143 research outputs found
A Jupiter-mass planet around the K0 giant HD 208897
For over 10 years, we have carried out a precise radial velocity (RV) survey
to find substellar companions around evolved G,K-type stars to extend our
knowledge of planet formation and evolution. We performed high precision RV
measurements for the giant star HD 208897 using an iodine (I2) absorption cell.
The measurements were made at T\"UB\.ITAK National Observatory (TUG, RTT150)
and Okayama Astrophysical Observatory (OAO). For the origin of the periodic
variation seen in the RV data of the star, we adopted a Keplerian motion caused
by an unseen companion. We found that the star hosts a planet with a minimum
mass of m2sini=1.40MJ, which is relatively low compared to those of known
planets orbiting evolved intermediate-mass stars. The planet is in a nearly
circular orbit with a period of P=353 days at about 1 AU distance from the host
star. The star is metal rich and located at the early phase of ascent along the
red giant branch. The photometric observations of the star at Ankara University
Kreiken Observatory (AUKR) and the HIPPARCOS photometry show no sign of
variation with periods associated with the RV variation. Neither bisector
velocity analysis nor analysis of the Ca II and Halpha lines shows any
correlation with the RV measurements
Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesis modelling is presented. The library consists of 985 stars spanning a large range in atmospheric parameters. The spectra were obtained at the 2.5-m Isaac Newton Telescope and cover the range λλ 3525-7500 Å at 2.3 Å (full width at half-maximum) spectral resolution. The spectral resolution, spectral-type coverage, flux-calibration accuracy and number of stars represent a substantial improvement over previous libraries used in population-synthesis model
Spectroscopic and Photometric Study of the Contact Binary BO CVn
We present the results of the study of the contact binary system BO CVn. We
have obtained physical parameters of the components based on combined analysis
of new, multi-color light curves and spectroscopic mass ratio. This is the
first time the latter has been determined for this object. We derived the
contact configuration for the system with a very high filling factor of about
88 percent. We were able to reproduce the observed light curve, namely the flat
bottom of the secondary minimum, only if a third light has been added into the
list of free parameters. The resulting third light contribution is significant,
about 20-24 percent, while the absolute parameters of components are: M1=1.16,
M2=0.39, R1=1.62 and R2=1.00 (in solar units). The O-C diagram shows an upward
parabola which, under the conservative mass transfer assumption, would
correspond to a mass transfer rate of dM/dt = 6.3 \times 10-8M\odot/yr, matter
being transferred from the less massive component to the more massive one. No
cyclic, short-period variations have been found in the O-C diagram (but
longer-term variations remain a possibility)Comment: 16 pages, 5 figures, 5 tables, accepted for publication by New
Astronom
Energy recovery modeling of pressure-retarded osmosis systems with membrane modules compatible with high salinity draw streams
Bisectors of the HARPS Cross-Correlation-Function. The dependence on stellar atmospheric parameters
Bisectors of the HARPS cross-correlation function (CCF) can discern between
planetary radial-velocity (RV) signals and spurious RV signals from stellar
magnetic activity variations. However, little is known about the effects of the
stellar atmosphere on CCF bisectors or how these effects vary with spectral
type and luminosity class. Here we investigate the variations in the shapes of
HARPS CCF bisectors across the HR diagram in order to relate these to the basic
stellar parameters, surface gravity and temperature. We use archive spectra of
67 well studied stars observed with HARPS and extract mean CCF bisectors. We
derive previously defined bisector measures (BIS, v_bot, c_b) and we define and
derive a new measure called the CCF Bisector Span (CBS) from the minimum radius
of curvature on direct fits to the CCF bisector. We show that the bisector
measures correlate differently, and non-linearly with log g and T_eff. The
resulting correlations allow for the estimation of log g and T_eff from the
bisector measures. We compare our results with 3D stellar atmosphere models and
show that we can reproduce the shape of the CCF bisector for the Sun.Comment: 13 pages, 20 figures. Accepted by A&
Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters (T-eff, log g, [Fe/H]) for MILES, a new spectral stellar library covering the range lambda lambda 3525-7500 angstrom at 2.3 angstrom (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones
Insulin resistance in type 1 diabetes: what is ‘double diabetes’ and what are the risks?
In this review, we explore the concept of ‘double diabetes’, a combination of type 1 diabetes with features of insulin resistance and type 2 diabetes. After considering whether double diabetes is a useful concept, we discuss potential mechanisms of increased insulin resistance in type 1 diabetes before examining the extent to which double diabetes might increase the risk of cardiovascular disease (CVD). We then go on to consider the proposal that weight gain from intensive insulin regimens may be associated with increased CV risk factors in some patients with type 1 diabetes, and explore the complex relationships between weight gain, insulin resistance, glycaemic control and CV outcome. Important comparisons and contrasts between type 1 diabetes and type 2 diabetes are highlighted in terms of hepatic fat, fat partitioning and lipid profile, and how these may differ between type 1 diabetic patients with and without double diabetes. In so doing, we hope this work will stimulate much-needed research in this area and an improvement in clinical practice
Genome wide association study and factors affecting semen volume and concentration in Ethiopian dairy bulls
New periodic variable stars coincident with ROSAT sources discovered using SuperWASP
We present optical lightcurves of 428 periodic variable stars coincident with ROSAT X-ray sources, detected using the first run of the SuperWASP photometric survey. Only 68 of these were previously recognised as periodic variables. A further 30 of these objects are previously known pre-main sequence stars, for which we detect a modulation period for the first time. Amongst the newly identified periodic variables, many appear to be close eclipsing binaries, their X-ray emission is presumably the result of RS CVn type behaviour. Others are probably BY Dra stars, pre-main sequence stars and other rapid rotators displaying enhanced coronal activity. A number of previously catalogued pulsating variables (RR Lyr stars and Cepheids) coincident with X-ray sources are also seen, but we show hat these are likely to be misclassifications. We identify four objects which are probable low mass eclipsing binary stars, based on
their very red colour and light curve morphology
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