COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                     Number 3140



                                    Konkoly Observatory
                                    Budapest
                                    28 January 1988

                                    HU ISSN 0374-0676


           HIGH SPEED PHOTOMETRY OF HAMUY'S VARIABLE

   During work on a photoelectric sequence for the Seyfert galaxy Arakelian
120, Mario Hamuy discovered a blue variable star with short term brightness
variations similar to those of cataclysmic variables (Hamuy and Maza, 1986a,b).
High speed photometry of Hamuy's star by Bond et al. (1987) confirmed the
presence of rapid flickering, with a total range of ~0.15 mag. A low quality
spectrum of the star showed the presence of a broad H-beta absorption line with a
central, possibly double, emission peak. The presence of the absorption 
component suggests that Hamuy's star belongs to the UX UMa class of cataclysmic
variables.

   On 30 December 1986 we obtained a 3.6 hr photometric run on Hamuy's star,
using the University of Texas High Speed Photometer (Nather 1973) on the 82-in
Struve reflector at McDonald Observatory. 3 sec integrations in 'white light'
(i.e. no photometric filter in front of the RCA 8850 photomultiplier) were 
obtained, starting at 06 hr 07 min 58 sec U.T. The light curve, with sky sub-
tracted and extinction removed, is shown in Figure 1. The ordinate is the
fractional intensity variation about the mean.
   
   The star shows rapid flickering activity with a total range of 0.25 mag.
Although the flickering is rather more rapid and of greater amplitude than is
characteristic of UX UMa itself (Warner and Nather 1972) or of other UX UMa stars such
as RW Sex (Hesser, Lasker and Osmer 1972) and V3885 Sgr (Cowley, Crampton and
Hesser 1977), the brightest of the UX UMa stars, IX Vel, does show rapid 
flickering, albeit of lower amplitude (Williams and Hiltner 1984). The UX UMa stars
have orbital periods 3-5 hours; our run is of sufficient length to exclude the
possibility of any large brightness modulation in this period range.

  However, there is also a resemblance between the light curve of Hamuy's
star and that of EX Hya (Warner 1973 and unpublished), which indicates that
an orbital period less than 2 hours should also be considered.
   
   The eclipses in EX Hya are narrow and often of irregular profile (Warner
1972 and unpublished). Such features, if they exist in Hamuy's star, would
be difficult to detect amidst the flickering activity. However, we note that


                             [FIGURE 1]

 Figure 1; Light curve of Hamuy's star at 3 sec time resolution. The
           vertical scale is relative intensity.


the separation of the two low dips in the light curve of Bond et al. (1987)
is 0.0592 days and the separation between the two narrow eclipse-like features
that occur in our light curve near times 6500 secs and 11800 secs is 0.0601.
The earlier feature, near time 2000 secs, is however separated by 0.054 day
from the next dip. The near coincidence of some of these separations, and
the similarity of the light curve with that of EX Hya, indicates that a more
extensive campaign of spectroscopy and photometry of Hamuy's star is 
justified.


                           BRIAN WARNER 1,2
                           R. EDWARD NATHER 1



   1 Department of Astronomy, University of Texas, Austin, Texas, U.S.A.
   2 Department of Astronomy, University of Cape Town, 7700 Rondebosch,
     South Africa





References:
Bond, H.E., Grauer, A.D., Burstein, D. and Marzke, R.O. 1987, Publ. astr.
     Soc. Pacific, 99, 1097. [BIBCODE 1987PASP...99.1097B ]
Cowley, A.P., Crampton, D. and Hesser, J.E., 1977, Astrophys, J. 214, 471. [BIBCODE 1977ApJ...214..471C ]
Hamuy, M., and Maza, J., 1986a, Int. Astr. Un. Circ. No. 4172. [BIBCODE 1986IAUC.4172....2M ]
Hamuy, M., and Maza, J., 1986b. Inf. Bull. Var. Stars, No. 2867.
Hesser, J.E., Lasker, B.M, and Osmer, P.S., 1972. Astrophys. J. 176, L31. [BIBCODE 1972ApJ...176L..31H ]
Nather, R.E., 1973, Vistas in Astr. 15, 91. [BIBCODE 1973VA.....15...91N ]
Warner, B., 1972, Mon. Not. R. astr, Soc., 158, 425. [BIBCODE 1972MNRAS.158..425W ]
Warner, B., 1973, Mon. Not. astr, Soc. S. Af., 32, 120. [BIBCODE 1973MNSSA..32..120W ]
Warner, B. and Nather, R.E., 1972, Mon. Not. R. astr. Soc. 159, 429. [BIBCODE 1972MNRAS.159..429W ]
Williams, G.A., and Hiltner, W.A. 1984, Mon. Not. R. astr. Soc., 211, 629. [BIBCODE 1984MNRAS.211..629W ]