COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 1144

                                   Konkoly Observatory
                                   Budapest
                                   1976 June 22



   APPEAL FOR PHOTOELECTRIC OBSERVATIONS OF UPSILON SAGITTARII
  (alpha (1900) = 19h 16m 0s, delta(1900) = -16d 8.6', m_v = 4.58)





   Upsilon Sagittarii is a remarkable spectroscopic binary. Lines
of H, CaII, [CaII], FeII and [FeII] have been observed in emission
in its spectrum, while Halpha and perhaps two HeI lines show at certain
phases a blue-shifted absorption component. The spectrum of only
one component has been detected in the visible region, a spectrum
which indicates an underabundance of hydrogen with respect to
helium. An infra-red excess has also been observed.
   Gaposchkin (1945) found this star to be an eclipsing binary, with
primary and secondary eclipse depths of 0.15 and 0.08 magnitudes.
This result is based on photographic measurements, and seems to
have been never confirmed photoelectrically.
   Observations of this star are important in the light of theories 
of close binary evolution. A study of far ultraviolet measurements 
conducted by M. Friedjung and M. Hack is in progress, and
should give some information concerning the component whose spectrum
is invisible in the visible region, and which is probably hotter
than that seen. Photoelectric observations of colour changes during 
eclipses in the visible, would also be useful from this point
of view. Unfortunately, this star is difficult to accurately 
observe from the northern hemisphere, while its relatively long 
period of 138 days makes it unattractive for those observatories
which allocate time for short observing runs only. It is because
of these difficulties that this appeal is launched.
  The eclipse dates for the next 1 1/2 years are using the 
elements of the 1969 edition of the "General Catalogue of Variable
Stars".

          Primary              Secondary
        October 13   1976       August 5   1976
       February 28   1977      December 21 1976
           July 16   1977          May 8   1977
        December 1   1977     September 23 1977
                              February 8   1978


  A convenient comparison star is 44 rho1 Sagittarii (alpha=19h15m52s,
delta= 18d02', 1900, V=3.94). It should be noted that all these eclipses
are not observable, because of the proximity of the Sun.



                          M. FRIEDJUNG
                        Institut d'Astrophysique
                        Paris, France.



Reference:
Gaposchkin, S. 1945, Astr.J., 51, 109 [BIBCODE 1945AJ.....51..109G ]