637 research outputs found
Chromospheric heating by acoustic waves compared to radiative cooling
Acoustic and magnetoacoustic waves are among the possible candidate
mechanisms that heat the upper layers of solar atmosphere. A weak chromospheric
plage near a large solar pore NOAA 11005 was observed on October 15, 2008 in
the lines Fe I 617.3 nm and Ca II 853.2 nm with the Interferometric
Bidimemsional Spectrometer (IBIS) attached to the Dunn Solar Telescope.
Analyzing the Ca II observations with spatial and temporal resolutions of 0.4"
and 52 s, the energy deposited by acoustic waves is compared with that released
by radiative losses. The deposited acoustic flux is estimated from power
spectra of Doppler oscillations measured in the Ca II line core. The radiative
losses are calculated using a grid of seven 1D hydrostatic semi-empirical model
atmospheres. The comparison shows that the spatial correlation of maps of
radiative losses and acoustic flux is 72 %. In quiet chromosphere, the
contribution of acoustic energy flux to radiative losses is small, only of
about 15 %. In active areas with photospheric magnetic field strength between
300 G and 1300 G and inclination of 20-60 degrees, the contribution increases
from 23 % (chromospheric network) to 54 % (a plage). However, these values have
to be considered as lower limits and it might be possible that the acoustic
energy flux is the main contributor to the heating of bright chromospheric
network and plages.Comment: 9 pages, 10 figures. Accepted for publication in The Astrophysical
Journa
Dynamics of the solar atmosphere above a pore with a light bridge
Context: Solar pores are small sunspots lacking a penumbra that have a
prevailing vertical magnetic field component. They can include light bridges at
places with locally reduced magnetic field. Like sunspots, they exhibit a wide
range of oscillatory phenomena.
Aims: A large isolated pore with a light bridge (NOAA 11005) is studied to
obtain characteristics of a chromospheric filamentary structure around the
pore, to analyse oscillations and waves in and around the pore, and to
understand the structure and brightness of the light bridge.
Methods: Spectral imaging observations in the line Ca II 854.2 nm and
complementary spectropolarimetry in Fe I lines, obtained with the DST/IBIS
spectrometer and HINODE/SOT spectropolarimeter, were used to measure
photospheric and chromospheric velocity fields, oscillations, waves, the
magnetic field in the photosphere, and acoustic energy flux and radiative
losses in the chromosphere.
Results: The chromospheric filamentary structure around the pore has all
important characteristics of a superpenumbra: it shows an inverse Evershed
effect and running waves, and has a similar morphology and oscillation
character. The granular structure of the light bridge in the upper photosphere
can be explained by radiative heating. Acoustic waves leaking up from the
photosphere along the inclined magnetic field in the light bridge transfer
enough energy flux to balance the total radiative losses of the light-bridge
chromosphere.
Conclusions: The presence of a penumbra is not a necessary condition for the
formation of a superpenumbra. The light bridge is heated by radiation in the
photosphere and by acoustic waves in the chromosphere.Comment: 14 pages, 14 figures, 3 tables, accepted for publication in
Astrononomy & Astrophysic
The dissimilar chemical composition of the planet-hosting stars of the XO-2 binary system
Using high-quality spectra of the twin stars in the XO-2 binary system, we
have detected significant differences in the chemical composition of their
photospheres. The differences correlate strongly with the elements' dust
condensation temperature. In XO-2N, volatiles are enhanced by about 0.015 dex
and refractories are overabundant by up to 0.090 dex. On average, our error bar
in relative abundance is 0.012 dex. We present an early metal-depletion
scenario in which the formation of the gas giant planets known to exist around
these stars is responsible for a 0.015 dex offset in the abundances of all
elements while 20 M_Earth of non-detected rocky objects that formed around
XO-2S explain the additional refractory-element difference. An alternative
explanation involves the late accretion of at least 20 M_Earth of planet-like
material by XO-2N, allegedly as a result of the migration of the hot Jupiter
detected around that star. Dust cleansing by a nearby hot star as well as age
or Galactic birthplace effects can be ruled out as valid explanations for this
phenomenon.Comment: ApJ, in press. Complete linelist (Table 3) available in the "Other
formats -> Source" downloa
Universidad libre de Berlín
Berlín fue dividido al terminar la segunda guerra mundial en dos zonas: Occidental y Oriental. Su, desde antiguo, famosa Universidad quedó situada casi en su totalidad en zona soviética. Se produjeron serias dificultades para el acceso a ella de los estudiantes del Berlín libre y, por este motivo, las autoridades del mismo, para dar solución rápida y definitiva a este problema, convocaron un concurso: «La Universidad libre de Berlín»
Isospin non-equilibrium in heavy-ion collisions at intermediate energies
We study the equilibration of isospin degree of freedom in intermediate
energy heavy-ion collisions using an isospin-dependent BUU model. It is found
that there exists a transition from the isospin equilibration at low energies
to non-equilibration at high energies as the beam energy varies across the
Fermi energy in central, asymmetric heavy-ion collisions. At beam energies
around 55 MeV/nucleon, the composite system in thermal equilibrium but isospin
non-equilibrium breaks up into two primary hot residues with N/Z ratios closely
related to those of the target and projectile respectively. The decay of these
forward-backward moving residues results in the strong isospin asymmetry in
space and the dependence of the isotopic composition of fragments on the N/Z
ratios of the target and projectile. These features are in good agreement with
those found recently in experiments at NSCL/MSU and TAMU, implications of these
findings are discussed.Comment: 9 pages, latex, + 3 figures available upon reques
Fragment Isospin as a Probe of Heavy-Ion Collisions
Isotope ratios of fragments produced at mid-rapidity in peripheral and
central collisions of 114Cd ions with 92Mo and 98Mo target nuclei at E/A = 50
MeV are compared. Neutron-rich isotopes are preferentially produced in central
collisions as compared to peripheral collisions. The influence of the size (A),
density, N/Z, E*/A, and Eflow/A of the emitting source on the measured isotope
ratios was explored by comparison with a statistical model (SMM). The
mid-rapidity region associated with peripheral collisions does not appear to be
neutron-enriched relative to central collisions.Comment: 12 pages including figure
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