465 research outputs found
Cartography of Landscape Dynamics in Central Spain
Depto. de Biodiversidad, EcologĂa y EvoluciĂłnFac. de Ciencias BiolĂłgicasTRUEMinisterio de EducaciĂłn y Ciencia (MEC)pu
Ten-Micron Observations of Nearby Young Stars
(abridged) We present new 10-micron photometry of 21 nearby young stars
obtained at the Palomar 5-meter and at the Keck I 10-meter telescopes as part
of a program to search for dust in the habitable zone of young stars. Thirteen
of the stars are in the F-K spectral type range ("solar analogs"), 4 have B or
A spectral types, and 4 have spectral type M. We confirm existing IRAS
12-micron and ground-based 10-micron photometry for 10 of the stars, and
present new insight into this spectral regime for the rest. Excess emission at
10 micron is not found in any of the young solar analogs, except for a possible
2.4-sigma detection in the G5V star HD 88638. The G2V star HD 107146, which
does not display a 10-micron excess, is identified as a new Vega-like
candidate, based on our 10-micron photospheric detection, combined with
previously unidentified 60-micron and 100-micron IRAS excesses. Among the
early-type stars, a 10-micron excess is detected only in HD 109573A (HR 4796A),
confirming prior observations; among the M dwarfs, excesses are confirmed in AA
Tau, CD -40 8434, and Hen 3-600A. A previously suggested N band excess in the
M3 dwarf CD -33 7795 is shown to be consistent with photospheric emission.Comment: 40 pages, 4 figures, 5 tables. To appear in the January 1, 2004 issue
of Ap
Kinematics of SDSS subdwarfs: Structure and substructure of the Milky Way halo
We construct a new sample of ~1700 solar neighbourhood halo subdwarfs from
the Sloan Digital Sky Survey, selected using a reduced proper motion diagram.
Radial velocities come from the SDSS spectra and proper motions from the
light-motion curve catalogue of Bramich et al. (2008). Using a photometric
parallax relation to estimate distances gives us the full phase-space
coordinates. Typical velocity errors are in the range 30-50 km/s. This halo
sample is one of the largest constructed to-date and the disc contamination is
at a level of < 1 per cent. This enables us to calculate the halo velocity
dispersion to excellent accuracy. We find that the velocity dispersion tensor
is aligned in spherical polar coordinates and that (sigma_r, sigma_phi,
sigma_theta) = (143 \pm 2, 82 \pm 2, 77 \pm 2) km/s. The stellar halo exhibits
no net rotation, although the distribution of v_phi shows tentative evidence
for asymmetry. The kinematics are consistent with a mildly flattened stellar
density falling with distance like r^{-3.75}. Using the full phase-space
coordinates, we look for signs of kinematic substructure in the stellar halo.
We find evidence for four discrete overdensities localised in angular momentum
and suggest that they may be possible accretion remnants. The most prominent is
the solar neighbourhood stream previously identified by Helmi et al. (1999),
but the remaining three are new. One of these overdensities is potentially
associated with a group of four globular clusters (NGC5466, NGC6934, M2 and
M13) and raises the possibility that these could have been accreted as part of
a much larger progenitor.Comment: 16 pages, 13 figures, MNRAS (in press). Revised following referee's
comments; using new and improved parallax relation. Results and conclusions
unchange
XMM-Newton Spectroscopy of the Cluster of Galaxies 2A 0335+096
We present here the results of a deep (130 ks) XMM-Newton observation of the
cluster of galaxies 2A 0335+096. The deep exposure allows us to study in detail
its temperature structure and its elemental abundances. We fit three different
thermal models and find that the multi-temperature wdem model fits our data
best. We find that the abundance structure of the cluster is consistent with a
scenario where the relative number of Type Ia supernovae contributing to the
enrichment of the intra-cluster medium is ~25%, while the relative number of
core collapse supernovae is ~75%. Comparison of the observed abundances to the
supernova yields does not allow us to put any constrains on the contribution of
Pop III stars to the enrichment of the ICM. Radial abundance profiles show a
strong central peak of both Type Ia and core collapse supernova products. Both
the temperature and iron abundance maps show an asymmetry in the direction of
the elongated morphology of the surface brightness. In particular the
temperature map shows a sharp change over a brightness edge on the southern
side of the core, which was identified as a cold front in the Chandra data.
This suggests that the cluster is in the process of a merger with a subcluster.
Moreover, we find that the blobs or filaments discovered in the core of the
cluster by Chandra are, contrary to the previous results, colder than the
ambient gas and they appear to be in pressure equilibrium with their
environment.Comment: Accepted for publication in A&A, 19 page
Three Wide-Separation L dwarf Companions from the Two Micron All Sky Survey: Gl 337C, Gl 618.1B, and HD 89744B
We present two confirmed wide separation L-dwarf common proper motion
companions to nearby stars and one candidate identified from the Two Micron All
Sky Survey. Spectral types from optical spectroscopy are L0 V, L2.5 V, and L8
V. Near-infrared low resolution spectra of the companions are provided as well
as a grid of known objects spanning M6 V -- T dwarfs to support spectral type
assignment for these and future L-dwarfs in the z'JHK bands. Using published
measurements, we estimate ages of the companions from physical properties of
the primaries. These crude ages allow us to estimate companion masses using
theoretical low-mass star and brown dwarf evolutionary models. The new L-dwarfs
in this paper bring the number of known wide-binary (Separation >= 100 AU)
L-dwarf companions of nearby stars to nine. One of the L-dwarfs is a wide
separation companion to the F7 IV-V + extrasolar planet system HD89744Ab.Comment: 20 pages including 6 tables and 4 figures, AJ, in pres
A Prograde, Low-Inclination Orbit for the Very Hot Jupiter WASP-3b
We present new spectroscopic and photometric observations of the transiting
exoplanetary system WASP-3. Spectra obtained during two separate transits
exhibit the Rossiter-McLaughlin (RM) effect and allow us to estimate the
sky-projected angle between the planetary orbital axis and the stellar rotation
axis, lambda = 3.3^{+2.5}_{-4.4} degrees. This alignment between the axes
suggests that WASP-3b has a low orbital inclination relative to the equatorial
plane of its parent star. During our first night of spectroscopic measurements,
we observed an unexpected redshift briefly exceeding the expected sum of the
orbital and RM velocities by 140 m/s. This anomaly could represent the
occultation of material erupting from the stellar photosphere, although it is
more likely to be an artifact caused by moonlight scattered into the
spectrograph.Comment: 23 pages, 4 figures, Accepted for publication in The Astrophysical
Journal, Replacement includes revised citation
The stellar content of the Hamburg/ESO survey VI. The metallicity distribution of main-sequence turnoff stars in the Galactic halo
We determine the metallicity distribution function (MDF) of the Galactic halo
based on metal-poor main-sequence turnoff-stars (MSTO) which were selected from
the Hamburg/ESO objective-prism survey (HES) database. Corresponding follow-up
moderateresolution observations (R ~ 2000) of some 682 stars (among which 617
were accepted program stars) were carried out with the 2.3m telescope at the
Siding Spring Observatory (SSO). Corrections for the survey volume covered by
the sample stars were quantitatively estimated and applied to the observed MDF.
The corrections are quite small, when compared with those for a previously
studied sample of metal-poor giants. The corrected observational MDF of the
turnoff sample was then compared with that of the giants, as well as with a
number of theoretical predictions of Galactic chemical evolution, including the
mass-loss modified Simple Model. Although the survey-volume corrected MDFs of
the metal-poor turnoff and the halo giants notably differ in the region of
[Fe/H] > -2.0, below [Fe/H] ~ -2.0, (the region we scientifically focus on
most) both MDFs show a sharp drop at [Fe/H] ~ -3.6 and present rather similar
distributions in the low-metallicity tail. Theoretical models can fit some
parts of the observed MDF, but none is found to simultaneously reproduce the
peak as well as the features in the metal-poor region with [Fe/H] between -2.0
to -3.6. Among the tested models only the GAMETE model, when normalized to the
tail of the observed MDF below [Fe/H] ~ -3.0, and with Z_{cr} =
10^{-3.4}Z_{\odot}, is able to predict the sharp drop at [Fe/H] ~ -3.6.Comment: 10 pages, 11 figures, accepted for publication in A&
Distribution area of Juniperus oxycedrus L. in Central Spain (Madrid)
The Iberian populations of Juniperus oxycedrus L. subsp. oxycedrus have been studied by several authors who consider their condition as unfavourable. In the Madrid Region, current status, dynamic and distribution area are unknown even when their populations, specifically those who form arborescent shrubs, are included in the type 5210 (Habitat Directive 92/43/EEC). These formations are developed in austere Mediterranean mountain typical of agro ecosystems of high value that have interesting dynamics of recolonization, especially in those areas where agricultural and livestock systems have suffered a setback. This study aims to understand the distribution of juniper in the region of Madrid as the first step to identify and assess the dynamic changes in recent decades. To update the cartography of this species the available information has been checked and completed with photointerpretation and fieldwork.
Based on this cartography and the information relating to the physical and biotic variables four types of juniper were differentiated by multivariate methods. On the other hand, two types of dynamics were recognized and it was studied in depth the genesis of changes produced in these forests in the last decades
The Gaia-ESO survey : Processing FLAMES-UVES spectra
Date of Acceptance: 19/03/2014The Gaia-ESO Survey is a large public spectroscopic survey that aims to derive radial velocities and fundamental parameters of about 105 Milky Way stars in the field and in clusters. Observations are carried out with the multi-object optical spectrograph FLAMES, using simultaneously the medium-resolution (R ~ 20 000) GIRAFFE spectrograph and the high-resolution (R ~ 47 000) UVES spectrograph. In this paper we describe the methods and the software used for the data reduction, the derivation of the radial velocities, and the quality control of the FLAMES-UVES spectra. Data reduction has been performed using a workflow specifically developed for this project. This workflow runs the ESO public pipeline optimizing the data reduction for the Gaia-ESO Survey, automatically performs sky subtraction, barycentric correction and normalisation, and calculates radial velocities and a first guess of the rotational velocities. The quality control is performed using the output parameters from the ESO pipeline, by a visual inspection of the spectra and by the analysis of the signal-to-noise ratio of the spectra. Using the observations of the first 18 months, specifically targets observed multiple times at different epochs, stars observed with both GIRAFFE and UVES, and observations of radial velocity standards, we estimated the precision and the accuracy of the radial velocities. The statistical error on the radial velocities is Ï ~ 0.4 km s-1 and is mainly due to uncertainties in the zero point of the wavelength calibration. However, we found a systematic bias with respect to the GIRAFFE spectra (~0.9 km s-1) and to the radial velocities of the standard stars (~0.5 km s-1) retrieved from the literature. This bias will be corrected in the future data releases, when a common zero point for all the set-ups and instruments used for the survey is be established.Peer reviewe
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