COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3625

                                               Konkoly Observatory
                                               Budapest
                                               18 June 1991

                                               HU ISSN 0374 - 0676


               Strömgren photometry of suspected
                 low amplitude delta Sct stars


Two stars, 21 LMi (HR 3974) and 40 Leo (HR 4054), included in the New Catalogue
of Suspected Variable Stars (1982) as probable delta Sct stars, were observed
photometrically by using the simultaneous uvby beta Stromgren photometer
attached to the 75 cm reflector at Sierra Nevada Observatory (Spain). In
addition, two other stars beta Leo (HR 4534) and FT Vir (HR 4746) were also
observed. In total, we carried out eight nights of observation in the years
1988 and 1989. 21 LMi is listed in the New Catalogue of Suspected Variable
Stars (1982) with an amplitude of luminosity variation of Delta V=0.05m,
while Delta V=0.06m is listed for 40 Leo in the same catalogue. Beta Leo is
included in the list of probable delta Sct stars from Frolov (1970). Bartolini
et al. (1981) reported an amplitude of Delta V=0.025m with a period of
P=0.05d for this star. FT Vir was found as variable by Eggen (1974) with
Delta V=0.01m and P=0.05d.

Table 1 lists, for each star, the b-y, m_1, c_1 and beta indices from Hauck &
Mermilliod (1990). In addition, the magnitudes in the V filter and spectral
types, from the Bright Star Catalogue (1982), are presented in columns 3 and 4,
respectively. Spectral types of A6V for 21 LMi and A2V for beta Leo are found
from the calibrations of Gray & Garrison (1987,1989b). For FT Vir, Breger
(1979) gives it as F0n, while Peniche et al. (1981) reported this star as
F4III- II. Furthermore, the calibrations from Gray & Garrison (1989a)
indicate that FT Vir must be of a spectral type later than F2. Figure 1 shows
the sample of delta Sct stars, from Lopez de Coca et al. (1990), in the H-R
diagram. The blue and red edges are from Breger (1979). These edges may not
be absolute, but are borders to indicate the regions beyond which pulsation is
less probable. As can be seen in the figure, the three stars 40 Leo, beta Leo
and FT Vir lie outside the drawn borders. Only the star 21 LMi is located
within the instability strip.


                               [FIGURE 1]

  Table 1

Star             V    S.T.  b-y     m_1     c_1   beta      s    Number  Time
                                                                     of  observed
Name     HR    (mag)        (mag)   (mag)   (mag)  (mag)  (mag)   points  hours

21 LMi   3974   4.48  A7V   0.111   0.196   0.870   2.836  0.0024   53     8.1
C2       4075   5.72                                       0.0026
40 Leo   4054   4.79  F6IV  0.297   0.171   0.459   2.654  0.0019   69     5.1
C2       4097   6.15                                       0.0025
beta Leo 4534   2.14  A3V   0.044   0.210   0.975   2.900  0.0028   55     6.6
C2       4564   5.53                                       0.0030
FT Vir   4746   6.22  A8n   0.278   0.173   0.649   2.675  0.0022   22     3.6
C2       4677   6.99                                       0.0036


Our results do not change the positions of these stars in the H-R diagram.
However, for all four stars, we do not find variability from our observations
as can be seen in Table 1. Columns 10 and 11 list the number of observations
and spans carried out for each star. Column 9 presents the constancy of the
measured light through the V filter, where s denotes the standard error
relative to the magnitude differences C1-star (C1=comparison 1). Similar
standard errors were obtained for all the other three uvb filters. For
comparison, in Table 1 we also list the standard errors obtained for the check
stars (C2) from the same observation periods.


                    E. RODRIGUEZ
                    P. LOPEZ DE COCA
                    A. ROLLAND

                    Instituto de Astrofisica de Andalucia
                    Apdo. 3004, Granada, Spain

ACKNOWLEDGMENTS: This research was supported by the
Junta de Andalucia and the Direccion Ceneral de Investigacion
Cientifica y Tecnica (DGICT) under project PB88-0310.

References:

Bartolini, C., Dapergolas, A. and Piccioni, A. 1981, I.B.V.S. No. 2010
Breger, M. 1979, P.A.S.P. 91, 5 [BIBCODE 1979PASP...91....5B ]
Bright Star Catalogue 1982, Yale University Observatory, New Haven
Eggen, O.J. 1974, I.B.V.S. No. 935
Frolov, M.S. 1970, I.B.V.S. No. 427
Gray, R.O. and Garrison, R.F. 1987, Ap.J.S.S. 65, 581 [BIBCODE 1987ApJS...65..581G ]
Gray, R.O. and Garrison, R.F. 1989a, Ap.J.S.S. 69, 301 [BIBCODE 1989ApJS...69..301G ]
Gray, R.O. and Garrison, R.F. 1989b, Ap.J.S.S. 70, 623 [BIBCODE 1989ApJS...70..623G ]
Hauck, B. and Mermilliod, M. 1990, A.Ap.S.S. 86,107 [BIBCODE 1990A&AS...86..107H ]
Lopez de Coca, P., Rolland, A., Rodriguez, E. and Garrido, R. 1990, 
    A.Ap.S.S. 83, 51 [BIBCODE 1990A&AS...83...51L ]
New Catalogue of Suspected Variable Stars 1982, Nauka, Moscow
Peniche, R., Pena, J.H. and Hobart, M.A. 1981, P.A.S.P. 93, 735 [BIBCODE 1981PASP...93..735P ]