Opacity ratios for Doppler-broadened lines from common upper levels

Kastner, S. O.; Kastner, Ruth E.

doi:10.1016/0022-4073(90)90033-3

Cited by 36 publications

(27 citation statements)

References 15 publications

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“…There are two possible geometries that we will consider (see Kastner & Kastner 1990). The first requires a homogeneous distribution of emitters and absorbers.…”

Section: Methodsmentioning

confidence: 99%

Opacity in the upper atmosphere of AU Mic

Bloomfield

Mathioudakis

Christian

et al. 2002

A&A

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Abstract. In this paper we investigate the validity of the optically thin assumption in the transition region of the late-type star AU Mic. We use Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the C  multiplet and O  resonance lines, hence yielding information at two different levels within the atmosphere. Significant deviations from the optically thin fluxes are found for C  in both quiescent and flare spectra, where only 60% of the flux is actually observed. This could explain the apparent deviation of C  observed in emission measure distributions. We utilize escape probabilities for both homogeneous and inhomogeneous geometries and calculate optical depths as high as 10 for the C  1175.71 Å component of the multiplet. Using a lower limit to the electron density (10 11 cm −3 ) we derive an effective thickness of <100 km for the scattering layer. The emission originates from very small and compact regions, consistent with a filling factor of 10 −5 derived for the flare plasma.

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“…There are two possible geometries that we will consider (see Kastner & Kastner 1990). The first requires a homogeneous distribution of emitters and absorbers.…”

Section: Methodsmentioning

confidence: 99%

Opacity in the upper atmosphere of AU Mic

Bloomfield

Mathioudakis

Christian

et al. 2002

A&A

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“…(4) in Bloomfield et al 2002). For each of these two categories of line pairs, we consider both homogeneous and inhomogeneous distributions of emitters and absorbers (Kastner & Kastner 1990;Bloomfield et al 2002). The emitters and absorbers are spatially distinct in the inhomogeneous case.…”

Section: Line Ratio Constraints On Plasma Emission Sizementioning

confidence: 99%

Opacity in the upper atmospheres of active stars

Christian

Mathioudakis

Bloomfield

et al. 2006

A&A

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We present FUV and UV spectroscopic observations of AD Leonis, with the aim of investigating opacity effects in the transition regions of late-type stars. The C iii lines in FUSE spectra show significant opacity during both the quiescent and flaring states of AD Leonis, with up to 30% of the expected flux being lost during the latter. Other FUSE emission lines tested for opacity include those of O vi, while C iv, Si iv and N v transitions observed with stis are also investigated. These lines only reveal modest amounts of opacity with losses during flaring of up to 20%. Optical depths have been calculated for homogeneous and inhomogeneous geometries, giving path lengths of ≈20-60 km and ≈10-30 km, respectively, under quiescent conditions. However path lengths derived during flaring are ≈2-3 times larger. These values are in excellent agreement with both estimates of the small-scale structure observed in the solar transition region, and path lengths derived previously for several other active late-type stars.

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“…Resonance scattering of the Fe XVII lines should be fairly well modeled with a homogeneous mixture of absorbers and emitters, as discussed by Kastner & Kastner (1990), while scattering of O VII (not available in the FCS data) is better modeled as a "" light bulb imbedded in a fog. ÏÏ Each of these simple cases will still depend on the actual geometry of the source or of the source and the surrounding volume.…”

Section: Relative Opacities Of Other L Inesmentioning

confidence: 99%

“…For low opacities, where single scatterings dominate, a negligible fraction (of order 10~10) should be scattered back into the narrow Ðeld of view. Kastner & Kastner (1990) give the relationship between the single-Ñight (i.e., unscattered) escape probability, P, from a homogeneous mixture of emitters and absorbers and the corresponding optical depth at line center, for a Doppler broadened line as : q 0 ,…”

Section: Magnitude Of Fcs Emission-l Ine Resonance Scatteringmentioning

confidence: 99%

“…Further, the upper limit on optical depth for the FIG. 3.ÈPlot of single Ñight (i.e., unscattered) escape probability P vs. optical depth at line center for a homogeneous mixture of emitters and q 0 absorbers in a slab geometry ; plot created from a subset of data from Kastner & Kastner (1990 A from a dipole-allowed transition that should, in principle, be the most amenable to calculation of the Fe XVII lines considered (for optically thin emission). The 17.05 line A should be the next most tractable, since the spin is unchanging and the angular momentum changes by 1 (see Table 1).…”

Section: Magnitude Of Fcs Emission-l Ine Resonance Scatteringmentioning

confidence: 99%

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FexviiSoft X‐Ray Lines: Theory and Data Comparisons

Saba

Schmelz

Bhatia³

et al. 1999

ApJ

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Fe XVII soft X-ray spectral emission lines are examined using data from the Flat Crystal Spectrometer (FCS) on the Solar Maximum Mission satellite. Results are compared with theoretical calculations and with other recent observational results. Disparate Ðndings from di †erent studies on the inferred opacity of the bright resonance line at 15.01 and on its center-to-limb behavior are reviewed. Present limi-A tations on the use of resonance scattering to infer coronal plasma densities and absolute elemental abundances are discussed. An analysis is made of the temperature-insensitive ratio of the 15.01 line of A Fe XVII to the optically thin 16.78 line. This analysis shows that approximately half of the photons A expected in the 15.01 line are missing from the bright emission cores of quiescent active regions on the A solar disk ; the missing fraction increases at most by 50% near the solar limb. If the missing Ñux has been resonantly scattered out of the line of sight, then the equivalent optical depth at line center of the 15.01 line is on the disk, based on a simple escape probability treatment for a slab geometry. A q 0 D 2 This suggests that the e †ects of resonance scattering for other FCS lines, with the possible exception of the O VIII doublet at 18.97should be negligible for quiescent active region conditions. This is consis-A , tent with the lack of systematic center-to-limb dependence found previously for FCS lines other than Fe XVII at 15.01Y ohkoh Soft X-ray Telescope measurements of the expected lines of sight for active A . regions as a function of location on the solar disk, and resonance scattering results from other soft X-ray active region data sets all support a trend of increased opacity at the limb compared to disk center.

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Opacity ratios for Doppler-broadened lines from common upper levels

Cited by 36 publications

References 15 publications

Opacity in the upper atmosphere of AU Mic

Opacity in the upper atmosphere of AU Mic

Opacity in the upper atmospheres of active stars

FexviiSoft X‐Ray Lines: Theory and Data Comparisons

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