5,630 research outputs found
The properties of Low Surface Brightness galaxies
A description is given of the samples of Low Surface Brightness galaxies
(LSBs) used for comparison with models of their chemical and
spectro-photometric evolution (Boissier et al., this Volume). These samples
show the large variation and scatter in observed global properties of LSBs,
some of which cannot be modeled without adding starbursts or truncations to
their star formation history.Comment: To appear in the Proceedings of the Euroconference on The Evolution
of Galaxies: III. From simple approaches to self-consistent models (Kluwer).
4 page
Strong Near-Infrared Emission Interior to the Dust-Sublimation Radius of Young Stellar Objects MWC275 and AB Aur
Using the longest optical-interferometeric baselines currently available, we
have detected strong near-infrared (NIR) emission from inside the
dust-destruction radius of Herbig Ae stars MWC275 and AB Aur. Our
sub-milli-arcsecond resolution observations unambiguously place the emission
between the dust-destruction radius and the magnetospheric co-rotation radius.
We argue that this new component corresponds to hot gas inside the
dust-sublimation radius, confirming recent claims based on spectrally-resolved
interferometry and dust evaporation front modeling.Comment: 12 pages, 4 figures, Accepted for publication in ApJ
Multi-epoch Near-Infrared Interferometry of the Spatially Resolved Disk Around the Be Star Zeta Tau
We present interferometric observations of the Be star Zeta Tau obtained
using the MIRC beam combiner at the CHARA Array. We resolved the disk during
four epochs in 2007-2009. We fit the data with a geometric model to
characterize the circumstellar disk as a skewed elliptical Gaussian and the
central Be star as a uniform disk. The visibilities reveal a nearly edge-on
disk with a FWHM major axis of ~ 1.8 mas in the H-band. The non-zero closure
phases indicate an asymmetry within the disk. Interestingly, when combining our
results with previously published interferometric observations of Zeta Tau, we
find a correlation between the position angle of the disk and the spectroscopic
V/R ratio, suggesting that the tilt of the disk is precessing. This work is
part of a multi-year monitoring campaign to investigate the development and
outward motion of asymmetric structures in the disks of Be stars.Comment: Accepted for publication in the Astronomical Journal. 27 pages, 7
Figure
The Inner Rim of YSO Disks: Effects of dust grain evolution
Dust-grain growth and settling are the first steps towards planet formation.
An understanding of dust physics is therefore integral to a complete theory of
the planet formation process. In this paper, we explore the possibility of
using the dust evaporation front in YSO disks (`the inner rim') as a probe of
the dust physics operating in circumstellar disks. The geometry of the rim
depends sensitively on the composition and spatial distribution of dust. Using
radiative transfer and hydrostatic equilibrium calculations we demonstrate that
dust growth and settling can curve the evaporation front dramatically (from a
cylindrical radius of about 0.5 AU in the disk mid-plane to 1.2 AU in the disk
upper layers for an A0 star). We compute synthetic images and interferometric
visibilities for our representative rim models and show that the current
generation of near-IR long-baseline interferometers (VLTI, CHARA) can strongly
constrain the dust properties of circumstellar disks, shedding light on the
relatively poorly understood processes of grain growth, settling and turbulent
mixing.Comment: 26 pages, 9 figures. Accepted for publication in Ap
High-pressure transport properties of CeRu_2Ge_2
The pressure-induced changes in the temperature-dependent thermopower S(T)
and electrical resistivity \rho(T) of CeRu_2Ge_2 are described within the
single-site Anderson model. The Ce-ions are treated as impurities and the
coherent scattering on different Ce-sites is neglected. Changing the
hybridisation \Gamma between the 4f-states and the conduction band accounts for
the pressure effect. The transport coefficients are calculated in the
non-crossing approximation above the phase boundary line. The theoretical S(T)
and \rho(T) curves show many features of the experimental data. The seemingly
complicated temperature dependence of S(T) and \rho(T), and their evolution as
a function of pressure, is related to the crossovers between various fixed
points of the model.Comment: 9 pages, 10 figure
Imaging the circumstellar envelopes of AGB stars
We report the results of an exploratory program to image the extended
circumstellar envelopes of asymptotic giant branch (AGB) stars in
dust-scattered galactic light. The goal is to characterize the morphology of
the envelopes as a probe of the mass-loss process. The observations consist of
short exposures with the VLT and longer exposures with 1-2m telescopes,
augmented with archival images from the Hubble Space Telescope. We observed 12
AGB stars and detected the circumstellar envelopes in 7. The detected envelopes
have mass loss rates more than about 5 10E-6 solar mass per year, and they can
be seen out to distances of about 1 kpc. The observations provide information
on the mass loss history on time scales up to about 10,000 years. For the five
AGB envelopes in which the circumstellar geometry is well determined by
scattered light observations, all except one (OH348.2-19.7) show deviations
from spherical symmetry. Two (IRC+10216 and IRC+10011) show roughly spherical
envelopes at large radii but asymmetry or bipolarity close to the star; one
(AFGL 2514) shows an extended, elliptical envelope, and one (AFGL 3068) shows a
spiral pattern. The non-spherical structures are all consistent with the
effects of binary interactions. Our observations are in accord with a scenario
in which binary companions play a role in shaping planetary nebulae, and show
that the circumstellar gas is already partly shaped on the AGB, before
evolution to the proto-planetary nebula phase.Comment: Accepted by AA 21 Feb 2006; 18 pages, 14 figs; for high resolution
images, contact mauron at graal.univ-montp2.f
Imaging the asymmetric dust shell around CI Cam with long baseline optical interferometry
We present the first high angular resolution observation of the B[e]
star/X-ray transient object CI Cam, performed with the two-telescope Infrared
Optical Telescope Array (IOTA), its upgraded three-telescope version (IOTA3T)
and the Palomar Testbed Interferometer (PTI). Visibilities and closure phases
were obtained using the IONIC-3 integrated optics beam combiner. CI Cam was
observed in the near-infrared H and K spectral bands, wavelengths well suited
to measure the size and study the geometry of the hot dust surrounding CI Cam.
The analysis of the visibility data over an 8 year period from soon after the
1998 outburst to 2006 shows that the dust visibility has not changed over the
years. The visibility data shows that CI Cam is elongated which confirms the
disc-shape of the circumstellar environment and totally rules out the
hypothesis of a spherical dust shell. Closure phase measurements show direct
evidence of asymmetries in the circumstellar environment of CI Cam and we
conclude that the dust surrounding CI Cam lies in an inhomogeneous disc seen at
an angle. The near-infrared dust emission appears as an elliptical skewed
Gaussian ring with a major axis a = 7.58 +/- 0.24 mas, an axis ratio r = 0.39
+/- 0.03 and a position angle theta = 35 +/- 2 deg.Comment: 9 pages, 5 figures, accepted MNRA
First astronomical unit scale image of the GW Ori triple. Direct detection of a new stellar companion
Young and close multiple systems are unique laboratories to probe the initial
dynamical interactions between forming stellar systems and their dust and gas
environment. Their study is a key building block to understanding the high
frequency of main-sequence multiple systems. However, the number of detected
spectroscopic young multiple systems that allow dynamical studies is limited.
GW Orionis is one such system. It is one of the brightest young T Tauri stars
and is surrounded by a massive disk. Our goal is to probe the GW Orionis
multiplicity at angular scales at which we can spatially resolve the orbit. We
used the IOTA/IONIC3 interferometer to probe the environment of GW Orionis with
an astronomical unit resolution in 2003, 2004, and 2005. By measuring squared
visibilities and closure phases with a good UV coverage we carry out the first
image reconstruction of GW Ori from infrared long-baseline interferometry. We
obtain the first infrared image of a T Tauri multiple system with astronomical
unit resolution. We show that GW Orionis is a triple system, resolve for the
first time the previously known inner pair (separation 1.4 AU) and
reveal a new more distant component (GW Ori C) with a projected separation of
8 AU with direct evidence of motion. Furthermore, the nearly equal (2:1)
H-band flux ratio of the inner components suggests that either GW Ori B is
undergoing a preferential accretion event that increases its disk luminosity or
that the estimate of the masses has to be revisited in favour of a more equal
mass-ratio system that is seen at lower inclination. Accretion disk models of
GW Ori will need to be completely reconsidered because of this outer companion
C and the unexpected brightness of companion B.Comment: 5 pages, 9 figures, accepted Astronomy and Astrophysics Letters. 201
Imaging the Algol Triple System in H Band with the CHARA Interferometer
Algol (Beta Per) is an extensively studied hierarchical triple system whose
inner pair is a prototype semi-detached binary with mass transfer occurring
from the sub-giant secondary to the main-sequence primary. We present here the
results of our Algol observations made between 2006 and 2010 at the CHARA
interferometer with the Michigan Infrared Combiner in the H band. The use of
four telescopes with long baselines allows us to achieve better than 0.5 mas
resolution and to unambiguously resolve the three stars. The inner and outer
orbital elements, as well as the angular sizes and mass ratios for the three
components are determined independently from previous studies. We report a
significantly improved orbit for the inner stellar pair with the consequence of
a 15% change in the primary mass compared to previous studies. We also
determine the mutual inclination of the orbits to be much closer to
perpendicularity than previously established. State-of-the-art image
reconstruction algorithms are used to image the full triple system. In
particular an image sequence of 55 distinct phases of the inner pair orbit is
reconstructed, clearly showing the Roche-lobe-filling secondary revolving
around the primary, with several epochs corresponding to the primary and
secondary eclipses
- …