2001A&A...375..553G


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.04CEST19:43:07

2001A&A...375..553G - Astronomy and Astrophysics, volume 375, 553-565 (2001/8-4)

Interstellar C2 and CN toward the Cyg OB2 association. A case study of X-ray induced chemistry.

GREDEL R., BLACK J.H. and YAN M.

Abstract (from CDS):

An analysis of deep optical echelle spectra towards six stars in the Cyg OB2 (VI Cygni) association is presented. Interstellar absorption lines up to J''=18 in the (2,0) and (3,0) bands of the C2 A1Πu - X1Σg+ system are detected towards Cyg OB2 No.12. The large number of rotational lines accurately constrains the gas-kinetic temperature T and the density n to T=35K and n=(600±100)cm–3. The inferred C2 column density is N(C2)=(20+4–2)x1013cm–2. The detection of various lines in the (1,0) and (2,0) band of the CN A2Πu - X2Σ+ red system suggest a column density of N(CN)=(8-13)x1013cm–2. C2 absorption lines are also detected towards Cyg OB2 No.5 and No.9. Inferred parameters are T=50K, n=(600±200)cm–3, N(C2)=(10+3.5–1.5)x1013cm–2 towards No.5, and T=100K, n≥800cm–3, N(C2)=(5.2±1)x1013cm–2 towards No.9. Marginal detections of C2 towards Cyg OB2 No.8A indicate N(C2)≃3.3x1013cm–2 and T≃100K. Upper limits are N(C2)≤3.3x1013cm–2 toward Cyg OB2 No.7 and No.11. The C2 observations eliminate the possibility that the molecular material along the line of sight towards Cyg OB2 No.12 is spread over a pathlength of several hundred parsecs of very low density n≃10cm–3. The observations provide some support to a recent chemical model which assumes a nested structure of the molecular gas. Alternatively, the C2 and CN abundances obtained towards Cyg OB2 No.12 are in agreement with the predictions of an X-ray induced chemistry driven by an ionisation rate of ζ=(0.6-3)x10–15s–1. Calculated equilibrium temperatures of T=25-50K agree with temperatures inferred from C2. The model also reproduces the observed column densities of CO and CH, and that of H3+ to within a factor of two. We predict a H2O+ column density of 2x1012cm–2 towards Cyg OB2 No.12 and H2O+ absorption lines which are detectable by optical absorption line techniques. We report the detection of interstellar Rubidium towards Cyg OB2 No.12 and No.5. Inferred column densities are N(Rb)=(13±2)x109cm–2 towards No.12 and N(Rb)=(13±2)x109cm–2 towards No.5.

Abstract Copyright:

Journal keyword(s): ISM: abundances - ISM: clouds - ISM: molecules - X-rays: general

Simbad objects: 10

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Number of rows : 10

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 * omi Per ** 03 44 19.13204 +32 17 17.6929 3.13 3.88 3.83 3.71 3.71 B1III 572 0
2 * zet Per V* 03 54 07.9224751 +31 53 01.081262 2.19 2.97 2.85 2.71 2.62 B1Ib 812 0
3 * zet Oph Be* 16 37 09.5390545 -10 34 01.529471 1.73 2.58 2.56 2.46 2.50 O9.2IVnn 1723 2
4 BD+40 4220 EB* 20 32 22.4241357648 +41 18 18.942382590 11.32 10.79 9.185     O6.5-7f+O5.5-6f 368 0
5 Schulte 12 s*b 20 32 40.9574572449 +41 14 29.276333992 16.1 14.45 11.702     B3-4Ia+ 358 0
6 Schulte 9 s*b 20 33 10.7366753544 +41 15 08.222187463 13.38 12.77 10.96     O4.5If 206 0
7 Ass Cyg OB 2 As* 20 33.2 +41 19           ~ 790 0
8 Schulte 7 * 20 33 14.1095790591 +41 20 21.903381641 12.24 12.00 10.55     O3If* 129 0
9 BD+40 4227A SB* 20 33 15.0780900764 +41 18 50.478859468 10.42 10.27 8.98 8.03 6.83 O6Ib(fc)+O4.5:III:(fc) 215 0
10 BD+41 3807 SB* 20 34 08.5147839926 +41 36 59.407506888 11.74 11.52 10.03     O5.5Ifc 112 0

    Equat.    Gal    SGal    Ecl

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2020.07.04-19:43:07

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