COMMISSION 27 OF THE I. A. U
     INFORMATION BULLETIN ON VARIABLE STARS
                  NUMBER 263

                              Konkoly Observatory
                              Budapest
                              1968 March 27


       REMARKS CONCERNING HD 209813


In number 253 of this Bulletin, Blanco and Catalano report the discovery that
HD 209813 shows a light variability of about 0.1 mag. They estimate that the
period is about 25.98 days, and, quoting an HD spectral type of K0, they
suggest that the star is a Cepheid.

Evidently overlooked by these authors, however, is the fact that HD 209813 is a
well-studied spectroscopic binary (Northcott 1947). The period is 24.431 days,
and the amplitude of the velocity curve is 66.3 km/sec. The star has also had
a quantitatively-determined spectral type of K0 II-III assigned to it by
Halliday 1955. Observations on a single night at rather large air mass lead to
the following UBV parameters for the star:

V=6.77
B-V=1.11
U-B=0.80

An examination of stars near the line of sight to HD 209813 indicate that the
colour excess of the star is E_B-V=0.09.

    These data prompt the following remarks:

a   The similarity of the two periods quoted above, and
    the fact that the period of Blanco and Catalano is
    only a preliminary one, suggest the probability that
    there is really only one period of 24.431 days. It
    would be most interesting to see the light-curves of
    Blanco and Catalano replotted with this period.

b   A spectral type of K0 II-III is unusual for a pulsating
    variable, and is definitely incompatible with the
    spectral types of Cepheids.

c   Blanco and Catalano report that the amplitude of light
    variation is the same in all three of U, B, and V,
    which is also unusual among pulsating variables.

d   If the velocity variation of 66 km/sec is taken as
    due to pulsation, then that amplitude is quite
    incompatible with the light amplitude of only 0.1 mag.,
    as is the sinusoidal shape of the velocity curve with
    the period.

e   The colours of the star, especially U-B;, are too
    blue for the spectral type.

f   A preliminary investigation reveals that the hydrogen
    lines in HD 209813 are too strong for the spectral
    type. Also, the H and K lines show emission cores.

These considerations lead us to suggest that HD 209813 is probably not a
pulsating variable, but is an eclipsing system composed of a K-giant and an
F-subgiant. If this is so, then the system is one of considerable importance,
since its space velocity is about 80 km/sec. It may, therefore, be the only
high velocity star known for which both radii and masses are obtainable, and we
urge that the discovery of Blanco and Catalano be followed up by further
detailed photometry.


                                    J.D. FERNIE
                                    JOAN O. HUBE
                                    JOHN L. SCHMITT
David Dunlap Observatory
Richmond Hill, Ontario, Canada.
March 19, 1968.

References:

Halliday, I., Ap.J. 122, 222, 1955. [BIBCODE 1955ApJ...122..222H ]
Northcott, R.J., Pub. David Dunlap Obs. 1, 369, 1947. [BIBCODE 1947PDDO....1..369N ]