Photoelectric Photometry Newsletter

Editor's Message

Let me begin by wishing you all a Happy New Year, and by thanking you for your interest in, and support for the AAVSO. I am looking forward to meeting many of you at the "Partners in Astronomy" meeting in Toronto, 1-7 July 1999. The meeting will be held on the main campus of the University of Toronto, close to the centre of the city, and to restaurants, shops, museums, parks and other attractions. A variety of reasonably-priced accommodation is available. Remember that your dollar goes 50 per cent further here! See the web site of the Astronomical Society of the Pacific: www.aspsky.org for more information.

The theme of this meeting is partnership. There are many types of participants in astronomy research and education: amateur and professional astronomers; teachers in schools, colleges, and universities; educators in science centers and planetariums; undergraduate and graduate students; scientific and educational societies; private, public, and national observatories; government agencies; industry; publishers and the media; and more. The number of possible links and partnerships therefore numbers in the dozens!

This meeting includes a major symposium on Amateur-Professional Partnerships in Astronomy Research and Education. This symposium is described in more detail at the end of this Newsletter. Its purpose is to strengthen existing partnerships, and develop new ones through the interactions at the meeting, through the proceedings (to be published in the ASP's Conference Series), and through other follow-up activities. The potential is enormous! Contributed poster papers are welcome, subject to acceptance by the Scientific Organizing Committee. The core OC consists of Bob Havlen (ASP), Janet Mattei (AAVSO and ASP), Leif Robinson (S&T) and myself (ASP and AAVSO and RASC), assisted by a much larger Advisory Board. If you are interested in participating and contributing a paper, please let me know as soon as possible.

The Fall Meeting was held in Cambridge MA, with the usual assortment of interesting scientific sessions, and enjoyable social events. Many of the attendees took a field trip to the observatories of Mario Motta and Gary Walker, and to the Boston Museum of Science. Several of the scientific papers dealt with photoelectric photometry and related topics.

Richard Stanton discussed the "V-Magnitude Experiment" to compare AAVSO visual observers' eyes' response to star color variations with that of the standard Johnson-Morgan BV and the Tycho BTVT photometric systems. Over 60 visual observers took part. The standard V filter evolved, over many decades, from the visual magnitude system.

Cullen Blake described photometric observations, in V, of the delta Scuti star V830 Herculis. These bright, numerous variables have amplitudes of a few hundredths of a magnitude, and periods of a few hours. They are suitable for "backyard photometry" as long as you can achieve precision of a few millimagnitudes, and use one or more check stars.

Jonathan Hale, Yvonne Tang, and I described our studies of the pe- culiar Population II Cepheid RU Cam, described below.

Elizabeth Walker described CCD photometry of the large-amplitude delta Scuti star CY Aqr; the period is about 1.5 hours. The large-amplitude delta Scuti stars are remarkable, in the sense that - even visually - you can observe changes in these stars within a few minutes!

Stephen Cook described CCD photometric V and R observations of the eclipsing binary V608 Cas. There are many benefits to observing eclipsing binaries photoelectrically - to determine precise times of minimum, to derive light curves for determination of the mass and radius, and to look for evidence of circumstellar material, tidal distortion, starspots, or other interesting astrophysical phenomena.

Wayne Lowder described visual observations of apparent brightenings of two eclipsing variables - RZ Cas and WW Aur - at maximum light. Some of us are unconvinced by these observations; there is nothing like good photoelectric photometry, with one or two check stars, to be sure of phenomena such as these.

Albert Holm described IUE observations of the pulsation of the R CrB star RY Sgr. This star has a pulsation amplitude of 0.5 mag, so the pulsation can actually be detected through careful visual observations. Other R CrB stars (including R CrB itself) have much smaller pulsation amplitudes, so the pulsation can only be studied with photoelectric photometry.

Ron Royer discussed the remarkable pulsating star FG Sge which, in the last century, has gone from magnitude 13.7 to 9.1 and, at the same time, has cooled by 250K each year; it has gone from a B type star to its present K2Ib type. Ron ends his abstract by asking "what will FG Sge become - an S-type (Mira) star or an R CrB star?".

Dorrit Hoffleit discussed the difficult problem of relating the Hipparcos magnitudes and the GCVS magnitudes of M-type (non-Mira) giants, mentioned below.

Margarita Marinova and I described AAVSO photoelectric photometry of the M5III star AG Cet, with Hipparcos photometry. The V and the Hipparcos photometric systems are quite different: the latter is a broad-band system which covers most of the visual range, and a bit of the near-infrared also; the former covers a much more restricted range of wavelengths - one which is very sensitive to temperature variations in M stars, because it coincides with the TiO bands in their spectra. The V observations show a "normal" M giant variation, with a period of about 75 days, undoubtedly due to pulsation. The Hipparcos observations show a much shorter period of about 1.7 days which, if real, may arise from a binary companion. There is independent evidence that such a companion may exist.