COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2606

                                    Konkoly Observatory
                                    Budapest
                                    16 October 1984

                                    HU ISSN 0374 - 0676





     H_alpha EMISSION IN RS CVn STARS: HD 8357, HD 175 742 AND HR 7428
      


Recently Hall et al.(1984) edited the "Hall Catalogue of RS CVn  Binary
Systems", in which twenty stars with H_alpha emission were reported. We observed
33 RS CVn stars i.n the H_alpha region using the coude Reticon system of the
McDonald Observatory 2.1 m telescope. The dispersion is 9.5 A/mm and the
resolution is 0.29 A. Three of these stars (HD 8357, HD 175742 and HR7428)
showed conspicuous H_alpha emission. Physical data and observational details are
listed in Table I. The individual systems are reported separately below.

                               Table    I
-----------------------------------------------------------------
star        sp          mag.   period   obs. J.D.(H)       phase
-----------------------------------------------------------------
HD 8357     G5          7.28   -        2445957.8848        -
            composite                        57.9428        -
                                             58.8243        -
                                             58.9799        -
                                             59.8129        -
                                             60.9638        -
HD 175742   K0V         8.4    -        2445958.6146        -
            K5- M2V                          58.6764        -
                                             59.6153        -
                                             60.5845        -
HR 7428     A?          6.36   108.6    2445957.6288        0.4835
            K2III-II                         58.5794        0.4922
                                             59.5774        0.5014
                                             59.6711        0.5023
                                             60.5669        0.5106
-------------------------------------------------------------------

HD 8357:

  The H_alpha profile changed significantly in both emission and absorption
components as shown in Figure 1. The peak of emission fluctuated somewhat
but was systematically shifted to the blue from the expected photospheric
velocity by 0.6 A. The intensity of the strongest emission is 1.29 times of
that of the continuum. The profile is similar to that of UX Ari. (Nations
and Ramsey, 1980).

                            [FIGURE 1]

Figure 1. Variation of the Halpha emission feature of HD8357

                            [FIGURE 2]

Figure 2. Variation of the Halpha emission of HD175742

 
HD 175 742:
  These H_alpha profiles are bizarre, and show extreme changes over three
nights (Figure 2). The interval between the two observations on Sep. 15 was
only 1.5 hours, but the two profiles are radically different, and the
emission peak shifted from red to blue. The period of variation will be very
short if the change is periodic.

HR 7428 :
  HR7428 shows double emission, the red element being stronger than the
blue one as shown in Figure 3, in which we only drew one plot since the
profiles show little change in blue emission. This star was observed by
Bopp et al. (1978), but they did not find H_alpha emission from two plates. Our
observations were near phase 0.5. The H_alpha emission may be related to the
phase, so more observations are needed.

                        [FIGURE 3]

         Figure 3. H_alpha emission feature of HR7428

We are especially grateful to Dr. H. Smith for scheduling the telescope
time.




                       LIU XUEFU and TAN HUISONG
                         McDonald Observatory
                         The University of Texas
                      (two visiting scholars from China)




References:

Bopp, B.W., and Talcott, J.C., 1978: A.J., 83, 1517. [BIBCODE 1978AJ.....83.1517B ]
Hall, D.S., Zeilik, M., and Nelson, E.R., 1984: IBVS, No. 2458.
Nations, H.L., and Ramsey, L.W., 1980: A.J., 85, 1086. [BIBCODE 1980AJ.....85.1086N ]