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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.
| Coronagraphic Imaging of Pre-Main-Sequence Stars with the Hubble Space Telescope Space Telescope Imaging Spectrograph. I. The Herbig Ae Stars
STIS white-light coronagraphic imaging has been carried out for 14nearby, lightly reddened Herbig Ae stars, providing data on theenvironments and disks associated with these stars. No disks aredetected in our data when the Herbig Ae star is accompanied by a stellarcompanion at r<=2''. We find that the optical visibilityof protoplanetary disks associated with Herbig Ae stars at r>=50-70AU from the star is correlated with the strength of the mid-IR PAHfeatures, particularly 6.2 μm. These features, like the FUVfluorescent H2 emission, trace the presence of materialsufficiently far above the disk midplane that it is directly illuminatedby the star's FUV radiation. In contrast, measures of the bulkproperties of the disk, including ongoing accretion activity, mass, andthe submillimeter slope of the SED, do not correlate with the surfacebrightness of the optical nebulosity. Modelers have interpreted theappearance of the IR SED and the presence of emission from warm silicategrains at 10 μm as a measure of geometrical shadowing by material inthe disk near the dust sublimation radius of 0.5 AU. Geometricalshadowing sufficient to render a disk dark to distances as large as 500AU from a star would require that the star be optically visible only ifviewed essentially pole-on, in disagreement with our program star systeminclinations. Rather than invoking shadowing to account for theoptically dark disks, the correlation of the STIS detections with PAHemission features suggests a correlation with disk flaring and ananticorrelation with the degree of dust settling toward the midplane. Ifthis correlation continues to lower levels, the STIS data suggest thatimprovements in coronagraph performance that suppress the residualscattered and diffracted stellar light by an additional factor of>=10 should render the majority of disks associated with nearbyHerbig Ae stars detectable.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by The Johns HopkinsUniversity under NASA contract NAS5-32985.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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| Takýmyýldýz: | Kurt |
| Sað Açýklýk: | 15h13m50.26s |
| Yükselim: | -33°31'04.7" |
| Görünürdeki Parlaklýk: | 8.569 |
| Uzaklýk: | 114.548 parsek |
| özdevim Sað Açýklýk: | -58.2 |
| özdevim Yükselim: | -20.1 |
| B-T magnitude: | 9.131 |
| V-T magnitude: | 8.616 |
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