[Aavso-photometry] RE AN #348 Request to Observe HMXBs

[arne]

Michael Sallman wrote:
> I notice that the comp star "d" for 1930+53 (AAVSO 1936+541) is much 
> redder than the target star:
> 
> 	The Hipparcos and Tycho Catalogues (ESA 1997)
> Star	RAJ2000		DEJ2000		Vmag	BTmag	VTmag	B-V
> ------	------------	------------	-----	------	------	------
> Target	19 32 52.313	+53 52 45.40	10.60	10.375	10.568	-0.170
> d	19 32 57.715	+53 53 38.57	10.24	11.987	10.398 	1.331
> A	19 32 44.504	+53 49 39.42	9.68	9.707 	9.683 	0.019
> 
> 	TASS Mark IV Photometric Survey of Northern Sky (Droege+, 2006)
> Star	RAJ2000		DEJ2000		TASS4ID	Vmag	Imag	V-I
> ______	___________	____________	_______	______	______	______
> Target	19 32 52.34	+53 52 46.1 	2668236 10.440 	10.359	0.081
> d	19 32 57.72	+53 53 39.0 	2668242 10.343 	9.032 	1.311
> A	19 32 44.52	+53 49 39.4 	2668229 9.680 	9.608	0.072
> 
> "A" is much closer in color to the target, though about a magnitude 
> brighter.
> Also the quoted magnitude for the target star (9.8) seems to be a little 
> bright (unless it's a maximum, and not an average).
> 
All four fields *have* been observed at SRO, and BVRcIc photometry
is available.  I expect Gordon and Richard to extract the magnitudes
for their comp stars sometime soon.  I agree that "d" is too red
for a good comparison star.

This will be a tough campaign, as there are 4 targets to follow
(instead of just SS Cyg); the necessary precision will tax your
ability to perform photometry (a good thing!); combining datasets
that have not been transformed will require significant overlap;
long time series will show trends due to extinction; etc.

The Sonoita data indicate DM+53_2262 is at V=10.4, similar to the
magnitudes quoted above.  Note that, while TASS does a good job
on comparison A, it misses the mark on comparison d.  Don't trust
Tycho at these levels, and use TASS carefully.
Arne