COMMISSIONS 27 AND 42 OF THE IAU 
             INFORMATION BULLETIN ON VARIABLE STARS 
                          Number 3781 
 
                                            Konkoly Observatory 
                                            Budapest 
                                            30 September 1992 

                                            HU ISSN 0374 - 0676 
 
 
 
 
 
       NO CHROMOSPHERIC ACTIVITY SEEN IN THE VERY ECCENTRIC
                  DOUBLE-LINED BINARY Gliese 586A 
 
 
 Two recent orbit determinations found Gliese 586A (= HD 137763, K1V + 
M0V, P = 890 days, V = 6.8 mag) to be a double-lined spectroscopic 
binary with an orbital eccentricity of 0.975 (Tokovinin 1991, 
Duquennoy et al. 1992). This is the highest eccentricity yet found 
among spectroscopic binaries. Due to the relatively long orbital 
period of 890 days the system still remains well detached at 
periastron passage but the two stars pass each other at a distance of 
only 10 R_Sun (Duquennoy et al. 1992). As was also noted by the latter 
authors, the distance at periastron would be equivalent to that of a 
circular orbit with a period of 3.5 days. Late-type stars in a binary 
system with such a short period could be suspected to show 
chromospheric emission from either of the two components due to 
magnetic activity. We might even have the rare possibility to explore 
the switching on (and off) of a stellar dynamo when the two 
components are closest assuming that some sort of differential 
rotation between the dynamo action to tidal forces. Glebocki & 
Stawikowski (1977, 1988) found some relation between chromospheric 
emissions and orbital parameters for late-type giants and suggested 
that tidal forces are somehow responsible for the enhanced 
chromospheric activity. Schrijver & Zwaan (1991) argued that in a 
synchronized close binary the axis for rotational effects is through 
the center of gravity of the binary system and thereby affects the 
stellar dynamo in such a way to produce enhanced magnetic activity. 
 
 Consequently we obtained a single high-resolution spectrum of the Ca 
II H and K lines of Gliese 586A to search for possible chromospheric 
emission lines. We used the 0.9-m coude feed telescope at Kitt Peak 
National Observatory equipped with camera 5 and grating A and a 
800-pixel TI CCD to obtain an effective wavelength resolution of 0.15 
A. No significant Ca II H and K emission is obvious from this spectrum 
(Fig. 1) which was taken at orbital phase 0.844 (HJD 2448718.417). 
However, we note that the periastron passage (phase 0.000) occurs 
within two days and was not covered by our observation. We emphasize 
the importance of further high-resolution monitoring of Gliese 586A 
especially around periastron passage (the next periastron passage will 
take place at HJD 2449746.782 = UT 1995 January 28 according to the 
elements of Duquennoy et al.). 


                            [FIGURE 1]

 Fig. 1: A high-resolution spectrum of Gliese 586A centered at CaII H and 
 K. No significant chromospheric emission is detected.


 
                          K. G. STRASSMEIER 
                          Institut fur Astronomie 
                          Universitat Wien 
                          Turkenschanzstrasse 17 
                          A-1180 Wien 
                          AUSTRIA 
                          (STRASSMEIER @ AVIA.UNA.AC.AT) 
 
 
References 
 
Duquennoy A., Mayor M., Andersen J., Carquillat J.-M., North P., 1992, 
  A&A 254, L13.  [BIBCODE 1992A&A...254L..13D ]
 
Glebocki R., Stawikowski A., 1877, Acta Astron. 27, 225.  [BIBCODE 1977AcA....27..225G ]
 
Glebocki R., Stawikowski A., 1988, A&A 189, 199.  [BIBCODE 1988A&A...189..199G ]
 
Schrijver C. J., Zwaan C., 1991, A&A 251, 183.  [BIBCODE 1991A&A...251..183S ]
 
Tokovinin A. A., 1991, A&AS 91, 497.  [BIBCODE 1991A&AS...91..497T ]