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				BITNET: aavso@cfa 	SPAN: cfa::aavso 
				Tel. 617-354-0484	FAX 617-354-0665

			AAVSO ALERT NOTICE 180 (February 8,1994)


This bright nova, discovered on December 7.47 UT by Syuichi Nakano of Japan at 
photographic magnitude 6.5 (see AAVSO Alert Notice 179), has been very well monitored 
by observers worldwide. Its optical light curve, created from observations reported to the 
AAVSO, indicates that it brightened to about visual magnitude 5.7 by mid-December, and 
then has slowly declined to magnitude 8.4 by February 7, with fluctuations as much as 1 
magnitude in amplitude.	.

In addition to the optical observations, multiwavelength monitoring has been done using 
satellites. S. N. Shore, S. Starrfield, P. H. Hauschildt, G. Sonneborn, and R. Gonzalez-
Riestra, observing with the ILTE satellite, report in IAU Circular 5925 that the IUE satellite 
has been observing N Cas 93 since shortly after its discovery. The first UV spectra on Dec. 
12.1 UT showed the nova at UV minimum, "with most of the opacity coming from 
overlapping absorption lines from the iron group elements: the iron curtain". IUE 
observations obtained about every 4 days indicate that "the ejected material has remained 
in an extremely optically thick shell stage". On Dec. 22 a UV rise by a factor of three 
occurred, and the integrated UV flux of the nova remained nearly constant through Jan. 12.

The optical light curve of N Cas 93 is similar to the light curve of the bright nova of 1934, 
1804+45 DQ Herculis, which reached magnitude 1.5 in brightness, and declined with 
fluctuations until it reached magnitude 4.8. At this time - 108 days after discovery - DQ 
Her showed a dramatic decline: it faded from magnitude 4.8 to 8.3 in 2 days and then 
continued to fade, reaching 13th magnitude in another 28 days. Following this impressive 
decline DQ Her slowly brightened to about magnitude 6.5 in another 75 days and then 
resumed its decline.

Novae such as DQ Her and, more recently, NQ Vulpeculae, form an optically-thick dust shell 
about two to four months after maximum light, resulting in the optical light curve fading 
dramatically and then recovering. The optical light curve and ultraviolet and infrared 
multiwavelength observations reported in IAU Cirrulars 5916, 5922, and 5925 suggest that 
Nova Cas 93 may behave like DQ Her, in which case a dramatic decline in brightness 
would be expected in late March.

Please use the accompanying b and d scale charts prepared by C. Scovil when making 
observations of the nova. Please record the exact time of observations to four decimals of 
the Julian Day. Please note that the accompanying b scale chart shows two revisions from 
the chart distributed with AAYSD Alert Notice 179 - the magnitude label 93 belongs to the 
brighter of the pair of stars southwest of the nova; the 71 comparison star to the northeast 
has been eliminated from the comparison star sequence. This former 71 star has been 
reported to be a small amplitude variable, and although the Geneva Observatory 
photometry does not indicate it as variable, the Hipparcos Input Catalog indicates it as a 
double star, so the recent variability reported may be due to this factor.

Our sincere thanks to all our visual and photoelectric observers who have been calling in 
observations of N Cas 93. Please continue to call in your observations using the charge-
free 800 number (800-642-3883). The answering machine is on nights and weekends for 
your convenience.


Astronomers wishing to observe outbursts of 2138 + 43 SS Cygni, 0409-71 VW Hyi, and 
1247-28 Hya with the EUVE and IUE satellites have requested our help in alerting them 
when these stars start to brighten. As always, we turn to you, our dedicated observers, to 
monitor these stars and call us when they go into outburst.

Many thanks for your efforts and valuable observations. Particularly this winter, when the 
midwestern and eastern parts of the US have been having arctic cold weather, 
contributions from our observers there and from our observers all around the world are 
acknowledged with much appreciation and gratitude.

Good Observing,

Janet A. Mattei 

NOTICE: Subscribers to the AAVSO Alert Notices can now also receive the ASCII text of 
the Alerts via email, transmitted when the paper copies of the alert are sent out by postal 
mail. To receive the email version of the AAVSO Alert Notices, please send us email, 
including your full name, email address, and postal address, at one of the email addresses 
below (whichever is best for you). Unfortunately, we do not have the ability to transmit the 
charts at this time - we are working on it.

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