Inferring the evolutionary stages of the internal structures of NGC 7538 S and IRS1 from chemistry

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Volume 593 (September 2016)

A&A, 593 (2016) A46

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Table 4

Best-fit 1D gas-grain modelled column densities compared to the observed values in MM1−MM3.


	MM3^f		MM2^f		MM1^f


Molecule^d,e	N _Observed ^g	N _Modeled ^h	N _Observed ^g	N _Modeled ^h	N _Observed ^g	N _Modeled ^h	Notes on the observed values
	(cm^-2)	(cm^-2)	(cm^-2)	(cm^-2)	(cm^-2)	(cm^-2)


H₂	5.25_{± 0.23}(24)	9.9(24)	1.70_{± 0.22}(24)	3.1(24)	1.69_{± 0.27}(24)	2.7(24)	derived from dust continuum
CO	2.39_{± 0.06}(18)	2.6(18)	2.21_{± 0.16}(19)	2.2(19)	1.35_{± 0.16}(20)	5.6(19)	derived from C¹⁸O with ¹⁶O /¹⁸O = 607^a
H₂CO	≤4.95(14)	7.0(14)	4.50_{± 0.51}(16)	3.3(16)	2.22_{± 0.34}(16)	1.6(16)	derived from with ¹²C /¹³C = 73^a
CH₂CO ^†	≤3.67(13)	2.6(14)	1.43_{± 0.12}(15)	1.0(15)	4.66_{± 0.37}(14)	1.3(15)
CH₃OH ^†	2.25_{± 0.02}(15)	4.5(14)	4.33_{± 0.58}(16)	2.2(16)	4.61_{± 0.88}(16)	7.2(16)
HCOOCH₃ ^†	≤4.95(14)	2.4(09) ^×	1.33_{± 0.13}(16)	1.2(14) ^×	2.91_{± 0.39}(16)	1.2(13) ^×
CH₃OCH₃ ^*, †	≤1.96(17)	4.8(11) ^×	1.97_{± 0.19}(17)	5.3(14) ^×	7.62_{± 0.57}(17)	1.1(14) ^×
HNCO ^†	≤2.44(13)	9.1(12)	1.89 ± 1.01(15)	1.8(16)	2.64 ± 1.35(15)	2.4(17) ^×
HC₃N ^†	≤6.60(12)	2.8(13)	2.11_{± 0.03}(14)	6.1(14)	6.33_{± 0.12}(14)	8.7(15) ^×
CH₃CN	≤ 1.18(15)	1.3(13) ^×	2.64 ± 0.96(15)	1.3(14) ^×	4.58 ± 1.97(16)	3.8(15)	derived from opacity corrected CH₃CN in Sect. 5.2.1
CH₃CH₂CN ^†	≤8.43(13)	1.3(10) ^×	≤3.77(13)	1.5(11) ^×	1.70_{± 0.13}(15)	6.3(12) ^×
NH₂CHO ^†	≤7.11(12)	2.3(13)	5.46_{± 0.50}(14)	1.8(14)	2.91_{± 0.13}(14)	2.9(14)
OCS	8.25_{± 0.11}(16)	1.3(16)	5.39_{± 1.71}(16)	2.5(17)	6.79_{± 0.14}(16)	4.6(16)	derived from O¹³CS with ¹²C /¹³C = 73^a
SO₂	≤ 4.29(14)	1.2(16) ^×	≤1.58(15)	1.6(16)	3.05_{± 0.43}(17)	2.7(16) ^×	derived from ³⁴SO₂ with ³²S /³⁴S = 22^b
SO	≤ 1.93(15)	1.8(16)	3.29_{± 0.58}(16)	3.5(16)	3.57_{± 0.38}(17)	3.4(17)	derived from ³³SO with ³²S /³³S = 127^b

Agreement		10/15 = 67%		11/15 = 73%		9/15 = 60%

Age^c		11 200 yr		11 210 yr		11 660 yr

Notes.

^(a)

Derived from galactic local isotope ratio (Giannetti et al. 2014).

^(b)

Derived from isotope ratio in solar system (Lodders 2003).

^(c)

The physical time moment when our chemical code describes the observed column densities most accurately in our assumed physical structures.

^(d)

“*” denotes the tentatively identified line.

^(e)

“†” denote the species which do not have rare isotopologues, so we derive their values by assuming they are optically thin.

^(f)

“×” denote the model predicted column densities inconsistent to the observation (N_Modeled/N_Observed< 0.1 or >10).

^(g)

Uncertainties of the observed value are determined from T_rot, partition function Q(T_rot), and Gaussian fit to .

^(h)

The values listed were obtained at the end of each evolutionary stage, corresponding to the values used in Fig. 6.

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