[vsnet-chat 4739] Upsilon Sagittarii status

["Sebastian Otero" <varsao@fullzero.com.ar>]

UPSILON SAGITTARII  is a very bright hydrogen-deficient binary (HdB) star.
The GCVS lists it as an EB/GS type with a 137.939 -day period and a
photographic range 4.53-4.61.
Some research on this star will reveal that this is totally wrong.
Actually the 138 day figure is only the orbital period.
Hipparcos data clearly show vagaries in the light curve and a period of
35.91 days is suggested.

But what is most important: we can find a lot of works in the literature
about the nature of upsilon Sgr.

This star is a short period yellow SR star. It is pulsating and not showing
eclipses. This truth is
known since at least 1986 when the first photoelectric lightcurve was
obtained (by Malcolm and Bell, 1986).
In "Photometric observations and interpretation of the extremely
hydrogen-deficient binary Upsilon Sagittarii" (Mon. Not. R. Astr. Soc.
233, 621-636(1988) ) K. Morrison explains clearly how
all the observations were sparse and misunderstood in the middle of  last
century  after Gaposchkin 1945's discovery announcement !!.

In 1989 a paper on infrared observations was written for A&A (Jascheck et
al, 1990) completely ignoring
the previous published findings and commenting "..is an eclipsing binary
with a period of 137 days"

Finally a 1995-paper by D. J. Frame and others ("Hydrogen-deficient
binaries: photometry and orbits", Mon. Not. R. Astr. Soc. 276,
383-396(1995) ) reconfirmed the SR classification and
found a period close to 20 days.

From all these sources we now have a very good coverage of the variations
of upsilon Sagittarii that can be resumed as follows for the V band:

V values for upsilon Sagittarii:

Morrison (1988)     V =  4.49 - 4.66
Frame et al (1995) V =  4.43 - 4.69
Hipparcos (1997)   V =  4.42 - 4.63

So the total range detected is 4.42 - 4.69.
Mean magnitude varies in a longer cycle.

I think it is very important to introduce this findings in the GCVS as soon
as they see the light, in order to avoid people using information that is
not correct.

Regards,
Sebastian.


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