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A search for clustering around Herbig Ae/Be stars - II. Atlas of the observed sources

We present large field infrared images of a sample of 45 Herbig Ae/Be stars. Stellar parameters, such as age and luminosity, have been derived for all of them in a consistent way. The images have been used to identify stellar groups or clusters associated with the Herbig Ae/Be star. The results presented in this paper form the database for a study of clustering around...

X-shooter spectroscopy of young stellar objects - VI. H i line decrements

Context. Hydrogen recombination emission lines commonly observed in accreting young stellar objects represent a powerful tracer for the gas conditions in the circumstellar structures (accretion columns, and winds or jets).Aims. Here we perform a study of the H i decrements and line profiles, from the Balmer and Paschen H i lines detected in the X-shooter spectra of a homogeneous...

Evidence for a correlation between mass accretion rates onto young stars and the mass of their protoplanetary disks

A&A Astronomy & Astrophysics Letter to the Editor C. F. Manara 3 G. Rosotti 1 L. Testi 0 6 7 A. Natta 5 7 J. M. Alcalá 4 J. P. Williams 9 M. Ansdell 9 A. Miotello 8 N. van der Marel 8 9 M. Tazzari

Evidence for a correlation between mass accretion rates onto young stars and the mass of their protoplanetary disks

A&A Astronomy & Astrophysics Letter to the Editor C. F. Manara 3 G. Rosotti 1 L. Testi 0 6 7 A. Natta 5 7 J. M. Alcalá 4 J. P. Williams 9 M. Ansdell 9 A. Miotello 8 N. van der Marel 8 9 M. Tazzari

Accurate determination of accretion and photospheric parameters in young stellar objects: The case of two candidate old disks in the Orion Nebula Cluster

Context. Current planet formation models are largely based on the observational constraint that protoplanetary disks have a lifetime of ~3 Myr. Recent studies, however, report the existence of pre-main-sequence stars with signatures of accretion (strictly connected with the presence of circumstellar disks) and photometrically determined ages of 30 Myr or more. Aims. Here, we...

Accurate determination of accretion and photospheric parameters in young stellar objects: The case of two candidate old disks in the Orion Nebula Cluster

Context. Current planet formation models are largely based on the observational constraint that protoplanetary disks have a lifetime of ~3 Myr. Recent studies, however, report the existence of pre-main-sequence stars with signatures of accretion (strictly connected with the presence of circumstellar disks) and photometrically determined ages of 30 Myr or more. Aims. Here, we...

X-shooter spectroscopy of young stellar objects - I. Mass accretion rates of low-mass T Tauri stars in σ Orionis

We present high-quality, medium-resolution X-shooter/VLT spectra in the range 300−2500 nm for a sample of 12 very low mass stars in the σ Orionis cluster. The sample includes eight stars with evidence of disks from Spitzer and four without disks, with masses ranging from 0.08 to 0.3 M⊙. The aim of this first paper is to investigate the reliability of the many accretion tracers...

Explaining millimeter-sized particles in brown dwarf disks

Context. Planets have been detected around a variety of stars, including low-mass objects, such as brown dwarfs. However, such extreme cases are challenging for planet formation models. Recent sub-millimeter observations of disks around brown dwarf measured low spectral indices of the continuum emission that suggest that dust grains grow to mm-sizes even in these very low mass...

The effect of local optically thick regions in the long-wave emission of young circumstellar disks

Multi-wavelength observations of protoplanetary disks in the sub-millimeter continuum have measured spectral indices values which are significantly lower than what is found in the diffuse interstellar medium. Under the assumption that mm-wave emission of disks is mostly optically thin, these data have been generally interpreted as evidence for the presence of mm/cm-sized pebbles...

X-shooter spectroscopy of young stellar objects - II. Impact of chromospheric emission on accretion rate estimates

Context. The lack of knowledge of photospheric parameters and the level of chromospheric activity in young low-mass pre-main sequence stars introduces uncertainties when measuring mass accretion rates in accreting (Class II) young stellar objects. A detailed investigation of the effect of chromospheric emission on the estimates of mass accretion rate in young low-mass stars is...

First spectro-interferometric survey of Be stars - I. Observations and constraints on the disk geometry and kinematics

Context. Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed infrared-excess and emission lines. The phenomena involved in the disk formation still remain highly debated.Aims. To progress in the understanding of the physical process or processes responsible for the mass ejections and test the hypothesis...

Discovery of an old photoevaporating disk in σ Orionis

The photoevaporation of circumstellar disks is a powerful process in the disk dissipation at the origin of the Orion proplyds. This Letter reports the first detection of a photoevaporating disk in the final but long-lasting phase of its evolution. The disk is associated to a low-mass T Tauri member of the σ Ori Cluster. It is characterized by a very low (if any) accretion rate...

Near-infrared interferometric observation of the Herbig Ae star HD 144432 with VLTI/AMBER

Aims. We study the sub-AU-scale circumstellar environment of the Herbig Ae star HD 144432 with near-infrared VLTI/AMBER observations to investigate the structure of its inner dust disk. Methods. The interferometric observations were carried out with the AMBER instrument in the H and K band. We interpret the measured H- and K-band visibilities, the near- and mid-infrared...

Accretion in Ophiuchus brown dwarfs: infrared hydrogen line ratios

Context.Mass accretion rate determinations are fundamental for an understanding of the evolution of pre-main sequence star circumstellar disks.Aims.Magnetospheric accretion models are used to derive values of the mass accretion rates in objects of very different properties, from brown dwarfs to intermediate-mass stars; we test the validity of these models in the brown dwarf...

Spatially resolved PAH emission in the inner disks of Herbig Ae/Be stars

We present adaptive-optics high-angular resolution (~0.1″) spectroscopic observations in the 3 μm region of eight well-known Herbig Ae/Be stars with circumstellar disks. We detected the aromatic emission feature at 3.3 μm for four out of six of our objects with flared disks (HD 169142, HD 97048, HD 100453, HD 100546), some additional features at 3.4 and 3.46 μm, and strong...

Spatially resolving the hot CO around the young Be star 51 Ophiuchi

Tatulli, E. , Millour , F. , Chelli , A. , et al. 2007a, A &A, 464 , 29 Tatulli, E. , Isella , A. , Natta , A. , et al. 2007b, A &A, 464 , 55 Tannirkulam, A. , Monnier , J. D. , Millan-Gabet , R. , et al

Large grains in the disk of CQ Tau

We present 7 mm observations of the dusty disk surrounding the 10 Myr old pre-main-sequence star CQ Tauri obtained at the Very Large Array with 0.8 arcsec resolution and 0.1 mJy rms sensitivity. These observations resolve the 7 mm emission in approximately the north-south direction, confirming previous results obtained with lower resolution. We use a two-layer flared disk model...

Vertical structure models of T Tauri and Herbig Ae/Be disks

In this paper we present detailed models of the vertical structure (temperature and density) of passive irradiated circumstellar disks around T Tauri and Herbig Ae/Be stars. In contrast to earlier work, we use full frequency- and angle-dependent radiative transfer instead of the usual moment equations. We find that this improvement of the radiative transfer has a strong influence...

Constraining the wind launching region in Herbig Ae stars: AMBER/VLTI spectroscopy of HD 104237

A&A Astronomy & Astrophysics E. Tatulli A. Isella A. Natta L. Testi A. Marconi F. Malbet P. Stee R.G. Petrov F. Millour A. Chelli G. Duvert P. Antonelli U. Beckmann Y. Bresson M. Dugué S. Gennari L ... . 2004 , ApJ, 608 , 809 Hartmann , L. , Hewett , R. , & Calvet , N. 1994 , ApJ, 426 , 669 Isella , A. , & Natta , A. 2005 , A &A, 438 , 899 Isella , A. , Testi , L. , & Natta , A. 2006 , A &A, 451 , 951