COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                       Number 2216


                                                     Konkoly Observatory
                                                     Budapest
                                                     1982 October 21

                                                     HU ISSN 0374-0676


                   HD 190540: A NEW VARIABLE STAR

  Because Bidelman and MacConnell (1973) reported Ca II H and K
emission, we suspected HD 190540 might be an RS CVn binary and therefore
might show the photometric wave characteristic of most stars of that type.
According to their table VII, mv = 8.4m and the spectral type is K0 IV + F.
  Henry, observing with the No. 4 16-inch Cassegrain at Kitt Peak,
obtained data on 3 nights between JD 2444716.9 and 2444719.9. Henry and
Sherlin, observing with the 48-inch Newtonian at Cloudcroft, obtained data
on 17 nights between JD 2444872.7 and 2445153.9. All observations were
made in V, with BD - 18deg5593 as the comparison star. The individual 
differential magnitudes, corrected for differential extinction and transformed
differentially to V of the UBV system, have been sent to the I.A.U. 
Commission 27 Archive for Unpublished Observations of Variable Stars (Breger
1979), where they are available as file no. 106.
  The figure below is a plot of nightly means of the Cloudcroft data,


                           [FIGURE 1]



where DeltaV is in the sense variable minus comparison. Points taken on 
consecutive nights are joined with straight line segments. It was immediately 
obvious that HD 190540 was variable, with an amplitude of DeltaV = 0.04m.
Further inspection of the data suggested that the period was around 8 days
or a bit longer. With a period-finding program based on an approach similar 
to that of Lafler and Kinman (1965), three periods were found (8.10d,
5.35d, and 8.60d) which produced light curves of comparable quality. All
three were somewhat unsatisfactory, however, in at least one respect.
Either the light curve is variable with time or else we somehow have failed
to find the correct period.

   Additional photometry should be obtained to determine more accurately
what the photometric period really is. We have been in communication with
Luis Balona and T. Lloyd Evans of the South African Astronomical Observatory, 
who tell us they have been obtaining spectroscopic and photometric
observations of this star (and all of the stars in table VII of Bidelman
and MacConnell). If radial velocity measures indicate HD 190540 is a binary
system with an orbital period around 8 days, then it would be a regular RS CVn
binary by the definition of Hall (1976).

                         GREGORY W. HENRY
                         JERRY SHERLIN

                         Cloudcroft Observatory
                         Cloudcroft, New Mexico 88317

                         DOUGLAS S. HALL

                         Dyer Observatory
                         Vanderbilt University
                         Nashville, Tennessee 37235





References:


Bidelman, W. P. and MacConnell, D. J. 1973, A. J. 78, 687. [BIBCODE 1973AJ.....78..687B ]
Breger, M. 1979, I.B.V.S. No. 1659.
Hall, D. S. 1976, I.A.U. Colloq. No. 29, 287. [BIBCODE 1976ASSL...60..287H ]
Lafler, J. and Kinman, T. D. 1965, Ap. J. Suppl. 11, 216. [BIBCODE 1965ApJS...11..216L ]


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