A reconsideration of disk properties in Herbig Ae stars ^*

¹ Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
² Astrophysics Division, Space Science Department of ESA, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands
³ IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 St. Martin d'Hères Cedex, France
⁴ NASA-Ames Research Center, Moffett Field, CA 94035, USA
⁵ Crimean Astrophysical Observatory, Crimea, 334413 Nauchny, Ukraine
⁶ St. Petersburgh University, 198904 St. Petersburgh, Russia
⁷ Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy Astrophysics Division, Space Science Department of ESA, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 St. Martin d'Hères Cedex, France NASA-Ames Research Center, Moffett Field, CA 94035, USA Crimean Astrophysical Observatory, Crimea, 334413 Nauchny, Ukraine St. Petersburgh University, 198904 St. Petersburgh, Russia SIRTF Science Center, California Institute of Technology, MS 314-6, Pasadena, CA 91125, USA

Corresponding author: A. Natta, natta@arcetri.astro.it

Received: 12 February 2001
Accepted: 5 March 2001

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.