[vsnet-alert 12510] (fwd) 1RXS J184542.4+483134: polar?

[Taichi Kato]

(fwd) 1RXS J184542.4+483134: polar?

From: Denis Denisenko <denis at hea.iki.rssi.ru>
Date: Fri, 17 Dec 2010 15:25:46 +0300
Subject: [cvnet-discussion] Re: Polars (was Re: Call for obs of new faint CVs)

I wrote yesterday regarding 1RXS J184542.4+483134:

> We have submitted an article to "Peremennye Zvezdy - Prilozhenie"
> (Variable Stars - Supplement) two weeks ago. 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. 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.

Speaking of this object and another polar, I have news related to them 
and some questions on the possible nature of J1845+4831.

Just checked CRTS light curve of J020929.0+283243 at the link from AAVSO 
VSX (found by Google):
http://nesssi.cacr.caltech.edu/catalina/20010514/105141290114100008p.html
This object (confirmed polar with a period of 0.066855d = 96.27 min) has 
obviously entered a low state in 2010 after several years of being at 
high state!  In October 2005 it had magnitude range from 17.0 to 21.5 
with deep eclipses:
http://hea.iki.rssi.ru/~denis/J020929-RTT_LC-051025.gif
In CRTS data from November 2004 to January 2010 the maximum was always 
at 16.5-17.0 level, but somewhere between Feb. 15 and Mar. 16 it has 
dropped to 18.6-19.0m!  And it keeps low during Sep.-Nov. observations.

Of course, two-mag difference between low and high states is not record 
high in polars.  For example, Catalina transient CSS081231:071126+440405 
(J0711+4404) has jumped from average magnitude about 18 to 14.5 between 
May 2008 and Oct. 2008, then faded and brightened back and forth:
http://nesssi.cacr.caltech.edu/catalina/20081231/812311430294141229p.html

The shape of J0711+4404's phased light curve at the high and low states 
differs dramatically.
At maximum: http://pics.livejournal.com/bigdenru/pic/00059s0p - more or 
less sinusoidal bottom and the dip due to the self-eclipse of accretion 
column *before* the primary eclipse, and the amplitude outside the 
eclipses about 1.8m.
At minimum: http://www.konkoly.hu/pub/ibvs/5901/5923-f1.jpg - almost 
flat bottom at phases 0.25-0.75 (just like in J020929.0+283243 at 
maximum, see above) and the dip due to the self-eclipse of accretion hot 
spot lagging *behind* the primary eclipse by 10 degree!

Amazing thing is that the light curve of 1RXS J184542.4+483134 at its 
current _low_ state reminds that of J0711+4404, but at its *high* state!!!
http://hea.iki.rssi.ru/~denis/J1845+4831-LC_Smirnov.gif

This brings me a lot of questions, and I hope experts on this list could 
clarify at least some of them.

1. Was the change of hot spot's longitude on the WD in CVs observed 
before, and by how much?  Are there any articles on this effect in other 
systems published?
1a. Could be the accretion spot on the WD surface shifted in longitude 
by ~180 deg relative to the secondary?  (That is, ballistic stream 
having apocenter at Lagrangian point of the system, and the pericenter - 
on the primary's surface from the opposite side?)

2. Could 1RXS J184542.4+483134 be a polar with the difference between 
low and high states as much as 5m?  Are there other systems of AM Her 
type with such a huge brightness jump between the extreme states?

3. If J0711+4404 is a polar, why wasn't it detected by ROSAT in 1RXS 
catalogue downto 0.01 cnts/s, while optically fainter 1RXS 
J020929.0+283243 has 0.054 cnts/s and 1RXS J184542.4+483134 - 0.051 cnts/s?

4. Does anybody has an access to archival photographic plates covering 
the position of 1RXS J184542.4+483134 in Draco?  It would be of great 
interest to reconstruct the historical light curve of this object!

Denis