170 research outputs found
Le principe de transparence dans le canton de Vaud : évaluation des chapitres I, III, IV et VI de la Loi du 24 septembre 2002 sur l'information
La Loi vaudoise sur l'information (LInfo), en vigueur depuis le 1er septembre 2003, contient les bases légales relatives à l'information communiquée par l'Etat aux médias et au public. A l'image de plus en plus de législations en la matière, elle consacre le principe de l'information sur demande, selon lequel tout individu a désormais le droit de consulter des documents officiels et d'obtenir de l'information de la part des autorités sans devoir motiver sa demande. La présente évaluation s'intéresse à comprendre comment ce principe de transparence est défini dans cette loi, quelle est son application par l'administration, dans quelle mesure il est utilisé par les citoyens et enfin quels sont ses effets six ans après son entrée en vigueur. Das waadtländische Informationsgesetz (LInfo), in Kraft seit dem 1. September 2003, liefert die rechtliche Grundlage betreffend Informationen die durch den Kanton an die Medien und die Öffentlichkeit kommuniziert werden. Als Grundlage dient dazu das Prinzip um Erhalt von Informationen, nach welchem jede Person das Recht hat offizielle Dokumente einzusehen und Informationen von den Behörden zu erhalten ohne die Anfrage begründen zu müssen. Der vorliegende Beitrag hinterfragt wie dieses Transparenzprinzip im Gesetz definiert ist und wie es durch die Verwaltung angewendet wird. Weiter wird untersucht in welchem Ausmass es durch die Bürger und Bürgerinnen angewendet wird und was das Gesetz sechs Jahre nach seinem Inkrafttreten bewirkt hat
AMBER on the VLTI: data processing and calibration issues
We present here the current performances of the AMBER / VLTI instrument for
standard use and compare these with the offered modes of the instrument. We
show that the instrument is able to reach its specified precision only for
medium and high spectral resolution modes, differential observables and bright
objects. For absolute observables, the current achievable accuracy is strongly
limited by the vibrations of the Unit Telescopes, and also by the observing
procedure which does not take into account the night-long transfer function
monitoring. For low-resolution mode, the current limitation is more in the data
reduction side, since several effects negligible at medium spectral resolution
are not taken into account in the current pipeline. Finally, for faint objects
(SNR around 1 per spectral channel), electromagnetic interferences in the VLTI
interferometric laboratory with the detector electronics prevents currently to
get unbiased measurements. Ideas are under study to correct in the data
processing side this effect, but a hardware fix should be investigated
seriously since it limits seriously the effective limiting magnitude of the
instrument.Comment: 10 page
V838 Monocerotis: the central star and its environment a decade after outburst
Aims. V838 Monocerotis erupted in 2002, brightened in a series of outbursts,
and eventually developed a spectacular light echo. A very red star emerged a
few months after the outburst. The whole event has been interpreted as the
result of a merger. Methods. We obtained near-IR and mid-IR interferometric
observations of V838 Mon with the AMBER and MIDI recombiners located at the
Very Large Telescope Interferometer (VLTI) array. The MIDI two-beam
observations were obtained with the 8m Unit Telescopes between October 2011 and
February 2012. The AMBER three-beam observations were obtained with the compact
array (Bm) in April 2013 and the long array (B140m) in May 2014,
using the 1.8m Auxiliary Telescopes. Results. A significant new result is the
detection of a compact structure around V838 Mon, as seen from MIDI data. The
extension of the structure increases from a FWHM of 25 mas at 8 {\mu}m to 70
mas at 13 {\mu}m. At the adopted distance of D = 6.1 0.6 kpc, the dust is
distributed from about 150 to 400 AU around V838 Mon. The MIDI visibilities
reveal a flattened structure whose aspect ratio increases with wavelength. The
major axis is roughly oriented around a position angle of -10 degrees, which
aligns with previous polarimetric studies reported in the literature. This
flattening can be interpreted as a relic of the 2002 eruption or by the
influence of the currently embedded B3V companion. The AMBER data provide a new
diameter for the pseudo-photosphere, which shows that its diameter has
decreased by about 40% in 10yrs, reaching a radius R = 750 200
R (3.5 1.0 AU). Conclusions. After the 2002 eruption,
interpreted as the merging of two stars, it seems that the resulting source is
relaxing to a normal state. The nearby environment exhibits an equatorial
over-density of dust up to several hundreds of AU.Comment: Astronomy and Astrophysics (2014) Will be set by the publishe
Grown-up stars physics with MATISSE
MATISSE represents a great opportunity to image the environment around
massive and evolved stars. This will allow one to put constraints on the
circumstellar structure, on the mass ejection of dust and its reorganization ,
and on the dust-nature and formation processes. MATISSE measurements will often
be pivotal for the understanding of large multiwavelength datasets on the same
targets collected through many high-angular resolution facilities at ESO like
sub-millimeter interferometry (ALMA), near-infrared adaptive optics (NACO,
SPHERE), interferometry (PIONIER, GRAVITY), spectroscopy (CRIRES), and
mid-infrared imaging (VISIR). Among main sequence and evolved stars, several
cases of interest have been identified that we describe in this paper.Comment: SPIE, Jun 2016, Edimbourgh, Franc
The environment of the fast rotating star Achernar - Thermal infrared interferometry with VLTI/MIDI and SIMECA modeling
Context: As is the case of several other Be stars, Achernar is surrounded by
an envelope, recently detected by near-IR interferometry.
Aims: We search for the signature of circumstellar emission at distances of a
few stellar radii from Achernar, in the thermal IR domain.
Methods: We obtained interferometric observations on three VLTI baselines in
the N band (8-13 mic), using the MIDI instrument.
Results: From the measured visibilities, we derive the angular extension and
flux contribution of the N band circumstellar emission in the polar direction
of Achernar. The interferometrically resolved polar envelope contributes 13.4
+/- 2.5 % of the photospheric flux in the N band, with a full width at half
maximum of 9.9 +/- 2.3 mas (~ 6 Rstar). This flux contribution is in good
agreement with the photometric IR excess of 10-20% measured by fitting the
spectral energy distribution. Due to our limited azimuth coverage, we can only
establish an upper limit of 5-10% for the equatorial envelope. We compare the
observed properties of the envelope with an existing model of this star
computed with the SIMECA code.
Conclusions: The observed extended emission in the thermal IR along the polar
direction of Achernar is well reproduced by the existing SIMECA model. Already
detected at 2.2mic, this polar envelope is most probably an observational
signature of the fast wind ejected by the hot polar caps of the star.Comment: A&A Letter, in pres
First results from VLTI near-infrared interferometry on high-mass young stellar objects
This is the author accepted manuscript. The final version is available from SPIE via the DOI in this record.Due to the recent dramatic technological advances, infrared interferometry can now be applied to new classes of objects, resulting in exciting new science prospects, for instance, in the area of high-mass star formation. Although extensively studied at various wavelengths, the process through which massive stars form is still only poorly understood. For instance, it has been proposed that massive stars might form like low-mass stars by mass accretion through a circumstellar disk/envelope, or otherwise by coalescence in a dense stellar cluster. Therefore, clear observational evidence, such as the detection of disks around high-mass young stellar objects (YSOs), is urgently needed in order to unambiguously identify the formation mode of the most massive stars. After discussing the technological challenges which result from the special properties of these objects, we present first near-infrared interferometric observations, which we obtained on the massive YSO IRAS 13481-6124 using VLTI/AMBER infrared long-baseline interferometry and NTT speckle interferometry. From our extensive data set, we reconstruct a model-independent aperture synthesis image which shows an elongated structure with a size of ~ 13 x 19 AU, consistent with a disk seen under an inclination of - 45°. The measured wavelengthdependent visibilities and closure phases allow us to derive the radial disk temperature gradient and to detect a dust-free region inside of 9.5 AU from the star, revealing qualitative and quantitative similarities with the disks observed in low-mass star formation. In complementary mid-infrared Spitzer and sub-millimeter APEX imaging observations we detect two bow shocks and a molecular outflow, which are oriented perpendicular to the disk plane and indicate the presence of a bipolar outflow emanating from the inner regions of the system.This work was performed in part under contract with the California Institute of Technology (Caltech) funded by
NASA through the Sagan Fellowship Program
A hot compact dust disk around a massive young stellar object
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Circumstellar disks are an essential ingredient of the formation of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses, in which strong radiation pressure might halt mass infall. Massive stars may form by stellar merging, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, non-spherical infall geometries. Clear observational evidence, such as the detection of compact dusty disks around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical-unit-scale distribution of hot material around a high-mass ( approximately 20 solar masses) young stellar object. The image shows an elongated structure with a size of approximately 13 x 19 astronomical units, consistent with a disk seen at an inclination angle of approximately 45 degrees . Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system.This work was done in part under contract with the California Institute of Technology (Caltech), funded by NASA through the Sagan Fellowship Program (S.K. is a Sagan Fellow). We thank the ESO Paranal staff for support and their efforts in improving the VLTI. This paper is based on observations made with ESO telescopes at the La Silla Paranal Observatory and archival data obtained with the Spitzer Space Telescope, operated by the Jet Propulsion Laboratory, Caltech, under a contract with NASA. We also used data acquired with APEX, a collaboration between the Max-Planck-Institut für Radioastronomie, ESO, and the Onsala Space Observatory
Spectral and spatial imaging of the Be+sdO binary phi Persei
The rapidly rotating Be star phi Persei was spun up by mass and angular
momentum transfer from a now stripped-down, hot subdwarf companion. Here we
present the first high angular resolution images of phi Persei made possible by
new capabilities in longbaseline interferometry at near-IR and visible
wavelengths. We observed phi Persei with the MIRC and VEGA instruments of the
CHARA Array. Additional MIRC-only observations were performed to track the
orbital motion of the companion, and these were fit together with new and
existing radial velocity measurements of both stars to derive the complete
orbital elements and distance. The hot subdwarf companion is clearly detected
in the near-IR data at each epoch of observation with a flux contribution of
1.5% in the H band, and restricted fits indicate that its flux contribution
rises to 3.3% in the visible. A new binary orbital solution is determined by
combining the astrometric and radial velocity measurements. The derived stellar
masses are 9.6+-0.3Msol and 1.2+-0.2Msol for the Be primary and subdwarf
secondary, respectively. The inferred distance (186 +- 3 pc), kinematical
properties, and evolutionary state are consistent with membership of phi Persei
in the alpha Per cluster. From the cluster age we deduce significant
constraints on the initial masses and evolutionary mass transfer processes that
transformed the phi Persei binary system. The interferometric data place strong
constraints on the Be disk elongation, orientation, and kinematics, and the
disk angular momentum vector is coaligned with and has the same sense of
rotation as the orbital angular momentum vector. The VEGA visible continuum
data indicate an elongated shape for the Be star itself, due to the combined
effects of rapid rotation, partial obscuration of the photosphere by the
circumstellar disk, and flux from the bright inner disk.Comment: 16 pages, 6 figures, 1 Anne
Time, spatial, and spectral resolution of the Halpha line-formation region of Deneb and Rigel with the VEGA/CHARA interferometer
BA-type supergiants are amongst the most optically-bright stars. They are
observable in extragalactic environments, hence potential accurate distance
indicators. Emission activity in the Halpha line of the BA supergiants Rigel
(B8Ia) and Deneb (A2Ia) is indicative of presence of localized time-dependent
mass ejections. Here, we employ optical interferometry to study the Halpha
line-formation region in these stellar environments. High spatial- (0.001
arcsec) and spectral- (R=30 000) resolution observations of Halpha were
obtained with the visible recombiner VEGA installed on the CHARA
interferometer, using the S1S2 array-baseline (34m). Six independent
observations were done on Deneb over the years 2008 and 2009, and two on Rigel
in 2009. We analyze this dataset with the 1D non-LTE radiative-transfer code
CMFGEN, and assess the impact of the wind on the visible and near-IR
interferometric signatures, using both Balmer-line and continuum photons. We
observe a visibility decrease in Halpha for both Rigel and Deneb, suggesting
that the line-formation region is extended (1.5-1.75 R*). We observe a
significant visibility decrease for Deneb in the SiII6371 line. We witness time
variations in the differential phase for Deneb, implying an inhomogeneous and
unsteady circumstellar environment, while no such variability is seen in
differential visibilities. Radiative-transfer modeling of Deneb, with allowance
for stellar-wind mass loss, accounts fairly well for the observed decrease in
the Halpha visibility. Based on the observed differential visibilities, we
estimate that the mass-loss rate of Deneb has changed by less than 5%
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