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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...

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...

X-shooter spectroscopy of young stellar objects in Lupus - Accretion properties of class II and transitional objects

The mass accretion rate, Ṁacc, is a key quantity for the understanding of the physical processes governing the evolution of accretion discs around young low-mass (M⋆ ≲ 2.0 M⊙) stars and substellar objects (YSOs). We present here the results of a study of the stellar and accretion properties of the (almost) complete sample of class II and transitional YSOs in the Lupus I, II, III...

Constraints on the radial distribution of the dust properties in the CQ Tauri protoplanetary disk

Context. Grain growth in protoplanetary disks is the first step towards the formation of the rocky cores of planets. Models predict that grains grow, migrate, and fragment in the disk and predict varying dust properties as a function of radius, age, and physical properties. High-angular resolution observations at more than one (sub-)mm wavelength are the essential tool for...

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

X-shooter spectroscopy of young stellar objects - V. Slow winds in T Tauri stars

Disks around T Tauri stars are known to lose mass, as best shown by the profiles of the forbidden emission lines of low-ionization species. At least two separate kinematic components have been identified, one characterized by velocity shifts of tens to hundreds of km s-1 (HVC) and one with a much lower velocity of a few km s-1 (LVC). The HVC are convincingly associated to the...

X-shooter spectroscopy of FU Tauri A

We have analyzed a broad-band optical and near-infrared spectrum of FU Tau A, which is a presumed young brown dwarf in the Taurus star forming region that has intrigued both theorists and observers by its overluminosity in the Hertzsprung-Russell (HR) diagram with respect to standard pre-main sequence evolutionary models. FU Tau A is brighter than any other Taurus member of the...

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...

U-band study of the accretion properties in the σ Orionis star-forming region

This paper presents the results of an U band survey with FORS1/VLT of a large area in the σ Ori star-forming region. We combine the U-band photometry with literature data to compute accretion luminosity and mass accretion rates from the U-band excess emission for all objects (187) detected by Spitzer in the FORS1 field and classified by Hernandez et al. as likely members of the...

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...

Millimetre spectral indices of transition disks and their relation to the cavity radius

Context. Transition disks are protoplanetary disks with inner depleted dust cavities that are excellent candidates for investigating the dust evolution when there is a pressure bump. A pressure bump at the outer edge of the cavity allows dust grains from the outer regions to stop their rapid inward migration towards the star and to efficiently grow to millimetre sizes. Dynamical...

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...

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...

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...

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...