78 research outputs found
The Stellar Composition of the Star Formation Region CMa R1. II. Spectroscopic and Photometric Observations of 9 Young Stars
We present new high and low resolution spectroscopic and photometric data of
nine members of the young association CMa R1. All the stars have circumstellar
dust at some distance as could be expected from their association with
reflection nebulosity. Four stars (HD 52721, HD 53367, LkHalpha 220 and
LkHalpha 218) show Halpha emission and we argue that they are Herbig Be stars
with discs. Our photometric and spectroscopic observations on these stars
reveal new characteristics of their variability. We present first
interpretations of the variability of HD 52721, HD 53367 and the two LkHalpha
stars in terms of a partially eclipsing binary, a magnetic activity cycle and
circumstellar dust variations, respectively. The remaining five stars show no
clear indications of Halpha emission in their spectra, although their spectral
types and ages are comparable with those of HD 52721 and HD 53367. This
indicates that the presence of a disc around a star in CMa R1 may depend on the
environment of the star. In particular we find that all Halpha emission stars
are located at or outside the arc-shaped border of the H II region, which
suggests that the stars inside the arc have lost their discs through
evaporation by UV photons from nearby O stars, or from the nearby (< 25 pc)
supernova, about 1 Myr ago.Comment: 17 pages, 13 figures, accepted by MNRA
Representation theory of finite W algebras
In this paper we study the finitely generated algebras underlying
algebras. These so called 'finite algebras' are constructed as Poisson
reductions of Kirillov Poisson structures on simple Lie algebras. The
inequivalent reductions are labeled by the inequivalent embeddings of
into the simple Lie algebra in question. For arbitrary embeddings a coordinate
free formula for the reduced Poisson structure is derived. We also prove that
any finite algebra can be embedded into the Kirillov Poisson algebra of a
(semi)simple Lie algebra (generalized Miura map). Furthermore it is shown that
generalized finite Toda systems are reductions of a system describing a free
particle moving on a group manifold and that they have finite symmetry. In
the second part we BRST quantize the finite algebras. The BRST cohomology
is calculated using a spectral sequence (which is different from the one used
by Feigin and Frenkel). This allows us to quantize all finite algebras in
one stroke. Explicit results for and are given. In the last part
of the paper we study the representation theory of finite algebras. It is
shown, using a quantum version of the generalized Miura transformation, that
the representations of finite algebras can be constructed from the
representations of a certain Lie subalgebra of the original simple Lie algebra.
As a byproduct of this we are able to construct the Fock realizations of
arbitrary finite algebras.Comment: 62 pages, THU-92/32, ITFA-28-9
Vortices on Higher Genus Surfaces
We consider the topological interactions of vortices on general surfaces. If
the genus of the surface is greater than zero, the handles can carry magnetic
flux. The classical state of the vortices and the handles can be described by a
mapping from the fundamental group to the unbroken gauge group. The allowed
configurations must satisfy a relation induced by the fundamental group. Upon
quantization, the handles can carry ``Cheshire charge.'' The motion of the
vortices can be described by the braid group of the surface. How the motion of
the vortices affects the state is analyzed in detail.Comment: 28 pages with 10 figures; uses phyzzx and psfig; Caltech preprint
CALT-68-187
T-cell responses against 4-tert-butylphenol-exposed pigmented cells in a patient with occupational vitiligo
The Stellar Composition of the Star Formation Region CMa R1 -- III. A new outburst of the Be star component in Z CMa
We report on a recent event in which, after more than a decade of slowly
fading, the visual brightness of the massive young binary Z CMa suddenly
started to rise by about 1 magnitude in December 1999, followed by a rapid
decline to its previous brightness over the next six months. This behaviour is
similar to that exhibited by this system around its eruption in February 1987.
A comparison of the intrinsic luminosities of the system with recent
evolutionary calculations shows that Z CMa may consist of a 16 M_sun B0 IIIe
primary star and a ~ 3 M_sun FUOr secondary with a common age of ~ 3 x 10^5 yr.
We also compare new high-resolution spectra obtained in Jan. and Feb. 2000,
during the recent rise in brightness, with archive data from 1991 and 1996. The
spectra are rich in emission lines, which originate from the envelope of the
early B-type primary star. The strength of these emission lines increased
strongly with the brightness of Z CMa. We interpret the collected spectral data
in terms of an accretion disc with atmosphere around the Herbig B0e component
of Z CMa, which has expanded during the outbursts of 1987 and 2000. A high
resolution profile of the 6300 A [O I] emission line, obtained by us in March
2002 shows an increase in flux and a prominent blue shoulder to the feature
extending to ~ -700 km/s, which was much fainter in the pre-outburst spectra.
We propose that this change in profile is a result of a strong change in the
collimation of a jet, as a result of the outburst at the start of this century.Comment: 22 pages, 12 figures, accepted for publication in MNRA
On realizations of nonlinear Lie algebras by differential operators
We study realizations of polynomial deformations of the sl(2,R)- Lie algebra
in terms of differential operators strongly related to bosonic operators. We
also distinguish their finite- and infinite-dimensional representations. The
linear, quadratic and cubic cases are explicitly visited but the method works
for arbitrary degrees in the polynomial functions. Multi-boson Hamiltonians are
studied in the context of these ``nonlinear'' Lie algebras and some examples
dealing with quantum optics are pointed out.Comment: 21 pages, Latex; New examples added in Sect.
A low optical depth region in the inner disk of the HerbigAe star HR5999
Circumstellar disks surrounding young stars are known to be the birthplaces
of planets, and the innermost astronomical unit is of particular interest. We
present new long-baseline spectro-interferometric observations of the HerbigAe
star, HR5999, obtained in the H and K bands with the AMBER instrument at the
VLTI, and aim to produce near-infrared images at the sub-AU spatial scale. We
spatially resolve the circumstellar material and reconstruct images using the
MiRA algorithm. In addition, we interpret the interferometric observations
using models that assume that the near-infrared excess is dominated by the
emission of a circumstellar disk. We compare the images reconstructed from the
VLTI measurements to images obtained using simulated model data. The K-band
image reveals three main elements: a ring-like feature located at ~0.65 AU, a
low surface brightness region inside, and a central spot. At the maximum
angular resolution of our observations (1.3 mas), the ring is resolved while
the central spot is only marginally resolved, preventing us from revealing the
exact morphology of the circumstellar environment. We suggest that the ring
traces silicate condensation, i.e., an opacity change, in a circumstellar disk
around HR 5999. We build a model that includes a ring at the silicate
sublimation radius and an inner disk of low surface brightness responsible for
a large amount of the near-infrared continuum emission. The model successfully
fits the SED, visibilities, and closure phases, and provides evidence of a low
surface brightness region inside the silicate sublimation radius. This study
provides additional evidence that in HerbigAe stars, there is material in a low
surface brightness region, probably a low optical depth region, located inside
the silicate sublimation radius and of unknown nature.Comment: 11 pages, 10 figure
Near infrared and the inner regions of protoplanetary disks
We examine the ``puffed-up inner disk'' model (Dullemond, Dominik & Natta
2001), proposed for explaining the near-IR excess radiation from Herbig Ae/Be
stars. Detailed model computations show that the observed near-IR excess
requires more hot dust than is contained in the puffed-up disk rim. The rim can
produce the observed near-IR excess only if its dust has perfectly gray
opacity, but such dust is in conflict with the observed 10m spectral
feature. We find that a compact ( 10 AU) tenuous (\tau_V \la 0.4) dusty
halo around the disk inner regions contains enough dust to readily explain the
observations. Furthermore, this model also resolves the puzzling relationship
noted by Monnier and Millan-Gabet (2002) between luminosity and the
interferometric inner radii of disks.Comment: 14 pages, 10 figures, accepted in Ap
A Photometric Catalogue of Southern Emission-Line Stars
We present a catalogue of previously unpublished optical and infrared
photometry for a sample of 162 emission-line objects and shell stars visible
from the southern hemisphere. The data were obtained between 1978 and 1997 in
the Walraven (WULBV), Johnson/Cousins (UBV(RI)_c) and ESO and SAAO
near-infrared (JHKLM) photometric systems. Most of the observed objects are
Herbig Ae/Be (HAeBe) stars or HAeBe candidates appearing in the list of HAeBe
candidates of Th\'e et al. (1994), although several B[e] stars, LBVs and T
Tauri are also included in our sample. For many of the stars the data presented
here are the first photo-electric measurements in the literature. The resulting
catalogue consists of 1809 photometric measurements. Optical variability was
detected in 66 out of the 116 sources that were observed more than once. 15 out
of the 50 stars observed multiple times in the infrared showed variability at
2.2 microns (K band).Comment: 42 pages, no figures, to appear in Astronomy & Astrophysic
Abnormal cytokine production by bone marrow stromal cells of multiple myeloma patients in response to RPMI8226 myeloma cells
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