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1. ALICANTE CONFERENCE
TITLE:
The Be Phenomenon in Early-Type Stars
DATE:
28 June-2 July, 1999
VENUE:
Conference Hall of the Caja de Ahorros del Mediterraneo,
Alicante, Spain
SPONSORING
IAU COMMISSIONS:
27 (Variable Stars)
25 (Stellar Photometry & Polarimetry)
29 (Stellar Spectra)
42 (Close Binaries)
44 (Space & High Energy Astrophysics)
THE SCIENTIFIC ORGANIZING COMMITTEE (SOC):
Balona, L. (South Africa)
Bjorkman, J. (United States)
Fabregat, J. (Spain)
Fullerton, A. (Canada)
Hummel, W. (Germany)
Kambe, E. (Japan)
Marlborough, M. (Canada)
Mennickent, R. (Chile)
Roche, P. (United Kingdom)
Smith, M. (United States, Chair)
Stefl, S. (Czech Republic)
Wang, Z. (China)
LOCAL ORGANIZING COMMITTEE (LOC):
J. Fabregat(Chair)
J. Berna
G. Bernabeu
E. Enjuto
J. Perez-Ortiz
The LOC members are members of the two sponsoring universities.
2. DETAILS OF THE CONFERENCE
2.1 The Venue
In 1997 the Universities of Alicante and Valencia extended an
invitation to the Organizing Committee of the Working Group on Active
B Stars to hold a conference in Valencia, Spain. It is easy to
understand why the proposed venue was readily accepted by the
Organizing Committee. Alicante is an affordable site for Asian and
North American as well as European participants. It is both a tourist
and university city which offers a variety of natural and cultural
attractions for visitors. Moreover, it is appropriate to salute the
longstanding observational work on Be stars by astronomers at two
sponsoring institutions, and thirdly to acknowledge the expanding role
of Spain in providing modern astronomical observing sites in Europe
which are well equipped for studies of variable stars and galaxies.
2.2 Accommodation and other costs
The LOC is currently in the process of searching for funding to defray
the expenses of some conference participants, particularly those
astronomers who are young, must travel far, or come from developing
countries. The registration fee is expected to be about $150. This
price includes the cost of publishing the proceedings.
Accommodations include dormitory housing ($12/night; approx), with
shared baths, and hotels. The following are estimates of hotel room
rates in Alicante available to the participants: Single Room: $25-75
Double Room: $35-100.
The hotel rooms are equipped with bathrooms and TV. The CAM conference
hall itself is in the center of Alicante and has a large auditorium
which is equipped with audiovisual facilities.
2.3 The Date and Duration of the meeting
The choice of late June was dictated by the availability of the
conference center, the University of Alicante's academic schedule, and
the local tourist season. Late June is a time when the spring academic
semester is nearing completion and university dormitories are still
open for rental of available and economical rooms. During this time
the average temperature is still rising, so the tourist influx (with
attendant higher hotel costs) will have not yet started. This time
also assures that the home obligations of most conference participants
who have university jobs will be ended. The conference is planned for
4-1/2 days.
2.4 Structure of the meeting
The structure of the meeting will be in a conventional dual format of
oral talks and poster presentations which will run eight hours
(including coffee breaks) per day. The oral presentations will be a
series of review summaries and invited talks (dominated by the work of
one or two groups) of a series of subfields pertaining to the main
subject of the Be phenomenon. An attempt will be made in the oral
talks to weave findings from relevant poster papers into the
presentation. In addition, there are many arguments circulating within
the Be scientific community, so adequate time will be set aside for
discussion following major talks. Time will be provided for personal
reconnaissance of the posters every day, and two sessions of summaries
of poster papers, which will be followed by short group
discussion. The conference will be ended with a short summary by the
Chair and by a discussion of future research directions needed for the
field.
2.5 Dedication
The meeting will be dedicated to the works of Dr. Arne
Slettebak and Mercedes Jaschek.
Dr. Slettebak is currently semi-retired. For more than three decades
he led a research group devoted to the observations of Be stars and to
the role rotation and other possible physical process which might be
responsible for the appearance of Balmer line emission in early-type
stellar spectra. Dr. Slettebak and collaborators initially carried out
his studies from ground-based data and later extended them into the
ultraviolet. He has taught all of us the importance of setting high
standards in data description and measurements and caution in
interpretation.
Many of his publications
have remained benchmarks over the years for describing spectral
signatures of the Be phenomenon.
Dr. Mercedes Jaschek
was also well known for her
spectroscopic observations of Be stars. She began these in
Argentina and continued them when she and her husband Carlos moved to
Strasbourg. One of her major contributions was the construction of the
Catalog of Stellar Groups, which listed all types of stars with
peculiarities, including an extensive listing of Be stars. She chaired
IAU Symposium No. 98 on Be stars and also started the Be Star
Newsletter. The conference will be opened by a public lecture on
stars in Spanish to the local lay public. We plan to ask
Dr. Carlos Jaschek
to give this talk as an added memorial to his wife's contributions.
Dr. Jaschek has retired in Spain and frequently conducts informal
seminars with the public on outreach themes.
2.6 The Proceedings
Written versions of the talks and posters will be published within a
few months of the conference. As much space as possible will be given
for poster papers (but no limit to posters per participant), but the
number of pages could be limited by coverage of discussions following
major talks. The proposed editors of the proceedings are M. A. Smith
(talks) and H. F. Henrichs (posters).
PRELIMINARY AGENDA
"The Be Phenomenon in Early Type Stars"
Session 1: Overview of the Be Phenomenon
Session 2: New Missions and Technologies
-
Positions of B/Be Stars on the HRD from HIPPARCOS
(T. Lanz)
-
Direct Optical Imaging of Be Disks
(Ph. Stee)
-
An Infrared View of Be Star Disks
(R. Waters)
-
A View of Isolated Be Stars at High Energies
(D. Cohen)
-
Recent Attempts to Detect Zeeman Signal in Be Stars
(G. Mathys)
Session 3: Time Variability -
The Role of Stellar & Atmospheric Processes in Isolated Be Stars
-
Subsession 1: The Nature of Periodic Variations
-
Subsession 2: Reports on Campaigns
-
Subsession 3: Aperiodic Variations
-
Photospheric Activity
(M. Smith)
-
Physical Requirements for Magnetic Flaring in an Early-Type Stars
(B. Haisch)
Session 4: The Circumstellar Environment of Be Stars
-
Subsession 1: Observational Diagnostics
-
Subsession 2: Theoretical Models
-
Theory of Global Disk Oscillations
(One-Armed Density Wave Model)
(A. Okazaki)
-
Review of Theoretical Models of Disk Formation
(Wind Compressed, Mass-Transfer Accretion Disks, etc.)
(J. Bjorkman)
Session 5: The Be Phenomenon and Binary Systems
Session 6: Future Directions
-
What Have We Concluded? (Synthesis of Current Understanding)
(M. Marlborough)
-
Where Do We Go from Here? (Key Questions/Problems)
3. Detailed Motivation
3.1 Overview
The most important focus of the conference is to place the classical
Be stars within a larger context of early-type stars with emission
lines. The conference will begin with an overview of the phenomenology
of "classical" Be stars and recent progress in understanding them as
a class.
Next, we will contrast the classical Be stars with overviews of the
B[e] and related stars, which are thought to lose or gain mass by some
combination of radiation pressure, nonradial pulsations, magnetic
fields and mass accretion processes. The relative importance of these
and doubtless other mechanisms probably differs among these classes
and in suitable parameter spaces. This will be the first time in which
participants of the classical Be, massive variable supergiant, and
X-ray Be stars, and flare-physics communities have been assembled in
order to explore the commonality of these subclasses and to pool
knowledge obtained among them.
3.2 Results from New Missions and Technologies
Results from the
HIPPARCOS
mission have led to a number of important advances in the study of Be
stars, including the first reliable distances and luminosities in Be
stars and the first meaningful period-luminosity diagram for pulsating
B stars. These studies will lead to an improved understanding of what
role evolution may play in development of the Be phenomenon.
HIPPARCOS has also been used as a monitor of nonradial pulsations in
Be stars. Its observations have been made of a variety of objects at
essentially random times, which will be more effective in the
detection of multiple mode than most previous ground-based
efforts. One long-term study, which should be completed by the time of
this conference, will have searched for the existence of many
low-amplitude pulsation modes in several Be stars from a sample which
is selection-free as possible. This research promises to supply an
answer to a new degree of confidence as to whether rare constructive
superpositions of these modes can produce atmospheric shocks over
short durations and eject matter from the star.
Interferometric measurements have been made already of a number of
disks around Be stars in H-alpha, and in some cases in wavelengths of
an optical He I line and nearby continuum. By comparing these with
kinematic studies of the line profiles, this work has revealed for the
first time the size and geometry of their circumstellar
disks. Moreover, their apparent obliquity provides a reliable estimate
of the aspect ratio of the disk (and rotation) axes. Currently, two
research groups are continuing these studies, with a third to come on
line by the time of the conference, and will study the internal
velocities and degrees of inhomogeneities in disks. These are
critical parameters for testing theories of disk formation. We expect
that these results could be announced in this conference. It is
anticipated that these results may be compared directly with new
optical and UV spectropolarimetry of the same Be-disk systems.
Results from several new X-ray satellites (
RXTE,
BeppoSax,
ASCA,
AXAF)
will be available at the time of the conference and will further
illuminate the possible role of high-energy phenomena in classical Be
stars as well as the connection between X-ray and optical variability
in X-ray Be binary systems. This conference will also be the first
opportunity to present and discuss with the hot-star community results
from
ISO
which bear on the question of Be disk formation and
maintenance. Finally, it is anticipated that a new generation of
zeeman observations will be made of photospheric lines in several Be
stars by groups from Europe and Canada.
3.3 Temporal Phenomena in Isolated Classical Be Stars
Some periodic process (either nonradial pulsations or magnetic signals
carried by rotational modulation) is generally thought to be the
trigger of atmospheric instabilities which result in spasmodic mass
ejections. This conference will be the first occasion in which
monitoring of stars by HIPPARCOS over 3.5 years without seasonal gaps
will be reported. A comprehensive report on multiple periods in Be
stars, the first of its kind and scope, can discuss the differences in
mode structure and amplitude (if any) between stars which have
undergone recent Be episodes and those which have not.
Some of the periods discovered in these long-term campaigns may be due
to rotational passages of surface structures, particularly if
examination of archival reprocessed IUE data should show variations in
chemical abundances of He or Si. Moreover at this writing, some of the
first reports are being published of co-rotating magnetospheric lobes
over the surfaces of Be stars. The study of these periods will provide
evidence for the existence of quasi- stable magnetic structures on
these stars. These studies will address past hints of a connection
between the Be and Bp (peculiar abundance) phenomena.
A variety of studies over optical, UV, and X-ray energies have
recently shown that rapid high-energy transients occur often on
selected Be stars. These events are evidenced as variations of UV
continuum flux, ephemeral features in profiles of optical He~I and H
lines, and X-ray flares and "shots." Detailed studies of the
processes causing these signatures, and of their cascades to lower
wavelengths, are currently underway and will provide exciting
discussion topics for an audience composed both of X-ray and
optical/UV astronomers. A reanalysis of reprocessed IUE data can
exploit the key He II 1640 Angstrom line as link between the
high-energy transients and warm-star thermal background. Anticipating
that at least some of these signatures could be caused by the
dissipation of magnetic energy, the conference will include a talk on
the conditions needed in plasma above a hot star for flares to erupt
by a prominent expert from the cool star community.
3.4 Circumstellar Wind and Disk Environment
In the early 1990's the
"Wind-Compressed Disk" model
was formulated and first advanced to the Be star community at the Juan
les Pins symposium. This picture was attractive because it predicted
the formation of disks in the outflows from single stars with
moderately high rotation rates. However, recent HD simulations have
shown that additional effects can prevent the formation of the disk,
depending on the details of the wind driving mechanism. In the
meantime, the one-armed density wave model has been proposed to
explain the cyclical variations of the "V/R" emission-component of
Balmer lines of several Be stars. A key difference between these
pictures is whether the disks are Keplerian or angular
momentum-conserving - a testable prediction. This conference will
present both pictures, suggest possible observational tests,
investigate hybrid models combining attributes of both, and discuss
the physical forces responsible for their characteristics. An
important contribution to the conference will be a summary of the
results of IR observations (
ISO,
SIRTF)
of Be disks.
3.5 Interacting Be Binary Stars
Be interacting binary systems generally are members of two groups,
Algol-related and Be X-Ray Binaries (BeXRBs). Each of these
represents a different evolutionary stage of the mass-exchange/loss
process in these systems. Somewhere between these stages a Type II
supernova can be produced. Several high energy studies have shown that
high temperature accretion regions occur as the result of mass flow
between these stars. Similar types of structures have been searched
for in BeXRB systems with interestingly different results. This
meeting will be the first to examine the results of searches since the
last few episodes of the IUE mission
when many such searches were carried out. The conference SOC will ask
that typical parameter spaces of the mass- transfer, energy-release
processes be compared for these two types of binary systems. The
conference participants will be invited to suggest observations with
new X-ray satellites with enhanced spectral capability, broad energy
range and large effective aperture (ASCA, RXTE, BeppoSax, AXAF) to
search for the elusive (but supposedly frequent) Be-white dwarf
systems.
4. Conclusions
Be stars as a group, and even individually, display a large variety of
physical processes and therefore require a complex array of
observational approaches to understand them. Within about two years we
can hope for a "considered" assessment of what has been learned from
UV (IUE) data. The Be community will be intensively engaged in
research in the X-ray and IR regimes. The UV data have so far led to a
picture of sudden violent mass ejections from the Be star's surface. A
new generation of X-ray and IR missions is now poised to provide us
with new insights into the physics of Be star disks. The Alicante
conference stands at a historical crossroads of these space-borne
missions, the consolidation of results by one, and a guide for future
work by the other. The Spanish venue of this conference is appropriate
as this country has undertaken to fully exploit
its Canary island observing sites
and to expand its already substantial contributions in variable star
astronomy.
Myron Smith (SOC Chair)
msmith@nebula.gsfc.nasa.gov
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