In the framework of the activities of the Combination Research Centers (CRC) of the International Earth Rotation and Reference Systems Service (IERS), the French Groupe de Recherche en Géodésie ...Spatiale (GRGS) studies the benefit of combining space‐geodetic techniques (Doppler orbitography and radiopositioning integrated by satellite, GPS, satellite laser ranging, and very long baseline interferometry) at the observational level. This combination aims to produce a global and consistent solution for Earth orientation parameters (EOPs), polar motion xp and yp, and universal time UT1 with a 1‐day or a 6‐hour sampling, as well as weekly station positions. In this paper we present a methodology for multitechnique combination at the observational level. We process the measurements of the four techniques over a 1‐year period (the year 2002) in order to illustrate and validate our method. All techniques are processed with the same computational framework, thus with the same models and a priori values for parameters. By using the same software and conventions, we avoid inconsistencies in individual computations. We process each technique individually and inside the combination. The comparison between these solutions is a way of analyzing the power of our method even if the actual status of our software does not reproduce the state‐of‐the‐art analyses of each technique. However, we produce an analysis of the quality of our individual computations so that readers can get an informed appreciation of the current capabilities of our software. Finally, we present the capability of such combinations in terms of accuracy and precision, we underline the main issues of our method and propose solutions to solve them in the future.
Context. High-precision interferometric measurements of pulsating stars help to characterize their close environment. In 1974, a close companion was discovered around the pulsating star β Cep using ...the speckle interferometry technique, and features at the limit of resolution (20 milli-arcsec or mas) of the instrument were mentioned that may be due to circumstellar material. β Cep has a magnetic field that might be responsible for a spherical shell or ring-like structure around the star as described by the MHD models. Aims. Using the visible recombiner VEGA installed on the CHARA long-baseline interferometer at Mt. Wilson, we aim to determine the angular diameter of β Cep and resolve its close environment with a spatial resolution up to 1 mas level. Methods. Medium spectral resolution (R = 6000) observations of β Cep were secured with the VEGA instrument over the years 2008 and 2009. These observations were performed with the S1S2 (30 m) and W1W2 (100 m) baselines of the array. Results. We investigated several models to reproduce our observations. A large-scale structure of a few mas is clearly detected around the star with a typical flux relative contribution of 0.23 ± 0.02. Our best model is a co-rotational geometrical thin ring around the star as predicted by magnetically-confined wind shock models. The ring inner diameter is 8.2 ± 0.8 mas and the width is 0.6 ± 0.7 mas. The orientation of the rotation axis on the plane of the sky is PA = 60 ± 1 deg, while the best fit of the mean angular diameter of β Cep gives ΦUDV = 0.22 ± 0.05 mas. Our data are compatible with the predicted position of the close companion of β Cep. Conclusions. These results bring additional constraints on the fundamental parameters and on the future MHD and asteroseismological models of the star.
This paper reports the results of an analysis of the Doppler tracking data of Pioneer probes which did show an anomalous behaviour. A software has been developed for the sake of performing a data ...analysis as independent as possible from that of Anderson et al. Anderson, J., Laing, P.A., Lau, E.L., Liu, A.S., Nieto, M.M., Turyshev, S.G. Study of the anomalous acceleration of Pioneer 10 and 11. Phys. Rev. D 65, 082004, 2002, using the same data set. A first output of this new analysis is a confirmation of the existence of a secular anomaly with an amplitude about 0.8
nm
s
−2 compatible with that reported by Anderson et al. A second output is the study of periodic variations of the anomaly, which we characterize as functions of the azimuthal angle
φ
defined by the directions Sun–Earth Antenna and Sun-Pioneer. An improved fit is obtained with periodic variations written as the sum of a secular acceleration and two sinusoids of the angles
φ
and
2
φ
. The tests which have been performed for assessing the robustness of these results are presented.
Context.
Optical interferometry is at a key development stage. The Very Large Telescope Interferometer (VLTI) has established a stable, robust infrastructure for long-baseline interferometry that is ...usable by general astronomical observers. The present second-generation instruments offer a wide wavelength coverage and improved performance. Their sensitivity and measurement accuracy lead to data and images of high reliability.
Aims.
We have developed the Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) to access, for the first time, high resolution imaging in a wide spectral domain. Many front-line topics are explored with this new equipment, including: stellar activity and mass loss; planet formation and evolution in the gas and dust disks around young stars; and environment interaction and accretion processes around super massive black holes in active galactic nuclei.
Methods.
The instrument is a spectro-interferometric imager in the transmission windows called
L
,
M
, and
N
, from 2.8 to 13.0 microns, combining four optical beams from the VLTI’s unit or auxiliary telescopes. Its concept, related observing procedure, data reduction, and calibration approach, is the product of 30 years of instrumental research and has benefitted from the expertise developed in the frame of the VLTI’s first generation instruments. The instrument utilises a multi-axial beam combination that delivers spectrally dispersed fringes. The signal provides the following quantities at several spectral resolutions: photometric flux, coherent fluxes, visibilities, closure phases, wavelength differential visibilities and phases, and aperture-synthesis imaging.
Results.
This article provides an overview of the physical principle of the instrument and its functionalities. The motivation of the choice of the instrumental concept and the characteristics of the delivered signal are detailed with a description of the observing modes and of their performance limit. MATISSE offers four spectral resolutions in
L
&
M
bands, namely 30, 500, 1000 and 3400, and 30 and 220 in the
N
band, and it provides an angular resolution down to 3 mas for the shortest wavelengths. The MATISSE stand-alone sensitivity limits are 60 mJy in
L
and 300 mJy in
N
. The paper gives details of the sensitivity limits for the different measurables and their related precision criteria, considering telescope configurations and spectral resolutions. We also discuss the gain provided with the GRA4MAT fringe tracker. An ensemble of data and reconstructed images illustrate the first acquired key observations.
Conclusions.
The instrument has been in operation at Cerro Paranal, ESO, Chile, since 2018, and has been open for science use by the international community since April 2019. The first scientific results are being published now.
The dusty heart of Circinus Isbell, J. W.; Meisenheimer, K.; Pott, J.-U. ...
Astronomy and astrophysics (Berlin),
07/2022, Volume:
663
Journal Article
Peer reviewed
Open access
Context.
Active galactic nuclei play a key role in the evolution of galaxies, but their inner workings and physical connection to the host are poorly understood due to a lack of angular resolution. ...Infrared interferometry makes it possible to resolve the circumnuclear dust in the nearby Seyfert 2 galaxy, the Circinus Galaxy. Previous observations have revealed complex structures and polar dust emission but interpretation was limited to simple models. The new Multi AperTure mid-Infrared Spectro-Scopic Experiment (MATISSE) makes it possible to image these structures for the first time.
Aims.
We aim to precisely map the morphology and temperature of the dust surrounding the supermassive black hole through interferometric imaging.
Methods.
We observed the Circinus Galaxy with MATISSE at the Very Large Telescope Interferometer (VLTI), producing 150 correlated flux spectra and 100 closure phase spectra. The novel inclusion of closure phases makes interferometric imaging possible for the first time. We reconstructed images in the
N
-band at ∼10 mas resolution. We fit blackbody functions with dust extinction to several aperture-extracted fluxes from the images to produce a temperature distribution of central dusty structures.
Results.
We find significant substructure in the circumnuclear dust: central unresolved flux of ∼0.5 Jy, a thin disk 1.9 pc in diameter oriented along ∼45°, and a ∼4 × 1.5 pc polar emission extending orthogonal to the disk. The polar emission exhibits patchiness, which we attribute to clumpy dust. Flux enhancements to the east and west of the disk are seen for the first time. We distinguish the temperature profiles of the disk and of the polar emission: the disk shows a steep temperature gradient indicative of denser material; the polar profile is flatter, indicating clumpiness and/or lower dust density. The unresolved flux is fitted with a high temperature, ∼370 K. The polar dust remains warm (∼200 K) out to 1.5 pc from the disk. We attribute approximately 60% of the 12 μm flux to the polar dust, 10% to the disk, and 6% is unresolved; the remaining flux was resolved out. The recovered morphology and temperature distribution resembles modeling of accretion disks with radiation-driven winds at large scales, but we placed new constraints on the subparsec dust.
Conclusions.
The spatially resolved subparsec features imaged here place new constraints on the physical modeling of circumnuclear dust in active galaxies; we show strong evidence that the polar emission consists of dust clumps or filaments. The dynamics of the structures and their role in the Unified Model remain to be explored.
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