THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
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AAVSO ALERT NOTICE 173 (July 7,1993)
REQUEST TO MONITOR CATACLYSMIC VARIABLES DURING ORFEUS MISSION
ORFEUS Mission: On July 17, 1993, the NASA's Space Shuttle Discovery is scheduled to launch a German-built, free-flying space platform equipped with an international cargo of science instruments. This first mission m the ASTRO-SPAS series of NASA and the German Space Agency (DARA) is called ORFEUS (Orbiting and Retrievable Far and Extreme Ultraviolet Spectrograph). The mission's primary goal during the planned 5-day science mission is to observe stars that emit most of their light in the ultraviolet band of the electromagnetic spectrum to help understand the evolution of these stars and their interaction with the interstellar medium. Once the instruments have completed their observations, the platform and the instruments will be retrieved and returned to Earth, where they will refurbished for later shuttle flights, at least three more over the next four years. NASA-Astrophysics Division is supplying us with a very informative pamphlet on ORFEUS mission which will be sent to you separately.
OBSERVATIONS OF CATACLYSMIC VARIABLES with the ORFEUS Mission: Astronomers at the Harvard-Smithsonian Center for Astrophysics and Lawrence Livermore National Laboratories at Livermore, California, will be observing some cataclysmic variables - dwarf novae (DN) and magnetic novalike (NL) variables - during the ORFEUS Mission and have requested our assistance. Below is a list of their primary observing targets during this mission.
Designation Star Type Magnitude Range
0058+40 RX And DN 10.3-14.5
0409-71 VW Hyi DN 8.4-14.4
0814+73 Z Cam DN 10.2-13.8
1813+49 AM Her NL 12.4-15.3
2138+43 SS Cyg DN 8.1-12.4
2209+12 RU Peg DN 9.4-13.1
The astronomers are particularly interested in monitoring outbursts of the dwarf novae and the different states ("down" or "up") of the novalike stars.
Please monitor these stars between now and the end of the mission or the end July (which ever is later - in case of change in the launch date), and call in your observations of the outbursts of the dwarf novae, and the brightness state of AM Her, to AAVSO Headquarters, using the charge free 800 number (800-642-3883) that was established for the monitoring of cataclysmic variables for NASA's EUVE mission.
In addition to the stars above, if any of the brighter dwarf novae go into outburst (i.e, with outbursts brighter than 12.0 magnitude), please inform us at Headquarters, as these stars may also be observed during the ORFEUS Mission.
SPECIAL NOTES ON 2138+43 SS CYGNI and 0409-71 VW HYDRI
SS Cygni: This dwarf nova went into outburst on May 22, right before the ASCA mission (see AAVSO Alert Notice 171). This outburst was an anomalous one, in which the rise to maximum was slow, and the outburst was faint and short. Since then, SS Cyg has been particularly active during quiescence, with our observers reporting it brightening to 10.6 and oscillating between 10.6 and 12.1 over the last few weeks. This behavior is rare for SS Cyg and has happened only few times since its discovery in 1896. It is particularly important to monitor SS Cyg closely at this time and to record the exact time of the observations. We have prepared a special information package to help observers determine the exact time of their observations, particularly in converting local time to Greenwich Mean Astronomical Time (GMAT). If you need this package, please let us know.
VW Hydri: This bright southern-hemisphere dwarf novae has been of interest to astronomers with observing programs with several satellites, such as the International Ultraviolet Explorer (IUE) and the Hubble Space Telescope (HST) and ORFEUS. HST is scheduled to observe VW Hyi in the coming months during quiescence in order to study the primary component (white dwarf) of this close binary system. Please monitor VW Hyi closely and inform us of its outbursts from now until December 1993. It is particularly important to know if the outburst is a superoutburst (predicted to occur in the coming months).
1908+01 NOVA AQUILAE 1993 [V1419 Aql]
Accompanying are 'b' and 'd' scale charts recently prepared by C. Scovil. Please use the 'd' scale chart as this nova continues to fade. N Aql 93 was reported at magnitudes 12.5 and 12.8 on July 6.1 UT by J. Bortle and C. Scovil, respectively.
FADING OF 1910-33 RY SAGITTARII
Our observers J. Bortle, P. Collins, L. Hiett, D. Overbeek, and D. York have reported that the R Coronae Borealis type variable RY Sgr has started to fade. From June 15 to July 7 it has faded from magnitude 6.5 to 9.1. Its last fading was in 1990. Please monitor RY Sgr closely as it continues to fade and call in your observations to AAVSO Headquarters.
REQUEST TO MONITOR 1834-23 V348 SAGITTARII
This interesting variable, whose light curve resembles that of an R CrB type variable, has been at its minimum state. Astronomers at Louisiana State University are interested to observe it with the IUE satellite when it starts to brighten. Please keep a close eye on it and call in your observations to Headquarters when it is brighter than magnitude 13.0.
As always, thank you very much for your efforts and for your valuable contributions to variable star research.
Clear skies and good observing!
Director
files: N Aql 1993 'b' and 'd' preliminary charts;
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