COMMISSIONS 27 AND 42 OF THE IAU 
             INFORMATION BULLETIN ON VARIABLE STARS 
                          Number 3736 
 
                                         Konkoly Observatory 
                                         Budapest 
                                         4 June 1992 
                                         HU ISSN 0374 - 0676 
 
 
    IAU STANDARD STAR HD 42397 IS A DOUBLE-LINED BINARY 
 
 
 Twenty years ago, it was proposed by Heard and Fehrenbach (1972) to 
add about twenty stars of roughly eighth magnitude to the list of 
stars deemed to be suitable for use as radial velocity standards. 
These objects were adopted as such by the IAU, and most of them are 
currently included in the list of standards in the Astronomical 
Almanac. 
 
 Although Heard and Fehrenbach presented observations of their objects 
obtained from three observatories over three years, and thus felt 
fairly confident that they had eliminated obvious variables, 
observations of the K-type giants on their list by Griffin (1975) 
showed that at least one, HD 14969, was in fact variable, and he 
subsequently (Griffin 1980) published a spectroscopic orbit for that 
object. To my knowledge, however, no further observations of those 
giants have been published, and none at all of the F and G dwarfs 
which make up the rest of the list, save for a handful reported to the 
IAU by Heard in 1976. 
 
 I have for some years been making occasional observations of IAU 
radial velocity standard stars, including those of Heard and 
Fehrenbach, with the radial velocity spectrometer (Fletcher et al. 
1982) at the coude focus of the Dominion Astrophysical Observatory's 
1.2m telescope. Unfortunately Victoria's cloudy winter skies permit 
only infrequent observations of objects near six hours of right 
ascension. Prior to 1991, as a result, I had accumulated only four 
observations of HD 42397, none of which suggested anything unusual. 
 
 However, on 1991 February 3 (UT), the "dip" produced by the 
spectrometer for HD 42397 proved to be double, indeed well resolved, 
with the stronger component to the red. Soon thereafter, the star 
moved into the daytime sky, and I was unable to observe it again until 
the following September. It still appeared to be double then, with 
slightly larger separation and the stronger component still to the red. 
During the fall and winter of 1991-2 the separation gradually 
decreased, until in 1992 April the dips were no longer fully resolved 
by the spectrometer. The available observations are set out in Table I. 
 Although the observations were obtained through several different 
masks; those presented above have been adjusted by small amounts, in 
all cases less than 1.0 km/s, in an attempt to place them all on a 
standard system, which is thought to be very close to the IAU (Pearce 
1957) system. Some of the adjustments have been published by Fletcher 
et al. (1982), but others are my own unpublished ones. The 
uncertainty of a single observation is approximately 0.5 km/s. 
 
 Clearly it is impossible to obtain orbital elements from such a 
limited set of data, or even predict when next the spectra will be 
resolved, or indeed if they will ever be resolved with the stronger 
component to the blue. However, by comparing the average of the four 
early velocities, 38.2 km/s, with the averages of the six resolved 
velocities for each component, 49.3 km/s and 25.8 km/s for the 
primary and secondary respectively, we can estimate the mass ratio to 
be close to 0.9, which is roughly consistent with the approximate 
magnitude difference of 0.5 magnitudes, estimated from the dip areas. 
Both dips are of about the same width, and give no suggestion of 
rotational broadening. 
 
 
Table 1 - The Observations 
 
Hel. J.D.   Radial Velocity (km/s) 
244000+                 (combined) 
 
5246.040                37.3 
5770.762                38.0 
7073.0542               38.9 
7878.8711               38.8 
                (component A)   (component B) 
8290.7711       47.0            26.9 
8521.0253       50.9            23.2 
8530.0165       50.0            25.3 
8585.8900       49.5            24.9 
8604.9400       50.0            25.4 
8606.8655       48.4            28.9 
8730.7263       46.3            (unresolved) 
8735.7202       44.3            (unresolved) 
 
 
 I hope to continue to observe HD 42397 occasionally, in order to 
obtain more information about its orbit, but am publishing this short 
note now to encourage others to do likewise, and to warn those who 
might wish to use the object as a standard. It is of course possible 
that the period is very long, and that the pair may be resolvable in 
the future by interferometric techniques, and I commend it to the 
attention of the appropriate observers. 
 
 
 
                        C. D. SCARFE 
                        Department of Physics and Astronomy 
                        University of Victoria 
                        Victoria, B. C. V8W 3P6, CANADA 
 
References: 
 
Fletcher, J. M., Harris, H. C., McClure, R. D. and Scarfe, 
   C. D.: 1982, Pub. Astron. Soc. Pac. 94, 1017  [BIBCODE 1982PASP...94.1017F ]
 
Heard, J. F. and Fehrenbach, C.: 1972, Pub. Davis Dunlap 
   Obs. 3, 113  [BIBCODE 1972PDDO....3..113H ]
 
Griffin, R. F.: 1975, Mon. Not. Roy. Astron. Soc. 171, 407  [BIBCODE 1975MNRAS.171..407G ]
 
Griffin, R. F.: 1980, Mon. Not. Roy. Astron. Soc. 190, 711  [BIBCODE 1980MNRAS.190..711G ]
 
Pearce, J. A.: 1957, Trans. Int. Astron. Union 9, 441