Contents
Images
Upload your image
DSS Images Other Images
Related articles
Hubble's top 10.
Not Available
| Exploring the Potential of Integral Field Spectroscopy for Observing Extrasolar Planet Transits: Ground-based Observations of the Atmospheric Na in HD 209458b
We explore the use of integral field spectroscopy (IFS) for observingextrasolar planet transits. Although this technique should find its fullpotential in space-based observations (e.g., James Webb Space Telescope,Terrestrial Planet Finder), we have tested its basics with ground-basedtime-series observations of HD 209458b obtained with the WilliamHerschel Telescope optical fiber system INTEGRAL during a transit in2004 August 17/18. For this analysis we have used 5550 spectra (from apotential of ~30,000) obtained in 150 exposures during a period of morethan 7 hr. We have found that IFS offers three fundamental advantageswith respect to previously used methods (based on imaging or standardslit spectroscopy). First, it improves the effective signal-to-noiseratio in photon-limited observations by distributing the light comingfrom the star into the two dimensions of the detector. Second, this typeof IFS data allows us to ``autocalibrate'' instrumental and backgroundeffects. Third, since the star image characteristics (i.e., seeing,spatial shifts, etc.) as well as its photometric properties areextracted from the same data cube, it is possible to decorrelatephotometric instabilities induced by point-spread function (orinstrument) variations. These data have also allowed us to explore theaccuracy limits of ground-based relative spectrophotometry. This wasdone using a photometric index that probes the Na D lines, for which weobtained a nominal 1 σ error of ~1.0 × 10-4. Thisresult, based on observations of only one transit, indicates that thistype of ground observation can constrain the characterization of thetransmission spectrum of extrasolar planets, especially if they covermultiple transits under good weather conditions. The presentobservations are compatible with no extra Na D depression during thetransit. Although this result seems to be inconsistent with the recentlyreported Hubble Space Telescope STIS findings, we point out its limitedstatistical meaning: the results disagree within 1 σ, but agreewithin 2 σ. This method requires careful and specific reductions,and details about this process are given. We also give somerecommendations to instrument developers in order to enhance theefficiency of the method.
| Are we far from testing general relativity with the transitting extrasolar planet HD 209458b ‘Osiris’?
In this paper, we investigate the possibility of measuring the generalrelativistic gravitoelectric correction P(GE) to the orbitalperiod P of the transitting exoplanet HD 209458b ‘Osiris’.It turns out that the predicted magnitude of such an effect is 0.1s, while the most recent determinations of the orbital period of HD209458b with the photometric transit method are accurate to 0.01 s.It turns out that the major limiting factor is the error in themeasurement of the projected semiamplitude of the star’s radialvelocity KM. Indeed, it affects the determination of the massm of the planet which, in turn, induces a systematic error in theKeplerian period P(0) of 8 s. However, the presentsituation may change if future 1 2 orders of magnitude improvements inthe Doppler spectroscopy technique will occur.
| Extrasolar planets, stellar winds and chromospheric hotspots
Recent observations have shown what is believed to be planet-inducedchromospheric activity on stars with hot Jupiters. We present a model ofthe magnetic interaction between a planet and a star with a dipolarmagnetic field. Reconnection between the fields of the star and planetaccelerates electrons along the field lines that connect the star andplanet. By determining the locations at which these field lines connectto the stellar surface, we can model the surface pattern of thechromospheric response to the planet-star interaction. We find that theinclination of the rotation axis of the star determines the magnitude ofthe emission, while a misalignment of the magnetic and rotation axesproduces a phase shift between the peak of the observed chromosphericemission and the phase where the planet is directly in front of thestar. This phase shift increases as the extent of the stellar coronaincreases. This model reproduces the cyclic signature of chromosphericenhancement seen in stars with hot Jupiters. It can reproduce the65° phase lag reported for HD 179949 if the closed corona of thestar extends out to the orbital radius of the planet at8.5R*. It cannot, however, reproduce the phase lag of169° reported for υ And.
| Upper limits on the hot Jupiter fraction in the field of NGC 7789
We describe a method of estimating the abundance of short-periodextra-solar planets based on the results of a photometric survey forplanetary transits. We apply the method to a 21-night survey with the2.5-m Isaac Newton Telescope of ~32000 stars in a ~0.5 ×0.5deg2 field including the open cluster NGC 7789. From thecolour-magnitude diagram, we estimate the mass and radius of each starby comparison with the cluster main sequence. We search for injectedsynthetic transits throughout the light curve of each star in order todetermine their recovery rate, and thus calculate the expected number oftransit detections and false alarms in the survey. We take properaccount of the photometric accuracy, time sampling of the observationsand criteria (signal-to-noise ratio and number of transits) adopted fortransit detection. Assuming that none of the transit candidates found inthe survey will be confirmed as real planets, we place conservativeupper limits on the abundance of planets as a function of planet radius,orbital period and spectral type.
| Colour-differential interferometry for the observation of extrasolar planets
We present the high angular resolution technique of colour-differentialinterferometry for direct detection of extrasolar giant planets (EGPs).The measurement of differential phase with long-baseline ground-basedinterferometers in the near-infrared could allow the observation ofseveral hot giant extrasolar planets in tight orbit around the nearbystars, and thus yield their low- or mid-resolution spectroscopy,complete orbital data set and mass. Estimates of potentially achievablesignal-to-noise ratios are presented for a number of planets alreadydiscovered by indirect methods. The limits from the instrumental andatmospheric instability are discussed, and a subsequent observationalstrategy is proposed.
| Direct imaging photometry with the MOST satellite
Canada's first space telescope, MOST (Microvariablity and Oscillationsof Stars) was successfully launched on June 30, 2003 with a primarymission to perform ultra-high-precision photometry to detect acousticoscillations in solar-like stars. MOST has the ability to observe singlefields for uninterrupted periods of up to two months and targets can beobserved either through Fabry lens imaging or Direct imaging. Thisreport reviews the Direct imaging capabilities of the MOST satellite andthe extraction of accurate stellar photometry.MOST is a Canadian Space Agency mission, operated jointly by Dynacon, Inc., and the Universities of Toronto and British Columbia, with assistance from the University of Vienna.
| An Upper Limit on the Albedo of HD 209458b: Direct Imaging Photometry with the MOST Satellite
We present space-based photometry of the transiting exoplanetary systemHD 209458 obtained with the Microvariablity and Oscillations of Stars(MOST) satellite, spanning 14 days and covering 4 transits and 4secondary eclipses. The HD 209458 photometry was obtained in MOST'slower precision direct imaging mode, which is used for targets in thebrightness range 6.5>=V>=13. We describe the photometric reductiontechniques for this mode of observing, in particular the corrections forstray earthshine. We do not detect the secondary eclipse in the MOSTdata, to a limit in depth of 0.053 mmag (1 σ). We set a 1 σupper limit on the planet-star flux ratio of 4.88×10-5corresponding to a geometric albedo upper limit in the MOST bandpass(400-700 nm) of 0.25. The corresponding numbers at the 3 σ levelare 1.34×10-4 and 0.68, respectively. HD 209458b ishalf as bright as Jupiter in the MOST bandpass. This low geometricalbedo value is an important constraint for theoretical models of the HD209458b atmosphere, in particular ruling out the presence of reflectiveclouds. A second MOST campaign on HD 209458 is expected to be sensitiveto an exoplanet albedo as low as 0.13 (1 σ), if the star does notbecome more intrinsically variable in the meantime.MOST is a Canadian Space Agency mission, operated jointly by Dynacon,Inc., and the Universities of Toronto and British Columbia, withassistance from the University of Vienna.
| Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems
We present results of a reconnaissance for stellar companions to all 131radial velocity-detected candidate extrasolar planetary systems known asof 2005 July 1. Common proper-motion companions were investigated usingthe multiepoch STScI Digitized Sky Surveys and confirmed by matching thetrigonometric parallax distances of the primaries to companion distancesestimated photometrically. We also attempt to confirm or refutecompanions listed in the Washington Double Star Catalog, in the Catalogsof Nearby Stars Series by Gliese and Jahreiß, in Hipparcosresults, and in Duquennoy & Mayor's radial velocity survey. Ourfindings indicate that a lower limit of 30 (23%) of the 131 exoplanetsystems have stellar companions. We report new stellar companions to HD38529 and HD 188015 and a new candidate companion to HD 169830. Weconfirm many previously reported stellar companions, including six starsin five systems, that are recognized for the first time as companions toexoplanet hosts. We have found evidence that 20 entries in theWashington Double Star Catalog are not gravitationally bound companions.At least three (HD 178911, 16 Cyg B, and HD 219449), and possibly five(including HD 41004 and HD 38529), of the exoplanet systems reside intriple-star systems. Three exoplanet systems (GJ 86, HD 41004, andγ Cep) have potentially close-in stellar companions, with planetsat roughly Mercury-Mars distances from the host star and stellarcompanions at projected separations of ~20 AU, similar to the Sun-Uranusdistance. Finally, two of the exoplanet systems contain white dwarfcompanions. This comprehensive assessment of exoplanet systems indicatesthat solar systems are found in a variety of stellar multiplicityenvironments-singles, binaries, and triples-and that planets survive thepost-main-sequence evolution of companion 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.
| Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets
Precise radial velocity measurements have led to the discovery of ~170extrasolar planetary systems. Understanding the uncertainties in theorbital solutions will become increasingly important as the discoveryspace for extrasolar planets shifts to planets with smaller masses andlonger orbital periods. The method of Markov chain Monte Carlo (MCMC)provides a rigorous method for quantifying the uncertainties in orbitalparameters in a Bayesian framework (Paper I). The main practicalchallenge for the general application of MCMC is the need to constructMarkov chains that quickly converge. The rate of convergence is verysensitive to the choice of the candidate transition probabilitydistribution function (CTPDF). Here we explain one simple method forgenerating alternative CTPDFs that can significantly speed convergenceby 1-3 orders of magnitude. We have numerically tested dozens of CTPDFswith simulated radial velocity data sets to identify those that performwell for different types of orbits and suggest a set of CTPDFs forgeneral application. In addition, we introduce other refinements to theMCMC algorithm for radial velocity planets, including an improvedtreatment of the uncertainties in the radial velocity observations, analgorithm for automatically choosing step sizes, an algorithm forautomatically determining reasonable stopping times, and the use ofimportance sampling for including the dynamical evolution ofmultiple-planet systems. Together, these improvements make it practicalto apply MCMC to multiple-planet systems. We demonstrate theimprovements in efficiency by analyzing a variety of extrasolarplanetary systems.
| 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.
| Search for Planetary Candidates within the OGLE Stars
We develop a method to distinguish between planetary and stellarcompanions to stars that present a periodic decrease in brightness,interpreted as a transit. Light curves from a total of 177 stars fromthe OGLE project were fitted by a model that simulates planetarytransits using an opaque disk in front of an image of the Sun. Thesimulation results yield the orbital radius in units of stellar radii,the orbital inclination angle, and the ratio of the planet radius to thestar radius. Combining Kepler's third law with a mass-radius relationfor main-sequence stars, it was possible to estimate values for themasses and radii of both the primary and secondary objects. This modelwas successfully tested with the confirmed planets orbiting the stars HD209458, TrES-1, and OGLE-TR 10, 56, 111, 113, and 132. The methodconsists of selecting as planetary candidates only those objects withprimary densities between 0.7 and 2.3 solar densities (F, G, and Kstars) and secondaries with radii of less than 1.5 Jovian radii. Themethod is not able to distinguish between a planet and a dwarf star witha mass less than 0.1 Msolar, such as OGLE-TR 122. We proposea selection of 28 planetary candidates (OGLE-TR 49, 51, 55, 63, 71, 76,90, 97, 100, 109, 114, 127, 130, 131, 134, 138, 140, 146, 151, 155, 159,164, 165, 169, 170, 171, 172, and 174) for follow-up high-resolutionspectroscopy.
| How Dry is the Brown Dwarf Desert? Quantifying the Relative Number of Planets, Brown Dwarfs, and Stellar Companions around Nearby Sun-like Stars
Sun-like stars have stellar, brown dwarf, and planetary companions. Tohelp constrain their formation and migration scenarios, we analyze theclose companions (orbital period <5 yr) of nearby Sun-like stars. Byusing the same sample to extract the relative numbers of stellar, browndwarf, and planetary companions, we verify the existence of a very drybrown dwarf desert and describe it quantitatively. With decreasing mass,the companion mass function drops by almost 2 orders of magnitude from 1Msolar stellar companions to the brown dwarf desert and thenrises by more than an order of magnitude from brown dwarfs toJupiter-mass planets. The slopes of the planetary and stellar companionmass functions are of opposite sign and are incompatible at the 3σ level, thus yielding a brown dwarf desert. The minimum number ofcompanions per unit interval in log mass (the driest part of the desert)is at M=31+25-18MJ. Approximately 16%of Sun-like stars have close (P<5 yr) companions more massive thanJupiter: 11%+/-3% are stellar, <1% are brown dwarf, and 5%+/-2% aregiant planets. The steep decline in the number of companions in thebrown dwarf regime, compared to the initial mass function of individualstars and free-floating brown dwarfs, suggests either a differentspectrum of gravitational fragmentation in the formation environment orpost-formation migratory processes disinclined to leave brown dwarfs inclose orbits.
| On the Relation between Hot Jupiters and the Roche Limit
Many of the known extrasolar planets are ``hot Jupiters,'' giant planetswith orbital periods of just a few days. We use the observeddistribution of hot Jupiters to constrain the location of its inner edgein the mass-period diagram. If we assume a slope corresponding to theclassical Roche limit, then we find that the edge corresponds to aseparation close to twice the Roche limit, as expected if the planetsstarted on highly eccentric orbits that were later circularized. Incontrast, any migration scenario would predict an inner edge right atthe Roche limit, which applies to planets approaching on nearly circularorbits. However, the current sample of hot Jupiters is not sufficient toprovide a precise constraint simultaneously on both the location and theslope of the inner edge.
| The N2K Consortium. III. Short-Period Planets Orbiting HD 149143 and HD 109749
We report the detection of two short-period planets discovered at KeckObservatory. HD 149143 is a metal-rich G0 IV star with a planet ofMsini=1.33MJ and an orbital radius of 0.053 AU. The best-fitKeplerian model has an orbital period, P=4.072 days, semivelocityamplitude, K=149.6 m s-1, and eccentricity, e=0.016+/-0.01.The host star is chromospherically inactive and metal-rich, with[Fe/H]=0.26. Based on the Teff and stellar luminosity, wederive a stellar radius of 1.49 Rsolar. Photometricobservations of HD 149143 were carried out using the automatedphotometric telescopes at Fairborn Observatory. HD 149143 isphotometrically constant over the radial velocity period to0.0003+/-0.0002 mag, supporting the existence of the planetarycompanion. No transits were detected down to a photometric limit ofapproximately 0.02%, eliminating transiting planets with a variety ofcompositions and constraining the orbital inclination to less than83°. A short-period planet was also detected around HD 109749, a G3IV star. HD 109749 is chromospherically inactive, with [Fe/H]=0.25 and astellar radius of 1.24. The radial velocities for HD 109749 are modeledby a Keplerian with P=5.24 days and K=28.7 m s-1. Theinferred planet mass is Msini=0.28MJ and the semimajor axisof this orbit is 0.0635 AU. Photometry of HD 109749 was obtained withthe SMARTS consortium telescope, the PROMPT telescope, and bytransitsearch.org observers in Adelaide and Pretoria. These observationsdid not detect a decrement in the brightness of the host star at thepredicted ephemeris time, and they constrain the orbital inclination toless than 85° for gas giant planets with radii down to0.7RJ.Based on observations obtained at the W. M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California, and the National Aeronauticsand Space Administration (NASA). The Observatory was made possible bythe generous financial support of the W. M. Keck Foundation. The authorswish to recognize and acknowledge the very significant cultural role andreverence that the summit of Mauna Kea has always had within theindigenous Hawaiian community. We are most fortunate to have theopportunity to conduct observations from this mountain. Keck time hasbeen granted by the National Optical Astronomy Observatory (NOAO) andNASA.
| Transit Photometry of the Core-dominated Planet HD 149026b
We report g, V, and r photometric time series of HD 149026 spanningpredicted times of transit of the Saturn-mass planetary companion, whichwas recently discovered by Sato and collaborators. We present a jointanalysis of our observations and the previously reported photometry andradial velocities of the central star. We refine the estimate of thetransit ephemeris toTc=(2,453,527.87455+0.00085-0.00091)+(2.87598+0.00012-0.00017)N(HJD). Assuming that the star has a radius of 1.45+/-0.10Rsolar and a mass of 1.30+/-0.10 Msolar, weestimate the planet radius to be (0.726+/-0.064)RJup, whichimplies a mean density of 1.07+0.42-0.30 gcm-3. This density is significantly greater than predictedfor models that include the effects of stellar insolation and in whichthe planet has only a small core of solid material. Thus, we confirmthat this planet likely contains a large core and that the ratio of coremass to total planet mass is more akin to that of Uranus and Neptunethan to either Jupiter or Saturn.
| A search for wide visual companions of exoplanet host stars: The Calar Alto Survey
We have carried out a search for co-moving stellar and substellarcompanions around 18 exoplanet host stars with the infrared camera MAGICat the 2.2 m Calar Alto telescope, by comparing our images with imagesfrom the all sky surveys 2MASS, POSS I and II. Four stars of the samplenamely HD 80606, 55 Cnc, HD 46375 and BD-10°3166, arelisted as binaries in the Washington Visual Double Star Catalogue (WDS).The binary nature of HD 80606, 55 Cnc, and HD 46375 is confirmed withboth astrometry as well as photometry, thereby the proper motion of thecompanion of HD 46375 was determined here for the first time. We derivedthe companion masses as well as the longterm stability regions foradditional companions in these three binary systems. We can rule outfurther stellar companions around all stars in the sample with projectedseparations between 270 AU and 2500 AU, being sensitive to substellarcompanions with masses down to 60 {MJup} (S/N=3).Furthermore we present evidence that the two components of the WDSbinary BD-10°3166 are unrelated stars, i.e this system isa visual pair. The spectrophotometric distance of the primary (a K0dwarf) is 67 pc, whereas the presumable secondaryBD-10°3166 B (a M4 to M5 dwarf) is located at a distanceof 13 pc in the foreground.
| Dwarfs in the Local Region
We present lithium, carbon, and oxygen abundance data for a sample ofnearby dwarfs-a total of 216 stars-including samples within 15 pc of theSun, as well as a sample of local close giant planet (CGP) hosts (55stars) and comparison stars. The spectroscopic data for this work have aresolution of R~60,000, a signal-to-noise ratio >150, and spectralcoverage from 475 to 685 nm. We have redetermined parameters and derivedadditional abundances (Z>10) for the CGP host and comparison samples.From our abundances for elements with Z>6 we determine the meanabundance of all elements in the CGP hosts to range from 0.1 to 0.2 dexhigher than nonhosts. However, when relative abundances ([x/Fe]) areconsidered we detect no differences in the samples. We find nodifference in the lithium contents of the hosts versus the nonhosts. Theplanet hosts appear to be the metal-rich extension of local regionabundances, and overall trends in the abundances are dominated byGalactic chemical evolution. A consideration of the kinematics of thesample shows that the planet hosts are spread through velocity space;they are not exclusively stars of the thin disk.
| Frequency of Hot Jupiters and Very Hot Jupiters from the OGLE-III Transit Surveys toward the Galactic Bulge and Carina
We derive the frequencies of hot Jupiters (HJs) with 3-5 day periods andvery hot Jupiters (VHJs) with 1-3 day periods by comparing the planetsactually detected in the OGLE-III survey with those predicted by ourmodels. The models are constructed following Gould and Morgan (2003) bypopulating the line of sight with stars drawn from the HipparcosCatalogue. Using these, we demonstrate that the number of stars withsensitivity to HJs and VHJs is only 5-16% of those in the OGLE-IIIfields satisfying the spectroscopic-follow-up limit of V_max < 17.5mag. Hence, the frequencies we derive are much higher than a naiveestimate would indicate. We find that at 90% confidence the fraction ofstars with planets in the two period ranges is (1/320)(1^+1.37_-0.59)for HJs and (1/710)(1^+1.10_-0.54) for VHJs. The HJ rate isstatistically indistinguishable from that found in radial velocity (RV)studies. However, we note that magnitude-limited RV samples are heavilybiased toward metal-rich (hence, planet-bearing) stars, while transitsurveys are not, and therefore we expect that more sensitive transitsurveys should find a deficit of HJs as compared to RV surveys. Thedetection of three transiting VHJs, all with periods less than 2 days,is marginally consistent with the complete absence of such detections inRV surveys. The planets detected are consistent with being uniformlydistributed between 1.00 and 1.25 Jovian radii, but there are too few inthe sample to map this distribution in detail.
| Equations for the analysis of the light curves of extra-solar planetary transits
Easy to use analytical formulae are presented for the computation the oflight curves of extra-solar planetary transits. The equations are afunction of the fractional radii of the planet and the parent star, theinclination of the orbit, and the limb-darkening coefficients of thestar. Light curves can be solved for these parameters depending on theprecision of the available observations. When the radial velocity curveis also available, as is normally the case to ensure the nature of thesystem, the masses, radii, and average density of both the star and theplanet can be determined. The equations are valid for any degree of limbdarkening, as well as for any type of transit. The cases of eccentricorbits, third light, or a non-zero relative luminosity of the planet canbe easily taken into account. The basic assumption is that theprojections of both the star and the planet on the plane of the sky arewell represented by circular discs. The effects in case this assumptionis not valid are also discussed. Practical applications are shown,beginning with the light curve of the photometrically discovered planetOGLE-TR-113, obtained with a ground-based telescope. As a secondexample, results are shown from the study of the light curve obtainedfor the transit of the giant planet in HD 209458 with the Hubble SpaceTelescope. Procedures to get the best fit parameters are brieflydiscussed.
| 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.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Abundances of refractory elements in the atmospheres of stars with extrasolar planets
Aims.This work presents a uniform and homogeneous study of chemicalabundances of refractory elements in 101 stars with and 93 without knownplanetary companions. We carry out an in-depth investigation of theabundances of Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg and Al. The newcomparison sample, spanning the metallicity range -0.70< [Fe/H]<0.50, fills the gap that previously existed, mainly at highmetallicities, in the number of stars without known planets.Methods.Weused an enlarged set of data including new observations, especially forthe field "single" comparison stars . The line list previously studiedby other authors was improved: on average we analysed 90 spectral linesin every spectrum and carefully measured more than 16 600 equivalentwidths (EW) to calculate the abundances.Results.We investigate possibledifferences between the chemical abundances of the two groups of stars,both with and without planets. The results are globally comparable tothose obtained by other authors, and in most cases the abundance trendsof planet-host stars are very similar to those of the comparison sample.Conclusions.This work represents a step towards the comprehension ofrecently discovered planetary systems. These results could also beuseful for verifying galactic models at high metallicities andconsequently improve our knowledge of stellar nucleosynthesis andgalactic chemical evolution.
| Hipparcos astrometric orbits for two brown dwarf companions: HD 38529 and HD 168443
Context: .HD 38529 and HD 168443 have previously been identified assystems with two substellar companion candidates using precise radialvelocity measurements.Aims.We want to further constrain their orbits andthe nature of the outer companions.Methods.We fit astrometric orbits ofthe outer substellar companions in the two systems to the HipparcosIntermediate Astrometric Data.Results.The fit constrains all possiblesolutions to a small region in the parameter space of the two missingorbital parameters (inclination i and ascending node Ω). This canbe interpreted as a possible real detection of the astrometricsignatures of the companions in the Hipparcos data, although there isstill a 14-18% chance that the signal is not detectable in the data,according to an F-test. However, even in the case of a non-detection ofthe companion signal in the astrometric data, the knowledge of thespectroscopic orbital parameters enables us to place tight constraintson these two missing parameters, so that the astrometric orbit is fullydetermined (with confidence levels of around 80% for HD 38529, 95% forHD 168443). Inclinations derived from these astrometric fits enable usto calculate masses for the substellar companions rather than lower orupper limits. The best fit solution for HD 38529, (i, Ω) =(160°, 52°), yields a mass of 37+36-19M_Jup for the outer companion. For HD 168443, we derive best fitparameters of (i, Ω) = (150°, 19°), which imply acompanion mass of 34± 12 M_Jup.Conclusions.The outer companionsin both systems are thus brown dwarfs.
| The transmission spectrum of Earth-size transiting planets
A variety of terrestrial planets with different physical parameters andexotic atmospheres might plausibly exist outside our Solar System,waiting to be detected by the next generation of space-explorationmissions. Some of these planets might be transiting their parent star.We present here a detailed study of the atmospheric signatures oftransiting Earth-size exoplanets. We focus on a limited number ofsignificant examples, for which we discuss the detectability of some ofthe possible molecules present in their atmospheres, such as water(H2O), carbon dioxide (CO2), ozone (O3), or molecular oxygen (O2). Tothis purpose, we developed a model to simulate transmission spectra ofEarth-size exoplanets from the ultraviolet (UV) to the near infrared(NIR). According to our calculations, the signatures of planetaryatmospheres represent an absorption of a few parts-per-million (ppm) inthe stellar flux. The atmospheres of a few Earth-like planets can bedetected with a 30-40 m telescope. The detection of the extensiveatmospheres of tens of small satellites of giant exoplanets and hundredsof hypothetical ocean-planets can be achieved with 20-30 m and 10-20 minstruments, respectively, provided all these planets are frequent andthey are efficiently surveyed. We also found that planets around K starsare favored, mainly because these stars are more numerous and smallercompared to G or F stars. While not addressed in this study, limitationsmight come from stellar photometric micro-variability.
| The color signature of the transit of HD 209458: discrepancies between stellar atmospheric models and observations
Exoplanetary transits produce a double-horned color signature that isdistinct from both binaries and blends and can thus be used to separateexoplanets from false positives in transit searches. Color photometrywith precision sufficient to detect this signal in transits ofHD 209458 is available in the literature. Analysis of theseobservations reveals that, while the signature does exhibit the expectedshape, it is significantly stronger than PHOENIX atmospheric modelspredict.
| Ground-based direct detection of close-in extra-solar planets with nulling and high order adaptive optics
Ground-based direct detection of extra-solar planets is very challengingdue to high planet to star brightness contrasts. For giant close-inplanets, such as have been discovered by the radial velocity method,closer than 0.1 AU, the reflected light is predicted to be fairly highyielding a contrast ratio ranging from 10-4 to10-5 at near infra-red wavelengths. In this paper, weinvestigate direct detection of reflected light from such planets usingnulling interferometry, and high-order adaptive optics in conjunctionwith large double aperture ground-based telescopes. In thisconfiguration, at least 10-3 suppression of the entirestellar Airy pattern with small loss of planet flux as close as 0.03arcsec is achievable. Distinguishing residual starlight from the planetsignal is achieved by using the center of gravity shift method ormulticolor differential imaging. Using these assumptions, we deriveexposure times from a few minutes to several hours for direct detectionof many of the known extra-solar planets with several short-baselinedouble aperture telescopes such as the Large Binocular Telescope (LBT),the Very Large Telescope (VLT) and the Keck Telescope.
| Oxygen abundances in planet-harbouring stars. Comparison of different abundance indicators
We present a detailed and uniform study of oxygen abundances in 155solar type stars, 96 of which are planet hosts and 59 of which form partof a volume-limited comparison sample with no known planets. EWmeasurements were carried out for the [O I] 6300 Å line and the OI triplet, and spectral synthesis was performed for several OH lines.NLTE corrections were calculated and applied to the LTE abundanceresults derived from the O I 7771-5 Å triplet. Abundances from [OI], the O I triplet and near-UV OH were obtained in 103, 87 and 77dwarfs, respectively. We present the first detailed and uniformcomparison of these three oxygen indicators in a large sample ofsolar-type stars. There is good agreement between the [O/H] ratios fromforbidden and OH lines, while the NLTE triplet shows a systematicallylower abundance. We found that discrepancies between OH, [O I] and the OI triplet do not exceed 0.2 dex in most cases. We have studied abundancetrends in planet host and comparison sample stars, and no obviousanomalies related to the presence of planets have been detected. Allthree indicators show that, on average, [O/Fe] decreases with [Fe/H] inthe metallicity range -0.8< [Fe/H] < 0.5. The planet host starspresent an average oxygen overabundance of 0.1-0.2 dex with respect tothe comparison sample.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Pegasus |
| Right ascension: | 22h03m10.77s |
| Declination: | +18°53'03.6" |
| Apparent magnitude: | 7.641 |
| Distance: | 47.081 parsecs |
| Proper motion RA: | 29.9 |
| Proper motion Dec: | -16.3 |
| B-T magnitude: | 8.334 |
| V-T magnitude: | 7.699 |
Catalogs and designations:
|
