2,680 research outputs found
The stellar population of Sco OB2 revealed by Gaia DR2 data
Sco OB2 is the nearest OB association, extending over approximately 2000
sq.deg. on the sky. Only its brightest members are already known (from
Hipparcos) across its entire size, while studies of its lower-mass population
refer only to small portions of its extent. In this work we exploit the
capabilities of Gaia DR2 measurements to search for Sco OB2 members across its
entire size and down to the lowest stellar masses. We use both Gaia astrometric
and photometric data to select association members, using minimal assumptions
derived mostly from the Hipparcos studies. Gaia resolves small details in both
the kinematics of individual Sco OB2 subgroups and their distances from the
Sun. We develop methods to explore the 3D kinematics of stellar populations
covering large sky areas. We find ~11000 pre-main sequence (PMS) Sco OB2
members (with <3% contamination), plus ~3600 MS candidate members with a larger
(10-30%) field-star contamination. A higher-confidence subsample of ~9200 PMS
(and ~1340 MS) members is also selected (<1% contamination for the PMS),
affected however by larger (~15%) incompleteness. We classify separately stars
in compact and diffuse populations. Most members belong to a few kinematically
distinct diffuse populations, whose ensemble outlines the association shape.
Upper Sco is the densest part of Sco OB2, with a complex spatial and
kinematical structure, and no global pattern of motion. Other dense subclusters
are found in Upper Centaurus-Lupus and in Lower Centaurus-Crux. Most clustered
stars appear to be younger than the diffuse PMS population, suggesting star
formation in small groups which rapidly disperse and dilute, while keeping
memory of their original kinematics. We also find that the open cluster IC 2602
has a similar dynamics to Sco OB2, and its PMS members are evaporating and
forming a ~10 deg halo around its double-peaked core.Comment: 27 pages, 37 figures. Accepted for publication in Astronomy and
Astrophysic
A new eclipsing binary system with a pulsating component detected by CoRoT
We report the discovery of CoRoT 102980178 (R.A.= 06:50:12.10, Dec.=
-02:41:21.8, J2000) an Algol-type eclipsing binary system with a pulsating
component (oEA). It was identified using a publicly available 55 day long
monochromatic lightcurve from the CoRoT initial run dataset (exoplanet field).
Eleven consecutive 1.26m deep total primary and the equal number of 0.25m deep
secondary eclipses (at phase 0.50) were observed. The following light elements
for the primary eclipse were derived: HJD_MinI= 2454139.0680 + 5.0548d x E. The
lightcurve modeling leads to a semidetached configuration with the photometric
mass ratio q=0.2 and orbital inclination i=85 deg. The out-of-eclipse
lightcurve shows ellipsoidal variability and positive O'Connell effect as well
as clear 0.01m pulsations with the dominating frequency of 2.75 c/d. The
pulsations disappear during the primary eclipses, which indicates the primary
(more massive) component to be the pulsating star. Careful frequency analysis
reveals the second independent pulsation frequency of 0.21 c/d and numerous
combinations of these frequencies with the binary orbital frequency and its
harmonics. On the basis of the CoRoT lightcurve and ground based multicolor
photometry, we favor classification of the pulsating component as a gamma
Doradus type variable, however, classification as an SPB star cannot be
excluded.Comment: 16 pages, 7 figures, 3 tables, accepted to Communications in
Asteroseismolog
A PBW basis for Lusztig's form of untwisted affine quantum groups
Let be an untwisted affine Kac-Moody algebra over the field
, and let be the associated quantum enveloping
algebra; let be the Lusztig's integer form of , generated by -divided powers of Chevalley
generators over a suitable subring of . We prove a
Poincar\'e-Birkhoff-Witt like theorem for ,
yielding a basis over made of ordered products of -divided powers of
suitable quantum root vectors.Comment: 22 pages, AMS-TeX C, Version 2.1c. This is the author's final
version, corresponding to the printed journal versio
Convex Bases of PBW type for Quantum Affine Algebras
This note has two purposes. First we establish that the map defined in [L,
(a)] is an isomorphism for certain admissible sequences. Second we
show the map gives rise to a convex basis of Poincar\'e--Birkhoff--Witt (PBW)
type for \bup, an affine untwisted quantized enveloping algebra of
Drinfeld and Jimbo. The computations in this paper are made possible by
extending the usual braid group action by certain outer automorphisms of the
algebra.Comment: 7 pages, to appear in Comm. Math. Phy
VLT/Flames observations of the star forming region NGC 6530
Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. We want to select cluster members by using different membership criteria,to study the properties of pre-main sequence stars with or without circumstellar disks. We use intermediate resolution spectra including the Li I 6707.8 Angstroms line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined with X-ray data to study the cluster membership. Optical-IR data and Halpha spectra, these latter available for a subsample of our targets, are used to classify CTTS and WTTS and to compare the properties of stars with and without disks. We find a total of 237 certain members including 53 binaries. The rotational velocity distributions of stars with IR excesses are statistically different from that of stars without IR excesses, while the fraction of binaries with disks is significantly smaller than that of single stars. Stars with evidence for accretion show circumstellar disks; youth of cluster members is confirmed by the lithium abundance consistent with the initial content. As indicated by the disk-locking picture, stars with disks have in general rotational velocities lower than stars without disks. Binaries in NGC 6530 seem have undergone a significant disk evolution
No surviving companion in Kepler's supernova
We have surveyed Kepler's supernova remnant in search of the companion star
of the explosion. We have gone as deep as 2.6 solar luminosities in the stars
within 20% of the radius of the remnant. We use FLAMES at the VLT-UT2 telescope
to obtain high resolution spectra of the stellar candidates selected from HST
images. The resulting set of stellar parameters suggests that these stars come
from a rather ordinary mixture of field stars (mostly giants). A few of the
stars seem to have low [Fe/H] (< -1) and they are consistent with being
metal-poor giants. The radial velocities and rotational velocities vrot sin i
are very well determined. There are no fast rotating stars as vrot sin i < 20
km/s. The radial velocities from the spectra and the proper motions determined
from HST images are compatible with those expected from the Besan\c{c}on model
of the Galaxy. The strong limits placed on luminosity suggest that this
supernova could have arisen either from the core-degenerate scenario or from
the double-degenerate scenario.Comment: ApJ accepted, 7 figures and 7 table
Feedstocks for Second-Generation Biodiesel: Microalgae’s Biology and Oil Composition
The solar energy is an inexhaustible source, while other energy reserves, like fossil and nuclear fuels, are limited in quantity and are depleted as years go by. Renewable energy is necessary to replace petroleum-derived fuels. The first generation biofuels, which are produced from oil seeds and crops, are a possible alternative, but they are limited in their capacity to provide all the energy demanded in the world. Therefore, new sources for the sustainable production of renewable energy are being looked for. This concern has promoted the keen interest in developing second generation biofuels, which are produced from other feedstocks, such as microalgal oils (Schenk et al., 2008; Mata et al., 2010). Some microalgal species are capable of producing biomass yields containing high percentages of oils (Aaronson et. al., 1980). In addition, microalgal systems can use low value natural resources, such as arid lands and saline water, thus offering the potential for large biomass energy contributions without competing for prime agricultural or forest land. Most microalgae grow photoautotrophically by using solar energy and mainly carbon dioxide as carbon source. Alternatively, some species can grow heterotrophically or mixotrophically using organic compounds as energy and carbon sources.Fil: Leonardi, Patricia Ines. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de BiologĂa, BioquĂmica y Farmacia; ArgentinaFil: Popovich, Cecilia Angelines. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de BiologĂa, BioquĂmica y Farmacia; ArgentinaFil: Damiani, Maria Cecilia. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de BiologĂa, BioquĂmica y Farmacia; Argentin
Results from DROXO. III. Observation, source list and X-ray properties of sources detected in the "Deep Rho Ophiuchi XMM-Newton Observation"
X-rays from very young stars are powerful probes to investigate the
mechanisms at work in the very first stages of the star formation and the
origin of X-ray emission in very young stars. We present results from a 500 ks
long observation of the Rho Ophiuchi cloud with a XMM-Newton large program
named DROXO, aiming at studying the X-ray emission of deeply embedded Young
Stellar Objects (YSOs). The data acquired during the DROXO program were reduced
with SAS software, and filtered in time and energy to improve the signal to
noise of detected sources; light curves and spectra were obtained. We detected
111 sources, 61 of them associated with rho Ophiuchi YSOs as identified from
infrared observations with ISOCAM. Specifically, we detected 9 out of 11 Class
I, 31 out of 48 Class II and 15 out 16 Class III objects. Six objects out of 21
classified Class III candidates are also detected. At the same time we suggest
that 15 Class III candidates that remain undetected at log Lx < 28.3 are not
related to the cloud population. The global detection rate is ~64%. We have
achieved a flux sensitivity of ~5 x 10^{-15} erg s^{-1} cm^{-2}. The Lx to
L_bol ratio shows saturation at a value of ~ -3.5 for stars with T_eff <= 5000
K or 0.7 M_sun as observed in the Orion Nebula. The plasma temperatures and the
spectrum absorption show a decline with YSO class, with Class I YSOs being
hotter and more absorbed than Class II and III YSOs. In one star (GY 266) with
infrared counterpart in 2MASS and Spitzer catalogs we have detected a soft
excess in the X-ray spectrum which is best fitted by a cold thermal component
less absorbed than the main thermal component of the plasma. Such a soft
component hints to the presence of plasma heated by shocks due to jets outside
the dense circumstellar material.Comment: Accepted for publication on Astronomy & Astrophysics journa
XMM-Newton observation of the young open cluster Blanco 1. I. X-ray spectroscopy and photometry
We present an X-ray study of the high metallicity young open cluster Blanco 1
based on XMM--Newton data. X-ray spectroscopy of cluster members is presented
for the first time as well as new X-ray distribution functions of late-type
stars. We detected all known dF and dG stars in the EPIC field and 80% and 90%
of dK and dM stars, respectively. The X-ray spectral analysis of the X-ray
brightest cluster stars and X-ray color analysis of a larger sample show that a
model with two temperatures (at about 0.3 and 1 keV) explains the quiescent
activity phase spectra. We discuss also the nature of unidentified X-ray
sources in the observed region and their X-ray spectral properties.Comment: 18 pages, 8 figures, paper accepted for publication on A&
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