596 research outputs found
Kepler-539: a young extrasolar system with two giant planets on wide orbits and in gravitational interaction
We confirm the planetary nature of Kepler-539b (aka Kepler object of interest
K00372.01), a giant transiting exoplanet orbiting a solar-analogue G2 V star.
The mass of Kepler-539b was accurately derived thanks to a series of precise
radial velocity measurements obtained with the CAFE spectrograph mounted on the
CAHA 2.2m telescope. A simultaneous fit of the radial-velocity data and Kepler
photometry revealed that Kepler-539b is a dense Jupiter-like planet with a mass
of Mp = 0.97 Mjup and a radius of Rp = 0.747 Rjup, making a complete circular
revolution around its parent star in 125.6 days. The semi-major axis of the
orbit is roughly 0.5 au, implying that the planet is at roughly 0.45 au from
the habitable zone. By analysing the mid-transit times of the 12 transit events
of Kepler-539b recorded by the Kepler spacecraft, we found a clear modulated
transit time variation (TTV), which is attributable to the presence of a planet
c in a wider orbit. The few timings available do not allow us to precisely
estimate the properties of Kepler-539c and our analysis suggests that it has a
mass between 1.2 and 3.6 Mjup, revolving on a very eccentric orbit (0.4<e<0.6)
with a period larger than 1000 days. The high eccentricity of planet c is the
probable cause of the TTV modulation of planet b. The analysis of the CAFE
spectra revealed a relatively high photospheric lithium content, A(Li)=2.48
dex, which, together with both a gyrochronological and isochronal analysis,
suggests that the parent star is relatively young.Comment: 11 pages, 14 figures, accepted for publication in Astronomy &
Astrophysic
Early optical spectra of nova V1369 Cen show presence of Lithium
We present early high resolution spectroscopic observations of the nova V1369
Cen. We have detected an absorption feature at 6695.6 \AA\, that we have
identified as blue--shifted Li I 6708 \AA. The absorption line,
moving at -550 km/s, was observed in five high-resolution spectra of the nova
obtained at different epochs. On the basis of the intensity of this absorption
line we infer that a single nova outburst can inject in the Galaxy
0.3 - 4.8 M. Given the current estimates of
Galactic nova rate, this amount is sufficient to explain the puzzling origin of
the overabundance of Lithium observed in young star populations.Comment: 6 pages, 5 figures, accepted for publication in ApJLetter
Precision stellar radial velocity measurements with FIDEOS at the ESO 1-m telescope of La Silla
We present results from the commissioning and early science programs of
FIDEOS, the new high-resolution echelle spectrograph developed at the Centre of
Astro Engineering of Pontificia Universidad Catolica de Chile, and recently
installed at the ESO 1m telescope of La Silla. The instrument provides spectral
resolution R = 43,000 in the visible spectral range 420-800 nm, reaching a
limiting magnitude of 11 in V band. Precision in the measurement of radial
velocity is guaranteed by light feeding with an octagonal optical fibre,
suitable mechanical isolation, thermal stabilisation, and simultaneous
wavelength calibration. Currently the instrument reaches radial velocity
stability of = 8 m/s over several consecutive nights of observation
Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars
CONTEXT. Exoplanet searches have demonstrated that giant planets are
preferentially found around metal-rich stars and that their fraction increases
with the stellar mass. AIMS. During the past six years, we have conducted a
radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this
information, we aim to study the role of the stellar evolution in the orbital
parameters of the companions, and to unveil possible correlations between the
stellar properties and the occurrence rate of giant planets. METHODS. Using
FEROS and CHIRON spectra, we have computed precision radial velocities and we
have derived atmospheric and physical parameters for all of our targets.
Additionally, velocities computed from UCLES spectra are presented here. By
studying the periodic radial velocity signals, we have detected the presence of
several substellar companions. RESULTS. We present four new planetary systems
around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we find that giant planets are more frequent around metal-rich stars, reaching
a peak in the detection of = 16.7% around stars with
[Fe/H] 0.35 dex. Similarly, we observe a positive correlation of the
planet occurrence rate with the stellar mass, between M 1.0 -2.1
M, with a maximum of = 13.0%, at M = 2.1
M. CONCLUSIONS. We conclude that giant planets are preferentially
formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the mass range of M
1.0 - 2.1 M. These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support
to the core-accretion formation model.Comment: Accepted for publication in A&
Pheochromocytoma, polycythemia and venous thrombosis
Polycythemia is rarely associated with pheochromocytoma. A patient with a 22-year history of malignant pheochromocytoma is presented in whom major complications developed as a result of long-standing polycythemia, apparently due to secretion of erythropoletin by the tumors. Despite attempts to reduce tumor burden by surgery, chemotherapy, and large doses of 1-131-metalodobenzyl guanidine, polycythemia persisted. Extensive venous thrombosis developed requiring hospitalization and anticoagulation. Thus, polycythemia itself may be a cause of major morbidity in patients with pheochromocytoma, and prophylactic measures may be warranted. Review of the 130 patients with benign and malignant pheochromocytoma studied since the introduction of I-131-metaiodobenzylguanidine in 1980 revealed another six patients with hematocrits over 50 but only one had a hematocrit greater than 55 and required regular phlebotomy. In contrast, anemia (hematocrit less than 35) due to variety of causes was present in 18 cases.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26991/1/0000558.pd
Resummation Methods at Finite Temperature: The Tadpole Way
We examine several resummation methods for computing higher order corrections
to the finite temperature effective potential, in the context of a scalar
theory. We show by explicit calculation to four loops that dressing
the propagator, not the vertex, of the one-loop tadpole correctly counts
``daisy'' and ``super-daisy'' diagrams.Comment: 18 pages, LaTeX, CALT-68-1858, HUTP-93-A011, EFI-93-2
The Mass-Radius Relationship for Very Low Mass Stars: Four New Discoveries from the HATSouth Survey
We report the discovery of four transiting F-M binary systems with companions
between 0.1-0.2 Msun in mass by the HATSouth survey. These systems have been
characterised via a global analysis of the HATSouth discovery data, combined
with high-resolution radial velocities and accurate transit photometry
observations. We determined the masses and radii of the component stars using a
combination of two methods: isochrone fitting of spectroscopic primary star
parameters, and equating spectroscopic primary star rotation velocity with
spin-orbit synchronisation. These new very low mass companions are HATS550-016B
(0.110 -0.006/+0.005 Msun, 0.147 -0.004/+0.003 Rsun), HATS551-019B (0.17
-0.01/+0.01 Msun, 0.18 -0.01/+0.01 Rsun), HATS551-021B (0.132 -0.005/+0.014
Msun, 0.154 -0.008/+0.006 Rsun), HATS553-001B (0.20 -0.02/+0.01 Msun, 0.22
-0.01/+0.01 Rsun). We examine our sample in the context of the radius anomaly
for fully-convective low mass stars. Combining our sample with the 13 other
well-studied very low mass stars, we find a tentative 5% systematic deviation
between the measured radii and theoretical isochrone models.Comment: 17 pages, 8 figures, accepted for publication in MNRA
Electroweak bubbles and sphalerons
We consider non-perturbative solutions of the Weinberg-Salam model at finite
temperature. We employ an effective temperature-dependent potential yielding a
first order phase transition. In the region of the phase transition, there
exist two kinds of static, spherically symmetric solutions: sphalerons and
bubbles. We analyze these solutions as functions of temperature. We consider
the most general spherically symmetric fluctuations about the two solutions and
construct the discrete modes in the region of the phase transition. Sphalerons
and bubbles both possess a single unstable mode. We present simple
approximation formulae for these levels.Comment: 14 pages, plain tex, 9 figures appended as postscript files at the
end of the paper. THU-93/0
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