The interstellar Ca II distance scale

Megier, A.; Strobel, A.; Галазутдинов, Г. А.; Krełowski, J.

doi:10.1051/0004-6361/20079144

Cited by 86 publications

(121 citation statements)

References 41 publications

(46 reference statements)

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“…Authors including Beals & Oke (1953), Megier et al (2005Megier et al ( , 2009) and Welsh et al (2010) find a slowly-increasing Ca ii equivalent width with increasing distance, although with a large scatter. 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.…”

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

confidence: 96%

“…Authors such as Megier et al (2009) these observations are used with archive data to investigate the parallax -column density relationship for Ca ii K.…”

Section: Feros and Uves Archive Data Towards The Magellanic Systemmentioning

confidence: 99%

“…Additionally, we have used results from Sembach et al (1993);Hunter et al (2006) and Smoker et al (2011a,b) to produce a sample of 125 sightlines with parallaxes ranging from ∼11 mas down to zero. Superimposed on the plot is the best-fit line from Megier et al (2009) which has the form π = 1/(2.29 × 10 −13 × N CaII + 0.77) (n = 262), where N CaII is in cm −2 . At small distances (large values of parallax), the equation from Megier et al predicts larger parallaxes at a given log(N CaII ) than observed in our present dataset, ranging from a ∼25 per cent difference at 100 pc distance, to ∼15 per cent at 200 pc.…”

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

confidence: 99%

“…More recently, Megier et al (2005Megier et al ( , 2009) have compared the strength of the Ca ii K interstellar absorption with distances from the Hipparcos catalogue (ESA 1997) and open cluster distances to determine whether the line strength can be used to estimate distances to faraway objects. They found several cases of significant column density difference in the interstellar component of stars in the same cluster or association, but were unable to determine whether this was caused by a local contribution to the derived profiles, or by background or foreground stars being misclassified as cluster objects.…”

Section: Introductionmentioning

confidence: 99%

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

confidence: 96%

“…Authors such as Megier et al (2009) these observations are used with archive data to investigate the parallax -column density relationship for Ca ii K.…”

Section: Feros and Uves Archive Data Towards The Magellanic Systemmentioning

confidence: 99%

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

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…The H parallax (van Leeuwen 2007) is π = 4.54 ± 0.2 millisecond of arc (mas), which gives a distance d = 220 ± 10 pc. Using the interstellar Ca II distance scale, Megier et al (2009) estimate a distance of d = 195 ± 32 pc.…”

Section: Main Characteristics Of ϕ Perseimentioning

confidence: 99%

Spectral and spatial imaging of the Be+sdO binaryϕPersei

Mourard

Monnier

Meilland

et al. 2015

A&A

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Aims. The rapidly rotating Be star ϕ Persei was spun up by mass and angular momentum transfer from a now stripped-down, hot subdwarf companion. Here we present the first high angular resolution images of ϕ Persei made possible by new capabilities in longbaseline interferometry at near-IR and visible wavelengths. We analyzed these images to search for the companion, to determine the binary orbit, stellar masses, and fluxes, and to examine the geometrical and kinematical properties of the outflowing disk surrounding the Be star. Methods. We observed ϕ Persei with the MIRC and VEGA instruments of the CHARA Array. MIRC was operated in six-telescope mode, whereas VEGA was configured in four-telescope mode with a change of quadruplets of telescopes during two nights to improve the (u, v) plane coverage. Additional MIRC-only observations were performed to track the orbital motion of the companion, and these were fit together with new and existing radial velocity measurements of both stars to derive the complete orbital elements and distance. We also used the MIRC data to reconstruct an image of the Be disk in the near-IR H-band. VEGA visible broadband and spectro-interferometric Hα observations were fit with analytical models for the Be star and disk, and image reconstruction was performed on the spectrally resolved Hα emission line data. Results. The hot subdwarf companion is clearly detected in the near-IR data at each epoch of observation with a flux contribution of 1.5% in the H band, and restricted fits indicate that its flux contribution rises to 3.3% in the visible. A new binary orbital solution is determined by combining the astrometric and radial velocity measurements. The derived stellar masses are 9.6 ± 0.3 M and 1.2 ± 0.2 M for the Be primary and subdwarf secondary, respectively. The inferred distance (186 ± 3 pc), kinematical properties, and evolutionary state are consistent with membership of ϕ Persei in the α Per cluster. From the cluster age we deduce significant constraints on the initial masses and evolutionary mass transfer processes that transformed the ϕ Persei binary system. The interferometric data place strong constraints on the Be disk elongation, orientation, and kinematics, and the disk angular momentum vector is coaligned with and has the same sense of rotation as the orbital angular momentum vector. The VEGA visible continuum data indicate an elongated shape for the Be star itself, due to the combined effects of rapid rotation, partial obscuration of the photosphere by the circumstellar disk, and flux from the bright inner disk.

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