[Aavso-photometry] HD37605 photometry/possible field variable

[Arne Henden]

Shawn Dvorak (RHO) wrote:
> I got a good run on HD37605 last night 03:13 to 06:55 UT.  The skies were quite transparent and probably as close to photometric as we can get here near sea level in Florida.  There was no sign of any change in HD37605 even at the few-millimag level.  This star is just about the perfect brightness for V filter photometry with my 25cm: I was able to go with 10sec images to avoid scintillation effects, but still collected plenty of photons.
> 
> While reducing the data I did notice that one of the comp/chk stars I used *may* be variable.  When plotting the brightness of the 86 comp against the 99 chk I see a sinusoidal curve with an amplitude of about 0.006 mag and a period around 0.08d (~2 hours).  Unfortunately there's no other stars bright enough in the field to provide a secondary check to see which of the two stars is variable (if either).  You can see a graph of the light curves at http://www.rollinghillsobs.org/images/HD37605_2004-12-26.jpg
> 
Variation could be real, but it will take a bit of work to convince
everyone.  I'd estimate the period and start phasing multiple
series and see if the period stays constant (not always the case
with delta Sct of course).  At the 0.01mag level, there are many
effects that can simulate a variation, including a bad pixel on
the edge of an aperture, shifting of the field on the CCD, etc., so
you have to work really hard to eliminate all sources of error.
   At the millimag level, I'd guess most stars are variables.  That
is one reason why it is best to do ensemble photometry when doing
final reductions of small amplitude features.  I know single-comp-star
was requested for this field, but save your images and consider
ensemble analysis if something is discovered and needs to be studied
more carefully.
Arne