COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1378

                                   Konkoly Observatory
                                   Budapest
                                   1978 January 6




         alpha SCULPTORIS - A LONG PERIOD BINARY




     This prototype (HD 5737, B8III, V = 4.30) of the alpha Scl-
subgroup of weak helium line stars has been investigated e.g.
by Jugaku and Sargent (1961), Guthrie (1965), Norris (1971),
Vilhu (1972) and Schmitt (1973). Bernacca and Molnar (1972)
found it to be a photometric variable on the basis of UV-
observations (2 observations). According to Bernacca and Molnar the
strengthening of TiII, CrII and SrII lines around 2400 Angstrom 
appears to redistribute flux longwards of the Balmer discontinuity. 
It is not known whether this strengthening is periodic or
accidental, and what is its reason.
     Figure 1 shows radial velocity variations of alpha Scl. Old
Lick Observatory measurements (Campbell and Moore, 1928) were
supplemented by new measurements of four Mt. Wilson plates from
years 1944 and 1955 (Ce 3656, 10092, 10097, 10161, 2.8 Angstrom/mm).
These same spectrograms have previously been analysed for 
abundances (Vilhu, 1972). Radial velocities were measured from 
several lines of HeI, MgII, SiII and FeII with accuracy +-2 km/s.
     One point obtained from ultraviolet observations with
Copernicus-satellite (Upson and Vilhu, 1975) is included. This
point represents the mean value of several lines in regions
1046-1051 Angstrom, 1154-1166 Angstrom and 1300-1305 Angstrom (ArI, CI, 
OI, FeII, FeIII, CrIII). The known interstellar line ArI 1048 seems to
follow the velocity variation. Thus it probably originates from
a circumstellar cloud participating in orbital motion.

                        [FIGURE 1]

Fig. 1. Radial velocity variations of alpha Scl. Points: old Lick
Observatory measurements (Campbell and Moore, 1928). Crosses: new
measurements of Mt. Wilson plates (this paper). Circle: a value
from UV-region (see text, Upson and Vilhu, 1975).

     Due to the apparent long period, the variability cannot
be related with the rotation of the star as is the case in many
Ap stars (for alpha Scl V sini =15 km/sec, Vilhu (1972)). The binary
motion is then the most probable reason for the variability.
From the radial velocities of Fig. 1 it is rather difficult to
derive the period and amplitude. Estimating P = 100 years and
K_1 = 6 km/s, a value 0.8 for the mass function f(M) can be 
calculated (assuming e = 0). If the mass of alpha Scl is about 7 M_sun
(Norris, 1971), this gives a minimum mass 4 M_sun for the companion
(if i = 90d). If the eccentricity is different from zero, smaller
companion masses will result. The 4 M_sun companion would thus be
a B9 star having 7 times smaller luminosity than alpha Scl (assuming 
main-sequence). With these values it is quite reasonable
that the companion is not seen in the spectrum.
    Further, using the above values for P and K_1 we obtain
for the semi-major axis a_1 sin i a value of 4000 R_sun. This means
that the system is very wide. Even for the so called case C
evolution of close binaries the system is rather wide, if the
orbit is not eccentric. It is not, of course, precluded that
the period and separation may have increased (for instance mass
and angular momentum loss and kick from the companion by supernova-
explosion). If the secondary is more massive than 4 M_sun, it
should then be a black hole.
    More radial velocity measurements are clearly needed to
get better estimates for the orbital parameters and for the
companion mass.




                            O. VILHU

                            Observatory and Astrophysics
                            Laboratory
                            University of Helsinki
                            Finland





References :
Bernacca, P.L., Molnar, M.R. 1972, Astrophys.J. 178, 189 [BIBCODE 1972ApJ...178..189B ]
Campbell, W.W., Moore, J.H. 1928, Lick Obs. Publ. XVI, p.12
Guthrie, B.N.G. 1965, Publ.Roy.Obs. Edinburgh 3, 264 [BIBCODE 1965PROE....3..264G ]
Jugaku, J., Sargent, W.L.W. 1961, P.A.S.P. 73, 249 [BIBCODE 1961PASP...73..249J ]
Norris, J. 1971, Astrophys. J. Suppl. 23, 213 [BIBCODE 1971ApJS...23..213N ]
Schmitt, A. 1973, Astron. Astrophys. Suppl. 9, 427 [BIBCODE 1973A&AS....9..427S ]
Upson, W.L., Vilhu, O. 1975, as guest investigators using the
     Princeton telescope on the satellite Copernicus (unpublished 
     observations)
Vilhu, O. 1972, Ann.Acad.Sci. Fennicae, Ser. A VI Physica, No. 394