Related papers: Abundance analysis of stars hosting gas-rich debri…
Protoplanetary disks, debris disks, and disrupted or evaporating planets can all feed accretion onto stars. The photospheric abundances of such stars may then reveal the composition of the accreted material. This is especially likely in B…
Around 2% of all A stars have photospheres depleted in refractory elements. This is hypothesized to arise from a preferential accretion of gas rather than dust, but the specific processes and the origin of the material -- circum- or…
Millimeter sized dust grains experience radial velocities exceeding the gas velocities by orders of magnitude. The viscous evolution of the accretion disk adds disk material onto the central star's convective envelope, influencing its…
We present preliminary results of a detailed chemical abundance analysis for a sample of solar-type stars known to exhibit excess infrared emission associated with dusty debris disks. Our sample of 28 stars was selected based on results…
While most debris disks consist of dust with little or no gas, a fraction has significant amounts of gas detected via emission lines of CO, ionized carbon, and/or atomic oxygen. Almost all such gaseous debris disks known are around A-type…
We report the discovery of accretion disks associated with ~ 13 Myr-old intermediate/low-mass stars in h and chi Persei. Optical spectroscopy of ~ 5000 stars in these clusters and a surrounding halo population reveal 32 A-K stars with…
We conducted a survey for infrared excess emission from 16 nearby main sequence shell stars using the Multiband Imaging Photometer for Spitzer (MIPS) on the Spitzer Space Telescope. Shell stars are early-type stars with narrow absorption…
Many disc-type post-asymptotic giant branch (post-AGB) stars are chemically peculiar, showing underabundances of refractory elements in their photospheres that correlate with condensation temperature. The aim of this paper is to investigate…
According to the current paradigm of circumstellar disk evolution, gas-rich primordial disks evolve into gas-poor debris disks compose of second-generation dust. To explore the transition between these phases, we searched for $^{12}$CO,…
Accretion rates from disks around pre-main sequence stars are of importance for our understanding of planetary formation and disk evolution. We provide in this paper estimates of the mass accretion rates in the disks around a large sample…
We describe Spitzer IRAC and MIPS observations of the nearby 25 Myr-old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly…
We present a chemical abundance analysis on the basis of high signal-to- noise and high resolution spectra for 12 stars of our newly defined sample. The selection criterion for the stars of this sample was their position in the `RV Tauri'…
We investigate the age-chemical abundance structure of the outer Galactic disc at a galactocentric distance of r > 10 kpc as recently revealed by the SDSS/APOGEE survey. Two sequences are present in the [alpha/Fe]-[Fe/H] plane with…
Young stars surrounded by disks with very low mass accretion rates are likely in the final stages of inner disk evolution and therefore particularly interesting to study. We present ultraviolet (UV) observations of the ~5-9 Myr old stars…
Debris disks are second generation dusty disks thought to be devoid of gas. However, this idea has been challenged in the last years by gas detections in some systems. We compiled a database of 301 debris disks and collected…
HD 100453 has an IR spectral energy distribution (SED) which can be fit with a power-law plus a blackbody. Previous analysis of the SED suggests that the system is a young Herbig Ae star with a gas-rich, flared disk. We reexamine the…
Stars collect most of their mass during the protostellar stage, yet the accretion luminosity and stellar parameters, which are needed to compute the mass accretion rate, are poorly constrained for the youngest sources. The aim of this work…
A classical paradox in high-mass star formation is that powerful radiation pressure can halt accretion, preventing further growth of a central star. Disk accretion has been proposed to solve this problem, but the disks and the accretion…
We report on the discovery of correlations between dust and CO gas tracers of the 0.1-10 au region in planet-forming disks around young intermediate-mass stars. The abundance of refractory elements on stellar photospheres decreases as the…
Debris disks are usually thought to be gas-poor, the gas being dissipated by accretion or evaporation during the protoplanetary phase. HD141569A is a 5 Myr old star harboring a famous debris disk, with multiple rings and spiral features. We…