[vsnet-alert 10789] re Re: ST CHA in outburst? - ST Cha and CY Cha are CPM pair

[bydra at Safe-mail.net]

Berto Monard presented :-

"Just for interest's sake. I observed ST Cha for about 4 hours on 12 Dec 2006. There was no sign of modulation around the then 14.1 (unfiltered CCD) magnitude. The only star that varied was the check star I chose..."

There's a few similar mag variables around here.  [An interesting point about it appears at the end of this, one I didn't notice till I wrote this].

Until Berto M.'s post I hadn't bothered checking the similar mag nearby variable to any great depth, but when I do I find that mean V mag 13.2 variable CY Cha, an EW/KW that lies at 85.7 arcsecs in 169 degrees of Position Angle is common proper motion pair with ST Cha according to UCAC2.

The variability class is reasonable enough, and the variability type and period safe enough :-

<http://www.astrouw.edu.pl/cgi-asas/asas_variable/104723-7929.5,asas3,%20%20%200.570710,0,1000,0>

ST Cha has a J-Ks of 0.28, which is okayish for NL type variable, but also okayish for a mid to late G dwarf.

And here it is with about -20.4 mas/y RAcos(dec) (~ -110 raw, we're ~ -80 deg South here) and 9.2 in Dec, whereas CY Cha is -20.6 (~ 100 raw) and 7.7 respectively.

So, can a UGZ or NL have the same absolute magnitude as a late G to early K contact binary?

Caveats are that the UCAC2 data is from only two catalogues (likely inclusive of ucac2 itself) the high Celestial Latitude causes tricky situations for proper motion determinations, and the value is on the edge of significance, and UCAC2 don't always solve variables' proper motions too cleanly (though usually it's high amplitude stuff that suffers).

These values aren't inappropriate for Cha I membership, at least as outliers, though admittedly not conclusively so.  I can't find a goodly reservoir of WTTS spectra for comparison, or NTTS or whatever, but G/K dwarfs, near the Chameleon Cloud complexes and T Associations, and the thing not behaving like any usual UGZ nor most NL.

Everything's a CV nowadays I've noticed.

Anyway, not withstanding, V ~ 14.6 is fairly normal and not an outburst, thanks to literature checks and some clues from others (no name - no blame) and Rod Stubbins kindly forwarding his observations of this star, the 17.6 minimum is off old plates around the Thirties, newer plates around the Sixties quote minima nearer 14 to 15, Rod's data tallies with that, however fainter times do occur, including < 15.5 visual reports.  No UGZ type lightcurve profile on comparison with similar mag range UGZ+E star EM Cyg.  Literature reported 7h period, or rather 0.285 days, gives a really, really broad and very dirty eclipse profile, no cleaner than one at around 0.225 ish days which looks more like a pulsator's lightcurve, and due to a 0.40 day aliasing.  The rising branch is populated by about three data points, whereas the rest of the lightcurve is well populated, and as 6.8 ish hours isn't some clean submultiple of 24 I can't see why the full phase shouldn't be equally populated on a multiepoch sourced phaseplot.

And stuff like that.

And finally, given the putative single "eclipse" lightcurve from a periodogram peak at ~ 0.285 days in the IBVS 1049 data for ST Cha, what can anyone tell me about the two minima based period for the much later discovered adjacent variable CY Cha according to the above ASAS3 plot...?

Answers on a postcard in not less than ten thousand words.

Cheers

John