[vsnet-alert 12508] (fwd) 1RXS J184542.4+483134

[Taichi Kato]

(fwd) 1RXS J184542.4+483134

Date: Thu, 16 Dec 2010 18:45:59 +0300
Subject: Re: [cvnet-discussion] Call for observations of new faint CVs
From: Denis Denisenko <denis at hea.iki.rssi.ru>

Hello all!

I wrote on Tue, 13 Jul 2010 00:21:36 -0000 [cvnet-discussion 1289]:

> I would like to point your attention towards the new cataclysmic 
> variables we have just published at astro-ph with my friend and 
> colleague Kirill Sokolovsky. We have discovered eight cataclysmic 
> variables and two probable optically violent variable quasars using 
> just the photomeric data of USNO-B1.0 catalogue alone!
>
> By coincidence, 4 of 10 new variable objects reside in Draco 
> constellation! Bad news is that all our objects are quite faint, with 
> the brightest at 15m in outburst. So they are definitely the targets 
> for CCD observers. But the good news, again, is that virtually nothing 
> is known about these objects! No type of variability, no orbital 
> periods, no outburst interval, not even the exact variability range! 
> So if you start following them up, you can discover a lot of new things.

Even more good news is that Russian amateur astronomer Evgeniy (Eugene) 
Smirnov has started follow-up of one of two "possible QSOs" in Draco 
1RXS J184542.4+483134 = USNO-B1.0 1385-0291789 (see [cvnet-discussion 
1390]) and discovered a lot of great new things, indeed!  First of all, 
it is not a quasar at all.  Instead it is a cataclysmic variable with 
the short period (79.07 min) and a *very* interesting light curve.

We have submitted an article to "Peremennye Zvezdy - Prilozhenie" 
(Variable Stars - Supplement) two weeks ago reporting our findings 
(orbital period, phased light curve and discussion).  But we were not 
able to come to the final agreement on the star's nature, once again!  
It might be UGWZ, polar or a classical nova with an outburst caught on 
1990 DSS plates.  The star was at ~21m in 1953, brightened up to at 
least ~16.5m in 1990, then gradually faded to 19-19.5m by 1991-1992.  In 
September-October 2010 it is varying from 17.4m to 19.2m with a period 
of 0.05491d.  The shape of light curve is a combination of sine wave 
(reflection effect?) with two humps ~0.2m high at phases 0.1 and 0.6 
with a hint of ~0.8m dip at 0.1 after maximum.  But there is *no* 
primary eclipse - as I said, bottom of the light curve is nearly 
sinusoidal, unlike the polars with a hot spot which is visible about 50% 
of a period and have a flat bottom during the rest half period or so.  
And overall amplitude of 1.8m is too much for non-eclipsing cataclysmic 
variable.  All in all, this is the most interesting X-ray selected CV 
that I have found since the discovery of deep eclipses in 1RXS 
J020929.0+283243 back in October 2005.

Thus, I call for observations of this intriguing object.  Though it is 
approaching the solar conjunction soon, it will be 70 degree away from 
ecliptic, and with its +48.5 declination the star is circumpolar for 
Canada and nothern Europe.  E. Smirnov was taking 5-minute exposures 
with a 30-cm scope.  So much more details in the light curve can be 
found with a larger aperture and/or shorter exposures.

Preliminary finder chart with approximate magnitudes of several 
comparison stars specified:

http://hea.iki.rssi.ru/~denis/J1845+4831-comps.gif

Best regards,

Denis in Moscow

> The list of objects with the coordinates and 10'x10' color combined 
> finder charts are available at my page:
>
> http://hea.iki.rssi.ru/~denis/CV-USNO.html
>
> The article is accepted to Russian Astronomy Letters. Meanwhile you 
> can download the pdf or PostScript file from the archive of electronic 
> preprints at this link:
>
> http://arxiv.org/abs/1007.1798