34,694 research outputs found
Spectroscopic signature of Alfv\'en waves damping in a polar coronal hole up to 0.4 solar radii
Between February 24-25, 2009, the EIS spectrometer onboard the Hinode
spacecraft performed special "sit & stare" observations above the South polar
coronal hole continuously over more than 22 hours. Spectra were acquired with
the 1" slit placed off-limb covering altitudes up to 0.48 R
( Mm) above the Sun surface, in order to study with EIS the
non-thermal spectral line broadenings. Spectral lines such as Fe {\sc xii}
186.88, Fe {\sc xii} 193.51, Fe {\sc xii} 195.12 and
Fe {\sc xiii} 202.04 are observed with good statistics up to high
altitudes and they have been analyzed in this study. Results show that the FWHM
of Fe {\sc xii} 195.12 line increases up to R,
then decreases higher up. EIS stray light has been estimated and removed.
Derived electron density and non-thermal velocity profiles have been used to
estimate the total energy flux transported by Alfv\'en waves off-limb in polar
coronal hole up to R. The computed Alfv\'en wave energy
flux density progressively decays with altitude from erg cm s at 0.03 R down to erg cm s at 0.4 R, with an average energy
decay rate erg cm
s. Hence, this result suggests energy deposition by Alfv\'en waves in a
polar coronal hole, thus providing a significant source for coronal heating.Comment: Physical units of the Alfv\'en wave Energy Decay Rate revised with respect to the published version. Scientific results
and conclusions unchange
Symmetric discrete coherent states for n qubits
We put forward a method of constructing discrete coherent states for n
qubits. After establishing appropriate displacement operators, the coherent
states appear as displaced versions of a fiducial vector that is fixed by
imposing a number of natural symmetry requirements on its Q-function. Using
these coherent states we establish a partial order in the discrete phase space,
which allows us to picture some n-qubit states as apparent distributions. We
also analyze correlations in terms of sums of squared Q-functions.Comment: Published in J. Phys. A. Special issue on Coherent State
PO and PN in the wind of the oxygen-rich AGB star IK Tau
Phosphorus-bearing compounds have only been studied in the circumstellar
environments (CSEs) of the asymptotic giant branch (AGB) star IRC +10216 and
the protoplanetary nebula CRL 2688, both C-rich objects, and the O-rich red
supergiant VY CMa. The current chemical models cannot reproduce the high
abundances of PO and PN derived from observations of VY CMa. No observations
have been reported of phosphorus in the CSEs of O-rich AGB stars. We aim to set
observational constraints on the phosphorous chemistry in the CSEs of O-rich
AGB stars, by focussing on the Mira-type variable star IK Tau. Using the IRAM
30m telescope and the Submillimeter Array (SMA), we observed four rotational
transitions of PN (J=2-1,3-2,6-5,7-6) and four of PO
(J=5/2-3/2,7/2-5/2,13/2-11/2,15/2-13/2). The IRAM 30m observations were
dedicated line observations, while the SMA data come from an unbiased spectral
survey in the frequency range 279-355 GHz.
We present the first detections of PN and PO in an O-rich AGB star and
estimate abundances X(PN/H2) of about 3x10^-7 and X(PO/H2) in the range
0.5-6.0x10^-7. This is several orders of magnitude higher than what is found
for the C-rich AGB star IRC +10216. The diameter (<=0.7") of the PN and PO
emission distributions measured in the interferometric data corresponds to a
maximum radial extent of about 40 stellar radii. The abundances and the spatial
occurrence of the molecules are in very good agreement with the results
reported for VY CMa. We did not detect PS or PH3 in the survey. We suggest that
PN and PO are the main carriers of phosphorus in the gas phase, with abundances
possibly up to several 10^-7. The current chemical models cannot account for
this, underlining the strong need for updated chemical models that include
phosphorous compounds.Comment: Accepted for publication in Astronomy & Astrophysics, 10 pages, 8
figure
Exact solutions for the spatial de Vaucouleurs and Sersic laws and related quantities
Using the Mathematica package, we find exact analytical expressions for the
so-called de-projected De Vaucouleurs and Sersic laws as well as for related
spatial (3D) quantities, such the mass, gravitational potential, the total
energy and the central velocity dispersion, generally involved in astronomical
calculations expressed in terms of the Meijer G functions.Comment: 11 pages, accepted in A
The molecular polar disc in NGC 2768
We present CO(1-0) and CO(2-1) maps of the molecular polar disc in the
elliptical galaxy NGC 2768 obtained at the IRAM Plateau de Bure Interferometer.
The maps have a resolution of 2.6" x 2.3" and 1.2" x 1.2" for the CO(1-0) and
CO(2-1) lines, respectively. The CO maps complete the unique picture of the
interstellar medium (ISM) of NGC 2768; the dust, molecular gas, ionised gas and
neutral hydrogen (HI) trace the recent acquisition of cold and cool gas over
two orders of magnitude in radii (and much more in density). In agreement with
the other ISM components, the CO distribution extends nearly perpendicularly to
the photometric major axis of the galaxy. Velocity maps of the CO show a
rotating polar disc or ring in the inner kiloparsec. This cool gas could lead
to kinematic substructure formation within NGC 2768. However, the stellar
velocity field and H-beta absorption linestrength maps from the optical
integral-field spectrograph SAURON give no indication of a young and
dynamically cold stellar population coincident with the molecular polar disc.
Very recent or weak star formation, undetectable in linestrengths, nevertheless
remains a possibility and could be at the origin of some of the ionised gas
observed. Millimetre continuum emission was also detected in NGC 2768, now one
of only a few low-luminosity active galactic nuclei with observed millimetre
continuum emission.Comment: Accepted for publication in MNRAS, 11 pages, 8 figure
Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations
Context: Pluto possesses a thin atmosphere, primarily composed of nitrogen,
in which the detection of methane has been reported.
Aims: The goal is to constrain essential but so far unknown parameters of
Pluto's atmosphere such as the surface pressure, lower atmosphere thermal
stucture, and methane mixing ratio.
Methods: We use high-resolution spectroscopic observations of gaseous
methane, and a novel analysis of occultation light-curves.
Results: We show that (i) Pluto's surface pressure is currently in the 6.5-24
microbar range (ii) the methane mixing ratio is 0.5+/-0.1 %, adequate to
explain Pluto's inverted thermal structure and ~100 K upper atmosphere
temperature (iii) a troposphere is not required by our data, but if present, it
has a depth of at most 17 km, i.e. less than one pressure scale height; in this
case methane is supersaturated in most of it. The atmospheric and bulk surface
abundance of methane are strikingly similar, a possible consequence of the
presence of a CH4-rich top surface layer.Comment: AA vers. 6.1, LaTeX class for Astronomy & Astrophysics, 9 pages with
5 figures Astronomy and Astrophysics Letters, in pres
A new 1.6-micron map of Titanâs surface
We present a new map of Titan's surface obtained in the spectral 'window' at âŒ1.6 ÎŒm between strong methane absorption. This pre-Cassini view of Titan's surface was created from images obtained using adaptive optics on the W.M. Keck II telescope and is the highest resolution map yet made of Titan's surface. Numerous surface features down to the limits of the spatial resolution (âŒ200â300 km) are apparent. No features are easily identifiable in terms of their geologic origin, although several are likely craters
The Cool ISM in Elliptical Galaxies. II. Gas Content in the Volume - Limited Sample and Results from the Combined Elliptical and Lenticular Surveys
We report new observations of atomic and molecular gas in a volume limited
sample of elliptical galaxies. Combining the elliptical sample with an earlier
and similar lenticular one, we show that cool gas detection rates are very
similar among low luminosity E and SO galaxies but are much higher among
luminous S0s. Using the combined sample we revisit the correlation between cool
gas mass and blue luminosity which emerged from our lenticular survey, finding
strong support for previous claims that the molecular gas in ellipticals and
lenticulars has different origins. Unexpectedly, however, and contrary to
earlier claims, the same is not true for atomic gas. We speculate that both the
AGN feedback and merger paradigms might offer explanations for differences in
detection rates, and might also point towards an understanding of why the two
gas phases could follow different evolutionary paths in Es and S0s. Finally we
present a new and puzzling discovery concerning the global mix of atomic and
molecular gas in early type galaxies. Atomic gas comprises a greater fraction
of the cool ISM in more gas rich galaxies, a trend which can be plausibly
explained. The puzzle is that galaxies tend to cluster around
molecular-to-atomic gas mass ratios near either 0.05 or 0.5.Comment: 37 pages, including 4 tables and 12 figures. Accepted for publication
in the Astrophysical Journa
Interplay of thermal and quantum spin fluctuations on the kagome lattice
We present a Raman spectroscopic investigation of the Herbertsmithite
ZnCu3(OH)6Cl2, the first realization of a Heisenberg s=1/2 antiferromagnet on a
perfect kagome lattice. The magnetic excitation spectrum of this compound is
dominated by two components, a high temperature quasi elastic signal and a low
temperature, broad maximum. The latter has a linear low energy slope and
extends to high energy. We have investigated the temperature dependence and
symmetry properties of both signals. Our data agree with previous calculations
and point to a spin liquid ground state.Comment: 5 figure
Molecular gas in the galaxy M83. I - The molecular gas distribution
We present CO(1-0) and CO(2-1) Swedish-ESO Submillimetre Telescope (SEST)
observations of the barred spiral galaxy M83 (NGC5236). The maps cover the
entire optical disk. The CO emission is strongly peaked toward the nucleus,
which breaks up into two separate components in the CO(2-1) data due to the
higher spatial resolution. Emission from the bar is strong, in particular on
the leading edges of the bar. The molecular gas arms are clearly resolved and
can be traced for more than 360\degr . Emission in the inter-arm regions is
detected. The average CO CO(2-1)/CO(1-0) line ratio is 0.77. The ratio is lower
than this on the spiral arms and higher in the inter-arm regions. The arms show
regularly spaced concentrations of molecular gas, Giant Molecular Associations
(GMA's), whose masses are of the order 10^7 Msun. The total molecular gas mass
is estimated to be 3.9*10^9 Msun. This mass is comparable to the total HI mass,
but H_2 dominates in the optical disk. In the disk, H_2 and HI show very
similar distributions, including small scale clumping. We compare the molecular
gas distribution with those of other star formation tracers, such as B and
H_alpha images.Comment: 20 pages, 15 figures, A&A accepted. A higher resolution version
available at http://www.astro.su.se/~andreas/publications
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