[vsnet-chat 4195] Re: DK CAM hipep.. THANKS!

[Thom Gandet <tgandet@mindspring.com>]

Dear Sebastian and Kari,

   DA Dra = 71 Dra = HD193964.  This star is also a known spectroscopic
binary.  The 8th catalogue of SB orbital elements (Batten A.H., et al,
Publ. Dominion Astrophys. Obs. 17 (1989), gives a somewhat different
period of 5.2981, T0=JD 2441140.485 (time of periastron passage), based
on spectra obtained prior to 1973; the eccentricity is 0.04, omega is
291.2º.  However, the 4th edition of the Bright Star Catalogue (1982)
gives a more precise (not necessarily more accurate) value of the
spectrographic period: P=5.298111 days.  I don't know the origin of 
that more precise period.

   Using the spectrographic orbital elements each of the reported
periods, predicted times of eclipse could be calculated and compared
to Meinunger's or Hipparcos's photometric observations.  A more
accurate value of the period might be obtained from that comparison;
other periods may also be ruled out.

   The potential error in the predicted times of eclipse from using
the spectrographic period and the photometric period is roughly 0.1
day.  If the duration of primary eclipse is short, as I suspect, then
the Hipparcos observations could well have missed it.

   DE Dra is also a known visual binary, with P=18.75 years and
a=0.153 arc seconds.  There are several bright, late-type, short-
period B-stars (mostly dwarfs) that are known spectroscopic binaries
and that are members of long-period visual binaries with periods of
around 10-20 years.  The spectrum of one, HR 6928, showed uniquely
unusual absorption lines during periastron passage (in 1973); the
star is a suspected eclipsing binary with a period of about 3-days,
and may also show photometric activity during periastron passage 
during the long-period orbit.  All of these stars - including DA Dra
- are being followed photoelectrically at Lizard Hollow Observatory.

   Keep observing, and good luck!  New observations are definitely
needed, from whatever source.

Cordially,
Thom Gandet


Sebastian Otero wrote:
> 
> > Also DE DRA is EA but
> > I've found also strange ~ 90 d cycle,
> > DE DRA or its compare reddish star varies.
> >
> > With Best Regards,
> >  Mr. Kari A. Tikkanen
> 
> Dear Kari:
>                 Hipparcos did not catch any eclipse of DE Draconis which is
> at V= 5.72 at maximum.
 [etc.]
> Maybe a small error in the period could have accumulated with years and this
> results in a wrong prediction, but new observations are probably needed.
> Maybe someone else knows something about this bright star.

-- 
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                      Lizard Hollow Observatory
                      Thomas L. Gandet, Director
                            PO Box 77021                   
                      Tucson, AZ 85703-7021  USA
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