[Message Prev][Message Next][Thread Prev][Thread Next][Message Index][Thread Index]
[vsnet-be 68] Re: Periods for Be stars
Hello, all:
Sebastian Otero wrote:
>
> I have compared my visual data with Hipparcos' and observations from
> different papers and this are some interesting things on southern
> bright Be stars:
>
> - delta Sco: My visual observations clearly show a cycle of +-76 days in
> agreement with Gandet's and others spectroscopic studies. The outbursts or
> GCAS activity seem to be related with the orbital period: 10.583 years.
The spectra of GCAS stars and Be stars are very different, even
though both have emission lines in their spectra at some times.
While they have similarities, the physical processes taking place
and the spectra are different enough that a clear distinction can
be made between them. The underlying physical situations are also
different.
GCAS stars are shell stars: Their spectra have intense and narrow
hydrogen absorption lines. The emission line width is very broad,
about twice what it is for Be-stars.
Be stars' hydrogen absorption line are very broad and arise in
an optically thin disk of gas. Some of the longer periods, like
the ~70-day period in Delta Sco, may be caused by a rotating disk
inclined to the angle of site, perhaps by pulsation. Some of the
longer periods cannot be due to binarity.
The spectrum of Delta Sco has never shown shell lines. Also,
the emission lines in Delta Sco are significantly narrower than in
GCAS stars.
While the recent Delta Sco photometry may resemble a GCAS-
like "outburst", the spectrum of Delta Sco has never shown
indications of a shell spectrum.
> del Sco --?-- +-76 days -- 10.583 years
The published radial velocities show a possible periodicity
in the 6-8 day range; it is not from binarity. It's not clear
whether that period will be evident in the velocities once the
effects of the 10-year orbit and 70-day period are removed. But
it will be very interesting if the recent photometry reflects the
6-8 day period.
The ~70-day period, if confirmed, cannot be due to binarity
since the value of a sin i (essentially, the diameter of the
orbit) places the secondary *inside* the primary. (Not a happy
situation for the secondary!)
> Be stars are very interesting!!
>
> Regards,
> Sebastian.
Indeed!
Cordially,
Thom Gandet
--
************************************************************************
Lizard Hollow Observatory
Thomas L. Gandet, Director
PO Box 77021
Tucson, AZ 85703-7021 USA
************************************************************************
Sebastian Otero wrote:
>
> Dear friends:
> Since the delta Scorpii event I have been observing and
> comparing data for several Be stars. I have found very common the ocurrence
> of periods in the order of tens of days.
> What mechanism drives that variation? Is it a pulsation or
> is it related to binarity ?
> There are three different types of variability working in
> most of them:
> 1- variations in the order of a day or so (NRP?).
> 2- variations in the order of several tenths of days.
> 3- outbursts lasting from days to years (delta Sco, gamma Cas) and during
> which the amplitude of the shorter cycle is increased.
>
> I have compared my visual data with Hipparcos' and observations from
> different papers and this are some interesting things on southern bright Be
> stars:
>
> - delta Sco: My visual observations clearly show a cycle of +-76 days in
> agreement with Gandet's and others spectroscopic studies. The outbursts or
> GCAS activity seem to be related with the orbital period: 10.583 years.
> Amplitude and quiescent data is of course unknown since the activity is new.
> Full range: 1.70 - 2.33 V (up to now!!)
>
> - omega CMa: My visual observations clearly confirm Harmanec's period of
> 34.675 days. Amplitude is in the order of 0.15 magnitudes. There are 3300
> days between the outburst observed by the Hipparcos satellite and the
> current one. The light curves are similar. Quiescent state: 3.95 - 4.17 V.
> Full range: 3.60 - 4.18 V
>
> - kappa CMa: The 1.40 days period from Balona (1990) is confirmed by
> Hipparcos data. My visual observations show there is a cycle similar to the
> other stars present: +- 66.8 days. Amplitude is in the order of 0.10 - 0.15
> magnitudes.
> The star was at its brightest state ever when observed by Hipparcos,
> reaching V= 3.43 around JD 2448300.
> Current quiescent state: 3.58 - 3.73 V. This star was around 3.9 in past
> decades. Full range: 3.43 - 3.97 V.
>
> - mu Cen: Another case: my visual observations show a typical cycle of
> 57.9 days. Petr Harmanec ran a period analysis on Hipparcos data and found a
> similar 55.303 day-period. Amplitude is in the order of 0.10 - 0.15
> magnitudes. Quiescent state:
> 3.35 - 3.54 V. Full range: 2.92 - 3.54 V.
>
> - chi Oph: This is a very strange case: the star is at maximum brightness
> for years. I have found a short 0.52 days variation from Hipparcos data (in
> the order of 0.05 magnitudes between 4.18 - 4.24 V). However , Balona (1990)
> suggested 13.77 days and commented that it lied outside of the normal
> distribution of periods. My observations didn't detect long term activity.
> There is a 0.15 dimming cught by Hipparcos around JD 2448680, when the star
> faded to 4.34 V. Quiescent state: 4.17 - 4.24 V. Full range: GCVS lists a
> 5.0 V minimum. Could someone provide any information about it??
>
> - alpha Ara: Balona (1990) gives 0.981 day period. From Hipparcos data,
> 0.498 days seems to fit better. Amplitude is in the order of 0.04
> magnitudes. Mean brightness of alpha Arae has increased over the last
> decades. It used to lie between 2.9 and 3.0 but curently its quiescent state
> is at 2.80 - 2.85 V. Hipparcos detected variations between 2.78 and 2.89 V.
> The star wa brighter at the beginning of the mission. Full range: 2.78 -
> 3.0? V.
>
> - lambda Pav: Another star that shows little activity. BUT again , there
> seems to be some cycle this time from Hipparcos data: 22.9 days. Amplitude
> is less than 0.1 magnitudes so visual confirmation is very difficult.
> Quiescent state: 4.18 - 4.25 V.
> Full range: 4.00 - 4.26 V
>
> - eta Cen: Hipparcos has classified it as an EB star and a nice double
> waved lightcurve is shown. Cuypers et al (1989) mention this star is a
> convincing case for a triple-wave lightcurve. The period in Balona (1990) is
> 1.927 days but Hipparcos gives 1.28494 days. Amplitude is 0.08 magnitudes
> bor both sources.
> My visual observations are still few and poor due to lack of constant
> comparison stars, but a 18 day-cycle seems to be present with a less than
> 0.1 mag. amplitude. This star hasn't shown variability of more than 0.2
> magnitudes. Is it worth of the GCAS classification it attains in the GCVS??
> Full range: 2.30 - 2.49 V.
>
> In short:
>
> STAR -----Var1-----Var2-----Var3
>
> del Sco --?-- +-76 days -- 10.583 years
> ome CMa --1.37 d. -- 34.7 d.-- ?
> kap CMa --1.40 d.-- +-66.8 d. --?
> mu Cen --2.10 d.-- +- 56 d. --?
> chi Oph -- +-0.52 d.--? -- ?
> Alp Ara -- +-0.49 d.-- ? --?
> lam Pav --? -- +-22.9 d. --?
> eta Cen --1.285 d.-- +-18 d. --?
>
> Be stars are very interesting!!
>
> Regards,
> Sebastian.
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.262 / Virus Database: 132 - Release Date: 12/06/01
--
************************************************************************
Lizard Hollow Observatory
Thomas L. Gandet, Director
PO Box 77021
Tucson, AZ 85703-7021 USA
************************************************************************
vsnet-adm@kusastro.kyoto-u.ac.jp
Return to Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
VSNET Home Page