P=0.207852(1) days.

This period places the system is among the ~0.1% of ultra-short period
binary  systems known to have periods shorter than the 0.22 day contact 
binary
minimum (Rucinski 2007, MNRAS, 382, 393). Due to its unusual period the 
source
was  studied by Lohr et al. (2013) and Drake et al. (2014b, AJ, 790, 157).
2MASS_J162117 has SDSS magnitudes u =17.54, g=15.76, r=14.92, i=14.56 and
z=14.37, and GALEX mags FUV=20.5, NUV=20.2. The extinction corrected 
SDSS colors
are  consistent with a MS+MS (WUMa) binary. However, the object is near the
SDSS  saturation limit. The GALEX magnitudes are most consistent with a 
WD+MS
binary  system. Based on Drake et al. (2014b) we find that the shape of 
phase-folded

lightcurve is more consistent with the ellipsoidal (WD+MS) variables than
WUMa.
If this system is a MS+MS contact binary, the outburst could be the 
beginning

of a very rare binary merger event similar to V1309 Scorpii (Tylenda et
al. 2011,  A&A, 528, 114). However, based on the GALEX data and 
lightcurve shape,
we  suspect that the event is more likely an outburst from an unusual 
cataclysmic

variable system.
We request photometric and spectroscopic follow-up to determine the 
nature of the system and the outburst.
Archival photometry for this	source is public available from the <a 
href=http://nesssi.cacr.caltech.edu/DataRelease>CSDR2</a> pages. All 
CRTS transients are discovered within minutes of observation and openly

published. Links to all CRTS transients can be found at 
http://crts.caltech.edu/.

We are grateful to the all the observers involved in follow-up observations.

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