Re: HD 932 is a Cepheid Variable of 10.3: day period

[Tom Droege <tdroege2@earthlink.net>]

John,

Note that the V-Ic for the tass data is suspect.  That is what the current 
calibration fuss is all about.  Indications are that Ic can vary .2 mag 
peak to peak depending on where in the image the star is measured.  V seems 
to vary less over the image.   Possibly we can figure out a correction and 
then I can reprocess all the data.  This is one reason I have not 
"published" in a journal yet.

Tom Droege

At 02:18 PM 11/26/02 +0000, you wrote:

>Preliminary photometry by Tom Droege, consisting of 174 paired Johnson V
>and Cousins I measures (available via http://data.tass-survey.org/ , the
>"november" collection ) reveal
>
>HD 932 (RA 00h13m43.4 , Dec +06 56' 18" ; 2000)
>
>to be a Cepheid variable of around 10.2 to 10.3 days period, with
>amplitude ranging from V 8.9 to 9.4.
>
>The lightcurve appears on the whole symmetrical, although only the
>descending branch is well sampled enough to be certain of there being no
>marked 'humps' in that part.
>
>The spectrum is catalogued as A5, and the Tycho derived B-V of +0.3
>would seem to fit that, however the V-Ic measures mentioned here average
>+0.35, slightly more consistent with what would be expected from an
>earliest F type Cepheid.  Examination of the Tycho Epoch Photometry
>revealed it to be very scattered, with even negative BT-VT at times,
>suggesting that that mean value is not necessarily exact.  Neither
>SIMBAD nor VizieR had much to add, though a 1980 paper gave a _Johnson_
>V-I (ie _not_ a _Johnson-Cousins_ V-Ic) of +0.51 for V at 9.31.
>
>V-Ic reddenned slightly towards minimum, with a range of +0.31 to +0.44,
>ignoring 3 and 2 problematic and isolated measures (out of the 174 in
>total) at the blue and red ends respectively (there is a little scatter
>in the light curve on some nights).
>
>On the whole, the spectroscopy and the photometric colours appear to be
>just a little too early for a Cepheid, but none are that rigorous and
>the lightcurve and period fit well enough.
>
>Searches in many formal and informal variability and suspected
>variability lists show that variability is not previously known, whilst
>a cross identification check against many catalogues revealed no
>infrared, xray or other exotic source coincident with this object.
>
>Further monitoring is required to fully sample the lightcurve in order
>to either confirm or deny this object's identity as a Cepheid, and if it
>is a Cepheid, to help decide if it is a dCep or CW (W Vir) star.
>
>
>
>John Greaves