COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3167

                                        Konkoly Observatory
                                        Budapest
                                        25 March 1988

                                        HU ISSN 0374-0676


        NEW TIMES OF MAXIMUM BRIGHTNESS FOR SX Phe (*)

  SX Phe is the prototype of a well known class of variable stars belonging
to the spherical component of the old galactic disk population with periods
less than 0.10 d and amplitude of a few tenths of a magnitude. Coates et al.
(1979) reviewed all the available timings of maximum light and established
accurate values for the two periods simultaneously excited, i.e. P0= 0.054964438
and P1=0.042772692 d identified as the fundamental mode and the first overtone
respectively. The analysis led to the ephemeris

     Max = Hel. J.D. 2438636.6170 d + 0.054964438 x E
               - 0.00325 sin 2pi (0.28503575 x E - 0.107)              (1)

This ephemeris is reported in the Fourth Edition of the General Catalogue of
Variable Stars (Kholopov et al., 1985) and curiously enough the only maxima
observed photoelectrically after 1978 seem to be the 17 timings by Coates et al.
(1980), made a few months after the publication of their ephemeris.
  In order to fill the gap and upon request of some Guest Investigators at the
IUE satellite interested by a correlation between spectral features and the
phase of the light variation, photometry of SX Phe was included in an observing
run carried out daring November 1987 with the 50 cm telescope of the
European Southern Observatory (La Silla, Chile) and devoted to much less studied
Delta Sct stars. Observations were carried out with a Stromgren b filter on the
nights of November 9-10 and 13-14, logging a total of 4.0 hours. The comparison
star chosen by Stock and Tapia (1971), i.e. HD 223011, was used. Two maxima
with a difference in brightness of about 0.10 mag were observed. The Figure
reproduces the light curve for November 13-14: a third maximum occurred just
at the beginning of the observations, but cannot be determined reliably. The
observed times of maxima are

     Hel. J.D. 2 447 109.5509            O-C = + 0.0011 d
                     113.5628                  - 0.0026 d

O-C's refer to ephemeris (1) with E = 154153 and 154226 respectively. Taking
observational errors and uncertainties of P0 and P1 into account the small
O-C's suggest no large change in the periods from 1960 to now. However,

(*) Based on observations collected at European Southern Observatory,
  La Silla, Chile


                              [FIGURE 1]


it is interesting to note that the linear term of the (1) fits better the
observed times of maxima: O-C's are + 0.0009 d and + 0.0004 d respectively. Of
course, further checks of ephemeris (1) are recommended. The project looks 
particularly attractive for southern amateur astronomers with small telescopes 
equipped with photoelectric photometers.

  The observational data can be requested from the author.



                         ENNIO PORETTI

                         Osservatorio Astronomico di Brera
                         Via E. Bianchi, 46
                         22055 Merate (CO)
                         Italy

References:

Coates, D.W., Dale, M. Halprin, L. Robinson, J., Thompson, K.: 1979, Monthly Not.
    Royal Astron. Soc., 187, 83 [BIBCODE 1979MNRAS.187...83C ]
Coates, D.W., Halprin, L., Heintze, G.N., Thompson, K.: 1980, 
    Inf.Bull.Var.Stars, No. 1756
Kholopov, P.N., et al.: 1985, General Catalogue of Variable Stars, Fourth
    Edition, Moscow
Stock, J. Tapia, S.: 1971, Astron. Astrophys. Suppl. 3, 253 [BIBCODE 1971A&AS....3..253S ]