[vsnet 268] NSV 6819 - an eruptive variable?

[MATI MOREL <morel@ozemail.com.au>]

VSNet  readers,
NSV 6819 is an obscure southern variable, about which virtually nothing is 
known. Its variability was first mentioned in the _Spectral Survey of the 
Southern Milky Way  I_  ,Table 7 (Sundman et al 1974). To their list of M stars 
they appended one star, A9 (later named NSV 6819), as having a definite M 
spectrum, and considered to be variable. Rough coordinates only were given 
(reproduced in the NSV cat.).  No other useful data was given. The published 
field photos do not show the variable with certainty, but appears to mark the 
position with reasonable clarity, considering the small scale.
In 1992 I thought that NSV 6819 might be an unrecognized Mira variable, or 
other red variable, so I enlarged the published finder chart and precisely 
matched it to a plot of SAO stars, thereby deriving the improved position of a 
star  at or near the position of NSV 6819:
(J2000): 14h 50m 01.0s  -56 54'35".
Neither the GSC nor IRAS list any star at this position.
In 1993 Dr William Liller of Vina del Mar, Chile, kindly mounted a min-campaign 
on NSV 6819 to see if any variable of large amplitude could be found here. He 
took CCD images of the region on 16 nights between 1993 May 23 and !993 Nov. 
11. No red variable was found, and there was no apparent change in any of the 
tight group of stars around GSC 8688-02493 [the nearest GSC star, m=13.80].
However, on the night of August 20-21, a  NEW image appeared very close to my 
presumed position of NSV 6819. The bew stellar image is not present on an image 
taken 7 nights later, nor on any other of 15 images taken between 23 May and 11 
Nov. The mag. of this object is 13.72 v.  Position of the "new" star relative 
to the GSC star is (J2000) 14h50m02.4s  -56 54'31".
Liller writes: " I suppose there is the possibility that the image was left by 
a cosmic ray, but from a close examination of the image, I'd say it is a real 
star; ie it looks like no cosmic ray that I have ever seen."
The close positional coincidence between NSV 6819 and Liller's "star" lends 
heavy weight to the theory that there is a photometrically variable object at 
this spot.
Considering the rapid rise and fall, a U Gem type is a possibility, but the 
published spectral type M points to a late-type variable, a flare star?
The object is normally invisible, fainter than 16.5, on Liller's CCD frames, 
and also
fainter than 17 on the digitized SKYVIEW frame.  The rise is therefore greater 
than 2.8 mag.
A careful examination of archival patrol plates may be very helpful in 
determining the nature of the object.  I can supply a detailed finder chart  to 
anyone wishing to look for this variable, as it is in a rich Milky Way field.
Regards,
/Mati
Reference:
Sundman, A., Loden, L.O. and Nordstrom, B. 1974.  Astron. Astrophys. Suppl. 
16,445
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Morel Astrographics
c/o M. Morel
P.O. Box 66  Thornton  NSW 2322  AUSTRALIA
Fax:  61 49 662078              Internet:  morel@ozemail.com.au
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