[vsnet-chat 2570] NSV4189 Hydrae

["PETER F WILLIAMS" <PFWILLIAMS@onaustralia.com.au>]

Dear Reinder and Stan,

Vvsnet-chat 2560 (Reinder) notes a star of magnitude 13 a few arcmin north
of
NSV4189.  This is correct and is our comparison star F = GSC 5441-1840 mag
13.0, about 1.9 arcmin north and a little east.  Also, there is another
fainter star not in GSC, our star J with my eyeball estimate 15.0, about 25
arcsec due north of the variable.

A list of our comparisons with GSC mags are as follows:

STAR	GSC		Mag	Eyeball (January 1995)
A	5454-617	9.3	9.0	(SAO154543 mag 8.4)
B	5454-1011	9.8	9.5
C	5454-787	11.1	11.0
D	5441-1484	11.2	11.5
E	5441-1935	11.4	12.0
F	5441-1840	13.0	12.8
G	5441-1757	13.7	13.0
H	5441-1846	13.9	13.5
I	not listed		14.5
J	not listed		15.0

Star I is about one quarter distant (1 arcmin) from F to G and star J as
mentioned above about 25 arcsec north of NSV4189.  A look at my original
eyeball estimates suggests the difference with GSC may be only half
magnitude - my original comment about a 1 magnitude difference may be a
little overstated but the difference in GSC and SAO magnitude for star A
did not suggest a reliable zero point to start with.

Details of the Lasker field S633 have been supplied by Brian Skiff
(vsnet-chat 2563).  Thanks, Brian.

We opted to use the GSC mags for our preliminary study as these would be
readily available to all and therefore maintain some kind of consistancy. 
The use of differing sequence magnitudes between different observing groups
has always been a problem.  At least with GSC mags we can all be right (or
wrong) together.

Stan, thanks for your vsnet-chat 2567.  I do not think NSV4189 will prove
to be as exotic as BH Cru but we will just have to keep looking.  The light
curve for the 4 earlier cycles seemed very uniform and it was possible to
superimpose one cycle upon the other with surprisingly little scatter. 
This was not really phase stacking as with cepheids, however, due to the
greatly varying period.  The current bright cycle may,however, introduce
considerable scatter to this line of thinking!  

Our observations only go as faint as visual 15.5 at best so we do not know
what the star does below this limit. Yes, I need a larger telescope.

Regards

Peter Williams

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