COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2409

                                    Konkoly Observatory
                                    Budapest
                                    10 October 1983

                                    HU ISSN 0374-0676




            HD 37824 : A NEW VARIABLE STAR


Because Bidelman and MacConnell.(1973) reported Ca II H and K emission,
we suspected HD 37824 might be an RS CVn binary and therefore might show
the photometric wave characteristic of most stars of that type. According
to their table VII, m_v = 7.2m and the spectral type is K1 III + F. In a
preprint sent us by Bopp (1983), a spectral scan shows the H and K reversals
extending somewhat above the continuum.
During three observing seasons we obtained differential photometry in
V of the UBV system using BD +4d1008 as the comparison star. In 1980/81
54 observations were obtained on 18 nights at Dyer, Louth, and Scuppernong
Observatories. In 1981/82 36 observations were obtained on 12 nights at
Cloudcroft Observatory. In 1982/83 44 observations were obtained at
McDonald Observatory. The telescope apertures at those five observatories
were 24-inch, 11-inch, 10-inch, 48-inch, 36-inch, and 30-inch, respectively,
with the last two both at McDonald.
  HD 37824 is definitely variable. The 1982/83 photometry showed the
largest variation, 0.11m in V, and the most clearly defined light curve.
Inspection of that photometry indicated a period of about 26 days and a
nearly sinusoidal shape or about 52 days and a double-humped sinusoidal
shape. Two lines of reasoning led us to favor a period around 52 days.
(1) Although the 1980/81 and 1981/82, light curves showed smaller amplitudes
and were less well defined, the 1980/81 light curve plotted with respect to
a 52-day period showed one minimum considerably deeper than the other.
(2) Not-yet-published radial velocity measures obtained by Fekel (1983),
when analyzed with a period-finding program of Bopp et al. (1970), indicated
equally good fits with orbital periods of 53.6d and 25.1d. The shorter period,
however, implied a very large (and hence unlikely) orbital eccentricity.
   If the orbital period indeed is around 53.6d and if the photometric
variation is a. consequence of nearly synchronous rotation, then the correct
photometric period should be around 52 days. To refine that value we 


                             [FIGURE 1]

 Figure 1  The light curve (top) and the radial velocity curve (bottom).


determined times of minimum light from our three seasons of photometry, 
although gaps in the coverage made some of those determinations uncertain.
The result was 52.6d. The difference between P(phtm.) = 52.6d and P(orb.) =
53.6d indicates rotation 2% faster than synchronous.
   The upper part of Figure 1 shows the 1982/83 observations from McDonald
Observatory plotted versus phase computed with the ephemeris

            JD 2,445,000.0 + 52.6d n,

where the initial epoch has been chosen arbitrarily. Each point is a nightly
mean. The lower part of Figure 1 shows the radial velocity measures of Fekel
plotted versus phase computed with the ephemeris

            JD 2,444,000.0 + 53.6d n,

where again the initial epoch has been chosen arbitrarily. The ordinate has
units of km/sec.
   HD 37824 would profit from additional observation, both photometric and
spectroscopic. Better phase coverage would verify that the above periods
are not in error by a factor two, and a longer baseline in time would 
improve our determination of the difference between P(phtm.) and P(orb.). A
complete radial velocity curve would yield a solution for the orbital 
elements. And additional photometry might reveal interesting changes in the
shape of the double-humped light curve, which we suspect already occurred
between 1980/81 and 1982/83.
   We are all very grateful to Dr. Francis C. Fekel, Jr. for letting us
examine his radial velocity measures before they are published.


DOUGLAS S. HALL

Dyer Observatory
Vanderbilt University
Nashville, Tennessee  37235

GREGORY W. HENRY

McDonald Observatory_
University of Texas
Fort Davis, Texas 79734

HOWARD LOUTH

2199 Hathaway Road
Sedro Woolley, Washington 98284

THOMAS R. RENNER

Scuppernong Observatory
4512 Deerpark Drive
Dousman, Wisconsin 53118


References:

Bidelman, W. P. and MacConnell, D. J. 1973, A.J. 78, 687. [BIBCODE 1973AJ.....78..687B ]
Bopp, B. W. 1983, private communication.
Bopp, B. W., Evans, D. S., and Laing, J. D. 1970, M.N. 147, 355. [BIBCODE 1970MNRAS.147..355B ]
Fekel, F. C. 1983, private communication.