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Briquet M.,University of Liège | Briquet M.,Catholic University of Leuven | Briquet M.,University Paris Diderot | Neiner C.,University Paris Diderot | And 34 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f 1 = 7.14846d -1) and by rotational modulation (P rot = 3.638833d). Two non-radial low-amplitude modes (f 2 = 7.75603d -1 and f 3 = 6.82308d -1) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign and known in the literature. Using the photometric constraints on the degrees ℓ of the pulsation modes, we show that both f 2 and f 3 are prograde modes with (ℓ, m) = (4, 2) or (4, 3). These results allowed us to deduce ranges for the mass (M ∈ [8.2, 9.6]M ⊙) and central hydrogen abundance (X c ∈ [0.25, 0.32]) of V2052 Oph, to identify the radial orders n 1 = 1, n 2 = -3 and n 3 = -2, and to derive an equatorial rotation velocity v eq ∈ [71, 75]kms -1. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (α ov ∈ [0, 0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic β Cep star θ Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Smalley B.,Keele University | Niemczura E.,Wrocław 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.

Niemczura E.,Wrocław 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.

Lee B.-C.,Korea Astronomy and Space Science Institute | Han I.,Korea Astronomy and Space Science Institute | Park M.-G.,Kyungpook National University | Hatzes A.P.,Thuringer Landessternwarte Tautenburg TLS | Kim K.-M.,Korea Astronomy and Space Science Institute
Astronomy and Astrophysics | Year: 2014

Aims. We study the low-amplitude and long-period variations in evolved stars using precise radial velocity measurements. Methods. The high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used from September 2004 to May 2014 as part of the exoplanet search program at the Bohyunsan Optical Astronomy Observatory (BOAO). Results. We report the detection of low-amplitude and long-period orbital radial velocity variations in three evolved stars, HD 3574, 63 Cyg, and HD 216946. They have periods of 1061, 982, and 1382 days and semi-amplitudes of 376, 742, and 699 m s-1, respectively. © 2014 ESO.

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.

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.

Holdsworth D.L.,University of Central Lancashire | Holdsworth D.L.,Keele University | Kurtz D.W.,University of Central Lancashire | Smalley B.,Keele University | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present an analysis of the first Kepler K2 mission observations of a rapidly oscillating Ap (roAp) star, HD 24355 (V = 9.65). The star was discovered in SuperWASP broad-band photometry with a frequency of 224.31 d-1 (2596.18 μHz; P = 6.4 min) and an amplitude of 1.51 mmag, with later spectroscopic analysis of low-resolution spectra showing HD 24355 to be an A5 Vp SrEu star. The high-precision K2 data allow us to identify 13 rotationally split sidelobes to the main pulsation frequency of HD 24355. This number of sidelobes combined with an unusual rotational phase variation show this star to be the most distorted quadrupole roAp pulsator yet observed. In modelling this star, we are able to reproduce well the amplitude modulation of the pulsation, and find a close match to the unusual phase variations. We show this star to have a pulsation frequency higher than the critical cut-off frequency. This is currently the only roAp star observed with the Kepler spacecraft in short cadence mode that has a photometric amplitude detectable from the ground, thus allowing comparison between the mmag amplitude ground-based targets and the μmag spaced-based discoveries. No further pulsation modes are identified in the K2 data, showing this star to be a single-mode pulsator. © 2016 The Authors.

Lee B.-C.,Korea Astronomy and Space Science Institute | Lee B.-C.,Korea University | Han I.,Korea Astronomy and Space Science Institute | Park M.-G.,Kyungpook National University | And 6 more authors.
Astronomical Journal | Year: 2016

We report that the spectroscopic binary μ Ursae Majoris (μ UMa) has secondary RV variations of 471.2 days in addition to those of 230.0 days already known. Keplerian orbit analysis yields stellar mass companions of 1.6 M⊙ for the 230 day period and 0.14 M⊙ for the 471 day period. However, the HIPPARCOS photometries show a period similar to the stellar rotational period, which is one-quarter of the RV period. Variations in the bisector velocity curvature show a period of 463.6 days. We also find ∼473 day variations in the equivalent width (EW) measurements of the Hα and Hβ lines, whose origin is probably stellar activity. We note that the nature of 471 day variations is similar to one observed in "Sequence D" of Asymptotic Giant Branch pulsating stars. We therefore conclude that the RV and the EW variations in the spectroscopic binary M giant μ UMa A originate from the complex pulsations and the chromospheric activity. © 2016. The American Astronomical Society. All rights reserved.

Zechmeister M.,University of Gottingen | Zechmeister M.,Max Planck Institute for Astronomy | Kurster M.,Max Planck Institute for Astronomy | Endl M.,University of Texas at Austin | And 7 more authors.
Astronomy and Astrophysics | Year: 2013

Context. In 1992 we began a precision radial velocity survey for planets around solar-like stars with the Coudé Echelle Spectrograph and the Long Camera (CES LC) at the 1.4 m telescope in La Silla (Chile) resulting in the discovery of the planet ι Hor b. We have continued the survey with the upgraded CES Very Long Camera (VLC) and the HARPS spectrographs, both at the 3.6 m telescope, until 2007. Aims. In this paper we present additional radial velocities for 31 stars of the original sample with higher precision. The observations cover a time span of up to 15 years and permit a search for Jupiter analogues. Methods. The survey was carried out with three different instruments/instrument configurations using the iodine absorption cell and the ThAr methods for wavelength calibration. We combine the data sets and perform a joint analysis for variability, trends, and periodicities. We compute Keplerian orbits for companions and detection limits in case of non-detections. Moreover, the HARPS radial velocities are analysed for correlations with activity indicators (CaII H&K and cross-correlation function shape). Results. We achieve a long-term RV precision of 15 m/s (CES+LC, 1992-1998), 9 m/s (CES+VLC, 1999-2006), and 2.8 m/s (HARPS, 2003-2009, including archive data), respectively. This enables us to confirm the known planetary signals in ι Hor and HR 506 as well as the three known planets around HR 3259. A steady RV trend for Ïμ Ind A can be explained by a planetary companion and calls for direct imaging campaigns. On the other hand, we find previously reported trends to be smaller for β Hyi and not present for α Men. The candidate planet Ïμ Eri b was not detected despite our better precision. Also the planet announced for HR 4523 cannot be confirmed. Long-term trends in several of our stars are compatible with known stellar companions. We provide a spectroscopic orbital solution for the binary HR 2400 and refined solutions for the planets around HR 506 and ι Hor. For some other stars the variations could be attributed to stellar activity, as e.g. the magnetic cycle in the case of HR 8323. Conclusions. The occurrence of two Jupiter-mass planets in our sample is in line with the estimate of 10% for the frequency of giant planets with periods smaller than 10 yr around solar-like stars. We have not detected a Jupiter analogue, while the detections limits for circular orbits indicate at 5 AU a sensitivity for minimum mass of at least 1MJup (2M Jup) for 13% (61%) of the stars. © ESO, 2013.

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.

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