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Title: ANOMALOUS DIFFUSE INTERSTELLAR BANDS IN THE SPECTRUM OF HERSCHEL 36. II. ANALYSIS OF RADIATIVELY EXCITED CH{sup +}, CH, AND DIFFUSE INTERSTELLAR BANDS

Abstract

Absorption spectra toward Herschel 36 (Her 36) for the A-bar{sup 1}{Pi} Leftwards-Open-Headed-Arrow X-tilde{sup 1}{Sigma} transitions of CH{sup +} in the J = 1 excited rotational level and for the A-bar{sup 2}{Delta} Leftwards-Open-Headed-Arrow X-tilde{sup 2}{Pi} transitions of CH in the J = 3/2 excited fine structure level have been analyzed. These excited levels are above their ground levels by 40.1 K and {approx}25.7 K and indicate high radiative temperatures of the environment of 14.6 K and 6.7 K, respectively. The effect of the high radiative temperature is more spectacular in some diffuse interstellar bands (DIBs) observed toward Her 36; remarkable extended tails toward red (ETRs) were observed. We interpret these ETRs as being due to a small decrease of the rotational constants upon excitation of the excited electronic states. Along with radiative pumping of a great many high-J rotational levels, this causes the ETRs. In order to study this effect quantitatively, we have developed a model calculation in which the effects of collisions and radiation are treated simultaneously. The simplest case of linear molecules is considered. It has been found that the ETR is reproduced if the fraction of the variation of the rotational constant, {beta} {identical_to} (B' - B)/B, ismore » sufficiently high (3%-5%) and the radiative temperature is high (T{sub r} > 50 K). Although modeling for general molecules is beyond the scope of this paper, the results indicate that the prototypical DIBs {lambda}5780.5, {lambda}5797.1, and {lambda}6613.6 which show the pronounced ETRs are due to polar molecules that are sensitive to the radiative excitation. The requirement of high {beta} favors relatively small molecules with three to six heavy atoms. DIBs {lambda}5849.8, {lambda}6196.0, and {lambda}6379.3 that do not show the pronounced ETRs are likely due to non-polar molecules or large polar molecules with small {beta}.« less

Authors:
; ; ; ;  [1];  [2]
  1. Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States)
  2. Department of Physics and Astronomy, Carthage College, 2001 Alford Park Drive, Kenosha, WI 53140 (United States)
Publication Date:
OSTI Identifier:
22140256
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 773; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ABSORPTION SPECTRA; ATOMS; COLLISIONS; EXCITATION; EXCITED STATES; FINE STRUCTURE; GROUND LEVEL; INTERSTELLAR SPACE; MOLECULES

Citation Formats

Oka, Takeshi, Welty, Daniel E., Johnson, Sean, York, Donald G., Hobbs, L. M., and Dahlstrom, Julie. ANOMALOUS DIFFUSE INTERSTELLAR BANDS IN THE SPECTRUM OF HERSCHEL 36. II. ANALYSIS OF RADIATIVELY EXCITED CH{sup +}, CH, AND DIFFUSE INTERSTELLAR BANDS. United States: N. p., 2013. Web. doi:10.1088/0004-637X/773/1/42.
Oka, Takeshi, Welty, Daniel E., Johnson, Sean, York, Donald G., Hobbs, L. M., & Dahlstrom, Julie. ANOMALOUS DIFFUSE INTERSTELLAR BANDS IN THE SPECTRUM OF HERSCHEL 36. II. ANALYSIS OF RADIATIVELY EXCITED CH{sup +}, CH, AND DIFFUSE INTERSTELLAR BANDS. United States. https://doi.org/10.1088/0004-637X/773/1/42
Oka, Takeshi, Welty, Daniel E., Johnson, Sean, York, Donald G., Hobbs, L. M., and Dahlstrom, Julie. 2013. "ANOMALOUS DIFFUSE INTERSTELLAR BANDS IN THE SPECTRUM OF HERSCHEL 36. II. ANALYSIS OF RADIATIVELY EXCITED CH{sup +}, CH, AND DIFFUSE INTERSTELLAR BANDS". United States. https://doi.org/10.1088/0004-637X/773/1/42.
@article{osti_22140256,
title = {ANOMALOUS DIFFUSE INTERSTELLAR BANDS IN THE SPECTRUM OF HERSCHEL 36. II. ANALYSIS OF RADIATIVELY EXCITED CH{sup +}, CH, AND DIFFUSE INTERSTELLAR BANDS},
author = {Oka, Takeshi and Welty, Daniel E. and Johnson, Sean and York, Donald G. and Hobbs, L. M. and Dahlstrom, Julie},
abstractNote = {Absorption spectra toward Herschel 36 (Her 36) for the A-bar{sup 1}{Pi} Leftwards-Open-Headed-Arrow X-tilde{sup 1}{Sigma} transitions of CH{sup +} in the J = 1 excited rotational level and for the A-bar{sup 2}{Delta} Leftwards-Open-Headed-Arrow X-tilde{sup 2}{Pi} transitions of CH in the J = 3/2 excited fine structure level have been analyzed. These excited levels are above their ground levels by 40.1 K and {approx}25.7 K and indicate high radiative temperatures of the environment of 14.6 K and 6.7 K, respectively. The effect of the high radiative temperature is more spectacular in some diffuse interstellar bands (DIBs) observed toward Her 36; remarkable extended tails toward red (ETRs) were observed. We interpret these ETRs as being due to a small decrease of the rotational constants upon excitation of the excited electronic states. Along with radiative pumping of a great many high-J rotational levels, this causes the ETRs. In order to study this effect quantitatively, we have developed a model calculation in which the effects of collisions and radiation are treated simultaneously. The simplest case of linear molecules is considered. It has been found that the ETR is reproduced if the fraction of the variation of the rotational constant, {beta} {identical_to} (B' - B)/B, is sufficiently high (3%-5%) and the radiative temperature is high (T{sub r} > 50 K). Although modeling for general molecules is beyond the scope of this paper, the results indicate that the prototypical DIBs {lambda}5780.5, {lambda}5797.1, and {lambda}6613.6 which show the pronounced ETRs are due to polar molecules that are sensitive to the radiative excitation. The requirement of high {beta} favors relatively small molecules with three to six heavy atoms. DIBs {lambda}5849.8, {lambda}6196.0, and {lambda}6379.3 that do not show the pronounced ETRs are likely due to non-polar molecules or large polar molecules with small {beta}.},
doi = {10.1088/0004-637X/773/1/42},
url = {https://www.osti.gov/biblio/22140256}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 773,
place = {United States},
year = {Sat Aug 10 00:00:00 EDT 2013},
month = {Sat Aug 10 00:00:00 EDT 2013}
}