We present a spectroscopic survey of the stellar population of the {sigma} Orionis cluster. We have obtained spectral types for 340 stars. Spectroscopic data for spectral typing come from several spectrographs with similar spectroscopic coverage and resolution. More than half of the stars in our sample are members confirmed by the presence of lithium in absorption, strong H{alpha} in emission or weak gravity-sensitive features. In addition, we have obtained high-resolution (R~34000) spectra in the H{alpha} region for 169 stars in the region. Radial velocities were calculated from this data set. The radial velocity distribution for members of the cluster is in agreement with previous work. Analysis of the profile of the H{alpha} line and infrared observations reveals two binary systems or fast rotators that mimic the H{alpha} width expected in stars with accretion disks. On the other hand, there are stars with optically thick disks and narrow H{alpha} profiles not expected in stars with accretion disks. This contribution constitutes the largest homogeneous spectroscopic data set of the {sigma} Orionis cluster to date.
This paper presents and discusses information about the observations and data reductions of a time series of photometric measurements of sigma Sco that has been collected in 1972 and 1974. Nearly two thousand standardised uvby magnitude differences sigma Sco minus tau Sco, together with unpublished instrumental differential magnitudes, are herewith supplied. This extended dataset will enhance the applicability of these more than four decades old measurements when used in studies based on data obtained with modern-day techniques such as robotic and space telescopes.
For decades ever since the early detection in the 1990s of the emission spectral features of crystalline silicates in oxygen-rich evolved stars, there is a long-standing debate on whether the crystallinity of the silicate dust correlates with the stellar mass-loss rate. To investigate the relation between the silicate crystallinities and the mass-loss rates of evolved stars, we carry out a detailed analysis of 28 nearby oxygen-rich stars. We derive the mass-loss rates of these sources by modelling their spectral energy distributions from the optical to the far-infrared. Unlike previous studies in which the silicate crystallinity was often measured in terms of the crystalline-to-amorphous silicate mass ratio, we characterize the silicate crystallinities of these sources with the flux ratios of the emission features of crystalline silicates to that of amorphous silicates. This does not require the knowledge of the silicate dust temperatures, which are the major source of uncertainties in estimating the crystalline-to-amorphous silicate mass ratio. With a Pearson correlation coefficient of ~-0.24, we find that the silicate crystallinities and the mass-loss rates of these sources are not correlated. This supports the earlier findings that the dust shells of low mass-loss rate stars can contain a significant fraction of crystalline silicates without showing the characteristic features in their emission spectra.
SimDAL Data Access service for AMES-cond evolutionary tracks
Short Name:
AMES-cond tck
Date:
14 Mar 2019 08:14:12
Publisher:
SVO CAB
Description:
SimDAL data access service for AMES-cond evolutionary tracks. Dust in equilibrium with gas phase, with dust opacities ignored, (only GNS1993 available) valid for Teff smaller than 1400 K
SimDAL Data Access service for AMES-cond isochrones
Short Name:
AMES-cond iso
Date:
14 Mar 2019 08:14:12
Publisher:
SVO CAB
Description:
SimDAL data access service for AMES-cond isochrones. Dust in equilibrium with gas phase, with dust opacities ignored, (only GNS1993 available) valid for Teff smaller than 1400 K
SimDAL Data Access service for AMES-dusty evolutionary tracks
Short Name:
AMES-dusty tck
Date:
14 Mar 2019 08:14:12
Publisher:
SVO CAB
Description:
SimDAL data access service for AMES-dusty evolutionary tracks. Dust in equilibrium with gas phase, (only GNS1993 available) valid for Near-IR studies with Teff larger than 1700 K
SimDAL Data Access service for AMES-dusty isochrones
Short Name:
AMES-dusty iso
Date:
14 Mar 2019 08:14:12
Publisher:
SVO CAB
Description:
SimDAL data access service for AMES-dusty isochrones. Dust in equilibrium with gas phase, (only GNS1993 available) valid for Near-IR studies with Teff larger than 1700 K
SimDAL Search service for AMES-cond isochrones and evolutionary tracks
Short Name:
AMES-cond iso
Date:
14 Mar 2019 08:14:12
Publisher:
SVO CAB
Description:
SimDAL search service for AMES-cond isochrones and evolutionary tracks. Dust in equilibrium with gas phase, with dust opacities ignored, (only GNS1993 available) valid for Teff smaller than 1400 K
SimDAL Search service for AMES-dusty isochrones and evolutionary tracks
Short Name:
AMES-dusty iso
Date:
14 Mar 2019 08:14:12
Publisher:
SVO CAB
Description:
SimDAL search service for AMES-dusty isochrones and evolutionary tracks. Dust in equilibrium with gas phase, (only GNS1993 available) valid for Near-IR studies with Teff larger than 1700 K
The Transiting Exoplanet Survey Satellite (TESS) has a goal of detecting small planets orbiting stars bright enough for mass determination via ground-based radial velocity observations. Here, we present estimates of how many exoplanets the TESS mission will detect, the physical properties of the detected planets, and the properties of the stars that those planets orbit. This work uses stars drawn from the TESS Input Catalog (TIC) Candidate Target List and revises yields from prior studies that were based on Galactic models. We modeled the TESS observing strategy to select approximately 200000 stars at 2-minute cadence, while the remaining stars are observed at 30-minute cadence in full-frame image data. We placed zero or more planets in orbit around each star, with physical properties following measured exoplanet occurrence rates, and used the TESS noise model to predict the derived properties of the detected exoplanets. In the TESS 2-minute cadence mode we estimate that TESS will find 1250+/-70 exoplanets (90% confidence), including 250 smaller than 2R_{Earth}_. Furthermore, we predict that an additional 3100 planets will be found in full-frame image data orbiting bright dwarf stars and more than 10000 around fainter stars. We predict that TESS will find 500 planets orbiting M dwarfs, but the majority of planets will orbit stars larger than the Sun. Our simulated sample of planets contains hundreds of small planets amenable to radial velocity follow-up, potentially more than tripling the number of planets smaller than 4R_{Earth}_ with mass measurements. This sample of simulated planets is available for use in planning follow-up observations and analyses.