[vsnet-campaign-be 109] Re: Delta Scorpii rising again

[Thom Gandet <tgandet@mindspring.com>]

Sebasti疣,

   Bravo!  It is exactly the kind of accurate visual photometry you
have been doing that can detect the small changes in luminosity
to make a major contribution to the study of these relatively small
amplitude blue stars.

   I don't know what your techniques are, but you can read my posting
about Theta CrB this morning about how I do it and compare our
methods.  When our CCD camera comes on line, I will be focusing on
photometry of fainter Be stars; CCD photometry on bright stars is not
easy to do, and I'm not sure how I will do that yet (I have a few
ideas).

   The importance of "precise" amateur visual observations of bright
stars, such as the Be-stars and other blue variables, can't be
stressed enough.  Techniques which can result in higher precision
observations are possible, and I think that close to an order of
magnitude improvement in the precision of visual observations is
possible.

   It will be very interesting to see if the approx. 75-day period
you've tentatively identified in the photometry can be refined, and
how the luminosity changes correlate with the spectroscopic and radial
velocity observations.

   I will be posting something later today about a possible northern
"relative" of Beta Scorpii, V380 Cep (HD 200775), which is predicted
to reach a maximum H-alpha high state this month or next and both
PEP and precise visual estimates are very desperately needed.  This
is potentially a very important star in establishing the binarity of
Herbig Ae/Be stars (perhaps applicable to "classical" Be stars as
well).

   Congratulations!


Cordially,
Thom Gandet


Sebastian Otero wrote:
> 
> Thom Gandet wrote:
> 
> >>Delta Sco, considering its spectral type, its past spectroscopic
> behavior and its recent photometric behavior, may be a Herbig Be
> star rather than a classical Be star.  The prior lack of convincing
> evidence for a spectroscopic period ought to be re-examined, as the
> recent photometry by Sebastian and others (IBVS 5026) does show
> evidence for a period near 80-days.  However, it is difficult to
> measure radial velocities of Be stars that are meaningful in terms
> of Keplerian motion because of effects by gas streams, decretion/
> accretion disk activity, etc.
> 
> Dear friends:
>                    Tonight I observed delta Scorpii and Thom's words seem to
> ring true.
> The star is rising again and the activity is always in agreement with a 72 -
> 77 day period, slightly shorter than proposed by Thom.
>                    I supposed the star was going to fade at last, but the
> fading stopped near JD 2452015 that is exactly 3 cycles of 73 days later
> than the first well-observed 2.15 minimum. The star has brightened by 0.05
> magnitudes and it is very interesting to take a look at the following table
> with maxima and minima. (JD's are approximated [little gaps in the data] but
> they can't be off by more than 5 days)
> 
> FIRST CYCLE:
> 
> Maximum 1.91 -  JD 2451752
> Minimum  2.15 -  JD 2451793
> 
> SECOND CYCLE:
> 
> Maximum 1.85 -  JD 2451824
> Minimum  ??
> 
> THIRD CYCLE:  The star was not visible !!
> 
> FOURTH CYCLE:
> 
> Maximum  1.80 -  JD 2451978
> Minimum   1.85 -  JD 2452015
> 
> Tonight's observation is 1.81 again, and this means that the star will
> probably be VERY bright in a 20-25 days time. (maybe 1.7?).
> 
> I really don't know if there is a companion in a 75 day orbit inducing light
> changes but the changes are there. Maybe with another cycle going on as
> predicted, more can be said...
> 
> In 25 days we'll have another clue.
> 
> Best regards,
> Sebastian Otero,
> LIADA.
> 
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                      Thomas L. Gandet, Director
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