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Virtual planet sleuths.
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| The Effects of Multiple Companions on the Efficiency of Space Interferometry Mission Planet Searches
The Space Interferometry Mission (SIM) is expected to make preciseastrometric measurements that can be used to detect low-mass planetsaround nearby stars. Since most nearby stars are members ofmultiple-star systems, many of them will have a measurable accelerationdue to their companion, which must be included when solving forastrometric parameters and searching for planetary perturbations. Inaddition, many of the stars with one radial velocity planet showindications of additional planets. Therefore, astrometric surveys suchas SIM must be capable of detecting planets and measuring orbitalparameters in systems with multiple stellar and/or planetary companions.We have conducted Monte Carlo simulations to investigate how thepresence of multiple companions affects the sensitivity of anastrometric survey such as SIM. We find that the detection efficiencyfor planets in wide binary systems is relatively unaffected by thepresence of a binary companion if the planetary orbital period is lessthan half the duration of the astrometric survey. For longer orbitalperiods, there are significant reductions in the sensitivity of anastrometric survey. In addition, we find that the signal required todetect a planet can be increased significantly due to the presence of anadditional planet orbiting the same star. Fortunately, adding a modestnumber of precision radial velocity observations significantly improvesthe sensitivity for many multiple-planet systems. Thus, the combinationof radial velocity observations and astrometric observations by SIM willbe particularly valuable for studying multiple-planet systems.
| A rigorous statistical test for the existence of supermetallicity in F, G and K dwarfs
In this paper, the first statistically rigorous test is performed todetermine whether there are dwarfs in the solar neighbourhood with[Fe/H] > +0.2 dex. The possibility that no such stars exist isrejected with a confidence limit exceeding 99.994 per cent. If thethreshold value is raised to +0.38 dex, the corresponding hypothesis isrejected with a confidence limit of 98.5 per cent. It is tentativelyfound that this upper limit does not depend on the presence or absenceof planets orbiting metal-rich stars. In a result that is unchanged froma previous paper, the upper limit for the known metallicities of giantsis found to be about 0.2 dex lower than the limit for dwarfs. Stars thatmight be observed to improve the upper metallicity limit for dwarfs arelisted.
| Metallicity, debris discs and planets
We investigate the populations of main-sequence stars within 25 pc thathave debris discs and/or giant planets detected by Doppler shift. Themetallicity distribution of the debris sample is a very close match tothat of stars in general, but differs with >99 per cent confidencefrom the giant planet sample, which favours stars of above averagemetallicity. This result is not due to differences in age of the twosamples. The formation of debris-generating planetesimals at tens of authus appears independent of the metal fraction of the primordial disc,in contrast to the growth and migration history of giant planets withina few au. The data generally fit a core accumulation model, with outerplanetesimals forming eventually even from a disc low in solids, whileinner planets require fast core growth for gas to still be present tomake an atmosphere.
| Reducing the probability of capture into resonance
A migrating planet can capture planetesimals into mean motionresonances. However, resonant trapping can be prevented when the driftor migration rate is sufficiently high. Using a simple Hamiltoniansystem for first- and second-order resonances, we explore how thecapture probability depends on the order of the resonance, drift rateand initial particle eccentricity. We present scaling factors as afunction of the planet mass and resonance strength to estimate theplanetary migration rate above which the capture probability drops toless than half. Applying our framework to multiple extrasolar planetarysystems that have two planets locked in resonance, we estimate lowerlimits for the outer planet's migration rate, allowing resonance captureof the inner planet.Mean motion resonances are comprised of multiple resonant subterms. Wefind that the corotation subterm can reduce the probability of capturewhen the planet eccentricity is above a critical value. We presentfactors that can be used to estimate this critical planet eccentricity.Applying our framework to the migration of Neptune, we find thatNeptune's eccentricity is near the critical value that would make its 2: 1 resonance fail to capture twotinos. The capture probability isaffected by the separation between resonant subterms and so is also afunction of the precession rates of the longitudes of periapse of bothplanet and particle near resonance.
| Planetary migration and extrasolar planets in the 2/1 mean-motion resonance
In this paper, we present a new set of corotational solutions for the2/1 commensurability, including previously known solutions and newresults. Comparisons with observed exoplanets show that current orbitalfits of three proposed resonant planetary systems are consistent withapsidal corotations.We also discuss the possible relationship between the current orbitalelements fits of known exoplanets in the 2/1 mean-motion resonance andthe expected orbital configuration due to migration. We find that, aslong as the orbital decay was sufficiently slow to be approximated by anadiabatic process, all captured planets should be in apsidalcorotations. In other words, they should show a simultaneous librationof both the resonant angle and the difference in longitudes ofpericenter.
| Stability and 2:1 resonance in the planetary system HD 829431
We have explored the secular dynamical evolution of the HD 82943 systemwith two resonant giant planets, by simulating various planetaryconfigurations via direct numerical integration. We also studied theirorbital motions in phase space. In the numerical integrations over107 yr, we found that all the stable orbits are connectedwith the 2:1 resonance. Typically, there exists the libration of the tworesonant arguments 1 and (or) 2 on the sametimescale. Hence, both of the semi-major axes are strongly constrainedto behave in a regular way, due to the confinement of the libration ofthe related angles. Using the analytical model we considered the motionof the inner planet in phase space for different values of the outerplanet's eccentricity e2 and of the relative apsidallongitude . We found that the 2:1 orbital resonance is easily preservedwhen= 0† and when e2 is not too large. A moderatee2 can lock the two planets into deep resonance. The resultsby the analytical method agree well with those by the numericalsimulation, both revealing the 2:1 resonance architecture.
| 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.
| Predicting Planets in Known Extrasolar Planetary Systems. III. Forming Terrestrial Planets
Recent results have shown that many of the known extrasolar planetarysystems contain regions that are stable for both Earth-mass andSaturn-mass planets. Here we simulate the formation of terrestrialplanets in four planetary systems, 55 Cancri, HD 38529, HD 37124, and HD74156, under the assumption that these systems of giant planets arecomplete and that their orbits are well determined. Assuming that thegiant planets formed and migrated quickly, terrestrial planets may formfrom a second generation of planetesimals. In each case, Moon- toMars-sized planetary embryos are placed in between the giant planets andevolved for 100 Myr. We find that planets form relatively easily in 55Cnc, with masses up to 0.6 M⊕ and, in some cases,substantial water content and orbits in the habitable zone. HD 38529 islikely to support an asteroid belt, but no terrestrial planets ofsignificant mass. No terrestrial planets form in HD 37124 and HD 74156,although in some cases 1-2 lone embryos survive for 100 Myr. Ifmigration occurred later, depleting the planetesimal disk, then massiveterrestrial planets are unlikely to form in any of these systems.
| Giant Planet Accretion and Migration: Surviving the Type I Regime
In the standard model of gas giant planet formation, a large solid core(~10 times the Earth's mass) forms first, then accretes its massiveenvelope (100 or more Earth masses) of gas. However, inward planetmigration due to gravitational interaction with the protostellar gasdisk poses a difficulty in this model. Core-sized bodies undergo rapid``type I'' migration; for typical parameters their migration timescaleis much shorter than their accretion timescale. How, then, do growingcores avoid spiraling into the central star before they ever get thechance to become gas giants? Here, we present a simple model of coreformation in a gas disk that is viscously evolving. As the diskdissipates, accretion and migration timescales eventually becomecomparable. If this happens while there is still enough gas left in thedisk to supply a Jovian atmosphere, then a window of opportunity for gasgiant formation opens. We examine under what circumstances this happens,and thus, what predictions our model makes about the link betweenprotostellar disk properties and the likelihood of forming giantplanets.
| Dynamical Stability and Habitability of the γ Cephei Binary-Planetary System
It has been suggested that the long-lived residual radial velocityvariations observed in the precision radial velocity measurements of theprimary of γ Cephei (HR 8974, HD 222404, HIP 116727) are likelydue to a Jupiter-like planet orbiting this star. In this paper, thedynamics of this planet is studied, and the possibility of the existenceof a terrestrial planet around its central star is discussed.Simulations, which have been carried out for different values of theeccentricity and semimajor axis of the binary, as well as the orbitalinclination of its Jupiter-like planet, expand on previous studies ofthis system and indicate that, for the values of the binary eccentricitysmaller than 0.5, and for all values of the orbital inclination of theJupiter-like planet ranging from 0° to 40°, the orbit of thisplanet is stable. For larger values of the binary eccentricity, thesystem becomes gradually unstable. Integrations also indicate that,within this range of orbital parameters, a terrestrial planet, such asan Earth-like object, can have a long-term stable orbit only atdistances of 0.3-0.8 AU from the primary star. The habitable zone of theprimary, at a range of approximately 3.05-3.7 AU, is, however, unstable.
| The Search for Other Earths: Limits on the Giant Planet Orbits That Allow Habitable Terrestrial Planets to Form
Gas giant planets are far easier than terrestrial planets to detectaround other stars, and they are thought to form much more quickly thanterrestrial planets. Thus, in systems with giant planets, the latestages of terrestrial planet formation are strongly affected by thegiant planets' dynamical presence. Observations of giant planet orbitsmay therefore constrain the systems that can harbor potentiallyhabitable, Earth-like planets. We present results of 460 N-bodysimulations of terrestrial accretion from a disk of Moon- to Mars-sizedplanetary embryos. We systematically vary the orbital semimajor axis ofa Jupiter-mass giant planet between 1.6 and 6 AU, and eccentricitybetween 0 and 0.4. We find that for Sun-like stars, giant planets insideroughly 2.5 AU inhibit the growth of 0.3 Earth-mass planets in thehabitable zone. If planets accrete water from volatile-rich embryos past2-2.5 AU, then water-rich habitable planets can only form in systemswith giant planets beyond 3.5 AU. Giant planets with significant orbitaleccentricities inhibit both accretion and water delivery. The majorityof the current sample of extrasolar giant planets appears unlikely toform habitable planets.
| IRS Spectra of Solar-Type Stars: A Search for Asteroid Belt Analogs
We report the results of a spectroscopic search for debris diskssurrounding 41 nearby solar-type stars, including eight planet-bearingstars, using the Infrared Spectrometer (IRS) on the Spitzer SpaceTelescope. With the accurate relative photometry of the IRS between 7and 34 μm we are able to look for excesses as small as ~2% ofphotospheric levels, with particular sensitivity to weak spectralfeatures. For stars with no excess, the 3 σ upper limit in a bandat 30-34 μm corresponds to ~75 times the brightness of our zodiacaldust cloud. Comparable limits at 8.5-13 μm correspond to ~1400 timesthe brightness of our zodiacal dust cloud. These limits correspond tomaterial located within the <1 to ~5 AU region that, in our solarsystem, originates predominantly from debris associated with theasteroid belt. We find excess emission longward of ~25 μm from fivestars, of which four also show excess emission at 70 μm. Thisemitting dust must be located in a region starting around 5-10 AU. Onestar has 70 μm emission but no IRS excess. In this case, the emittingregion must begin outside 10 AU; this star has a known radial velocityplanet. Only two stars of the five show emission shortward of 25 μm,where spectral features reveal the presence of a population of small,hot dust grains emitting in the 7-20 μm band. One of these stars, HD72905, is quite young (300 Myr), while the other, HD 69830, is olderthan 2 Gyr. The data presented here strengthen the results of previousstudies to show that excesses at 25 μm and shorter are rare: only 1out of 40 stars older than 1 Gyr or ~2.5% shows an excess. Asteroidbelts 10-30 times more massive than our own appear are rare amongmature, solar-type stars.
| Extrasolar Planetary Systems Near a Secular Separatrix
Extrasolar planetary systems display a range of behavior that can beunderstood in terms of the secular theory of classical celestialmechanics, including the motions of the major axes. Four planet pairs inthe seventeen known extrasolar planetary systems with multiple planets(υ And, 47 UMa, 55 Cnc, and HD 128311), have trajectories inorbital element space that lie close to the separatrix between librationand circulation. Here we examine the dynamics of the first two, whichare not in mean motion resonance. The basics of secular theory arereviewed in order to develop insight into this behavior. The definitionof a secular resonance is discussed, correcting misconceptions in theliterature; it is not synonymous with libration and is not acommensurability of eigenfrequencies. The behavior of these twonear-separatrix systems is evaluated with updated orbital elements bycomparing both analytical and numerical results. We find that theapsidal motion from secular theory does not match the predictions fromN-body simulations and conclude that first-order secular theory shouldbe used with caution on extrasolar planetary systems. While theexistence of one near-separatrix system could be explained simply bychance initial conditions, the fact that there are several is improbableunless some physical process tends to set up systems near theseparatrix. Explanations based on an impulsive increase in theeccentricity of one planet are promising, but key issues remain open.
| Frequency of Debris Disks around Solar-Type Stars: First Results from a Spitzer MIPS Survey
We have searched for infrared excesses around a well-defined sample of69 FGK main-sequence field stars. These stars were selected withoutregard to their age, metallicity, or any previous detection of IRexcess; they have a median age of ~4 Gyr. We have detected 70 μmexcesses around seven stars at the 3 σ confidence level. Thisextra emission is produced by cool material (<100 K) located beyond10 AU, well outside the ``habitable zones'' of these systems andconsistent with the presence of Kuiper Belt analogs with ~100 times moreemitting surface area than in our own planetary system. Only one star,HD 69830, shows excess emission at 24 μm, corresponding to dust withtemperatures >~300 K located inside of 1 AU. While debris disks withLdust/L*>=10-3 are rare around oldFGK stars, we find that the disk frequency increases from 2%+/-2% forLdust/L*>=10-4 to 12%+/-5% forLdust/L*>=10-5. This trend in thedisk luminosity distribution is consistent with the estimated dust inour solar system being within an order of magnitude greater or less thanthe typical level around similar nearby stars. Although there is nocorrelation of IR excess with metallicity or spectral type, there is aweak correlation with stellar age, with stars younger than a gigayearmore likely to have excess emission.
| 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.
| No Detectable H+3 Emission from the Atmospheres of Hot Jupiters
H+3 emission is the dominant cooling mechanism inJupiter's thermosphere and a useful probe of temperature and iondensities. The H+3 ion is predicted to form in thethermospheres of close-in ``hot Jupiters,'' where its emission would bea significant factor in the thermal energy budget, affecting temperatureand the rate of hydrogen escape from the exosphere. Hot Jupiters arepredicted to have up to 105 times Jupiter'sH+3 emission because they experience extremestellar irradiation and enhanced interactions may occur between theplanetary magnetosphere and the stellar wind. Direct (but unresolved)detection of an extrasolar planet, or the establishment of useful upperlimits, may be possible because a small but significant fraction of thetotal energy received by the planet is reradiated in a few narrow linesof H+3 within which the flux from the star islimited. We present the observing strategy and results of our search foremission from the Q(1,0) transition of H+3 (3.953μm) from extrasolar planets orbiting six late-type dwarfs usingCSHELL, the high-resolution echelle spectrograph on NASA's InfraredTelescope Facility. We exploited the time-dependent Doppler shift of theplanet, which can be as large as 150 km s-1, by differencingspectra between nights, thereby removing the stellar photospheric signaland telluric lines. We set limits on the H+3emission from each of these systems and compare them with models in theliterature. Ideal candidates for future searches are intrinsically faintstars, such as M dwarfs, at very close distances.
| 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.
| Chemical Composition of the Planet-harboring Star TrES-1
We present a detailed chemical abundance analysis of the parent star ofthe transiting extrasolar planet TrES-1. Based on high-resolution KeckHIRES and Hobby-Eberly Telescope HRS spectra, we have determinedabundances relative to the Sun for 16 elements (Na, Mg, Al, Si, Ca, Sc,Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba). The resulting averageabundance of <[X/H]>=-0.02+/-0.06 is in good agreement withinitial estimates of solar metallicity based on iron. We compare theelemental abundances of TrES-1 with those of the sample of stars withplanets, searching for possible chemical abundance anomalies. TrES-1appears not to be chemically peculiar in any measurable way. Weinvestigate possible signs of selective accretion of refractory elementsin TrES-1 and other stars with planets and find no statisticallysignificant trends of metallicity [X/H] with condensation temperatureTc. We use published abundances and kinematic information forthe sample of planet-hosting stars (including TrES-1) and severalstatistical indicators to provide an updated classification in terms oftheir likelihood to belong to either the thin disk or the thick disk ofthe Milky Way. TrES-1 is found to be very likely a member of thethin-disk population. By comparing α-element abundances of planethosts and a large control sample of field stars, we also find thatmetal-rich ([Fe/H]>~0.0) stars with planets appear to besystematically underabundant in [α/Fe] by ~0.1 dex with respect tocomparison field stars. The reason for this signature is unclear, butsystematic differences in the analysis procedures adopted by differentgroups cannot be ruled out.
| A numerical study of the 2:1 planetary resonance
We numerically explore the long-term stability of planetary orbitslocked in a 2:1 mean motion resonance for a wide range of planetary massratios and orbital parameters. Our major tool is Laskar's frequency mapanalysis. Regions of low diffusion rate are outlined in a phase spacedefined by the two planetary eccentricities and the libration amplitudeof a critical resonance argument. Resonant systems that are dynamicallystable on a long timescale must lie within these regions. The resonancelocking between planets in high eccentric orbits may be destroyed bymutual close encounters. We discuss various dynamical protectionmechanisms related to the resonant configuration, among which is thewell-known apsidal corotation. In the case of moderate-to-loweccentricities, we find that apsidal circulators, little discussed tillnow, are very common among stable orbits. We also map the differenttypes of resonant behaviour predicted by analytical theories in thephase space.
| About putative Neptune-like extrasolar planetary candidates
Context: .We re-analyze the precision radial velocity (RV) data of HD208487 by the Anglo-Australian Planet Search Team, HD 190360, HD 188015,HD 114729 by the California and Carnegie Planet Search Team, and HD147513 by the Geneva Planet Search Team. All these stars are supposed tohost Jovian companions in long-period orbits. Aims.We test a hypothesisthat the residuals of the 1-planet model of the RV or an irregularscatter of the measurements around the synthetic RV curve may beexplained by the existence of additional planets in short-period orbits.Methods. We performed a global search for the best fits in the orbitalparameters space with genetic algorithms and simplex method. This makesit possible to verify and extend the results with an application ofcommonly used FFT-based periodogram analysis for identifying the leadingperiods. Results. Our analysis confirms the presence of a periodiccomponent in the RV of HD 190360 that may correspond to a hot-Neptuneplanet. We found four new cases in which the 2-planet model yieldssignificantly better fits to the RV data than the best 1-planetsolutions. If the periodic variability of the residuals of single-planetfits indeed has a planetary origin, then hot-Neptune planets may existin these extrasolar systems. We estimate their orbital periods as in therange of 7-20 d and minimal masses of about 20 masses of the Earth.
| 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.
| The HARPS search for southern extra-solar planets. V. A 14 Earth-masses planet orbiting HD 4308
We present here the discovery and characterisation of a very lightplanet around HD 4308. The planet orbits its star in 15.56 days. Thecircular radial-velocity variation presents a tiny semi-amplitude of 4.1m s-1 that corresponds to a planetary minimum mass m_2sin{i}= 14.1 Moplus (Earth masses). The planet was unveiled byhigh-precision radial-velocity measurements obtained with the HARPSspectrograph on the ESO 3.6-m telescope. The radial-velocity residualsaround the Keplerian solution are 1.3 m s-1, demonstratingthe very high quality of the HARPS measurements. Activity and bisectorindicators exclude any significant perturbations of stellar intrinsicorigin, which supports the planetary interpretation. Contrary to mostplanet-host stars, HD 4308 has a marked sub-solar metallicity ([Fe/H] =-0.31), raising the possibility that very light planet occurrence mightshow a different coupling with the parent star's metallicity than dogiant gaseous extra-solar planets. Together with Neptune-mass planetsclose to their parent stars, the new planet occupies a position in themass-separation parameter space that is constraining forplanet-formation and evolution theories. The question of whether theycan be considered as residuals of evaporated gaseous giant planets, icegiants, or super-earth planets is discussed in the context of the latestcore-accretion models.
| Can stellar wobble in triple systems mimic a planet?
The first extrasolar planets were detected by the measurement of thewobble of the parent star. This wobble leads to the periodic modulationof three observables: the radial velocity, the position on the sky andthe time of arrival of periodic signals. We show that the same wobble,and therefore the same modulation of the three observables, can be dueto the presence of a more distant binary stellar companion. Thus, the observation of the wobble does not, by itself, constitute a proof of aplanet detection. In particular, astrometric confirmation of a wobbledoes not necessarily provide a sufficient proof of the existence of aplanet candidate detected by radial velocity. Additional conditions,which we discuss here, must be fulfilled. We investigate the observedwobble for the planet candidates already detected and we find that, foreach case, a wobble due to a binary stellar companion can beexcluded.
However, for apparent Saturn-like planets in wideorbits, there may be an ambiguity in future detections, especially inspaceborne astrometric missions. We conclude that, in some cases, adefinitive proof of the presence of a planet requires furtherobservations such as direct imaging.
| 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.
| Planetary Harmony
Not Available
| The Hunt for Extrasolar Planets at McDonald Observatory
Currently every major telescope at McDonald Observatory is utilized inthe search for extrasolar planets. We review the different planet searchefforts and present the results of these programs. In particular wedescribe in detail the on-going precise Doppler surveys at the Harlan J.Smith 2.7 m telescope and at the Hobby-Eberly Telescope (HET). Thehighlight of the HET program was last year's discovery of a "HotNeptune" in the ρ planetary system. With a mass of only 17 Earthmasses this object demonstrates our ability to detect extrasolar planetswith masses below the gas giant range.
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