Re: GSC 00445-01993

[jg <jg@jgws.freeisp.co.uk>]

Michael Koppelman wrote:
> 
> Got a wee bit more data on this last night. Our baseline is now 42 days,
> so I think the period Chris came up with is holding its own. New phase
> plot and HJD-corrected data is here:
> 
> http://www.lolife.com/astronomy/gsc445-1993/
> 
> Aaron at the AAVSO may try help me with a paper on this that includes
> spectra and perhaps some data from the Harvard plate collection. I'm going
> to start researching the databases for more info on this one. If anyone
> wants to help, I always appreciate it. It would be great to get some
> high-quality photometry on the maximum.
> 
> Cheers,
> Michael Koppelman

Well, I've just discovered that you can now get Annex B Tycho Epoch
Photometry via Vizier, which is a lot easier than emailing off for it as
you used to have to.

For this star it is at
http://vizier.u-strasbg.fr/viz-bin/nph-Plot/Vgraph/htm?I/239/0&445-1993-1

You really need to know what all the flags mean etc to be able to
discard data and use what's left, but a quick glance (as an example)
suggests that there may well have been a deep eclipse time around BJD
2447987.4270. That observation is flagged zero in VT, which mean's data
okay, and the VT background was about five, which isn't bad either. 
Errors for all the photometry are about 0.2-0.3 which isn't useful mind.
There's a VT min here of about 9.8, which ain't gonna be that distant
from the VJ value for an object of this colour, and TASS VJ min looks to
be 9.7.

Anyway, a good way of testing any period you come up with is using such
a value and seeing if you can make it add up to an exact number of
periods ago measuring back from an HJD mid eclipse time of your own (an
exact plus a half is also possible in this EW's case).  Ignore HJD - BJD
difference here, that's gonna be the least of your worries, they're
gonna be essentially the same as far as you're concerned.

Not that good really, coz there's no guarantee that this Tycho one was
mid eclipse point, and use of Tycho epoch photometry is problematic at
the best of times (especially from Annex B), but give it a bash, you
never know you may be lucky ;)


On other stuff, remember that it is a bright xray source, but forget
entirely about any possible association with the open cluster NGC 6633. 
This thing has a fair old proper motion, whereas the cluster members
have next to none.

Cheers

John G.