CO Absorption Features Research Articles

CO absorption in luminous infrared galaxies

view Abstract Citations (57) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CO Absorption in Luminous Infrared Galaxies Ridgway, Susan E. ; Wynn-Williams, C. G. ; Becklin, E. E. Abstract We have taken 2.2 micron window spectra of the nuclear regions of a sample of 19 luminous infrared galaxies and used these to determine the 2.3 micron CO absorption feature. We have found a relationship between the depth of the 2.3 micron absorption bands and the H-K color of the galaxies. Galaxies with H-K colors in the range 0.4-0.8 tend to have deeper CO absorption than normal galaxies. Their near-infrared emission is therefore probably dominated by late-type supergiant or metal-rich giant stars that have been reddened by interstellar dust. Galaxies with H - K colors redder than 0.9 tend to have much weaker than normal CO absorption. Their near-infrared emission therefore cannot be simply reddened starlight from late-type giant stars, and they are likely to contain an additional source of near-infrared radiation. The most likely possibilities are an active galactic nucleus (AGN), or emission from very small transiently heated dust grains. Of the five objects with reddest H-K colors and weakest CO absorption, three (IRAS 05189-2524, UCG 5101 and Mrk 231) belong to the ultraluminous class of IRAS galaxies and are known to have Seyfert nuclei; two are off-nuclear components of the merging system Arp 299. We have also detected for the first time strong emission lines of molecular hydrogen in the infrared luminous galaxy NGC 4418, the galaxy with the deepest known 10 micron silicate absorption feature. Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/174269 Bibcode: 1994ApJ...428..609R Keywords: Absorption Spectra; Carbon Monoxide; Galaxies; Hydrogen; Infrared Sources (Astronomy); Infrared Spectra; Molecules; Silicates; Arrays; Gratings; Infrared Photometry; Spectrometers; Astronomy; GALAXIES: ISM; GALAXIES: NUCLEI; GALAXIES: PHOTOMETRY; INFRARED: GALAXIES full text sources ADS | data products SIMBAD (24) NED (24)

Evidence for a change of composition in the giant component of RS Oph after the 1985 outburst

The most recent outburst of the recurrent nova RS Oph occurred in 1985 January. K-band spectra were acquired of this object shortly after outburst, and on two occasions in 1992. The strength of the first-overtone CO absorption features has declined substantially over this 7-year period. We discuss a mechanism whereby the outburst contaminated the secondary with excess carbon, which has subsequently been convected away. We show that this mechanism is consistent with the observed data. Such contamination must have a major impact on the evolution of the secondary in nova systems.

Search for CO absorption bands in IUE far-ultraviolet spectra of cool stars

Observations of the red supergiant (M2 Iab) alpha Ori with the Goddard High Resolution Spectrograph (GHRS) on board the Hubble Space Telescope (HST) have provided an unambiguous detection of a far-ultraviolet (far-UV) chromospheric continuum on which are superposed strong molecular absorption bands. The absorption bands have been identified by Carpenter et al. (1994) with the fourth-positive A-X system of CO and are likely formed in the circumstellar shell. Comparison of these GHRS data with archival International Ultraviolet Explorer (IUE) spectra of alpha Ori indicates that both the continuum and the CO absorption features can be seen with IUE, especially if multiple IUE spectra, reduced with the post-1981 IUESIPS extraction procedure (i.e., with an oversampling slit), are carefully coadded to increase the signal to noise over that obtainable with a single spectrum. We therefore initiated a program, utilizing both new and archival IUE Short Wavelength Prime (SWP) spectra, to survey 15 cool, low-gravity stars, including alpha Ori, for the presence of these two new chromospheric and circumstellar shell diagnostics. We establish positive detections of far-UV stellar continua, well above estimated IUE in-order scattered light levels, in spectra of all of the program stars. However, well-defined CO absorption features are seen only in the alpha Ori spectra, even though spectra of most of the program stars have sufficient signal to noise to allow the dectection of features of comparable magnitude to the absorptions seen in alpha Ori. Clearly if CO is present in the circumstellar environments of any of these stars, it is at much lower column densities.

Infrared spectroscopy of symbiotic stars: carbon abundances and 12C/13C isotopic ratios

Intermediate-resolution spectra of a sample of symbiotic stars in the K and L bands have been obtained. In many objects, Pfund and Brackett emission lines are detected, as well as the first-overtone CO absorption bands. Synthetic spectra are used to fit the CO absorption features and to obtain carbon abundances and 12 C/ 13 C ratios. Subsolar carbon abundances in the symbiotic red giants are found, with little scatter from star to star. The 12 C/ 13 C ratios are also lower than the solar value. In terms of the C abundance and isotopic ratio, the surveyed symbiotic stars are indistinguishable from normal red giants, i.e. no modifications due to binarity are detected

Velocity dispersion and the stellar population in the central 1.2 parsecs of the Galaxy

New observations of the 2.3 micron absorption band head of CO in integrated stellar light in the central 1.2 pc of the Galaxy are presented. These data confirm that the velocity dispersion of the stars increases toward the Galactic center and totally dominates their systematic rotation at small radii. The velocity dispersion is constant an average value of 125 km/s within about 30 arcsec projected diameter central region. The strength of the CO features decreases in the integrated faint light within the same region. These observations are all consistent with the hypothesis that both the diffuse 2 micron light and the bright 2 micron point sources in the central region are dominated by sources that have little or no CO absorption feature. The observed CO feature at projected distances less than 0.6 pc thus actually arises in stars that are at true radii greater than 0.6 pc. The mass distribution at radius between 3.7 and 0.6 pc from IRS 16 is strong evidence for an increasing mass/2 micron radiation ratio toward the Galactic center.

Infrared transmission properties of CO, HCI, and SO 2 and their significance for the greenhouse effect on Venus

Low resolution (20 cm −1) transmission measurements were obtained for strong infrared absorption features of CO, HCI, and SO 2. Experiments were performed at room temperature with a Perkin-Elmer 621 grating spectrophotometer and a 10 cm pathlength cell having CsI windows. Some 4 meter CO studies were also made. The absorbers were placed in a carrier gas of nitrogen or carbon dioxide, and the partial pressures of absorber and diluent, respectively, were varied. The logarithm of the absorbance was represented as having a power law dependence on absorber amount and total pressure, where typically each variable varied over a larger range than an order of magnetude. The CO spectrum was synthesized theoretically and compared with the power law representation to explore the latter's range of validity. Finally, it was concluded that none of the above gases are significant for the strong greenhouse effect on Venus, either because they are not present in sufficient amounts, or because they produce opacity in spectral regions where carbon dioxide is already quite opaque.