THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS 25 Birch Street, Cambridge, MA 02138 USA Tel. 617-354-0484 Fax 617-354-0665 http://www.aavso.org * * * AAVSO NEWS FLASH * * * Subject: 0103+59 HT CAS 1552+72 SS UMI No. 472 LUNAR IMPACT 1723-46 AT ARA July 27, 1999 1925+42 V1504 CYG ---------------------------------------------------------------------------- 0103+59 HT CASSIOPEIAE The dwarf nova type (SU UMA subclass) cataclysmic variable HT CAS is in outburst (possible superoutburst), as indicated by the following observations: AAVSO Observer AAVSO Observer UT Mag. Initials UT Mag. Initials JUL 24.049 <15.5 PYG JUL 26.941 12.9 MUY JUL 24.051 <13.9 MGH JUL 27.090 12.7 SPK JUL 26.925 12.5: SPK JUL 27.093 12.3 SPK According to the AAVSO International Database the most recent bright superoutburst of this star occured in January 1985, when HT Cas reached mean visual magnitude 11.0. Observers are encouraged to keep a close eye on HT Cas, and if this is a superoutburst to search for superhumps (small amplitude oscillations that are 2% to 3% longer than the orbital period of the system). TO observe superhumps make observations every 5 minutes for at least three hours and record the times of the observations to four decimal places of the day. CCD observers are particularly encouraged to observe the superhumps. HT Cas is one of the few dwarf novae where eclipses can be observed. It has deep eclipses (1 to 2.5 magnitudes in amplitude) at the orbital period of 1 hour and 47 minutes. Eclipses last only 10 minutes. Very frequent (every 30 seconds) observations are needed. Careful observations and timing of the eclipses are important in mapping the luminosity of the system. The elements for the mid-eclipse are (AAVSO Alert Notice 72): J.D. min (heliocentric)=2,443,727.937 + 0.07364722 E AAVSO 'b' and 'd' scale standard charts for HT Cas are available via the AAVSO web page: http://www.aavso.org ---------------------------------------------------------------------------- IMPACT OF THE LUNAR PROSPECTOR We have received the following request from Dr. Tony Phillips, astronomer and science writer with the NASA Space Science News web site (http://science.nasa.gov) at NASA Marshall Space Flight Center, for observations of the impact of the Lunar Prospector on Saturday, July 31, 09:51 UT: Scientists involved with the Lunar Prospector crash into the Moon are encouraging amateurs to observe the impact this Saturday morning, July 31 at 0951 UTC. Most professional astronomers will be using large telescopes with sensitive spectrometers to look for a tenuous cloud of water vapor. The vapor cloud will be invisible through typical amateur telescopes. However, amateur astronomers can contribute by watching for a impact plume that may be visible for up to several minutes after impact. Theoretical calculations suggest that the plume will likely be very dim and probably impossible to see so near to the sunlit edge of the full moon. Nevertheless there are many uncertainties in the physical models so scientists are urging amateurs to monitor the impact. Telescopes equipped with low-light astro-video recorders are considered best for scientifically useful observations, but still cameras and simple visual observations are also valuable. Details and observing tips for amateurs may be found at http://www.LunarImpact.com All forms of data obtained by amateurs may be sent to Dr. Tony Phillips (phillips@spacesciences.com FAX: 760-872-1382) who will forward them to the appropriate scientists at NASA/Ames and the University of Texas at Austin. We would particularly appreciate digital images and video sent to Tony Phillips as email attachments as soon as possible after the July 31st collision for posting on LunarImpact.com . ---------------------------------------------------------------------------- 1552+72 SS URSAE MINORIS The dwarf nova type (SU UMA subclass) cataclysmic variable SS UMI appears to be in outburst, as indicated by the following observations: AAVSO Observer AAVSO Observer UT Mag. Initials UT Mag. Initials JUL 23.006 <15.4 PYG JUL 24.054 14.3 PYG JUL 23.972 14.3 PYG JUL 25.2535 <13.2 SXN ---------------------------------------------------------------------------- 1723-46 AT ARAE The dwarf nova type (SS CYG subclass) cataclysmic variable AT ARA appears to be in outburst, as indicated by the following observations: AAVSO Observer AAVSO Observer UT Mag. Initials UT Mag. Initials JUL 09.4000 <14.6 SRX JUL 27.5778 13.5 SRX JUL 26.4250 <13.6 SRX ---------------------------------------------------------------------------- 1925+42 V1504 CYGNI The dwarf nova type (SU UMA subclass) cataclysmic variable V1504 CYG appears to be in outburst, as indicated by the following observations: AAVSO Observer AAVSO Observer UT Mag. Initials UT Mag. Initials JUL 22.349 16.5 OCN JUL 24.004 15.0 PYG JUL 22.983 <15.5 PYG ---------------------------------------------------------------------------- We thank the following contributors for the data that they have provided for this News Flash: MGH - H. MCGEE, ENGLAND SPK - P. SCHMEER, GERMANY MUY - E. MUYLLAERT, BELGIUM SRX - R. STUBBINGS, AUSTRALIA OCN - S. O'CONNOR, CANADA SXN - M. SIMONSEN, USA PYG - G. POYNER, ENGLAND Please monitor these and other variable stars closely and phone-in, fax, or e-mail your observations to the AAVSO. Good observing! Janet A. Mattei, Director Rebecca Pellock, Technical Assistant ____________________________________________________________________________ Symbols may include: < = fainter than magnitude given (variable not seen) : = uncertain CCDV = Charge-coupled device with (V) filter If you would like to contribute to AAVSO NEWS FLASH, please send observations of unusual variable star activity to: observations@aavso.org Those who wish to subscribe (free of charge) or unsubscribe to NEWS FLASH may do so by visiting the following web page: http://www.aavso.org If you would like data from the AAVSO International Database for research purposes, please send your request to: Janet Mattei, AAVSO Director, at aavso@aavso.org An archive of past issues of the News Flash is available at the following web page: http://www.aavso.org/newsflash/ We look forward to including your observations in future editions of AAVSO NEWS FLASH! ____________________________________________________________________________