[vsnet-alert 12510] (fwd) 1RXS J184542.4+483134: polar?
tkato at kusastro.kyoto-u.ac.jp
Sat Dec 18 10:10:37 JST 2010
(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):
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:
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:
The shape of J0711+4404's phased light curve at the high and low states
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!!!
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
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!
More information about the vsnet-alert