Abstract
We present the Mid-infrared stellar Diameters and Fluxes compilation Catalogue (MDFC) dedicated to long-baseline interferometry at mid-infrared wavelengths (3–13 $\mu$m). It gathers data for ...half a million stars, i.e. nearly all the stars of the Hipparcos-Tycho catalogue whose spectral type is reported in the SIMBAD data base. We cross-match 26 data bases to provide basic information, binarity elements, angular diameter, magnitude and flux in the near and mid-infrared, as well as flags that allow us to identify the potential calibrators. The catalogue covers the entire sky with 465 857 stars, mainly dwarfs and giants from B to M spectral types closer than 18 kpc. The smallest reported values reach 0.16 $\mu$Jy in L and 0.1 $\mu$Jy in N for the flux, and 2 microarcsec for the angular diameter. We build four lists of calibrator candidates for the L and Nbands suitable with the Very Large Telescope Interferometer (VLTI) sub- and main arrays using the MATISSE instrument. We identify 1621 candidates for L and 44 candidates for N with the Auxiliary Telescopes (ATs), 375 candidates for both bands with the ATs, and 259 candidates for both bands with the Unit Telescopes (UTs). Predominantly cool giants, these sources are small and bright enough to belong to the primary lists of calibrator candidates. In the near future, we plan to measure their angular diameter with 1 per cent accuracy.
ABSTRACT
Understanding the geometry and kinematics of the broad line region (BLR) of active galactic nuclei (AGN) is important to estimate black hole masses in AGN and study the accretion process. ...The technique of reverberation mapping (RM) has provided estimates of BLR size for more than 100 AGN now; however, the structure of the BLR has been studied for only a handful number of objects. Towards this, we investigated the geometry of the BLR for a large sample of 57 AGN using archival RM data. We performed systematic modelling of the continuum and emission line light curves using a Markov chain Monte Carlo method based on Bayesian statistics implemented in PBMAP (Parallel Bayesian code for reverberation−MAPping data) code to constrain BLR geometrical parameters and recover velocity integrated transfer function. We found that the recovered transfer functions have various shapes such as single-peaked, double-peaked, and top-hat suggesting that AGN have very different BLR geometries. Our model lags are in general consistent with that estimated using the conventional cross-correlation methods. The BLR sizes obtained from our modelling approach is related to the luminosity with a slope of 0.583 ± 0.026 and 0.471 ± 0.084 based on H β and H α lines, respectively. We found a non-linear response of emission line fluxes to the ionizing optical continuum for 93 ${{\ \rm per\ cent}}$ objects. The estimated virial factors for the AGN studied in this work range from 0.79 to 4.94 having a mean at 1.78 ± 1.77 consistent with the values found in the literature.
Reverberation mapping (RM) estimates the size and kinematics of broad-line regions (BLR) in quasars and type I AGNs. It yields size-luminosity relation to make QSOs standard cosmological candles, and ...mass-luminosity relation to study the evolution of black holes and galaxies. The accuracy of these relations is limited by the unknown geometry of the BLR clouds distribution and velocities. We analyse the independent BLR structure constraints given by super-resolving differential interferometry. We developed a three-dimensional BLR model to compute all differential interferometry and RM signals. We extrapolate realistic noises from our successful observations of the QSO 3C 273 with AMBER on the VLTI. These signals and noises quantify the differential interferometry capacity to discriminate and measure BLR parameters including angular size, thickness, spatial distribution of clouds, local-to-global and radial-to-rotation velocity ratios, and finally central black hole mass and BLR distance. A Markov Chain Monte Carlo model-fit, of data simulated for various VLTI instruments, gives mass accuracies between 0.06 and 0.13 dex, to be compared to 0.44 dex for RM mass-luminosity fits. We evaluate the number of QSOs accessible to observe with current (AMBER), upcoming (GRAVITY) and possible (OASIS with new generation fringe trackers) VLTI instruments. With available technology, the VLTI could resolve more than 60 BLRs, with a luminosity range larger than four decades, sufficient for a good calibration of RM mass-luminosity laws, from an analysis of the variation of BLR parameters with luminosity.
ABSTRACT
Differential Interferometry allows to obtain the differential visibility and phase, in addition to the spectrum. The differential phase contains important information about the structure and ...motion of stellar photosphere such as stellar spots and non-radial pulsations, and particularly the rotation. Thus, this interferometric observable strongly helps to constrain the stellar fundamental parameters of fast rotators. The spectroastrometry mainly uses the photocentre displacements, which is a first approximation of the differential phase, and is applicable only for unresolved or marginally objects. We study here the sensitivity of relevant stellar parameters to the simulated photocentres using the scirocco code: a semi-analytical algorithm dedicated to fast rotators, applied to two theoretical modelling stars based on Achernar and Regulus, in order to classify the importance of these parameters and their impact on the modelling. We compare our simulations with published VLTI/AMBER data. This work sets the limits of application of photocentre displacements to fast rotators, and under which conditions we can use the photocentres and/or the differential phase, through a pre-established physical criterion. To validate our theoretical study, we apply our method of analysis on observed data of the edge-on fast rotator Regulus. For unresolved targets, with a visibility V ∼ 1, the photocentre can constrain the main stellar fundamental parameters of fast rotators, whereas from marginally resolved objects (0.8 ≤ V < 1), mainly the rotation axis position angle ($\rm PA_{\rm rot}$) can be directly deduced from the vectorial photocentre displacement, which is very important for young cluster studies.
To reach a suitable limiting magnitude with a multi-aperture interferometer, we need to cophase the different telescopes using a reference source. The latter should be located in the same isopistonic ...domain as the science source. We developed a direct analytical expression of deducing the isopistonic angle from atmospheric optical parameters as seeing, isoplanatic angle and outer scale. All of these atmospheric turbulence parameters are measured by the Generalized Seeing Monitor (GSM). The first statistics of the isopistonic angle obtained from the GSM data are presented and comparison between the major sites over the world are discussed (La Silla, Cerro Pachon, Paranal, San Pedro, Mt Palomar, Mauna Kea, La Palma, Oukaïmeden, Maydanak, Dome C). Implications of these isopistonic angle statistics on large interferometers cophasing in terms of sky coverage and limiting magnitude are discussed.
Context. VX Sgr is a cool, evolved, and luminous red star whose stellar parameters are difficult to determine, which affects its classification.
Aims. We aim to spatially resolve the photospheric ...extent as well as the circumstellar environment.
Methods. We used interferometric observations obtained with the MATISSE instrument in the L (3–4 μm), M (4.5–5 μm), and N (8–13 μm) bands. We reconstructed monochromatic images using the MIRA software. We used 3D radiation-hydrodynamics simulations carried out with CO5BOLD and a uniform disc model to estimate the apparent diameter and interpret the stellar surface structures. Moreover, we employed the radiative transfer codes OPTIM3D and RADMC3D to compute the spectral energy distribution for the L, M, and N bands, respectively.
Results. MATISSE observations unveil, for the first time, the morphology of VX Sgr across the L, M, and N bands. The reconstructed images show a complex morphology with brighter areas whose characteristics depend on the wavelength probed. We measured the angular diameter as a function of the wavelength and showed that the photospheric extent in the L and M bands depends on the opacity through the atmosphere. In addition to this, we also concluded that the observed photospheric inhomogeneities can be interpreted as convection-related surface structures. The comparison in the N band yielded a qualitative agreement between the N-band spectrum and simple dust radiative transfer simulations. However, it is not possible to firmly conclude on the interpretation of the current data because of the difficulty in constraing the model parameters using the limited accuracy of our absolute flux calibration.
Conclusions. MATISSE observations and the derived reconstructed images unveil the appearance of VX Sgr’s stellar surface and circumstellar environment across a very large spectral domain for the first time.
ABSTRACT
A good knowledge of the angular diameters of stars used to calibrate the observables in stellar interferometry is fundamental. As the available precision for giant stars is worse than the ...required per cent level, we aim to improve the knowledge of many diameters using MATISSE (Multiple AperTure mid-Infrared SpectroScopic Experiment) data in its different instrumental configurations. Using the squared visibility MATISSE observable, we compute the angular diameter value, which ensures the best-fitting curves, assuming an intensity distribution of a uniform disc. We take into account that the transfer function varies over the wavelength and is different from one instrumental configuration to another. The uncertainties on the diameters are estimated using the residual bootstrap method. Using the low spectral resolution mode in the Lband, we observed a set of 35 potential calibrators selected in the Mid-infrared stellar Diameter and Flux Compilation Catalogue with diameters ranging from about 1 to 3 mas. We reach a precision on the diameter estimates in the range 0.6 per cent to 4.1 per cent. The study of the stability of the transfer function in visibility over two nights makes us confident in our results. In addition, we identify one star, 75 Vir initially present in the calibrator lists, for which our method does not converge, and prove to be a binary star. This leads us to the conclusion that our method is actually necessary to improve the quality of the astrophysical results obtained with MATISSE, and that it can be used as a useful tool for ‘bad calibrator’ detection.
Context. Studying the physical conditions in circumstellar disks is a crucial step toward understanding planet formation and disk evolution. Of particular interest is the case of HD 100546, a Herbig ...Be star that presents a gap within the first 13 AU of its protoplanetary disk, a gap that may originate in the dynamical interactions of a forming planet with its hosting disk. Aims. We seek a more detailed understanding of the structure of the circumstellar environment of HD 100546 and refine our previous disk model that is composed of a tenuous inner disk, a gap and a massive outer disk (see Benisty et al. 2010, A&A, 511, A75). We also investigate whether planetary formation processes can explain the complex density structure observed in the disk. Methods. We gathered a large amount of new interferometric data using the AMBER/VLTI instrument in the H- and K-bands to spatially resolve the warm inner disk and constrain its structure. Then, combining these measurements with photometric observations, we analyze the circumstellar environment of HD 100546 in the light of a passive disk model based on 3D Monte-Carlo radiative transfer. Finally, we use hydrodynamical simulations of gap formation by planets to predict the radial surface density profile of the disk and test the hypothesis of ongoing planet formation. Results. The SED (spectral energy distribution) from the UV to the millimeter range, and the NIR (near-infrared) interferometric data are adequately reproduced by our model. We show that the H- and K-band emissions are coming mostly from the inner edge of the internal dust disk, located near 0.24 AU from the star, i.e., at the dust sublimation radius in our model. At such a short distance, the survival of hot (silicate) dust requires the presence of micron-sized grains, heated at ~1750 K. We directly measure an inclination of 33° ± 11° and a position angle of 140° ± 16° for the inner disk. This is similar to the values found for the outer disk (i ≃ 42°, PA ≃ 145°), suggesting that both disks may be coplanar. We finally show that 1 to 8 Jupiter mass planets located at ~8 AU from the star would have enough time to create the gap and the required surface density jump of three orders of magnitude between the inner and outer disk. However, no information on the amount of matter left in the gap is available, which precludes us from setting precise limits on the planet mass, for now.
PDF
