TY - JOUR
T1 - Gas phase Elemental abundances in Molecular cloudS (GEMS)
T2 - I. the prototypical dark cloud TMC 1
AU - Fuente, A.
AU - Navarro, D. G.
AU - Caselli, P.
AU - Gerin, M.
AU - Kramer, C.
AU - Roueff, E.
AU - Alonso-Albi, T.
AU - Bachiller, R.
AU - Cazaux, S.
AU - More Authors, null
PY - 2019/4/19
Y1 - 2019/4/19
N2 - 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 2 mm) 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 N 2 H + 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 ~ 3 to ~20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1-5 × 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 ~ 3 mag) where C/H ~ 8 × 10 -5 and C/O ~ 0.8-1, until the beginning of the dense phase at A V ~ 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 ~ (0.4-2.2) × 10 -6 , an abundance ~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 ~ 8 × 10 -8 ). Based on our chemical modeling, we constrain the value of ζ H 2 to ~(0.5-1.8) × 10 -16 s -1 in the translucent cloud.
AB - 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 2 mm) 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 N 2 H + 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 ~ 3 to ~20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1-5 × 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 ~ 3 mag) where C/H ~ 8 × 10 -5 and C/O ~ 0.8-1, until the beginning of the dense phase at A V ~ 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 ~ (0.4-2.2) × 10 -6 , an abundance ~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 ~ 8 × 10 -8 ). Based on our chemical modeling, we constrain the value of ζ H 2 to ~(0.5-1.8) × 10 -16 s -1 in the translucent cloud.
KW - Astrochemistry
KW - ISM: abundances
KW - ISM: kinematics and dynamics
KW - ISM: molecules
KW - Stars: formation
KW - Stars: low-mass
UR - http://www.scopus.com/inward/record.url?scp=85065037302&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/201834654
DO - 10.1051/0004-6361/201834654
M3 - Article
AN - SCOPUS:85065037302
SN - 0004-6361
VL - 624
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A105
ER -