66 research outputs found
Flexible Spectro Interferometric modelling of OIFITS data with PMOIRED
Despite image reconstruction becoming more widespread when interpreting
OIFITS Data, model fitting in u,v space often remains the best way to interpret
data, either because of the sparsity of the data, or because a quantitative
measurement needs to be done. PMOIRED, is a flexible Python library to
visualize, manipulate and model OIFITS data using simple geometric models. The
strength of PMOIRED resides in its capability to combine linearly various
simple components to create complex scenes, while linking, constraining, and
adding priors to fitted parameters. The code also enables grid search to find
global minima, as well as data resampling to better evaluate uncertainties. In
addition to analytical functions, arbitrary radial profiles, azimuthal
variations or sparse wavelet modelling of spectra are implemented.Comment: 8 pages, 3 figures. Proceeding of SPIE Telescopes+Instrumentation
2022. Code referenced at http://ascl.net/code/v/328
L’Europe dans la culture stratégique canadienne, 1949-2009
S’ appuyant sur la notion de culture stratégique, cet article démontre l’existence d’ une tension historique entre européanisme, continentalisme et internationalisme dans la politique étrangère canadienne. Cette tension fondatrice est explorée sur le plan conceptuel, mais également dans les prises de position concrètes des gouvernements et des partis politiques depuis la fin de la Deuxième Guerre mondiale. En s’ alignant plus ouvertement sur Washington, le gouvernement conservateur de Stephen Harper (2006-2009) est le premier à privilégier le continentalisme de manière aussi unidimensionnelle. Même si le déclin de l’ européanisme ne fait aucun doute, la résilience anticipée de la culture stratégique nous amène à relativiser cette tentative de transformation de la politique étrangère canadienne.Building on the notion of strategic culture, this article substantiates the existence of a historical tension between Europeanism, continentalism and internationalism in Canadian foreign policy. We explore this basic tension at the conceptual level, but also through the positions taken by governments and political parties since World War ii. We note that, by aligning itself on Washington, the Conservative government of Stephen Harper (2006-2009) is the first to privilege continentalism exclusively and at the expense of other perspectives. While the decline of Europeanism seems inevitable, the anticipated resilience of Canada’ s strategic culture leads us to question this attempt at transforming Canadian foreign policy
The circumstellar envelopes of the Cepheids L Car and RS Pup - Comparative study in the infrared with Spitzer, VLT/VISIR and VLTI/MIDI
19 pages, 16 figuresInternational audience[Abridged] - Context: Circumstellar envelopes (CSEs) around Cepheids are particularly interesting as they could impact the Cepheid distance scale, and imply stellar mass loss. Aims: Our goal is to establish the spatial and spectral properties of the CSEs of L Car and RS Pup. This is done through a parametrization of the envelopes in terms of fractional flux (with respect to the star) and angular size. - Methods: We retrieved archival Spitzer images of the two stars (3.5-70 mic), and obtained new imaging with the VLT/VISIR camera in BURST mode (8.6-11.9 mic), as well as interferometry with VLTI/MIDI (8-13 mic). This combination allows us to probe the envelopes over arcminute to milliarcsecond scales. - Results: The CSE of RS Pup is resolved at 24 and 70 mic by Spitzer, and around 10 mic by MIDI and VISIR. The compact envelope of L Car is resolved only in the VISIR and MIDI observations. However, the properties of the IR excesses differ considerably : a warm component is present around both stars at a spatial scale of a few 100 to a few 1 000 AU, but RS Pup presents in addition a large (several 100 000 AU) and cold (~40 K) dusty envelope. - Conclusions: We propose that the reflection nebula surrounding RS Pup has an interstellar origin, while the warm CSEs of both stars were created by ongoing stellar mass loss. Such warm circumstellar envelopes are probably common around Cepheids
A catalog of bright calibrator stars for 200-meter baseline near-infrared stellar interferometry
9 pagesWe present in this paper a catalog of reference stars suitable for calibrating infrared interferometric observations. In the K band, visibilities can be calibrated with a precision of 1 % on baselines up to 200 meters for the whole sky, and up to 300 meters for some part of the sky. This work, extending to longer baselines a previous catalog compiled by Bordé et al. (2002), is particularly well adapted to hectometric-class interferometers such as the Very Large Telescope Interferometer (VLTI, Glindemann et al. 2003) or the CHARA array (ten Brummelaar et al. 2003) when one is observing well-resolved, high-surface brightness objects (
Spatially extended emission around the Cepheid RS Puppis in near-infrared hydrogen lines. Adaptive optics imaging with VLT/NACO
It has been recently discovered that Cepheids harbor circumstellar envelopes
(CSEs). RS Pup is the Cepheid that presents the most prominent circumstellar
envelope known, the origin of which is not yet understood. Our purpose is to
estimate the flux contribution of the CSE around RS Pup at the one arcsecond
scale (~2000 AU) and to investigate its geometry, especially regarding
asymmetries, to constrain its physical properties. We obtained near-infrared
images in two narrow band filters centered on \lambda = 1.644 and 2.180 \mu m
(NB 1.64 and IB 2.18, respectively) that comprise two recombination lines of
hydrogen: the 12-4 and 7-4 (Brackett \gamma) transitions, respectively. We used
NACO's cube mode observations in order to improve the angular resolution with
the shift-and-add technique, and to qualitatively study the symmetry of the
spatially extended emission from the CSE with a statistical study of the
speckle noise. We probably detect at a 2\sigma level an extended emission with
a relative flux (compared with the star in the same filter) of 38 17% in
the NB 1.64 filter and 24 11% in the IB 2.18 filter. This emission is
centered on RS Pup and does not present any detectable asymmetry. We attribute
the detected emission to the likely presence of an hydrogen envelope
surrounding the star
Observational calibration of the projection factor of Cepheids I. The Type II Cepheid kappa Pavonis
The distances of pulsating stars, in particular Cepheids, are commonly
measured using the parallax of pulsation technique. The different versions of
this technique combine measurements of the linear diameter variation (from
spectroscopy) and the angular diameter variation (from photometry or
interferometry) amplitudes, to retrieve the distance in a quasi-geometrical
way. However, the linear diameter amplitude is directly proportional to the
projection factor (hereafter p-factor), which is used to convert spectroscopic
radial velocities (i.e., disk integrated) into pulsating (i.e., photospheric)
velocities. The value of the p-factor and its possible dependence on the
pulsation period are still widely debated. Our goal is to measure an
observational value of the p-factor of the type-II Cepheid kappa Pavonis, whose
parallax was measured with an accuracy of 5% using HST/FGS. We used this
parallax as a starting point to derive the p-factor of kappa Pav, using the
SPIPS technique, which is a robust version of the parallax-of-pulsation method
that employs radial velocity, interferometric and photometric data. We applied
this technique to a combination of new VLTI/PIONIER optical interferometric
angular diameters, new CORALIE and HARPS radial velocities, as well as
multi-colour photometry and radial velocities from the literature. We obtain a
value of p = 1.26 +/- 0.07 for the p-factor of kappa Pav. This result agrees
with several of the recently derived Period-p-factor relationships from the
literature, as well as previous observational determinations for Cepheids.
Individual estimates of the p-factor are fundamental to calibrating the
parallax of pulsation distances of Cepheids. Together with previous
observational estimates, the projection factor we obtain points to a weak
dependence of the p-factor on period.Comment: 8 pages, 6 figures, accepted in A&
Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements
The distance to pulsating stars is classically estimated using the
parallax-of-pulsation (PoP) method, which combines spectroscopic radial
velocity measurements and angular diameter estimates to derive the distance of
the star. An important application of this method is the determination of
Cepheid distances, in view of the calibration of their distance scale. However,
the conversion of radial to pulsational velocities in the PoP method relies on
a poorly calibrated parameter, the projection factor (p-factor). We aim to
measure empirically the value of the p-factors of a homogeneous sample of nine
Galactic Cepheids for which trigonometric parallaxes were measured with the
Hubble Space Telescope Fine Guidance Sensor. We use the SPIPS algorithm, a
robust implementation of the PoP method that combines photometry,
interferometry, and radial velocity measurements in a global modeling of the
pulsation. We obtained new interferometric angular diameters using the PIONIER
instrument at the Very Large Telescope Interferometer, completed by data from
the literature. Using the known distance as an input, we derive the value of
the p-factor and study its dependence with the pulsation period. We find the
following p-factors: 1.20 0.12 for RT Aur, 1.48 0.18 for T Vul,
1.14 0.10 for FF Aql, 1.31 0.19 for Y Sgr, 1.39 0.09 for X
Sgr, 1.35 0.13 for W Sgr, 1.36 0.08 for Dor, 1.41
0.10 for Gem, and 1.23 0.12 for Car. These values are
consistently close to p = 1.324 0.024. We observe some dispersion around
this average value, but the observed distribution is statistically consistent
with a constant value of the p-factor as a function of the pulsation period.
The error budget of our determination of the p-factor values is presently
dominated by the uncertainty on the parallax, a limitation that will soon be
waived by Gaia.Comment: 18 pages, 13 figure
Toward a renewed Galactic Cepheid distance scale from Gaia and optical interferometry
Through an innovative combination of multiple observing techniques and mod-
eling, we are assembling a comprehensive understanding of the pulsation and
close environment of Cepheids. We developed the SPIPS modeling tool that
combines all observables (radial velocimetry, photometry, angular diameters
from interferometry) to derive the relevant physical parameters of the star
(effective temperature, infrared ex- cess, reddening,...) and the ratio of the
distance and the projection factor d/p. We present the application of SPIPS to
the long-period Cepheid RS Pup, for which we derive p = 1.25 +/- 0.06. The
addition of this massive Cepheid consolidates the existing sample of p-factor
measurements towards long-period pulsators. This allows us to conclude that p
is constant or mildly variable around p = 1.29 +/- 0.04 (+/-3%) as a function
of the pulsation period. The forthcoming Gaia DR2 will provide a considerable
improvement in quantity and accuracy of the trigonometric parallaxes of
Cepheids. From this sample, the SPIPS modeling tool will enable a robust
calibration of the Cepheid distance scale.Comment: 5 pages, 4 figures, proceedings of the 22nd Los Alamos Stellar
Pulsation Conference "Wide-field variability surveys: a 21st-century
perspective" held in San Pedro de Atacama, Chile, Nov. 28-Dec. 2, 201
Spectro-Photo-Interferometry of Stellar Pulsation (SPIPS)
We present our implementation of the parallax of pulsation method which integrates all observables and physical modelling of the photosphere to get the best statistical precision and controlled biases. This method has been validated on well known stars and used to estimate observationally the projection factor of the HST-FGS sample. Our future developments include application to the Gaia Cepheids and modelling of the spectrum
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
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