Contents
Images
Upload your image
DSS Images Other Images
Related articles
Reliability Checks on the Indo-US Stellar Spectral Library Using Artificial Neural Networks and Principal Component Analysis
The Indo-US coudé feed stellar spectral library (CFLIB) madeavailable to the astronomical community recently by Valdes et al. (2004,ApJS, 152, 251) contains spectra of 1273 stars in the spectral region3460 to 9464Å at a high resolution of 1Å (FWHM) and a widerange of spectral types. Cross-checking the reliability of this databaseis an important and desirable exercise since a number of stars in thisdatabase have no known spectral types and a considerable fraction ofstars has not so complete coverage in the full wavelength region of3460-9464Å resulting in gaps ranging from a few Å to severaltens of Å. We use an automated classification scheme based onArtificial Neural Networks (ANN) to classify all 1273 stars in thedatabase. In addition, principal component analysis (PCA) is carried outto reduce the dimensionality of the data set before the spectra areclassified by the ANN. Most importantly, we have successfullydemonstrated employment of a variation of the PCA technique to restorethe missing data in a sample of 300 stars out of the CFLIB.
| Local subgiants and time-scales of disc formation
Detailed evolutionary tracks and basic stellar parameters for the nearbysubgiants 104 Tau and HD 168443 are presented and discussed. Both serveas invaluable key stars for accurate age-datings, especially as theypossess the chemical signatures intermediate to the stars of the thick-and thin-disc population. We derive τ =9.7-0.6+0.8 Gyr for 104 Tau and τ =9.8-0.8+1.0 Gyr for HD 168443, very much in linewith their local sibling HR 7569 at τ = 9.1 +/- 1.0 Gyr that wasformerly presented in Bernkopf, Fiedler & Fuhrmann. Both, 104 Tauand HD 168443, thus add to our local sample of the rare but veryrelevant subgiants for the disc formation time-scales and support thenotion of a thick disc as an extremely old τ >= 12 Gyrsingle-burst population, and a thin disc that has a local age of τ ~8 Gyr.
| Finding benchmark brown dwarfs to probe the substellar initial mass function as a function of time
Using a simulated disc brown dwarf (BD) population, we find that newlarge area infrared surveys are expected to identify enough BDs coveringwide enough mass-age ranges to potentially measure the present day massfunction down to ~0.03Msolar, and the BD formation historyout to 10Gyr, at a level that will be capable of establishing if BDformation follows star formation. We suggest these capabilities are bestrealized by spectroscopic calibration of BD properties (Teff,g and [M/H]) which when combined with a measured luminosity and anevolutionary model can give BD mass and age relatively independent of BDatmosphere models. Such calibration requires an empirical understandingof how BD spectra are affected by variations in these properties, andthus the identification and study of `benchmark BDs' whose age andcomposition can be established independently.We identify the best sources of benchmark BDs as young open clustermembers, moving group members, and wide (>1000au) BD companions toboth subgiant stars and high-mass white dwarfs (WDs). To accuratelyasses the likely number of wide companion BDs available, we haveconstrained the wide L dwarf companion fraction using the 2-Micron AllSky Survey (2MASS), and find a companion fraction of2.7+0.7-0.5percent for separations of~1000-5000au. This equates to a BD companion fraction of34+9-6percent if one assumes an α~ 1companion mass function. Using this BD companion fraction, we simulatepopulations of wide BD binaries, and estimate that80+21-14 subgiant-BD binaries, and50+13-10 benchmark WD-BD binaries could beidentified using current and new facilities. The WD-BD binaries shouldall be identifiable using the Large Area Survey component of the UnitedKingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey, combinedwith the Sloan Digital Sky Survey. Discovery of the subgiant-BD binarieswill require a near-infrared imaging campaign around a large (~900)sample of Hipparcos subgiants. If identified, spectral studies of thesebenchmark BD populations could reveal the spectral sensitivities acrossthe Teff, g and [M/H] space probed by new surveys.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| Astrometric Methods and Instrumentation to Identify and Characterize Extrasolar Planets: A Review
I present a review of astrometric techniques and instrumentation used tosearch for, detect, and characterize extrasolar planets. First, Ibriefly summarize the properties of the current sample of extrasolarplanets, in connection with predictions from theoretical models ofplanet formation and evolution. Next, the generic approach to planetdetection with astrometry is described, with significant discussion of avariety of technical, statistical, and astrophysical issues to be facedby future ground-based and space-borne efforts in order to achieve therequired degree of measurement precision. After a brief summary of pastand present efforts to detect planets via milliarcsecond astrometry, Ithen discuss the planet-finding capabilities of future astrometricobservatories aiming at microarcsecond precision. Finally, I outline anumber of experiments that can be conducted by means of high-precisionastrometry during the next decade, to illustrate its potential forimportant contributions to planetary science, compared to other indirectand direct methods for the detection and characterization of planetarysystems.
| Photospheric CNO Abundances of Solar-Type Stars
We determined the C, N, and O abundances of 160 nearby F, G, and Kdwarfs and subgiants by using spectra obtained with the HIDESspectrograph at Okayama Astrophysical Observatory, with the purposes of(1) establishing the runs of [C/Fe], [N/Fe], and [O/Fe] for thesegalactic disk stars in the metallicity range of -1 ≲ [Fe/H] ≲+0.4, (2) searching for any difference in the CNO abundances ofplanet-host stars as compared to non-planet-host stars, and (3)examining the consistency of the abundances derived from different linesto check the validity of the analysis. The non-LTE effect on theabundance determination was taken into consideration based on ourextensive statistical-equilibrium calculations. We confirmed thatconsistent abundances are mostly accomplished between different lines,and that [C/Fe] as well as [O/Fe] progressively increase with a decreasein [Fe/H] with the slope of the former ( 0.2‑0.3) beingshallower than the latter ( 0.4‑0.5), while [N/Fe] does notshow any clear systematic trend with the metallicity. The [C/Fe],[N/Fe], and [O/Fe] values of 27 planet-harboring stars (included in oursample of 160 stars) were shown to be practically indistinguishable fromthose exhibited by non-planet-harboring stars of similar metallicities.
| Lithium Abundances of F-, G-, and K-Type Stars: Profile-Fitting Analysis of the Li I 6708 Doublet
An extensive profile-fitting analysis was performed for the Li(+Fe)6707-6708Å feature of nearby 160 F-K dwarfs/subgiants (including27 planet-host stars) in the Galactic disk ( 7000 K ≳Teff ≳ 5000 K, -1 ≲ [Fe/H] ≲ +0.4), in orderto establish the photospheric lithium abundances of these stars. Thenon-LTE effect (though quantitatively insignificant) was taken intoaccount based on our statistical equilibrium calculations, which werecarried out on an adequate grid of models. Our results confirmed most ofthe interesting observational characteristics revealed by recentlypublished studies, such as the bimodal distribution of the Li abundancesfor stars at Teff ≳ 6000 K, the satisfactory agreementof the upper envelope of the A(Li) vs. [Fe/H] distribution with thetheoretical models, the existence of a positive correlation betweenA(Li) and the stellar mass, and the tendency of lower lithium abundancesof planet-host stars (as compared to stars without planets) at thenarrow ``transition'' region of 5900 K ≳ Teff ≳5800 K. The solar Li abundance derived from this analysis is 0.92 (H =12.00), which is by 0.24dex lower than the widely referenced standardvalue of 1.16.
| Spectroscopic Study on the Atmospheric Parameters of Nearby F--K Dwarfs and Subgiants
Based on a collection of high-dispersion spectra obtained at OkayamaAstrophysical Observatory, the atmospheric parameters (Teff,log g, vt, and [Fe/H]) of 160 mid-F through early-K starswere extensively determined by the spectroscopic method using theequivalent widths of Fe I and Fe II lines along with the numericaltechnique of Takeda et al. (2002, PASJ, 54, 451). The results arecomprehensively discussed and compared with the parameter values derivedby different approaches (e.g., photometric colors, theoreticalevolutionary tracks, Hipparcos parallaxes, etc.) as well as with thepublished values found in various literature. It has been confirmed thatour purely spectroscopic approach yields fairly reliable and consistentresults.
| A link between the semimajor axis of extrasolar gas giant planets and stellar metallicity
The fact that most extrasolar planets found to date are orbitingmetal-rich stars lends credence to the core accretion mechanism of gasgiant planet formation over its competitor, the disc instabilitymechanism. However, the core accretion mechanism is not refined to thepoint of explaining orbital parameters such as the unexpected semimajoraxes and eccentricities. We propose a model that correlates themetallicity of the host star with the original semimajor axis of itsmost massive planet, prior to migration, assuming that the coreaccretion scenario governs giant gas planet formation. The modelpredicts that the optimum regions for planetary formation shift inwardsas stellar metallicity decreases, providing an explanation for theobserved absence of long-period planets in metal-poor stars. We compareour predictions with the available data on extrasolar planets for starswith masses similar to the mass of the Sun. A fitting procedure producesan estimate of what we define as the zero-age planetary orbit (ZAPO)curve as a function of the metallicity of the star. The model hints thatthe lack of planets circling metal-poor stars may be partly caused by anenhanced destruction probability during the migration process, becausethe planets lie initially closer to their central star.
| Magnetospheric radio emission from extrasolar giant planets: the role of the host stars
We present a new analysis of the expected magnetospheric radio emissionfrom extrasolar giant planets (EGPs) for a distance limited sample ofthe nearest known extrasolar planets. Using recent results on thecorrelation between stellar X-ray flux and mass-loss rates from nearbystars, we estimate the expected mass-loss rates of the host stars ofextrasolar planets that lie within 20 pc of the Earth. We find that someof the host stars have mass-loss rates that are more than 100 times thatof the Sun and, given the expected dependence of the planetarymagnetospheric radio flux on stellar wind properties, this has a verysubstantial effect. Using these results and extrapolations of the likelymagnetic properties of the extrasolar planets, we infer their likelyradio properties.We compile a list of the most promising radio targets and conclude thatthe planets orbiting Tau Bootes, Gliese 86, Upsilon Andromeda and HD1237(as well as HD179949) are the most promising candidates, with expectedflux levels that should be detectable in the near future with upcomingtelescope arrays. The expected emission peak from these candidate radioemitting planets is typically ~40-50 MHz. We also discuss a range ofobservational considerations for detecting EGPs.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| Five New Multicomponent Planetary Systems
We report Doppler measurements for six nearby G- and K-typemain-sequence stars that show multiple low-mass companions, at least oneof which has planetary mass. One system has three planets, the fourthtriple-planet system known around a normal star, and another has anextremely low minimum mass of 18 M⊕. HD 128311 (K0 V)has two planets (one previously known) with minimum masses (Msini) of2.18MJ and 3.21MJ and orbital periods of 1.26 and2.54 yr, suggesting a possible 2:1 resonance. For HD 108874 (G5 V), thevelocities reveal two planets (one previously known) having minimummasses and periods of (Msinib=1.36MJ,Pb=1.08 yr) and (Msinic=1.02MJ,Pc=4.4 yr). HD 50499 (G1 V) has a planet with P=6.8 yr andMsini=1.7MJ, and the velocity residuals exhibit a trend of-4.8 m s-1 yr-1, indicating a more distantcompanion with P>10 yr and minimum mass of 2MJ. HD 37124(G4 IV-V) has three planets, one having Msini=0.61MJ andP=154.5 days, as previously known. We find two plausible triple-planetmodels that fit the data, both having a second planet near P=840 days,with the more likely model having its third planet in a 6 yr orbit andthe other one in a 29 day orbit. For HD 190360, we confirm the planethaving P=7.9 yr and Msini=1.5MJ as found by the Geneva team,but we find a distinctly noncircular orbit with e=0.36+/-0.03, renderingthis not an analog of Jupiter as had been reported. Our velocities alsoreveal a second planet with P=17.1 days and Msini=18.1M⊕. HD 217107 (G8 IV) has a previously known ``hotJupiter'' with Msini=1.4MJ and P=7.13 days, and we confirmits high eccentricity, e=0.13. The velocity residuals reveal an outercompanion in an eccentric orbit, having minimum mass ofMsini>2MJ, eccentricity e~0.5, and a period P>8 yr,implying a semimajor axis a>4 AU and providing an opportunity fordirect detection. We have obtained high-precision photometry of five ofthe six planetary host stars with three of the automated telescopes atFairborn Observatory. We can rule out significant brightness variationsin phase with the radial velocities in most cases, thus supportingplanetary reflex motion as the cause of the velocity variations.Transits are ruled out to very shallow limits for HD 217107 and are alsoshown to be unlikely for the prospective inner planets of the HD 37124and HD 108874 systems. HD 128311 is photometrically variable with anamplitude of 0.03 mag and a period of 11.53 days, which is much shorterthan the orbital periods of its two planetary companions. This rotationperiod explains the origin of periodic velocity residuals to thetwo-planet model of this star. All of the planetary systems here wouldbe further constrained with astrometry by the Space InterferometryMission.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. Keck time has been granted by both NASA and theUniversity of California.
| UVBLUE: A New High-Resolution Theoretical Library of Ultraviolet Stellar Spectra
We present an extended ultraviolet-blue (850-4700 Å) library oftheoretical stellar spectral energy distributions computed at highresolution, λ/Δλ=50,000. The UVBLUE grid, as wenamed the library, is based on LTE calculations carried out with ATLAS9and SYNTHE codes developed by R. L. Kurucz and consists of nearly 1800entries that cover a large volume of the parameter space. It spans arange in Teff from 3000 to 50,000 K, the surface gravityranges from logg=0.0 to 5.0 with Δlogg=0.5 dex, while sevenchemical compositions are considered:[M/H]=-2.0,-1.5,-1.0,-0.5,+0.0,+0.3, and +0.5 dex. For its coverageacross the Hertzsprung-Russell diagram, this library is the mostcomprehensive one ever computed at high resolution in theshort-wavelength spectral range, and useful application can be foreseenfor both the study of single stars and in population synthesis models ofgalaxies and other stellar systems. We briefly discuss some relevantissues for a safe application of the theoretical output to ultravioletobservations, and a comparison of our LTE models with the non-LTE (NLTE)ones from the TLUSTY code is also carried out. NLTE spectra are found,on average, to be slightly ``redder'' compared to the LTE ones for thesame value of Teff, while a larger difference could bedetected for weak lines, which are nearly wiped out by the enhanced coreemission component in case of NLTE atmospheres. These effects seem to bemagnified at low metallicity (typically [M/H]<~-1). A match with aworking sample of 111 stars from the IUE atlas, with availableatmosphere parameters from the literature, shows that UVBLUE modelsprovide an accurate description of the main mid- and low-resolutionspectral features for stars along the whole sequence from the B to ~G5type. The comparison sensibly degrades for later spectral types, withsupergiant stars that are in general more poorly reproduced than dwarfs.As a possible explanation of this overall trend, we partly invoke theuncertainty in the input atmosphere parameters to compute thetheoretical spectra. In addition, one should also consider the importantcontamination of the IUE stellar sample, where the presence of binaryand variable stars certainly works in the sense of artificiallyworsening the match between theory and observations.
| A Map of the Universe
We have produced a new conformal map of the universe illustrating recentdiscoveries, ranging from Kuiper Belt objects in the solar system to thegalaxies and quasars from the Sloan Digital Sky Survey. This mapprojection, based on the logarithm map of the complex plane, preservesshapes locally and yet is able to display the entire range ofastronomical scales from the Earth's neighborhood to the cosmicmicrowave background. The conformal nature of the projection, preservingshapes locally, may be of particular use for analyzing large-scalestructure. Prominent in the map is a Sloan Great Wall of galaxies 1.37billion light-years long, 80% longer than the Great Wall discovered byGeller and Huchra and therefore the largest observed structure in theuniverse.
| Planets and Infrared Excesses: Preliminary Results from a Spitzer MIPS Survey of Solar-Type Stars
As part of a large Spitzer MIPS Guaranteed Time Observation program, wehave searched for infrared excesses due to debris disks toward 26 FGKfield stars known from radial velocity (RV) studies to have one or moreplanets. While none of these stars show excesses at 24 μm, we havedetected 70 μm excesses around six stars at the 3 σ confidencelevel. The excesses are produced by cool material (<100 K) locatedbeyond 10 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. Theseplanet-bearing stars are, by selection for RV studies, typically olderthan 1 Gyr, and the stars identified here with excesses have a medianage of 4 Gyr. We find a preliminary correlation of both the frequencyand the magnitude of dust emission with the presence of known planets.These are the first stars outside the solar system identified as havingboth well-confirmed planetary systems and well-confirmed IR excesses.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| Prospects for Habitable ``Earths'' in Known Exoplanetary Systems
We have examined whether putative Earth-mass planets could remainconfined to the habitable zones (HZs) of the 111 exoplanetary systemsconfirmed by 2004 August. We find that in about half of these systemsthere could be confinement for at least the past 1000 Myr, though insome cases only in variously restricted regions of the HZ. The HZmigrates outward during the main-sequence lifetime, and we find that inabout two-thirds of the systems an Earth-mass planet could be confinedto the HZ for at least 1000 Myr sometime during the main-sequencelifetime. Clearly, these systems should be high on the target list forexploration for terrestrial planets. We have reached our conclusions bydetailed investigations of seven systems, which has resulted in anestimate of the distance from the giant planet within which orbitalstability is unlikely for an Earth-mass planet. This distance is givenby nRH, where RH is the Hill radius of the giantplanet and n is a multiplier that depends on the giant's orbitaleccentricity and on whether the Earth-mass planet is interior orexterior to the giant planet. We have estimated n for each of the sevensystems by launching Earth-mass planets in various orbits and followingtheir fate with a hybrid orbital integrator. We have then evaluated thehabitability of the other exoplanetary systems using nRHderived from the giant's orbital eccentricity without carrying outtime-consuming orbital integrations. A stellar evolution model has beenused to obtain the HZs throughout the main-sequence lifetime.
| Five New Extrasolar Planets
We report multiple Doppler measurements of five nearby FGK main-sequencestars and subgiants obtained during the past 4-6 yr at the KeckObservatory. These stars, namely, HD 183263, HD 117207, HD 188015, HD45350, and HD 99492, all exhibit coherent variations in their Dopplershifts consistent with a planet in Keplerian motion. The five newplanets occupy known realms of planetary parameter space, including awide range of orbital eccentricities, e=0-0.78, and semimajor axes,0.1-3.8 AU, that provide further statistical information about the truedistributions of various properties of planetary systems. One of theplanets, HD 99492b, has a low minimum mass of0.112MJup=36MEarth. Four of the five planets orbitbeyond 1 AU. We describe two quantitative tests of the false alarmprobability for Keplerian interpretations of measured velocities. Themore robust of these involves Monte Carlo realizations of scrambledvelocities as a proxy for noise. Keplerian orbital fits to that``noise'' yield the distribution of χ2ν tocompare with χ2ν from the original(unscrambled) velocities. We establish a 1% false alarm probability asthe criterion for candidate planets. All five of these planet-bearingstars are metal-rich, with [Fe/H]>+0.27, reinforcing the strongcorrelation between planet occurrence and metallicity. From the fullsample of 1330 stars monitored at Keck, Lick, and the Anglo-AustralianTelescope, the shortest orbital period for any planet is 2.64 days,showing that shorter periods occur less frequently than 0.1% in thesolar neighborhood. Photometric observations were acquired for four ofthe five host stars with an automatic telescope at Fairborn Observatory.The lack of brightness variations in phase with the radial velocitiessupports planetary-reflex motion as the cause of the velocityvariations. No transits were observed, but their occurrence is not ruledout by our observations.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. Keck time has been granted by both NASA and theUniversity of California.
| Spectral Types for Four OGLE-III Transit Candidates: Could These Be Planets?
We present spectral types for OGLE (Optical Gravitational LensingExperiment) transiting planet candidates OGLE-TR-134 through 137 basedon low-resolution spectra taken at Kitt Peak. Our main objective is toaid those planning radial velocity monitoring of transit candidates. Weobtain spectral types with an accuracy of 2 spectral subtypes, alongwith tentative luminosity classifications. Combining the spectral typeswith light-curve fits to the OGLE transit photometry, and with TwoMicron All Sky Survey counterparts in two cases, we conclude thatOGLE-TR-135 and 137 are not planetary transits, while OGLE-TR-134 and136 are good candidates and should be observed with precision radialvelocity monitoring to determine whether the companions are of planetarymass. OGLE-TR-135 is ruled out chiefly because a discrepancy between thestellar parameters obtained from the transit fit and those inferred fromthe spectra indicates that the system is a blend. OGLE-TR-137 is ruledout because the depth of the transit combined with the spectral type ofthe star indicates that the transiting object is stellar. OGLE-TR-134and 136, if unblended main-sequence stars, are each orbited by atransiting object with radius below 1.4 RJ. The caveats arethat our luminosity classification suggests that OGLE-TR-134 could be agiant (and therefore a blend), while OGLE-TR-136 shows a (much smaller)discrepancy of the same form as OGLE-TR-135, which may indicate that thesystem is a blend. However, since our luminosity classifications areuncertain at best, and the OGLE-TR-136 discrepancy can be explained ifthe primary is a slightly anomalous main-sequence star, the stars remaingood candidates.
| On the ages of exoplanet host stars
We obtained spectra, covering the CaII H and K region, for 49 exoplanethost (EH) stars, observable from the southern hemisphere. We measuredthe chromospheric activity index, R'{_HK}. We compiled previouslypublished values of this index for the observed objects as well as theremaining EH stars in an effort to better smooth temporal variations andderive a more representative value of the average chromospheric activityfor each object. We used the average index to obtain ages for the groupof EH stars. In addition we applied other methods, such as: Isochrone,lithium abundance, metallicity and transverse velocity dispersions, tocompare with the chromospheric results. The kinematic method is a lessreliable age estimator because EH stars lie red-ward of Parenago'sdiscontinuity in the transverse velocity dispersion vs dereddened B-Vdiagram. The chromospheric and isochrone techniques give median ages of5.2 and 7.4 Gyr, respectively, with a dispersion of 4 Gyr. The medianage of F and G EH stars derived by the isochrone technique is 1-2 Gyrolder than that of identical spectral type nearby stars not known to beassociated with planets. However, the dispersion in both cases is large,about 2-4 Gyr. We searched for correlations between the chromosphericand isochrone ages and L_IR/L* (the excess over the stellarluminosity) and the metallicity of the EH stars. No clear tendency isfound in the first case, whereas the metallicy dispersion seems toslightly increase with age.
| Sulphur abundance in Galactic stars
We investigate sulphur abundance in 74 Galactic stars by using highresolution spectra obtained at ESO VLT and NTT telescopes. For the firsttime the abundances are derived, where possible, from three opticalmultiplets: Mult. 1, 6, and 8. By combining our own measurements withdata in the literature we assemble a sample of 253 stars in themetallicity range -3.2 [Fe/H] +0.5. Two important features,which could hardly be detected in smaller samples, are obvious from thislarge sample: 1) a sizeable scatter in [S/Fe] ratios around [Fe/H]-1; 2) at low metallicities we observe stars with [S/Fe] 0.4, aswell as stars with higher [S/Fe] ratios. The latter do not seem to bekinematically different from the former ones. Whether the latter findingstems from a distinct population of metal-poor stars or simply from anincreased scatter in sulphur abundances remains an open question.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Jungfrau |
| Right ascension: | 13h28m25.80s |
| Declination: | +13°46'44.0" |
| Apparent magnitude: | 4.98 |
| Distance: | 18.109 parsecs |
| Proper motion RA: | -234 |
| Proper motion Dec: | -575.7 |
| B-T magnitude: | 5.843 |
| V-T magnitude: | 5.045 |
Catalogs and designations:
|
