COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1669

                                     Konkoly Observatory
                                     Budapest
                                     1979 September 7




   RAPID H_alpha EMISSION VARIABILITY IN V711 TAURI (= HR 1099)



   V711 Tau (HR 1099) is one of the few RS CVn binaries to show H_alpha as a
pure emission feature during radio-quiet intervals (Bopp and Talcott 1978).
Typically, the quiescent equivalent width (EW) of H_alpha is 0.5 - 1.0 A, though
there are significant night-to-night variations seen. We have previously
reported (Weiler et al. 1978) H_alpha to be strongly enhanced during radio flares:
in September 1976 the emission EW increased to ~1.5 A during a radio flare,
and during the great radio flare of February 1978 (Feldman et al. 1978) a


                             [FIGURE 1]

 Figure 1:  H_alpha emission EW data for HR 1099 during a non-flare interval
            in February 1977.


peak H_alpha EW of ~3 A was seen (Popper 1978; Fraquelli 1978).  We have also
commented on the apparent presence of rapid (~10-15 minute) variations in H_alpha
EW of V711 Tau during radio flares. In this note, we present our data for
the February 1978 flare graphically. The case for rapid variability at Ha
is strong, but we stress that additional measures, preferably by photoelectric
scanner or Reticon, are desirable.
Figure 1 plots the H_alpha EW versus time for a radio quiet interval in
February 1977. The EW's were obtained from spectrograms (dispersion 40 A/mm,
resolution ~1.3 A) obtained with the 1 meter Ritter Observatory reflector
and Cassegrain image-tube spectrograph.The sequence of spectrograms obtained
on 8 February 1977 illustrates the typical scatter of our measures, about
+-10% or less. Note that the next night shows H_alpha as ~50% stronger, but no
rapid variations are seen. The flare data of February 1978 (Figure 2) are  
quite different. On 21 and 22 February, when the 10.5 GHz flux was 500-600 mJy,


                               [FIGURE 2]

 Figure 2:  Same as Figure 1, during the radio-flare of February 1978.


the H_alpha EW was strongly enhanced and variable by about 40%. On 23 February,
when the radio flux had declined to 200-300 mJy, the H_alpha EW was sensibly constant.
   Since these H_alpha variations were present only at certain phases of the
radio outburst, we believe they represent real changes in the H-alpha emitting
region on a time-scale of 15 minutes or less. Certainly there is convincing
evidence for variations in radio flux and polarization of V711 Tau on similar
time-scales (Feldman et al. 1978; Brown and Crane 1978), though of course
the emitting regions involved are quite different.
   Though radio variations of ~20% were seen on 21 and 22 February, there
is no correlation with the rapid H_alpha variations. The only possible correlation
is with diminished radio flux on 23 February, and the lack of variations in
H_alpha seen on that date.
        The uncertainties in photographic spectrophotometry impose a
limit on the precision of an EW measurement of ~10%. It would be quite useful
to extend these observations using photoelectric techniques of greater 
precision; perhaps V711 Tau shows even non-flare H_alpha emission variations at the
few percent level. The high signal to noise Reticon data obtained by Tomkin
(reported in Fraquelli 1978) show ~20% H_alpha EW variations on 21 February 1978
between 3-4 hours UT, immediately after our observations.
   The question of profile variability on short time-scales also requires
further investigation. There is clear evidence of night-to-night profile
changes (Hearnshaw 1978, Fraquelli 1978) but high-resolution spectroscopic
observations with a time resolution of 10-15 minutes have not yet been obtained.



                             BERNARD W. BOPP
                             Ritter Observatory
                            University of Toledo
                             Toledo, OH 43606


References:

Bopp, B.W., and Talcott, J.C., 1978, Astron. J. 83, 1517. [BIBCODE 1978AJ.....83.1517B ]
Brown, R.L., and Crane, P.C. 1978, Astron. J. 83, 1504. [BIBCODE 1978AJ.....83.1504B ]
Feldman, P.A., Taylor, A.R., Gregory, P.C., Seaquist, E.R., Balonek, T.J.,
   and Cohen, N.L., 1978, Astron. J. 83, 1471. [BIBCODE 1978AJ.....83.1471F ]
Fraquelli, D.A. 1978, Astron. J. 83, 1535. [BIBCODE 1978AJ.....83.1535F ]
Hearnshaw, J.B., 1978, Astron. J. 83, 1531. [BIBCODE 1978AJ.....83.1531H ]
Popper, D.M. 1978, Astron. J. 83. 1522. [BIBCODE 1978AJ.....83.1522P ]
Weiler, E.J., Owen, F.N., Bopp, B.W., Schmitz, M., Hall, D.S., Fraquelli, D.A.,
   Piirola, V., Ryle, M., and Gibson, D.M. 1978, Astrophys. J. 225, 919. [BIBCODE 1978ApJ...225..919W ]