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Revealing the sub-AU asymmetries of the inner dust rim in the disk around the Herbig Ae star R Coronae Austrinae
Context: Unveiling the structure of the disks around intermediate-masspre-main-sequence stars (Herbig Ae/Be stars) is essential for ourunderstanding of the star and planet formation process. In particular,models predict that in the innermost AU around the star, the dust diskforms a “puffed-up” inner rim, which should result in astrongly asymmetric brightness distribution for disks seen underintermediate inclination. Aims: Our aim is to constrain the sub-AUgeometry of the inner disk around the Herbig Ae star R CrA and searchfor the predicted asymmetries. Methods: Using the VLTI/AMBERlong-baseline interferometer, we obtained 24 near-infrared (H- andK-band) spectro-interferometric observations on R CrA. Observing withthree telescopes in a linear array configuration, each data set samplesthree equally spaced points in the visibility function, providing directinformation about the radial intensity profile. In addition, theobservations cover a wide position angle range (~97°), also probingthe position angle dependence of the source brightness distribution. Results: In the derived visibility function, we detect the signaturesof an extended (Gaussian FWHM ~ 25 mas) and a compact component(Gaussian FWHM ~ 5.8 mas), with the compact component contributing abouttwo-thirds of the total flux (both in H- and K-band). The brightnessdistribution is highly asymmetric, as indicated by the strong closurephases (up to ~40°) and the detected position angle dependence ofthe visibilities and closure phases. To interpret these asymmetries, weemploy various geometric as well as physical models, including a binarymodel, a skewed ring model, and a puffed-up inner rim model with avertical or curved rim shape. For the binary and vertical rim model, noacceptable fits could be obtained. On the other hand, the skewed ringmodel and the curved puffed-up inner rim model allow us tosimultaneously reproduce the measured visibilities and closure phases.From these models we derive the location of the dust sublimation radius(~0.4 AU), the disk inclination angle (~35°), and a north-south diskorientation (PA ~ 180-190°). Our curved puffed-up rim model canreproduce reasonably well the interferometric observables and the SEDand suggests a luminosity of ~29 Lȯ and the presence ofrelatively large (⪆1.2 μm) Silicate dust grains. Our study alsoreveals discrepancies between the measured interferometric observablesand the puffed-up inner rim models, providing important constraints forfuture refinements of these theoretical models. Perpendicular to thedisk, two bow shock-like structures appear in the associated reflectionnebula NGC 6729, suggesting that the detected sub-AU size disk is thedriving engine of a large-scale outflow. Conclusions: Detecting,for the first time, strong non-localized asymmetries in the innerregions of a Herbig Ae disk, our study supports the existence of apuffed-up inner rim in YSO disks.Based on observations made with ESO telescopes at the La Silla ParanalObservatory under programme IDs 079.D-0370(A), 081.C-0272(A,B,C), and081.C-0321(A).
| The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry
Context: Accretion and outflow processes are of fundamental importancefor our understanding of the formation of stars and planetary systems.To trace these processes, diagnostic spectral lines such as theBrγ 2.166 μm line are widely used, although due to a lack ofspatial resolution, the origin of the line emission is still unclear.Aims: Employing the AU-scale spatial resolution which can beachieved with infrared long-baseline interferometry, we aim todistinguish between theoretical models which associate the Brγline emission with mass infall (magnetospheric accretion, gaseous innerdisks) or mass outflow processes (stellar winds, X-winds, or diskwinds). Methods: Using the VLTI/AMBER instrument, we spatiallyand spectrally (λ/Δλ = 1500) resolved the inner(⪉5 AU) environment of five Herbig Ae/Be stars (HD 163296, HD104237, HD 98922, MWC 297, V921 Sco) in the Brγ emission line aswell as in the adjacent continuum. From the measuredwavelength-dependent visibilities, we derive the characteristic size ofthe continuum and Brγ line-emitting region. Additional informationis provided by the closure phase, which we could measure both in thecontinuum wavelength regime (for four objects) as well as in thespectrally resolved Brγ emission line (for one object). Thespectro-interferometric data is supplemented by archival and newVLT/ISAAC spectroscopy. Results: For all objects (except MWC297), we measure an increase of visibility within the Brγ emissionline, indicating that the Brγ-emitting region in these objects ismore compact than the dust sublimation radius. For HD 98922, ourquantitative analysis reveals that the line-emitting region is compactenough to be consistent with the magnetospheric accretion scenario. ForHD 163296, HD 104237, MWC 297, and V921 Sco we identify an extendedstellar wind or a disk wind as the most likely line-emitting mechanism.Since the stars in our sample cover a wide range of stellar parameters,we also search for general trends and find that the size of theBrγ-emitting region does not seem to depend on the basic stellarparameters (such as the stellar luminosity), but correlates withspectroscopic properties, in particular with the Hα line profileshape. Conclusions: By performing the first high-resolutionspectro-interferometric survey on Herbig Ae/Be stars, we find evidencefor at least two distinct Brγ line-formation mechanisms. Mostsignificant, stars with a P-Cygni Hα line profile and a highmass-accretion rate seem to show particularly compact Brγ-emittingregions (RBrγ/Rcont < 0.2), while starswith a double-peaked or single-peaked Hα-line profile show asignificantly more extended Brγ-emitting region (0.6 ⪉RBrγ/Rcont ⪉ 1.4), possibly tracing astellar wind or a disk wind.Based on observationsmade with ESO telescopes at the La Silla Paranal Observatory under opentime programme IDs 077.C-0694, 078.C-0360, and 078.C-0680.
| A catalog of bright calibrator stars for 200-m baseline near-infrared stellar interferometry
We present in this paper a catalog of reference stars suitable forcalibrating infrared interferometric observations. In the K band,visibilities can be calibrated with a precision of 1% on baselines up to200 meters for the whole sky, and up to 300 meters for some part of thesky. This work, extending to longer baselines a previous catalogcompiled by Bordé et al. (2002, A&A, 393, 183), isparticularl y well adapted to hectometric-class interferometers such asthe Very Large Telescope Interferometer (VLTI, Glindemann et al. 2003,Proc. SPIE, 4838, 89) or the CHARA array (ten Brummelaar et al. 2003,Proc. SPIE, 4838, 69) when one is observing well-resolved, high-surfacebrightness objects (K 8). We use the absolute spectro-photometriccalibration method introduced by Cohen et al. (1999, AJ, 117, 1864) toderive the angular diameters of our new set of 948 G8-M0 calibratorstars extracted from the IRAS, 2MASS and MSX catalogs. Angular stellardiameters range from 0.6 mas to 1.8 mas (median is 1.1 mas) with amedian precision of 1.35%. For both the northern and southernhemispheres, the closest calibrator star is always less than 10°away.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
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