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Preliminary Program
Friday August 18, 9:00-10:30 & 11:00-12:30, Club C
09:00 Business Session
Activities during the past triennium, future
activities, report on the status of the Be Star
Newsletter, Discussion G. Peters
Scientific Session
09:20 Observations of the B[e] Star MWC349 with
mid-infrared interferometry A. Quirrenbach
09:35 The Kepler Mission's guest opportunity program:
opportunity for optical monitoring of B stars? M. Smith
10:00 Rotational velocities of Be stars I. Howarth
10:15 Analysis of the high temperature region in Be stars A. Torres
10:30 Coffee
11:00 Statistical Properties of a Sample of Periodically
Variable B-Type Supergiants: Evidence of a
Pulsation-Mass Loss Connection?
K. Lefever, J. Puls , C. Aerts
11:15 The Comings and Goings of Be Stars V. McSwain
11:30 HD 61273 : a new binary system with a hot
component showing an H-alpha emission line D. Briot, F. Royer
11:45 Spectropolarimetry of Be stars with FORS1
at the VLT revisited R. Yudin
12:00 Circumstellar disks from rotating stars with
and without magnetic fields
S. Owocki, A. ud-Doula, R. Townsend
12:30 Session Ends
Abstracts
HD 61273 : a new binary system with a hot component showing an H-alpha
emission line
Danielle Briot, Frederic Royer (Observatoire de Paris-Meudon, France)
A detailed spectroscopic and photometric analysis shows for the first
time that the 7th magnitude star HD 61273, up to now classified as B9, is
a binary system composed of a dwarf early-type star and a K0 giant.
The orbital period is P = 12.918990 d. The signature of an accretion disk
is detected in the H-alpha profile which shows a permanent and variable
emission.
Statistical properties of a sample of periodically variable B-type
supergiants: evidence of a pulsation-mass loss connection?
Karolien Lefever (Leuven, Belgium), Joachim Puls (Munich, Germany), Conny
Aerts (Leuven, Belgium)
We have studied a sample of 28 periodically variable B-type
supergiants discovered from the HIPPARCOS mission. This study aims to
investigate the mechanism behind the  Cygni variability of supergiants and to see
if it plays a role in the mass loss. We have used the NLTE atmosphere
and line prediction code FASTWIND to derive the atmospheric and wind
parameters of the sample stars through line profile fitting of
selected H, He, Si lines. We find that the variability of the sample
stars is not connected to their rotation. From the position of the
stars in the (Teff, log g) diagram, we suggest
that the stars undergo gravity mode oscillations causing the periodic
photometric variability which is stable over more than 3 years. We
find a positive correlation between the amplitude of the photometric
variability and the wind density.
The Comings and Goings of Be Stars
M. Virginia McSwain (Yale University, USA)
I will present preliminary findings from a spectroscopic monitoring
program of Be stars in 19 open clusters. From a 3- or 4-year time
baseline of photometric and spectroscopic data, I have identified several
Be stars that have undergone disk outbursts and others whose disks have
disappeared. The rate of disk variability does not seem to be constant
among clusters, and I have begun an investigation of the stellar and
cluster properties that may affect their long term variability.
Circumstellar Disks from Rotating Stars with and without Magnetic Fields
Stan Owocki, Asif ud-Doula, Rich Townsend (University of Delaware, USA)
Active OB Stars often exhibit Balmer line emission thought to originate in
circumstellar clouds or disks. This talk will briefly review the
dynamical issues for propelling material into such circumstellar environs
from the surface of a rotating hot star. Without magnetic fields, this
likely requires near-critical rotation, with perhaps pulsation providing a
final kick to place material into a Keplerian, orbiting disk. With a very
strong field, the star's radiatively driven wind outflow can be held into
a rigid-body rotation, confining material in circumstellar clouds
near the intersection between the magnetic and rotational equators. I
argue that generally the non-magnetic, Keplerian disks are likely most
relevant for Be stars, while the rigidly rotating clouds apply to Bp
stars, which are often inferred to have strong magnetic fields.
Analysis of The High Temperature Region In Be Stars
A. Ringuelet & A. Torres (La Plata University, Argentina)
The High Temperature Region (HTR) that surrounds the photospheres of
Be stars is studied in order to derive observational constraints for
modelling Be stars, in particular for the region where superionization
takes place. 50 Be stars, representative of a considerable range of
temperature, were chosen. From archival, high-dispersion IUE spectra,
different lines that originate in the HTR region were considered,
namely the resonance lines of Si IV, C IV and Al III,
and He II  1640.
Equivalent widths (corrected for
photospheric contribution), optical depths, atom columns and expansion
velocities were measured. From this observational data several
correlations between different observables were obtained. These
correlations permit us to discuss the geometry, density distribution
and heat input of the line formation regions (LFRs). The major results
can be summarised as follows:
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The circumstellar material contributes to the resonance lines of
Si IV, C IV, Al III and to the He II 1640 at all inclination
angles.
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In Si IV, C IV and Al III
the equivalent widths have a tendency to increase in objects with high
rotational velocities.
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Si IV and C IV equivalent widths are also
correlated to the kinetic energy of the expansion velocity. This means
that dissipation of mechanical energy is one of the heating
mechanisms.
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On the basis of the expansion velocities and the line
profiles, we establish a sequence for the LFRs: The LFR of He II is at
the base of the wind and the closest to the central star. The LFRs of
Si IV and C IV are inmersed in the stellar wind. The LFR of Al III is
an interface between the HTR and the cool envelope. The analysis
followed in this work is completely model-independent. Consequently,
these results could be useful to decide which are the facts that are
to be considered when modelling Be stars.
The Kepler Mission's Guest Opportunity Program: Opportunity for Optical
Monitoring of B Stars?
Myron Smith (STScI/CSC)
NASA will launch a satellite named Kepler into an Earth-trailing
orbit in November, 2008 in an Earth-trailing orbit. Kepler is a
Discovery-class mission designed to stare at a single 105 square degree
area of the sky in order to search for eclipses of Sun-like stars
eclipsed by exoterrestrial planets. 42 CCDs will read out broad and
single-band photometric every 30 minutes for its 4-6 year lifetime at
~100,000 predetermined locations and monitor the light curves of stars
to a precision of 0.01% or better. Early in its mission, and each annual
cycle there will be a small Guest Observer component of the program
specifically targeted at science other than the mission's primary
objective, that is, to continuously monitor variable objects of virtually
any type meeting instrumental criteria, for example,
V  9.
The total number of objects monitored at any one cycle will be limited
to 3000. Targets of these "GO" programs will have to be known before
the fact as interesting objects worthy of photometric monitoring. The
deadline for the first GO proposals has not yet been set. My guess,
based on the structure of GO programs for other NASA missions, is that
is that it will roughly coincide with the launch date. If the active B
star community is interested in participating in this program, it should
organize, identify suitable targets, and science objectives for this
program. Please contact me so we can decide on a chair for this effort and
get organized.
Gerrie Peters
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