הוסף תמונה שלך
DSS Images Other Images
הכנס מאמר חדש
|Detecting a rotation in the ɛ Eridani debris disc|
The evidence for a rotation of the ɛ Eridani debris disc isexamined. Data at 850-μm wavelength were previously obtained usingthe Submillimetre Common User Bolometer Array (SCUBA) over periods of1997-1998 and 2000-2002. By χ2 fitting after shift androtation operations, images from these two epochs were compared torecover proper motion and orbital motion of the disc. The sameprocedures were then performed on simulated images to estimate theaccuracy of the results.Minima in the χ2 plots indicate a motion of the disc ofapproximately 0.6 arcsec per year in the direction of the star's propermotion. This underestimates the true value of 1 arcsec per year,implying that some of the structure in the disc region is not associatedwith ɛ Eridani, originating instead from background galaxies.From the χ2 fitting for orbital motion, acounterclockwise rotation rate of per year is deduced. Comparisons withsimulated data in which the disc is not rotating show that noise andbackground galaxies result in approximately Gaussian fluctuations with astandard deviation of per year. Thus, counterclockwise rotation of discfeatures is supported at approximately a 2σ level, after a 4-yrtime difference. This rate is faster than the Keplerian rate of per yearfor features at ~65 au from the star, suggesting their motion istracking a planet inside the dust ring.Future observations with SCUBA-2 can rule out no rotation of theɛ Eridani dust clumps with ~4σ confidence. Assuming a rateof about per year, the rotation of the features after a 10-yr periodcould be shown to be >=1° per year at the 3σ level.
|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.
|Near-infrared imaging polarimetry of dusty young stars|
We have carried out JHK polarimetric observations of 11 dusty youngstars, by using the polarimeter module IRPOL2 with the near-infraredcamera UIST on the 3.8-m United Kingdom Infrared Telescope (UKIRT). Oursample targeted systems for which UKIRT-resolvable discs had beenpredicted by model fits to their spectral energy distributions. Ourobservations have confirmed the presence of extended polarized emissionaround TW Hya and around HD 169142. HD 150193 and HD 142666 show thelargest polarization values among our sample, but no extended structurewas resolved. By combining our observations with Hubble Space Telescope(HST) coronographic data from the literature, we derive the J- andH-band intrinsic polarization radial dependences of the disc of TW Hya.We find the polarizing efficiency of the disc is higher at H than at J,and we confirm that the J- and H-band percentage polarizations arereasonably constant with radius in the region between 0.9 and 1.3arcsecfrom the star. We find that the objects for which we have detectedextended polarizations are those for which previous modelling hassuggested the presence of flared discs, which are predicted to bebrighter than flat discs and thus would be easier to detectpolarimetrically.
|Spectral synthesis analysis and radial velocity study of the northern F-, G- and K-type flare stars|
In this paper, we present a study of the general physical and chemicalproperties and radial velocity monitoring of young active stars. Wederive temperatures, logg, [Fe/H], v sini and Rspec valuesfor eight stars. The detailed analysis reveals that the stars are nothomogeneous in their principal physical parameters or in the agedistribution. In 4/5, we found a periodic radial velocity signal whichoriginates in surface features; the fifth is surprisingly inactive andshows little variation.
|Asteroseismology and interferometry .|
Asteroseismology aims at constraining the stellar evolution theory, andallows to determine the age of stars together with other fundamentalparameters. We present recent results obtained by interferometry, andprospects for the future.
|A Comparative Study of Flaring Loops in Active Stars|
Dynamo activity in stars of different types is expected to generatemagnetic fields with different characteristics. As a result, adifferential study of the characteristics of magnetic loops in a broadsample of stars may yield information about dynamo systematics. In theabsence of direct imaging, certain physical parameters of a stellarmagnetic loop can be extracted if a flare occurs in that loop. In thispaper we employ a simple nonhydrodynamic approach introduced by Haisch,to analyze a homogeneous sample of all of the flares we could identifyin the EUVE DS database: a total of 134 flares that occurred on 44 starsranging in spectral type from F to M and in luminosity class from V toIII. All of the flare light curves that have been used in the presentstudy were obtained by a single instrument (EUVE DS). For each flare, wehave applied Haisch's simplified approach (HSA) in order to determineloop length, temperature, electron density, and magnetic field. For eachof our target stars, a literature survey has been performed to determinequantitatively the extent to which our results are consistent withindependent studies. The results obtained by HSA are found to be wellsupported by results obtained by other methods. Our survey suggeststhat, on the main sequence, short loops (with lengths<=0.5R*) may be found in stars of all classes, while thelargest loops (with lengths up to 2R*) appear to be confinedto M dwarfs. Based on EUVE data, the transition from small to largeloops on the main sequence appears to occur between spectral types K2and M0. We discuss the implications of this result for dynamo theories.
|A Spitzer IRAC Search for Substellar Companions of the Debris Disk Star ɛ Eridani|
We have used the Infrared Array Camera (IRAC) on board the Spitzer SpaceTelescope to search for low-mass companions of the nearby debris diskstar ɛ Eri. The star was observed in two epochs 39 days apart,with different focal plane rotation to allow the subtraction of theinstrumental point-spread function, achieving a maximum sensitivity of0.01 MJy sr-1 at 3.6 and 4.5 μm, and 0.05 MJysr-1 at 5.8 and 8.0 μm. This sensitivity is not sufficientto directly detect scattered or thermal radiation from the ɛ Eridebris disk. It is, however, sufficient to allow the detection of Jovianplanets with mass as low as 1MJ in the IRAC 4.5 μm band.In this band, we detected over 460 sources within the 5.70 arcmin fieldof view of our images. To test if any of these sources could be alow-mass companion to ɛ Eri, we have compared their colors andmagnitudes with models and photometry of low-mass objects. Of thesources detected in at least two IRAC bands, none fall into the range ofmid-IR color and luminosity expected for cool, 1 Gyr substellar andplanetary mass companions of ɛ Eri, as determined by both modelsand observations of field M, L, and T dwarfs. We identify three newsources that have detections at 4.5 μm only, the lower limit placedon their [3.6]-[4.5] color consistent with models of planetary massobjects. Their nature cannot be established with the currently availabledata, and a new observation at a later epoch will be needed to measuretheir proper motion in order to determine if they are physicallyassociated to ɛ Eri.
|An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium|
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
|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.
|Nearby Debris Disk Systems with High Fractional Luminosity Reconsidered|
By searching the IRAS and ISO databases, we compiled a list of 60 debrisdisks that exhibit the highest fractional luminosity values(fd>10-4) in the vicinity of the Sun (d<120pc). Eleven out of these 60 systems are new discoveries. Special carewas taken to exclude bogus disks from the sample. We computed thefractional luminosity values using available IRAS, ISO, and Spitzer dataand analyzed the Galactic space velocities of the objects. The resultsrevealed that stars with disks of high fractional luminosity oftenbelong to young stellar kinematic groups, providing an opportunity toobtain improved age estimates for these systems. We found thatpractically all disks with fd>5×10-4 areyounger than 100 Myr. The distribution of the disks in the fractionalluminosity versus age diagram indicates that (1) the number of oldsystems with high fd is lower than was claimed before, (2)there exist many relatively young disks of moderate fractionalluminosity, and (3) comparing the observations with a currenttheoretical model of debris disk evolution, a general good agreementcould be found.
|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.
|Coronal Emission Measures and Abundances for Moderately Active K Dwarfs Observed by Chandra|
We have used Chandra to resolve the nearby 70 Oph (K0 V+K5 V) and 36 Oph(K1 V+K1 V) binary systems for the first time in X-rays. The LETG/HRC-Sspectra of all four of these stars are presented and compared with anarchival LETG spectrum of another moderately active K dwarf, ɛEri. Coronal densities are estimated from O VII line ratios and emissionmeasure distributions are computed for all five of these stars. We seeno substantial differences in coronal density or temperature among thesestars, which is not surprising considering that they are all early Kdwarfs with similar activity levels. However, we do see significantdifferences in coronal abundance patterns. Coronal abundance anomaliesare generally associated with the first ionization potential (FIP) ofthe elements. On the Sun, low-FIP elements are enhanced in the coronarelative to high-FIP elements, the so-called FIP effect. Differentlevels of FIP effect are seen for our stellar sample, ranging from 70Oph A, which shows a prominent solar-like FIP effect, to 70 Oph B, whichhas no FIP bias at all or possibly even a weak inverse FIP effect. Thestrong abundance difference exhibited by the two 70 Oph stars isunexpected considering how similar these stars are in all other respects(spectral type, age, rotation period, X-ray flux). It will be difficultfor any theoretical explanation for the FIP effect to explain how twostars so similar in all other respects can have coronae with differentdegrees of FIP bias. Finally, for the stars in our sample exhibiting aFIP effect, a curious difference from the solar version of thephenomenon is that the data seem to be more consistent with the high-FIPelements being depleted in the corona rather than with a low-FIPenhancement.
|On the Temperature-Emission Measure Distribution in Stellar Coronae|
Strong peaks in the emission measure-temperature (EM-T ) distributionsin the coronae of some binary stars are associated with the presence ofhot (107 K), dense (up to 1013 cm -3)plasma. These peaks are very reminiscent of those predicted to arise inan impulsively heated solar corona. A coronal model comprised of manyimpulsively heated strands is adapted to stellar parameters. It is shownthat the properties of the EM-T distribution can be accounted for ingeneral terms provided the emission comes from many very small loops(length under 103 km) with intense magnetic fields (1 kG)distributed across part of the surface of the star. The heating requiresevents that generally dissipate between 1026 and 1028 ergs, which is in the range of solar microflares. This impliesthat such stars must be capable of generating regions of localizedintense magnetic fields.
|Variations in D/H and D/O from New Far Ultraviolet Spectroscopic Explorer Observations|
We use data obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) to determine the interstellar abundances of D I, N I, O I, Fe II,and H2 along the sight lines to WD 1034+001, BD +39 3226, andTD1 32709. Our main focus is on determining the D/H, N/H, O/H, and D/Oratios along these sight lines, with logN(H)>20.0, that probe gaswell outside of the Local Bubble. Hubble Space Telescope (HST) andInternational Ultraviolet Explorer (IUE) archival data are used todetermine the H I column densities along the WD 1034+001 and TD1 32709sight lines, respectively. For BD +39 3226, a previously published N(HI) is used. We find(D/H)×105=2.14+0.53-0.45,1.17+0.31-0.25, and1.86+0.53-0.43 and(D/O)×102=6.31+1.79-1.38,5.62+1.61-1.31, and7.59+2.17-1.76 for the WD 1034+001, BD +39 3226,and TD1 32709 sight lines, respectively (all 1 σ). The scatter inthese three D/H ratios exemplifies the scatter that has been found byother authors for sight lines with column densities in the range19.2
|Dust in Resonant Extrasolar Kuiper Belts: Grain Size and Wavelength Dependence of Disk Structure|
This paper considers the distribution of dust that originates in thebreakup of planetesimals that are trapped in resonance with a planet. Itis shown that there are three distinct grain populations with differentspatial distributions: (I) large grains have the same clumpy resonantdistribution as the planetesimals; (II) moderate-sized grains are nolonger in resonance and have an axisymmetric distribution; and (III)small grains are blown out of the system by radiation pressure and sohave a density distribution that falls off as τ~1/r. Population IIIcan be further divided into two subclasses: (IIIa) grains produced frompopulation I that exhibit trailing spiral structure that emanates fromthe resonant clumps and (IIIb) grains produced from population II thathave an axisymmetric distribution. Since observations in differentwavebands are sensitive to different dust sizes, multiwavelength imagingof debris disks can be used to test models that explain thesubmillimeter structure of debris disks as due to resonant trapping ofplanetesimals. For example, a collisional cascade without blowout grainswould appear clumpy in the submillimeter (which samples population I)and smooth at mid- to far-IR wavelengths (which sample population II).The wavelength of transition from clumpy to smooth structure isindicative of the mass of the perturbing planet. The size distributionof Vega's disk is modeled showing that the large quantities ofpopulation III grains detected recently by Spitzer must originate in thedestruction of the grains seen in the submillimeter images. Thus, athigh resolution and sensitivity the far- and mid-IR structure of Vega'sdisk is predicted to include spiral structure emanating from thesubmillimeter clumps.
|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.
|Coronal Density Diagnostics with Si X: Chandra LETGS Observations of Procyon, α Centauri A and B, Capella, and ɛ Eridani|
Electron density diagnostics based on the line intensity ratio of Si Xare applied to the X-ray spectra of Procyon, α Cen A and B,Capella, and ɛ Eri measured with the Low Energy TransmissionGrating Spectrometer combined with the High Resolution Camera on boardthe Chandra X-Ray Observatory. The ratio R1 of theintensities of the Si X lines at 50.524 and 50.691 Å is adopted. Acertain temperature effect in R1 appears near the low-densitylimit region, which is due to the contamination of the Si X line at50.703 Å. Using the emission measure distribution model derived byAudard and coworkers for Capella and emissivities calculated with theAstrophysical Plasma Emission Code model by Smith and coworkers, wesuccessfully estimate the contributions of the Fe XVI lines at 50.367and 50.576 Å (73% and 62%, respectively). A comparison between theobserved ratios and theoretical predictions constrains the (logarithmic)electron densities for Procyon to be8.61+0.24-0.20 cm-3, while for αCen A and B, Capella, and ɛ Eri they are8.81+0.27-0.23,8.60+0.39-0.32, 9.30-0.48, and9.11+1.40-0.38 cm-3, respectively. Thecomparison of our results with those constrained by the triplet ofHe-like carbon shows good agreement. For normal stars, our resultsdisplay a narrow uncertainty, while for active stars, a relativelylarger uncertainty due to contamination from Fe XVI lines is found.Another possible reason may be the uncertainty of the continuum level,since the emission lines of Si X become weak for active stars. Forɛ Eri, an electron density in the C V-forming region was firstestimated through Si X emission.
|Detection Limits from the McDonald Observatory Planet Search Program|
Based on the long-term radial velocity surveys carried out with theMcDonald Observatory 2.7 m Harlan J. Smith Telescope from 1988 to thepresent, we derive upper limits to long-period giant planet companionsfor 31 nearby stars. Data from three phases of the McDonald Observatory2.7 m planet-search program have been merged together, and for 17objects data from the pioneering Canada-France-Hawaii Telescope radialvelocity program have also been included in the companion-limitsdetermination. For those 17 objects, the baseline of observations is inexcess of 23 yr, enabling the detection or exclusion of giant planets inorbits beyond 8 AU. We also consider the possibility of eccentric orbitsin our computations. At an orbital separation of 5.2 AU, we can excludeon average planets of Msini>~(2.0+/-1.1)MJ (e=0) andMsini>~(4.0+/-2.8)MJ (e=0.6) for 25 of the 31 stars inthis survey. However, we are not yet able to rule out ``true Jupiters,''i.e., planets of Msini~1MJ in 5.2 AU orbits. These limits areof interest for the Space Interferometry Mission, Terrestrial PlanetFinder, and Darwin missions, which will search for terrestrial planetsorbiting nearby stars, many of which are included in this work.
|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.
|A Hybrid N-Body-Coagulation Code for Planet Formation|
We describe a hybrid algorithm to calculate the formation of planetsfrom an initial ensemble of planetesimals. The algorithm uses acoagulation code to treat the growth of planetesimals into oligarchs andexplicit N-body calculations to follow the evolution of oligarchs intoplanets. To validate the N-body portion of the algorithm, we use abattery of tests in planetary dynamics. Several complete calculations ofterrestrial planet formation with the hybrid code yield good agreementwith previously published calculations. These results demonstrate thatthe hybrid code provides an accurate treatment of the evolution ofplanetesimals into planets.
|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.
|Optical polarimetry of infrared excess stars|
We present UBRVI polarimetry measurements for a group of 38 IRASinfrared excess stars and complement these observations with V-band datataken from the literature for 87 additional objects. After correctingthe observed values by the interstellar contribution, we find that 48%of the analyzed sample has polarization excess. In addition, thepolarization of these stars may correlate with infrared color excesses,particularly at 60 and 100 μm. We caution, however, that poor IRASdata quality at longer wavelengths affects this correlation. We analyzethe wavelength dependence of the linear polarization of 15 polarizedobjects in relation to Serkowski's empirical interstellar law. We findthat for 6 to 7 objects (depending on the interstellar model) themeasured polarization differs significantly from the empiricalinterstellar law, suggesting an intrinsic origin. We analyze thepolarimetry distribution of IRAS infrared excess objects in relation tothe Exoplanet host stars (i.e., stars associated with at least onelikely planetary mass object). The corresponding polarimetrydistributions are different within a high confidence level. Finally, wecompare the metallicity distributions of F and G IRAS infrared excess,Exoplanet host and field main sequence stars, and find that F-G IRASinfrared excess objects have metallicities quite similar (although notidentical) to field main sequence stars and significantly different fromthe Exoplanet host group.
|Multi-aperture photometry of extended IR sources with ISOPHOT. I. The nature of extended IR emission of planetary Nebulae|
Context: .ISOPHOT multi-aperture photometry is an efficient method toresolve compact sources or to detect extended emission down torelatively faint levels with single detectors in the wavelength range 3to 100 μm. Aims: .Using ISOPHOT multi-aperture photometry andcomplementary ISO spectra and IR spectral energy distributions wediscuss the nature of the extended IR emission of the two PNe NGC 6543and NGC 7008. Methods: .In the on-line appendix we describe thedata reduction, calibration and interpretation methods based on asimultaneous determination of the IR source and background contributionsfrom the on-source multi-aperture sequences. Normalized profiles enabledirect comparison with point source and flat-sky references. Modellingthe intensity distribution offers a quantitative method to assess sourceextent and angular scales of the main structures and is helpful inreconstructing the total source flux, if the source extends beyond aradius of 1 arcmin. The photometric calibration is described and typicalaccuracies are derived. General uncertainty, quality and reliabilityissues are addressed, too. Transient fitting to non-stabilised signaltime series, by means of combinations of exponential functions withdifferent time constants, improves the actual average signals andreduces their uncertainty. Results: .The emission of NGC 6543 inthe 3.6 μm band coincides with the core region of the optical nebulaand is homogeneously distributed. It is comprised of 65% continuum and35% atomic hydrogen line emission. In the 12 μm band a resolved butcompact double source is surrounded by a fainter ring structure with allemission confined to the optical core region. Strong line emission of[ArIII] at 8.99 μm and in particular [SIV] at 10.51 μm shapes thisspatial profile. The unresolved 60 μm emission originates from dust.It is described by a modified (emissivity index β = 1.5) blackbodywith a temperature of 85 K, suggesting that warm dust with a mass of 6.4× 10-4 Mȯ is mixed with the ionisedgas. The gas-to-dust mass ratio is about 220. The 25 μm emission ofNGC 7008 is characterised by a FWHM of about 50´´ with anadditional spot-like or ring-like enhancement at the bright rim of theoptical nebula. The 60 μm emission exhibits a similar shape, but isabout twice as extended. Analysis of the spectral energy distributionsuggests that the 25 μm emission is associated with 120 K warm dust,while the 60 μm emission is dominated by a second dust component with55 K. The dust mass associated with this latter component amounts to 1.2× 10-3 Mȯ, significantly higher thanpreviously derived. The gas-to-dust mass ratio is 59 which, compared tothe average value of 160 for the Milky Way, hints at dust enrichment bythis object.
|The origins of the substellar companion to GQ Lupi|
The recently discovered substellar companion to GQ Lup possiblyrepresents a direct test of current planet formation theories. Weexamine the possible formation scenarios for the companion to GQ Lupassuming it is a ~2 M_Jup object. We determine that GQ Lup B most likelywas scattered into a large, eccentric orbit by an interaction withanother planet in the inner system. If this is the case, severaldirectly observable predictions can be made, including the presence of amore massive, secondary companion that could be detected throughastrometry, radial velocity measurements, or sculpting in GQ Lup'scircumstellar disk. This scenario requires a highly eccentric orbit forthe companion already detected. These predictions can be tested withinthe next decade or so. Additionally, we look at scenarios of formationif the companion is a brown dwarf. One possible formation scenario mayinvolve an interaction between a brown dwarf binary and GQ Lup. We lookfor evidence of any brown dwarfs that have been ejected from the GQ Lupsystem by searching the 2MASS all-sky survey.
|Simulating observable comets. III. Real stellar perturbers of the Oort cloud and their output|
Context: .This is the third of a series of papers on simulating themechanisms acting currently on the Oort cloud and producing the observedlong-period comets.Aims.In this paper we investigate the influence ofcurrent stellar perturbers on the Oort cloud of comets under thesimultaneous galactic disk tide. We also analyse the past motion of theobserved long-period comets under the same dynamical model to verify thewidely used definition of dynamically new comets. Methods.The action ofnearby stars and the galactic disk tide on the Oort cloud was simulated.The original orbital elements of all 386 long-period comets of qualityclasses 1 and 2 were calculated, and their motion was followednumerically for one orbital revolution into the past, down to theprevious perihelion. We also simulated the output of the close futurepass of GJ 710 through the Oort cloud. Results.The simulated flux of theobservable comets resulting from the current stellar and galacticperturbations, as well as the distribution of perihelion direction, wasobtained. The same data are presented for the future passage of GJ 710.A detailed description is given of the past evolution of aphelion andperihelion distances of the observed long-period comets. Conclusions. Weobtained no fingerprints of the stellar perturbations in the simulatedflux and its directional structure. The mechanisms producing observablecomets are highly dominated by galactic disk tide because all currentstellar perturbers are too weak. Also the effect of the close passage ofthe star GJ 710 is very difficult to recognise on the background of theGalactic-driven observable comets. For the observed comets we found only45 to be really dynamically "new" according to our definition based onthe previous perihelion distance value.
|Abundance ratios of volatile vs. refractory elements in planet-harbouring stars: hints of pollution?|
We present the [ X/H] trends as a function of the elemental condensationtemperature TC in 88 planet host stars and in avolume-limited comparison sample of 33 dwarfs without detected planetarycompanions. We gathered homogeneous abundance results for many volatileand refractory elements spanning a wide range of T_C, from a few dozento several hundred kelvin. We investigate possible anomalous trends ofplanet hosts with respect to comparison sample stars to detect evidenceof possible pollution events. No significant differences are found inthe behaviour of stars with and without planets. This is consistent witha "primordial" origin of the metal excess in planet host stars. However,a subgroup of 5 planet host and 1 comparison sample stars stands out ashaving particularly high [ X/H] vs. TC slopes.
|A search for water masers toward extrasolar planets|
Context: .Water is the most common triatomic molecule in the universeand the basis of life on Earth. Astrophysical masers have been widelystudied in recent years and have been shown to be invaluable probes ofthe details of the environment in which they are found. Water masers,for instance, are often detected toward low-mass star-forming regions.Doppler radial-velocity surveys have detected about 160exoplanets.Aims.Observations of water masers from exoplanetary systemswould give us a new detailed window through which to explorethem.Methods.We present a search for water masers toward eighteenextrasolar planets using the newly upgraded Australia Telescope CompactArray at 12 mm. A sensitivity of 25 mJy beam-1 and anangular resolution of ~10'' were achieved at 22.235 GHz. Results.Nomaser lines are clearly observed.
|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.
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