[vsnet-alert 11271] interesting object in GALEX Alerts

[kstars at Safe-mail.net]

http://www.galex.caltech.edu/researcher/tdsalerts.html

SDSS J145335.73+031802.6

http://www.galex.caltech.edu/researcher/files/alert661lc.png

Now, it's a lot brigher in ASAS3

<http://www.astrouw.edu.pl/cgi-asas/asas_variable/145336+0318.2,asas3,0,0,1000,0>

Colours suggest it's some sort of SRd star, which isn't particularly saying much, as that's a grab bag of a classification, both taxonomically (several quite different objects are bunged into that grouping, mostly because they're initially difficult to discern from each other when data is sparse, as long as they're semiregular and yellow) and inherently (SRd is a mix of giants and supergiants, as long as they are yellow, but further Pop II yellow supergiants are a very diverse set of objects in terms of variability expression).

This one's a very regular semiregular, just look at the phaseplot

<http://www.astrouw.edu.pl/cgi-asas/asas_variable/145336+0318.2,asas3,291.000000,0,1000,0>

or maybe the ASAS3 people are right and it is a very long period eclipser, a long period EW star.

Thing is, ultraviolet doesn't much seem to follow optical for quite a few variables, especially if the variables aren't hot blue star.   It's not usually from a photometric source you see for these sorts of stars, each usually from the more energetic chromospheric or coronal layers, and usually much, much fainter than the optical (many naked eye yellow stars have FUV and NUV mags of around 20 to 21, for instance).

One set of objects that do seem to emulate optical lightcurves in the UV, but more so, are the RR Lyrae variables.  More so in the sense that they're of higher amplitude the more energetic the UV passband.  ie, amplitude in NUV is higher than in optical, with FUV in turn being higher amplitude than in NUV.  And here V amplitude is less than half a magnitude ish, NUV at least two and a half and FUV about three or more.

So this thing might be a very regularly periodic metal poor Population II pulsating yellow supergiant of relatively very long period.

Or maybe it's just a W Virginis star.

I dunno.

Not in simbad so can't tell if anything else is known about it.

It's certainly different, regularly period, yellow, and low amplitude at that period.  Incidentally, the ASAS3 peirod of 291 days will be their eclipsing solution.  A pulsation period will be half that, probably not too bad for W Vir, in hindsight.

<http://www.astrouw.edu.pl/cgi-asas/asas_variable/145336+0318.2,asas3,145.5,0,1000,0>

Cheers

John