119,405 research outputs found
First, Second and Third Massive Stars in Open Clusters
The goal of this paper is to study possibilities of using first, second and
third massive stars in open clusters to estimate total cluster mass and
membership. We built estimator functions with the use of numerical simulations
and analytical approximations and studied the precision and error distribution
of the obtained estimator functions. We found that the distribution of the mass
of first, second and third massive stars shows strong power-law tails at the
high-mass end, thus it is better to use median or mode values instead of
average ones.
We show that the third massive star is a much better estimator then the first
as it is more precise and less dependent on parameters such as maximum allowed
stellar mass.Comment: 24 pages, 5 figures, 5 tables, to appear in Ap
Higgs boson search significance deformations due to mixed-in scalars
The existence of exotic scalars that mix with the Standard Model (SM) Higgs
boson can affect Higgs boson phenomenology in a multitude of ways. We consider
two light Higgs bosons with shared couplings to SM fields and with masses close
to each other, in the range where the h \to WW \to l \nu l \nu is an important
search channel. In this channel, we do not find the dilution of significance of
the `SM-like' Higgs boson that is naively expected because of the mixing. This
is because of leakage of events from the decay of the other scalar into its
signal region. Nevertheless, we show that the broadening of the h\to WW \to l
\nu l \nu significance plots of Standard Model Higgs boson searches could
indicate the first evidence of the the extra scalar state.Comment: 6 pages, 6 figures; v2: all plots now made with the lighter Higgs
mass equal to 125 GeV and other minor corrections made, to be published in
Physics Letters
A Unified tool to estimate Distances, Ages and Masses (UniDAM) from spectrophotometric data
Galactic archaeology - the study of the formation and evolution of the Milky
Way by reconstructing its past from its current constituents - requires precise
and accurate knowledge of stellar parameters for as many stars as possible. To
achieve this a number of large spectroscopic surveys have been undertaken and
are still ongoing. So far consortia carrying out the different spectroscopic
surveys have used different tools to determine stellar parameters of stars from
their derived effective temperatures (Teff), surface gravities (log g) and
metallicities ([Fe/H]) possibly combined with photometric, astrometric,
interferometric or asteroseismic information. Here we aim to homogenise the
stellar characterisation by applying a unified tool to a large set of publicly
available spectrophotometric data. We use spectroscopic data from a variety of
large surveys combined with infra-red photometry from 2MASS and AllWISE and
compare these in a Bayesian manner with PARSEC isochrones to derive probability
density functions (PDFs) for stellar masses, ages and distances. We treat PDFs
of pre-helium-core burning, helium-core burning and post helium-core burning
solutions as well as different peaks in multi-modal PDFs (i.e. each unimodal
sub-PDF) of the different evolutionary phases separately. For over 2.5 million
stars we report mass, age and distance estimate for each evolutionary phase and
unimodal sub-PDF. We report Gaussian, skewed Gaussian, truncated Gaussian,
modified truncated exponential distribution or truncated Student's
t-distribution functions to represent each sub-PDF, allowing to reconstruct
detailed PDFs. Comparisons with stellar parameter estimates from the literature
show good agreement within uncertainties. We present UniDAM - the unified tool
applicable to spectrophotometric data of different surveys to obtain a
homogenised set of stellar parameters
A close look at the Centaurus A group of galaxies: I. Metallicity distribution functions and population gradients in early-type dwarfs
We study dwarf galaxies in the Centaurus A group to investigate their
metallicity and possible environmental effects. The Centaurus A group (at ~4
Mpc from the Milky Way) contains about 50 known dwarf companions of different
morphologies and stellar contents, thus making it a very interesting target to
study how these galaxies evolve. Here we present results for the early-type
dwarf galaxy population in this group. We use archival HST/ACS data to study
the resolved stellar content of 6 galaxies, together with isochrones from the
Dartmouth stellar evolutionary models. We derive photometric metallicity
distribution functions of stars on the upper red giant branch via isochrone
interpolation. The 6 galaxies are moderately metal-poor (=-1.56 to
-1.08), and metallicity spreads are observed (internal dispersions of
sigma_[Fe/H]=0.10 to 0.41 dex). We also investigate the possible presence of
intermediate-age stars, and discuss how these affect our results. The dwarfs
exhibit flat to weak radial metallicity gradients. For the two most luminous,
most metal-rich galaxies, we find statistically significant evidence for at
least two stellar subpopulations: the more metal-rich stars are found in the
center of the galaxies, while the metal-poor ones are more broadly distributed
within the galaxies. We find no clear trend of the derived physical properties
as a function of (present-day) galaxy position in the group, which may be due
to the small sample we investigate. We compare our results to the early-type
dwarf population of the Local Group, and find no outstanding differences,
despite the fact that the Centaurus A group is a denser environment that is
possibly in a more advanced dynamical stage.Comment: 21 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
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