Utilizamos cookies propias y de terceros para el correcto funcionamiento del sitio web y mejorar nuestros servicios. Pulse el siguiente botón para aceptar su uso. Puede cambiar la configuración u obtener más información en nuestra Política de cookies.
We use our own and third-party cookies for the correct functioning of the website and to improve our services. Click the following button to accept its use. You can change the settings or obtain more information in our Cookies Policy.
A Euroconference Organised by the ING:
“Symbiotic Stars Probing Stellar Evolution”, La Palma, 27–31 May 2002
Romano L. M. Corradi (ING)
Half or maybe
two thirds of stars in the Universe are binaries. Among them, symbiotic stars
are long-period interacting binaries composed of an evolved giant primary
and a hot and luminous companion surrounded by an ionised nebula. There are
two distinct classes of symbiotic stars: one containing normal red giants
and having orbital periods of about 1–15 years, and the other with Mira primaries
usually surrounded by a warm dust shell, and orbital periods generally longer
than 10 years. Symbiotic stars are thus the interacting binaries with the
largest orbital separations, and their study is essential to understand the
evolution and interactions of detached or semi-detached binary stars. They
are also among the (intrinsically) brightest stars, which makes them excellent
observational targets both in our Galaxy and in nearby galaxies.
Mass accretion onto the hot component plays a fundamental role in determining
the properties and evolution of symbiotic stars, and involves energetic phenomena
relevant to many other astrophysical fields. The hot component of the vast
majority of symbiotic systems is in fact a luminous (~1,000 solar luminosities)
and hot (100,000 K) white dwarf powered by thermonuclear burning of the material
accreted from its companion’s wind. Depending on the accretion rate, these
systems can be either in a steady burning configuration or undergo hydrogen
shell flashes, which in many cases last for decades due to the low mass of
the white dwarf. In addition, in many systems the hot component shows activity
on time scales of a few years that cannot be simply accounted for by the
thermonuclear models. Possible and promising explanations of this activity
involve changes in mass transfer and/or accretion instabilities in a disk.
Surrounding the interacting stars, a rich and luminous
circumstellar environment is found, which is the result of the presence of
both an evolved giant with a heavy mass loss and of a hot companion copious
in ionising photons and often producing its own wind. In particular, strongly
different environments are expected, such as ionised and neutral regions,
dust forming regions, accretion/ excretion disks, interacting winds, bipolar
outflows and jets. The best known, spectacular example of a ionised nebula
around a symbiotic stars is very likely the Southern Crab (Henize 2–104),
whose inner region is displayed in the conference poster shown in the figure.
Such a complex multi-component structure makes symbiotic stars a very attractive
laboratory to study many aspects of stellar evolution in low-mass binary
systems.
For these reasons, a EuroConference with the title “Symbiotic stars probing
stellar evolution” was organised by the ING on La Palma from May 27 to 31,
2002. Financial support to the conference was provided by the ING and the
European Commission, High-Level Scientific conferences. The main scientific
goal of the conference was to bring together the leading scientists in the
world to revise thoroughly the current state of our knowledge in this field.
This attracted to La Palma one hundred astronomers from thirty different
countries who set, for the first time, firm links between symbiotic stars
and related objects, helping to understand for instance the role of such
interacting binaries in the formation of stellar jets, planetary nebulae,
novae, supersoft X-ray sources, and SNIa. Many of them are issues concerning
the late stages of stellar evolution of which at present little is known,
but with important implications for our understanding of the stellar populations
and chemical evolution of galaxies, as well of the extragalactic distance
scale.
Left: Conference attendants at the
observatory [ JPEG | TIFF
]. Right: Conference poster [ JPEG | TIFF ]
So far, most of the research in the field of symbiotic stars has been conducted
by European astronomers, spread among almost every European country. Therefore
this Euroconference was also the occasion to strengthen the links and collaborations
between researchers from different European institutions. Moreover, more
than 50 young researchers and PhD students (especially European) were able
to attend the conference thanks to the EU and ING funds. The event was a
unique experience for many of them, in which they found guidelines and suggestions
to direct their future research toward important issues in modern astrophysics.
Special training sessions entirely dedicated to these young researchers were
organised with this aim.
The list of invited speakers included: B. Balick (USA), M. Bode (UK), R.
Corradi (UK), I. Iben (USA), A. Jorissen (Belgium), J. Mikolajewska (Poland),
U. Munari (Italy), H. Nussbaumer (Switzerland), H. M. Schmid (Switzerland),
H. Schwarz (Chile), E. Sion (USA), N. Soker (Israel), J. Sokoloski
(USA), T. Tomov (Poland), and P. Whitelock (South Africa).
