Akademik Veri Yönetim Sistemi
The Molecular Universe, 280th Symposium of the International Astronomical Union, Toledo, İspanya, 30 Mayıs - 03 Haziran 2011, ss.388, (Tam Metin Bildiri)
CO line emission is the main tracer of the physical structure and column density of molecular clouds in which young stellar objects (YSOs) are forming. This work focusses on the earliest and most deeply embedded YSOs where the molecular envelopes are hiding the protostars. A sample of 26 low-mass YSOs has been observed with the Heterodyne Instrument for the Far-Infrared (HIFI) onboard Herschel as part of the guaranteed time key program ``Water In Star-forming regions with Herschel'' (WISH). High-J CO lines, including 12CO, 13CO and C18O 10--9 and C18O 5--4 lines are observed (Eup/kB ∼ 250-300 K), which trace the warmer material (T ≥ 50 K) in the envelope. CO observations are highly complementary to those of water performed by WISH, since the chemistry is simpler and better understood, allowing for an independent determination of the physical structure. The CO HIFI data are compared with lower-J CO lines (e.g., J = 3--2) obtained over the last decade with various ground-based telescopes, including the APEX--CHAMP+ array receiver. The goal of this project is to derive physical and kinematical properties of the envelope by comparing both low- and high-J CO lines in a coherent manner. Analysis of the C18O lines in several sources provides evidence for significant freeze-out in the coldest regions and evaporation back into the gas phase in the parts of the envelope where the temperature exceeds 25 K. This work will allow further quantification of the different physical processes taking place in the envelope accounting for the origin of both low- and high-J CO emission.