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: Current and Upcoming Observing Campaigns No. 613 May 2, 2000 ---------------------------------------------------------------------------- 1247-28 EX HYDRAE - MULTIWAVELENGTH OBSERVING CAMPAIGN STARTS FRIDAY Astronomers at the Planetary Science Institute in Tucson, Arizona, have scheduled an international multiwavelength observing campaign on the cataclysmic variable EX Hya from May 5 through June 10. Our assistance has been requested to provide close visual coverage during the satellite campaign in order to help correlate the observations obtained from x-ray to infrared by the different satellites. EX Hya is an intermediate polar, which is an interacting binary subtype of cataclysmic variable (CV). It is the only CV to show emission lines in the extreme ultraviolet (EUV) spectral region when not in outburst. The astronomers inform us that they have obtained 1,000,000 continuous seconds of observing time with the EUVE satellite between May 5 and June 10, which will be the longest single observation ever performed by the satellite for a star. EX Hya will also be observed during this campaign by the following satellites: Chandra, RXTE, possibly XMM, USA, FUSE, HST, and UKIRT as well as several large ground-based telescopes. Good optical coverage during the observing interval is essential to the success of this program. Please monitor EX Hya very closely from now through the end of June. Observations made every 5 minutes for as long as possible every clear night would be very valuable. Please record the time of your observations to three decimal places and report your observations of EX Hya to AAVSO Headquarters so we may keep the astronomers informed of its status. For observers who have access to CCD, we strongly recommend CCD observations every 5 minutes for as long as possible. If you can carry out BVRI CCD observations, please contact AAVSO Headquarters for information on the BVRI comparison star magnitudes. An "e" scale AAVSO preliminary chart of EX Hya is available through the AAVSO web page at the following address: http://www.aavso.org/alerts/alert272/ Please use this chart to observe EX Hya, and be sure to indicate which comparison stars you used to make your estimates when you report your observations. Your participation is essential to the success of this ground-breaking observing campaign! ============================================================================== 2138+43 SS CYGNI BEING OBSERVED WITH RXTE and Chandra Astronomers at the University of Leicester, England, have obtained time to make extended observations of the cataclysmic variable SS Cyg with the RXTE satellite. Observations began in mid-March, and the satellite will continue to observe SS Cyg every twelve hours through mid-June. Our assistance has been requested to monitor SS Cyg throughout this period in order to provide good optical data for correlation with the x-ray data from the satellite. We are also collaborating with astronomers at Livermore National Loboratory, CA, on an observing campaign involving Chandra, RTXE, and EUVE satellites. SS Cyg will be observed during an outburst by these satellites early this summer. Immediate notification of the star's brightening so that these satellite observations can be triggered are extremely important. SS Cyg is known to exhibit short periods of brightening between outbursts. Below are recent observations of SS Cyg which show a recent brightening of this type. UT MAG OBSERVER APR 30.101 12.1 PYG APR 30.4472 11.8 HSG MAY 01.0764 11.6 DPV MAY 01.08 11.5 VET MAY 01.085 11.9 PYG MAY 01.3299 11.0 HK MAY 01.3410 10.6 SCE MAY 01.9 11.8 GUN MAY 02.0625 12.1 DPV MAY 02.2958 11.3 HK MAY 02.4194 11.3 HK Please monitor SS Cyg closely throughout the summer and report your observations to AAVSO Headquarters so we may keep the astronomers informed. Good visual coverage will be crucial to the success of this unique, extended observing run. AAVSO Standard charts for SS Cyg may be downloaded from the AAVSO website, or obtained from Headquarters on request. When reporting your observations, please be sure to indicate which comparison stars you used. 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! ____________________________________________________________________________