COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2848

                                    Konkoly Observatory
                                    Budapest
                                    15 January 1986

                                    HU ISSN 0374 - 0676




           HD174853 - A NEW ECLIPSING BINARY


    HD174853 = HR7109 was found to be a spectroscopic binary
by one of us (Hube, 1970) who noted spectral line doubling on
one of eleven low dispersion plates. The star has also long
been suspected as a photometric variable (Hoffleit, 1964). In
this note we briefly describe recent observations which confirm
that HD174853 is a double-lined spectroscopic binary, and that
the suspected photometric variations are real and due to two
nearly-equal eclipses in each short period orbital cycle.

    Spectroscopic observations have been made intermittently
during the past fifteen years at the Dominion Astrophysical
Observatory, Victoria, using the Cassegrain spectrograph on the
1.88-m telescope at a dispersion of 1.5 nm/mm. Due to very
severe blending of the rotationally broadened lines of the two
components very little progress has been made. Even using an
oscilloscopic-setting comparator it was never possible to
confidently and unambiguously resolve the lines and measure the
radial velocities of each component.
    Recently, we have scanned most of the spectrograms on a
PDS microdensitometer and reduced the data using the
cross-correlation procedures developed at the DAO (Hill, 1982)
and which are proving invaluable in resolving secondary
spectroscopic components (c.f. Gulliver, et al, 1985).
Spectroscopically, the two components are quite similar though



sufficiently different to permit one to distinguish the primary
from the secondary in the cross-correlation functions. The
semi-amplitude of the velocity variation of each component is
approximately 170 km/s. Over a time interval as short as 2
hours on a given night the radial velocities changed markedly,
suggesting a very short orbital period and the possibility that
the previously detected photometric variations are due to
eclipses.
    Using a 0.45-m telescope and a 1P21 PMT-equipped single
channel photometer built by one of us (A.M.), HD174853 was
observed on twelve nights between May and December 1985.
HD175592 was the comparison star and HD176232 (see following
note) served as a rough check star. Corrections were made for
differential extinction. A total of approximately 200
observations was obtained with a V filter.
    We find that HD174853 is, indeed, an eclipsing binary with
two nearly-equal minima occurring in an orbital period of
approximately 1.3907 days. The observations are plotted with
this period in Figure 1 where phases are measured from
JD(hel) = 2446201.161. There is substantial uncertainty in both
the orbital period and epoch of primary minimum due to the
paucity of data. Due to an unfortunate distribution of clear
nights almost an entire half-cycle has gone unobserved. In
addition, what we take to be the secondary minimum was observed
on only one night, and sky conditions were deteriorating
rapidly toward the end.
     Cowley, et al.(1969) classified the star as B8Vnn and list
colour indices which imply reddening of at most a few


                      [FIGURE 1]


hundredths of a magnitude. The photometry of Crawford, et al.
(1973) is also consistent with a very small amount of
reddening. The measured beta-index implies an absolute magnitude
of approximately +0.3 (Crawford, 1978) which is appropriate for
a normal B8 dwarf (Allen, 1973; Underhill and Doazan, 1982).
In the beta-c1 diagram HD174853 is close to the zero-age main
sequence.
    In summary, HD174853 appears to be a relatively young,
contact or near-contact binary with similar components.
    We plan to obtain a complete light curve during the next
observing season. The spectroscopic observing and analysis are
being done in collaboration with Graham Hill and Wes Fisher,



Dominion Astrophysical Observatory, from whom we have obtained
the benefit of preliminary discussions on this system. A      
complete discussion and analysis of all the data will be
presented elsewhere.


                     DOUGLAS P. HUBE
                     Department of Physics

                     MARK ANDERSON
                     Department of Electric Engineering
                     University of Alberta
                     Edmonton, Alberta, Canada





References:

Allen, C.W., 1973, Astrophysical Quantities (3rd edition),
    The Athlone Press. [BIBCODE 1973asqu.book.....A ]

Cowley, A., Cowley, C., Jaschek, M. and Jaschek, C., 1969,
    Astron. J. 74, 375. [BIBCODE 1969AJ.....74..375C ]

Crawford, D.L., 1978, Astron. J. 83, 48. [BIBCODE 1978AJ.....83...48C ]

Crawford, D.L., Barnes, J.V., Golson, J.C. and Hube, D.P., 1973,
    Astron. J. 78, 738. [BIBCODE 1973AJ.....78..738C ]

Gulliver, A.F., Hube, D.P. and Hill, G., 1985, Astron.
    Astrophys. 151, 254. [BIBCODE 1985A&A...151..254G ]

Hill, G., 1982, Publ. Dom. Astrophys. Obs. 16, 59. [BIBCODE 1982PDAO...16...59H ]

Hoffleit, D., 1964, Catalogue of Bright Stars (3rd edition),
     Yale University Observatory. [BIBCODE 1964cbs..book.....H ]

Hube, D.P., 1970, Mem. Roy. Astron. Soc. 72, 233. [BIBCODE 1970MmRAS..72..233H ]

Underhill, A. and Doazan, V., 1982, B Stars with and Without
     Emission Lines, NASA SP-456. [BIBCODE 1982bsww.book.....U ]