X‐Ray Spectroscopy of II Pegasi: Coronal Temperature Structure, Abundances, and Variability

Huenemoerder, David P.; Canizares, C. R.; Schulz, Norbert S.

doi:10.1086/322419

Cited by 97 publications

(137 citation statements)

References 37 publications

(45 reference statements)

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“…For short times, the luminosity can be several times higher; the flare of OID 7 emitted about 10 35 ergs. This is a typical size for RS CVn binaries (e.g., Maggio et al 2000;Huenemoerder et al 2001), but there have been flares 2 orders of magnitude larger (Ottmann & Schmitt 1994;Kuerster & Schmitt 1996). Perhaps the flare we missed in X-rays was of such a magnitude, given the large X-ray to EUV enhancement ratio we see near orbit 2.4 (see Fig.…”

Section: Discussionmentioning

confidence: 95%

The Coronae of AR Lacertae

Huenemoerder

Canizares

Drake

et al. 2003

ApJ

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We observed the coronally active eclipsing binary AR Lac with the High Energy Transmission Grating on Chandra for a total of 97 ks, spaced over five orbits, at quadratures and conjunctions. Contemporaneous and simultaneous EUV spectra and photometry were also obtained with the Extreme Ultraviolet Explorer. Significant variability in both X-ray and EUV fluxes were observed, dominated by at least one X-ray flare and one EUV flare. We saw no evidence of primary or secondary eclipses, but exposures at these phases were short and intrinsic variability compromised detection of any geometric modulation. X-ray flux modulation was largest at high temperature, indicative of flare heating of coronal plasma rather than changes in emitting volume or global emission measure. Analysis of spectral line widths interpreted in terms of Doppler broadening suggests that both binary stellar components are active. On the basis of line fluxes obtained from total integrated spectra, we have modeled the emission measure and abundance distributions. The EUV spectral line fluxes were particularly useful for constraining the parameters of the '' cool '' ( 2 Â 10 6 K) plasma. A strong maximum was found in the differential emission measure, characterized by two apparent peaks at log T ¼ 6:9 and 7.4, together with a weak but significant cooler maximum near log T ¼ 6:2 and a moderately strong hot tail from log T ¼ 7:6 8:2. Coronal abundances have a broad distribution and show no simple correlation with first ionization potential. While the resulting model spectrum generally agrees very well with the observed spectrum, there are some significant discrepancies, especially among the many Fe L lines. Both the emission measure and abundance distributions are qualitatively similar to prior determinations from other X-ray and ultraviolet spectra, indicating some long-term stability in the overall coronal structure.

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Section: Discussionmentioning

confidence: 95%

The Coronae of AR Lacertae

Huenemoerder

Canizares

Drake

et al. 2003

ApJ

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“…Phillips et al (1996Phillips et al ( , 1997 used SMM data to infer electron density and emitting path lengths for the 15.01 Å emission using photon escape probability techniques. More recent observations of the 15-17 Å lines in stellar spectra obtained with Chandra and XMM-Newton (Canizares et al 2000;Brinkman et al 2000;Huenemoerder et al 2001) also reveal discrepancies between observed and theoretical ratios involving these transitions.…”

Section: Optical Depths Of the Coronal Plasmamentioning

confidence: 94%

“…The abundance of aluminum is constrained by the resonance transition of the helium-like ion at 7.76 Å , which is a significant detection (4 in HEG and 7 in MEG) and suggests an enhanced aluminum abundance. We compared this region of the spectrum with other active binary spectra reported in the literature: Capella, HR 1099 (Ayres et al 2001), II Peg , and AR Lac (Huenemoerder, Canizares, & Tibbetts 2002), the last three having similar temperature distributions to 2 CrB, and thus the spectra should be comparable. There is no feature of moderate strength at 7.22 Å in any of these spectra.…”

Section: -(A)mentioning

confidence: 99%

“…Biases related to the analysis method could possibly explain some of the differences in the shapes of the derived DEMs. In active stars, the coronal iron abundance appears to be subsolar (Brinkman et al 2001;Gü del et al 2001b;Drake et al 2001;Huenemoerder et al 2001). Higher first ionization potential (FIP) elements appear to be enhanced relative to low-FIP elements Huenemoerder et al 2001;Brinkman et al 2001;Gü del et al 2001b).…”

Section: Introductionmentioning

confidence: 99%

“…In active stars, the coronal iron abundance appears to be subsolar (Brinkman et al 2001;Gü del et al 2001b;Drake et al 2001;Huenemoerder et al 2001). Higher first ionization potential (FIP) elements appear to be enhanced relative to low-FIP elements Huenemoerder et al 2001;Brinkman et al 2001;Gü del et al 2001b). Abundance increases during flares have been observed (Audard et al 2001b;Gü del et al 2001aGü del et al , 2001b with the largest changes in low-FIP elements, although there is another observation of a flare that did not show any appreciable increase in elemental abundances .…”

Section: Introductionmentioning

confidence: 99%

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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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Elemental Abundances in the Solar Corona

Raymond

2004

The Sun and the Heliosphere as an Integrated System

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X‐Ray Spectroscopy of II Pegasi: Coronal Temperature Structure, Abundances, and Variability

Cited by 97 publications

References 37 publications

The Coronae of AR Lacertae

The Coronae of AR Lacertae

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

Elemental Abundances in the Solar Corona

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X‐Ray Spectroscopy of II Pegasi: Coronal Temperature Structure, Abundances, and Variability

Cited by 97 publications

References 37 publications

The Coronae of AR Lacertae

The Coronae of AR Lacertae

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

Elemental Abundances in the Solar Corona

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Product

Resources

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