289 research outputs found
Low altitude temperature and humidity profile data for application to aircraft noise propagation
A data search of the weather statistics from 11 widely dispersed geographical locations within the continental United States was conducted. The sites, located long both sea-coasts and in the interior, span the northern, southern, and middle latitudes. The weather statistics, retrieved from the records of these 11 sites, consist of two daily observations taken over a 10-year period. The data were sorted with respect to precipitation and surface winds and classified into temperature intervals of 5 C and relative humidity intervals of 10 percent for the lower 1400 meters of the atmosphere. These data were assembled in a statistical format and further classified into altitude increments of 200 meters. The data are presented as sets of tables for each site by season of the year and include both daily observations
Chemical similarities between Galactic bulge and local thick disk red giant stars
The evolution of the Milky Way bulge and its relationship with the other
Galactic populations is still poorly understood. The bulge has been suggested
to be either a merger-driven classical bulge or the product of a dynamical
instability of the inner disk. To probe the star formation history, the initial
mass function and stellar nucleosynthesis of the bulge, we performed an
elemental abundance analysis of bulge red giant stars. We also completed an
identical study of local thin disk, thick disk and halo giants to establish the
chemical differences and similarities between the various populations.
High-resolution infrared spectra of 19 bulge giants and 49 comparison giants in
the solar neighborhood were acquired with Gemini/Phoenix. All stars have
similar stellar parameters but cover a broad range in metallicity. A standard
1D local thermodynamic equilibrium analysis yielded the abundances of C, N, O
and Fe. A homogeneous and differential analysis of the bulge, halo, thin disk
and thick disk stars ensured that systematic errors were minimized. We confirm
the well-established differences for [O/Fe] (at a given metallicity) between
the local thin and thick disks. For the elements investigated, we find no
chemical distinction between the bulge and the local thick disk, which is in
contrast to previous studies relying on literature values for disk dwarf stars
in the solar neighborhood. Our findings suggest that the bulge and local thick
disk experienced similar, but not necessarily shared, chemical evolution
histories. We argue that their formation timescales, star formation rates and
initial mass functions were similar.Comment: Accepted for publication in A&A, 5 page
Early Galactic Evolution of Carbon, Nitrogen and Oxygen
We present results on carbon, nitrogen, and oxygen abundances for a sample of
unevolved metal-poor stars with metallicities in the range -0.3< [Fe/H]< -3.
Oxygen abundances derived from different indicators are compared showing
consistently that in the range 0.3 >[Fe/H]>-3.0, the [O/Fe] ratio increases
from approximately 0 to 1. We find a good agreement between abundances based on
the forbidden line, the OH and IR triplet lines when gravities based on
Hipparcos} parallaxes are considered for the sample stars. Gravities derived
from LTE ionization balance in metal-poor stars with [Fe/H]< -1 are likely too
low, and could be responsible for an underestimation of the oxygen abundances
derived using the [OI] line. [C/Fe] and [N/Fe] ratios appear to be constant,
independently of metallicity, in the same range. However, they show larger
scatter than oxygen at a given metallicity, which could reflect the larger
variety of stellar production sites for these other elements.Comment: 10 pages, 3 figures, To appear in the proceedings of the conference
"The Chemical Evolution of The Milky Way: Stars versus Clusters", eds. F.
Matteucci and F. Giovannelli, Vulcano, Italy, September 20-24 199
Population Response of Three Quail Species to Habitat Restoration in South Texas
Maintaining and increasing usable space is paramount for maintaining and increasing wild quail. Aside from weather and other factors that can temporarily reduce densities, range-wide, no factor has as much influence on quail populations as the amount of habitat present across the landscape. In the field of quail management, ââbad newsââ is the norm, as many articles begin by explaining how a select species has declined. Here we provide good news and use 4 empirical examples of population increases for 3 quail species following creation of usable space and restoration of patch connectivity. From 2008â2014, a suite of independent projects aimed at increasing usable space for quail was initiated across South Texas. These projects included 3 focused on northern bobwhites (Colinus virginianus), 1 focused on scaled quail (Callipepla squamata), and 1 landowner-executed project focused on Montezuma quail (Cyrtonyx montezumae). Through the correction of attributes limiting habitat, bobwhite numbers increased 22â378% across 2 studies. On one particular study site, native grassland restoration resulted in the colonization of bobwhites from adjacent areas to 1 bobwhite/1.2 ha from nearly 0. For scaled quail in South Texas, reducing buffelgrass standing crop via grazing from about 2,240 kg/ha to 1,008 kg/ha resulted in the recolonization of a previously unoccupied habitat patch to a density of 1 scaled quail/6 ha. Finally, clearing monotypic stands of the invasive native plant, ash juniper (Juniperus ashei) in the Edwards Plateau of Texas, resulted in the reestablishment of native grasses and forbs and thus recolonization by Montezuma quail from nearby areas. Although habitat restoration and management can be a painstaking and lengthy process, addressing limiting factors to quail occupancy is the only known way to increase wild quail populations. We hope that highlighting these particular studies will provide inspiration to those interested in restoring and increasing quail across the US
The RAVE Survey: Constraining the Local Galactic Escape Speed
We report new constraints on the local escape speed of our Galaxy. Our
analysis is based on a sample of high velocity stars from the RAVE survey and
two previously published datasets. We use cosmological simulations of disk
galaxy formation to motivate our assumptions on the shape of the velocity
distribution, allowing for a significantly more precise measurement of the
escape velocity compared to previous studies. We find that the escape velocity
lies within the range 498\kms < \ve < 608 \kms (90 per cent confidence), with
a median likelihood of 544\kms. The fact that \ve^2 is significantly
greater than 2\vc^2 (where \vc=220\kms is the local circular velocity)
implies that there must be a significant amount of mass exterior to the Solar
circle, i.e. this convincingly demonstrates the presence of a dark halo in the
Galaxy. For a simple isothermal halo, one can calculate that the minimum radial
extent is kpc. We use our constraints on \ve to determine the mass
of the Milky Way halo for three halo profiles. For example, an adiabatically
contracted NFW halo model results in a virial mass of
and virial radius of
kpc (90 per cent confidence). For this model the circular
velocity at the virial radius is 142^{+31}_{-21}\kms. Although our halo
masses are model dependent, we find that they are in good agreement with each
other.Comment: 19 pages, 9 figures, MNRAS (accepted). v2 incorporates minor cosmetic
revisions which have no effect on the results or conclusion
Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants
We obtained FLAMES-GIRAFFE spectra (R=22,500) at the ESO Very Large Telescope
for 650 bulge red giant branch (RGB) stars and performed spectral synthesis to
measure Mg, Ca, Ti, and Si abundances. This sample is composed of 474 giant
stars observed in 3 fields along the minor axis of the Galactic bulge and at
latitudes b=-4, b=-6, b=-12. Another 176 stars belong to a field containing the
globular cluster NGC 6553, located at b=-3 and 5 degrees away from the other
three fields along the major axis. Our results confirm, with large number
statistics, the chemical similarity between the Galactic bulge and thick disk,
which are both enhanced in alpha elements when compared to the thin disk. In
the same context, we analyze [alpha/Fe] vs. [Fe/H] trends across different
bulge regions. The most metal rich stars, showing low [alpha/Fe] ratios at b=-4
disappear at higher Galactic latitudes in agreement with the observed
metallicity gradient in the bulge. Metal-poor stars ([Fe/H]<-0.2) show a
remarkable homogeneity at different bulge locations. We have obtained further
constrains for the formation scenario of the Galactic bulge. A metal-poor
component chemically indistinguishable from the thick disk hints for a fast and
early formation for both the bulge and the thick disk. Such a component shows
no variation, neither in abundances nor kinematics, among different bulge
regions. A metal-rich component showing low [alpha/Fe] similar to those of the
thin disk disappears at larger latitudes. This allows us to trace a component
formed through fast early mergers (classical bulge) and a disk/bar component
formed on a more extended timescale.Comment: 13 pages, 17 figures. Accepted for publication in Astronomy and
Astrophysic
Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. II. Ages, metallicities, detailed elemental abundances, and connections to the Galactic thick disc
The Bulge is the least understood major stellar population of the Milky Way.
Most of what we know about the formation and evolution of the Bulge comes from
bright giant stars. The underlying assumption that giants represent all the
stars, and accurately trace the chemical evolution of a stellar population, is
under debate. In particular, recent observations of a few microlensed dwarf
stars give a very different picture of the evolution of the Bulge from that
given by the giant stars. [ABRIDGED] We perform a detailed elemental abundance
analysis of dwarf stars in the Galactic bulge, based on high-resolution spectra
that were obtained while the stars were optically magnified during
gravitational microlensing events. [ABRIDGED] We present detailed elemental
abundances and stellar ages for six new dwarf stars in the Galactic bulge.
Combining these with previous events, here re-analysed with the same methods,
we study a homogeneous sample of 15 stars, which constitute the largest sample
to date of microlensed dwarf stars in the Galactic bulge. We find that the
stars span the full range of metallicities from [Fe/H]=-0.72 to +0.54, and an
average metallicity of =-0.08+/-0.47, close to the average metallicity
based on giant stars in the Bulge. Furthermore, the stars follow well-defined
abundance trends, that for [Fe/H]<0 are very similar to those of the local
Galactic thick disc. This suggests that the Bulge and the thick disc have had,
at least partially, comparable chemical histories. At sub-solar metallicities
we find the Bulge dwarf stars to have consistently old ages, while at
super-solar metallicities we find a wide range of ages. Using the new age and
abundance results from the microlensed dwarf stars we investigate possible
formation scenarios for the Bulge.Comment: New version accepted for publication in Astronomy and Astrophysic
Multi-Element Abundance Measurements from Medium-Resolution Spectra. II. Catalog of Stars in Milky Way Dwarf Satellite Galaxies
We present a catalog of Fe, Mg, Si, Ca, and Ti abundances for 2961 red giant
stars that are likely members of eight dwarf satellite galaxies of the Milky
Way (MW): Sculptor, Fornax, Leo I, Sextans, Leo II, Canes Venatici I, Ursa
Minor, and Draco. For the purposes of validating our measurements, we also
observed 445 red giants in MW globular clusters and 21 field red giants in the
MW halo. The measurements are based on Keck/DEIMOS medium-resolution
spectroscopy combined with spectral synthesis. We estimate uncertainties in
[Fe/H] by quantifying the dispersion of [Fe/H] measurements in a sample of
stars in monometallic globular clusters. We estimate uncertainties in Mg, Si,
Ca, and Ti abundances by comparing our medium-resolution spectroscopic
measurements to high-resolution spectroscopic abundances of the same stars. For
this purpose, our DEIMOS sample included 132 red giants with published
high-resolution spectroscopy in globular clusters, the MW halo field, and dwarf
galaxies. The standard deviations of the differences in [Fe/H] and [alpha/Fe]
(the average of [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe]) between the two samples
is 0.15 and 0.16, respectively. This catalog represents the largest sample of
multi-element abundances in dwarf galaxies to date. The next papers in this
series draw conclusions on the chemical evolution, gas dynamics, and star
formation histories from the catalog presented here. The wide range of dwarf
galaxy luminosity reveals the dependence of dwarf galaxy chemical evolution on
galaxy stellar mass.Comment: 26 pages, 22 figures, 4 machine-readable tables (available in the
source file; click "Other formats"); accepted for publication in ApJ
Supplements; updated acknowledgments in v
A precision study of two eclipsing white dwarf plus M dwarf binaries
We use a combination of X-shooter spectroscopy, ULTRACAM high-speed
photometry and SOFI near-infrared photometry to measure the masses and radii of
both components of the eclipsing post common envelope binaries SDSS J1212-0123
and GK Vir. For both systems we measure the gravitational redshift of the white
dwarf and combine it with light curve model fits to determine the inclinations,
masses and radii. For SDSS J1212-0123 we find a white dwarf mass and radius of
0.439 +/- 0.002 Msun and 0.0168 +/- 0.0003 Rsun, and a secondary star mass and
radius of 0.273 +/- 0.002 Msun and 0.306 +/- 0.007 Rsun. For GK Vir we find a
white dwarf mass and radius of 0.564 +/- 0.014 Msun and 0.0170 +/- 0.0004 Rsun,
and a secondary star mass and radius of 0.116 +/- 0.003 Msun and 0.155 +/-
0.003 Rsun. The mass and radius of the white dwarf in GK Vir are consistent
with evolutionary models for a 50,000K carbon-oxygen core white dwarf. Although
the mass and radius of the white dwarf in SDSS J1212-0123 are consistent with
carbon-oxygen core models, evolutionary models imply that a white dwarf with
such a low mass and in a short period binary must have a helium core. The mass
and radius measurements are consistent with helium core models but only if the
white dwarf has a very thin hydrogen envelope, which has not been predicted by
evolutionary models. The mass and radius of the secondary star in GK Vir are
consistent with evolutionary models after correcting for the effects of
irradiation by the white dwarf. The secondary star in SDSS J1212-0123 has a
radius ~9 per cent larger than predicted.Comment: 21 pages, 14 Figures and 11 Tables. Accepted for publication in MNRA
Evolutionary synthesis of galaxies at high spectral resolution with the code PEGASE-HR
We present PEGASE-HR, a new stellar population synthesis program generating
high resolution spectra (R=10 000) over the optical range lambda=400--680 nm.
It links the spectro-photometric model of galaxy evolution PEGASE.2 (Fioc &
Rocca-Volmerange 1997) to an updated version of the ELODIE library of stellar
spectra observed with the 193 cm telescope at the Observatoire de
Haute-Provence (Prugniel & Soubiran 2001a). The ELODIE star set gives a fairly
complete coverage of the Hertzprung-Russell (HR) diagram and makes it possible
to synthesize populations in the range [Fe/H]=-2 to +0.4. This code is an
exceptional tool for exploring signatures of metallicity, age, and kinematics.
We focus on a detailed study of the sensitivity to age and metallicity of the
high-resolution stellar absorption lines and of the classical metallic indices
proposed until now to solve the age-metallicity degeneracy. Validity tests on
several stellar lines are performed by comparing our predictions for Lick
indices to the models of other groups. The comparison with the lower resolution
library BaSeL (Lejeune et al. 1997) confirms the quality of the ELODIE library
when used for simple stellar populations (SSPs) from 10 Myr to 20 Gyr.
Predictions for the evolved populations of globular clusters and elliptical
galaxies are given and compared to observational data. Two new high-resolution
indices are proposed around the Hgamma line. They should prove useful in the
analysis of spectra from the new generation of telescopes and spectrographs.Comment: 18 pages, 18 figures. Astronomy & Astrophysics, in press. The models
are available at http://www.iap.fr/pegase
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