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Published May 3, 2001 | Published
Journal Article Open

A reconsideration of disk properties in Herbig Ae stars

Abstract

This paper presents state-of-the-art spectral energy distributions (SEDs) of four Herbig Ae stars, based in part on new data in the mid and far-infrared and at millimeter wavelengths. The SEDs are discussed in the context of circumstellar disk models. We show that models of irradiated disks provide a good fit to the observations over the whole range of wavelengths. We offer a possible solution to the long-standing puzzle caused by the excess emission of Herbig Ae stars, where a large fraction of the stellar luminosity is re-radiated between ~1.25 and 7 μm, with a peak at about 3 μm. We suggest that this general behaviour can be caused by dust evaporation in disks where the gas component is optically thin to the stellar radiation, as expected if the accretion rate is very low. The creation of a puffed-up inner wall of optically thick dust at the dust sublimation radius can account for the near-infrared characteristics of the SEDs. It can also naturally explain the H and K band interferometric observations of AB Aur (Millan-Gabet et al. [CITE]), which reveal a ring of emission of radius ~0.3 AU. Finally, irradiated disk models can easily explain the observed intensity of the 10 μm silicate features and their variation from star to star.

Additional Information

© 2001 ESO. Article published by EDP Sciences. Received 12 February 2001; Accepted 5 March 2001; Published online 15 May 2001. Based in part on observations obtained with ISO and with the IRAM Plateau de Bure Interferometer. ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). The discussion of the disk structure in HAe stars has involved many of our collegues, without whom this paper would have not been possible. Among them, I (AN) want to thank in particular Jeroen Bouwman, Carsten Dominik, Kees Dullemond, Alex de Koter and Rens Waters, who have made my visit in Amsterdam most pleasant and fruitful. Very interesting conversations with Nuria Calvet, Claude Bertout and Caroline Terquem have helped in clarifying a number of issues addressed in this paper. We gratefully aknowledge the support of ASI (grants ARS-99-15 and 1/R/27/00) to the Osservatorio Astrofisico di Arcetri. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.

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