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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
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| UBV(RI)C photometry of Hipparcos red stars
We present homogeneous and standardized UBV(RI)C photometryfor nearly 550 M stars selected from the Hipparcos satellite data baseusing the following selection criteria: lack of obvious variability (noHipparcos variability flag); δ<+10°(V-I)>1.7 and Vmagnitude fainter than about 7.6. Comparisons are made between thecurrent photometry, other ground-based data sets and Hipparcosphotometry. We use linear discriminant analysis to determine aluminosity segregation criterion for late-type stars, and principalcomponent analysis to study the statistical structure of the colourindices and to calibrate absolute magnitude in terms of (V-I) for thedwarf stars. Various methods are used to determine the mean absolutemagnitude of the giant stars. We find 10 dwarf stars, apparentlypreviously unrecognized (prior to Hipparcos) as being within 25pc,including five within 20pc.
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Osservazione e dati astrometrici
| Costellazione: | Scorpione |
| Ascensione retta: | 17h39m20.76s |
| Declinazione: | -43°09'52.7" |
| Magnitudine apparente: | 7.852 |
| Distanza: | 714.286 parsec |
| Moto proprio RA: | -5.7 |
| Moto proprio Dec: | -13.3 |
| B-T magnitude: | 10.111 |
| V-T magnitude: | 8.039 |
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