THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS 25 Birch Street, Cambridge, MA 02138 USA INTERNET: aavso@aavso.org Tel. 617-354-0484 FAX 617-354-0665 AAVSO ALERT NOTICE 221 (May 9, 1996) FADING OF 2007+20 FG SAGITTAE We have been informed by the Central Bureau for Astronomical Telegrams that S. Shugarov, Sternberg Astronomical Institute, Moscow, reported that FG Sge, the central star of a planetary nebula, has faded dramatically to approximately V magnitude 16 and B magnitude 17 on April 24.04 UT (IAU Circular 6323). Our member Monsignor Ron Royer has confirmed the fading and his CCD observations made with IR-blocking filter indicated that this star was at magnitude 16.0 on May 7.3556 UT. FG Sge started to decline from its about 25-year long average maximum magnitude of 9.2 in August 1992. By October 1992 it reached magnitude 13.7 (see AAVSO Alert Notice 163). Since then, it has brightened to magnitude 10.2 several times but has never fully reached maximum, and has faded, reaching as faint as magnitude 14.4 in August 1994. Recent observations indicate that in January 1996 it reached 10.2 and started to fade slowly, as shown by the observations below. The current magnitude is the faintest FG Sge has been since 1894 (see AAVSO Alert Notice 163). Recent observations include: Feb 21.224 UT, 10.8, A. Diepvens, Balen, Belgium; 24.1701, 10.6, B. Hassforther, Heidelberg, Germany; 26.2, 10.5, G. Krisch, Bockenem, Germany; 27.1875, 10.9, W. Kriebel, Leiblfing-Hailing, Germany; 29.13, 11.9, P. Maurer, Bad Friedrichshall, Germany; Mar 2.2, 11.5:, Krisch; 3.16, 11.8, Maurer; 9.18, 11.9, B. Granslo, Fjellhamar, Norway; 21.177, 12.4, Diepvens; 28.1, 12.5, J. Speil, Walbrzych, Poland; Apr 8.0, 13.9, L. Szentasko, Budapest, Hungary; 22.126, 14.4:, G. Poyner, Birmingham, England; 27.102, 14.5:, Poyner; 28.097, 14.3:, Poyner; May 5.072, <13.7, Poyner; 6.079, <13.7, Poyner; 7.3556, 16.0 CCD with IR-blocking filter, R. Royer, Lakewood, CA; 8.049, <13.7, Poyner. There are two very close stars to the east of FG Sge. Observers should be aware of these stars. The star about 8 - 10 arcseconds east is a suspected variable; R. Royer reported this star to be at magnitude 12.3 on May 7.3556 UT. The star to the east of this suspected variable was reported by Royer at magnitude 15.0 on May 7.3556 UT. J. Bortle informs us that the apparent magnitude of FG Sge is very strongly influenced by its close companion. He recommends that high magnification (several hundred times) be employed in making estimates. One must not only resolve the pair, but the pair must also appear well separated before a proper brightness determination can be made. Accompanying is a CCD image provided by R. Royer, which shows the very faint FG Sge together with its two companion stars to the east. Also accompanying is the AAVSO 'e' scale preliminary chart for FG Sge prepared by C. Scovil. The companion star suspected as variable is indicated as 'var?' on the chart, and is located closer to FG Sge than can be accurately indicated on the chart. Observers with large-aperture telescopes and those with CCDs are strongly urged to monitor FG Sge and call in your observations to AAVSO Headquarters. Also accompanying is a light curve of FG Sge since 1985, showing its maximum phase as well as the decline since 1992; we have also placed this light curve on our ftp site. 157 AAVSO observers contributed 5,544 observations to this light curve; we acknowledge each observer's contribution with gratitude. REQUEST TO MONITOR 2138+43 SS CYGNI FOR OBSERVATIONS WITH HST, EUVE, AND XTE We are collaborating with astronomers from Lawrence Livermore National Laboratory in the observations of SS Cyg in an exciting observing program that will involve the Hubble Space Telescope (HST), Extreme Ultraviolet Explorer (EUVE), and the X-ray Timing Explorer (XTE). From now until the end of December, these three satellites have been scheduled to observe SS Cyg as a target-of-opportunity object during a maximum, in search of very small- amplitude and very short-period oscillations of the white dwarf. In order to be able to carry out these observations, we have been requested to inform the investigating astronomers when SS Cyg starts to go into outburst, i.e., brightens, and to continue to keep them informed throughout the outburst so that these satellites may be scheduled to observe SS Cyg. Small-amplitude, short-period, coherent oscillations with a period of 7.5 seconds were obtained during outburst for SS Cyg by R. Hildebrand and his colleagues in the late 1970's and early 1980's. We assisted them in these observations while they were observing several dwarf novae with ground-based telescopes. However, this particular study has not been carried out using multiple satellites and multiwavelength observations, thus the current study will be a pioneering one in the study of small-amplitude, short-period oscillations of the white dwarf in dwarf novae-type cataclysmic variables. The success of these observations very much depends on your observations and the early alerts and continuous information we can provide to our colleagues. Presently, SS Cyg is fading slowly from an outburst, as indicated by the following observations: Apr 28.051 UT, 12.3, G. Poyner, Birmingham, England; 28.3222, 12.2, G. Hanson, Cave Creek, AZ; 28.3229, 11.9, M. Dombrowski, Glastonbury, CT; 29.1215, 11.7, M. Biesmans, Essen, Belgium; 30.053, 11.4, Poyner; 30.1257, 10.7, Biesmans; 30.5139, 9.8, R. Royer, Lakewood, CA; 30.939, 8.6, L. Teist Jensen, Farum, Denmark; May 1.4271, 8.7, W. Dillon, Missouri City, TX; 2.2889, 8.6, M. Komorous, London, Ontario, Canada; 2.3535, 8.4, M. Gable, Oregon, OH; 2.4771, 8.4, P. Collins, Scottsdale, AZ; 2.96, 8.3, J. Gunther, St. Oze, France; 3.0, 8.5, L. Kiss, Szeged, Hungary; 3.2931, 8.6, Komorous; 3.4743, 8.4, Collins; 5.051, 8.7, Poyner; 5.5521, 8.2, G.-L. Schott, Wesel, Germany; 6.050, 8.8, Poyner; 6.99, 8.4, G. Comello, Groningen, Netherlands; 7.052, 8.8, Poyner; 7.0757, 8.3, Biesmans; 7.2625, 8.2, J. Griese, Stamford, CT; 7.3514, 8.4, T. Rogers, Amherst, MA; 8.3493, 8.6, Komorous; 9.00, 8.3, Comello; 9.0611, 8.5, Biesmans. Please monitor SS Cyg closely, and inform us by phone, fax, or email when it starts to brighten, i.e., becomes brighter than 11.5. Once SS Cyg goes into outburst, please send in your observations daily so we may keep the astronomers informed regarding this very interesting star. 1058+38 MARKARIAN 421 IN OUTBURST We have been informed by Dr. J. Pesce, Space Telescope Science Institute, that the Whipple Gamma Ray Collaboration has reported an extraordinary outburst of gamma ray activity from Markarian 421 (see AAVSO Alert Notice 220). P. Garnavich, observing with the Whipple 1.2-m optical telescope, has detected brightening of 0.25 magnitude in the R band in this object containing an active galactic nucleus. Please continue to monitor Markarian 421 closely, and report your observations to AAVSO Headquarters. Accompanying is a revised 'e' scale AAVSO preliminary chart prepared by C. Scovil of Markarian 421: the position of this object has been revised and additional comparison stars have been added. ACTIVITY OF 1814+39 AM HERCULIS CONTINUES The magnetic variable AM Her continues to fade very slowly, as indicated by the following observations: Apr 16.8667, <13.5, M. Kohl, Laupen, Switzerland; 17.21, 13.8, P. Steffey, Daytona Beach, FL; 18.0273, <13.1, O. Trondal, Oslo, Norway; 18.3556, 13.8, M. Komorous, London, Ontario, Canada; 19.12, 13.8, G. Dyck, Assonet, MA; 20.0, 13.8, M. Verdenet, Bourbon-Lancy, France; 21.0806, 13.6, Kohl; 23.3222, 13.8, R. Harvan, Leonardstown, MD; 23.5174, 14.2 CCDV, R. Royer, Lakewood, CA; 25.20, 13.7, Steffey; 25.3299, 13.4, Harvan; 27.059, 13.6, P. Skalak, Karlovy Vary, Czech Republic; 28.1007, 14.0, J. Bortle, Stormville, NY; 28.3139, 13.7, Harvan; 28.3264, 13.7, G. Hanson, Cave Creek, AZ; 29.071, 14.0, L. Teist Jensen, Farum, Denmark; May 2.3014, 13.7, Komorous; 3.3139, 13.7, Komorous; 4.983, 13.9, G. Poyner, Birmingham, England; 5.9, 14.4, Verdenet; 5.985, 13.9, Poyner; 6.2069, 13.8, Hanson; 7.008, 14.1, Poyner; 7.0958, 14.2, Bortle; 7.229, 14.2 CCDV, R. Zissell, S. Hadley, MA; 7.2458, 13.9, J. Griese, Stamford, CT; 7.2646, 13.9, Hanson; 9.2361, 14.1, Hanson. If AM Her is indeed fading and reaches its down state, multiwavelength observations will be carried out as an international observing campaign (see AAVSO Alert Notice 220). Please continue to monitor AM Her and report your observations to AAVSO Headquarters. 1746-17 -- SGR IS A NEW PLANETARY-NEBULA NUCLEUS IN SAGITTARIUS The Central Bureau for Astronomical Telegrams announced (IAU Circular 6322) that S. Nakano, Sumoto, Japan, reported the discovery by Yukio Sakurai, Otsuka-cho, Mito, Ibaraga-ken, Japan, of an object thought to be a possible slow nova on Feb 20.806 UT, using Fuji G400 film and a 300-mm f/2.8 lens. The object was red and of photographic magnitude 11.4. Patrol films Sakurai took in 1993 and 1994 showed no object, but it was visible at about magnitude 12.5 on films beginning in January 1995. The precise position of -- Sgr, reported by S. Nakano, Sumoto, Japan, for Y. Kushida, Yatsugatake South Base Observatory, Japan (IAU Circular 6323), is: R.A. = 17h 52m 32.69s Decl. = -17 degrees 41' 07.7" (2000) M. Hazen, Harvard-Smithsonian Center for Astrophysics, reported that some 200 plates in the Harvard plate collection, quite evenly distributed over 1930 to 1951 and reaching blue magnitude 14 (earlier plates) to 16 (later plates), showed no variable star at the location (IAU Circular 6322). S. Benetti and H. W. Duerbeck, European Southern Observatory, reported that observations made on Feb 23.3 UT by E. Cappellaro, Osservatorio Astronomico di Padova, using the Dutch 0.9-m telescope at La Silla (ESO), showed a new star. A fully reduced CCD spectrogram (range 375-985 nm; resolution 1.6 nm) taken by B. Leibundgut (ESO) on Feb 23.4 UT with the ESO 3.6-m reflector (+ EFOSC1) revealed a spectrum consistent with a reddened early G-type star of high luminosity; no emission lines were visible (IAU Circular 6322). This object is in fact the nucleus of a planetary nebula, and is similar to V605 Aql, according to private communication we have received from H. Bond of the Space Telescope Science Institute. He writes, "V605 Aql was bright for several years around 1919, and the outburst was probably a late helium shell flash occurring in a massive white dwarf. It would be very important for the AAVSO to observe the outburst of [-- Sgr] over the next several years. If similar to V605 Aql, it will continue to brighten for a year or two, and then fade away over a similar timescale..." Accompanying is a 'd' scale AAVSO preliminary chart of -- Sgr prepared by C. Scovil. Please add -- Sgr to your observing program if it is within the reach of your telescope and monitor it, and report your observations to AAVSO Headquarters with your regular monthly reports. If you see any sudden change in brightness or behavior, please phone/fax/email your observations to us. CHARTS AVAILABLE ON AAVSO FTP SITE AND AAVSO WEB SITE HOME PAGE Electronic copies of the AAVSO charts of FG Sge and -- Sgr, the revised chart of Markarian 421, and the CCD image of FG Sge mentioned in this Alert Notice are available from our FTP site: ftp.aavso.org (198.116.78.2), in /pub/alert221 The charts, along with the light curve and CCD image of FG Sge, have also been placed on our Web site at the following address: http://www.aavso.org 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 observations@aavso.org. We would appreciate it very much if you would report your observations in Universal Time. Many thanks for your valuable astronomical contributions and your efforts. Good observing! Janet A. Mattei Director