Ca II K interstellar observations towards early-type disc and halo stars

Smoker, J. V.; Rolleston, W. R. J.; Kay, H.R.M.; Kilkenny, D.; Morras, R.; Arnal, Michelle; Keenan, F. P.; Mooney, C. J.; Dufton, P. L.; Ryans, R.; Hambly, N. C.; O’Donoghue, D.; McGillivray, H.T.

doi:10.1046/j.1365-2966.2003.07074.x

Cited by 21 publications

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References 59 publications

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“…There seems to be a clear distinction between the large, 21-cm selected HVC complexes and the much lower mass clouds that dominate optical and uv surveys toward distant halo stars, described by Wakker, Ben-Bekhti, Nasoudi-Shoar, and Fox, and earlier by Smoker et al (2003), Lockman & Savage (1995), and see the historical data discussed by Benjamin & Danly (1997). The clouds seen in these surveys are similar to clouds seen in extragalactic absorption studies; at least some of them are classical fountain-return clouds.…”

Section: Theme -Structures In the Mw Halomentioning

confidence: 86%

Conference Summary: Themes and Questions about the Disk-Halo Interaction

Dickey

2012

EAS Publications Series

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The papers in this volume represent a broad spectrum of observational, theoretical, and computational astrophysics, sharing as a unifying core the Disk-Halo Interaction in the Milky Way and other spiral galaxies. This topic covers a wide range of Galactic and extragalactic research, built on a foundation of numerous and diverse physical processes. This summary groups the papers according to six themes, with some historical background and finally a look to the future. The final message is that the astrophysical techniques discussed and reviewed at this conference will grow over the next decade to answer even more fundamental questions about galaxy evolution and the history of the universe.c EDP Sciences 2018 DOI: (will be inserted later)

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Section: Theme -Structures In the Mw Halomentioning

confidence: 86%

Conference Summary: Themes and Questions about the Disk-Halo Interaction

Dickey

2012

EAS Publications Series

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The interstellar Ca II distance scale

Megier

Strobel

Галазутдинов

et al. 2009

A&A

100

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Aims. We attempt to extend the relation between the strengths of the interstellar Ca ii lines and the distances to early-type stars to objects beyond 1 kiloparsec, with the line saturation taken into account.Methods. We measure the Ca ii K and Ca ii H equivalent widths, and compute Ca ii column densities for 262 lines of sight towards early-type stars with available Hipparcos parallaxes (π). The targets are located within a few hundred parsecs of the Galactic plane, and span all the range of Galactic longitudes. We fit the N Ca ii -parallax relation with a function of the form π = 1/(a · N Ca ii + b), using a maximum-likelihood approach to take account of errors in both variables. We use the resultant formula to estimate distances to stars in OB associations and clusters, and compare them to those found in the literature, usually estimated by spectrophotometric methods. 1.3, we obtain the following approximate formula for the distance: D Ca ii = 77 + (2.78 + Results. For lines of sight with EW(K)/EW(H) > EW(K) EW(H) −0.932 )EW(H), where the equivalent widths EW(K) and EW(H) are in mÅ, and the distance D Ca ii in parsecs.The errors in D Ca ii , resulting from the uncertainty in the fit parameters and errors in the equivalent widths, are typically about 15% of the distance. We can also expect the equation not to hold for objects situated farther than a few hundred parsecs from the Galactic plane. We find several cases of significant column density differences between association or cluster members, especially notable in the Trumpler 16 cluster, indicating either a local contribution to the Ca ii column density, or background/foreground stars being confused with members. The ratio D Ca ii /D assoc appears to depend on the Galactic longitude, being highest in the range 70 • < l < 120 • and lowest for 200 • < l < 300 • . This effect may be due to large-scale structure being present in the Ca ii layer, or to the nonmember confusion being enhanced in these directions.

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The large- and small-scale Ca II K structure of the Milky Way from observations of Galactic and Magellanic sightlines

Smoker

Keenan

2015

A&A

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Aims. The large and small-scale (pc) structure of the Galactic interstellar medium can be investigated by utilising spectra of earlytype stellar probes of known distances in the same region of the sky. This paper determines the variation in line strength of Ca ii at 3933.661 Å as a function of probe separation for a large sample of stars, including a number of sightlines in the Magellanic Clouds. Methods. FLAMES-GIRAFFE data taken with the Very Large Telescope towards early-type stars in 3 Galactic and 4 Magellanic open clusters in Ca ii are used to obtain the velocity, equivalent width, column density, and line width of interstellar Galactic calcium for a total of 657 stars, of which 443 are Magellanic Cloud sightlines. In each cluster there are between 43 and 111 stars observed.Additionally, FEROS and UVES Ca ii K and Na i D spectra of 21 Galactic and 154 Magellanic early-type stars are presented and combined with data from the literature to study the calcium column density -parallax relationship.Results. For the four Magellanic clusters studied with FLAMES, the strength of the Galactic interstellar Ca ii K equivalent width on transverse scales from ∼0.05−9 pc is found to vary by factors of ∼1.8−3.0, corresponding to column density variations of ∼0.3−0.5 dex in the optically-thin approximation. Using FLAMES, FEROS, and UVES archive spectra, the minimum and maximum reduced equivalent widths for Milky Way gas are found to lie in the range ∼35−125 mÅ and ∼30−160 mÅ for Ca ii K and Na i D, respectively.The range is consistent with a previously published simple model of the interstellar medium consisting of spherical cloudlets of filling factor ∼0.3, although other geometries are not ruled out. Finally, the derived functional form for parallax (π) and Ca ii column density (N CaII ) is found to be π(mas) = 1/(2.39 × 10 −13 × N CaII (cm −2 ) + 0.11). Our derived parallax is ∼25 per cent lower than predicted by Megier et al. (2009, A&A, 507, 833) at a distance of ∼100 pc and ∼15 percent lower at a distance of ∼200 pc, reflecting inhomogeneity in the Ca ii distribution in the different sightlines studied.

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Ca II K interstellar observations towards early-type disc and halo stars

Cited by 21 publications

References 59 publications

Conference Summary: Themes and Questions about the Disk-Halo Interaction

Conference Summary: Themes and Questions about the Disk-Halo Interaction

The interstellar Ca II distance scale

The large- and small-scale Ca II K structure of the Milky Way from observations of Galactic and Magellanic sightlines

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