[vsnet-alert 2422] QR And campaign (Sobotka)

[Taichi Kato <tkato>]

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

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