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Revealing the Structure of a Pre-Transitional Disk: The Case of the Herbig F Star SAO 206462 (HD 135344B)
SAO 206462 (HD 135344B) has previously been identified as a Herbig Fstar with a circumstellar disk with a dip in its infrared excess near 10μm. In combination with a low accretion rate estimated from Brγ, it may represent a gapped, but otherwise primordial or"pre-transitional" disk. We test this hypothesis with Hubble SpaceTelescope coronagraphic imagery, FUV spectroscopy and imagery andarchival X-ray data, and spectral energy distribution (SED) modelingconstrained by the observed system inclination, disk outer radius, andouter disk radial surface brightness (SB) profile using the WhitneyMonte Carlo Radiative Transfer Code. The essentially face-on (i lsim20°) disk is detected in scattered light from 0farcs4 to 1farcs15(56-160 AU), with a steep (r -9.6) radial SB profilefrom 0farcs6 to 0farcs93. Fitting the SB data requires a concave upwardor anti-flared outer disk, indicating substantial dust grain growth andsettling by 8 ± 4 Myr. The warm dust component is significantlyvariable in near to mid-IR excess and in temperature. At its warmest, itappears confined to a narrow belt from 0.08 to 0.2 AU. The steep SED forthis dust component is consistent with grains with a<= 2.5 μm. Forcosmic carbon to silicate dust composition, conspicuous 10 μmsilicate emission would be expected and is not observed. This mayindicate an elevated carbon to silicate ratio for the warm dust, whichis not required to fit the outer disk. At its coolest, the warm dust canbe fit with a disk from 0.14 to 0.31 AU, but with a higher inclinationthan either the outer disk or the gaseous disk, providing confirmationof the high inclination inferred from mid-IR interferometry. In tandem,the compositional and inclination difference between the warm dust andthe outer dust disk suggests that the warm dust may be ofsecond-generation origin, rather than a remnant of a primordial diskcomponent. With its near face-on inclination, SAO 206462's disk is aprime location for planet searches.Based in part on data collected at Subaru Telescope, which is operatedby the National Astronomical Observatory of Japan.
| Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs
Dusty debris disks around main-sequence stars are signposts for theexistence of planetesimals and exoplanets. From cross-correlatingHipparcos stars with the IRAS catalogs, we identify 146 stars within 120pc of Earth that show excess emission at 60 μm. This search tookspecial precautions to avoid false positives. Our sample is reasonablywell distributed from late B to early K-type stars, but it contains veryfew later type stars. Even though IRAS flew more than 20 years ago andmany astronomers have cross-correlated its catalogs with stellarcatalogs, we were still able to newly identify debris disks at as manyas 33 main-sequence stars; of these, 32 are within 100 pc of Earth. Thepower of an all-sky survey satellite like IRAS is evident when comparingour 33 new debris disks with the total of only 22 dusty debris diskstars first detected with the more sensitive, but pointed, satelliteISO. Our investigation focuses on the mass, dimensions, and evolution ofdusty debris disks.
| The N2K Consortium. VII. Atmospheric Parameters of 1907 Metal-rich Stars: Finding Planet-Search Targets
We report high-precision atmospheric parameters for 1907 stars in theN2K low-resolution spectroscopic survey, designed to identify metal-richFGK dwarfs likely to harbor detectable planets. Of these stars, 284 arein the ideal temperature range for planet searches,Teff<=6000 K, and have a 10% or greater probability ofhosting planets based on their metallicities. The stars in thelow-resolution spectroscopic survey should eventually yield >60 newplanets, including 8-9 hot Jupiters. Short-period planets have alreadybeen discovered orbiting the survey targets HIP 14810 and HD 149143.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| Dusty Debris Disks as Signposts of Planets: Implications for Spitzer Space Telescope
Submillimeter and near-infrared images of cool dusty debris disks andrings suggest the existence of unseen planets. At dusty but nonimagedstars, semimajor axes of associated planets can be estimated from thedust temperature. For some young stars these semimajor axes are greaterthan 1" as seen from Earth. Such stars are excellent targets forsensitive near-infrared imaging searches for warm planets. To probe thefull extent of the dust and hence of potential planetary orbits, Spitzerobservations should include measurements with the 160 μm filter.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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