367 research outputs found
Interactions of the magnetospheres of stars and close-in giant planets
Since the first discovery of an extrasolar planetary system more than a
decade ago, hundreds more have been discovered. Surprisingly, many of these
systems harbor Jupiter-class gas giants located close to the central star, at
distances of 0.1 AU or less. Observations of chromospheric 'hot spots' that
rotate in phase with the planetary orbit, and elevated stellar X-ray
luminosities,suggest that these close-in planets significantly affect the
structure of the outer atmosphere of the star through interactions between the
stellar magnetic field and the planetary magnetosphere. Here we carry out the
first detailed three-dimensional MagnetoHydroHynamics (MHD) simulation
containing the two magnetic bodies and explore the consequences of such
interactions on the steady-state coronal structure. The simulations reproduce
the observable features of 1) increase in the total X-ray luminosity, 2)
appearance of coronal hot spots, and 3) phase shift of these spots with respect
to the direction of the planet. The proximate cause of these is an increase in
the density of coronal plasma in the direction of the planet, which prevents
the corona from expanding and leaking away this plasma via a stellar wind. The
simulations produce significant low temperature heating. By including dynamical
effects, such as the planetary orbital motion, the simulation should better
reproduce the observed coronal heating
Identifying Nearby, Young, Late-type Stars by Means of Their Circumstellar Disks
It has recently been shown that a significant fraction of late-type members
of nearby, very young associations (age <10 Myr) display excess emission at
mid-IR wavelengths indicative of dusty circumstellar disks. We demonstrate that
the detection of mid-IR excess emission can be utilized to identify new nearby,
young, late-type stars including two definite new members ("TWA 33" and "TWA
34") of the TW Hydrae Association. Both new TWA members display mid-IR excess
emission in the Wide-field Infrared Survey Explorer (WISE) catalog and they
show proper motion and youthful spectroscopic characteristics -- namely H\alpha
emission, strong lithium absorption, and low surface gravity features
consistent with known TWA members. We also detect mid-IR excess -- the first
unambiguous evidence of a dusty circumstellar disk -- around a previously
identified UV-bright, young, accreting star (2M1337) that is a likely member of
the Lower-Centaurus Crux region of the Scorpius Centaurus Complex.Comment: ApJ, Accepte
MOST detects variability on tau Bootis possibly induced by its planetary companion
(abridged) There is considerable interest in the possible interaction between
parent stars and giant planetary companions in 51 Peg-type systems. We
demonstrate from MOST satellite photometry and Ca II K line emission that there
has been a persistent, variable region on the surface of tau Boo A which
tracked its giant planetary companion for some 440 planetary revolutions and
lies ~68deg (phi=0.8) in advance of the sub-planetary point. The light curves
are folded on a range of periods centered on the planetary orbital period and
phase dependent variability is quantified by Fourier methods and by the mean
absolute deviation (MAD) of the folded data for both the photometry and the Ca
II K line reversals. The region varies in brightness on the time scale of a
rotation by ~1 mmag. In 2004 it resembled a dark spot of variable depth, while
in 2005 it varied between bright and dark. Over the 123 planetary orbits
spanned by the photometry the variable region detected in 2004 and in 2005 are
synchronised to the planetary orbital period within 0.0015 d. The Ca II K line
in 2001, 2002 and 2003 also shows enhanced K-line variability centered on
phi=0.8, extending coverage to some 440 planetary revolutions. The apparently
constant rotation period of the variable region and its rapid variation make an
explanation in terms of conventional star spots unlikely. The lack of
complementary variability at phi=0.3 and the detection of the variable region
so far in advance of the sub-planetary point excludes tidal excitation, but the
combined photometric and Ca II K line reversal results make a good case for an
active region induced magnetically on the surface of tau Boo A by its planetary
companion.Comment: 7 pages, 7 figures; accepted for publication in A&
On the chromospheric activity of stars with planets
Context. Signatures of chromospheric activity enhancement have been found for
a dozen stars, pointing to a possible star-planet interaction. Nevertheless in
the coronal activity regime, there is no conclusive observational evidence for
such an interaction. Does star-planet interaction manifest itself only for a
few particular cases, without having a major effect on stars with planets in
general? Aims. We aim to add additional observational constraints to support or
reject the major effects of star-planet interactions in stellar activity, based
on CaII chromospheric emission flux. Methods. We performed a statistical
analysis of CaII emission flux of stars with planets, as well as a comparison
between CaII and X-ray emission fluxes, searching for dependencies on planetary
parameters. Results. In the present sample of stars with planets, there are no
significant correlations between chromospheric activity indicator log(R'HK) and
planetary parameters. Further, the distribution of the chromospheric activity
indicator for stars without planets is not distinguishable from the one with
planets.Comment: 6 pages, 5 figures, submitted to A&
A detailed spectropolarimetric analysis of the planet hosting star WASP-12
The knowledge of accurate stellar parameters is paramount in several fields
of stellar astrophysics, particularly in the study of extrasolar planets, where
often the star is the only visible component and therefore used to infer the
planet's fundamental parameters. Another important aspect of the analysis of
planetary systems is the stellar activity and the possible star-planet
interaction. Here we present a self-consistent abundance analysis of the planet
hosting star WASP-12 and a high-precision search for a structured stellar
magnetic field on the basis of spectropolarimetric observations obtained with
the ESPaDOnS spectropolarimeter. Our results show that the star does not have a
structured magnetic field, and that the obtained fundamental parameters are in
good agreement with what was previously published. In addition we derive
improved constraints on the stellar age (1.0-2.65 Gyr), mass (1.23-1.49 M/M0),
and distance (295-465 pc). WASP-12 is an ideal object to look for pollution
signatures in the stellar atmosphere. We analyse the WASP-12 abundances as a
function of the condensation temperature and compare them with those published
by several other authors on planet hosting and non-planet hosting stars. We
find hints of atmospheric pollution in WASP-12's photosphere, but are unable to
reach firm conclusions with our present data. We conclude that a differential
analysis based on WASP-12 twins will probably clarify if an atmospheric
pollution is present, the nature of this pollution and its implications in the
planet formation and evolution. We attempt also the direct detection of the
circumstellar disk through infrared excess, but without success.Comment: 49 pages, 11 figures, Accepted for publication on Ap
Investigation of using sulfur-containing gases in low-temperature fuel cell at sulfuric acid production site
The possibility and effectiveness of using sulfur dioxide and hydrogen sulfide as the fuel in lowtemperature
fuel cells at the sulfuric acid production site has been investigated. A fuel cell has been designed
and constructed using palladium as a catalyst, which enables conversion of the energy of oxidation of sulfur
dioxide and hydrogen sulfide to the electric energy. The experimental data showed that the use of hydrogen
sulfide and sulfur dioxide as a fuel allows achieving the power of 1.0 and 0.5 mW, respectively. The
comparative studies with the use of hydrogen in the same fuel cell resulted in the power of about 2.0 mW,
i.e. the use of hydrogen sulfide delivers a performance comparable with that of the hydrogen. The processes
of oxidizing of the sulfur containing gases are used in our company in production of sulfuric acid. Oxidation
of these gases conducted using the conventional technological processes. The use of these processes to
produce energy as a byproduct could be an attractive way to reduce the energy consumption of the whole
process. Considering the relatively high power obtained in this work for the sulfur containing gases fed fuel
cells, the substitution of conventional oxidation of sulfur containing gases in this technological chain by the
fuel cell oxidation, and by-producing the electric energy, could be very profitable for the energy efficiency
enhancement of the main production process. In the future work, the design and development of fuel cell
catalysts and membranes to enhance the performances of sulfur containing fuel cells will be significant
A New Method to Identify Nearby, Young, Low-mass Stars
We describe a new method to identify young, late-type stars within ~150 pc of
the Earth that employs visual or near-infrared data and the GALEX GR4/5
database. For spectral types later than K5, we demonstrate that the ratio of
GALEX near-ultraviolet (NUV) to visual and near-IR emission is larger for stars
with ages between 10 and 100 Myr than for older, main sequence stars. A search
in regions of the sky encompassing the TW Hya and Scorpius-Centaurus
Associations has returned 54 high-quality candidates for followup.
Spectroscopic observations of 24 of these M1-M5 objects reveal Li 6708 angstrom
absorption in at least 17 systems. Because GALEX surveys have covered a
significant fraction of the sky, this methodology should prove valuable for
future young star studies.Comment: 27 pages, 8 figures, accepted for publication in ApJ. Some
significant changes were made in proof, we recommend readers use the ApJ
versio
The Tucana/Horologium, Columba, AB Doradus, and Argus Associations: New Members and Dusty Debris Disks
We propose 35 star systems within ~70 pc of Earth as newly identified members
of nearby young stellar kinematic groups; these identifications include the
first A- and late-B type members of the AB Doradus moving group and field Argus
Association. All but one of the 35 systems contain a bright solar- or
earlier-type star that should make an excellent target for the next generation
of adaptive optics (AO) imaging systems on large telescopes. AO imaging has
revealed four massive planets in orbit around the {\lambda} Boo star HR 8799.
Initially the planets were of uncertain mass due in large part to the uncertain
age of the star. We find that HR 8799 is a likely member of the ~30 Myr old
Columba Association implying planet masses ~6 times that of Jupiter. We
consider Spitzer Space Telescope MIPS photometry of stars in the ~30 Myr old
Tucana/Horologium and Columba Associations, the ~40 Myr old field Argus
Association, and the ~70 Myr old AB Doradus moving group. The percentage of
stars in these young stellar groups that display excess emission above the
stellar photosphere at 24 and 70 \mu m wavelengths - indicative of the presence
of a dusty debris disk - is compared with corresponding percentages for members
of 11 open clusters and stellar associations with ages between 8 and 750 Myr,
thus elucidating the decay of debris disks with time.Comment: Accepted for publication in Ap
Searching for star-planet magnetic interaction in CoRoT observations
Close-in massive planets interact with their host stars through tidal and
magnetic mechanisms. In this paper, we review circumstantial evidence for
star-planet interaction as revealed by the photospheric magnetic activity in
some of the CoRoT planet-hosting stars, notably CoRoT-2, CoRoT-4, and CoRoT-6.
The phenomena are discussed in the general framework of activity-induced
features in stars accompanied by hot Jupiters. The theoretical mechanisms
proposed to explain the activity enhancements possibly related with hot Jupiter
are also briefly reviewed with an emphasis on the possible effects at
photospheric level. The unique advantages of CoRoT and Kepler observations to
test these models are pointed out.Comment: Invited review paper accepted by Astrophysics and Space Science, 13
pages, 5 figure
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