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Forming the Dusty Ring in HR 4796A
We describe planetesimal accretion calculations for the dusty ringobserved in the nearby A0 star HR 4796A. Models with initial masses of10-20 times the minimum-mass solar nebula produce a ring with a width of7-15 AU and a height of 0.3-0.6 AU at 70 AU in ~10 Myr. The ring has aradial optical depth of ~1. These results agree with limits derived frominfrared images and from the excess infrared luminosity.
| NICMOS Imaging of the HR 4796A Circumstellar Disk
We report the first near-infrared (NIR) imaging of a circumstellarannular disk around the young (~8 Myr), Vega-like star HR 4796A. NICMOScoronagraph observations at 1.1 and 1.6 μm reveal a ringlikesymmetrical structure that peaks in reflected intensity 1.05"+/-0.02"(~70 AU) from the central A0 V star. The ring geometry, with aninclination of 73.1d+/-1.2d and a major axis position angle of26.8d+/-0.6d, is in good agreement with recent 12.5 and 20.8 μmobservations of a truncated disk. The ring is resolved with acharacteristic width of less than 0.26" (17 AU) and appears abruptlytruncated at both the inner and outer edges. The region of thedisk-plane inward of ~60 AU appears to be relatively free of scatteringmaterial. The integrated flux density of the part of the disk that isvisible (greater than 0.65" from the star) is found to be 7.6+/-0.5 and7.4+/-1.2 mJy at 1.1 and 1.6 mum, respectively. Correcting for theunseen area of the ring yields total flux densities of 12.8+/-1.0 and12.5+/-2.0 mJy, respectively (Vega magnitudes equal to 12.92+/-0.08 and12.35+/-0.18). The NIR luminosity ratio is evaluated from these resultsand ground-based photometry of the star. At these wavelengths,L_disk(lambda)/L_*(lambda) is equal to 1.4+/-0.2x10^-3 and2.4+/-0.5x10^-3, giving reasonable agreement between the stellar fluxscattered in the NIR and that which is absorbed in the visible andreradiated in the thermal infrared. The somewhat red reflectance of thedisk at these wavelengths implies a mean particle size in excess ofseveral microns, which is larger than typical interstellar grains. Theconfinement of material to a relatively narrow annular zone impliesdynamical constraints on the disk particles by one or more as yet unseenbodies.
| Molecular line observations of southern main-sequence stars with dust disks: alpha PS A, beta Pic, epsilon ERI and HR 4796 A. Does the low gas content of the beta PIC and varepsilon ERI disks hint of planets?
The results of molecular line observations with the 15 m Sest(star ) ofsouthern Vega-excess stars are presented. The stars alpha Ps A,varepsilon Eri and HR 4796 A were observed in the CO (1-0) and (2-1)lines and beta Pic was observed in the vibrational ground state of SiO,in the (2-1) and (5-4) transitions. In spite of considerably moresensitive observations than in previous attempts, none of these systemswas detected with the Sest. We use theoretical models of stellaratmospheres, of the structure and chemistry of interface regions (Pdr s)and of molecular excitation in Keplerian disks of gas and dust toanalyze these observational results. Among the observed objects, the K2V star varepsilon Eri appears particularly suitable and the analysisfocusses on this system. A disk model with simple geometry is capable ofexplaining recent dust continuum observations. Applying this model tothe associable molecular gas leads to the conclusion that it is mostlikely that the disk/ring around varepsilon Eri is largely devoid of anygas (m_gas/m_dust less than 10^{-3} of the interstellar value),presumably due to consumption during planetary system formation. Wepropose that varepsilon Eri should be a prime candidate for searches forextrasolar planets. In the beta Pic disk, the gas content may be as low,or even lower, as for varepsilon Eri which could be taken as indirectsupport of the suggested existence of a planetary system associated withthis star. Based on observations collected with the Swedish EsoSubmillimetre Telescope, Sest, in La Silla, Chile.
| Secondary standards for H-beta photometry in the Southern Hemisphere (second series).
Not Available
| UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
| UBV(RI)c photometry of some standard sequences in the Harvard F regions and in the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988MNRAS.231.1047M&db_key=AST
| Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL. III - 790 late-type bright stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&AS...59...15A&db_key=AST
| DDO Observations of Southern Stars
Not Available
| Standard Stars for VRI Photometry with S25 Response Photocathodes
Not Available
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