Small-scale interstellar medium structure: The remarkable sight line toward μ crucis

David M. Meyer; J. C. Blades

doi:10.1086/310111

Small-scale interstellar medium structure: The remarkable sight line toward μ crucis

David M. Meyer^*, J. C. Blades

^*Corresponding author for this work

Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

70 Scopus citations

Abstract

We present very high resolution (Δv ≈ 0.4 km s^-1) observations of the interstellar Na I D and Ca II K lines toward the binary μ Cru, which consists of two B stars separated by 38.8″ at a distance of 170 pc. These observations reveal line strength variations in four velocity components, indicative of interstellar medium structure on scales less than the projected binary separation of 6600 AU (0.03 pc). The components exhibiting the greatest Na I column density variations have the narrowest line widths and the largest N(Na I)/N(Ca II) ratios. The most visually striking of these variations involves a Na I component seen at a heliocentric velocity of -8.6 km s^-1 toward μ¹ Cru but not at all toward μ² Cru. This component has an appreciable column density [N(Na I) = 7 X 10¹⁰ cm^-2], and it clearly exhibits hyperfine splitting with a Na I line width (b = 0.4 km s^-1) indicative of a cloud temperature below 220 K. It is likely that the μ Cru variations are sampling a widespread pattern of small-scale structure in the cold diffuse interstellar gas that could easily have been missed in previous observations.

Original language	English (US)
Pages (from-to)	L179-L182
Journal	Astrophysical Journal
Volume	464
Issue number	2 PART II
DOIs	https://doi.org/10.1086/310111
State	Published - Jun 20 1996

Funding

It is a pleasure to thank Sean Ryan and the staff at the Anglo-Australian Observatory for their expert assistance with the observations. This work was supported in part by the National Science Foundation through grant AST 93-15728 to Northwestern University.

Keywords

ISM: clouds
ISM: structure

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.1086/310111

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@article{f557483c93f24092ab986023dccc9886,

title = "Small-scale interstellar medium structure: The remarkable sight line toward μ crucis",

abstract = "We present very high resolution (Δv ≈ 0.4 km s-1) observations of the interstellar Na I D and Ca II K lines toward the binary μ Cru, which consists of two B stars separated by 38.8″ at a distance of 170 pc. These observations reveal line strength variations in four velocity components, indicative of interstellar medium structure on scales less than the projected binary separation of 6600 AU (0.03 pc). The components exhibiting the greatest Na I column density variations have the narrowest line widths and the largest N(Na I)/N(Ca II) ratios. The most visually striking of these variations involves a Na I component seen at a heliocentric velocity of -8.6 km s-1 toward μ1 Cru but not at all toward μ2 Cru. This component has an appreciable column density [N(Na I) = 7 X 1010 cm-2], and it clearly exhibits hyperfine splitting with a Na I line width (b = 0.4 km s-1) indicative of a cloud temperature below 220 K. It is likely that the μ Cru variations are sampling a widespread pattern of small-scale structure in the cold diffuse interstellar gas that could easily have been missed in previous observations.",

keywords = "ISM: clouds, ISM: structure",

author = "Meyer, \{David M.\} and Blades, \{J. C.\}",

note = "Funding Information: It is a pleasure to thank Sean Ryan and the staff at the Anglo-Australian Observatory for their expert assistance with the observations. This work was supported in part by the National Science Foundation through grant AST 93-15728 to Northwestern University.",

year = "1996",

month = jun,

day = "20",

doi = "10.1086/310111",

language = "English (US)",

volume = "464",

pages = "L179--L182",

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T1 - Small-scale interstellar medium structure

T2 - The remarkable sight line toward μ crucis

AU - Meyer, David M.

AU - Blades, J. C.

N1 - Funding Information: It is a pleasure to thank Sean Ryan and the staff at the Anglo-Australian Observatory for their expert assistance with the observations. This work was supported in part by the National Science Foundation through grant AST 93-15728 to Northwestern University.

PY - 1996/6/20

Y1 - 1996/6/20

N2 - We present very high resolution (Δv ≈ 0.4 km s-1) observations of the interstellar Na I D and Ca II K lines toward the binary μ Cru, which consists of two B stars separated by 38.8″ at a distance of 170 pc. These observations reveal line strength variations in four velocity components, indicative of interstellar medium structure on scales less than the projected binary separation of 6600 AU (0.03 pc). The components exhibiting the greatest Na I column density variations have the narrowest line widths and the largest N(Na I)/N(Ca II) ratios. The most visually striking of these variations involves a Na I component seen at a heliocentric velocity of -8.6 km s-1 toward μ1 Cru but not at all toward μ2 Cru. This component has an appreciable column density [N(Na I) = 7 X 1010 cm-2], and it clearly exhibits hyperfine splitting with a Na I line width (b = 0.4 km s-1) indicative of a cloud temperature below 220 K. It is likely that the μ Cru variations are sampling a widespread pattern of small-scale structure in the cold diffuse interstellar gas that could easily have been missed in previous observations.

AB - We present very high resolution (Δv ≈ 0.4 km s-1) observations of the interstellar Na I D and Ca II K lines toward the binary μ Cru, which consists of two B stars separated by 38.8″ at a distance of 170 pc. These observations reveal line strength variations in four velocity components, indicative of interstellar medium structure on scales less than the projected binary separation of 6600 AU (0.03 pc). The components exhibiting the greatest Na I column density variations have the narrowest line widths and the largest N(Na I)/N(Ca II) ratios. The most visually striking of these variations involves a Na I component seen at a heliocentric velocity of -8.6 km s-1 toward μ1 Cru but not at all toward μ2 Cru. This component has an appreciable column density [N(Na I) = 7 X 1010 cm-2], and it clearly exhibits hyperfine splitting with a Na I line width (b = 0.4 km s-1) indicative of a cloud temperature below 220 K. It is likely that the μ Cru variations are sampling a widespread pattern of small-scale structure in the cold diffuse interstellar gas that could easily have been missed in previous observations.

KW - ISM: clouds

KW - ISM: structure

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JO - Astrophysical Journal

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IS - 2 PART II

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Small-scale interstellar medium structure: The remarkable sight line toward μ crucis

Abstract

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Keywords

ASJC Scopus subject areas

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