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| Millimagnitude-Precision Photometry of Bright Stars with a 1 m Telescope and a Standard CCD
This paper summarizes a three-night observing campaign aimed atachieving millimagnitude-precision photometry of bright stars (V <9.0 mag) with the 1 m Swope Telescope at Las Campanas Observatory. Thetest targets were the main-sequence stars HD 205739 and HD 135446. Theresults show that by placing a concentric diaphragm in front of theaperture of the telescope, it is possible to avoid saturation andachieve a photometric precision of 0.0008-0.0010 mag per data point,with a cadence of less than 4 minutes. It is also possible to reach anoverall precision of less that 0.0015 mag for time series of 6 hr ormore. The photometric precision of this setup is only limited byscintillation. Scintillation could be reduced, and therefore thephotometric precision further improved, by using a neutral-densityfilter instead of the aperture stop. Given the expected median depth ofabout 0.01 mag for extrasolar-planet transits, plus their typicalduration of several hours, the results of this paper show that 1 mtelescopes equipped with standard CCDs can be used to detect planettransits as shallow as 0.002 mag around bright stars.
| Catalog of Nearby Exoplanets
We present a catalog of nearby exoplanets. It contains the 172 knownlow-mass companions with orbits established through radial velocity andtransit measurements around stars within 200 pc. We include fivepreviously unpublished exoplanets orbiting the stars HD 11964, HD 66428,HD 99109, HD 107148, and HD 164922. We update orbits for 83 additionalexoplanets, including many whose orbits have not been revised sincetheir announcement, and include radial velocity time series from theLick, Keck, and Anglo-Australian Observatory planet searches. Both thesenew and previously published velocities are more precise here due toimprovements in our data reduction pipeline, which we applied toarchival spectra. We present a brief summary of the global properties ofthe known exoplanets, including their distributions of orbital semimajoraxis, minimum mass, and orbital eccentricity.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. The Keck Observatory was made possible by thegenerous financial support of the W. M. Keck Foundation.
| Strong Infrared Emission from the Extrasolar Planet HD 189733b
We report detection of strong infrared thermal emission from the nearby(d=19 pc) transiting extrasolar planet HD 189733b by measuring the fluxdecrement during its prominent secondary eclipse. A 6 hr photometricsequence using Spitzer's infrared spectrograph in peak-up imaging modeat 16 μm shows the secondary eclipse depth to be 0.551%+/-0.030%,with accuracy limited by instrumental baseline uncertainties, but with32 σ precision (σ=0.017%) on the detection. The 16 μmbrightness temperature of this planet (1117+/-42 K) is very similar tothe Spitzer detections of TrES-1 and HD 209458b, but the observedplanetary flux (660 μJy) is an order of magnitude greater. This largesignal will allow a detailed characterization of this planet in theinfrared. Our photometry has sufficient signal-to-noise ratio (~400 perpoint) to motivate a search for structure in the ingress/egress portionsof the eclipse curve, caused by putative thermal structure on the diskof the planet. We show that by binning our 6 s sampling down to ~6minute resolution, we detect the modulation in the intensity derivativeduring ingress/egress due to the overall shape of the planet, but oursensitivity is not yet sufficient to distinguish between realisticmodels of the temperature distribution across the planet's disk. Wepoint out the potential for extending Spitzer secondary eclipsedetections down to the regime of transiting hot Neptunes, if suchsystems are discovered among nearby lower main-sequence stars.
| Atmosphere, Interior, and Evolution of the Metal-rich Transiting Planet HD 149026b
We investigate the atmosphere and interior of the new transiting planetHD 149026b, which appears to be very rich in heavy elements. We firstcompute model atmospheres at metallicities ranging from solar to 10times solar and show how for cases with high metallicity or inefficientredistribution of energy from the dayside, the planet may develop a hotstratosphere due to absorption of stellar flux by TiO and VO. Thespectra predicted by these models are very different than cooleratmosphere models without stratospheres. The spectral effects arepotentially detectable with the Spitzer Space Telescope. In addition,the models with hot stratospheres lead to a large limb brightening,rather than darkening. We compare the atmosphere of HD 149026b to otherwell-known transiting planets, including the recently discovered HD189733b, which we show has a planet-to-star flux ratio twice that of HD209458 and TrES-1. The methane abundance in the atmosphere of HD 189733bis a sensitive indicator of atmospheric temperature and metallicity andcan be constrained with Spitzer IRAC observations. We then turn tointerior studies of HD 149026b and use a grid of self-consistent modelatmospheres and high-pressure equations of state for all components tocompute thermal evolution models of the planet. We estimate that themass of heavy elements within the planet is in the range of 60-93M⊕. Finally, we discuss trends in the radii oftransiting planets with metallicity in light of this new member of theclass.
| A Stellar Companion in the HD 189733 System with a Known Transiting Extrasolar Planet
We show that the very close-by (19 pc) K0 star HD 189733, already foundto be orbited by a transiting giant planet, is the primary of a doublestar system, with the secondary being a mid-M dwarf with projectedseparation of about 216 AU from the primary. This conclusion is based onastrometry, proper-motion and radial velocity measurements, spectraltype determination, and photometry. We also detect differential propermotion of the secondary. The data appear consistent with the secondary'sorbiting the primary in a clockwise orbit, lying nearly in the plane ofthe sky (i.e., nearly perpendicular to the orbital plane of thetransiting planet), and with period of about 3200 years.
| Survey for Transiting Extrasolar Planets in Stellar Systems. III. A Limit on the Fraction of Stars with Planets in the Open Cluster NGC 1245
We analyze a 19 night photometric search for transiting extrasolarplanets in the open cluster NGC 1245. An automated transit searchalgorithm with quantitative selection criteria finds six transitcandidates; none are bona fide planetary transits. We characterize thesurvey detection probability via Monte Carlo injection and recovery ofrealistic limb-darkened transits. We use this to derive upper limits onthe fraction of cluster members with close-in Jupiter radii,RJ, companions. The survey sample contains ~870 clustermembers, and we calculate 95% confidence upper limits on the fraction ofthese stars with planets by assuming that the planets have an evenlogarithmic distribution in semimajor axis over the Hot Jupiter (HJ;3.0
| High resolution spectroscopy of stars with transiting planets. The cases of OGLE-TR-10, 56, 111, 113, and TrES-1
Context: .During the past years photometric surveys, later complementedby follow-up radial-velocity measurements, have revealed the presence ofseveral new extra-solar transiting planets, in very short-period orbits.Many of the host stars are extremely faint (V16), makinghigh-precision spectroscopic measurements challenging. Aims: .Weused the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolutionspectra of 5 stars hosting transiting planets, namely for OGLE-TR-10,56, 111, 113, and TrES-1. The immediate objective is to derive accuratestellar parameters and chemical abundances. Methods: .The stellarparameters were derived from an LTE analysis of a set of Fe I and Fe IIlines. Results: .Complementing the spectroscopic information withphotometric transit curves and radial-velocity data from the literature,we then refined the stellar and planetary radii and masses. The obtaineddata were also used to study the relation between the stellarmetallicity and orbital period of the planets.
| A posteriori detection of the planetary transit of HD 189733 b in the Hipparcos photometry
Context: . Aims: .Using observations performed at theHaute-Provence Observatory, the detection of a 2.2-day orbital periodextra-solar planet that transits the disk of its parent star, HD 189733,has been recently reported. We searched in the Hipparcos photometryCatalogue for possible detections of those transits. Methods:.Statistic studies were performed on the Hipparcos data in order todetect transits of HD 189733 b and to quantify the significance of theirdetection. Results: .With a high level of confidence, we find thatHipparcos likely observed one transit of HD 189733 b in October 1991,and possibly two others in February 1991 and February 1993. Using therange of possible periods for HD 189733 b, we find that the probabilitythat none of those events are due to planetary transits but are insteadall due to artifacts is lower than 0.15%. Using the 15-year temporalbaseline available, we can measure the orbital period of the planet HD189733 b with particularly high accuracy. We obtain a period of2.218574+0.000006-0.000010 days, corresponding toan accuracy of 1 s. Such accurate measurements might provide cluesfor the presence of companions. Conclusions: .
| ELODIE metallicity-biased search for transiting Hot Jupiters. II. A very hot Jupiter transiting the bright K star HD 189733
Context: .Among the 160 known exoplanets, mainly detected in largeradial-velocity surveys, only 8 have a characterization of their actualmass and radius thanks to the two complementary methods of detection:radial velocities and photometric transit. Aims: .We started inMarch 2004 an exoplanet-search programme biased toward high-metallicitystars which are more frequently host extra-solar planets. This surveyaims to detect close-in giant planets, which are most likely to transittheir host star. Methods: .For this programme, high-precisionradial velocities are measured with the ELODIE fiber-fed spectrograph onthe 1.93-m telescope, and high-precision photometry is obtained with theCCD Camera on the 1.20-m telescope, both at the Haute-ProvenceObservatory. Results: .We report here the discovery of a newtransiting hot Jupiter orbiting the star HD 189733. The planetary natureof this object is confirmed by the observation of both the spectroscopicand photometric transits. The exoplanet HD 189733 b, with an orbitalperiod of 2.219 days, has one of the shortest orbital periods detectedby radial velocities, and presents the largest photometric depth in thelight curve (3%) observed to date. We estimate for the planet amass of 1.15±0.04 MJ and a radius of 1.26±0.03RJ. Considering that HD 189733 has the same visual magnitudeas the well known exoplanet host star HD 209458, further ground-basedand space-based follow-up observations are very promising and willpermit a characterization of the atmosphere and exosphere of this giantexoplanet.
| 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
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| 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.
| K dwarfs and the chemical evolution of the solar cylinder
K dwarfs have lifetimes older than the present age of the Galactic disc,and are thus ideal stars for investigating the chemical evolution of thedisc. We have developed several photometric metallicity indicators for Kdwarfs, based on a sample of accurate spectroscopic metallicities for 34disc and halo G and K dwarfs. The photometric metallicities lead us todevelop a metallicity index for K dwarfs based only on their position inthe colour-absolute-magnitude diagram. Metallicities have beendetermined for 431 single K dwarfs drawn from the Hipparcos catalogue,selecting the stars by absolute magnitude and removing multiple systems.The sample is essentially a complete reckoning of the metal content innearby K dwarfs. We use stellar isochrones to mark the stars by mass,and select a subset of 220 of the stars, which is complete within anarrow mass interval. We fit the data with a model of the chemicalevolution of the solar cylinder. We find that only a modest cosmicscatter is required to fit our age-metallicity relation. The modelassumes two main infall episodes for the formation of the halo-thickdisc and thin disc, respectively. The new data confirm that the solarneighbourhood formed on a long time-scale of the order of 7 Gyr.
| Late-type members of young stellar kinematic groups - I. Single stars
This is the first paper of a series aimed at studying the properties oflate-type members of young stellar kinematic groups. We concentrate ourstudy on classical young moving groups such as the Local Association(Pleiades moving group, 20-150Myr), IC 2391 supercluster (35Myr), UrsaMajor group (Sirius supercluster, 300Myr), and Hyades supercluster(600Myr), as well as on recently identified groups such as the Castormoving group (200Myr). In this paper we compile a preliminary list ofsingle late-type possible members of some of these young stellarkinematic groups. Stars are selected from previously established membersof stellar kinematic groups based on photometric and kinematicproperties as well as from candidates based on other criteria such astheir level of chromospheric activity, rotation rate and lithiumabundance. Precise measurements of proper motions and parallaxes takenfrom the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, andpublished radial velocity measurements are used to calculate theGalactic space motions (U, V, W) and to apply Eggen's kinematic criteriain order to determine the membership of the selected stars to thedifferent groups. Additional criteria using age-dating methods forlate-type stars will be applied in forthcoming papers of this series. Afurther study of the list of stars compiled here could lead to a betterunderstanding of the chromospheric activity and their age evolution, aswell as of the star formation history in the solar neighbourhood. Inaddition, these stars are also potential search targets for directimaging detection of substellar companions.
| A revision of the solar neighbourhood metallicity distribution
We present a revised metallicity distribution of dwarfs in the solarneighbourhood. This distribution is centred on solar metallicity. Weshow that previous metallicity distributions, selected on the basis ofspectral type, are biased against stars with solar metallicity orhigher. A selection of G-dwarf stars is inherently biased againstmetal-rich stars and is not representative of the solar neighbourhoodmetallicity distribution. Using a sample selected on colour, we obtain adistribution where approximately half the stars in the solarneighbourhood have metallicities higher than [Fe/H]=0. The percentage ofmid-metal-poor stars ([Fe/H]<-0.5) is approximately 4 per cent, inagreement with present estimates of the thick disc. In order to have ametallicity distribution comparable to chemical evolution modelpredictions, we convert the star fraction to mass fraction, and showthat another bias against metal-rich stars affects dwarf metallicitydistributions, due to the colour (or spectral type) limits of thesamples. Reconsidering the corrections resulting from the increasingthickness of the stellar disc with age, we show that the simpleclosed-box model with no instantaneous recycling approximation gives areasonable fit to the observed distribution. Comparisons with theage-metallicity relation and abundance ratios suggest that the simpleclosed-box model may be a viable model of the chemical evolution of theGalaxy at solar radius.
| The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars
We present the results from a spectroscopic Ca ii H&K survey of 1058late-type stars selected from a color-limited subsample of the Hipparcoscatalog. Out of these 1058 stars, 371 stars were found to showsignificant H&K emission, most of them previously unknown; 23% withstrong emission, 36% with moderate emission, and 41% with weak emission.These spectra are used to determine absolute H&K emission-linefluxes, radial velocities, and equivalent widths of theluminosity-sensitive Sr ii line at 4077 Ä. Red-wavelengthspectroscopic and Strömgren y photometric follow-up observations ofthe 371 stars with H&K emission are used to additionally determinethe absolute Hα -core flux, the lithium abundance from the Li i6708 Å equivalent width, the rotational velocity vsin i, theradial velocity, and the light variations and its periodicity. Thelatter is interpreted as the stellar rotation period due to aninhomogeneous surface brightness distribution. 156 stars were found withphotometric periods between 0.29 and 64 days, 11 additional systemsshowed quasi-periodic variations possibly in excess of ~50 days. Further54 stars had variations but no unique period was found, and four starswere essentially constant. Altogether, 170 new variable stars werediscovered. Additionally, we found 17 new SB1 (plus 16 new candidates)and 19 new SB2 systems, as well as one definite and two possible new SB3systems. Finally, we present a list of 21 stars that we think are mostsuitable candidates for a detailed study with the Doppler-imagingtechnique. Tables A1--A3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. IV. The northern hemisphere sample
We present high-precision photometry, high- and medium-resolutionspectroscopy for a sample of 32 stars likely to be the opticalcounterparts of X-ray sources serendipitously detected by the EXOSATsatellite. Using also recent results from the Hipparcos satellite, weinfer spectral types, compute X-ray luminosities and Li abundances andinvestigate the single or binary nature of the sample stars. We foundeleven new variable stars, whose photometric periods fall in the1.2-27.5 day range, for most of which the optical variability isconsistent with the presence of photospheric cool spots. For our sampleof X-ray selected stars we confirm the existence of a strong correlationbetween the stellar rotation rate and the level of activity, and alsobetween the X-ray and bolometric luminosities. Two stars in our sampleare likely to be pre-main sequence objects, one is likely to be apreviously unknown M-type star within 25 pc. Based on data collected atCatania Astrophysical Observatory (Mt. Etna, Italy), at ObservatorioAstronomico Nacional (UNAM, S. Pedro Martir, BC, Mexico) and at KittPeak National Observatory (Kitt Peak, AZ, USA) Table 1 is available inthe on-line version; Table 3 and the complete data set are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr orvia http://cdsweb.u-strasbg.fr/Abstract.html}
| Photometric Measurements of the Fields of More than 700 Nearby Stars
In preparation for optical/IR interferometric searches for substellarcompanions of nearby stars, we undertook to characterize the fields ofall nearby stars visible from the Northern Hemisphere to determinesuitable companions for interferometric phase referencing. Because theKeck Interferometer in particular will be able to phase-reference oncompanions within the isoplanatic patch (30") to about 17th magnitude atK, we took images at V, r, and i that were deep enough to determine iffield stars were present to this magnitude around nearby stars using aspot-coated CCD. We report on 733 fields containing 10,629 measurementsin up to three filters (Gunn i, r and Johnson V) of nearby stars down toabout 13th magnitude at V.
| The ROSAT all-sky survey catalogue of the nearby stars
We present X-ray data for all entries of the Third Catalogue of NearbyStars \cite[(Gliese & Jahreiss 1991)]{gli91} that have been detectedas X-ray sources in the ROSAT all-sky survey. The catalogue contains1252 entries yielding an average detection rate of 32.9 percent. Inaddition to count rates, source detection parameters, hardness ratios,and X-ray fluxes we also list X-ray luminosities derived from Hipparcosparallaxes. Catalogue also available at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Preliminary Version of the Third Catalogue of Nearby Stars
Not Available
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| קבוצת-כוכבים: | שועלון |
| התרוממות ימנית: | 20h00m43.71s |
| סירוב: | +22°42'39.1" |
| גודל גלוי: | 7.682 |
| מרחק: | 19.253 פארסק |
| תנועה נכונה: | -2.8 |
| תנועה נכונה: | -250.7 |
| B-T magnitude: | 8.847 |
| V-T magnitude: | 7.779 |
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