6,893 research outputs found
The Mass of the Convective Zone in FGK Main Sequence Stars and the Effect of Accreted Planetary Material on Apparent Metallicity Determinations
The mass of the outer convective zone in FGK main sequence stars decreases
dramatically with stellar mass. Therefore, any contamination of a star's
atmosphere by accreted planetary material should affect hotter stars much more
than cool stars. If recent suggestions that high metal abundances in stars with
planets are caused by planetesimal accretion are correct, then metallicity
enhancements in earlier-type stars with planets should be very pronounced. No
such trend is seen, however.Comment: Submitted ApJ Letters March 26th; accepted April 30th. 12 pages, 2
figure
Visualizing the Doppler Effect
The development of Information and Communication Technologies suggests some spectacular changes in the methods used for teaching scientific subjects. Nowadays, the development of software and hardware makes it possible to simulate processes as close to reality as we want. However, when we are trying to explain some complex physical processes, it is better to simplify the problem under study using simplified pictures of the total process by eliminating some elements that make it difficult to understand this process. In this work we focus our attention on the Doppler effect which requires the space-time visualization that is very difficult to obtain using the traditional teaching resources. We have designed digital simulations as a complement of the theoretical explanation in order to help students understand this phenomenon
Frequency of Debris Disks around Solar-Type Stars: First Results from a Spitzer/MIPS Survey
We have searched for infrared excesses around a well defined sample of 69 FGK
main-sequence field stars. These stars were selected without regard to their
age, metallicity, or any previous detection of IR excess; they have a median
age of ~4 Gyr. We have detected 70 um excesses around 7 stars at the 3-sigma
confidence level. This extra emission is produced by cool material (< 100 K)
located beyond 10 AU, well outside the ``habitable zones'' of these systems and
consistent with the presence of Kuiper Belt analogs with ~100 times more
emitting surface area than in our own planetary system. Only one star, HD
69830, shows excess emission at 24 um, corresponding to dust with temperatures
> 300 K located inside of 1 AU. While debris disks with Ld/L* > 10^-3 are rare
around old FGK stars, we find that the disk frequency increases from 2+-2% for
Ld/L* > 10^-4 to 12+-5% for Ld/L* > 10^-5. This trend in the disk luminosity
distribution is consistent with the estimated dust in our solar system being
within an order of magnitude, greater or less, than the typical level around
similar nearby stars.Comment: 11 figure
The INTEGRAL view of the Soft Gamma-ray Repeater SGR 1806-20
We present the results obtained by INTEGRAL on the Soft-Gamma Ray Repeater
SGR 1806-20. In particular we report on the temporal and spectral properties of
the bursts detected during a moderately active period of the source in
September and October 2003 and on the search for quiescent emission.Comment: To appear in the proceedings (ESA-SP) of the 5th INTEGRAL Workshop,
"The INTEGRAL UNIVERSE", Munich, 16-20 February 200
Perturbative expansions from Monte Carlo simulations at weak coupling: Wilson loops and the static-quark self-energy
Perturbative coefficients for Wilson loops and the static-quark self-energy
are extracted from Monte Carlo simulations at weak coupling. The lattice
volumes and couplings are chosen to ensure that the lattice momenta are all
perturbative. Twisted boundary conditions are used to eliminate the effects of
lattice zero modes and to suppress nonperturbative finite-volume effects due to
Z(3) phases. Simulations of the Wilson gluon action are done with both periodic
and twisted boundary conditions, and over a wide range of lattice volumes (from
to ) and couplings (from to ).
A high precision comparison is made between the simulation data and results
from finite-volume lattice perturbation theory. The Monte Carlo results are
shown to be in excellent agreement with perturbation theory through second
order. New results for third-order coefficients for a number of Wilson loops
and the static-quark self-energy are reported.Comment: 36 pages, 15 figures, REVTEX documen
Seroprevalencia de Toxoplasma gondii en cerdos faenados en frigoríficos de la provincia de La Pampa, Argentina
La toxoplasmosis es una importante enfermedad zoonótica con distribución mundial. En Argentina existe escasa información sobre la prevalencia en cerdos. El objetivo del este trabajo fue determinar la prevalencia de anticuerpos contra Toxoplasma gondii en cerdos de faena en dos frigoríficos porcinos de la provincia de La Pampa. Se obtuvieron 86 muestras de suero, que fueron testeadas por la Prueba de Aglutinación de Látex Toxotest Latex y la titulación se realizó con Toxotest HAI (Weiner laboratorio S.A.I.C.). Se consideraron positivos los títulos de anticuerpos en diluciones ≥ 1:8. La prevalencia de títulos positivos fue de 6,98% (n=6). En diluciones 1:8 la seroprevalencia fue de 16,67% (IC: 0,00, 46,40%) (n=1); para diluciones 1:32 se obtuvo el 50% (IC: 10,11%, 89,89%) de títulos positivos, (n=3); y en diluciones 1:64 se obtuvieron el 33,33% (33,33%, 70,94%) de títulos positivos (n=2). La prevalencia en cada uno de los frigoríficos fue: 16,13% y de 1,82%; respectivamente. Este estudio preliminar aporta información válida para la actualización de registros epidemiológicos de la provincia, e incentiva a seguir profundizando en la temática
V2368 Oph: An eclipsing and double-lined spectroscopic binary used as a photometric comparison star for U Oph
The A-type star HR 6412 = V2368 Oph was used by several investigators as a
photometric comparison star for the known eclipsing binary U Oph but was found
to be variable by three independent groups, including us. By analysing series
of new spectral and photometric observations and a critical compilation of
available radial velocities, we were able to find the correct period of light
and radial-velocity variations and demonstrate that the object is an eclipsing
and double-lined spectroscopic binary moving in a highly eccentric orbit. We
derived a linear ephemeris T min.I = HJD (2454294.67 +/- 0.01) + (38.32712 +/-
0.00004)d x E and estimated preliminary basic physical properties of the
binary. The dereddened UBV magnitudes and effective temperatures of the primary
and secondary, based on our light- and velocity-curve solutions, led to
distance estimates that agree with the Hipparcos distance within the errors. We
find that the mass ratio must be close to one, but the limited number and
wavelength range of our current spectra does not allow a truly precise
determination of the binary masses. Nevertheless, our results show convincingly
that both binary components are evolved away from the main sequence, which
makes this system astrophysically very important. There are only a few
similarly evolved A-type stars among known eclipsing binaries. Future
systematic observations and careful analyses can provide very stringent tests
for the stellar evolutionary theory.Comment: 10 pages, 7 figs, in press 2011 A&
Hickson-like compact groups inhabiting different environments
Although Compact Groups of galaxies (CGs) have been envisioned as isolated
extremely dense structures in the Universe, it is accepted today that many of
them could be not as isolated as thought. In this work, we study Hickson-like
CGs identified in the Sloan Digital Sky Survey Data Release 16 to analyse these
systems and their galaxies when embedded in different cosmological structures.
To achieve this goal, we identify several cosmological structures where CGs can
reside: Nodes of filaments, Loose Groups, Filaments and cosmic Voids. Our
results indicate that 45 per cent of CGs do not reside in any of these
structures, i.e., they can be considered non-embedded or isolated systems. Most
of the embedded CGs are found inhabiting Loose Groups and Nodes, while there
are almost no CGs residing well inside cosmic Voids. Some physical properties
of CGs vary depending on the environment they inhabit. CGs in Nodes show the
largest velocity dispersions, the brightest absolute magnitude of the
first-ranked galaxy, and the smallest crossing times, while the opposite occurs
in Non-Embedded CGs. When comparing galaxies in all the environments and
galaxies in CGs, CGs show the highest fractions of red/early-type galaxy
members in most of the absolute magnitudes ranges. The variation between
galaxies in CGs inhabiting one or another environment is not as significant as
the differences caused by belonging or not to a CG. Our results suggest a
plausible scenario for galaxy evolution in CGs in which both, large-scale and
local environments play essential roles.Comment: 16 pages, 9 figures, 1 table, accepted for publication in MNRA
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