A Minisurvey of Interstellar Titanium from the Southern Hemisphere

Welsh, Barry Y.; Sasseen, T. P.; Craig, N.; Jelinsky, Sharon R.; Albert, C. E.

doi:10.1086/313044

Cited by 34 publications

(50 citation statements)

References 34 publications

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“…This sight-line has a NaI/CaII column density ratio of 7.8 (Welsh et al 1997), which is typical for many interstellar sight-lines. We propose that, given its proximity to the interface between the LB and Radio Loop I, this gas cloud is most probably associated with a local disruption of the neutral boundary between the two interstellar gas shells.…”

Section: Condensations Of Gas In the Cavitymentioning

confidence: 85%

3D mapping of the dense interstellar gas around the Local Bubble

Lallement

Welsh

Vergely

et al. 2003

A&A

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Abstract. We present intermediate results from a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, motivated by the availability of accurate and consistent parallaxes from the Hipparcos satellite. Equivalent widths of the interstellar NaI D-line doublet at 5890 Å are presented for the lines-of-sight towards some 311 new target stars lying within ∼350 pc of the Sun. Using these data, together with NaI absorption measurements towards a further ∼240 nearby targets published in the literature (for many of them, in the directions of molecular clouds), and the ∼450 linesof-sight already presented by , we show 3D absorption maps of the local distribution of neutral gas towards 1005 sight-lines with Hipparcos distances as viewed from a variety of different galactic projections. The data are synthesized by means of two complementary methods, (i) by mapping of iso-equivalent width contours, and (ii) by density distribution calculation from the inversion of column-densities, a method devised by Vergely et al. (2001). Our present data confirms the view that the local cavity is deficient in cold and neutral interstellar gas. The closest dense and cold gas "wall", in the first quadrant, is at ∼55-60 pc. There are a few isolated clouds at closer distance, if the detected absorption is not produced by circumstellar material. The maps reveal narrow or wide "interstellar tunnels" which connect the Local Bubble to surrounding cavities, as predicted by the model of Cox & Smith (1974). In particular, one of these tunnels, defined by stars at 300 to 600 pc from the Sun showing negligible sodium absorption, connects the well known CMa void , which is part of the Local Bubble, with the supershell GSH 238+00+09 (Heiles 1998). High latitude lines-of-sight with the smallest absorption are found in two "chimneys", whose directions are perpendicular to the Gould belt plane. The maps show that the Local Bubble is "squeezed" by surrounding shells in a complicated pattern and suggest that its pressure is smaller than in those expanding regions. We discuss the locations of several HI and molecular clouds. Using comparisons between NaI and HI or CO velocities, in some cases we are able to improve the constraints on their distances. According to the velocity criteria, MBM 33−37, MBM 16−18, UT 3−7, and MBM 54−55 are closer than ∼100 pc, and MBM 40 is closer than 80 pc. Dense HI clouds are seen at less than 90 pc and 85 pc in the directions of the MBM 12 and MBM 41−43 clouds respectively, but the molecular clouds themselves may be far beyond. The above closest molecular clouds are located at the neutral boundary of the Bubble. Only one translucent cloud, G192−67, is clearly embedded within the LB and well isolated. These maps of the distribution of local neutral interstellar NaI gas are also briefly compared with the distribution of both interstellar dust and neutral HI gas within 300 pc.

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Section: Condensations Of Gas In the Cavitymentioning

confidence: 85%

3D mapping of the dense interstellar gas around the Local Bubble

Lallement

Welsh

Vergely

et al. 2003

A&A

Self Cite

360

463

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“…At distances greatly exceeding 100 pc, Welsh et al (1997) note that the increase in column density is more associated with the number of clouds sampled along a particular sight-line as opposed to the actual distance. Figure 12a shows the Hipparcos parallax plotted against the log of the Ca ii K column density for all the objects in the current paper for which both quantities are available.…”

Section: The Parallax -Column Density Correlation For Ca II and Othermentioning

confidence: 96%

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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“…Because of the distance (∼156 pc) similar to that of WASP-18 (∼126 pc), κ Eri is the most interesting of the two stars. For this star, Welsh et al (1994) and Welsh et al (1997) reported ISM column densities for H I, Ca II, and Na I of log(N X [cm ]) = 19.58, 12.29±0.05, and 11.27, respectively. They also listed a E(B − V) value of 0.02 mag.…”

Section: Interstellar Extinctionmentioning

confidence: 99%

Suppressed Far-UV Stellar Activity and Low Planetary Mass Loss in the WASP-18 System*

Fossati

Koskinen

Cubillos

et al. 2018

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WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (<1 Gyr), the star presents an anomalously low stellar activity level: the measured log R ′ HK activity parameter lies slightly below the basal level; there is no significant time-variability in the log R ′ HK value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of Hubble Space Telescope aimed at explaining this anomaly. From the star's spectral energy distribution, we infer the extinction (E(B − V) ≈ 0.01 mag) and then the interstellar medium (ISM) column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C II, C III, C IV, Si IV). Comparing the C II/C IV flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5 Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star-planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si IV line, yields an XUV integrated flux at the planet orbit of 10.2 erg s . For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape.

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A Minisurvey of Interstellar Titanium from the Southern Hemisphere

Cited by 34 publications

References 34 publications

3D mapping of the dense interstellar gas around the Local Bubble

3D mapping of the dense interstellar gas around the Local Bubble

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

Suppressed Far-UV Stellar Activity and Low Planetary Mass Loss in the WASP-18 System*

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