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L. M. Hobbs,
D. G. York,
J. A. Thorburn,
T. P. Snow,
M. Bishof,
S. D. Friedman, B. J. McCall,
T Oka,
B. Rachford,
P. Sonnentrucker,
D. E. Welty
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ABSTRACT: Echelle spectra of HD 183143 [B7Iae, E(B-V) = 1.27] were obtained on three nights, at a resolving power R = 38,000 and with a signal-to-noise ratio ~1000 at 6400 A in the final, combined spectrum. A catalog is presented of 414 diffuse interstellar bands (DIBs) measured between 3900 and 8100 A in this spectrum. The central wavelengths, the widths (FWHM), and the equivalent widths of nearly all of the bands are tabulated, along with the minimum uncertainties in the latter. Among the 414 bands, 135 (or 33%) were not reported in four previous, modern surveys of the DIBs in the spectra of various stars, including HD 183143. The principal result of this study is that the great majority of the bands in the catalog are very weak and fairly narrow. Typical equivalent widths amount to a few mA, and the bandwidths (FWHM) are most often near 0.7 A. No preferred wavenumber spacings among the 414 bands are identified which could provide clues to the identities of the large molecules thought to cause the DIBs. At generally comparable detection limits in both spectra, the population of DIBs observed toward HD 183143 is systematically redder, broader, and stronger than that seen toward HD 204827 (Paper II). In addition, interstellar lines of C2 molecules have not been detected toward HD 183143, while a very high value of N(C2)/E(B-V) is observed toward HD 204827. Therefore, either the abundances of the large molecules presumed to give rise to the DIBs, or the physical conditions in the absorbing clouds, or both, must differ significantly between the two cases. Comment: Additional data and figures available at http://dibdata.org. To appear as Astrophysical Journal, 705, 32-45 (Nov. 1, 2009)
10/2009;
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ABSTRACT: H+3 has been detected using infrared absorption spectroscopy along the lines of sight to six infrared sources in dense molecular clouds: AFGL 2136, W33A, Mon R2 IRS 3, AFGL 961E, AFGL 2591, and AFGL 490. Upper limits to the column densities of H+3 are reported for an additional nine sources. The column densities of CO toward Mon R2 IRS 3 and AFGL 961E have been determined from observations of the first-overtone lines of CO. For the six sources toward which H+3 was detected, a simple model of H+3 chemistry has been used together with column densities of H2 derived from infrared CO measurements to estimate column lengths, mean number densities, and temperatures of molecular clouds. The derived column lengths are on the order of a parsec, the number densities are 104-105 cm-3, and the temperatures are ~25-50 K.
The Astrophysical Journal 01/2009; 522(1):338. · 6.02 Impact Factor
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ABSTRACT: Absorption lines of H3+ have been detected in the spectra of two infrared sources in the Galactic center and also toward the heavily reddened star Cygnus OB2 No. 12, whose line of sight is believed to include only diffuse interstellar gas. The absorptions toward the Galactic center sources (IRS 3 and GCS 3-2) probably are due to H3+ both in diffuse gas and in molecular clouds. The ratios of H3+ line equivalent width to extinction toward these three sources are much greater than those toward dense clouds where H3+ has been detected previously. Analysis of the spectra coupled with a simple model for the abundance of H3+ in the diffuse interstellar medium implies that the observed H3+ is present at low densities along long path lengths. These are the first detections of H3+ in the diffuse interstellar medium.
The Astrophysical Journal 01/2009; 510(1):251. · 6.02 Impact Factor
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L. M. Hobbs,
D. G. York,
T. P. Snow,
T. Oka,
J. A. Thorburn,
M. Bishof,
S. D. Friedman, B. J. McCall,
B. Rachford,
P. Sonnentrucker,
and D. E. Welty
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ABSTRACT: Echelle spectra of the double-lined spectroscopic binary HD 204827 were obtained on five nights, at a resolving power R = 38,000 and with a S/N = 750 near 6000 Å in the final, combined spectrum. The stars show E(B − V) = 1.11 and spectral types near O9.5 V and B0.5 III. A catalog is presented of 380 diffuse interstellar bands (DIBs) measured between 3900 and 8100 Å in the stars' spectrum. The central wavelengths, the widths (FWHM), and the equivalent widths of nearly all of the bands are tabulated, along with the minimum uncertainties in the latter. The reliable removal of very weak stellar lines from the catalog, and of some stellar lines from the less severe blends with DIBs, is made generally easy by the highly variable radial velocities of both stars. The principal result of this investigation is that the great majority of the bands in the catalog are very weak and relatively narrow. Typical equivalent widths amount to a few mÅ, and the bandwidths (FWHM) are most often near 0.55 Å. Therefore, most of these DIBs can be detected only in spectra obtained at a resolving power and a S/N at least comparable to those used here. In addition, the anomalous interstellar reddening and the very high value of the ratio N(C2)/E(B − V) seen toward HD 204827 indicate that the physical conditions in one or more of the several interstellar clouds seen in this direction differ significantly from those found toward the prototypical DIB target HD 183143, for example. Probably primarily for these reasons, 113 of the 380 bands (30%) were not detected in four previous modern surveys of the DIBs seen in the spectra of stars other than HD 204827. No preferred wavenumber spacings among the 380 bands are reliably identified which could provide clues to the identities of the large molecules thought to cause the DIBs.
The Astrophysical Journal 12/2008; 680(2):1256. · 6.02 Impact Factor
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ABSTRACT: Surprisingly large column densities of H have been detected using infrared absorption spectroscopy in seven diffuse cloud sight lines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating that H is ubiquitous in the diffuse interstellar medium. Using the standard model of diffuse cloud chemistry, our H column densities imply unreasonably long path lengths (~1 kpc) and low densities (~3 cm-3). Complimentary millimeter-wave, infrared, and visible observations of related species suggest that the chemical model is incorrect and that the number density of H must be increased by 1-2 orders of magnitude. Possible solutions include a reduced electron fraction, an enhanced rate of H2 ionization, and/or a smaller value of the H dissociative recombination rate constant than implied by laboratory experiments.
The Astrophysical Journal 12/2008; 567(1):391. · 6.02 Impact Factor
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ABSTRACT: Recent advances in laboratory gas-phase spectroscopy of large molecules and their ions permit a direct comparison between the diffuse interstellar bands (DIBs) and proposed carriers. On the basis of gas-phase data, Tulej et al. recently suggested that five A2Πu ← X2Πg electronic transitions of the linear carbon-chain anion C match with DIBs. We have obtained high-resolution visible spectra of four reddened stars (HD 46711, HD 50064, HD 183143, and Cyg OB2 12) to make a detailed comparison with the C laboratory data. Our data show that three of the C bands (0 at 6270.2 Å, 3 at 6064.0 Å, and 13 at 4963.0 Å) are in good agreement with DIBs in wavelength and relative intensity. A fourth band (1 at 5612.8 Å) also agrees in intensity but is apparently off by 2 Å in wavelength. All other laboratory bands of C are not expected to be detectable in astronomical spectra with the current level of sensitivity. The gas-phase spectrum of C agrees with the DIBs better than that of any previously proposed molecule. However, the question of whether C is a DIB carrier cannot be definitively answered until (1) better laboratory measurements confirm, refute, or explain the wavelength discrepancy for the 1 band and/or (2) better astronomical spectra reveal the presence or absence of other C bands.
The Astrophysical Journal 12/2008; 531(1):329. · 6.02 Impact Factor
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ABSTRACT: A search for H line emission, reported to have been detected toward the young star HD 141569A and possibly originating in a clump of planet-forming gas orbiting the star, has yielded negative results. Observations made at the United Kingdom Infrared Telescope and the Subaru Telescope during 2001-2005 covered 11 major transitions of H from 3.42 to 3.99 μm. No H emission lines were detected; one marginal detection at 3.9855 μm in 2002 June was not confirmed in later spectra. The upper limits to the line strengths were significantly lower than the previously reported detections. Supplemental slit-scanning spectroscopy using adaptive optics was performed within 038 of HD 141569A to search for extended emission from H, but no emission was detected. We compare our upper limit to the luminosity in H from HD 141569A with that possible from a gas giant protoplanet and also from a jovian mass exoplanet in close orbit about its central star.
The Astrophysical Journal 12/2008; 629(2):865. · 6.02 Impact Factor
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ABSTRACT: We have investigated the correlations between the equivalent widths of 21 selected diffuse interstellar bands (DIBs) and the corresponding interstellar column densities N(C2), N(CN), and N(CH), toward 53 stars with color excesses 0.11 ≤ E(B-V) ≤ 1.99. The observational data were derived primarily from echelle spectra acquired at R = 38,000 as part of our extensive, continuing survey of the bands. All but six of the 53 final spectra show signal-to-noise ratios ≥800 at 5780 Å. The principal result presented here is that seven of the 21 bands prove to be examples of "the C2 DIBs," a class of weak, narrow bands whose normalized equivalent widths Wλ(X)/Wλ (λ6196) are well correlated specifically with N(C2)/E(B-V) via power laws. In contrast, the similarly normalized equivalent widths of the 14 other, well-known DIBs analyzed here are uncorrelated, or weakly anticorrelated, with N(C2)/E(B-V), to within the observational uncertainties. Thus, the polyatomic molecule(s) presumed to cause these seven C2 DIBs may bear a direct chemical relation to C2 that is not shared by the polyatomic molecules putatively responsible for the other 14 bands. The C2 DIBs also show positive correlations with N(CN)/E(B-V) and N(CH)/E(B-V) in our particular sample of light paths, although generally with shallower slopes in the case of N(CN) and with greater scatter in the case of N(CH). Eleven additional C2 DIBs are also identified but are not analyzed here. Among the 18 C2 DIBs identified, four apparently have not been previously detected. The λ4963 band is generally the strongest of the 18 C2 DIBs, while the λ4734 band shows the most sensitive correlation with N(C2).
The Astrophysical Journal 12/2008; 584(1):339. · 6.02 Impact Factor
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ABSTRACT: It has recently been suggested by J. P. Maier's group that the origin band and three vibronic bands of the linear propadienylidene anion l-C3H match the diffuse interstellar bands (DIBs). We have examined the wavelength ranges in question using data from our ongoing DIB survey at the Apache Point Observatory. We find that the strongest DIB (λ6993) is not an acceptable wavelength match to the origin band of l-C3H, based on high-resolution laboratory data. The nondetection of interstellar features corresponding to the K = 2 ← 1 and K = 0 ← 1 branches of para l-C3H also argues against the assignment of λ6993 to the K = 1 ← 0 branch of ortho l-C3H. Two of the three DIBs that have been attributed to vibronic bands do not correlate in intensity with λ6993, providing further evidence against the assignment of this set of DIBs to l-C3H.
The Astrophysical Journal 12/2008; 567(2):L145. · 6.02 Impact Factor
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ABSTRACT: We confirm the first detection of the molecular ion H3+ in an extragalactic object, the highly obscured ultraluminous galaxy IRAS 08572+3915 NW. We also have detected absorption lines of the fundamental band of CO in this galaxy. The CO absorption consists of a cold component close to the systemic velocity and warm, highly blueshifted and redshifted components. The warm blueshifted component is remarkably strong and broad and extends at least to -350 km/s. Some analogies can be drawn between the H3+ and cold CO in IRAS08572+3915 NW and the same species seen toward the Galactic center. The profiles of the warm CO components are not those expected from a dusty torus of the type thought to obscure active galactic nuclei. They are probably formed close to the dust continuum surface near the buried and active nucleus and are probably associated with an unusual and energetic event there. Comment: 21 pages, 4 postscript figures, accepted by ApJ
03/2006;
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ABSTRACT: Using an absorption line from the metastable (J, K) = (3, 3) level of H3+ together with other lines of H3+ and CO observed along several sightlines, we have discovered a vast amount of high temperature (T ~ 250 K) and low density (n ~ 100 cm-3) gas with a large velocity dispersion in the Central Molecular Zone (CMZ) of the Galaxy, i.e., within 200 pc of the center. Approximately three fourths of the H3+ along the line of sight to the brightest source we observed, the Quintuplet object GCS 3-2, is inferred to be in the CMZ, with the remaining H3+ located in intervening spiral arms. About half of H3+ in the CMZ has velocities near ~ - 100 km s-1 indicating that it is associated with the 180 pc radius Expanding Molecular Ring which approximately forms outer boundary of the CMZ. The other half, with velocities of ~ - 50 km s-1 and ~ 0 km s-1, is probably closer to the center. CO is not very abundant in those clouds. Hot and diffuse gas in which the (3, 3) level is populated was not detected toward several dense clouds and diffuse clouds in the Galactic disk where large column densities of colder H3+ have been reported previously. Thus the newly discovered environment appears to be unique to the CMZ. The large observed H3+ column densities in the CMZ suggests an ionization rate much higher than in the diffuse interstellar medium in the Galactic disk. Our finding that the H3+ in the CMZ is almost entirely in diffuse clouds indicates that the reported volume filling factor (f ≥ 0.1) for n ≥ 104 cm-3 clouds in the CMZ is an overestimate by at least an order of magnitude. Comment: 33 pages, 5 figures, 3 tables
07/2005;
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ABSTRACT: Using observations of a line from the metastable (3,3) rotational level
of H3+ combined with measurements of other lines
of H3+ and CO, we have discovered a large quantity
of high temperature (T ˜250K) and low density (n ˜100
cm-3) gas within the central few hundred parsecs of the
Galaxy. Some of this gas has velocities near -100 km s-1
(LSR) and apparently is associated with the Expanding Molecular Ring at
a distance of 180 pc from the nucleus; most of the remainder is at
velocities near -50, 0, and + 50 km s-1. Previous
interpretations of the interstellar gas in the central few hundred
parsecs have been that it is mostly in the form of dense clouds which
have a filling factor of ˜0.1. The observations reported here
suggest that the filling factor of dense gas is much smaller than this.
The metastable H3+ level is not populated in a
number of star-forming clouds far from the Galactic Center.
04/2005; 37:488.
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ABSTRACT: A search for H3+ line emission, reported to have been detected toward the young star HD 141569A and possibly originating in a clump of planet-forming gas orbiting the star, has yielded negative results. Observations made at the United Kingdom Infrared Telescope and at the Subaru Telescope during 2001-2005 covered 11 major transitions of H3+ from 3.42 to 3.99 um. No H3+ emission lines were detected; one marginal detection at 3.9855 um in June 2002 was not confirmed in later spectra. The upper limits to the line strengths are significantly lower than the previously reported detections. Supplemental slit-scanning spectroscopy using adaptive optics was performed within 0.38 of HD 141569A to search for extended emission from H3+, but no emission was detected. We compare our upper limit to the luminosity in H3+ from HD 141569A with that possible from a gas giant protoplanet and also from a jovian mass exoplanet in close orbit about its central star. Comment: 8 pages, 7 figures, Accepted for publication in Astrophysical Journal
04/2005;
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B. J. McCall,
A. J. Huneycutt,
N. Djuric,
J. Semaniak and O. Novotny,
A. Al-Khalili,
A. Ehlerding,
F. Hellberg,
S. Kalhori,
A. Neau,
R. D. Thomas,
A. Paal,
F. Österdahl,
M. Larsson
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ABSTRACT: This paper presents the first dissociative recombination (DR) measurement of electrons with rotationally and vibrationally cold H3+ ions. A dc discharge pinhole supersonic jet source was developed and characterized using infrared cavity ringdown spectroscopy before installation on the CRYRING ion storage ring for the DR measurements. Rotational state distributions (Trot∼30 K) produced using the source were comparable to those in the diffuse interstellar medium. Our measurement of the electron energy dependence of the DR cross section showed resonances not clearly seen in experiments using rotationally hot ions, and allowed calculation of the thermal DR rate coefficient for ions at interstellar temperatures, αDR(23 K)=2.6×10−7 cm3 s−1. This value is in general agreement with recent theoretical predictions by Kokoouline and Greene Phys. Rev. A 68 012703 (2003)]. The branching fractions of the two breakup channels, H+H+H and H+H2, have also been measured for rotationally and vibrationally cold H3+.
Phys. Rev. A. 11/2004; 70(5).
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B J McCall,
A J Huneycutt,
R J Saykally,
T R Geballe,
N Djuric,
G H Dunn,
J Semaniak,
O Novotny,
A Al-Khalili,
A Ehlerding,
F Hellberg,
S Kalhori,
A Neau,
R Thomas,
F Osterdahl,
M Larsson
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ABSTRACT: The H3+ molecular ion plays a fundamental role in interstellar chemistry, as it initiates a network of chemical reactions that produce many molecules. In dense interstellar clouds, the H3+ abundance is understood using a simple chemical model, from which observations of H3+ yield valuable estimates of cloud path length, density and temperature. But observations of diffuse clouds have suggested that H3+ is considerably more abundant than expected from the chemical models. Models of diffuse clouds have, however, been hampered by the uncertain values of three key parameters: the rate of H3+ destruction by electrons (e-), the electron fraction, and the cosmic-ray ionization rate. Here we report a direct experimental measurement of the H3+ destruction rate under nearly interstellar conditions. We also report the observation of H3+ in a diffuse cloud (towards Persei) where the electron fraction is already known. From these, we find that the cosmic-ray ionization rate along this line of sight is 40 times faster than previously assumed. If such a high cosmic-ray flux is ubiquitous in diffuse clouds, the discrepancy between chemical models and the previous observations of H3+ can be resolved.
Nature 05/2003; 422(6931):500-2. · 36.28 Impact Factor
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ABSTRACT: We report the results of our preliminary investigations into the suitability of condensed-phase parahydrogen as a Raman-shifting medium for infrared cavity ringdown laser absorption spectroscopy. We have observed the conversion of ∼10-ns pulses of 532-nm radiation into first-, second-, and third-order vibrational Stokes radiation in bulk liquid and solid parahydrogen after a single 11-cm pass. Unexpectedly, we find that liquid H2 yields more efficient conversion than solid H2 with certain focal geometries, and that in the case of the solid, a collimated or loosely focused pump geometry is more efficient than a tight focus. © 2003 American Institute of Physics.
Applied Physics Letters 03/2003; 82(9):1350-1352. · 3.84 Impact Factor
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ABSTRACT: We present high-resolution (R = 20000) spectroscopy of H3+ absorption toward the luminous Galactic center sources GCS 3-2 and GC IRS 3. With the efficient wavelength coverage afforded by Subaru IRCS, six absorption lines of H3+ have been detected in each source from 3.5 to 4.0 um, three of which are new. In particular the 3.543 um absorption line of the R(3, 3)^l transition arising from the metastable (J, K) = (3, 3) state has been tentatively detected for the first time in the interstellar medium, where previous observations of H3+ had been limited to absorption lines from the lowest levels: (J, K) = (1, 0) of ortho-H3+ and (1, 1) of para-H3+. The H3+ absorption toward the Galactic center takes place in dense and diffuse clouds along the line of sight as well as the molecular complex close to the Galactic nucleus. At least four kinematic components are found in the H3+ absorption lines. We suggest identifications of the velocity components with those of HI, CO, and H2CO previously reported from radio and infrared observations. H3+ components with velocities that match those of weak and sharp CO and H2CO lines are attributed to diffuse clouds. Our observation has revealed a striking difference between the absorption profiles of H3+ and CO, demonstrating that the spectroscopy of H3+ provides information complementary to that obtained from CO spectroscopy. The tentative detection of the R(3, 3)^l line and the non-detection of spectral lines from other J > 1 levels provide observational evidence for the metastability of the (3, 3) level, which is theoretically expected. This suggests that other metastable J = K levels with higher J may also be populated.
01/2003;
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ABSTRACT: The diffuse interstellar bands (DIBs) are absorption features observed
in the visible spectra of nearly all red- dened stars, and were first
observed in the early decades of the 20th century when many lines in
astronomical spectra were unassigned. As laboratory spectroscopy
progressed, most of the stronger lines were identified with atomic or
diatomic species the DIBs are those lines (more numerous and generally
broader) that remain unidentified.
Since the DIBs have remained unassigned for over 75 years despite
extensive laboratory efforts, we are trying a new approach. Our goal is
to obtain moderate resolution (λδλ ± 37,500),
high signal-to-noise spectra of a large sample of reddened stars. We are
using the ARCES echelle spectrograph at the Apache Point Observatory,
which offers complete spectral coverage from 3700-1O,000Å. So far,
we have taken data on 75 nights and have obtained S/N > 1000 on 63
stars, and S/N > 500 on 60 additional stars. Our hope is that this
extensive DIB dataset, coupled with complementary measurements of known
species at ultraviolet, visible, and infrared wavelengths, will yield
new insights into the origin of the DIBs this paper presents some of onr
early results.
10/2002; -1:138.
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ABSTRACT: Using the new high resolution (~ 8 km/s) echelle spectrograph on the 3.5-m telescope at the Apache Point Observatory, we have begun a high sensitivity survey of the diffuse interstellar bands in a large sample of reddened stars. Now that we are two years into this long-term survey, our sample includes over 20 reddened stars which show at least one of the DIBs that had been suggested to be caused by C7-, based on the gas phase measurement of the C7- spectrum by J. P. Maier's group. The high quality astronomical data from this larger sample of stars, along with the spectroscopic constants from the new laboratory work recently reported by Maier's group, have enabled us to examine more carefully the agreement between C7- and the DIBs. We find that none of the C7- bands matches the DIBs in wavelength or expected profile. One of the DIBs (lambda5748) attributed to C7- is actually a stellar line. The two strongest DIBs attributed to C7- (lambda 6270 and lambda4964) do not vary together in strength, indicating that they do not share the same carrier. On the whole, we find no evidence supporting the hypothesis that C7- is a carrier of the diffuse interstellar bands.
06/2001;
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ABSTRACT: The molecular ion H3+ is considered the cornerstone of interstellar chemistry because it initiates the reactions responsible for the production of many larger molecules. Recently discovered in dense molecular clouds, H3+ has now been observed in the diffuse interstellar medium toward Cygnus OB2 No. 12. Analysis of H3+ chemistry suggests that the high H3+ column density (3.8 x 10(14) per square centimeter) is due not to a high H3+ concentration but to a long absorption path. This and other work demonstrate the ubiquity of H3+ and its potential as a probe of the physical and chemical conditions in the interstellar medium.
Science 03/1998; 279(5358):1910-3. · 31.20 Impact Factor
