COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 160


                                  Konkoly Observatory
                                  Budapest
                                  6 October 1966

    TON S 120: A NEW VERY SHORT-PERIOD ECLIPSING BINARY

During the photoelectric UBV survey of faint U Gem-type and
nova-like stars it was found that Ton S 120 /alpha  =23h47.5m,
delta=-26d39', 1950.0/ is an eclipsing binary with a period of
3h28m. This star was listed by Chavira /1958/ as a "decidedly
violet" object in his survey of blue stars near the South
Galactic Pole; its galactic coordinates are: l^II=33d,
b^II=-76d. Greenstein /1966/ in his spectroscopic investigation 
of faint blue stars near the galactic poles found it to
be a strong emission-line object resembling a U Gem star or
an old nova with very broad emission lines of H, HeI and
HeII.

The present photoelectric observations were secured in July
and September 1966 on the Mount Wilson 100-inch telescope
with the offset photometer and pulse counting system. The
light-curve of Ton S 120 resembles that of Nova DQ Her
/Walker 1956/ but with much deeper eclipses. The eclipse is
partial, its depth is 2.5 mag., its duration is about 30
minutes. Secondary  eclipse  has not been detected. The UBV
measurements outside eclipses are V=15.6, B-V=+0.1, U-B=-0.8
mag. The preliminary light elements are: primary minimum Hel.
JD 2439326.981+ 0.144623d E. The star is not known  to
undergo any outbursts that  have  been  recorded  in  the
available astronomical literature. 


  September 29, 1966
  Mount Wilson and Palomar Observatories
  Pasadena California, U.S.A.               W. KRZEMINSKI

   References:
 Chavira, E. 1958.  Bol.Obs.Tonantzintla y Tacubaya, 2, No.
                   17, 15. [BIBCODE 1958BOTT....2q..15C ]
 Greenstein, J.L. 1966, Ap.J., 144, 496. [BIBCODE 1966ApJ...144..496G ]
 Walker, M.F. 1956, Ap.J., 123, 68. [BIBCODE 1956ApJ...123...68W ]