COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3680

                                              Konkoly Observatory
                                              Budapest
                                              11 November 1991

                                              HU ISSN 0374 - 0676


           GLIESE 559.1 - A YOUNG SPOTTED SINGLE STAR


An interesting group of spotted single stars belonging to the Local Association
has been picked out by Chugainov (1991) and Chugainov et al. (1991). This
paper contains the results of photoelectric observations of the single star Gl
559.1 = HD 129333 belonging to the Local Association according to its space
velocity vector as given by Gliese (1969). Observations of Soderblom (1981)
have shown that this G0V star possesses very intense CaII emission lines.
According to the relation found by Noyes et al. (1984) between CaII H and K
emission level, spectral type and rotation period, the latter is about 2 days
for Gl 559.1.

We have found the light variability of Gl 559.1 from photoelectric observations 
obtained in the period of March-August 1991 with the 125-cm telescope 
of the Crimean Astrophysical Observatory and the 60-cm telescope of the
Southern Station State Sternberg Astronomical Institute in UBVRI and UBV
systems respectively. The results have been analysed for the presence of
periodicities by means of Scargle's (1982) method. The highest probability
peak corresponds to 1/P_1=0.357 day^-1 but we cannot exclude the periodicity
of 1/P_2=0.642 day^-1. It seems likely that the latter is an alias due to the
one-day repetition of observations, i.e. 1/P_2=1-1/P_1. If the rotation
period is P_1=2.801d then the equatorial velocity of the star is v= 2 pi
R/P_1=18 km/s supposing that the radius R corresponds to the main sequence.
The projected velocity v sin i of Gl 559.1 is not known. The value of v sin i
has to be also determined from observations in order to verify the adopted
values of period and radius.


                                [FIGURE 1]


Figure 1 shows the light curve of Gl 559.1 folded with the period of 2.801d.
Delta V is the magnitude difference with respect to the comparison star
BD+64d 1018. We can derive the amplitudes of brightness and colour variations 
from our observations only approximately. Their values are equal to
0.05m for the V magnitude and 0.01m for each of colour indices U-B, B-V, V-R
and R-I. The variations of colour indices show the star to become redder at
light minima. Thus the observed variability may be attributed to the 
presence of cool spots. The observed brightness and colour amplitudes would
correspond to the maximum fraction of the stellar disk covered by spots, f=0.2,
and the difference between the spot and photospheric temperatures Delta T=300
K. This estimate ignores limb darkening and inclination of the star.

The spectral type of Gl 559.1 is the earliest in the group of 24 spotted single
stars belonging to the Local Association. The stars FK Com and V1794 Cyg are
the nearest to it by spectral types and rotation periods but they differ from
it showing luminosities to be larger. V368 Cep, LQ Hya and V838 Cen have
rotation periods similar to that of Gl 559.1 but their spectral types are
later. Periods of rapidly rotating early G-stars in young stellar clusters are
0.60d for HeII 520 in alpha Per cluster (Stauffer et al. 1985) and 1.26d for
HII 996 in Pleiades (Panov and Geyer 1991). In general, for G-M main-sequence
stars rotation periods range from 0.2-0.6 days to 20- 70 days and this range is
independent of the spectral type as Soderblom (1991) has concluded. However
the scarcity of observational data for early spotted single G stars is worth
noting. New observations are needed to improve the relation between rotation
periods and CaII emission strengths, to have independent determinations of the
rotation periods and projection velocities v sin i, and to study stars with
different luminosities and lithium abundances. Spotted main-sequence stars
with rotation periods of 0.2d-0.4d are now known only in the G8-M1 interval
of spectral types but not in early G stars. This difference, if confirmed, may
be considered as a consequence of a dependence of the spinning-up phenomenon on
the stellar mass. One can suppose that early G stars increase their rotational
velocity during the evolution to the main sequence not as strongly as G8-M1
stars do.



       P.F. CHUGAINOV, M.N. LOVKAYA
       Crimean Astrophysical Observatory, U.S.S.R. Academy of Sciences

       G.V. ZAJTSEVA
       State Sternberg Institute, U.S.S.R.

References:

Chugainov, P.F.: 1991 in Angular Momentum Evolution of Young Stars, S.
      Catalano, J.R. Stauffer eds., Kluwer Acad. Publ., p. 175. [BIBCODE 1991amey.conf..175C ]
Chugainov, P.F., Lovkaya, M.N., Petrov, P.P.: 1991, I.B.V.S., No. 3623.
Gliese, W.: 1969, Veroff. Astr. Rechen-Inst. Heidelberg No. 22. [BIBCODE 1969VeARI..22....1G ]
Noyes, R.W., Hartmann, L.W., Baliunas, S.L., Duncan, D.K., Vaughan, A.H.:
      1984, Ap.J. 279, 763. [BIBCODE 1984ApJ...279..763N ]
Panov, K.P., Geyer, E.H.: 1991, Astr. Ap. 242, 112. [BIBCODE 1991A&A...242..112P ]
Scargle, J.D.: 1982, Ap.J. 263, 835. [BIBCODE 1982ApJ...263..835S ]
Soderblom, D.R.: 1981, Ap.J. 248, 651.
Soderblom, D.R.: 1991 in Angular Momentum Evolution of Young Stars, S.
      Catalano, J.R. Stauffer eds., Kluwer Acad. Publ., p. 151. [BIBCODE 1991amey.conf..151S ]
Stauffer, J.R., Hartmann, L.W., Burnham, J.N.: 1985, Ap.J. 289, 247. [BIBCODE 1985ApJ...289..247S ]