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Публикации по объекту
A massive planet to the young disc star HD 81040
We report the discovery of a massive planetary companion orbiting theyoung disc star HD 81040. Based on five years of precise radial-velocitymeasurements with the HIRES and ELODIE spectrographs, we derive aspectroscopic orbit with a period P =1001.0 days and eccentricity e =0.53. The inferred minimum mass for the companion of m_2 sin i = 6.86M_Jup places it in the high-mass tail of the extrasolar planet massdistribution. From the ELODIE spectra we derive a Lithium abundance oflogɛ(Li) = 1.90, and from the HIRES spectra of the cores of theCa II H and K lines we derive an activity index of < log R'_HK> =-4.48, suggesting an age of about 0.8 Gyr. The radial-velocity residualsexhibit a scatter significantly larger than the typical internalmeasurement precision of the instruments. We attribute this excessvelocity jitter to activity on the surface of the moderately young hoststar. However, the amplitude of the jitter is much too small and theexpected period of rotation is much too short to explain the observedorbital motion, which we conclude is due to a massive planetarycompanion.
| An 850 μm Survey for Dust around Solar-Mass Stars
We present the results of an 850 μm JCMT/SCUBA survey for dust around13 nearby solar-mass stars. The dust mass sensitivity ranged from5×10-3 to 0.16 M⊕. Three sources weredetected in the survey, one of which (HD 107146) has been previouslyreported. One of the other two submillimeter sources, HD 104860, was notdetected by IRAS and is surrounded by a cold, massive dust disk with adust temperature and mass of Tdust=33 K andMdust=0.16 M⊕, respectively. The thirdsource, HD 8907, was detected by IRAS and ISO at 60-87 μm and has adust temperature and mass of Tdust=48 K andMdust=0.036 M⊕, respectively. We find thatthe deduced masses and radii of the dust disks in our sample are roughlyconsistent with models for the collisional evolution of planetesimaldisks with embedded planets. We also searched for residual gas in two ofthe three systems with detected submillimeter excesses and place limitson the mass of gas residing in these systems. When the propertiesmeasured for the detected excess sources are combined with the largerpopulation of submillimeter excess sources from the literature, we findstrong evidence that the mass in small grains declines significantly ona ~200 Myr timescale, approximately inversely with age. However, we alsofind that the characteristic dust radii of the population, obtained fromthe dust temperature of the excess and assuming blackbody grains, isuncorrelated with age. This is in contrast to self-stirred collisionalmodels for debris disk evolution, which predict a trend of radiusincreasing with age tage~R3d. The lackof agreement suggests that processes beyond self-stirring, such as giantplanet formation, play a role in the evolutionary histories ofplanetesimal disks.
| Binarity, activity and metallicity among late-type stars. I. Methodology and application to HD 27536 and HD 216803
We present the first in a series of papers that attempt to investigatethe relation between binarity, magnetic activity, and chemical surfaceabundances of cool stars. In the current paper, we lay out and test twoabundance analysis methods and apply them to two well-known, active,single stars, HD 27536 (G8IV-III) and HD216803 (K5V), presenting photospheric fundamental parametersand abundances of Li, Al, Ca, Si, Sc, Ti, V, Cr, Fe, Co and Ni. Theabundances from the two methods agree within the errors for all elementsexcept calcium in HD 216803, which means that either method yields thesame fundamental model parameters and the same abundances. Activity isdescribed by the radiative loss in the Ca ii H and K lines with respectto the bolometric luminosity, through the activity index R_HK. Binarityis established by very precise radial velocity (RV) measurements usingHARPS spectra. The spectral line bisectors are examined for correlationsbetween RV and bisector shape to distinguish between the effects ofstellar activity and unseen companions. We show that HD 27536 exhibit RVvariations mimicking the effect of a low-mass (m 4 M_J) companionin a relatively close (a 1 AU) orbit. The variation is stronglycorrelated with the activity, and consistent with the known photometricperiod P = 306.9 d, demonstrating a remarkable coherence between R_HKand the bisector shape, i.e. between the photosphere and thechromosphere. We discuss the complications involved in distinguishingbetween companion and activity induced RV variations.
| The N2K Consortium. II. A Transiting Hot Saturn around HD 149026 with a Large Dense Core
Doppler measurements from Subaru and Keck have revealed radial velocityvariations in the V=8.15, G0 IV star HD 149026 consistent with aSaturn-mass planet in a 2.8766 day orbit. Photometric observations atFairborn Observatory have detected three complete transit events withdepths of 0.003 mag at the predicted times of conjunction. HD 149026 isnow the second-brightest star with a transiting extrasolar planet. Themass of the star, based on interpolation of stellar evolutionary models,is 1.3+/-0.1 Msolar together with the Doppler amplitudeK1=43.3 m s-1, we derive a planet massMsini=0.36MJ and orbital radius 0.042 AU. HD 149026 ischromospherically inactive and metal-rich with spectroscopically derived[Fe/H]=+0.36, Teff=6147 K, logg=4.26, and vsini=6.0 kms-1. Based on Teff and the stellar luminosity of2.72 Lsolar, we derive a stellar radius of 1.45Rsolar. Modeling of the three photometric transits providesan orbital inclination of 85.3d+/-1.0d and (including the uncertainty inthe stellar radius) a planet radius of (0.725+/-0.05)RJ.Models for this planet mass and radius suggest the presence of a ~67M⊕ core composed of elements heavier than hydrogen andhelium. This substantial planet core would be difficult to construct bygravitational instability.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.Based on observations obtained at the W. M. Keck Observatory, which isoperated by the University of California and the California Institute ofTechnology. Keck time has been granted by NOAO and NASA.
| Line bisectors and radial velocity jitter from SARG spectra
We present an analysis of spectral line bisector variations for a fewstars observed in the SARG high precision radial velocity planet survey,and discuss their relationship with differential radial velocities. Thespectra we consider are the same used for determining radial velocities.The iodine cell lines employed in the measurement of radial velocitieswere removed before bisector analysis. The line bisectors were thencomputed from average absorption profiles obtained by cross correlationof the stellar spectra with a mask made from suitable lines of a solarcatalog. Bisector velocity spans were then determined: errors in thesequantities compare well with theoretical expectations based onresolution, S/N and line shape. The plot of bisector velocity spanagainst radial velocity was studied to search for correlations betweenline asymmetries and radial velocity variations. A correlation was seenfor HD 166435 due to stellar activity, and for HD 8071B due to spectralcontamination by the companion. No correlation was seen for 51 Peg andρ CrB, stars hosting planets. We conclude that this technique may beuseful to separate radial velocity variations due to barycenter motionfrom spurious signals in spectra acquired with the iodine cell.
| Asteroseismology of the planet-hosting star μ Arae. I. The acoustic spectrum
We present HARPS spectroscopy of μ Arae (HD 160691) performed forstudying the origin of the metallicity excess in this planet-hostingstars. The asteroseismologic campaign led to the previously reporteddiscovery of a 14 earth mass planetary companion (Santos et al. 2004b,A&A, 426, L19). The present analysis reinforces this interpretationby excluding other possible processes for explaining the observedDoppler variation and leads to the identification of up to 43 p-modeoscillations with l = 0-3, frequencies in the range 1.3-2.5 mHz andamplitudes in the range 10-40 cm s-1.
| Kinematics, ages and metallicities for F- and G-type stars in the solar neighbourhood
A new metallicity distribution and an age-metallicity relation arepresented for 437 nearby F and G turn-off and sub-giant stars selectedfrom radial velocity data of Nidever et al. Photometric metallicitiesare derived from uvby- Hβ photometry, and the stellar ages from theisochrones of Bergbusch & VandenBerg as transformed to uvbyphotometry using the methods of Clem et al.The X (stellar population) criterion of Schuster et al., which combinesboth kinematic and metallicity information, provides 22 thick-discstars. σW= 32 +/- 5 km s-1,= 154 +/- 6 km s-1 and<[M/H]>=-0.55 +/- 0.03 dex for these thick-disc stars, which is inagreement with values from previous studies of the thick disc.α-element abundances which are available for some of thesethick-disc stars show the typical α-element signatures of thethick disc, supporting the classification procedure based on the Xcriterion.Both the scatter in metallicity at a given age and the presence of old,metal-rich stars in the age-metallicity relation make it difficult todecide whether or not an age-metallicity relation exists for the olderthin-disc stars. For ages greater than 3 Gyr, our results agree with theother recent studies that there is almost no correlation between age andmetallicity, Δ([M/Fe])/Δ(age) =-0.01 +/- 0.005 dexGyr-1. For the 22 thick-disc stars there is a range in agesof 7-8 Gyr, but again almost no correlation between age and metallicity.For the subset of main-sequence stars with extra-solar planets, theage-metallicity relation is very similar to that of the total sample,very flat, the main difference being that these stars are mostlymetal-rich, [M/H]>~-0.2 dex. However, two of these stars have[M/H]~-0.6 dex and have been classified as thick-disc stars. As for thetotal sample, the range in ages for these stars with extra-solarplanetary systems is considerable with a nearly uniform distributionover 3 <~ age <~ 13 Gyr.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| A giant planet around the massive giant star HD 13189
Most extrasolar planet discoveries using radial velocity measurementshave been for solar-like G-stars. In order to understand better the rolestellar mass for the formation of planets we must learn more about thefrequency of planetary companions around both high- and low-mass stars.Radial velocity searches for planets around high mass main-sequencestars are difficult due to the paucity of lines and often rapid rotationof these early-type stars. On the other hand, evolved stars that havemoved off the main sequence offer us the possibility of searching forplanets around higher mass stars by means of precise radial velocitymeasurements. Here we present radial velocity measurements for the starHD 13189 using measurements taken at the Thüringer LandessternwarteTautenburg, the Harlan J. Smith Telescope at McDonald Observatory, andthe Hobby-Eberly Telescope. We classify the spectral type of this staras K2 with luminosity class II. The radial velocity measurements showlong-period variations with a period of 472 days and an amplitude of 173m s-1. The Ca II S-index is consistent with an inactive starand this shows no variations with the radial velocity period. We alsoinvestigated possible changes in the line shapes by measuring spectralline bisectors. These show no variations with the radial velocityperiod. We interpret the 472-day period as being caused by a sub-stellarcompanion. Based on the estimated absolute magnitude and a comparison toevolutionary tracks we estimate the mass of the progenitor star between2 and 7 M_ȯ which results in a projected mass of the companion of msin i = 8 20 M_J. HD 13189 may be the most massive star known to possessan extrasolar planet. This suggests that the formation of giant planetscan also occur around early-type stars. HD 13189 also shows significantshort term radial velocity variability on time scales of days that ismost likely due to stellar oscillations. This behavior is typical for Kgiant stars.
| α-, r-, and s-process element trends in the Galactic thin and thick disks
From a detailed elemental abundance analysis of 102 F and G dwarf starswe present abundance trends in the Galactic thin and thick disks for 14elements (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, Ba, and Eu).Stellar parameters and elemental abundances (except for Y, Ba and Eu)for 66 of the 102 stars were presented in our previous studies (Bensbyet al. [CITE], A&A, 410, 527, [CITE], A&A, 415, 155). The 36stars that are new in this study extend and confirm our previous resultsand allow us to draw further conclusions regarding abundance trends. Thes-process elements Y and Ba, and the r-element Eu have also beenconsidered here for the whole sample for the first time. With this newlarger sample we now have the following results: 1) smooth and distinctabundance trends that for the thin and thick disks are clearlyseparated; 2) the α-element trends for the thick disk show typicalsignatures from the enrichment of SN Ia; 3) the thick disk stellarsample is in the mean older than the thin disk stellar sample; 4) thethick disk abundance trends are invariant with galactocentric radii(R_m); 5) the thick disk abundance trends appear to be invariant withvertical distance (Z_max) from the Galactic plane. Adding furtherevidence from the literaure we argue that a merger/interacting scenariowith a companion galaxy to produce a kinematical heating of the stars(that make up today's thick disk) in a pre-existing old thin disk is themost likely formation scenario for the Galactic thick disk. The 102stars have -1 ≲ [Fe/H] ≲ +0.4 and are all in the solarneighbourhood. Based on their kinematics they have been divided into athin disk sample and a thick disk sample consisting of 60 and 38 stars,respectively. The remaining 4 stars have kinematics that make themkinematically intermediate to the two disks. Their chemical abundancesalso place them in between the two disks. Which of the two diskpopulations these 4 stars belong to, or if they form a distinctpopulation of their own, can at the moment not be settled. The 66 starsfrom our previous studies were observed with the FEROS spectrograph onthe ESO 1.5-m telescope and the CES spectrograph on the ESO 3.6-mtelescope. Of the 36 new stars presented here 30 were observed with theSOFIN spectrograph on the Nordic Optical Telescope on La Palma, 3 withthe UVES spectrograph on VLT/UT2, and 3 with the FEROS spectrograph onthe ESO 1.5-m telescope. All spectra have high signal-to-noise ratios(typically S/N≳ 250) and high resolution (R 80 000, 45 000,and 110 000 for the SOFIN, FEROS, and UVES spectra, respectively).Based on observations collected at the Nordic Optical Telescope on LaPalma, Spain, and at the European Southern Observatories on La Silla andParanal, Chile, Proposals # 65.L-0019(B), 67.B-0108(B), 69.B-0277. FullTables [see full text], [see full text] and [see full text] are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/185
| Searching for Planetary Transits in Galactic Open Clusters: EXPLORE/OC
Open clusters potentially provide an ideal environment for the searchfor transiting extrasolar planets, since they feature a relatively largenumber of stars of the same known age and metallicity at the samedistance. With this motivation, over a dozen open clusters are now beingmonitored by four different groups. We review the motivations andchallenges for open cluster transit surveys for short-period giantplanets. Our photometric monitoring survey of Galactic southern openclusters, the Extrasolar Planet Occultation Research/Open Clusters(EXPLORE/OC) project, was designed with the goals of maximizing thechance of finding and characterizing planets and of providing astatistically valuable astrophysical result in the case of nodetections. We use the EXPLORE/OC data from two open clusters, NGC 2660and NGC 6208, to illustrate some of the largely unrecognized issuesfacing open cluster surveys, including severe contamination by Galacticfield stars (>80%) and the relatively low number of cluster membersfor which high-precision photometry can be obtained. We discuss how acareful selection of open cluster targets under a wide range of criteriasuch as cluster richness, observability, distance, and age can meet thechallenges, maximizing chances to detect planet transits. In addition,we present the EXPLORE/OC observing strategy to optimize planetdetection, which includes high-cadence observing and continuouslyobserving individual clusters rather than alternating between targets.
| Evolution of Cold Circumstellar Dust around Solar-type Stars
We present submillimeter (Caltech Submillimeter Observatory 350 μm)and millimeter (Swedish-ESO Submillimetre Telescope [SEST] 1.2 mm, OwensValley Radio Observatory [OVRO] 3 mm) photometry for 127 solar-typestars from the Formation and Evolution of Planetary Systems SpitzerLegacy program that have masses between ~0.5 and 2.0 Msolarand ages from ~3 Myr to 3 Gyr. Continuum emission was detected towardfour stars with a signal-to-noise ratio>=3: the classical T Tauristars RX J1842.9-3532, RX J1852.3-3700, and PDS 66 with SEST, and thedebris-disk system HD 107146 with OVRO. RX J1842.9-3532 and RXJ1852.3-3700 are located in projection near the R CrA molecular cloud,with estimated ages of ~10 Myr (Neuhäuser et al.), whereas PDS 66is a probable member of the ~20 Myr old Lower Centaurus-Crux subgroup ofthe Scorpius-Centaurus OB association (Mamajek et al.). The continuumemission toward these three sources is unresolved at the 24" SESTresolution and likely originates from circumstellar accretion disks,each with estimated dust masses of ~5×10-5Msolar. Analysis of the visibility data toward HD 107146(age~80-200 Myr) indicates that the 3 mm continuum emission is centeredon the star within the astrometric uncertainties and resolved with aGaussian-fit FWHM size of (6.5"+/-1.4")×(4.2"+/-1.3"), or185AU×120 AU. The results from our continuum survey are combinedwith published observations to quantify the evolution of dust mass withtime by comparing the mass distributions for samples with differentstellar ages. The frequency distribution of circumstellar dust massesaround solar-type stars in the Taurus molecular cloud (age~2 Myr) isdistinguished from that around 3-10 Myr and 10-30 Myr old stars at asignificance level of ~1.5 and ~3 σ, respectively. These resultssuggest a decrease in the mass of dust contained in small dust grainsand/or changes in the grain properties by stellar ages of 10-30 Myr,consistent with previous conclusions. Further observations are needed todetermine if the evolution in the amount of cold dust occurs on evenshorter timescales.
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| Extra-solar system planets: searches, discoveries and characteristics
The study of planets outside our solar system constitutes a new branchof astronomy that literally did not exist a decade ago. This discussionbegins with how people have thought about other worlds in the past andsome of the reported detections that turned out not to be true. Itcontinues with a brief description of several successful ways of findingexoplanets and the properties of the planets found and their host stars,and concludes with an attempt to look ahead. Most of the planets nowknown revealed themselves because their mutual orbits with their parentstars impose small, periodic radial velocity shifts in the stellarspectra, and most of the host stars are rich in heavy elements by thestandards of the solar neighbourhood. The inventory of actual andpotential detection methods has reached about two dozen.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Searching for Planets in the Hyades. III. The Quest for Short-Period Planets
We have been using the Keck I High Resolution Spectrograph to search forplanetary companions in the Hyades cluster. We selected four stars fromthis sample that showed significant radial velocity variability on shorttimescales to search for short-period planetary companions. The radialvelocities of these four stars were monitored regularly with theHobby-Eberly Telescope for approximately 2 months, while sparse datawere also taken over ~4 months: we also obtained near-simultaneousphotometric observations with one of the automatic photoelectrictelescopes at Fairborn Observatory. For three of the stars, we detectphotometric variability with the same period present in the radialvelocity (vr) measurements, compatible with the expectedrotation rates for Hyades members. The fourth star continues to showvr variations and minimal photometric variability but with nosignificant periodicity. This study shows that for the three stars withperiodic behavior, a significant portion of the vrfluctuations are likely due primarily to magnetic activity modulated bystellar rotation rather than planetary companions. Using simple modelsfor the vr perturbations arising from spot and plage, wedemonstrate that both are likely to contribute to the observedvr variations. Thus, simultaneous monitoring of photometric(photospheric) and spectroscopic (chromospheric) variations is essentialfor identifying the cause of Doppler-shifted absorption lines in moreactive stars.Some data were obtained with the Hobby-Eberly Telescope (HET). The HETis operated by McDonald Observatory on behalf of The University of Texasat Austin, the Pennsylvania State University, Stanford University,Ludwig-Maximilians-Universität München, andGeorg-August-Universität Göttingen.Additional data presented herein were obtained at the W.M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration (NASA). TheObservatory was made possible by the generous financial support of theW.M. Keck Foundation.
| The SARG exo-planets search
We present the status of the SARG Extrasolar Planets search. Thisprogram started about 2.5 years ago. It consists in a search for planetsin about 50 wide solar type binaries using high precision radialvelocities gathered with SARG. We also perform a high precisionabundance analysis of the two components of each system. We obtaindifferential radial velocities with typical accuracies of 2-3 m/s forbright standard stars, and of 5 m/s for the fainter program stars.Abundance differences between the two components have typical precisionof about 0.016 dex. Preliminary results are presented, with emphasis onthe case of HD219542, a binary for which we found a difference of about0.09 dex in the Fe abundance between the two components. While no giantplanet in close in orbit is found around the primary, we found radialvelocity variations compatible with a Saturn mass orbiting the secondaryon a Mercury-like orbit. However, we cannot still exclude that theobserved small amplitude radial velocity variations are due to amoderate stellar activity.
| A Planetary Companion to γ Cephei A
We report on the detection of a planetary companion in orbit around theprimary star of the binary system γ Cephei. High-precision radialvelocity measurements using four independent data sets spanning the timeinterval 1981-2002 reveal long-lived residual radial velocity variationssuperposed on the binary orbit that are coherent in phase and amplitudewith a period or 2.48 yr (906 days) and a semiamplitude of 27.5 ms-1. We performed a careful analysis of our Ca II H and KS-index measurements, spectral line bisectors, and Hipparcos photometry.We found no significant variations in these quantities with the 906 dayperiod. We also reanalyzed the Ca II λ8662 measurements of Walkeret al., which showed possible periodic variations with the ``planet''period when first published. This analysis shows that periodic Ca IIequivalent width variations were only present during 1986.5-1992 andabsent during 1981-1986.5. Furthermore, a refined period for the Ca IIλ8662 variations is 2.14 yr, significantly less than the residualradial velocity period. The most likely explanation of the residualradial velocity variations is a planetary-mass companion withMsini=1.7MJ and an orbital semimajor axis ofa2=2.13 AU. This supports the planet hypothesis for theresidual radial velocity variations for γ Cep first suggested byWalker et al. With an estimated binary orbital period of 57 yr, γCep is the shortest period binary system in which an extrasolar planethas been found. This system may provide insights into the relationshipbetween planetary and binary star formation.
| The ELODIE survey for northern extra-solar planets. I. Six new extra-solar planet candidates
Precise radial-velocity observations at Haute-Provence Observatory (OHP,France) with the ELODIE echelle spectrograph have been undertaken since1994. In addition to several discoveries described elsewhere, includingand following that of 51 Peg b, they reveal new sub-stellar companionswith essentially moderate to long periods. We report here about suchcompanions orbiting five solar-type stars (HD 8574,HD 23596, HD 33636, HD50554, HD 106252) and one sub-giant star(HD 190228). The companion of HD8574 has an intermediate period of 227.55 days and asemi-major axis of 0.77 AU. All other companions have long periods,exceeding 3 years, and consequently their semi-major axes are around orabove 2 AU. The detected companions have minimum masses m2sin i ranging from slightly more than 2 MJup to 10.6MJup. These additional objects reinforce the conclusion thatmost planetary companions have masses lower than 5 MJup butwith a tail of the mass distribution going up above 15 MJup.The orbits are all eccentric and 4 out of 6 have an eccentricity of theorder of 0.5. Four stars exhibit solar metallicity, one is metal-richand one metal-poor. With 6 new extra-solar planet candidates discovered,increasing their total known to-date number to 115, the ELODIE PlanetSearch Survey yield is currently 18. We emphasize that 3 out of the 6companions could in principle be resolved by diffraction-limited imagingon 8 m-class telescopes depending on the achievable contrast, andtherefore be primary targets for first attempts of extra-solar planetdirect imaging.Based on observations made at the Haute-Provence Observatory (operatedby French CNRS), the 1.2-m Euler swiss telescope at ESO-La SillaObservatory (Chile) and the 1.52-m ESO telescope also at La SillaObservatory.The ELODIE measurements discussed in this paper are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/1039Appendix A is only available in electronic form athttp://www.edpsciences.org
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| The CORALIE survey for southern extra-solar planets. XI. The return of the giant planet orbiting HD 192263
The presence of a planet around the K dwarf HD 192263was recently called into question by the detection of a periodicphotometric signal with the same period as the one observed in radialvelocity. In this paper, we investigate this possibility, using acombination of radial-velocity, photometry, and bisector measurementsobtained simultaneously. The results show that while the observedradial-velocity variation is always very stable in phase, period, andamplitude, the photometric signal changes with time. The combinedinformation strongly suggests that the observed radial-velocityvariation is being produced by the presence of a planet, as firstlyproposed. The photometric variations are either not connected to theplanetary companion, or can eventually be induced by the interactionbetween the planet and the star. Finally, the radial-velocity datafurther show the presence of a long term trend, whose origin, still notclear, might be related to the presence of another companion to thesystem.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and at the La Palma Observatory, Spain, with the P7 photometerat the 1.2-m MERCATOR Belgian telescope.
| Seven New Keck Planets Orbiting G and K Dwarfs
Planetary mass companions orbiting seven nearby G and K dwarfs have beenfound from the Keck Precision Doppler Survey. A ``51 Peg-like'' planetorbiting HD 49674 has the smallest mass yet found, Msini=0.12MJ. This system does not transit. A double-planet systemorbits HD 37124, with periods of 153 days and 6 yr and minimum masses of0.91 and 1.70 MJ. Single companions with moderateeccentricity have been found orbiting HD 108874, HD 72659, HD 114729,and HD 145675 with orbital periods ranging from 1.09 to 5.98 yr,yielding minimum masses ranging from 0.90 to 4.87 MJ.Periodic Doppler velocity variations, consistent with a mildly eccentricplanet in a 1 AU orbit, are reported for the chromospherically active K0dwarf HD 128311. It remains plausible that these velocity variations aredue to stellar photospheric ``jitter.'' Based on observations obtainedat the W. M. Keck Observatory, which is operated jointly by theUniversity of California and the California Institute of Technology.Keck time has been granted by both NASA and the University ofCalifornia.
| Precision Radial Velocities of Active Stars
A search for line profile variations correlated with stellar radialvelocities (RVs) is presented. The goal is to develop a correctionmethod of RVs for activity effects enabling the search for planetsorbiting active, i.e., young stars. The Coude Echelle Spectrometer (CES)at the ESO 3.6m telescope with its high spectral resolution (R=220,000)has been used to monitor some active stars for changes in their RVs andabsorption line profiles. In the case of HD 166435 it is demonstratedthat a correction of the measured RVs for line profile variations isfeasible and improves the RVs scatter down to the measurement precision.
| Extrasolar Planets: from Individual Detections to Statistical Properties
Ten new planet candidates are announced as part of our ELODIE andCORALIE planet search programs in both hemispheres. Most of thempresent properties common to the known extrasolar planets. One candidate(HD190360a) shares similarities with our own Jupiter (circular, verylong period orbit). The global statistical properties of the orbitalelement distributions are discussed. Emerging features are pointed out,like the lack of massive planets on short period orbits and theappearance of a period valley between 30 and 100 days for the lighterplanets, bringing strong observational constraints for the migrationscenario. Finally, detection "black sheep" are discussed as well asmore complex candidates presently put into questions.
| Extra-solar planets
Not Available
| A False Planet around HD 192263
We present new high-precision Strömgren photometry and Ca II H andK spectrophotometry of HD 192263. Based on radial velocity variationsdetected previously by two groups, this K2 V star was thought to host a0.75 MJup (minimum mass) planetary companion in a 24 dayorbit. Our photometric observations reveal periodic variations thatmatch the purported planetary orbital period, while the Ca II H and Kemission fluxes are modulated on half the planetary period. Thissuggests that rotational modulation of the visibility of stellar surfaceactivity is the source of the observed radial velocity variations.Therefore, HD 192263 should be removed from lists of stars withwell-established planetary companions unless further observations andanalysis can support the existence of the planet in spite of the star'sintrinsic variations.
| The CORALIE survey for southern extra-solar planets. IX. A 1.3-day period brown dwarf disguised as a planet
In this article we present the case of HD 41004 AB, a system composed ofa K0V star and a 3.7-mag fainter M-dwarf companion. We have obtained 86CORALIE spectra of this system with the goal of obtaining preciseradial-velocity measurements. Since HD 41004 A and B are separated byonly 0.5\arcsec, in every spectrum taken for the radial-velocitymeasurement, we are observing the blended spectra of the two stars. Ananalysis of the measurements has revealed a velocity variation with anamplitude of about 50 m s-1 and a periodicity of 1.3 days.This radial-velocity signal is consistent with the expected variationinduced by the presence of a companion to either HD 41004 A or HD 41004B, or to some other effect due to e.g. activity related phenomena. Inparticular, such a small velocity amplitude could be the signature ofthe presence of a very low mass giant planetary companion to HD 41004 A,whose light dominates the spectra. The radial-velocity measurements werethen complemented with a photometric campaign and with the analysis ofthe bisector of the CORALIE Cross-Correlation Function (CCF). While theformer revealed no significant variations within the observationalprecision of ~ 0.003-0.004 mag (except for an observed flare event), thebisector analysis showed that the line profiles are varying in phasewith the radial-velocity. This latter result, complemented with a seriesof simulations, has shown that we can explain the observations byconsidering that HD 41004 B has a brown-dwarf companion orbiting withthe observed 1.3-day period. As the spectrum of the fainter HD 41004 B``moves'' relative to the one of HD 41004 A (with an amplitude of a fewkm s-1), the relative position of the spectral lines of thetwo spectra changes, thus changing the blended line-profiles. Thisvariation is large enough to explain the observed radial-velocity andbisector variations, and is compatible with the absence of anyphotometric signal. If confirmed, this detection represents the firstdiscovery of a brown dwarf in a very short period (1.3-day) orbit aroundan M dwarf. Finally, this case should be taken as a serious warningabout the importance of analyzing the bisector when looking for planetsusing radial-velocity techniques. Based on observations collected at theLa Silla Observatory, ESO (Chile), with the CORALIE spectrograph at the1.2-m Euler Swiss telescope and with the Strömgren AutomaticTelescope (SAT).
| Radial Velocities for 889 Late-Type Stars
We report radial velocities for 844 FGKM-type main-sequence and subgiantstars and 45 K giants, most of which had either low-precision velocitymeasurements or none at all. These velocities differ from the standardstars of Udry et al. by 0.035 km s-1 (rms) for the 26 FGKstandard stars in common. The zero point of our velocities differs fromthat of Udry et al.: =+0.053km s-1. Thus, these new velocities agree with the best knownstandard stars both in precision and zero point, to well within 0.1 kms-1. Nonetheless, both these velocities and the standardssuffer from three sources of systematic error, namely, convectiveblueshift, gravitational redshift, and spectral type mismatch of thereference spectrum. These systematic errors are here forced to be zerofor G2 V stars by using the Sun as reference, with Vesta and day sky asproxies. But for spectral types departing from solar, the systematicerrors reach 0.3 km s-1 in the F and K stars and 0.4 kms-1 in M dwarfs. Multiple spectra were obtained for all 889stars during 4 years, and 782 of them exhibit velocity scatter less than0.1 km s-1. These stars may serve as radial velocitystandards if they remain constant in velocity. We found 11 newspectroscopic binaries and report orbital parameters for them. Based onobservations obtained at the W. M. Keck Observatory, which is operatedjointly by the University of California and the California Institute ofTechnology, and on observations obtained at the Lick Observatory, whichis operated by the University of California.
| Starspots and exoplanets
The discovery of exoplanets has resulted from a significant increase inthe precision of stellar radial velocity measurements. In the pastdecade this precision has improved from several hundreds of ms-1 to a few m s-1. In the near future astrometricmeasurements will make a similar increase in their precision by factorsof several hundred. Although discovering exoplanets is driving the needfor these precise measurements, these can also be used to studystarspots on Sun-like stars. The largest sunspots can produce a radialvelocity variation of several m s-1 and an astrometric signalof order tens of micro-arcseconds in a nearby solar-type star. Thelatter is well above the measurement precision of 4 micro-arcsecsprovided by the Space Interferometry Mission (SIM). A combination ofprecise photometric, radial velocity, and astrometric measurements mayenable us to derive spot distributions on slowly rotating late-typestars with solar-like levels of activity.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Геркулес |
| Прямое восхождение: | 18h09m21.38s |
| Склонение: | +29°57'06.1" |
| Видимая звёздная величина: | 6.838 |
| Расстояние: | 25.24 парсек |
| Собственное движение RA: | 71.4 |
| Собственное движение Dec: | 59.4 |
| B-T magnitude: | 7.596 |
| V-T magnitude: | 6.901 |
Каталоги и обозначения:
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