COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1998

                                  Konkoly Observatory
                                  Budapest
                                  1981 July 28

                                  HU ISSN 0374-0676


  SEARCH FOR THE PERIOD OF THE BINARY SHELL STAR V 505
                   MONOCEROTIS


  The variability of the radial velocity of the star HD 48 914
(V 505 Mon) was discovered by Pearce and Petrie (1950). Hoag and
Smith (1959) classified it as B5 Ib, Turner (1976) as B5 II.
Petrie and Pearce (1962) pointed out that the hydrogen lines are
shell-like. They classified the star as B4.

                          [FIGURE 1]

  The light variability of the star was discovered by Wachmann
(1966). According to him, the amplitude is 0.5 mag. and period
shorter than one day. Eggen (1978) made (u,v,b,y,beta) photometric
observations of the star in the years 1975-76. He found only small
light variations of 0.15 mag.
  At the spectrogram with dispersion 1.7 nm/mm taken by the 2m
telescope at Ondrejov Observatory on January 31,1981 emission feature 
of H_alpha line (Fig.1) was discovered which indicate that V 505
Mon is a shell star. The spectral classification made from this
spectrogram is B3 II-III.
  The star was observed at Skalnate Pleso Observatory by a 
photoelectric photometer installed in the Cassegrain focus of the 0.6 m
telescope in V colour from 1977 to 1981. The star HD 48 956 was
used as comparison star. We found the changes of the light of
V 505 Mon with an amplitude of 0.5 mag. The programs for period
search Hec 18 and Hec 21 (Harmanec, 1981) were used to find the
period. The best period connected with the eclipses of the 
components is 26.94745 days (Figure 2). But the period 53.7805 days
is possible too (Figure 3). The ephemeris for former period is

     JD (Min) - 2444635.318 + 26.94745 x E.           (1)

                        [FIGURE 2]
                        [FIGURE 3]

  It is possible to see on Figure 2 and Figure 3 that short term
variations with the amplitude 0.15 mag. are present on the light
curve. We found the period of the variations as 0.9912467 day.
It was believed that the period of eclipses is shorter than one
day. These variations are responsible for it.
  Pearce and Petrie (1950, 1962) measured radial velocities on
9 spectra covering a period from the year 1929 to 1959. They
obtained the range of radial velocities from + 90 km/s to - 40
km/s. We tried to find the radial velocity curve with the periods
mentioned above, but we failed. The determination of radial 
velocities in shell stars is a serious problem. There are long term
variations of the radial velocities there, so it is necessary to
obtain many spectra in a short time interval.
  The further photometric and spectroscopic observations of the
star V 505 Mon are highly desirable.      




                          D. CHOCHOL, A. KUCERA
                     Astronomical Institute of the Slovak
                     Academy of Sciences, 059 60 Tatranska            
                     Lomnica, Czechoslovakia

References:

Eggen, O.J. 1978, Astron. J. 83, 288. [BIBCODE 1978AJ.....83..288E ]
Harmanec, P. 1981, private communication.
Hoag, A.A., Smith, E.P. 1959, Publ. Astron. Soc. Pacific 71, 32. [BIBCODE 1959PASP...71...32H ]
Pearce, J.A., Petrie, R.M. 1950, Publ. Dominion Astrophys. Obs.
               8, 409. [BIBCODE 1951PDAO....8..409P ]
Petrie, R.M., Pearce, J.A. 1962, Publ. Dominion Astrophys. Obs.
               12, 1. [BIBCODE 1961PDAO...12....1P ]
Turner, D.G. 1976, Astrophys. J. 210, 65. [BIBCODE 1976ApJ...210...65T ]
Wachmann, A.A. 1966, Astron. Abhandl. Hamburger Sternw. 7, 341. [BIBCODE 1966AAHam...7..341W ]