COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3351

                                           Konkoly Observatory
                                           Budapest
                                           10 July 1989

                                           HU ISSN 0374 - 0676


   H_ALPHA OBSERVATIONS OF THE RS CVN BINARY HR 7275 (V1762 CYG)


HR 7275 (V1762 Cyg, HD 179094) is an RS CVn binary with an orbital period of
28.6 days. Extensive photometry of HR 7275 (Seeds and Nations 1986, Nations
and Seeds 1986) shows the star to have a highly variable amplitude, with
changes evident on a timescale of one orbital cycle or less. An average
photometric period of 27.78 days has been derived, but this value shows
variability as well. A recent spectroscopic study of the H_alpha profile in HR
7275 by Eker (1989) reports that maximum emission occurred during photometric
minimum for one orbital cycle in June/July 1984.

As part of a spectroscopic monitoring program of active chromosphere stars at
Ritter Observatory, we observed HR 7275 in 1987 and 1988. We obtained 20
Reticon scans of the H_alpha region with spectral resolution 0.3 angstrom and
signal to noise ratio about 50:1. On all the scans, H_alpha is seen as an
absorption feature. The equivalent width (EW) of the feature is always lower
(weaker) than what is seen in ordinary, inactive K1 III stars, and is variable
by nearly a factor of two, indicating that the line is partly filled by
variable emission. In contrast to the results reported by Eker (1989), we find
no correlation of H_alpha EW with orbital phase (Figure 1). Since our
observations extend over several rotational and orbital cycles, this presumably
is a confirmation of the photometric behavior that indicates that activity on
HR 7275 is strongly variable on timescales less than a month.


                            [FIGURE 1]

 Figure 1: The H_alpha EW of HR 7275 in mA plotted versus orbital phase
 (Eker 1989). Data from 1987 are indicated by open circles and from
 1988 by asterisks.


         TABLE 1

Radial Velocities of HR 7275

HJD - 2,447,000     V_r (km/s)

332.8141            -35.5
343.7598            +32.9
344.7417            +37.4
345.7522            +41.8
347.7168            +43.7
355.7221            -12.8
356.7318            -17.9
394.6311            -13.1
399.6491            +27.4
403.5994            +45.1
412.5718             -8.3
430.5464            +40.7

Examination of Figure 1 shows that the H_alpha feature usually has an EW of
approximately 800 mA, with variations of +-10%. However, two
observations from 1987, at phases 0.33 and 0.78, show an EW of only about 500
mA. This abrupt weakening of the line suggests a flare-like event
as the cause.

Finally, Reticon data obtained during 1988 was used to derive radial velocities
by cross-correlation with alpha Boo (Bopp and Dempsey 1989). The resulting
velocities (with precision 1 km/s or better) are listed in Table 1. A least
squares orbital solution using these data, along with the velocity measures
given by Young (1944) and Eker (1989), confirm Eker's revised orbital elements:
the orbit is found to be circular with a period of 28.5895 days.


BERNARD W. BOPP    ROBERT C. DEMPSEY    GREG PIERCE
Ritter Observatory and Dept. of Physics and Astronomy
University of Toledo
Toledo, OH 43606 USA

References:

Bopp, B. W., and Dempsey, R. C., 1989, Publ. Astron. Soc. Pacific 101, 516. [BIBCODE 1989PASP..101..516B ]
Eker, Z., 1989, Mon. Not. R. Astron. Soc. 238, 675. [BIBCODE 1989MNRAS.238..675E ]
Nations, H. L., and Seeds, M. A., 1986, Publ. Astron. Soc. Pacific 98, 1105. [BIBCODE 1986PASP...98.1105N ]
Seeds, M. A., and Nations, H. L., 1986, I.A.P.P.P. Comm. 25, 50. [BIBCODE 1986IAPPP..25...50S ]
Young, R. K., 1944, J. R. Astron. Soc. Canada 38, 366. [BIBCODE 1944JRASC..38..366Y ]