תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Interstellar Medium Sculpting of the HD 32297 Debris Disk
We detect the HD 32297 debris disk in scattered light at 1.6 and 2.05?m. We use these new observations together with a previous scatteredlight image of the disk at 1.1 ?m to examine the structure andscattering efficiency of the disk as a function of wavelength. Inaddition to surface brightness asymmetries and a warped morphologybeyond ~1farcs5 for one lobe of the disk, we find that there exists anasymmetry in the spectral features of the grains between thenortheastern and southwestern lobes. The mostly neutral color of thedisk lobes implies roughly 1 ?m-sized grains are responsible for thescattering. We find that the asymmetries in color and morphology canplausibly be explained by HD 32297's motion into a dense interstellarmedium cloud at a relative velocity of 15 km s-1. Wemodel the interaction of dust grains with H I gas in the cloud. Weargue that supersonic ballistic drag can explain the morphology of thedebris disks of HD 32297, HD 15115, and HD 61005.
| 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.
| The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| 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.
| Discovery of a Nearly Edge-on Disk around HD 32297
We report the discovery of a nearly edge-on disk about the A0 star HD32297 seen in light scattered by the disk grains revealed in NICMOSPSF-subtracted coronagraphic images. The disk extends to a distance ofat least 400 AU (3.3") along its major axis with a 1.1 μm fluxdensity of 4.81 +/- 0.57 mJy beyond a radius of 0.3" from thecoronagraphically occulted star. The fraction of 1.1 μm starlightscattered by the disk, 0.0033 +/- 0.0004, is comparable to itsfractional excess emission at 25 + 60 μm of ~0.0027 as measured fromIRAS data. The disk appears to be inclined 10.5d +/- 2.5d from anedge-on viewing geometry, with its major axis oriented 236.5d +/- 1°eastward of north. The disk exhibits unequal brightness on opposingsides and a break in the surface brightness profile along the NE-sidedisk major axis. Such asymmetries might implicate the existence of oneor more (unseen) planetary mass companions.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | לינכס |
| התרוממות ימנית: | 09h42m29.14s |
| סירוב: | +40°58'24.6" |
| גודל גלוי: | 7.922 |
| מרחק: | 67.613 פארסק |
| תנועה נכונה: | -31.3 |
| תנועה נכונה: | -68.7 |
| B-T magnitude: | 8.753 |
| V-T magnitude: | 7.991 |
קטלוגים וכינוים:
|
