COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3111


                                     Konkoly Observatory
                                     Budapest
                                     11 November 1987

                                     HU ISSN 0374-0676


           THE NATURE OF THE VARIABILITY OF 42 Per

  The star 42 Persei (HD 23848, V467 Per) is listed in the latest edition
of the General Catalogue of Variable Stars (Kholopov et al. 1987) as an 
eclipsing variable with a period of 22.58 - a period derived by Kolykhalova et
al. (1978) from photoelectric observations. The total range in V is less than
0.1m. W.S. Adams (1912) first identified the star as a spectroscopic binary,
on the basis of four radial velocity observations.
  Observations were made at several other observatories, especially Allegheny
(Beardsley 1969) but the only orbital elements to have been determined were
computed by Morbey and Brosterhus (1974), These elements depend strongly on
the Allegheny observations. While it might be possible to improve the
elements if modern observations were to be made from a single observatory,
it seems unlikely to the present writer that the period of 1.765346d is
seriously in error.
   Although the light-curve published by Kolykhalova et al. does resemble that
of a system displaying very shallow eclipses, the period is not reconcilable
with that found spectroscopically. The photometric period is not a simple
multiple of the spectroscopic one, nor is it one of the spurious periods
associated with the 1.8d period (although it is about ten times as long as
one of the spurious periods). The distribution of the photometric observations
is not favourable for the detection of a period as short as 1.8d.
In Figure 1, those observations are plotted on the 1.8d period (the zero of
phase is the time of periastron passage
as given by Morbey and Brosterhus). Except for those labeled 1,2 and 3, the
observations define a double wave within the orbital period. The minima of
the wave occur close to the predicted phases of spectroscopic conjunctions
(0.02 P and 0.53 P) which are probably well determined despite the
uncertainties in e and omega. Of the three deviant points, No, 1 is marked
as uncertain by Kolykhalova et al. and No, 2 is some 0.02 mag. brighter than
any other measurement. In the light-curve published by Kholykhalova et al.
point No. 2 is still deviant, occuring near the phase of secondary minimum;
in the present plot, at least it is found close to the phase of maximum
brightness, Thus, only the point No. 3 is deviant without any a priori reason 
to reject it. If it should be in error by as much as the other two (but in
the opposite sense) it would fit the curve quite well. On the other hand
the Allegheny observations of radial velocity make no sense on the period
of 22.58 d.


                               [FIGURE 1]

 Figure 1: Photometric observations of 42 Per plotted on the 
           spectroscopic period. See text for details.


   The minima of the light-curve are poorly defined by the available 
observations and very shallow eclipses still cannot be ruled out from the shape of
the light-curve alone. The very small mass-function (0.0074 m_sun) makes
eclipses seem unlikely, however. If the visible A3 V star is plausibly
assumed to have a mass of about 2 m, no credible value for the mass of the
invisible component can be deduced for any value of the orbital inclination
that produces eclipses.
  For an inclination of around 25, it would be possible to satisfy the mass-
function with individual masses of about 2 m and 1 m, and the system would
then consist of stars on or near the main sequence. These figures have been
deliberately kept approximate but they serve to indicate that 42 Per should
probably be classified as an ellipsoidal variable. The star may repay further
observation.


                           A.H. BATTEN
                      Dominion Astrophysical Observatory
                      Herzberg Institute of Astrophysics
                      5071 W. Saanich Road
                      Victoria, B.C. V8X 4M6
                      CANADA

References

Adams, W.S.: 1912, Pub. Astr. Soc. 24, 129 [BIBCODE 1912PASP...24..129A ]
Beardsley, W.R.: 1969, Pub. Allegheny Obs. 8, No. 7. [BIBCODE 1969PAllO...8....7B ]
Kholopov, P.N. et al.: 1987, General Catalogue of Variable Stars, 4th Ed.
         Vol. 3. Nauka, Moscow [BIBCODE 1987gcvs.book.....K ]
Kolykhalova, O.M., Mironov, A.V. and Moshkalev, V.G.: 1978, Per.Zvezd 21, 105. [BIBCODE 1978PZ.....21..105K ]
Morbey, C.L. and Brosterhus, E.B.: 1974, Pub.Astr.Soc.Pacific 86, 455 [BIBCODE 1974PASP...86..455M ]