QR And campaign (Sobotka) Date: Mon, 7 Dec 1998 13:04:25 +0100 (CET) From: Petr Sobotka <sobotka@physics.muni.cz> Subject: QR And - campaign Dear colleagues, please read carefully the article I send. I do not know which format of data you like, so I am sendig .txt, .doc, .pdf - you can coose any of them - they are the same. I am coordinator of MEDUZA group. MEDUZA is group of variable stars observers in Czech Republic. We declare worldwide observing campaign for interesting star QR And. It would be very useful to add our declaration on VSNET web. I think this campaign is opportunity for all observers on the world. I prepare WWW page for QR And. It will be finished within a few days. http://astro.sci.muni.cz/variables Petr Sobotka --- Observing Campaign for QR And (= RX J0019.8+2156) 1. Introduction V. Simon, Ondrejov Observatory and the MEDUZA Group declare an observing campaign for QR And. Ondrejov Observatory is a professional astrophysical center in the Czech Republic. MEDUZA is a group of observers included in the B.R.N.O. - Brno Regional Network of Observers - the Variable Star Section of the Czech Astronomical Society. 2. Why to observe QR And QR And is very interesting and relatively bright variable star in the north sky. It has been detected as a soft X-ray source quite recently and identified with a yet unrecognized variable star (Beuermann et al. 1995, A&A, 294, L1). As QR And is not in an observing programme of any other variable star society, no long-term visual series are existing. Observers have not been aware of its particularity. And professional astronomers need more data to explain its behaviour. For these reasons we have decided to invite all observers to a worldwide campaign to monitor this variable star. 3. Optical variability of QR And We chose some pieces of information from the only one existing long-term light curve, deduced from the Harvard and Sonneberg archival photographic plates (Greiner and Wenzel, 1995, A&A 294, L5): (a) Orbital modulation (P=15.8 hours) with an amplitude of about 0.5 mag resembles a beta Lyr-type, i.e. brightness varies smoothly, there are not any flat portions in the light curve. The modulation is highly variable from cycle to cycle (Meyer-Hofmeister et al., 1998, A&A, 331, 612). Following lightcurve elements were derived: Min.(hel.) = 2 435 799,247 + 0,6604565 * E, which is valid at least for the years 1955 - 1993. (b) Irregular fluctuations on timescales of weeks to months - amplitude about 1 mag. (c) Long-term variations, seemingly non-periodic, with timescales of up to 20 years and an amplitude of 2 mag. There are two large optical brightness jumps by about 1 magnitude. The rise time of the jump in 1969 is shorter than 10 month, while the jump in 1931/32 has a rise time 14 month. Both of these intensity jumps are followed by a slow relaxation continuing over cca 20 years. Whether or not there was a similar jump at the end of the last century (which would imply a nearly periodic recurrence time scale of cca 40 years) cannot be decided due to the sparse coverage. But certainly, at these times the object also showed the full amplitude of variability (>1 mag). Many of seasonal means are averages over irregular fluctuations. These variations occur on timescales of weeks to months, and the variability patterns are different from year to year. Thus, a considerable part of the scatterning can be assigned to these irregular, short-term fluctuations with the resulting mean being dependent on the different coverage of bright and faint episodes. 4. Why is QR And so unique? QR And is a member of the group of the socalled supersoft X-ray sources. According to the current model (van den Heuvel et al., 1992, A&A, 262, 97), these objects are close binaries, similar to "classic" cataclysmic variables (CV). They differ in the higher mass of the mass-donating star. This star is even more massive than its companion, white dwarf. Therefore matter flows from the more massive star onto less massive companion - it is called "evolution on the thermal time scale". This phase is a brief episode in the evolution of a binary - the mass transfer rate is extremely high that time, much higher than in classic CV, and the mass-losing star tends to become less massive than its companion. Due to relatively short duration of this phase, it is only a very little chance for its detection. QR And is one of rare exceptions. The high mass transfer rate dm/dt makes the accretion disc much more luminous than in common CV. Moreover, the large amount of incoming mass is able to maintain the socalled steady-state hydrogen burning on the surface of the white dwarf. This thermonuclear reaction is a powerfull source of extremely soft X-rays, not observed by any other kind of binary with accreting compact object. A part of these X-rays is absorbed by the accretion disc, it heats it up, and the energy is re-radiated in the optical region. The luminosity of "super-soft" binary comes therefore not only from the accretion process, but also from the re-emitted X-rays, and makes the system much brighter than clssic CV. Unfortunately, although the "super-soft" binary is a very powerful source of soft X-rays, in fact they can be only rarely observed, because they are easily absorbed in the interstellar medium. The X-ray emission of QR And has been observed - even this makes a rare exception of it. Acquiring possibly much information on its light changes in the optical band of spectrum will make easier identification of more distant members of this class of binaries, whose X-rays have been extinguished too much to be observed. The well known variable star V Sge may be a promising candidate (Steiner and Diaz, 1998, PASP, 110, 276). 5. How to observe, where to send the observations Because of variability on diverse timescales it would be advantageous to make several visual estimates or CCD measurements a night but if impossible one will be of good use, too. Please send all visual observations to sobotka@physics.muni.cz and all CCD measurements to simon@sunstel.asu.cas.cz. If you can稚 use e-mail, send your observations to Petr Sobotka, Nicholas Copernicus Observatory, Kravi hora 2, 616 00 Brno, Czech Republic. In November, a finding chart for QR And was compiled using Tycho Catalogue (Hipparcos) and GSC. QR And varies between 11.5 - 13.0 mag(pg). Its amplitude in visual region has been unknown therefore comparison stars cover a broad interval 9.98 - 13.9 mag (V). There can be objections to given magnitudes of the stars of comparison because the precision of GSC magnitudes is rather poor but it does not matter. We are going to measure the magnitudes of comparison stars by the CCD. In our database not only magnitudes and times of estimates are stored but the records of the estimates as well. In such a way it is ensured that it will be possible - now and any time in future - to re-process the content of the database with regard to new values of magnitudes of comparison stars. 6. Observation form Please, send all data in the following format: Position 1 11 25 35 55 65 Entry Star name Julian Date Magnitude Date (UT) Observer's Code Estimate or Estimates Example QR And 2451139.256 11.28 1998-11-21.756 PM E4V2F, E4V9G Julian Date and date are rounded for three decimal places and mag for two ones. Observer's code will be assigned to him (her) after the arrival of first estimates. In case of more than one estimate in the same time, please write all of them on the same line, detached by commas. For denomination of the stars of comparison please use the characters given in respective MEDUZA chart. If the estimate is unsure, write colon. Please send to us your full name, address and e-mail. For CCD measuring use as check star, comparison star "C", GSC 1185:1414, V= 10,55 mag, B-V= 1,46 mag. All new observations, information and the latest light curve of QR And can be found in http://astro.sci.muni.cz/variables. Petr Sobotka Dr. Vojtech Simon