174 research outputs found
Oscillations in Arcturus from WIRE photometry
Observations of the red giant Arcturus (Alpha Boo) obtained with the star
tracker on the Wide Field Infrared Explorer (WIRE) satellite during a baseline
of 19 successive days in 2000 July-August are analysed. The amplitude spectrum
has a significant excess of power at low-frequencies. The highest peak is at
about 4.1 micro-Hz (2.8 d), which is in agreement with previous ground-based
radial velocity studies. The variability of Arcturus can be explained by sound
waves, but it is not clear whether these are coherent p-mode oscillations or a
single mode with a short life-time.Comment: 6 pages, 1 Latex file, 4 .eps figures, 2 .sty files, ApJL, 591, L151
See erratum (astro-ph/0308424
Asteroseismology with the WIRE satellite. I. Combining Ground- and Space-based Photometry of the Delta Scuti Star Epsilon Cephei
We have analysed ground-based multi-colour Stromgren photometry and
single-filter photometry from the star tracker on the WIRE satellite of the
delta scuti star Epsilon Cephei. The ground-based data set consists of 16
nights of data collected over 164 days, while the satellite data are nearly
continuous coverage of the star during 14 days. The spectral window and noise
level of the satellite data are superior to the ground-based data and this data
set is used to locate the frequencies. However, we can use the ground-based
data to improve the accuracy of the frequencies due to the much longer time
baseline. We detect 26 oscillation frequencies in the WIRE data set, but only
some of these can be seen clearly in the ground-based data. We have used the
multi-colour ground-based photometry to determine amplitude and phase
differences in the Stromgren b-y colour and the y filter in an attempt to
identify the radial degree of the oscillation frequencies. We conclude that the
accuracies of the amplitudes and phases are not sufficient to constrain
theoretical models of Epsilon Cephei. We find no evidence for rotational
splitting or the large separation among the frequencies detected in the WIRE
data set. To be able to identify oscillation frequencies in delta scuti stars
with the method we have applied, it is crucial to obtain more complete coverage
from multi-site campaigns with a long time baseline and in multiple filters.
This is important when planning photometric and spectroscopic ground-based
support for future satellite missions like COROT and KEPLER.Comment: 13 pages, 12 figures, 4 tables. Fig. 4 reduced in quality. Accepted
by A&
The effects of booster sessions on self-management interventions for chronic musculoskeletal pain: a systematic review and meta-analysis of randomised controlled trials
Our objective was to investigate the effectiveness of booster sessions after self-management interventions as a means of maintaining self-management behaviours in the treatment of chronic musculoskeletal pain. We searched MEDLINE, EMBASE, Science Citation Index, Cochrane Central Register of Controlled Trials and PsycINFO. Two authors independently identified eligible trials and collected data. We calculated the odds ratio (OR) for the analyses of dichotomous data, and standardised mean differences (SMD) with 95% confidence interval (CI) for continuous variables. Our search identified 14 studies with a total of 1695 patients. All studies were at high risk of bias and provided very low quality evidence. For the primary outcomes, booster sessions had no evidence of an effect on improving patient-reported outcomes on physical function (SMD-0.13, 95%CI -0.32 to -0.06; P=0.18), pain-related disability (SMD-0.16, 95%CI -0.36 to 0.03; P=0.11) and pain self-efficacy (SMD 0.15, 95%CI -0.07 to 0.36; P=0.18). For the secondary outcomes, booster sessions caused a significant reduction in patient-reported pain catastrophising (SMD-0.42, 95%CI -0.64 to -0.19; P=0.0004), and no evidence of an effect on patient-reported pain intensity, depression, coping or treatment adherence. There is currently little evidence that booster sessions are an effective way to prolong positive treatment effects or improve symptoms of long-term musculoskeletal conditions following self-management interventions. However, the studies were few with high heterogeneity, high risk of bias and overall low quality of evidence. Our review argues against including booster sessions routinely to self-management interventions for the purpose of behaviour maintenance
Testing the Stellar Rotation vs. Age Paradigm Using Wide Binaries in the Kepler & K2 Fields
Essential to understanding the history of the Galaxy’s stellar populations, ages are among the most difficult to measure properties of stars. Accurate stellar ages would provide key leverage on problems ranging from the habitability of exoplanets to the Galaxy’s chemical evolution and age. Gyrochronology, the empirical relation between rotation and age, is believed to be among the best current methods of stellar age determination. Using several hundred wide non-interacting binaries identified in the Kepler mission “K2” extended mission fields we are testing this paradigm. Such wide pairs afford a unique opportunity to unravel and calibrate the effects of mass, rotation, activity and age because components of a given binary should have rotation and activity levels consistent with their masses and a common age. We present preliminary results for several dozen wide pairs in which both components exhibit detectable rotational modulation
Sounding stellar cycles with Kepler - II. Ground-based observations
We have monitored 20 Sun-like stars in the Kepler field-of-view for excess
flux with the FIES spectrograph on the Nordic Optical Telescope since the
launch of Kepler spacecraft in 2009. These 20 stars were selected based on
their asteroseismic properties to sample the parameter space (effective
temperature, surface gravity, activity level etc.) around the Sun. Though the
ultimate goal is to improve stellar dynamo models, we focus the present paper
on the combination of space-based and ground-based observations can be used to
test the age-rotation-activity relations.
In this paper we describe the considerations behind the selection of these 20
Sun-like stars and present an initial asteroseismic analysis, which includes
stellar age estimates. We also describe the observations from the Nordic
Optical Telescope and present mean values of measured excess fluxes. These
measurements are combined with estimates of the rotation periods obtained from
a simple analysis of the modulation in photometric observations from Kepler
caused by starspots, and asteroseismic determinations of stellar ages, to test
relations between between age, rotation and activity.Comment: Accepted for publication in MNRA
Properties of 42 Solar-type Kepler Targets from the Asteroseismic Modeling Portal
Recently the number of main-sequence and subgiant stars exhibiting solar-like oscillations that are resolved
into individual mode frequencies has increased dramatically. While only a few such data sets were available
for detailed modeling just a decade ago, the Kepler mission has produced suitable observations for hundreds
of new targets. This rapid expansion in observational capacity has been accompanied by a shift in analysis
and modeling strategies to yield uniform sets of derived stellar properties more quickly and easily. We use
previously published asteroseismic and spectroscopic data sets to provide a uniform analysis of 42 solar-type
Kepler targets from the Asteroseismic Modeling Portal (AMP). We find that fitting the individual frequencies
typically doubles the precision of the asteroseismic radius, mass and age compared to grid-based modeling of
the global oscillation properties, and improves the precision of the radius and mass by about a factor of three
over empirical scaling relations. We demonstrate the utility of the derived properties with several applications
Stellar Coronal Spectroscopy with the Chandra HETGS
Spectroscopy with the Chandra High Energy Transmission Grating Spectrometer
provides details on X-ray emission and activity from young and cool stars
through resolution of emission lines from a variety of ions. We are beginning
to see trends in activity regarding abundances, emission measures, and
variability. Here we contrast spectra of TV Crt, a weak-lined T Tauri star,
with TW Hya, a Classical T Tauri star. TV Crt has a spectrum more like magnetic
activity driven coronae, relative to the TW Hya spectrum, which we have
interpreted as due to accretion-produced X-rays. We have also observed the long
period system, IM Pegasi to search for rotational modulation, and to compare
activity in a long period active binary to shorter period systems and to the
pre-main sequence stars. We detected no rotational modulation, but did see
long-duration flares.Comment: 5 pages, 2 figures; to be published in IAU Symposium 219: "Stars as
Suns: Activity, Evolution, Planets" (Ed. A. Dupree and A. O. Benz
A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry
Observations of Epsilon UMa obtained with the star tracker on the Wide Field
Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed.
This is one of the most precise photometry of an Ap star. The amplitude
spectrum is used to set an upper limit of 75 parts per million for the
amplitude of stellar pulsations in this star unless it accidentally oscillates
with a single mode at the satellite orbit, its harmonics or their one day
aliases. This is the tightest limit put on the amplitude of oscillations in an
Ap star. As the rotation period of Epsilon UMa is relatively short (5.1 d), it
cannot be argued that the observations were made at a wrong rotational phase.
Our results thus support the idea that some Ap stars do not pulsate at all.Comment: 4 pages, 4 figures, 2 style files, accepted for publication in ApJ
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