November 23, 1981
THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
187 Concord Avenue, Cambridge, MA 02138 USA
Tel. 617-354-0484
SPECIAL AAVSO ALERT NOTICE ON DWARF NOVAE
Do continue your close monitoring of dwarf novae. Dr. Stiening from Stanford University and his colleagues will be observing these stars from Nov. 25th to Dec. 4th at Mt. Lemon, Arizona, and they have requested our help once again.
The goal of their observing is to monitor dwarf novae during outburst with a high speed photometer in order to detect the very small amplitude (0.02m - 0.008m), periodic (period between 8 and 39 seconds) oscillations observed only during outburst, in these stars. These oscillations have been interpreted as being related to the white dwarf component (white dwarf pulsation, or rotation) of the system.
Dr. Stiening and his colleagues are interested in all observable dwarf novae up to 60o in declination. Objects of particular interest are:
0130+50 KT Per
0547-05 CN Ori
0640-16 -- CMa (X-ray object near Sirius) [HL CMa]
0749+22 U Gem
0804+28 YZ Cnc
0855+18 SY Cnc
1934+30 EM Cyg
2138+43 SS Cyg
2209+12 RU Peg
Please monitor the stars above and the rest of dwarf novae closely, and alert me by phone (HQ 617-354-0484) weekdays; Home 617-xxx-xxxx weekends, holidays, and evenings until midnight).
Once again, your contribution is crucial to the success of this experiment. Since the periodic fast oscillations are observable ony at maximum, Dr. Stiening and his colleagues are depending on your information as to what stars to observe. I am aware of the expense of phone calls during these observing runs which we have had in recent months. If necessary, call collect, but call if you observe an outburst.
NOTE: YZ Cnc is going through a supermaximum that started on November 16th. Please observe it closely on its decline so that we would have a good series of observations at that phase. From the analysis of our light curves, we found that during supermaximum SU UMa stars stay at maximum for about one week, then the decline to minimum is very rapid - as rapidly as in a narrow maximum. To confirm this we need more observations on the decline. Several observations throughout the night are particularly valuable.
Astronomers observing at Kitt Peak and with the IUE satellite (see Alert Notice 45) were able to observe YZ Cnc last week during its supermaximum thanks to your alerts! There are very excited with the photometric and spectroscopic data obtained which include superhumps.
Many, many thanks for all your efforts, valuable observations, and your phone calls. Keep up your excellent contributions to variable star astronomy.
Happy Thanksgiving to you and your family.
Good Observing!
Janet A. Mattei