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Search Results: 1 - 10 of 593037 matches for " L. A. Buchhave "
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The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars
T. T. Hansen,J. Andersen,B. Nordstr?m,T. C. Beers,J. Yoon,L. A. Buchhave
Physics , 2015, DOI: 10.1051/0004-6361/201526812
Abstract: The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later mass transfer of processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. High-resolution, low signal-to-noise spectra of the stars were obtained at roughly monthly intervals over 8 years with the FIES spectrograph at the Nordic Optical Telescope. From these spectra, radial velocities with an accuracy of ~100 m/s were determined by cross-correlation against an optimized template. 14 of the programme stars exhibit no significant RV variation over this period, while 3 are binaries with orbits of typical eccentricity for their periods, resulting in a normal binary frequency of ~18+-6% for the sample. Our results confirm our preliminary conclusion from 2011, based on partial data, that the chemical peculiarity of the r-I and r-II stars is not caused by any putative binary companions. Instead, it was imprinted on the natal molecular clouds of these stars by an external, distant source. Models of the ISM in early galaxies should account for such mechanisms.
The role of binaries in the enrichment of the early Galactic halo. II. Carbon-Enhanced Metal-Poor Stars - CEMP-no stars
T. T. Hansen,J. Andersen,B. Nordstr?m,T. C. Beers,V. M. Placco,J. Yoon,L. A. Buchhave
Physics , 2015,
Abstract: The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon - the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds, or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Most programme stars exhibit no statistically significant radial-velocit variation over this period and appear to be single, while four are found to be binaries with orbital periods of 300-2,000 days and normal eccentricity; the binary frequency for the sample is 17+-9%. The single stars mostly belong to the recently-identified ``low-C band'', while the binaries have higher absolute carbon abundances. We conclude that the nucleosynthetic process responsible for the strong carbon excess in these ancient stars is unrelated to their binary status; the carbon was imprinted on their natal molecular clouds in the early Galactic ISM by an even earlier, external source, strongly indicating that the CEMP-no stars are likely bona fide second-generation stars. We discuss potential production sites for carbon and its transfer across interstellar distances in the early ISM, and implications for the composition of high-redshift DLA systems. Abridged.
Planetary Candidates from the First Year of the K2 Mission
Andrew Vanderburg,David W. Latham,Lars A. Buchhave,Allyson Bieryla,Perry Berlind,Michael L. Calkins,Gilbert A. Esquerdo,Sophie Welsh,John Asher Johnson
Physics , 2015,
Abstract: The Kepler Space Telescope is currently searching for planets transiting stars along the ecliptic plane as part of its extended K2 mission. We processed the publicly released data from the first year of K2 observations (Campaigns 0, 1, 2, and 3) and searched for periodic eclipse signals consistent with planetary transits. Out of 59,174 targets we searched, we detect 234 planetary candidates around 208 stars. These candidates range in size from gas giants to smaller than the Earth, and range in orbital periods from hours to over a month. We conducted initial reconnaissance spectroscopy of 68 of the brighter candidate host stars, and present high resolution optical spectra for these stars. We make all of our data products, including light curves, spectra, and vetting diagnostics available to users online.
The Metallicities of Stars With and Without Transiting Planets
Lars A. Buchhave,David W. Latham
Physics , 2015, DOI: 10.1088/0004-637X/808/2/187
Abstract: Host star metallicities have been used to infer observational constraints on planet formation throughout the history of the exoplanet field. The giant planet metallicity correlation has now been widely accepted, but questions remain as to whether the metallicity correlation extends to the small terrestrial-sized planets. Here, we report metallicities for a sample of 518 stars in the Kepler field that have no detected transiting planets and compare their metallicity distribution to a sample of stars that hosts small planets (Rp < 1.7 R_Earth). Importantly, both samples have been analyzed in a homogeneous manner using the same set of tools (Stellar Parameters Classification tool; SPC). We find the average metallicity of the sample of stars without detected transiting planets to be [m/H]_SNTP,dwarf = -0.02 +- 0.02 dex and the sample of stars hosting small planets to be [m/H]_STP = -0.02 +- 0.02 dex. The average metallicities of the two samples are indistinguishable within the uncertainties, and the two-sample Kolmogorov-Smirnov test yields a p-value of 0.68 (0.41 sigma), indicating a failure to reject the null hypothesis that the two samples are drawn from the same parent population. We conclude that the homogeneous analysis of the data presented here support the hypothesis that stars hosting small planets have a metallicity similar to stars with no known transiting planets in the same area of the sky.
HD 285507b: An Eccentric Hot Jupiter in the Hyades Open Cluster
S. N. Quinn,R. J. White,D. W. Latham,L. A. Buchhave,G. Torres,R. P. Stefanik,P. Berlind,A. Bieryla,M. C. Calkins,G. A. Esquerdo,G. Fürész,J. C. Geary,A. H. Szentgyorgyi
Physics , 2013, DOI: 10.1088/0004-637X/787/1/27
Abstract: We report the discovery of the first hot Jupiter in the Hyades open cluster. HD 285507b orbits a V=10.47 K4.5V dwarf ($M_* = 0.734 M_\odot$; $R_* = 0.656 R_\odot$) in a slightly eccentric ($e = 0.086^{+0.018}_{-0.019}$) orbit with a period of $6.0881^{+0.0019}_{-0.0018}$ days. The induced stellar radial velocity corresponds to a minimum companion mass of $M_{\rm p} \sin{i} = 0.917 \pm 0.033 M_{\rm Jup}$. Line bisector spans and stellar activity measures show no correlation with orbital phase, and the radial velocity amplitude is independent of wavelength, supporting the conclusion that the variations are caused by a planetary companion. Follow-up photometry indicates with high confidence that the planet does not transit. HD 285507b joins a small but growing list of planets in open clusters, and its existence lends support to a planet formation scenario in which a high stellar space density does not inhibit giant planet formation and migration. We calculate the circularization timescale for HD 285507b to be larger than the age of the Hyades, which may indicate that this planet's non-zero eccentricity is the result of migration via interactions with a third body. We also demonstrate a significant difference between the eccentricity distributions of hot Jupiters that have had time to tidally circularize and those that have not, which we interpret as evidence against Type II migration in the final stages of hot Jupiter formation. Finally, the dependence of the circularization timescale on the planetary tidal quality factor, $Q_{\rm p}$, allows us to constrain the average value for hot Jupiters to be $\log{Q_{\rm p}} = 6.14^{+0.41}_{-0.25}$.
Constraining planet structure from stellar chemistry: the cases of CoRoT-7, Kepler-10, and Kepler-93
N. C. Santos,V. Adibekyan,C. Mordasini,W. Benz,E. Delgado-Mena,C. Dorn,L. Buchhave,P. Figueira,A. Mortier,F. Pepe,A. Santerne,S. G. Sousa,S. Udry
Physics , 2015, DOI: 10.1051/0004-6361/201526850
Abstract: We explore the possibility that the stellar relative abundances of different species can be used to constrain the bulk abundances of known transiting rocky planets. We use high resolution spectra to derive stellar parameters and chemical abundances for Fe, Si, Mg, O, and C in three stars hosting low mass, rocky planets: CoRoT-7, Kepler-10, and Kepler-93. These planets follow the same line along the mass-radius diagram, pointing toward a similar composition. The derived abundance ratios are compared with the solar values. With a simple stoichiometric model, we estimate the iron mass fraction in each planet, assuming stellar composition. We show that in all cases, the iron mass fraction inferred from the mass-radius relationship seems to be in good agreement with the iron abundance derived from the host star's photospheric composition. The results suggest that stellar abundances can be used to add constraints on the composition of orbiting rocky planets.
Generation of Polarization Squeezing with Periodically Poled KTP at 1064 nm
Mikael Lassen,Metin Sabuncu,Preben Buchhave,Ulrik L. Andersen
Physics , 2007, DOI: 10.1364/OE.15.005077
Abstract: We report the experimental demonstration of directly produced polarization squeezing at 1064 nm from a type I optical parametric amplifier (OPA) based on a periodically poled KTP crystal (PPKTP). The orthogonal polarization modes of the polarization squeezed state are both defined by the OPA cavity mode, and the birefringence induced by the PPKTP crystal is compensated for by a second, but inactive, PPKTP crystal. Stokes parameter squeezing of 3.6 dB and anti squeezing of 9.4 dB is observed.
Squeezing based on nondegenerate frequency doubling internal to a realistic laser
Ulrik L. Andersen,Peter Tidemand-Lichtenberg,Preben Buchhave
Physics , 2003, DOI: 10.1103/PhysRevA.69.013808
Abstract: We investigate theoretically the quantum fluctuations of the fundamental field in the output of a nondegenerate second harmonic generation process occuring inside a laser cavity. Due to the nondegenerate character of the nonlinear medium, a field orthogonal to the laser field is for some operating conditions indepedent of the fluctuations produced by the laser medium. We show that this fact may lead to perfect squeezing for a certain polarization mode of the fundamental field. The experimental feasibility of the system is also discussed.
HAT-P-28b and HAT-P-29b: Two Sub-Jupiter Mass Transiting Planets
L. A. Buchhave,G. A. Bakos,J. D. Hartman,G. Torres,D. W. Latham,J. Andersen,G. Kovacs,R. W. Noyes,A. Shporer,G. A. Esquerdo,D. A. Fischer,J. A. Johnson,G. W. Marcy,A. W. Howard,B. Beky,D. D. Sasselov,G. Furesz,S. N. Quinn,R. P. Stefanik,T. Szklenar,P. Berlind,M. L. Calkins,J. Lazar,I. Papp,P. Sari
Physics , 2011, DOI: 10.1088/0004-637X/733/2/116
Abstract: We present the discovery of two transiting exoplanets. HAT-P-28b orbits a V=13.03 G3 dwarf star with a period P = 3.2572 d and has a mass of 0.63 +- 0.04 MJ and a radius of 1.21 + 0.11 -0.08 RJ yielding a mean density of 0.44 +- 0.09 g cm-3. HAT-P-29b orbits a V=11.90 F8 dwarf star with a period P = 5.7232 d and has a mass of 0.78 +0.08 -0.04 MJ and a radius of 1.11 +0.14 -0.08 RJ yielding a mean density of 0.71 +- 0.18 g cm-3. We discuss the properties of these planets in the context of other known transiting planets.
HAT-P-20b--HAT-P-23b: Four Massive Transiting Extrasolar Planets
G. á. Bakos,J. Hartman,G. Torres,D. W. Latham,Géza Kovács,R. W. Noyes,D. A. Fischer,J. A. Johnson,G. W. Marcy,A. W. Howard,D. Kipping,G. A. Esquerdo,A. Shporer,B. Béky,L. A. Buchhave,G. Perumpilly,M. Everett,D. D. Sasselov,R. P. Stefanik,J. Lázár,I. Papp,P. Sári
Physics , 2010, DOI: 10.1088/0004-637X/742/2/116
Abstract: We report the discovery of four relatively massive (2-7MJ) transiting extrasolar planets. HAT-P-20b orbits a V=11.339 K3 dwarf star with a period P=2.875317+/-0.000004d. The host star has a mass of 0.760+/-0.03 Msun, radius of 0.690+/-0.02 Rsun, Teff=4595+/-80 K, and metallicity [Fe/H]=+0.35+/-0.08. HAT-P-20b has a mass of 7.246+/-0.187 MJ, and radius of 0.867+/-0.033 RJ yielding a mean density of 13.78+/-1.50 gcm^-3 , which is the second highest value among all known exoplanets. HAT-P-21b orbits a V=11.685 G3 dwarf on an eccentric (e=0.2280+/-0.016) orbit, with a period of P=4.1244810+/-000007d. The host star has a mass of 0.95+/-0.04Msun, radius of 1.10+/-0.08Rsun, Teff=5588+/-80K, and [Fe/H]=+0.01+/-0.08. HAT-P-21b has a mass of 4.063+/-0.161MJ, and radius of 1.024+/-0.092RJ. HAT-P-22b orbits the V=9.732 G5 dwarf HD233731, with P=3.2122200+/-0.000009d. The host star has a mass of 0.92+/-0.03Msun, radius of 1.04+/-0.04Rsun, Teff=5302+/-80K, and metallicity of +0.24+/-0.08. The planet has a mass of 2.147+/-0.061 MJ, and compact radius of 1.080+/-0.058RJ. The host star also harbors an M-dwarf companion at a wide separation. Finally, HAT-P-23b orbits a V=12.432 G0 dwarf star, with a period P=1.212884+/-0.000002d. The host star has a mass of 1.13+/-0.04sun, radius of 1.20+/-0.07Rsun, Teff=5905+/-80K, and [Fe/H]=+0.15+/-0.04. The planetary companion has a mass of 2.090+/-0.111MJ, and radius of 1.368+/-0.090RJ (abridged).
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