Fe<scp>xvii</scp>Soft X‐Ray Lines: Theory and Data Comparisons

Saba, J. L. R.; Schmelz, J. T.; Bhatia, A. K.; Strong, K. T.

doi:10.1086/306590

Cited by 61 publications

(59 citation statements)

References 19 publications

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“…Several investigations of solar active region and flare spectra in the 15-17 Å region indicate anomalously low observed line fluxes in strong transitions of Fe xvii, compared to the values predicted assuming effectively thin, coronal conditions. For example, Saba et al (1999) analyzed Flat Crystal Spectrometer data from SMM and Fig. 14.-Temperatures from helium-like triplet ratios in the Chandra quiescent spectra, tabulated for different electron densities (from Porquet et al 2001). Observed values of the ratios are dotted lines; 1 error bars are full lines.…”

Section: Optical Depths Of the Coronal Plasmamentioning

confidence: 99%

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis

Osten

Ayres

Brown

et al. 2003

ApJ

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We present the results of a coordinated observing campaign on the short-period RS CVn binary 2 Coronae Borealis (F6V þ G0V; P orb ¼ 1:14 days) with the Very Large Array, the Extreme Ultraviolet Explorer, and the Chandra X-Ray Observatory High-Energy Transmission Grating Spectrometer. The radio emission is consistent with previously determined quiescent gyrosynchrotron properties. Multiple flares were seen with Extreme Ultraviolet Explorer, five occurring within two consecutive orbital periods. The first of these flares was observed with Chandra. The Chandra observations of 2 CrB showed no systematic variations of line fluxes, widths, or Doppler shifts with orbital phase, nor any response in line width or offset due to the flare. This is consistent with both stars being equally active coronal emitters. We have developed a self-consistent method of spectral analysis to derive information from the line and continuum emissions concerning the distribution of plasma with temperature and elemental abundances. A bimodal temperature distribution is appropriate for both quiescent and flare intervals, with a stable peak at 6-8 MK and another variable enhancement at higher temperatures, with evidence for significant contribution from temperatures up to 50 MK during the flare, compared to 30 MK during quiescence. The iron abundance is subsolar during quiescence but is enriched by about a factor of 2 during a large flare seen with Chandra. The noble gas elements neon and argon show elevated abundances with respect to iron, but there is no clear evidence for any first ionization potential-based abundance pattern during quiescence or the flare. We have determined coronal electron densities from the helium-like ions O vii, Ne ix, Mg xi, and Si xiii, which imply densities !10 10 cm À3 . There is a small enhancement in the electron densities derived for the flare, but it is not statistically significant. We call attention to electron temperature constraints provided by the ratios of 1s 2 1 S 0 -1snp 1 P 1 transitions of the helium-like ions O vii, Ne ix, Mg xi, and Si xiii. The derived coronal electron pressures change by 1-2 orders of magnitude over a 25% change in temperature, implying nonisobaric coronal conditions. We find no evidence for significant departures from the effectively thin coronal assumption. The electron densities inferred from the soft X-ray spectra are inconsistent with cospatial gyrosynchrotron emission; further observations are necessary to discriminate the relative locations of the radio and soft X-ray-emitting plasma.

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Section: Optical Depths Of the Coronal Plasmamentioning

confidence: 99%

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis

Osten

Ayres

Brown

et al. 2003

ApJ

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“…7, where the different ratios can be recognized. In order to compare our measurements with solar measurements we include the solar measurements from Saba et al (1999) in the form of shaded areas in Figs. 3 and 4.…”

Section: Fe XVII Line Ratiosmentioning

confidence: 99%

“…They found differences between theoretical and observed values of the temperature sensitive G-ratio ( f + i)/r (Gabriel & Jordan 1969) and interpreted these differences as being due to resonant scattering effects. Schmelz et al (1997) and Saba et al (1999) measured five different line ratios and found significant optical depths only for the Fe  line at 15.03 Å ( 1 S 0 → 1 P 1 with a high oscillator strength f = 2.66). They compared the 15.03 Å line flux with line flux measurements for Fe  lines with lower oscillator strengths, namely two intercombination lines 1 S 0 → 3 D 1 at 15.27 Å with f = 0.593 and 1 S 0 → 3 P 1 at 16.78 Å with f = 0.1.…”

Section: Introductionmentioning

confidence: 99%

Are stellar coronae optically thin in X-rays?

Ness

Schmitt

Audard

et al. 2003

A&A

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Abstract. The relevance of resonant scattering in the solar corona has always been discussed controversially. Ratios of emission lines from identical ions but different oscillator strengths have been used in order to estimate damping of resonance lines due to possible resonant scattering, i.e., absorption by photo-excitation and re-emission out of the line of sight. The analysis of stellar spectra in analogy to previous works for the Sun is possible now with XMM-Newton and Chandra grating spectra and requires this issue to be considered again. In this work we present a sample of 45 X-ray spectra obtained for 26 stellar coronae with the RGS on board XMM-Newton and the LETGS and HETGS on board Chandra. We use ratios of the Fe  lines at 15.27 Å and 16.78 Å lines to the resonance line at 15.03 Å as well as the He-like f /r ratio of O  and Ne  to measure optical depth effects and compare them with ratios obtained from optically thin plasma atomic databases such as MEKAL, Chianti, and APEC. From the Fe  line ratios we find no convincing proof for resonance line scattering. Optical depths are basically identical for all kinds of stellar coronae and we conclude that identical optical depths are more probable when effects from resonant scattering are generally negligible. The 15.27/15.03 Å ratio shows a regular trend suggesting blending of the 15.27 Å line by a cooler Fe line, possibly Fe . The He-like f /r ratios for O and Ne show no indication for significant damping of the resonance lines. We mainly attribute deviations from the atomic databases to still uncertain emissivities which do not agree well with laboratory measurements and which come out with differing results when accounting for one or the other side effect. We attribute the discrepancies in the solar data to geometrical effects from observing individual emitting regions in the solar corona but only overall emission for stellar coronae including photons eventually scattered into the line of sight.

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“…2e and f. In stellar coronal observations there is a large discrepancy of their line intensities, relative to that of the 3d−2p transitions, between the observations and theoretical predictions for Fe XVII−XIX (Desai et al 2005). Some authors (Schrijver et al 1994;Schmelz et al 1997;Saba et al 1999;Mewe et al 2001) explain this as being due to stronger opacities in observations of stellar coronae for these strong 3d−2p transitions than for transitions with small g f -values. Here (see Fig.…”

Section: Chandra Letg Observationmentioning

confidence: 95%

R-matrix electron-impact excitation data for B-like Si and its application in cool stars

Liang

Whiteford

Badnell³

2009

A&A

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We present the results of an intermediate coupling frame-transformation R-matrix calculation for the electron-impact excitation of Si 9+ . The target and close-coupling expansions are both taken to be the 125 fine-structure levels (58 LS terms) belonging to the configurations 2s x 2p y (x + y = 3) and 2s α 2p β 3l (α+ β = 2, l = s, p, and d). Due to the additional resonances included in our calculation, we find significant differences at low temperatures with the widely used n = 2 → 2 excitation rates, also obtained with the R-matrix method, as well as with the n = 2 → 3 excitation rates calculated by using the distorted wave (DW) approximation. We present a list of prominent transition lines and comparisons with SERTS and Hinode/EIS EUV spectra of the solar corona, SUMER observations for the quiet sun, as well as Chandra LETG and Rocket soft X-ray spectra of the Procyon corona and solar flares, respectively. Line emissivities of some transitions are enhanced up to 40% when compared with those obtained from using the previous atomic data at the same electron density (1.6 × 10 9 cm −3 ) and temperature (1.3 × 10 6 K). The comparison with Chandra LETG observation of Procyon reveals that the 3s−2p line flux was significantly underestimated (by a factor of 4−5) in previous analyses. Some EUV and soft X-ray emission line ratios are n e -sensitive and T e -insensitive. Estimated electron densities from them shift downwards due to the new resonant-enhanced excitation data used in the present modelling.

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FexviiSoft X‐Ray Lines: Theory and Data Comparisons

Cited by 61 publications

References 19 publications

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis

Are stellar coronae optically thin in X-rays?

R-matrix electron-impact excitation data for B-like Si and its application in cool stars

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FexviiSoft X‐Ray Lines: Theory and Data Comparisons

Cited by 61 publications

References 19 publications

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ2Coronae Borealis

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ2Coronae Borealis

Are stellar coronae optically thin in X-rays?

R-matrix electron-impact excitation data for B-like Si and its application in cool stars

Contact Info

Product

Resources

About

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis

Chandra,Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ²Coronae Borealis