Info

5.3.1 Observation of the Disk of HR 4796A

HR 4796A is a star of type A0V, lying at the end of the pre-Main-Sequence stage (or at the very beginning of the Main Sequence phase), and thus well past the T-Tauri

Fig. 5.21 Thediskof HD 4796A, imaged with the NICMOS camera on the HST (Schneideretal., 1999)

Fig. 5.21 Thediskof HD 4796A, imaged with the NICMOS camera on the HST (Schneideretal., 1999)

or FU-Orionis phases, and far younger than P Pic. Its disk (Fig. 5.21) is denser than that of P Pic, and its luminosity, when compared with that of its star, is the highest among stars of this age class (LIR/LS = 10~3; Artymowicz, 2000). The disk has been observed by imagery at 18 |m and then in the near infrared with the HST (Schneider et al., 1999). The observations are in good agreement with a radial distribution of dust according to a power law, out to distances from the star between 55 and 120 AU. The disk is thin, with an abrupt limit at 120 AU, which might be caused by perturbations by the other star, HR 4796B, in the binary.

By comparison of images a different infrared wavelengths, the size of the grains has been determined to be 2-3 |m (Telesco et al., 2000). If the grains primarily consist of silicates - material commonly observed in the interstellar medium - then we would expect that these grains would be swept outwards by radiation pressure. The presence of small grains in the disk of HR 4796A therefore presents a problem that has yet to be resolved (Artymowicz, 2000).

Was this article helpful?

0 0

Post a comment