[vsnet-alert 9942] On a new UV Cet variable in PZP 8 10

[da55 at Safe-mail.net]

Here's something off the normal track.

http://www.astronet.ru/db/varstars/msg/1225940

appears, from USNO A2.0 and CMC14 (Carlsbeg Merididan Catalogue 14) positions combined to be a common proper motion pair with

USNO A2.0 0900-20386586

position angle 266 degrees in 38.2" separation, epoch average of 1976 and 1985 (one the blue plate, the other the red plate), so both stars are likely red dwarfs.

>From CMC14 the position angle is 266 degrees and separation 38.0", with a true epoch of mid 2000, but note CMC14 astrometry is usually more accurate than USNO A2.0.

If the USNO A2.0 positions are means of the two plates then these two stars' motions are 2.8 arcseconds over nearly 20 years, or a proper motion of very roughly 140 milliarcseconds per year in position angle 225 degrees.

The nearby ROSAT Bright Source might well be associated with the pair, too, as the hardness ratios are well into negative, which I think means quite "soft", possibly suitable for a chromospherically active variable like a flare star.


Interestingly, the combined r' and 2MASS colours for nearby AC Psc (extending concepts from Bessell and Brett 1988), on the extreme edge of the paper's finder chart, also suggest a red dwarf, and it has had a similar amount of motion in the same time period, but at a somewhat different position angle of about 190 degrees, so likely not truly common.  Whether it's a moving group, I know not.  (Khruslov correctly identified AC Psc (itself of corrected position and cross identity in more recent GCVS incarnations) as an eclipsing binary in IBVS 5699

http://www.konkoly.hu/cgi-bin/IBVS?5699#45

and possibly a pair of red dwarfs may well explain the very short period for an EA (although the phase plot looks a little like an EA / EB intermediate???).

I believe there is some interest in red dwarf eclipsers nowadays, in terms of refining the mass luminosity relation for red dwarfs which is actually not that well constrained, and which generates some interest in the literature nowadays.

Certainly an EA star of a third of a day period isn't an everyday thing, although the lightcurve is suggestive some extra things going off besides simple eclipsing (for instance the downward then upward slant towards and away from minima, which I think sometimes is indicative of reflection effects, but I'm no eclipser expert).  Unfortunately just coming out of season though, but possibly a near full cycle can be followed in one night when at its best.

Just thought it might be of interest, a little different from the usual.

Certainly all could be safely encompassed within a ten arcminute imaging field.

Cheers

John

(c) John Greaves 2008