Optical "anti-transient" detected by MASTER

ATel #4784; D. Denisenko, E. Gorbovskoy, V. Lipunov, P. Balanutsa, V. Yecheistov, N. Tiurina, V. Kornilov, A. Belinski, N. Shatskiy, V. Chazov, A. Kuznetsov, D. Zimnukhov (Moscow State University, SAI), V. Krushinsky, I. Zalozhnih, A. Popov, A. Bourdanov, A. Punanova (Ural Federal University), K. Ivanov, S. Yazev, N. Budnev, E. Konstantinov, O. Chuvalaev, V. Poleshchuk, O. Gress (Irkutsk State University), A. Parkhomenko, A. Tlatov, D. Dormidontov, V. Senik (Kislovodsk solar station of the Pulkovo observatory RAS), V. Yurkov, Y. Sergienko, D. Varda, E. Sinyakov (Blagoveshchensk Educational University),S. Shurpakov, V. Shumkov, P. Podvorotny (MASTER team members), H. Levato, C. Saffe (ICATE), C. Mallamaci, C. Lopez and F. Podest (Observatorio Astronomico Felix Aguilar; OAFA)
on 4 Feb 2013; 17:18 UT
Credential Certification: Vladimir Lipunov (lipunov2007@gmail.com)

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MASTER OT J095310.04+335352.8 - fading of TYC 2505-672-1

We have started the search for the disappearing stars (optical "anti-transients", OATs) in the MASTER database. The first result is the detection of a deep (~3.5 magnitudes) fading of the bright star TYC 2505-672-1 whose variability was previously unknown. This star has the coordinates 09 53 10.00 +33 53 52.7 and magnitudes V=10.71, B=12.51 in Tycho2 catalogue and J=7.61, H=6.78, K=6.57 in 2MASS. It was bright (unfiltered magnitude about 10.5) in 2010 and January-April 2011, but was found fading from R=13.0 to R=14.1 in November 2011 - March 2012 after the seasonal gap in observations due to the conjunction with the Sun. Since then it resides at a low state for almost a year.

The light curve from MASTER-Amur observations is posted at http://master.sai.msu.ru/static/OT/TYC2505-672-1-MASTER-Amur-LC.gif and selected magnitudes are listed in the table below.

 
2011-02-03 15:15:47  10.34W  MASTER-Amur 
2011-03-14 10:43:18  10.03V  MASTER-Amur 
2011-04-07 12:30:22  10.44W  MASTER-Amur 
--- seasonal gap due to solar conjunction --- 
2011-11-03 23:44:28  12.62W  MASTER-Kislovodsk 
2011-11-04 00:17:08  12.64W  MASTER-Kislovodsk 
2011-11-09 17:42:27  12.99R  MASTER-Amur 
2011-11-20 16:58:19  13.10R  MASTER-Amur 
2011-11-29 16:47:27  13.27R  MASTER-Amur 
2011-12-09 16:14:25  13.44R  MASTER-Amur 
2012-01-08 13:37:51  13.85R  MASTER-Amur 
2012-03-01 12:50:18  14.06R  MASTER-Amur 
2012-03-17 14:40:17  14.31V  MASTER-Amur 
2012-04-02 18:09:36  13.81W  MASTER-Amur 
--- seasonal gap due to solar conjunction --- 
2012-09-29 20:02:30  13.98W  MASTER-Amur 
2012-10-25 19:23:53  14.03W  MASTER-Amur 
2012-12-19 15:46:57  14.01W  MASTER-Amur 
2013-01-07 16:46:19  13.77W  MASTER-Amur 
2013-02-01 16:51:19  13.82W  MASTER-Amur 

The spectral class of TYC 2505-672-1 is reported as M2III in Pickles et al., 2010 with the estimated distance 1179 pc. Combined with the proper motion (3.5, -7.4) mas/yr from UCAC4 catalogue (Zacharias et al., 2012) this corresponds to the tangential velocity 46 km/s which is reasonable. Galactic coordinates are (191.7, +51.3).

In general, the object's behavior is similar to that of R CrB variables (red supergiants forming clouds of carbon at irregular intervals of time). However, the typical dimming phase of R CrB stars is lasting from 1 week to 1 month while TYC 2505-672-1 took more than 3 months to fade from 10m to 14m. The star was nearly constant in 1999-2000 during the observations by NSVS (ROTSE-I) project, see light curve of NSVS 7507001. No previous fadings were detected on 9 Palomar plates taken from 1955 to 1996 and on 31 Palomar/NEAT images taken during 9 different nights in 2001-2003. The object was not detected in 1RXS and IRAS bright source catalogs.

We encourage the spectroscopic and photometric observations of TYC 2505-672-1. We also note that the new variable is located 21.5' SE of the cataclysmic variable RZ LMi (of ER UMa type) which is extensively monitored by CV researchers. Observers are requested to check their images of RZ LMi obtained in April-June 2011 and especially in September-October 2011 to localize the beginning of fading episode. Archival searches for the historical fadings are also requested.

MASTER-Amur discovery and reference images are posted at http://master.sai.msu.ru/static/OT/J095310+335353-MASTER.jpg

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