274 research outputs found
Predicting the detectability of oscillations in solar-type stars observed by Kepler
Asteroseismology of solar-type stars has an important part to play in the
exoplanet program of the NASA Kepler Mission. Precise and accurate inferences
on the stellar properties that are made possible by the seismic data allow very
tight constraints to be placed on the exoplanetary systems. Here, we outline
how to make an estimate of the detectability of solar-like oscillations in any
given Kepler target, using rough estimates of the temperature and radius, and
the Kepler apparent magnitude.Comment: 21 pages, 6 figures, accepted for publication Astrophysical Journa
Rotator cuff isokinetic strength of young group aged swimmers in a competitive training program
Introduction: In any given sports activity, muscular or movement instability is
pointed out as having a high influence for the maintenance of correct joint
functionality. In swimming, due to the repetitive use of shoulder muscles, there is a
higher tendency to promote injuries at the shoulder joint, especially when instability
between the internal (IR) and external (ER) shoulder rotators is present. The aims of
this study were to evaluate the rotator cuff isokinetic strength in order to determine
any possible muscular over compensation or imbalance, and to assess differences
between the dominant and non-dominant side, of young group aged swimmers.
Methods: Forty young aged swimmers in a competitive training program were
evaluated, and divided in two groups. Only subjects without any previous history of
strength training were included. Group 1 (n=19), age 15 to 16 (years); height [mean
(SD)] 168.6 (6.5) (centimeters); weight 59.6 (6.0) (kilograms), training/week 113.7
(12.6) (minutes); experience 5.3 (1.6) (years) and Group 2 (n=21); age 13 to 14;
height 160.5 (12.2); weight 50.4 (10.8); training/week 88.6 (17.7); experience 4.1
(2.2) (years). The maximal unilateral isokinetic strength was measured (Biodex
System 3) on the shoulder IR and ER during concentric action at 60°/second,
bilaterally. Data was examined by the application of appropriate statistical tests for
the analysis of variance.
Results: Statistical differences were found on peak torque (Nm) at the
agonist/antagonist ratio measured unilaterally [Group 1: right shoulder 35.8 (7.9) (IR)
and 25.8 (4.7) (ER) (p=0.001) and left shoulder 32.7 (6.7) (IR) and 23.9 (5.1) (ER)
(p=0.001) / Group 2: right shoulder 23.4 (6.5) (IR) and 19.0 (5.4) (ER) (p=0.048) and
left shoulder 22.4 (5.4) (IR) and 16.8 (6.1) (ER) (p=0.027)]. However, no statistical
differences were found between the maximal rotation strength measured bilaterally
[Group 1: ER (p=0.280) and IR (p=0.246) / Group 2: ER (p=0.186) and IR
(p=0.522)].
Conclusion: Young swimmers involved in a competitive training program can suffer
from unilateral over compensation at shoulder IR or ER. This compensation seems to
increase with the number of training years. To enable a higher stability between the
internal and external shoulder rotators it is recommended that shoulder muscle
strengthening should be considered in young aged swimmers training programs
The Factory and The Beehive I. Rotation Periods For Low-Mass Stars in Praesepe
Stellar rotation periods measured from single-age populations are critical
for investigating how stellar angular momentum content evolves over time, how
that evolution depends on mass, and how rotation influences the stellar dynamo
and the magnetically heated chromosphere and corona. We report rotation periods
for 40 late-K to mid-M stars members of the nearby, rich, intermediate-age
(~600 Myr) open cluster Praesepe. These rotation periods were derived from ~200
observations taken by the Palomar Transient Factory of four cluster fields from
2010 February to May. Our measurements indicate that Praesepe's mass-period
relation transitions from a well-defined singular relation to a more scattered
distribution of both fast and slow rotators at ~0.6 Msun. The location of this
transition is broadly consistent with expectations based on observations of
younger clusters and the assumption that stellar-spin down is the dominant
mechanism influencing angular momentum evolution at 600 Myr. However, a
comparison to data recently published for the Hyades, assumed to be coeval to
Praesepe, indicates that the divergence from a singular mass-period relation
occurs at different characteristic masses, strengthening the finding that
Praesepe is the younger of the two clusters. We also use previously published
relations describing the evolution of rotation periods as a function of color
and mass to evolve the sample of Praesepe periods in time. Comparing the
resulting predictions to periods measured in M35 and NGC 2516 (~150 Myr) and
for kinematically selected young and old field star populations suggests that
stellar spin-down may progress more slowly than described by these relations.Comment: To appear in the ApJ. 18 pages, 12 figures; version with higher
resolution figures available at
http://www.astro.columbia.edu/~marcel/papers/praesepe.pdf. Paper title
inspired by local news; see http://tinyurl.com/redhone
Detection of a transit of the super-Earth 55 Cnc e with Warm Spitzer
We report on the detection of a transit of the super-Earth 55 Cnc e with warm
Spitzer in IRAC's 4.5-micron band. Our MCMC analysis includes an extensive
modeling of the systematic effects affecting warm Spitzer photometry, and
yields a transit depth of 410 +- 63 ppm, which translates to a planetary radius
of 2.08 +- 0.16 R_Earth as measured in IRAC 4.5-micron channel. A planetary
mass of 7.81 +- 0.58 M_Earth is derived from an extensive set of
radial-velocity data, yielding a mean planetary density of 4.8 +- 1.3 g cm-3.
Thanks to the brightness of its host star (V = 6, K = 4), 55 Cnc e is a unique
target for the thorough characterization of a super-Earth orbiting around a
solar-type star.Comment: Accepted for publication in A&A on 31 July 2011. 9 pages, 7 figures
and 3 tables. Minor changes. The revised version includes a baseline models
comparison and a new figure presenting the spatially- and time-dependent
terms of the model function used in Eq.
Solar-like oscillations in KIC11395018 and KIC11234888 from 8 months of Kepler data
We analyze the photometric short-cadence data obtained with the Kepler
Mission during the first eight months of observations of two solar-type stars
of spectral types G and F: KIC 11395018 and KIC 11234888 respectively, the
latter having a lower signal-to-noise ratio compared to the former. We estimate
global parameters of the acoustic (p) modes such as the average large and small
frequency separations, the frequency of the maximum of the p-mode envelope and
the average linewidth of the acoustic modes. We were able to identify and to
measure 22 p-mode frequencies for the first star and 16 for the second one even
though the signal-to-noise ratios of these stars are rather low. We also derive
some information about the stellar rotation periods from the analyses of the
low-frequency parts of the power spectral densities. A model-independent
estimation of the mean density, mass and radius are obtained using the scaling
laws. We emphasize the importance of continued observations for the stars with
low signal-to-noise ratio for an improved characterization of the oscillation
modes. Our results offer a preview of what will be possible for many stars with
the long data sets obtained during the remainder of the mission.Comment: 39 pages, 9 figures. Accepted for publication in Ap
Probing dust grain evolution in IM Lupi's circumstellar disc. Multi-wavelength observations and modelling of the dust disc
We present a panchromatic study, involving a multiple technique approach, of
the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). We have
undertaken a comprehensive observational study of IM Lupi using photometry,
spectroscopy, millimetre interferometry and multi-wavelength imaging. For the
first time, the disc is resolved from optical and near-infrared wavelengths in
scattered light, to the millimetre regime in thermal emission. Our data-set, in
conjunction with existing photometric data, provides an extensive coverage of
the spectral energy distribution, including a detailed spectrum of the silicate
emission bands. We have performed a simultaneous modelling of the various
observations, using the radiative transfer code MCFOST, and analysed a grid of
models over a large fraction of the parameter space via Bayesian inference. We
have constructed a model that can reproduce all of the observations of the
disc. Our analysis illustrates the importance of combining a wide range of
observations in order to fully constrain the disc model, with each observation
providing a strong constraint only on some aspects of the disc structure and
dust content. Quantitative evidence of dust evolution in the disc is obtained:
grain growth up to millimetre-sized particles, vertical stratification of dust
grains with micrometric grains close to the disc surface and larger grains
which have settled towards the disc midplane, and possibly the formation of
fluffy aggregates and/or ice mantles around grains.Comment: 20 pages, 13 figures. Accepted for publication in A&
Lamost observations in the kepler field. I. Database of low-resolution spectra*
The nearly continuous light curves with micromagnitude precision provided by the space mission Kepler are revolutionizing our view of pulsating stars. They have revealed a vast sea of low-amplitude pulsation modes that were undetectable from Earth. The long time base of Kepler light curves allows for the accurate determination of the frequencies and amplitudes of pulsation modes needed for in-depth asteroseismic modeling. However, for an asteroseismic study to be successful, the first estimates of stellar parameters need to be known and they cannot be derived from the Kepler photometry itself. The Kepler Input Catalog provides values for the effective temperature, surface gravity, and metallicity, but not always with sufficient accuracy. Moreover, information on the chemical composition and rotation rate is lacking. We are collecting low-resolution spectra for objects in the Kepler field of view with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, Xinglong observatory, China). All of the requested fields have now been observed at least once. In this paper, we describe those observations and provide a useful database for the whole astronomical communit
Improved precision on the radius of the nearby super-Earth 55 Cnc e
We report on new transit photometry for the super-Earth 55 Cnc e obtained
with Warm Spitzer/IRAC at 4.5 microns. An individual analysis of these new data
leads to a planet radius of 2.21-0.16+0.15 Rearth, in good agreement with the
values previously derived from the MOST and Spitzer transit discovery data. A
global analysis of both Spitzer transit time-series improves the precision on
the radius of the planet at 4.5 microns to 2.20+-0.12 Rearth. We also performed
an independent analysis of the MOST data, paying particular attention to the
influence of the systematic effects of instrumental origin on the derived
parameters and errors by including them in a global model instead of performing
a preliminary detrending-filtering processing. We deduce an optical planet
radius of 2.04+0.15 Rearth from this reanalysis of MOST data, which is
consistent with the previous MOST result and with our Spitzer infrared radius.
Assuming the achromaticity of the transit depth, we performed a global analysis
combining Spitzer and MOST data that results in a planet radius of 2.17+-0.10
Rearth (13,820+-620 km). These results point to 55 Cnc e having a gaseous
envelope overlying a rocky nucleus, in agreement with previous works. A
plausible composition for the envelope is water which would be in
super-critical form given the equilibrium temperature of the planet.Comment: 7 pages, 7 figures. Submitted to A&A on 21/10/2011. Accepted for
publication in A&A on . 28/12/2011. Accepted version uploade
A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
Exoplanets orbiting close to their parent stars could lose some fraction of
their atmospheres because of the extreme irradiation. Atmospheric mass loss
primarily affects low-mass exoplanets, leading to suggest that hot rocky
planets might have begun as Neptune-like, but subsequently lost all of their
atmospheres; however, no confident measurements have hitherto been available.
The signature of this loss could be observed in the ultraviolet spectrum, when
the planet and its escaping atmosphere transit the star, giving rise to deeper
and longer transit signatures than in the optical spectrum. Here we report that
in the ultraviolet the Neptune-mass exoplanet GJ 436b (also known as Gliese
436b) has transit depths of 56.3 +/- 3.5% (1 sigma), far beyond the 0.69%
optical transit depth. The ultraviolet transits repeatedly start ~2 h before,
and end >3 h after the ~1 h optical transit, which is substantially different
from one previous claim (based on an inaccurate ephemeris). We infer from this
that the planet is surrounded and trailed by a large exospheric cloud composed
mainly of hydrogen atoms. We estimate a mass-loss rate in the range of
~10^8-10^9 g/s, which today is far too small to deplete the atmosphere of a
Neptune-like planet in the lifetime of the parent star, but would have been
much greater in the past.Comment: Published in Nature on 25 June 2015. Preprint is 28 pages, 12
figures, 2 table
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