The Properties of Molecular Hydrogen toward the Orion Belt Stars from Observations by the Interstellar Medium Absorption Profile Spectrograph

Jenkins, Edward B.; Woźniak, P. R.; Sofia, U. J.; Sonneborn, G.; Tripp, Todd M.

doi:10.1086/309130

Cited by 17 publications

(16 citation statements)

References 73 publications

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“…equations suggest a similar, roughly linear relationship for cm~2, as long as the local density is not too N(H 2 ) [ 1015 highÈas seems to be indicated by the data in Figure 27. Higher resolution far-UV spectra of absorption toward H 2 f, d, and v Ori obtained with IMAPS (Jenkins & Peimbert 1996 ;Jenkins et al 2000) indicate that the general Na IÈH 2 relationship shown in Figure 27 holds as well for each of several groups of components along those three lines of sight. Figure 26 shows similar behavior for N(K I) versus though only the higher column density regime is N(H 2 ), well sampled.…”

Section: I Versus K I and Na Imentioning

confidence: 85%

“…The values for d Ori, v Ori, and f Ori H 2 are from higher resolution spectra obtained with IMAPS (Jenkins & Peimbert 1996 ;Jenkins et al 2000). There are a number of sight lines for which has not been measured, but may well be signiÐcant, based on the available CH column densities H 2 and the generally tight relationship found by Danks, Federman, & Lambert (1984) (e.g., for AE Aur, s2 Ori, f1 N(CH)ÈN(H 2 ) Sco).…”

Section: Discussionmentioning

confidence: 99%

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A High‐Resolution Survey of Interstellar K i Absorption

Welty

Hobbs

2001

ASTROPHYS J SUPPL S

168

287

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We present high-resolution (FWHM D0.4È1.8 km s~1) spectra, obtained with the AAT UHRF, the McDonald Observatory 2.7 m spectrograph, and/or the KPNO feed, of interstellar K I coude coude absorption toward 54 Galactic stars. These new K I spectra reveal complex structure and narrow, closely blended components in many lines of sight. Multicomponent Ðts to the line proÐles yield estimates for the column densities, line widths, and velocities for 319 individual interstellar cloud components. The median component width (FWHM) and the true median separation between adjacent components are both km s~1. The median and maximum individual component K I column densities, about [1.2 4 ] 1010 and 1012 cm~2, correspond to individual component hydrogen column densities of about 2 ] 1020 and 1021 cm~2 and E(B[V ) D 0.03 and 0.17, respectively. If T is typically D100 K, then at least half the individual components have subsonic internal turbulent velocities. We also reexamine the relationships between the column densities of K I, Na I, C I, Li I, and CH. The four trace H tot , H 2 , neutral species exhibit essentially linear relationships with each other over wide ranges in overall column density. If C is uniformly depleted by 0.4 dex, then Li, Na, and K are each typically depleted by 0.6È0.7 dex. The total line of sight values for N(K I) and N(Na I) show roughly quadratic dependences on but the relationships for the ensemble of individual clouds could be signiÐcantly steeper. These N(H tot ), quadratic (or steeper) dependences appear to rule out signiÐcant contributions to the ionization from cosmic rays, X-rays, and/or charge exchange with C II in most cases. Charge exchange with negatively charged large molecules may often be more important than radiative recombination in neutralizing most singly ionized atomic species in cool H I clouds, howeverÈsuggesting that the true and thermal n e , n H , pressures may be signiÐcantly smaller than the values estimated by considering only radiative recombination. Both N(CH) and are nearly linearly proportional to N(K I) and N(Na I) [except for 1015 N(H 2 ) cm~2, over which makes the transition to the self-shielded regime]. Those cm~2 [ N(H 2 ) [ 1019 H 2 relationships appear also to hold for many individual components and component groups, suggesting that high-resolution spectra of K I and Na I can be very useful for interpreting lower resolution molecular data. The scatter about all these mean relationships is generally small dex), if certain con-([0.1È0.2 sistently "" discrepant ÏÏ sight lines are excludedÈsuggesting that both the relative depletions and the relative ionization of Li, C, Na, and K are generally within factors of 2 of their mean values. Di †erences noted for sight lines in Sco-Oph, in the Pleiades, near the Orion Trapezium, and in the LMC and SMC may be due to di †erences in the strength and/or shape of the ambient radiation Ðelds, perhaps ampliÐed by the e †ects of charge transfer with large molecules.

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Section: I Versus K I and Na Imentioning

confidence: 85%

Section: Discussionmentioning

confidence: 99%

A High‐Resolution Survey of Interstellar K i Absorption

Welty

Hobbs

2001

ASTROPHYS J SUPPL S

168

287

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“…To arrive at a total column density for H 2 , we must make a special assumption about the distribution in different rotational states. If the rotational temperature T rot of the H 2 were as high as about 1000 K, about the largest value seen in the general interstellar medium (ISM ) of our Galaxy (Spitzer et al 1974;Savage et al 1977;Jenkins et al 2000b) and elsewhere (Levshakov et al 2002), the occupations of the J ¼ 1 and 3 levels would be about equal to each other and together they would comprise 62% of the total over all levels. Thus, for T rot % 1000 K, we expect that our upper limit for H 2 in all J levels would be about 1:7 ; 10 15 cm À2 .…”

Section: Molecular Hydrogenmentioning

confidence: 95%

A Near‐Solar Metallicity, Nitrogen‐deficient Lyman Limit Absorber Associated with Two S0 Galaxies

Jenkins

Bowen

Tripp³

et al. 2005

ApJ

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The UV spectrum of the bright quasar PHL 1811 at z em ¼ 0:192 reveals a foreground gas system at z ¼ 0:080923 with log N (H i) ¼ 17:98 AE 0:05. We have determined the abundances of various atomic species in this system from a spectrum covering the wavelength range 1160-1730 8 recorded at 7 km s À1 resolution by the E140M grating of the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST ), supplemented by coverage at shorter wavelengths by the Far Ultraviolet Spectroscopic Explorer (FUSE ). The abundances of C ii, Si ii, S ii, and Fe ii compared to that of O i indicate that a considerable fraction of the gas is in locations where the hydrogen is ionized. An oxygen abundance ½O/ H ¼ À0:19 AE 0:08 in the H i-bearing gas indicates that the chemical enrichment of the gas is unusually high for an extragalactic QSO absorption system. However, this same material has an unusually low abundance of nitrogen, ½N/ O < À0:59, indicating that there may not have been enough time during this enrichment for secondary nitrogen to arise from low-and intermediate-mass stars. From the convergence of high Lyman series lines we can determine the velocity width of H i, and after correcting for turbulent broadening shown by the O i absorption feature, we derive a temperature T ¼ 7070 þ3860 À4680 K. We determine a lower bound for the electron density n(e) > 10 À3 cm À3 by modeling the ionization by the intergalactic radiation field and an upper bound n(e) < 0:07 cm À3 from the absence of much C ii in an excited fine-structure level. The thermal pressure in the range 4 cm À3 K < p / k < 140 cm À3 K could be confined by a warm-hot intergalactic medium (WHIM) structure with /¯$ 20 that might accompany a wall of galaxies at the same redshift, seen in data from the Sloan Digital Sky Survey. An r-band image of the field surrounding PHL 1811 recorded by the ACS instrument on HST shows that two galaxies at the same redshift as the gas are S0 galaxies, separated by only 34 and 87 h À1 70 kpc from the line of sight. One or both of these galaxies may be the source of the material in the Lyman limit system, which may have been expelled from them in a fast wind, by tidal stripping, or by ram pressure stripping. Subtraction of the ACS point-spread function from the image of the QSO reveals the presence of a face-on spiral galaxy under the glare of the quasar; while it is possible that this galaxy may be responsible for the Lyman limit absorption, the exact alignment of the QSO with the center of the galaxy suggests that the spiral is the quasar host.

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“…Large f H2 will be found when the sight line is dominated by the cores of diffuse molecular clouds, but the actual f H2 cannot be determined for individual velocity components because the strong low-J lines of H 2 are generally broader than the typical velocity separations between those components (Morton 1975). Based on higher resolution spectra of H 2 in low-N(H 2 ) sight lines obtained with IMAPS (Jenkins et al 2000), on even higher resolution spectra of other atomic and molecular species that are well correlated with H 2 (e.g., Welty & Hobbs 2001), and on the bvalues inferred from higher-J H 2 lines (e.g., Jensen et al 2010), it is likely that multiple components are present for most of the sight lines in which H 2 is detected. The highest integrated values of f H2 in the FUSE survey of highly reddened sight lines are between 0.65 and 0.76 (Rachford et al 2002(Rachford et al , 2009, slightly higher than the highest values found for the typically less reddened sight lines observed with Copernicus (Savage et al 1977).…”

Section: Diffuse Atomic and Molecular Gasmentioning

confidence: 99%

The Behavior of Selected Diffuse Interstellar Bands with Molecular Fraction in Diffuse Atomic and Molecular Clouds

Fan

Welty

York

et al. 2017

ApJ

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Abstract:We study the behavior of eight diffuse interstellar bands (DIBs) in different interstellar environments, as characterized by the fraction of hydrogen in molecular form (f H2 ), with comparisons to the corresponding behavior of various known atomic and molecular species. The equivalent widths of the five "normal" DIBs (ll5780.5, 5797.1, 6196.0, 6283.8, and 6613.6), normalized to E B-V , show a "Lambda-shaped" behavior: they increase at low f H2 , peak at f H2 ~ 0.3, and then decrease. The similarly normalized column densities of Ca, Ca + , Ti + , and CH + also decline for f H2 > 0.3. In contrast, the normalized column densities of Na, K, CH, CN, and CO increase monotonically with f H2 , and the trends exhibited by the three C 2 DIBs (ll4726.8, 4963.9, and 4984.8) lie between those two general behaviors. These trends with f H2 are accompanied by cosmic scatter, the dispersion at any given f H2 being significantly larger than the individual errors of measurement. The Lambda-shaped trends suggest the balance between creation and destruction of the DIB carriers differs dramatically between diffuse atomic and diffuse molecular clouds; additional processes besides ionization and shielding are needed to explain those observed trends. Except for several special cases, the highest W l (5780)/W l (5797) ratios, characterizing the so-called "sigma-zeta effect", occur only at f H2 < 0.2. We propose a sequence of DIBs based on trends in their pair-wise strength ratios with increasing f H2 . In order of increasing environmental density, we find the l6283.8 and l5780.5 DIBs, the l6196.0 DIB, the l6613.6 DIB, the l5797.1 DIB, and the C 2 DIBs.

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The Properties of Molecular Hydrogen toward the Orion Belt Stars from Observations by the Interstellar Medium Absorption Profile Spectrograph

Abstract: Absorption features from the Lyman and Werner bands of interstellar molecular hydrogen were recorded by the Interstellar Medium Absorption

Cited by 17 publications

References 73 publications

A High‐Resolution Survey of Interstellar K i Absorption

A High‐Resolution Survey of Interstellar K i Absorption

A Near‐Solar Metallicity, Nitrogen‐deficient Lyman Limit Absorber Associated with Two S0 Galaxies

The Behavior of Selected Diffuse Interstellar Bands with Molecular Fraction in Diffuse Atomic and Molecular Clouds

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