COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2314

                                   Konkoly Observatory
                                   Budapest
                                   19 April 1983

                                   HU ISSN 0374 - 0676



     VARIABLE F-TYPE SUPERGIANTS FAR ABOVE THE GALACTIC PLANE



    Supergiant variability in general is now well established. Still, the
wide class of variable B - G-type supergiants is very heterogeneous.
    However, several F-type supergiants seem to be strikingly similar as
regards their photometric behaviour, galactic distribution and kinematics.
Most typical representatives are UU Her, 89 Her, HD 161796, BL Tel (F) and
HD 112374. Obviously, similar stars fainter than 7m are not yet known to be
variable due to their small amplitudes. Various aspects were discussed 
separately in recent papers of van Genderen (1977, 1980) for BL Tel (F); Percy
et al. (1979, 1981), Burki et al. (1980) and Fernie (1981) for 89 Her and
HD 161796; Arellano Ferro (1981) for HD 112374; and Sasselov (1981) for
UU Her. The set of many-sided criteria that brings them together comes from
our conception that three supergiants are unique luminous objects situated
far above the galactic plane; being, also, outside the Cepheid instability
strip and exhibiting (probably non-radial) pulsations. The latter seem to
account for the quite specific light and radial velocity variations. These
variable stars occupy a compact isolated area on the P - C diagram and do not
obey the semi-period - L - C relation for "normal" supergiants (see Maeder,
1980). Probably other common features are their normal Population I abundances 
and mild infrared excess radiation (however, little information about
these features is available up to now). The latter feature is quite interesting 
as most Population I supergiants do not have it.
    Hence, we suspect the possible existence of a group of variable F-type
supergiants obeying the following criteria:

a) semi-regular light variations <= 0.6m (usually 0.2m);
b) periods (two or three alternating) from about 30 to 120 days;
c) spectral type F0 - F7 (<B-V>_0 from +0.10 to +0.50);
d) luminosity class Ib to Ia;
e) |z| >= 1 kpc;
f) velocity is typical for Population II stars.

    The five stars listed above obey strictly these criteria and about
twenty other members of this group are suspected, as well. Our criteria 
reflect the fact that these supergiants differ unambiguously from all 
established types of variable stars.
    The problem of how can such luminous and, probably, young objects be
so away from the plane, i.e. the luminosity - high-galactic-latitude 
controversy, remains equally puzzling even if such non-variable stars exist. We
have detected an interesting compact swarm of seven F-type supergiants 
around SA 28 far above the galactic plane which will be tested for light 
variability. These suspected new members of the group are: BSD 125 (SAO 42538),
BSD 475 (SAO 42524), BSD 820 (SAO 42496), BSD 482, BSD 870 (SAO 42514),
BSD 940, and BSD 1050 (SAO 42582), using data from Bartaya (1979). Two 
similar sets of five and seven stars are to be found nearby (around SA 27 and
SA 11, respectively).
    As regards 89 Her and HD 161796, Burki et al. (1980) discuss the 
luminosity - high-galactic-latitude controversy for them. No explanation can
be favoured yet. The group of Cepheid-like variables proposed by Percy (1980)
is very heterogeneous and most of its members do not obey the above criteria.
Such surveys may be, however, quite valuable in discovering very long period
Cepheids in our Galaxy.
    A careful examination of Bartaya's catalogue (1979) down to 11m makes
us suspect that luminous F-type supergiants at high galactic latitudes are
not so rare as they obviously are thought to (see, e.g. Burki et al., 1980).
Their further investigation is evidently quite important.
    The author is much indebted to N. Nikolov and G. Ivanov for their
continuing support and encouragement.



                         DIMITAR D. SASSELOV
                       Department of Astronomy
                        University of Sofia
                             Bulgaria



References:

Arellano Ferro, A. 1981, Publ. A.S.P., 93, 351. [BIBCODE 1981PASP...93..351A ]
Bartaya, R.A. 1979, Bull. Abastuman Astr. Obs., 51.
Burki, G., Mayor, M. and Rufener, F. 1980, Astron. Astrophys. Suppl., 41, 383. [BIBCODE 1980A&AS...42..383B ]
Fernie, J.D. 1981, Astrophys. J., 243, 576. [BIBCODE 1981ApJ...243..576F ]
Maeder, A. 1980, Astron. Astrophys., 90, 311. [BIBCODE 1980A&A....90..311M ]
Percy, J. 1980, J. AAVSO, 9, No. 2, 64. [BIBCODE 1980JAVSO...9...64P ]
Percy, J., Baskerville, I. and Trevorrow, D. 1979, Publ. A.S.P., 91, 368. [BIBCODE 1979PASP...91..368P ]
Percy, J. and Welch, D. 1981, Publ. A.S.P., 93, 367. [BIBCODE 1981PASP...93..367P ]
Sasselov, D.D. 1981, Astron. Circ., No. 1167, 6. [BIBCODE 1981ATsir1167....6S ]
van Genderen, A. 1977, Astron. Astrophys., 58, 439. [BIBCODE 1977A&A....58..439V ]
van Genderen, A. 1980, Astron. Astrophys., 88, 77. [BIBCODE 1980A&A....88...77V ]