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Lee B.-C.,Korea Astronomy and Space Science Institute | Han I.,Korea Astronomy and Space Science Institute | Park M.-G.,Kyungpook National University | Mkrtichian D.E.,National Astronomical Research Institute of Thailand | And 3 more authors.
Astronomy and Astrophysics | Year: 2014

Aims. The aim of our paper is to investigate the low-amplitude and long-period variations in evolved stars with a precise radial velocity survey. Methods. The high-resolution, the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used from 2003 to 2013 for a radial velocity survey of giant stars as part of the exoplanet search program at Bohyunsan Optical Astronomy Observatory (BOAO). Results. We report the detection of three new planetary companions orbiting the K giants β Cnc, μ Leo, and β UMi. The planetary nature of the radial velocity variations is supported by analyzes of ancillary data. The Hipparcos photometry shows no variations with periods close to those in radial velocity variations and there is no strong correlation between the bisector velocity span (BVS) and the radial velocities for each star. Furthermore, the stars show weak or no core reversal in Ca II H lines indicating that they are inactive stars. The companion to β Cnc has a minimum mass of 7.8 MJup in a 605-day orbit with an eccentricity of 0.08. The giant μ Leo is orbited by a companion of minimum mass of 2.4 M Jup having a period of 357 days and an eccentricity of 0.09. The giant β UMi is a known barium star and is suspected of harboring a white dwarf or substellar mass companion. Its companion has a minimum mass of 6.1 MJup, a period of 522 days, and an eccentricity e = 0.19. © 2014 ESO. Source


Smalley B.,Keele University | Niemczura E.,Wroclaw University | Murphy S.J.,University of Sydney | Murphy S.J.,University of Aarhus | And 12 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We report the identification of 61.45 d-1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of Teff =8100±200 K, log g=4.0±0.2, [Fe/H]=+0.31±0.24 and v sin i=14.8±1.6 kms-1. Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar Teffand log g. Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Linz H.,Max Planck Instritut fur Astronomie MPIA Heidelberg | Krause O.,Max Planck Instritut fur Astronomie MPIA Heidelberg | Beuther H.,Max Planck Instritut fur Astronomie MPIA Heidelberg | Henning T.,Max Planck Instritut fur Astronomie MPIA Heidelberg | And 6 more authors.
Astronomy and Astrophysics | Year: 2010

The intermediate-mass star-forming core UYSO 1 has previously been found to exhibit intriguing features. While deeply embedded and previously only identified by means of its (sub-)millimeter emission, it drives two powerful, dynamically young, molecular outflows. Although the process of star formation has obviously started, the chemical composition is still pristine. We present Herschel PACS and SPIRE continuum data of this presumably very young region. The now complete coverage of the spectral energy peak allows us to precisely constrain the elevated temperature of 26-28 K for the main bulge of gas associated with UYSO1, which is located at the interface between the hot H ii region Sh 2-297 and the cold dark nebula LDN 1657A. Furthermore, the data identify cooler compact far-infrared sources of just a few solar masses, hidden in this neighbouring dark cloud. © 2010 ESO. Source


Niemczura E.,Wroclaw University | Murphy S.J.,University of Sydney | Murphy S.J.,University of Aarhus | Smalley B.,Keele University | And 22 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

The Kepler space mission provided near-continuous and high-precision photometry of about 207 000 stars, which can be used for asteroseismology. However, for successful seismic modeling it is equally important to have accurate stellar physical parameters. Therefore, supplementary ground-based data are needed.We report the results of the analysis of high-resolution spectroscopic data of A- and F-type stars from the Kepler field, which were obtained with the HERMES spectrograph on the Mercator telescope. We determined spectral types, atmospheric parameters and chemical abundances for a sample of 117 stars. Hydrogen Balmer, Fe I, and Fe II lines were used to derive effective temperatures, surface gravities, and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. The atmospheric parameters obtained were compared with those from the Kepler Input Catalogue (KIC), confirming that the KIC effective temperatures are underestimated for A stars. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined from the spectral line analysis. The analysed sample comprises stars with approximately solar chemical abundances, as well as chemically peculiar stars of the Am, Ap, and λ Boo types. The distribution of the projected rotational velocity, vsin i, is typical for A and F stars and ranges from 8 to about 280 km s-1, with a mean of 134 km s-1. © 2015 The Authors. Source


Lehmann H.,Thuringer Landessternwarte Tautenburg TLS | Zechmeister M.,University of Gottingen | Dreizler S.,University of Gottingen | Schuh S.,University of Gottingen | Kanzler R.,University of Gottingen
Astronomy and Astrophysics | Year: 2012

Context. KIC 4247791 is an eclipsing binary observed by the Kepler satellite mission. Aims. We wish to determine the nature of its components and in particular the origin of a shallow dip in its Kepler light curve that previous investigations have been unable to explain in a unique way. Methods. We analyse newly obtained high-resolution spectra of the star using synthetic spectra based on atmosphere models, derive the radial velocities of the stellar components from cross-correlation with a synthetic template, and calculate the orbital solution. We use the JKTEBOP program to model the Kepler light curve of KIC 4247791. Results. We find KIC 4247791 to be a SB4 star. The radial velocity variations of its four components can be explained by two separate eclipsing binaries. In contradiction to previous photometric findings, we show that the observed composite spectrum as well as the derived masses of all four of its components correspond to spectral type F. Conclusions. The observed small dip in the light curve is not caused by a transit-like phenomenon but by the eclipses of the second binary system. We find evidence that KIC 4247791 might belong to the very rare hierarchical SB4 systems with two eclipsing binaries. © 2012 ESO. Source

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