2,156 research outputs found
X-rays from Cepheus A East and West
We report the discovery of X-rays from both components of Cepheus A, East and
West, with the XMM-Newton Observatory. HH 168 joins the ranks of other
energetic Herbig Haro objects that are sources of T~10^6 K X-ray emission. The
HH 168 effective temperature is T = 5.8 (+3.5,-2.3) x 10^6 K and its unabsorbed
luminosity is 1.1 x 10^29 erg s^-1, making it hotter and less luminous than
other representatives of its class. We also detect prominent X-ray emission
from the complex of compact radio sources believed to be the power sources for
Cep A. We call this source HWX and it is distinguished by its hard X-ray
spectrum, T = 1.2 (+1.2,-0.5) x 10^8 K, and complex spatial distribution. It
may arise from one or more protostars associated with the radio complex, the
outflows, or a combination of the two. We detect 102 X-rays sources; many
presumed to be pre-main sequence stars based upon the reddening of their
optical/IR counterparts.Comment: 15 pages, 8 figures, data table not included because of size limit
An apodizing phase plate coronagraph for VLT/NACO
We describe a coronagraphic optic for use with CONICA at the VLT that
provides suppression of diffraction from 1.8 to 7 lambda/D at 4.05 microns, an
optimal wavelength for direct imaging of cool extrasolar planets. The optic is
designed to provide 10 magnitudes of contrast at 0.2 arcseconds, over a
D-shaped region in the image plane, without the need for any focal plane
occulting mask.Comment: 9 pages, 5 figures, to appear in Proc. SPIE Vol. 773
Tackling 3D ToF Artifacts Through Learning and the FLAT Dataset
Scene motion, multiple reflections, and sensor noise introduce artifacts in
the depth reconstruction performed by time-of-flight cameras. We propose a
two-stage, deep-learning approach to address all of these sources of artifacts
simultaneously. We also introduce FLAT, a synthetic dataset of 2000 ToF
measurements that capture all of these nonidealities, and allows to simulate
different camera hardware. Using the Kinect 2 camera as a baseline, we show
improved reconstruction errors over state-of-the-art methods, on both simulated
and real data.Comment: ECCV 201
Status and new operation modes of the versatile VLT/NACO
This paper aims at giving an update on the most versatile adaptive optics fed
instrument to date, the well known and successful NACO . Although NACO is only
scheduled for about two more years at the Very Large Telescope (VLT), it keeps
on evolving with additional operation modes bringing original astronomical
results. The high contrast imaging community uses it creatively as a test-bench
for SPHERE and other second generation planet imagers. A new visible wavefront
sensor (WFS) optimized for Laser Guide Star (LGS) operations has been installed
and tested, the cube mode is more and more requested for frame selection on
bright sources, a seeing enhancer mode (no tip/tilt correction) is now offered
to provide full sky coverage and welcome all kind of extragalactic
applications, etc. The Instrument Operations Team (IOT) and Paranal engineers
are currently working hard at maintaining the instrument overall performances
but also at improving them and offering new capabilities, providing the
community with a well tuned and original instrument for the remaining time it
is being used. The present contribution delivers a non-exhaustive overview of
the new modes and experiments that have been carried out in the past months.Comment: 10 pages, 7 figures, SPIE 2010 Astronomical Instrumentation
Proceedin
PANIC: the new panoramic NIR camera for Calar Alto
PANIC is a wide-field NIR camera, which is currently under development for
the Calar Alto observatory (CAHA) in Spain. It uses a mosaic of four Hawaii-2RG
detectors and covers the spectral range from 0.8-2.5 micron(z to K-band). The
field-of-view is 30x30 arcmin. This instrument can be used at the 2.2m
telescope (0.45arcsec/pixel, 0.5x0.5 degree FOV) and at the 3.5m telescope
(0.23arcsec/pixel, 0.25x0.25 degree FOV). The operating temperature is about
77K, achieved by liquid Nitrogen cooling. The cryogenic optics has three flat
folding mirrors with diameters up to 282 mm and nine lenses with diameters
between 130 mm and 255 mm. A compact filter unit can carry up to 19 filters
distributed over four filter wheels. Narrow band (1%) filters can be used. The
instrument has a diameter of 1.1 m and it is about 1 m long. The weight limit
of 400 kg at the 2.2m telescope requires a light-weight cryostat design. The
aluminium vacuum vessel and radiation shield have wall thicknesses of only 6 mm
and 3 mm respectively.Comment: This paper has been presented in the SPIE of Astronomical Telescopes
and Instrumentation 2008 in Marseille (France
Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI and Direct Adaptive Optics Imaging Surveys: Giant Planets are Rare at Large Separations
We examine the implications for the distribution of extrasolar planets based
on the null results from two of the largest direct imaging surveys published to
date. Combining the measured contrast curves from 22 of the stars observed with
the VLT NACO adaptive optics system by Masciadri et al. (2005), and 48 of the
stars observed with the VLT NACO SDI and MMT SDI devices by Biller et al.
(2007) (for a total of 60 unique stars; the median star for our survey is a 30
Myr K2 star at 25 pc), we consider what distributions of planet masses and
semi-major axes can be ruled out by these data, based on Monte Carlo
simulations of planet populations. We can set this upper limit with 95%
confidence: the fraction of stars with planets with semi-major axis from 20 to
100 AU, and mass >4 M_Jup, is 20% or less. Also, with a distribution of planet
mass of dN/dM ~ M^-1.16 between 0.5-13 M_Jup, we can rule out a power-law
distribution for semi-major axis (dN/da ~ a^alpha) with index 0 and upper
cut-off of 18 AU, and index -0.5 with an upper cut-off of 48 AU. For the
distribution suggested by Cumming et al. (2007), a power-law of index -0.61, we
can place an upper limit of 75 AU on the semi-major axis distribution. At the
68% confidence level, these upper limits state that fewer than 8% of stars have
a planet of mass >4 M_Jup between 20 and 100 AU, and a power-law distribution
for semi-major axis with index 0, -0.5, and -0.61 cannot have giant planets
beyond 12, 23, and 29 AU, respectively. In general, we find that even null
results from direct imaging surveys are very powerful in constraining the
distributions of giant planets (0.5-13 M_Jup) at large separations, but more
work needs to be done to close the gap between planets that can be detected by
direct imaging, and those to which the radial velocity method is sensitive.Comment: 46 pages, 17 figures, accepted to Ap
Rotating molecular outflows: the young T Tauri star in CB26
The disk-outflow connection is thought to play a key role in extracting
excess angular momentum from a forming proto-star. Though jet rotation has been
observed in a few objects, no rotation of molecular outflows has been
unambiguously reported so far. We report new millimeter-interferometric
observations of the edge-on T Tauri star - disk system in the isolated Bok
globule CB26. The aim of these observations was to study the disk-outflow
relation in this 1Myr old low-mass young stellar object. The IRAM PdBI array
was used to observe 12CO(2-1) at 1.3mm in two configurations, resulting in
spectral line maps with 1.5 arcsec resolution. We use an empirical
parameterized steady-state outflow model combined with 2-D line radiative
transfer calculations and chi^2-minimization in parameter space to derive a
best-fit model and constrain parameters of the outflow. The data reveal a
previously undiscovered collimated bipolar molecular outflow of total length
~2000 AU, escaping perpendicular to the plane of the disk. We find peculiar
kinematic signatures that suggest the outflow is rotating with the same
orientation as the disk. However, we could not ultimately exclude jet
precession or two misaligned flows as possible origin of the observed peculiar
velocity field. There is indirect indication that the embedded driving source
is a binary system, which, together with the youth of the source, could provide
the clue to the observed kinematic features of the outflow. CB26 is so far the
most promising source to study the rotation of a molecular outflow. Assuming
that the outflow is rotating, we compute and compare masses, mass flux, angular
momenta, and angular momentum flux of disk and outflow and derive disk
dispersal timescales of 0.5...1 Myr, comparable to the age of the system.Comment: 14 pages, 6 figures, to appear in Astronomy & Astrophysic
Orbit of the young very low-mass spectroscopic binary CHXR 74
The pre-main sequence star CHXR74 (M4.25) in ChaI was detected a few years
ago to be a very low-mass spectroscopic binary. Determination of its mass would
provide a valuable dynamical mass measurement at young ages in the poorly
constrained mass regime of <0.3 Msun. We carried out follow-up radial velocity
(RV) monitoring with UVES/VLT between 2008 and 2011 and high-resolution
adaptive optic assisted imaging with NACO/VLT in 2008 with the aim to constrain
the binary orbit. We present an orbital solution of the system based on the
combined RV data set which spans more than 11 years of UVES monitoring for
CHXR74. The best-fit Kepler model has an orbital period of 13.1 yrs, zero
eccentricity, and a RV semi-amplitude of 2.2 km/s. A companion mass M2sini of
0.08 Msun is derived by using a model-dependent mass estimate for the primary
of 0.24 Msun. The binary separation for i=90deg is 3.8 AU (23 mas).
Complementary NACO images of CHXR74 were taken with the aim to directly resolve
the binary. While there are marginal signs of an extended PSF, we have no
convincing companion detected to CHXR74 in these images. From the non-detection
of the companion together with a prediction of the binary separation at the
time of the NACO observations, we derive an upper limit for the K-band
brightness ratio of 0.5. This allows us to estimate an upper limit of the
companion mass of 0.14 Msun by applying evolutionary models. Thus, we have
confirmed that CHXR74 is a very low-mass spectroscopic binary and constrained
the secondary mass to lie within the range of about 0.08 and 0.14 Msun. We
predict an astrometric signal of the primary between 0.2 and 0.4 mas when
taking into account the luminosity of the companion. The GAIA astrometric
mission might well be able to solve the astrometric orbit of the primary and in
combination with the presented RV data to determine an absolute companion mass.Comment: accepted for publication in A\&A, minor changes (language editing
The instrumental polarization of the Nasmyth focus polarimetric differential imager NAOS/CONICA (NACO) at the VLT - Implications for time-resolved polarimetric measurements of Sgr A*
We report on the results of calibrating and simulating the instrumental
polarization properties of the ESO VLT adaptive optics camera system
NAOS/CONICA (NACO) in the Ks-band. We use the Stokes/Mueller formalism for
metallic reflections to describe the instrumental polarization. The model is
compared to standard-star observations and time-resolved observations of bright
sources in the Galactic center. We find the instrumental polarization to be
highly dependent on the pointing position of the telescope and about 4% at
maximum. We report a polarization angle offset of 13.28{\deg} due to a position
angle offset of the half-wave plate that affects the calibration of NACO data
taken before autumn 2009. With the new model of the instrumental polarization
of NACO it is possible to measure the polarization with an accuracy of 1% in
polarization degree. The uncertainty of the polarization angle is < 5{\deg} for
polarization degrees > 4%. For highly sampled polarimetric time series we find
that the improved understanding of the polarization properties gives results
that are fully consistent with the previously used method to derive the
polarization. The small difference between the derived and the previously
employed polarization calibration is well within the statistical uncertainties
of the measurements, and for Sgr A* they do not affect the results from our
relativistic modeling of the accretion process.Comment: 16 pages, 15 figures, 5 tables, accepted by A&A on 2010 October 1
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