[vsnet-chat 148] Re: "NN" Sgr (N. Sgr 1990)

[bas@bom.gov.au (Bruce Sumner)]

Re: Taichi's reply to Berto on Nova Sgr 1990

> Anyway, your "NN" Sgr at 17 59 18 -29 10 is called Nova Sgr 1990 (as
> called in IAUCs), which was first discovered as a possible nova, later
> turned out to be by spectroscopy a possblie WZ Sge-type object.  If only
> the star erupted three months later, I might have tried CCD photometry.

This star definetely warrants monitoring. It was discovered by Bill Liller,
Vina del Mar, on Feb 23 1990. His photographic magnitude estimates were 
as follows:  
	    Feb 20.4 1990 <11
                23.4   "    8.0
                24.3   "    8.9
            Mar  2.4   "    9.8

Rob McNaught reported additional fading of about 0.3-0.4 mag between 
March 8.7 and March 9.8 on films taken with the Uppsala Southern Schmidt.

The variable appears to be in quiescence on POSS-I O and E plates as a
blue object at about magnitude 18.3B. The following positions are available:

         RA (2000)     Dec (2000)
	17 59 18.20   -29 09 52.9   McNaught 1990, precessed from B1950
	17 59 17.535  -29 09 52.81  USNO A1.0 (POSS-I (O), Apr 1958)
	17 59 17.54   -29 09 53.8   DSS (UK SRC-J, Apr 1987)			

McNaught's position is the outburst position, while the USNO and DSS
positions are of the proposed candidate at minimum. McNaught's position,
some 10 arcsec east of the candidate, is empty to about magnitude 20B
in the DSS and empty to about mag 21B in USNO A1.0. The colour index
(blue-red) of the candidate in A1.0 is -0.4, and even allowing 
for the very poor photometic calibration of A1.0 (see vsnet 983 from
Brian Skiff), it seems probable that this is the variable at minimum.
Thus with a range of about 10 magnitudes, a classification of WZ Sge
is quite possible. Lets keep it under observation.

Bruce Sumner
Melbourne, Australia

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