Journal
ASTRONOMY & ASTROPHYSICS
Volume 624, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201834654
Keywords
astrochemistry; ISM: abundances; ISM: kinematics and dynamics; ISM: molecules; stars: formation; stars: low-mass
Categories
Funding
- Spanish MINECO [AYA2016-75066-C2-1/2-P]
- ERC under ERC-2013-SyG [610256 NANOCOSMOS]
- ERC-2015-STG [679852 RADFEEDBACK]
- European Union's Horizon 2020 research and innovation program [639459]
- Simons Foundation (SCOL) [321183]
- [AYA2017-85322-R]
- [AYA2016-79006-P]
- STFC [ST/R000786/1] Funding Source: UKRI
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GEMS is an IRAM 30 m Large Program whose aim is determining the elemental depletions and the ionization fraction in a set of prototypical star-forming regions. This paper presents the first results from the prototypical dark cloud Taurus molecular cloud (TMC) 1. Extensive millimeter observations have been carried out with the IRAM 30 m telescope (3 and 2mm) and the 40 m Yebes telescope (1.3 cm and 7 mm) to determine the fractional abundances of CO, HCO+, HCN, CS, SO, HCS+, and N2H+ in three cuts which intersect the dense filament at the well-known positions TMC 1-CP, TMC 1-NH3, and TMC 1-C, covering a visual extinction range from A(v) similar to 3 to similar to 20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1-5 x 10(3) cm(-3); and (ii) the dense phase, located at A(v) > 10 mag, with molecular hydrogen densities >10(4) cm(-3). Observations and modeling show that the gas phase abundances of C and O progressively decrease along the C+/C/CO transition zone (A(v) similar to 3 mag) where C/H similar to 8 x 10(-5) and C/O similar to 0.8-1, until the beginning of the dense phase at A(v) similar to 10 mag. This is consistent with the grain temperatures being below the CO evaporation temperature in this region. In the case of sulfur, a strong depletion should occur before the translucent phase where we estimate an S/H similar to (0.4-2.2) x 10(-6), an abundance similar to 7-40 times lower than the solar value. A second strong depletion must be present during the formation of the thick icy mantles to achieve the values of S/H measured in the dense cold cores (S/H similar to 8 x 10(-8)). Based on our chemical modeling, we constrain the value of zeta(H2) to similar to(0.5-1.8) x 10(-16) s(-1) in the translucent cloud.
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