1,471 research outputs found

    Intra-Day Variability and the Interstellar Medium Towards 0917+624

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    The intra-day variable source 0917+624 displays annual changes in its timescale of variability. This is explained in terms of a scintillation model in which changes in the variability timescale are due to changes in the relative velocity of the scintillation pattern as the Earth orbits the sun. (see also astro-ph/0102050)Comment: 4 pages, 1 figure. Accepted for A&A Letter

    Modeling of Closure Phase Measurements with AMBER/VLTI - Towards Characterization of Exoplanetary Atmospheres

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    Differential phase observations with a near-IR interferometer offer a way to obtain spectra of extrasolar planets. The method makes use of the wavelength dependence of the interferometer phase of the planet/star system, which depends both on the interferometer geometry and on the brightness ratio between the planet and the star. The differential phase is strongly affected by instrumental and atmospheric dispersion effects. Difficulties in calibrating these effects might prevent the application of the differential phase method to systems with a very high contrast, such as extrasolar planets. A promising alternative is the use of spectrally resolved closure phases, which are immune to many of the systematic and random errors affecting the single-baseline phases. We have modeled the response of the AMBER instrument at the VLTI to realistic models of known extrasolar planetary systems, taking into account their theoretical spectra as well as the geometry of the VLTI. We present a strategy to determine the geometry of the planetary system and the spectrum of the extrasolar planet from closure phase observations in two steps. We show that there is a close relation between the nulls in the closure phase and the nulls in the corresponding single-baseline phases: every second null of a single-baseline phase is also a null in the closure phase. In particular, the nulls in the closure phase do not depend on the spectrum but only on the geometry. Therefore the geometry of the system can be determined by measuring the nulls in the closure phase, and braking the remaining ambiguity due to the unknown system orientation by means of observations at different hour angles. Based on the known geometry, the planet spectrum can then be directly synthesized from the closure phases.Comment: replaced version with corrected Fig.5; 9 pages, 6 figures, Proceeding of the SPIE conference, Glasgow, 2004, Proc. SPIE 5491, in pres

    Precise radial velocities of giant stars. X. Bayesian stellar parameters and evolutionary stages for 372 giant stars from the Lick planet search

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    The determination of accurate stellar parameters of giant stars is essential for our understanding of such stars in general and as exoplanet host stars in particular. Precise stellar masses are vital for determining the lower mass limit of potential substellar companions with the radial velocity method. Our goal is to determine stellar parameters, including mass, radius, age, surface gravity, effective temperature and luminosity, for the sample of giants observed by the Lick planet search. Furthermore, we want to derive the probability of these stars being on the horizontal branch (HB) or red giant branch (RGB), respectively. We compare spectroscopic, photometric and astrometric observables to grids of stellar evolutionary models using Bayesian inference. We provide tables of stellar parameters, probabilities for the current post-main sequence evolutionary stage, and probability density functions for 372 giants from the Lick planet search. We find that 81%81\% of the stars in our sample are more probably on the HB. In particular, this is the case for 15 of the 16 planet host stars in the sample. We tested the reliability of our methodology by comparing our stellar parameters to literature values and find very good agreement. Furthermore, we created a small test sample of 26 giants with available asteroseismic masses and evolutionary stages and compared these to our estimates. The mean difference of the stellar masses for the 24 stars with the same evolutionary stages by both methods is only ΔM=0.01±0.20  M\langle\Delta M\rangle=0.01\pm0.20\;\mathrm{M_\odot}. We do not find any evidence for large systematic differences between our results and estimates of stellar parameters based on other methods. In particular we find no significant systematic offset between stellar masses provided by asteroseismology to our Bayesian estimates based on evolutionary models.Comment: 15 pages, 7 figures, accepted for publication in A&

    Precise radial velocities of giant stars. XI. Two brown dwarfs in 6:1 mean motion resonance around the K giant star ν\nu Ophiuchi

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    We present radial-velocity (RV) measurements for the K giant ν\nu Oph (= HIP88048, HD163917, HR6698), which reveal two brown dwarf companions with a period ratio close to 6:1. For our orbital analysis we use 150 precise RV measurements taken at Lick Observatory between 2000 and 2011, and we combine them with RV data for this star available in the literature. Using a stellar mass of M=2.7MM = 2.7\,M_\odot for ν\nu Oph and applying a self-consistent N-body model we estimate the minimum dynamical companion masses to be m1sini22.2MJupm_1\sin i \approx 22.2\,M_{\mathrm{Jup}} and m2sini24.7MJupm_2\sin i \approx 24.7\,M_{\mathrm{Jup}}, with orbital periods P1530P_1 \approx 530 d and P23185P_2 \approx 3185 d. We study a large set of potential orbital configurations for this system, employing a bootstrap analysis and a systematic χν2\chi_{\nu}^2 grid-search coupled with our dynamical fitting model, and we examine their long-term stability. We find that the system is indeed locked in a 6:1 mean motion resonance (MMR), with Δω\Delta \omega and all six resonance angles θ1,,θ6\theta_{1}, \ldots, \theta_{6} librating around 0^\circ. We also test a large set of coplanar inclined configurations, and we find that the system will remain in a stable resonance for most of these configurations. The ν\nu Oph system is important for probing planetary formation and evolution scenarios. It seems very likely that the two brown dwarf companions of ν\nu Oph formed like planets in a circumstellar disk around the star and have been trapped in a MMR by smooth migration capture.Comment: 17 pages, 9 figures. New version with corrected number in title. No other change

    Dynamical analysis of the circumprimary planet in the eccentric binary system HD59686

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    We present a detailed orbital and stability analysis of the HD~59686 binary-star planet system. HD~59686 is a single-lined moderately close (aB=13.6a_{B} = 13.6\,AU) eccentric (eB=0.73e_{B} = 0.73) binary, where the primary is an evolved K giant with mass M=1.9MM = 1.9 M_{\odot} and the secondary is a star with a minimum mass of mB=0.53Mm_{B} = 0.53 M_{\odot}. Additionally, on the basis of precise radial velocity (RV) data a Jovian planet with a minimum mass of mp=7MJupm_p = 7 M_{\mathrm{Jup}}, orbiting the primary on a nearly circular S-type orbit with ep=0.05e_p = 0.05 and ap=1.09a_p = 1.09\,AU, has recently been announced. We investigate large sets of orbital fits consistent with HD 59686's radial velocity data by applying bootstrap and systematic grid-search techniques coupled with self-consistent dynamical fitting. We perform long-term dynamical integrations of these fits to constrain the permitted orbital configurations. We find that if the binary and the planet in this system have prograde and aligned coplanar orbits, there are narrow regions of stable orbital solutions locked in a secular apsidal alignment with the angle between the periapses, Δω\Delta \omega, librating about 00^\circ. We also test a large number of mutually inclined dynamical models in an attempt to constrain the three-dimensional orbital architecture. We find that for nearly coplanar and retrograde orbits with mutual inclination 145Δi180145^\circ \lesssim \Delta i \leq 180^\circ, the system is fully stable for a large range of orbital solutions.Comment: 17 pages, 11 figures, accepted for publication by A

    Precise radial velocities of giant stars VIII. Testing for the presence of planets with CRIRES Infrared Radial Velocities

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    We have been monitoring 373 very bright (V < 6 mag) G and K giants with high precision optical Doppler spectroscopy for more than a decade at Lick Observatory. Our goal was to discover planetary companions around those stars and to better understand planet formation and evolution around intermediate-mass stars. However, in principle, long-term, g-mode nonradial stellar pulsations or rotating stellar features, such as spots, could effectively mimic a planetary signal in the radial velocity data. Our goal is to compare optical and infrared radial velocities for those stars with periodic radial velocity patterns and to test for consistency of their fitted radial velocity semiamplitudes. Thereby, we distinguish processes intrinsic to the star from orbiting companions as reason for the radial velocity periodicity observed in the optical. Stellar spectra with high spectral resolution have been taken in the H-band with the CRIRES near-infrared spectrograph at ESO's VLT for 20 stars of our Lick survey. Radial velocities are derived using many deep and stable telluric CO2 lines for precise wavelength calibration. We find that the optical and near-infrared radial velocities of the giant stars in our sample are consistent. We present detailed results for eight stars in our sample previously reported to have planets or brown dwarf companions. All eight stars passed the infrared test. We conclude that the planet hypothesis provides the best explanation for the periodic radial velocity patterns observed for these giant stars.Comment: 14 pages, 6 figures, 3 tables, accepted by Astronomy & Astrophysic
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