Author:

Keywords:

circumstellar matter, stars : emission-line, stars : evolution, stars : 51 oph, infrared : stars, wavelength spectrometer, ae/be stars, spectroscopy, 51-ophiuchi, system, atmosphere, emission, southern, Science & Technology, Physical Sciences, Astronomy & Astrophysics, stars : 51 Oph, WAVELENGTH SPECTROMETER, BETA-PICTORIS, AE/BE STARS, SPECTROSCOPY, SOUTHERN, SYSTEM, 51-OPHIUCHI, VELOCITIES, ATMOSPHERE, EMISSION, 0201 Astronomical and Space Sciences, 5101 Astronomical sciences, 5107 Particle and high energy physics, 5109 Space sciences

Abstract:

We analyze ISO archive data of the nearby bright emission-line star 51 Oph, previously classified as a proto-planetary system similar to beta Pic. The infrared spectrum reveals the presence of gas-phase emission bands of hot ( ~ 850 K) CO, CO_2, H_2O and NO. In addition to this, partially crystalline silicate dust is present. The solid-state bands and the energy distribution are indicative of dust that has formed recently, rather than of debris dust. The presence of hot molecular gas and the composition of the circumstellar dust are highly unusual for a young star and are reminiscent of what is found around evolved (AGB) stars, although we exclude the possibility of 51 Oph belonging to this group. We suggest several explanations for the nature of 51 Oph, including a recent episode of mass loss from a Be star, and the recent destruction of a planet-sized body around a young star. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA