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Re: Suspected Variables in TASS data



aah@nofs.navy.mil wrote:

>   John, you once wrote:
> >I've found 3 possible eclipsing binaries with periods of 1.0 days, or
> >possibly a multiple on CD 23.
> 
> >The difference between exactly a day and the value doesn't seem to
> >amount to the expected roughly 4 minutes sidereal day - solar day
> >difference.
> 
> >Lots have stars have been observed by the TASS data, but I'd more expect
> >something like 1.1 or 0.9 days to turn up. No surprise that there should
> >be unknown eclipsers around these periods because the are usually biased
> >against by selection effects.
>   Actually, 1.00d periods should be selected *for* in the dataset, for
> two reasons:  the data was taken at roughly the same time window every night,
> and any variability index is going to be maximum for variables that show
> the most variation each observing session; 1.0d variables will do it
> every session.

I was half wondering if that would be the case.  Thanks.

>   FASTT had a spatial filter:  it was just great at finding 4arcsec doubles.
> These stars would blend or split, depending on the seeing, and so the
> photometry was quite variable.  I can give you a list of several hundred
> such pairs.  We added an extra astrometric test to remove these false
> variables.  I expect TASS to have many such outliers, so I'd prefer that
> we look at the newly discovered 'variables' quite closely, with different
> equipment, to understand the frequency of false detections.

A long time ago I looked at the ASAS stars published as periodic (well,
on line available data) and it had one or two of these "duplicity
induced variability" objects, as the Tycho catalogue likes to refer to
them.

Interestingly these were seriously low amplitude (it was a long time
ago, I can't remember exactly, but probably around 0.1 or less).  I
don't remember them that well unfortunately (I've stared at too many
other things since then), but if they'd been about a day I'd have
remembered.  More like fractions of a day.  I

I actually remember asking Michael R at the time if TASS had this
problem, and remembering saying something about it being something he'd
be seriously looking in to re when Mk IV got under way.

It's summat I look for usually.  Often why I frequently use the aladin
interface at CDS so I can load plates and measure angular distances on
screen, as well as using Guide which displays graphically.

http://aladin.u-strasbg.fr/java/nph-aladin.pl?-rm=14.1&-server=Aladin

for online version, but *nix and winblows standalones available.  Quite
easy to pick up actually, and fully interfaced to both SIMBAD and
ViZieR, over plotting the DSS or whatever loaded up plates with symbols
at position that can be clicked on for short info, which itself is often
further hyperlinked into SIMBAD, ViZieR and/or the bibliography system
at CDS, which can then get you a look at the paper via the ADS at
adsabs.harvard.edu, just by clicking links and not really knowing what
urls you're following!

Ooops, got sidetracked again.  Actually, just found note of those ASAS
stars in the archives at

ftp://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/Mail/vsnet-survey/13

It seems that the stars in question were being deemed guilty of
variation that actually belonged to an adjacent and true variable.

Yes I keep a look out for duplicity induced variation in the sense of
checking out close comites.

Cheers

John