SIMBAD references

We report on high sensitivity observations of the β Pic system in four molecular transitions with the 15mSest, tracing carbon, silicon and sulphur bearing species (CO, SiO and CS) and, as such, the gaseous component of the circumstellar disk. The lack of signal in the CO(2-1) line is consistent with an interstellar value of CO/H and a very low column density of hydrogen gas [N(H)<10¹⁹cm^–2]. The data do not require that CO is severely depleted with respect to hydrogen. Rather, we find that the gas-to-dust mass ratio in the disk is abnormally low, viz. m_gas/m_dust<0.1 (<0.05 at the 1σ level), implying an upper limit to the mass of hydrogen gas m(H)<2x10^–2M_⊕ (5M_☽). Evidently, any nebular disk gas from the formation stage of β Pic has been consumed in planet formation and/or blown out during the early mass loss history of the system. The sensitive search for SiO gas, believed to be presently produced in evaporative grain-grain collisions, gave likewise negative results. From the modeling of the line emission from the β Pic disk we deduce that this non-detection could be explained by insufficient filling of the Sest beam and that the testing of the theory has to await the advent of the new generation of millimeter interferometers in the southern hemisphere.