869 research outputs found
Model of the polarized foreground diffuse Galactic emissions from 33 to 353 GHz
We present 3D models of the Galactic magnetic field including regular and
turbulent components, and of the distribution of matter in the Galaxy including
relativistic electrons and dust grains. By integrating along the line of sight,
we construct maps of the polarized Galactic synchrotron and thermal dust
emissions for each of these models. We perform a likelihood analysis to compare
the maps of the Ka, Q, V and W bands of the Wilkinson Microwave Anisotropy
Probe (Wmap) and the 353 GHz Archeops data to the models obtained by varying
the pitch angle of the regular magnetic field, the relative amplitude of the
turbulent magnetic field and the extrapolation spectral indices of the
synchrotron and thermal dust emissions. The best-fit parameters obtained for
the different frequency bands are very similar and globally the data seem to
favor a negligible isotropic turbulent magnetic field component at large
angular scales (an anisotropic line-of-sight ordered component can not be
studied using these data). From this study, we conclude that we are able to
propose a consistent model of the polarized diffuse Galac- tic synchrotron and
thermal dust emissions in the frequency range from 33 to 353 GHz, where most of
the CMB studies are performed and where we expect a mixture of these two main
foreground emissions. This model can be very helpful to estimate the
contamination by foregrounds of the polarized CMB anisotropies, for experiments
like the Planck satellite.Comment: 22 pages, 4 figure
A Sunyaev-Zel'dovich map of the massive core in the luminous X-ray cluster RXJ1347-1145
We have mapped the Sunyaev-Zel'dovich decrement (hereafter SZ) in the
direction of the most luminous X-ray cluster known to date, RXJ1347-1145, at
z=0.451. This has been achieved with an angular resolution of about 23'' using
the Diabolo photometer running on the IRAM 30 meter radio telescope. We present
here a map of the cluster central region at 2.1mm. The Comptonization parameter
towards the cluster center, \yc=(12.7^{+2.9}_{-3.1})\times 10^{-4},
corresponds to the deepest SZ decrement ever observed. Using the gas density
distribution derived from X-ray data, this measurement implies a gas
temperature \te=16.2 \pm 3.8 keV. The resulting total mass of the cluster is,
under hydrostatic equilibrium, for a corresponding gas fraction .Comment: 16 pages, 2 figures, accepted for publication in ApJ Letter
Search for grain growth towards the center of L1544
In dense and cold molecular clouds dust grains are surrounded by thick icy
mantles. It is however not clear if dust growth and coagulation take place
before the switch-on of a protostar. This is an important issue, as the
presence of large grains may affect the chemical structure of dense cloud
cores, including the dynamically important ionization fraction, and the future
evolution of solids in protoplanetary disks. To study this further, we focus on
L1544, one of the most centrally concentrated pre-stellar cores on the verge of
star formation, and with a well-known physical structure. We observed L1544 at
1.2 and 2 mm using NIKA, a new receiver at the IRAM 30 m telescope, and we used
data from the Herschel Space Observatory archive. We find no evidence of grain
growth towards the center of L1544 at the available angular resolution.
Therefore, we conclude that single dish observations do not allow us to
investigate grain growth toward the pre-stellar core L1544 and high sensitivity
interferometer observations are needed. We predict that dust grains can grow to
200 m in size toward the central ~300 au of L1544. This will imply a dust
opacity change by a factor of ~2.5 at 1.2 mm, which can be detected using the
Atacama Large Millimeter and submillimeter Array (ALMA) at different
wavelengths and with an angular resolution of 2".Comment: 12 pages, 14 figures. Accepted for publication in A&
A Characterization of the Diffuse Galactic Emissions in the Anticenter of the Galaxy
Using the Archeops and WMAP data, we perform a study of the anticenter Galactic diffuse emissionsâthermal dust, synchrotron, free-free, and anomalous emissionsâat degree scales. The high-frequency data are used to infer the thermal dust electromagnetic spectrum and spatial distribution allowing us to precisely subtract this component at lower frequencies. After subtraction of the thermal dust component, a mixture of standard synchrotron and free-free emissions does not account for the residuals at these low frequencies. Including the all-sky 408âMHz Haslam data we find evidence for anomalous emission with a spectral index of â2.5 in units. However, we are not able to provide coclusion regarding the nature of this anomalous emission in this region. For this purpose, data between 408âMHz and 20âGHz covering the same sky region are needed
Deep Galaxy survey at 6.75 micron with the ISO satellite
Deep 6.75um mid-IR ISOCAM observations were obtained of the Canada-France
Redshift Survey (CFRS) 1415+52 field with the Infrared Space Observatory. The
identification of the sources with optical counterparts is described in detail,
and a classification scheme is devised which depends on the S/N of the
detection and the inverse probability of chance coincidence. 83% of the 54
ISOCAM sources are identified with Iab<23.5 counterparts. The (I-K)ab colors,
radio properties, spectrophotometric properties and frequency of nuclear
activity of these counterparts differ on average from those of typical CFRS
galaxies. CFRS spectra are available for 21 of the sources which have Iab <=
22.5 (including 7 stars). Most of the strongest sources are stars or AGN. Among
the non--stellar counterparts with spectra, 40% are AGNs, and 53% are galaxies
that display star formation activity and/or significant contributions of A
stars. The ISOCAM sources also display an IR excess, even when compared with
heavily-reddened local starburst galaxies. An upper limit of 30% of
extragalactic ISO sources could be at z>1 of the 44 S6.75um > 150uJy sources
which are non-stellar (7 "spectroscopic" and 3 "photometric" stars excluded)Comment: 13 pages, 12 figures. Accepted for publication in A
Simulations of the Microwave Sky and of its ``Observations''
Here follows a preliminary report on the construction of fake millimeter and
sub-millimeter skies, as observed by virtual instruments, e.g. the COBRA/SAMBA
mission, using theoretical modeling and data extrapolations. Our goal is to
create maps as realistic as possible of the relevant physical contributions
which may contribute to the detected signals. This astrophysical modeling is
followed by simulations of the measurement process itself by a given
instrumental configuration. This will enable a precise determination of what
can and cannot be achieved with a particular experimental configuration, and
provide a feedback on how to improve the overall design. It is a key step on
the way to define procedures for the separation of the different physical
processes in the future observed maps. Note that this tool will also prove
useful in preparing and analyzing current (\eg\ balloon borne) Microwave
Background experiments. Keywords: Cosmology -- Microwave Background
Anisotropies.Comment: 6 pages of uuencoded compressed postscript (1.2 Mb uncompressed), to
appear in the proceedings of the meeting "Far Infrared and Sub-millimeter
Space Missions in the Next Decade'', Paris, France, Eds. M. Sauvage, Space
Science Revie
Gran Telescopio Canarias OSIRIS Transiting Exoplanet Atmospheric Survey: Detection of potassium in XO-2b from narrowband spectrophotometry
We present Gran Telescopio Canarias (GTC) optical transit narrow-band
photometry of the hot-Jupiter exoplanet XO-2b using the OSIRIS instrument. This
unique instrument has the capabilities to deliver high cadence narrow-band
photometric lightcurves, allowing us to probe the atmospheric composition of
hot Jupiters from the ground. The observations were taken during three transit
events which cover four wavelengths at spectral resolutions near 500, necessary
for observing atmospheric features, and have near-photon limited sub-mmag
precisions. Precision narrow-band photometry on a large aperture telescope
allows for atmospheric transmission spectral features to be observed for
exoplanets around much fainter stars than those of the well studied targets
HD209458b and HD189733b, providing access to the majority of known transiting
planets. For XO-2b, we measure planet-to-star radius contrasts of
R_pl/R_star=0.10508+/-0.00052 at 6792 Ang, 0.10640+/-0.00058 at 7582 Ang, and
0.10686+/-0.00060 at 7664.9 Ang, and 0.10362+/-0.00051 at 8839 Ang. These
measurements reveal significant spectral features at two wavelengths, with an
absorption level of 0.067+/-0.016% at 7664.9 Ang due to atmospheric potassium
in the line core (a 4.1-sigma significance level), and an absorption level of
0.058+/-0.016% at 7582 Ang, (a 3.6-sigma significance level). When comparing
our measurements to hot-Jupiter atmospheric models, we find good agreement with
models which are dominated in the optical by alkali metals. This is the first
evidence for potassium in an extrasolar planet, an element that has long been
theorized along with sodium to be a dominant source of opacity at optical
wavelengths for hot Jupiters.Comment: 11 pages, 6 figures, accepted in A&A, minor changes to wording,
primarily section 4.2, and the title has also been slightly modifie
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