Detection of the S(1) Rotational Line of H2 toward IRC+10216: A Simultaneous Measurement of the Mass-loss Rate and CO Abundance

被引:5
作者
Fonfria, J. P. [1 ]
DeWitt, C. N. [2 ]
Montiel, E. J. [2 ]
Cernicharo, J. [1 ]
Richter, M. J. [3 ]
机构
[1] IFF CSIC, Inst Fis Fundamental, Mol Astrophys Grp, C Serrano 123, E-28006 Madrid, Spain
[2] NASA, Ames Res Ctr, SOFIA USRA, MS 232-12, Moffett Field, CA 94035 USA
[3] Univ Calif Davis, Phys Dept, One Shields Ave, Davis, CA 95616 USA
基金
欧洲研究理事会;
关键词
DUST FORMATION ZONE; CIRCUMSTELLAR ENVELOPE; CARBON STARS; CHEMICAL-COMPOSITION; INNER LAYERS; AGB; EMISSION; SPECTRA; MODELS; SHELLS;
D O I
10.3847/2041-8213/ac5a58
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We report the first detection of the S(1) pure rotational line of ortho-H-2 at 17.04 mu m in an asymptotic giant branch star, using observations of IRC+10216 with the Echelon-cross-echelle Spectrograph (EXES) mounted on the Stratospheric Observatory for Infrared Astronomy. This line, which was observed in a very high-sensitivity spectrum (rms noise similar or equal to 0.04% of the continuum), was detected in the wing of a strong telluric line and displayed a P Cygni profile. The spectral ranges around the frequencies of the S(5) and S(7) ortho-H-2 transitions were observed as well but no feature was detected in spectra with sensitivities of 0.12% and 0.09% regarding the continuum emission, respectively. We used a radiation transfer code to model these three lines and derived a mass-loss rate of (2.43 +/- 0.21) x 10(-5) M (circle dot) yr(-1) without using the CO abundance. The comparison of this rate with previous estimates derived from CO observations suggests that the CO abundance relative to H-2 is (6.7 +/- 1.4) x 10(-4). From this quantity and previously reported molecular abundances, we estimate the O/H and C/H ratios to be (3.3 +/- 0.7) x 10(-4) and >(5.2 +/- 0.9) x 10(-4), respectively. The C/O ratio is >1.5 +/- 0.4. The absence of the S(5) and S(7) lines of ortho-H-2 in our observations can be explained by the opacity of hot dust within 5 R from the center of the star. We estimate the intensity of the S(0) and S(2) lines of para-H-2 to be similar or equal to 0.1% and 0.2% of the continuum, respectively, which are below the detection limit of EXES.
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页数:6
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