18 research outputs found
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 (
A catalog of reference stars for long baseline stellar interferometry
The calibration process of long baseline stellar interferometers requires the
use of reference stars with accurately determined angular diameters. We present
a catalog of 374 carefully chosen stars among the all-sky network of infrared
sources provided by Cohen et al. 1999. The catalog benefits from a very good
sky coverage and a median formal error on the angular diameters of only 1.2%.
Besides, its groups together in a homogeneous handy set stellar coordinates,
uniform and limb-darkened angular diameters, photometric measurements, and
other parameters relevant to optical interferometry. In this paper, we describe
the selection criteria applied to qualify stars as reference sources. Then, we
discuss the catalog's statistical properties such as the sky coverage or the
distributions of magnitudes and angular diameters. We study the number of
available reference stars as a function of the baseline and the precision
needed on the visibility measurements. Finally, we compare the angular
diameters predicted in Cohen et al. 1999 with existing determinations in the
literature, and find a very good agreement.Comment: Conference "Interferometry for Optical Astronomy II", SPIE 200
Cepheid distances from the SpectroPhoto-Interferometry of Pulsating Stars (SPIPS) - Application to the prototypes delta Cep and eta Aql
The parallax of pulsation, and its implementations such as the
Baade-Wesselink method and the infrared surface bright- ness technique, is an
elegant method to determine distances of pulsating stars in a quasi-geometrical
way. However, these classical implementations in general only use a subset of
the available observational data. Freedman & Madore (2010) suggested a more
physical approach in the implementation of the parallax of pulsation in order
to treat all available data. We present a global and model-based
parallax-of-pulsation method that enables including any type of observational
data in a consistent model fit, the SpectroPhoto-Interferometric modeling of
Pulsating Stars (SPIPS). We implemented a simple model consisting of a
pulsating sphere with a varying effective temperature and a combina- tion of
atmospheric model grids to globally fit radial velocities, spectroscopic data,
and interferometric angular diameters. We also parametrized (and adjusted) the
reddening and the contribution of the circumstellar envelopes in the
near-infrared photometric and interferometric measurements. We show the
successful application of the method to two stars: delta Cep and eta Aql. The
agreement of all data fitted by a single model confirms the validity of the
method. Derived parameters are compatible with publish values, but with a
higher level of confidence. The SPIPS algorithm combines all the available
observables (radial velocimetry, interferometry, and photometry) to estimate
the physical parameters of the star (ratio distance/ p-factor, Teff, presence
of infrared excess, color excess, etc). The statistical precision is improved
(compared to other methods) thanks to the large number of data taken into
account, the accuracy is improved by using consistent physical modeling and the
reliability of the derived parameters is strengthened thanks to the redundancy
in the data.Comment: 10 pages, 4 figures, A&A in pres
Extended envelopes around Galactic Cepheids III. Y Oph and alpha Per from near-infrared interferometry with CHARA/FLUOR
Unbiased angular diameter measurements are required for accurate distances to
Cepheids using the interferometric Baade Wesselink method (IBWM). The precision
of this technique is currently limited by interferometric measurements at the
1.5% level. At this level, the center-to-limb darkening (CLD) and the presence
of circumstellar envelopes (CSE) seem to be the two main sources of bias. The
observations we performed aim at improving our knowledge of the interferometric
visibility profile of Cepheids. In particular, we assess the systematic
presence of CSE around Cepheids in order determine accurate distances with the
IBWM free from CSE biased angular diameters. We observed a Cepheid (Y Oph) for
which the pulsation is well resolved and a non-pulsating yellow supergiant
(alpha Per) using long-baseline near-infrared interferometry. We interpreted
these data using a simple CSE model we previously developed. We found that our
observations of alpha Per do not provide evidence for a CSE. The measured CLD
is explained by an hydrostatic photospheric model. Our observations of Y Oph,
when compared to smaller baseline measurements, suggest that it is surrounded
by a CSE with similar characteristics to CSE found previously around other
Cepheids. We have determined the distance to Y Oph to be d=491+/-18 pc.
Additional evidence points toward the conclusion that most Cepheids are
surrounded by faint CSE, detected by near infrared interferometry: after
observing four Cepheids, all show evidence for a CSE. Our CSE non-detection
around a non-pulsating supergiant in the instability strip, alpha Per, provides
confidence in the detection technique and suggests a pulsation driven mass-loss
mechanism for the Cepheids.Comment: accepted for publication in Ap
The projection factor of delta Cephei A calibration of the Baade-Wesselink method using the CHARA Array
6 pages (including an electronic table), accepted for publication in A&A lettersCepheids play a key role in astronomy as standard candles for measuring intergalactic distances. Their distance is usually inferred from the Period-Luminosity relationship, calibrated using the semi-empirical Baade-Wesselink method. Using this method, the distance is known to a multiplicative factor, called the projection factor. Presently, this factor is computed using numerical models - it has hitherto never been measured directly. Based on our new interferometric measurements obtained with the CHARA Array and the already published parallax, we present a geometrical measurement of the projection factor of a Cepheid, delta Cep. The value we determined, p = 1.270.06, confirms the generally adopted value of p = 1.36 within 1.5 sigmas. Our value is in line with recent theoretical predictions of Nardetto et al. (2004)
Current results of the PERSEE testbench: the cophasing control and the polychromatic null rate
Stabilizing a nulling interferometer at a nanometric level is the key issue
to obtain deep null depths. The PERSEE breadboard has been designed to study
and optimize the operation of a cophased nulling bench in the most realistic
disturbing environment of a space mission. This presentation focuses on the
current results of the PERSEE bench. In terms of metrology, we cophased at 0.33
nm rms for the piston and 80 mas rms for the tip/tilt (0.14% of the Airy disk).
A Linear Quadratic Gaussian (LQG) control coupled with an unsupervised
vibration identification allows us to maintain that level of correction, even
with characteristic vibrations of nulling interferometry space missions. These
performances, with an accurate design and alignment of the bench, currently
lead to a polychromatic unpolarised null depth of 8.9E-6 stabilized at 3E-7 on
the [1.65-2.45] \mum spectral band (37% bandwidth).Comment: 17 pages, 10 figures, proceedings of the Optics+Photonics SPIE
conference, San Diego, 201
Etude à haute résolution spatiale des Céphéides
PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF
Cophasage de télescopes multi-pupilles sur point source (application à l'interféromètre en frange noire Persée)
PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF
L' évaluation des échelles de temps de turbulence atmosphérique aux emplacements d'observatoire
PARIS7-Bibliothèque centrale (751132105) / SudocMEUDON-Observatoire (920482302) / SudocSudocFranceF