<i>IUE</i>
                    Absorption‐Line Observations of the Moderately and Highly Ionized Interstellar Medium toward 164 Early‐Type Stars

Savage, Blair D.; Meade, M. R.; Sembach, Kenneth R.

doi:10.1086/322537

Cited by 43 publications

(73 citation statements)

References 89 publications

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“…It was assigned different spectral types and luminosity classes in the past, ranging from O9 to B3 and from II to V. The most recent classification is the one given by Mathys (1988): O9.5 III. Savage et al (2001) reported the spectroscopic parallax distance d ¼ 2740 pc, with an accuracy estimated to be about 30% (i.e., about 800 pc here). This value is in good agreement with the one reported by Diplas & Savage (1994), d ¼ 2716 pc.…”

Section: The Targetmentioning

confidence: 58%

FUSEDetermination of a Low Deuterium Abundance along an Extended Sight Line in the Galactic Disk

Hébrard

Tripp

Chayer

et al. 2005

ApJ

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We present a study of the deuterium abundance along the extended sight line toward HD 90087 with the Far Ultraviolet Spectroscopic Explorer (FUSE ). HD 90087 is a O9.5 III star located in the Galactic disk at a distance of $2.7 kpc away from the Sun. Both in terms of distance and column densities, HD 90087 has the longest and densest sight line observed in the Galactic disk for which a deuterium abundance has been measured from ultraviolet absorption lines so far. Because many interstellar clouds are probed along this sight line, possible variations in the properties of individual clouds should be averaged out. This would yield a deuterium abundance that is characteristic of the interstellar medium on scales larger than the Local Bubble. The FUSE spectra of HD 90087 show numerous blended interstellar and stellar features. We have measured interstellar column densities of neutral atoms, ions, and molecules by simultaneously fitting the interstellar absorption lines detected in the different FUSE channels. As far as possible, saturated lines were excluded from the fits in order to minimize possible systematic errors. IUE (International Ultraviolet Explorer) archival data are also used to measure neutral hydrogen. We report D/O ¼ (1:7 AE 0:7) ; 10 À2 and D/H ¼ (9:8 AE 3:8) ; 10 À6 (2 ). Our new results confirm that the gas-phase deuterium abundance in the distant interstellar medium is significantly lower than the one measured within the Local Bubble. We supplement our study with a revision of the oxygen abundance toward Feige 110, a moderately distant ($200 pc) sdOB star, located $150 pc below the Galactic plane. Excluding saturated lines from the fits of the FUSE spectra is critical; this led us to derive an O i column density about 2 times larger than the one previously reported for Feige 110. The corresponding updated D/O ratio on this sight line is D/O ¼ (2:6 AE 1:0) ; 10 À2 (2 ), which is lower than the one measured within the Local Bubble. The data set available now outside the Local Bubble, which is based primarily on FUSE measurements, shows a contrast between the constancy of D/O and the variability of D/ H. As oxygen is considered to be a good proxy for hydrogen within the interstellar medium, this discrepancy is puzzling.

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Section: The Targetmentioning

confidence: 58%

FUSEDetermination of a Low Deuterium Abundance along an Extended Sight Line in the Galactic Disk

Hébrard

Tripp

Chayer

et al. 2005

ApJ

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“…We then focused on kinematic evidence for feedback. In the ISM, enhancements in velocity width are found in regions of higher than average SFRs such as Orion (Cowie, Songaila, & York 1979) and Carina (Walborn et al 1998;Savage, Meade, & Sembach 2001). Evidently, gas in these regions is stirred up by increased supernova activity.…”

Section: Search For Evidence Of Star Formation and Feedbackmentioning

confidence: 99%

Cii* Absorption in Damped Lyα Systems. II. A New Window on the Star Formation History of the Universe

Wolfe

Gawiser

Prochaska

2003

ApJ

115

146

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Starting from the star formation rate (SFR) per unit area, _ Ã Ã , determined for damped Ly systems (DLAs) using the C ii* method, we obtain the SFR per unit comoving volume, _ Ã Ã ðzÞ, at z % 3. Pure warm neutral medium (WNM) solutions are ruled out since they generate more bolometric background radiation than observed, but the two-phase solutions dominated by the cold neutral medium (CNM) are consistent with the backgrounds. We find that _ Ã Ã ðzÞ for DLAs agrees with the _ Ã Ã ðzÞ for the Lyman break galaxies (LBGs). Although the mass of produced stars indicated by the SFRs is consistent with the current densities of known stellar populations, the mass of metals produced by z ¼ 2:5 is 30 times larger than detected in absorption in DLAs. Of the three possible solutions to this '' missing metals '' problem, the most likely appears to be that star formation occurs in compact bulge regions. We search for evidence of feedback and find no correlations between _ Ã Ã and N(H i), but possible correlations between _ Ã Ã and low-ion velocity width and _ Ã Ã and metal abundance. We show that (1) the correlation between cooling rate and dust-to-gas ratio is positive evidence for grain photoelectric heating, (2) the cosmic microwave background (CMB) does not significantly populate the C ii excited fine-structure states, and (3) the ratio of C ii* to resonance-line optical depths is a sensitive probe of the multiphase structure of the DLA gas. We address recent arguments that DLAs are comprised only of WNM gas and show them to be inconclusive. Despite the rough agreement between _ Ã Ã ðzÞ for DLAs and LBGs, current evidence indicates that these are distinct populations.

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“…Typically the profile widths of CIV, SiIV and NV absorption lines have been found to be quite broad in the general interstellar medium (b > 10 km s −1 ), indicating their origin in high temperature, often collisionally ionized regions (Savage et al 2001). However, we have found surprisingly small values (<4.5 km s −1 ) for the doppler b-values for the CIV and NV absorption component seen at V ∼ −1.0 km s −1 towards HD 127381.…”

Section: Interstellar Absorption Towards Hd 128345 Andmentioning

confidence: 99%

Highly ionized gas in the local ISM: Some like it hot?

Welsh¹,

Lallement

2005

A&A

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Abstract. We present HST-STIS medium-resolution spectra (R ∼ 6.5 km s −1 ) of the ultraviolet interstellar absorption lines observed towards 4 early-type stars located within the local interstellar medium (ISM), with sight-line distances <186 pc in the general direction of the Loop I superbubble (l = 330• , b = +18 • ). These data have been supplemented with high resolution (R ∼ 3 km s −1 ) visible absorption observations of the NaI D-lines towards these 4 stars. Our main discovery is the detection of highly ionized absorption components of CIV, SiIV and NV towards the two most distant targets, HD 127381 and HD 142256. These lines-of-sight are known to cross both the near and far neutral interface boundaries to the Loop I cavity, in addition to intersecting the fragmented shell of neutral and partially ionized gas that defines the boundary to the Local Bubble. However, the presently measured narrow line profile-widths and their measured absorption intensities are found to be incompatible with theoretical models that predict high ion absorption due to the presence of evaporating cloud conduction interfaces. We conclude that the formation of high ions in the local ISM is highly dependent on the location of the absorbing gas clouds with respect to nearby sources of both hot X-ray emitting gas and/or photo-ionization. Our observations have also revealed at least 6 gas clouds with distances ranging from 5 pc to 150 pc along these sight-lines. We have detected a cloud of neutral and partially ionized gas with a velocity of −15 km s −1 and a hydrogen column density of log N(HI + HII) ∼ 19.3 cm −2 that is thought to define the boundary to the Local Bubble cavity at a distance of ∼90 pc in this galactic direction. The far neutral boundary to the Loop I superbubble cavity is also detected at a distance of 150−180 pc and is composed of two cold clouds moving at velocities close to V helio ∼ 0 km s −1 possessing a combined hydrogen column density of log N(HI + HII) 19.5 cm −2 . In contrast, we have also detected three low density, warm and partially ionized diffuse clouds with average velocities of ∼−10, −23 and −32 km s −1 , that are all located within a distance of ∼150 pc. The cloud component at V ∼ −23 km s −1 may be associated with the very local "G-cloud" at a distance of <5 pc, but we also provide evidence for its placement at a greater distance. The measured velocities of the majority of the gas clouds we have detected along all 4 sight-lines are consistent with an inflow of gas into the LB cavity from the direction of the Loop I superbubble. This gas is flowing through a region of fragmentation at a distance of ∼90 pc that represents the interaction region between the Loop I and Local Bubble cavities.

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IUE Absorption‐Line Observations of the Moderately and Highly Ionized Interstellar Medium toward 164 Early‐Type Stars

Cited by 43 publications

References 89 publications

FUSEDetermination of a Low Deuterium Abundance along an Extended Sight Line in the Galactic Disk

FUSEDetermination of a Low Deuterium Abundance along an Extended Sight Line in the Galactic Disk

Cii* Absorption in Damped Lyα Systems. II. A New Window on the Star Formation History of the Universe

Highly ionized gas in the local ISM: Some like it hot?

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