2,296 research outputs found
The distribution of [/Fe] in the Milky Way disc
Using a sample of red giant stars from the Apache Point Observatory Galactic
Evolution Experiment (APOGEE) Data Release 16, we infer the conditional
distribution in the Milky Way disk
for the -elements Mg, O, Si, S, and Ca. In each bin of [Fe/H] and
Galactocentric radius , we model as a sum of two
Gaussians, representing "low-" and "high-" populations with
scale heights and , respectively.
By accounting for age-dependent and -dependent selection effects in APOGEE,
we infer the [/Fe] distributions that would be found for a fair sample
of long-lived stars covering all . Near the Solar circle, this distribution
is bimodal at sub-solar [Fe/H], with the low- and high- peaks
clearly separated by a minimum at intermediate [/Fe]. In agreement with
previous results, we find that the high- population is more prominent
at smaller , lower [Fe/H], and larger , and that the sequence
separation is smaller for Si and Ca than for Mg, O, and S. We find significant
intrinsic scatter in [/Fe] at fixed [Fe/H] for both the low-
and high- populations, typically -dex. The means,
dispersions, and relative amplitudes of this two-Gaussian description, and the
dependence of these parameters on , [Fe/H], and -element, provide a
quantitative target for chemical evolution models and a test for hydrodynamic
simulations of disk galaxy formation. We argue that explaining the observed
bimodality will probably require one or more sharp transitions in the disk's
gas accretion, star formation, or outflow history in addition to radial mixing
of stellar populations.Comment: Accepted for publication in MNRA
StarHorse: A Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars
Understanding the formation and evolution of our Galaxy requires accurate
distances, ages and chemistry for large populations of field stars. Here we
present several updates to our spectro-photometric distance code, that can now
also be used to estimate ages, masses, and extinctions for individual stars.
Given a set of measured spectro-photometric parameters, we calculate the
posterior probability distribution over a given grid of stellar evolutionary
models, using flexible Galactic stellar-population priors. The code (called
{\tt StarHorse}) can acommodate different observational datasets, prior
options, partially missing data, and the inclusion of parallax information into
the estimated probabilities. We validate the code using a variety of simulated
stars as well as real stars with parameters determined from asteroseismology,
eclipsing binaries, and isochrone fits to star clusters. Our main goal in this
validation process is to test the applicability of the code to field stars with
known {\it Gaia}-like parallaxes. The typical internal precision (obtained from
realistic simulations of an APOGEE+Gaia-like sample) are in
distance, in age, in mass, and mag in
. The median external precision (derived from comparisons with earlier
work for real stars) varies with the sample used, but lies in the range of
for distances, for ages,
for masses, and mag for . We provide StarHorse distances and
extinctions for the APOGEE DR14, RAVE DR5, GES DR3 and GALAH DR1 catalogues.Comment: 21 pages, 12 figures, accepte
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