1,174 research outputs found
Single Stellar Populations in the Near-Infrared - I. Preparation of the IRTF spectral stellar library
We present a detailed study of the stars of the IRTF spectral library to
understand its full extent and reliability for use with Stellar Population (SP)
modeling. The library consist of 210 stars, with a total of 292 spectra,
covering the wavelength range of 0.94 to 2.41 micron at a resolution R = 2000.
For every star we infer the effective temperature (Teff), gravity (logg) and
metallicity ([Z/Zsun]) using a full-spectrum fitting approach in a section of
the K band (2.19 to 2.34 micron) and temperature-NIR colour relations. We test
the flux calibration of these stars by calculating their integrated colours and
comparing them with the Pickles library colour-temperature relations. We also
investigate the NIR colours as a function of the calculated effective
temperature and compared them in colour-colour diagrams with the Pickles
library. This latter test shows a good broad-band flux calibration, important
for the SP models. Finally, we measure the resolution R as a function of
wavelength. We find that the resolution increases as a function of lambda from
about 6 angstrom in J to 10 angstrom in the red part of the K-band. With these
tests we establish that the IRTF library, the largest currently available
general library of stars at intermediate resolution in the NIR, is an excellent
candidate to be used in stellar population models. We present these models in
the next paper of this series.Comment: 17 pages, 19 figures. Accepted for publication in Astronomy and
Astrophysic
Frequency modulated few-cycle optical pulse trains induced controllable ultrafast coherent population oscillations in three-level atomic systems
We report a study on the ultrafast coherent population oscillations (UCPO) in
two level atoms induced by the frequency modulated few-cycle optical pulse
train. The phenomenon of UCPO is investigated by numerically solving the
optical Bloch equations beyond the rotating wave approximation. We demonstrate
that the quantum state of the atoms and the frequency of UCPO may be controlled
by controlling the number of pulses in the pulse trains and the pulse
repetition time respectively. Moreover, the robustness of the population
inversion against the variation of the laser pulse parameters is also
investigated. The proposed scheme may be useful for the creation of atoms in
selected quantum state for desired time duration and may have potential
applications in ultrafast optical switching
Evidence for intermediate-age stellar populations in early-type galaxies from K-band spectroscopy
The study of stellar populations in early-type galaxies in different
environments is a powerful tool for constraining their star formation
histories. This study has been traditionally restricted to the optical range,
where dwarfs around the turn-off and stars at the base of the RGB dominate the
integrated light at all ages. The near-infrared spectral range is especially
interesting since in the presence of an intermediate-age population, AGB stars
are the main contributors. In this letter, we measure the near-infrared indices
NaI and D for a sample of 12 early-type galaxies in low density
environments and compare them with the Fornax galaxy sample presented by Silva
et al. (2008). The analysis of these indices in combination with Lick/IDS
indices in the optical range reveals i) the NaI index is a metallicity
indicator as good as C4668 in the optical range, and ii) D is a
tracer of intermediate-age stellar populations. We find that low-mass galaxies
in low density environments show higher NaI and D than those located
in Fornax cluster, which points towards a late stage of star formation for the
galaxies in less dense environments, in agreement with results from other
studies using independent methods.Comment: 7 pages, 3 figures, accepted for publication in ApJ
(—)-3-(1-Phenylpropyl)-4-hydroxycoumarin
The title compound [generic name: (—)-phenprocoumon], C18H16O3, monoclinic, P21. Z = 4 with two molecules/asymmetric unit, a= 7·171 (1), b = 17·751 (5), c = 11·752 (2) Å, β = 92·58 (2)°, V = 1494 Å3, Dc = 1·28, d0 = 1·30 (2) g cm-3 is pseudoisostructural with the crystalline racemate as suggested by a similarity in cell constants and symmetry. Structural differences involve small translations and where the racemate crystal contains layers of (—) and layers of (+) enantiomers, the (—) crystal contains one layer nearly identical with the (—) layer in the racemate while the 01olecules in the other layer adopt a different conformation so that packing is similar to that in the (+) layer of the racemate. Already high thermal motion in the racemate is dramatically increased in the enantiomeric structure which has a larger cell volume. Hydrogen bonding occurs along the a direction with O···O distances of 2·617 (5) and 2·587 (6) Å. The final R is 0·094 on 3060 counter-collected data
The X-shooter Spectral Library (XSL): I. DR1. Near-ultraviolet through optical spectra from the first year of the survey
We present the first release of XSL, the X-Shooter Spectral Library. This
release contains 237 stars spanning the wavelengths 3000--10200 \AA\ observed
at a resolving power . The spectra
were obtained at ESO's 8-m Very Large Telescope (VLT). The sample contains O --
M, long-period variable (LPV), C and S stars. The spectra are flux-calibrated
and telluric-corrected. We describe a new technique for the telluric
correction. The wavelength coverage, spectral resolution and spectral type of
this library make it well suited to stellar population synthesis of galaxies
and clusters, kinematical investigation of stellar systems and studying the
physics of cool stars.Comment: 41 pages, 38 figures, 5 tables. Accepted for publication in A&A.
Webpage: http://xsl.u-strasbg.fr
The Crystal and Molecular Structure and Absolute Configuration of (—)-(\u3ci\u3eS\u3c/i\u3e)-Warfarin
The crystal and molecular structure and the absolute configuration of (—)-(S)-warfarin, C19H1604, have been determined by X-ray crystallographic techniques. Crystals of (—)-(S)-warfarin are orthorhombic, space group P212121, with a=10·883 (3), b=9·562 (3), and c=14·902 (5) Å. Solution of the structure was by direct methods, and refinement by least-squares calculations led to a conventional R of 0·053 (Mo Kα data). The molecule crystallizes as the intramolecular hemiketal and thus may be described as (2S,4S)-2,3H-2-methyl-4-phenyl-5-oxobenzopyrano[3,4-e]dihydropyran-2-ol. The absolute configuration was confirmed by recollecting with Cu Kα radiation a group of reflect ions predicted to have the greatest observable Bijvoet differences based on the anomalous scattering of oxygen and the parameters from the refinement with Mo Kα data. A group of 51 Friedel pairs, 86% of which indicate the S enantiomer, gave a 17% decrease in the residual over the R enantiomer. Refinement of the imaginary part of the anomalous dispersion of oxygen gave a value of 0·037 for Δf
Cosmological formation and chemical evolution of an elliptical galaxy
We aim at studying the effect of a cosmologically motivated gas infall law
for the formation of a massive elliptical galaxy in order to understand its
impact on the formation of the spheroids. We replace the empirical infall law
of the model by Pipino & Matteucci with a cosmologically derived infall law for
the formation of an elliptical galaxy. We constrast our predictions with
observations. We also compare the obtained results with those of Pipino &
Matteucci. We computed models with and without galactic winds: we found that
models without wind predict a too large current SNIa rate. In particular, the
cosmological model produces a current SNIa which is about ten times higher than
the observed values. Moreover models without wind predict a large current SNII
rate, too large even if compared with the recent GALEX data. The predicted SNII
rate for the model with wind, on the other hand, is too low if compared with
the star formation histories given by GALEX. Last but not least, the mean value
for the [Mg/Fe] ratio in the dominant stellar population of the simulated
galaxy, as predicted by the cosmological model, is too low if compared to
observations. This is, a very important result indicating that the cosmological
infall law is in contrast with the chemical evolution. A cosmologically derived
infall law for an elliptical galaxy cannot reproduce all the chemical
constraints given by the observations. The problem resides in the fact that the
cosmologically derived infall law implies a slow gas accretion with consequent
star formation rate active for a long period. In this situation low [Mg/Fe]
ratios are produced for the dominant stellar population in a typical
elliptical, at variance with observations.Comment: 8 pages, 6 figures, accepted for publication by A&
Diagnosing the interstellar medium of galaxies with far-infrared emission lines I. The [C II] 158 microns line at z~0
Atomic fine structure lines have been detected in the local Universe and at
high redshifts over the past decades. The [C II] emission line at 158 m is
an important observable as it provides constraints on the interstellar medium
(ISM) cooling processes. We develop a physically motivated framework to
simulate the production of far-infrared line emission from galaxies in a
cosmological context. This first paper sets out our methodology and describes
its first application, simulating the [C II] 158 m line emission in the
local Universe. We combine the output from EAGLE cosmological hydrodynamical
simulations with a multi-phase model of the ISM. Gas particles are divided into
three phases: dense molecular gas, neutral atomic gas and diffuse ionised gas
(DIG). We estimate the [C II] line emission from the three phases using a set
of Cloudy cooling tables. Our results agree with previous findings regarding
the contribution of these three ISM phases to the [C II] emission. Our model
shows good agreement with the observed -star formation rate
(SFR) relation in the local Universe within 0.4 dex scatter. The fractional
contribution to the [C II] line from different ISM phases depends on the total
SFR and metallicity. The neutral gas phase dominates the [C II] emission in
galaxies with -, but the
ionised phase dominates at lower SFRs. Galaxies above solar metallicity exhibit
lower /SFR ratios for the neutral phase. In comparison, the
/SFR ratio in the DIG is stable when metallicity varies. We
suggest that the reduced size of the neutral clouds, caused by increased SFRs,
is the likely cause for the deficit at high infrared
luminosities, although EAGLE simulations do not reach these luminosities at
.Comment: Accepted for publication in A&A; 16 pages, 11 figures, 4 tables (plus
appendix
Carbon stars in the X-shooter Spectral Library
We provide a new collection of spectra of 35 carbon stars obtained with the
ESO/VLT X-shooter instrument as part of the X-shooter Spectral Library project.
The spectra extend from 0.3m to 2.4m with a resolving power above
8000. The sample contains stars with a broad range of (J-K) color and
pulsation properties located in the Milky Way and the Magellanic Clouds. We
show that the distribution of spectral properties of carbon stars at a given
(J-K) color becomes bimodal (in our sample) when (J-K) is larger than about
1.5. We describe the two families of spectra that emerge, characterized by the
presence or absence of the absorption feature at 1.53m, generally
associated with HCN and CH. This feature appears essentially only in
large-amplitude variables, though not in all observations. Associated spectral
signatures that we interpret as the result of veiling by circumstellar matter,
indicate that the 1.53m feature might point to episodes of dust production
in carbon-rich Miras.Comment: 29 pages, 21 figures, 9 tables, Accepted for publication in A&
The MeerKAT Fornax Survey
We present the science case and observations plan of the MeerKAT Fornax
Survey, an HI and radio continuum survey of the Fornax galaxy cluster to be
carried out with the SKA precursor MeerKAT. Fornax is the second most massive
cluster within 20 Mpc and the largest nearby cluster in the southern
hemisphere. Its low X-ray luminosity makes it representative of the environment
where most galaxies live and where substantial galaxy evolution takes place.
Fornax's ongoing growth makes it an excellent laboratory for studying the
assembly of clusters, the physics of gas accretion and stripping in galaxies
falling in the cluster, and the connection between these processes and the
neutral medium in the cosmic web.
We will observe a region of 12 deg reaching a projected distance of 1.5
Mpc from the cluster centre. This will cover a wide range of environment
density out to the outskirts of the cluster, where gas-rich in-falling groups
are found. We will: study the HI morphology of resolved galaxies down to a
column density of a few times 1e+19 cm at a resolution of 1 kpc; measure
the slope of the HI mass function down to M(HI) 5e+5 M(sun); and attempt to
detect HI in the cosmic web reaching a column density of 1e+18 cm at a
resolution of 10 kpc.Comment: Proceedings of Science, "MeerKAT Science: On the Pathway to the SKA",
Stellenbosch, 25-27 May 201
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