858 research outputs found
A data base of synthetic photometry in the GALEX ultraviolet bands for the stellar sources observed with the International Ultraviolet Explorer
The Galaxy Evolution Explorer (GALEX) has produced the largest photometric
catalogue of ultraviolet (UV) sources. As such, it has defined the new standard
bands for UV photometry: the near UV band (NUV) and the far UV band (FUV).
However, due to brightness limits, the GALEX mission has avoided the Galactic
plane which is crucial for astrophysical research and future space missions.
The International Ultraviolet Explorer (IUE) satellite obtained 63,755 spectra
in the low dispersion mode during its 18 years lifetime. We have derived the
photometry in the GALEX bands for the stellar sources in the IUE Archive to
extend the GALEX data base with observations including the Galactic plane.Good
quality spectra have been selected for all IUE classes of stellar sources. The
GALEX FUV and NUV magnitudes have been computed using the GALEX transmission
curves, as well as the conversion equations between flux and magnitudes
provided by the mission (galexgi.gsfc.nasa.gov). Consistency between GALEX and
IUE synthetic photometries has been tested using White Dwarfs (WD) contained in
both samples. The non-linear response performance of GALEX inferred from this
data agrees with the results from GALEX calibration. The photometric data base
is made available to the community through the services of the Centre de
Donn\'ees Stellaires at Strasbourg (CDS). The catalogue contains FUV magnitudes
for 1,631 sources, ranging from FUV=1.81 to FUV=18.65 mag. In the NUV band, the
catalogue includes observations for 1,005 stars ranging from NUV = 3.08 to NUV=
17.74 mag . UV photometry for 1,493 not included in the GALEX AIS GR5 catalogue
is provided; most of them are hot (O-A spectral type) stars. The sources in the
catalogue are distributed over the full sky, including the Galactic plane.Comment: Submitted to Astronomy & Astrophysic
Variation of the ultraviolet extinction law across the Taurus-Auriga star forming complex. A GALEX based study
The Taurus-Auriga molecular complex (TMC) is the main laboratory for the
study of low mass star formation. The density and properties of interstellar
dust are expected to vary across the TMC. These variations trace important
processes such as dust nucleation or the magnetic field coupling with the
cloud. In this article, we show how the combination of near ultraviolet (NUV)
and infrared (IR) photometry can be used to derive the strength of the 2175
\AA\ bump and thus any enhancement in the abundance of small dust grains and
PAHs in the dust grains size distribution. This technique is applied to the
envelope of the TMC, mapped by the GALEX All Sky Survey (AIS). UV and IR
photometric data have been retrieved from the GALEX-AIS and the 2MASS
catalogues. NUV and K-band star counts have been used to identify the areas in
the cloud envelope where the 2175 \AA\ bump is weaker than in the diffuse ISM
namely, the low column density extensions of L1495, L1498 and L1524 in Taurus,
L1545, L1548, L1519, L1513 in Auriga and L1482-83 in the California region.
This finding agrees with previous results on dust evolution derived from
Spitzer data and suggests that dust grains begin to decouple from the
environmental galactic magnetic field already in the envelope.Comment: Accepted in Monthly Notices of the Royal Astronomical Societ
WUVS Simulator: Detectability of spectral lines with the WSO-UV spectrographs
The World Space Observatory - Ultraviolet (WSO-UV) space telescope is
equipped with high dispersion (55,000) spectrographs working in the 1150-3100
{\AA} spectral range. To evaluate the impact of the design on the scientific
objectives of the mission, a simulation software tool has been developed. This
simulator builds on the development made for the PLATO space mission, and it is
designed to generate synthetic time-series of images by including models of all
important noise sources. In this article, we describe its design and
performance. Moreover, its application to the detectability of important
spectral features for star formation and exoplanetary research is addressed.Comment: 8 pages, 5 figure
Signatures of diffuse interstellar gas in the Galaxy Evolution Explorer all sky survey
The all sky survey run by the Galaxy Evolution Explorer (GALEX AIS) mapped
about 85% of the Galaxy at ultraviolet (UV) wavelengths and detected the
diffuse UV background produced by the scattering of the radiation from OBA
stars by interstellar dust grains. Against this background, diffuse weak
structures are detected as well as the UV counterparts to nebulae and molecular
clouds. To make full profit of the survey, unsupervised and semi-supervised
procedures need to be implemented. The main objective of this work is to
implement and analyze the results of the method developed by us for the blind
detection of ISM features in the GALEX AIS . Most ISM features are detected at
very low signal levels (dark filaments, globules) against the already faint UV
background. We have defined an index, the UV background fluctuations index (or
UBF index), to identify areas of the sky where these fluctuations are detected.
The algorithm is applied to the images obtained in the FUV (1344 -1786
Angstroms) band since this is less polluted by stellar sources, facilitating
the automated detection. The UBF index is shown to be sensitive to the main
star forming regions within the Gould's Belt, as well as to some prominent
loops like Loop I or the Eridanus and Monogem areas. The catalogue with the UBF
index values is made available on-line to the community.Comment: The online catalogue will be made available through the CDS services
and in the jcuva.ucm.es website. Accepted A&
Large-scale structures in the stellar wind of fast-rotating stars spawned by the presence of Earth-like planets
Forming planets around young, fast-rotating solar-like stars are exposed to
an intense X-ray/extreme ultraviolet radiation field and strongly magnetized
stellar winds, as a consequence of the high magnetic activity of these stars.
Under these conditions, Earth-like exoplanets may experience a rapid loss of
their primordial hydrogen atmospheres, resulting in atmosphere-less rocky
obstacles for the stellar winds. The interaction of stellar winds with those
planets leads to the formation of potentially observable structures due to the
formation of large-scale magnetic field and density disturbances in the
vicinity of these planets, such as bow shocks, induced magnetospheres and
comet-like tails. In this work, we study the interaction between the stellar
winds of active, fast-rotating solar-like stars in the superfast-magnetosonic
regime with Earth-like, unmagnetized, tenuous atmosphere, planetary obstacles
through numerical 3D simulations using the PLUTO magnetohydrodynamical code.
The properties of AB Doradus, a nearby young star with a small rotation period
(0.51 days) and a strong flaring activity, have been used to parameterize this
early wind state. Bow shock and induced magnetosphere formation are
characterized through the alfv\'enic Mach number MA of the wind, for different
stellar wind configurations. Large bow shocks, up to an extension of ~7.0
planetary radii are found for low-MA winds. The general increase of density,
temperature and magnetic field in these large-scale structures formed around
planets may result in potentially detectable spectral signatures
The World Space Observatory - Ultraviolet (WSO-UV) Space Telescope; Status Update in 2013
This is a short primer and a brief update on the status of the World Space Observatory-Ultraviolet (WSO-UV) project dated in May 2013. WSO-UV is a 170m primary space telescope equipped for ultraviolet imaging and spectroscopy that will be operational in 2017 hosting an open science program for the world-wide scientic community
AK Sco, first detection of a highly disturbed atmosphere in a pre-main sequence close binary
AK Sco is a unique source: a ~10 Myrs old pre-main sequence spectroscopic
binary composed of two nearly equal F5 stars that at periastron are separated
by barely eleven stellar radii so, the stellar magnetospheres fill the Roche
lobe at periastron. The orbit is not yet circularized (e=0.47) and very strong
tides are expected. This makes of AK Sco, the ideal laboratory to study the
effect of gravitational tides in the stellar magnetic field building up during
pre-main sequence (PMS) evolution. In this letter, the detection of a highly
disturbed (sigma ~ 100 km/s) and very dense atmosphere (ne = 1.6e10cm-3) is
reported. Significant line broadening blurs any signs of ion belts or bow
shocks in the spectrum of the atmospheric plasma. The radiative loses cannot be
accounted solely by the dissipation of energy from the tidal wave propagating
in the stellar atmosphere; neither by the accreting material. The release of
internal energy from the star seems to be the most likely source of the plasma
heating. This is the first clear indication of a highly disturbed atmosphere
surrounding a pre-main sequence close binary.Comment: 10 pages 2 figures. Astrophysical Journal Letters, accepte
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