COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1680

                                    Konkoly Observatory
                                    Budapest
                                    1979 October 1



                 V 810 CENTAURI



    On the basis of observations available until the end of
1978, it has been proposed that the bright star V 810 Cen
= HD 101947 = HR 4511 is probably an extremely long-period low-
amplitude classical Cepheid (Eichendorf and Reipurth, 1978, 1979).
The period is about 125 days, thus making it the hitherto longest
period Cepheid known in our Galaxy. The amplitudes in the uvby-
passbands are ranging from 0.13m to 0.25m. A detailed discussion
of the star, which is situated in the open cluster Stock 14, is
given by Eichendorf and Reipurth (1979).
    Further photometric and spectroscopic observations during
1979 confirm the published results; from IUE spectra it is 
evident that a hot blue companion is present which probably does
not affect the lightcurve.
    To establish the nature of this important star and to
study its pulsations in more detail, it is necessary to observe
V 810 Cen photometrically and spectroscopically over at least
4-5 months from the southern hemisphere - a program most observers
(including the authors) cannot undertake.
    During a meeting of commission 27 at the General Assembly
of the IAU at Montreal it was agreed that all observers should
be urged to include V 810 Cen in their running photometric and
spectroscopic measurements. Unfortunately in most cases observers
will not be able to obtain enough data to publish the material
themselves. We would therefore be extremely grateful to all 
observers involved for sending us their reduced photometric 
measurements or copies of spectra taken. Otherwise we would be 
grateful for preprints. Due to the brightness of the star observations
take only few minutes.
    Since the star is observable from November to July we shall
include all material sent to us until the end of September 1980 
in a forthcoming publication together with our own observations.
Hopefully this helps to reveal the nature of V 810 Cen better
than it is possible at the moment.
  Please forward this information to all southern observers
who might not have seen it !

  
           Data on V 810 Cen

            V 810 Cen   Comparison 1  Comparison 2
  
  HD        101947      102350        101021
  HR        4511        4522          4475
  alpha2000 11h43m31s   11h46m30s     11h37m01s
  delta2000 -62d29'     -61d10'       -61d17'
  Sp.       G0 Ia       G3 III        K1 III
  V         ~5.0m       4.10m         5.14m

In general comparison star 1 should be used; if too bright please
take comparison star 2 or use a neutral density filter. Both
stars have been checked over a few years.





	W. EICHENDORF                 BO REIPURTH
	Astronomisches Institut der   Copenhagen University
	Universitat Bochum            Observatory
	Postfach 102148               Oster Voldgade 3
	D-4630 Bochum 1               DK-1350 Copenhagen K





References :
Eichendorf, W., Reipurth, B.: 1978, I.B.V.S. No. 1450
Eichendorf, W., Reipurth, B.: 1979, Astron.Astrophys. 77, 227 [BIBCODE 1979A&A....77..227E ]