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			Tel. 617-354-0484	FAX 617-354-0665 

			AAVSO ALERT NOTICE 217 (November 16,1995)


N Cas 95 (see AAVSO Alert Notices 213 and 214) has started to brighten, by about half a 
magnitude in October as the observations in the accompanying light curve show. Our thanks go 
to all observers who have been observing this very ihterestmg nova and reporting their 
observations to AAVSO Headquarters. The optical behavior of N Cas 95 continues to appear 
quite similar to the early stages of the slow nova HR Del (N De11967), whose light curve from 
the AAVSO archives was published in AAVSO Alert Notice 214.

There has been quite a discussion as to the nature of this interesting slow nova, N Cas 95. U. 
Munari, Asiago Observatory, Padua, and A. Lepardo, R. Passuello, and G. Sostero, 
Associazione Friulana di Astronomia e Meteorologia, in IAU Circular 6259 and in their 
message to vsnet, state that their spectroscopic and photometric observations obtained with the 
Asiago 1.82-m telescope show features that may classify this object not with classical novae but 
with symbiotic novae (similar to PU Vul). H. W. Duerbeck, in his message to vsnet, indicates 
that this object shows more similarity to HR Del than to symbiotic novae with respect to the 
optical and spectroscopic behavior. He states that N Cas 95 may still be considered to be in its 
premaximum phase, and, based on the available information, classifies it still as a slow nova.

Observers are strongly recommended to continue to monitor the behavior of N Cas 95, and to 
report their observations to AAVSO Headquarters, indicating which comparison stars were 


The interesting dwarf nova HT Cas is scheduled to be observed with the Hubble Space 
Telescope on November 23 for about 15 hours, and our assistance has been requested in 
monitoring this star closely. Below is a request we have received from Dr. W. Welch, Keele 

"On November 23, the Hubble Space Telescope is scheduled to observe the dwarf nova HT 
Cas. I encourage observers to pay particular attention to this system for the next two weeks.

"HT Cas is a faint, eclipsing CV [cataclysmic variable], with a V magnitude of about 16.5 when 
in quiescence. Sometimes it falls into a low state (< 17 mag), and on very rare occasions it will 
go into outburst (as bright as 10.8 mag). The eclipses, which occur every 106 minutes, are about 
2 magnitudes deep (when in the 'normal' quiescent state.

"When analysing the HST data, it will be important to know what state the system was in during 
the time of the observations (quiescent, low, or outburst), and this is where your observations 
can make a significant contribution. Even upper limits (non-detections) are useful because 
they show that the system is not in outburst.

"Please try to record the time of your observations as accurately as possible; the eclipse of the 
white dwarf only takes 40 seconds, and the entire eclipse lasts < 6 minutes; things happen fast 
and you can be fooled if you're not careful!

"Though HT Cas is a faint and difficult target, I encourage you to observe this important CV. 
Much of our understanding of the details of CVs and accretion discs comes from systems like 
this (e.g. Z Cha and OY Car), and HT Cas seems eager to reveal its secrets. As Joe Patterson 
put it, 'HT Cas is truly the Rosetta Stone of dwarf novae...' (1981 ApJS 45, 517)."

Dr. Welch provides the following ephemeris for the eclipses:

		HJD (mid-eclipse) = 2443727.93721 + 0.0736472039E days

The last recorded outburst of HT Cas in the AAVSO International Database was in February 
1987, when it reached magnitude 12.6 at maximum. Since then, the visual observations have 
been all fainter-thans - mostly fainter than 15.5 to 16.0.

R. Zissell, S. Hadley, MA, has been observing HT Cas with CCD(V) between 16.2 and 17.8 in 
1995, and P. Van Cauteren, Aartselaar, Belgium, observed with unfiltered CCD between 17.4 
and 17.7 in August 1995.

Accompanying is an 'f' scale AAVSO preliminary chart of HT Cas. Please use this chart in 
making observations, and report your observations to AAVSO Headquarters. Those observers 
with CCDs are strongly encouraged to monitor HT Cas, particularly to go after the eclipses 
using the above ephemeris.


The dwarf nova SS Cyg will be observed with the Japanese satellite ASCA on November 27, 
and our assistance has been requested by astronomers at the University of Leicester to monitor 
SS Cyg during this time so that their x-ray observations may be correlated with the optical data. 
Presently, SS Cyg is fading from an outburst that started on November 1.

The goal of the ASCA observations is to observe SS Cyg in quiescence. The ASCA 
observations were initially scheduled for November 16. Thanks to the observations you have 
been reporting of the outburst of SS Cyg, we were able to inform the astronomers that SS Cyg is 
still in outburst, and they were able to have the date of the ASCA observations changed - 
without your observations they would have observed SS Cyg on November 16 and it would not 
have been in the quiescent state they needed.

Please continue to observe SS Cyg and report your observations to AAVSO Headquarters.


We have prepared electronic copies of the AAVSO chart of HT Cas and the light curve of N 
Cas 95 mentioned in this Alert Notice. They are available from our FT? site: (, in /pub/alert217


The current US federal budget impasse may affect our Internet access - beginning tonight, our 
Internet account (at AAVSO and on the FTP site) may NOT be accessible, and may remain 
inaccessible until the impasse is resolved. Please download any charts or light curves from the 
FTP site as soon as possible in case the service is interrupted. Should our account become 
inaccessible, we would not be able to receive your emailed observations; please telephone or 
fax them instead. We apologize for any inconvenience you may experience!

The answering machine at AAVSO Headquarters is on nights and weekends for your 
convenience. Please call our charge-free number (800-642-3883) to report your observations. 
We also encourage observers to send observations by fax to 617-354-0665 or by e-mail through 
the Internet to observationsQa

Many thanks for your significant astronomical observations and efforts.

Good observing!

Janet A. Mattei 

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484