508 research outputs found
The Gaia-ESO Survey: Membership probabilities for stars in 32 open clusters from 3D kinematics
The Gaia-ESO Survey (GES) observed many open clusters as part of its
programme to spectroscopically characterise the various Milky Way populations.
GES spectroscopy and Gaia astrometry from its second data release are used here
to assign membership probabilities to targets towards 32 open clusters with
ages from 1-3800 Myr, based on maximum likelihood modelling of the 3D
kinematics of the cluster and field populations. From a parent catalogue of
14398 individual targets, 5033 stars with uniformly determined 3D velocities,
, and chemistry are assigned cluster membership with
probability , and with an average probability of 0.991. The robustness of
the membership probabilities is demonstrated using independent membership
criteria (lithium and parallax) in two of the youngest clusters. The addition
of radial velocities improves membership discrimination over proper motion
selection alone, especially in more distant clusters. The
kinematically-selected nature of the membership lists, independent of
photometry and chemistry, makes the catalogue a valuable resource for testing
stellar evolutionary models and investigating the time evolution of various
parameters
The Gaia-ESO Survey: Pre-Main Sequence Stars in the Young Open Cluster NGC 3293
The young open cluster NGC3293 is included in the observing program of the Gaia-ESO survey (GES). The radial velocity values provided have been used to assign cluster membership probabilities by means of a single-variable parametric analysis. These membership probabilities are compared to the results of the photometric membership assignment of NGC3293, based on UBV RI photometry. The agreement of the photometric and kinematic member samples amounts to 65%, and could increase to 70% as suggested by the analysis of the differences between both samples. A number of photometric PMS candidate members of spectral type F are found, which are confirmed by the results from VPHAS photometry and SED fitting for the stars in common with VPHAS and GES data sets. Excesses at mid- and near-infrared wavelengths, and signs of Hα emission, are investigated for them. Marginal presence of Hα emission or infilling is detected for the candidate members. Several of them exhibit moderate signs of U excess and weak excesses at mid-IR wavelengths. We suggest that these features originate from accretion disks in their last stages of evolution
The Gaia-ESO Survey: membership and initial mass function of the. Velorum cluster
Context. Understanding the properties of young open clusters, such as the Initial Mass Function (IMF), star formation history and dynamic evolution, is crucial to obtain reliable theoretical predictions of the mechanisms involved in the star formation process.
Aims. We want to obtain a list, as complete as possible, of confirmed members of the young open cluster γ Velorum, with the aim of deriving general cluster properties such as the IMF.
Methods. We used all available spectroscopic membership indicators within the Gaia-ESO public archive together with literature photometry and X-ray data and, for each method, we derived the most complete list of candidate cluster members. Then, we considered photometry, gravity and radial velocities as necessary conditions to select a subsample of candidates whose membership was confirmed by using the lithium and Hα lines and X-rays as youth indicators.
Results.We found 242 confirmed and 4 possible cluster members for which we derived masses using very recent stellar evolutionary models. The cluster IMF in the mass range investigated in this study shows a slope of α = 2.6 ± 0.5 for 0.5 < M/M⊙ < 1.3 and α = 1.1 ± 0.4 for 0.16 < M/M⊙ < 0.5 and is consistent with a standard IMF.
Conclusions. The similarity of the IMF of the young population around γ2Vel to that in other star forming regions and the field suggests it may have formed through very similar processes
The Gaia-ESO Survey: the selection function of the Milky Way field stars
The Gaia-ESO Survey was designed to target all major Galactic components (i.e. bulge, thin and thick discs, halo and clusters), with the goal of constraining the chemical and dynamical evolution of the Milky Way. This paper presents the methodology and considerations that drive the selection of the targeted, allocated and successfully observed Milky Way field stars. The detailed understanding of the survey construction, specifically the influence of target selection criteria on observed Milky Way field stars is required in order to analyse and interpret the survey data correctly. We present the target selection process for the Milky Way field stars observed with Very Large Telescope/Fibre Large Array Multi Element Spectrograph and provide the weights that characterize the survey target selection. The weights can be used to account for the selection effects in the Gaia-ESO Survey data for scientific studies. We provide a couple of simple examples to highlight the necessity of including such information in studies of the stellar populations in the Milky Way
The Gaia-ESO Survey: Pre-main-sequence stars in the young open cluster NGC 3293
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.The young open cluster NGC3293 is included in the observing program of the Gaia-ESO survey (GES). The radial velocity values provided have been used to assign cluster membership probabilities by means of a single-variable parametric analysis. These membership probabilities are compared to the results of the photometric membership assignment of NGC3293, based on UBVRI photometry. The agreement of the photometric and kinematic member samples amounts to 65 per cent, and could increase to 70 per cent as suggested by the analysis of the differences between both samples. A number of photometric PMS candidate members of spectral type F are found, which are confirmed by the results from VPHAS photometry and SED fitting for the stars in common with VPHAS and GES data sets. Excesses at mid- and near-infrared wavelengths, and signs of Hα emission, are investigated for them. Marginal presence of Hα emission or infilling is detected for the candidate members. Several of them exhibit moderate signs of U excess and weak excesses at mid-IR wavelengths. We suggest that these features originate from accretion discs in their last stages of evolution
Gaia-ESO Survey: Gas dynamics in the Carina nebula through optical emission lines
Aims. We present observations from the Gaia-ESO Survey in the lines of Hα, [N II], [S II] and He I of nebular emission in the central part of the Carina Nebula.
Methods. We investigate the properties of the two already known kinematic components (approaching and receding, respectively), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV >50 km/s) gas emission.
Results. We show that gas giving rise to Hα and He I emission is dynamically well correlated, but not identical, to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arises from several distinct shell-like expanding regions, the most evident found around η Car, the Trumpler 14 core, and the starWR25. Such “shells" are non-spherical, and show distortions probably caused by collisions with other shells or colder, higher-density gas. Part of them is also obscured by foreground dust lanes, while only very little dust is found in their interior. Preferential directions, parallel to the dark dust lanes, are found in the shell geometries and physical properties, probably related to strong density gradients in the studied region. We also find evidence that the ionizing flux emerging from η Car and the surrounding Homunculus nebula varies with polar angle. The high-velocity components in the wings of Hα are found to arise from expanding dust reflecting the η Car spectrum
The Gaia-ESO Survey: pre-main-sequence stars in the young open cluster NGC 3293
The young open cluster NGC3293 is included in the observing program of the Gaia-ESO survey (GES). The radial velocity values provided have been used to assign cluster membership probabilities by means of a single-variable parametric analysis. These membership probabilities are compared to the results of the photometric membership assignment of NGC3293, based on UBVRI photometry. The agreement of the photometric and kinematic member samples amounts to 65 per cent, and could increase to 70 per cent as suggested by the analysis of the differences between both samples. A number of photometric PMS candidate members of spectral type F are found, which are confirmed by the results from VPHAS photometry and SED fitting for the stars in common with VPHAS and GES data sets. Excesses at mid- and near-infrared wavelengths, and signs of Hα emission, are investigated for them. Marginal presence of Hα emission or infilling is detected for the candidate members. Several of them exhibit moderate signs of U excess and weak excesses at mid-IR wavelengths. We suggest that these features originate from accretion discs in their last stages of evolution
The Gaia-ESO Survey: evidence of atomic diffusion in M67?
Investigating the chemical homogeneity of stars born from the same molecular cloud at virtually the same time is very important for our understanding of the chemical enrichment of the interstellar medium and with it the chemical evolution of the Galaxy. One major cause of inhomogeneities in the abundances of open clusters is stellar evolution of the cluster members. In this work, we investigate variations in the surface chemical composition of member stars of the old open cluster M67 as a possible consequence of atomic diffusion effects taking place during the main-sequence phase. The abundances used are obtained from high-resolution UVES/FLAMES spectra within the framework of the Gaia-ESO Survey. We find that the surface abundances of stars on the main sequence decrease with increasing mass reaching a minimum at the turn-off. After deepening of the convective envelope in subgiant branch stars, the initial surface abundances are restored. We found the measured abundances to be consistent with the predictions of stellar evolutionary models for a cluster with the age and metallicity of M67. Our findings indicate that atomic diffusion poses a non-negligible constraint on the achievable precision of chemical tagging methods
The Gaia-ESO survey: Matching chemodynamical simulations to observations of the Milky Way
The typical methodology for comparing simulated galaxies with observational
surveys is usually to apply a spatial selection to the simulation to mimic the
region of interest covered by a comparable observational survey sample. In this
work we compare this approach with a more sophisticated post-processing in
which the observational uncertainties and selection effects (photometric,
surface gravity and effective temperature) are taken into account. We compare a
`solar neighbourhood analogue' region in a model Milky Way-like galaxy
simulated with RAMSES-CH with fourth release Gaia-ESO survey data. We find that
a simple spatial cut alone is insufficient and that observational uncertainties
must be accounted for in the comparison. This is particularly true when the
scale of uncertainty is large compared to the dynamic range of the data, e.g.
in our comparison, the [Mg/Fe] distribution is affected much more than the more
accurately determined [Fe/H] distribution. Despite clear differences in the
underlying distributions of elemental abundances between simulation and
observation, incorporating scatter to our simulation results to mimic
observational uncertainty produces reasonable agreement. The quite complete
nature of the Gaia-ESO survey means that the selection function has minimal
impact on the distribution of observed age and metal abundances but this would
become increasingly more important for surveys with narrower selection
functions
The Gaia-ESO Survey: The inner disk, intermediate-age open cluster Trumpler 23
Milky Way open clusters are very diverse in terms of age, chemical
composition, and kinematic properties. Intermediate-age and old open clusters
are less common, and it is even harder to find them inside the solar
Galactocentric radius, due to the high mortality rate and strong extinction
inside this region. NGC 6802 is one of the inner disk open clusters (IOCs)
observed by the -ESO survey (GES). This cluster is an important target
for calibrating the abundances derived in the survey due to the kinematic and
chemical homogeneity of the members in open clusters. Using the measurements
from -ESO internal data release 4 (iDR4), we identify 95 main-sequence
dwarfs as cluster members from the GIRAFFE target list, and eight giants as
cluster members from the UVES target list. The dwarf cluster members have a
median radial velocity of km s, while the giant cluster
members have a median radial velocity of km s and a median
[Fe/H] of dex. The color-magnitude diagram of these cluster
members suggests an age of Gyr, with and
. We perform the first detailed chemical abundance analysis of NGC
6802, including 27 elemental species. To gain a more general picture about
IOCs, the measurements of NGC 6802 are compared with those of other IOCs
previously studied by GES, that is, NGC 4815, Trumpler 20, NGC 6705, and
Berkeley 81. NGC 6802 shows similar C, N, Na, and Al abundances as other IOCs.
These elements are compared with nucleosynthetic models as a function of
cluster turn-off mass. The , iron-peak, and neutron-capture elements
are also explored in a self-consistent way
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