The Sun as an X‐Ray Star. II. Using the<i>Yohkoh</i>/Soft X‐Ray Telescope–derived Solar Emission Measure versus Temperature to Interpret Stellar X‐Ray Observations

Peres, G.; Orlando, S.; Reale, F.; Rosner, R.; Hudson, H. S.

doi:10.1086/308136

Cited by 183 publications

(215 citation statements)

References 21 publications

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“…These temperatures are significantly higher than those obtained for the hot component in our analysis. Part of this discrepancy might be explained by the different sensitivity of the instruments, due to the different spectral band, that would lead the instruments to be sensitive to different parts a broad emission measure distribution (Peres et al 2000;Hannah et al 2011). The average emission measure obtained from thermal fitting of RHESSI microflares is about 2−3 × 10 46 cm −3 , which is much larger than the emission measure of the hot components that we obtain.…”

Section: Discussioncontrasting

confidence: 64%

X-ray emitting hot plasma in solar active regions observed by the SphinX spectrometer

Miceli

Reale

Gburek

et al. 2012

A&A

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Aims. The detection of very hot plasma in the quiescent corona is important for diagnosing heating mechanisms. The presence and the amount of such hot plasma is currently debated. The SphinX instrument on-board the CORONAS-PHOTON mission is sensitive to X-ray emission of energies well above 1 keV and provides the opportunity to detect the hot plasma component. Methods. We analysed the X-ray spectra of the solar corona collected by the SphinX spectrometer in May 2009 (when two active regions were present). We modelled the spectrum extracted from the whole Sun over a time window of 17 days in the 1.34−7 keV energy band by adopting the latest release of the APED database. Results. The SphinX broadband spectrum cannot be modelled by a single isothermal component of optically thin plasma and two components are necessary. In particular, the high statistical significance of the count rates and the accurate calibration of the spectrometer allowed us to detect a very hot component at ∼7 million K with an emission measure of ∼2.7 × 10 44 cm −3 . The X-ray emission from the hot plasma dominates the solar X-ray spectrum above 4 keV. We checked that this hot component is invariably present in both the high and low emission regimes, i.e. even excluding resolvable microflares. We also present and discuss the possibility of a non-thermal origin (which would be compatible with a weak contribution from thick-target bremsstrahlung) for this hard emission component. Conclusions. Our results support the nanoflare scenario and might confirm that a minor flaring activity is ever-present in the quiescent corona, as also inferred for the coronae of other stars.

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Section: Discussioncontrasting

confidence: 64%

X-ray emitting hot plasma in solar active regions observed by the SphinX spectrometer

Miceli

Reale

Gburek

et al. 2012

A&A

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“…The intrinsic quiescent X-ray luminosity in LkHα 312 is 6 × 10 30 erg s −1 in the Chandra band (0.5-8 keV) and probably ∼10 31 erg s −1 in a full bolometric X-ray band. In contrast, the bolometric X-ray luminosity of the non-flaring solar corona is only 3 × 10 27 erg s −1 during solar minimum to 3 × 10 28 erg s −1 during solar maximum (Peres et al 2000). Note that the surface area of LkHα 312 is only 6.8 times that of the Sun (see Sect.…”

Section: Quiescent Emissionmentioning

confidence: 95%

“…5.2.1, Table 4). In contrast, the non-flaring solar corona has average (weighted over the emission measure) temperature of ∼2 MK (Peres et al 2000). The intrinsic quiescent X-ray luminosity in LkHα 312 is 6 × 10 30 erg s −1 in the Chandra band (0.5-8 keV) and probably ∼10 31 erg s −1 in a full bolometric X-ray band.…”

Section: Quiescent Emissionmentioning

confidence: 99%

Chandra observation of an unusually long and intense X-ray flare from a young solar-like star in M 78

Grosso

Montmerle

Feigelson

et al. 2004

A&A

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Abstract. LkHα 312 has been observed serendipitously with the ACIS-I detector on board the Chandra X-ray Observatory with a 26 h continuous exposure. This Hα emission line star belongs to M 78 (NGC 2068), one of the star-forming regions of the Orion B giant molecular cloud at a distance of 400 pc. From the optical and the near-infrared (NIR) data, we show that LkHα 312 is a pre-main sequence (PMS) low-mass star with a weak NIR excess. This genuine T Tauri star displayed an X-ray flare with an unusually long rise phase (∼8 h). The X-ray emission was nearly constant during the first 18 h of the observation, and then increased by a factor of 13 during a fast rise phase (∼2 h), and reached a factor of 16 above the quiescent X-ray level at the end of a gradual phase (∼6 h) showing a slower rise. To our knowledge this flare, with ∼0.4-0.5 cts s −1 , has the highest count rate observed so far with Chandra from a PMS low-mass star. By chance, the source position, 8.2 off-axis, protected this observation from pile-up. We make a spectral analysis of the X-ray emission versus time, showing that the plasma temperature of the quiescent phase and the flare peak reaches 29 MK and 88 MK, respectively. The quiescent and flare luminosities in the energy range 0.5-8 keV corrected from absorption (N H ≈ 1.7 × 10 21 cm −2 ) are 6 × 10 30 erg s −1 and ∼10 32 erg s −1 , respectively. The ratio of the quiescent X-ray luminosity on the LkHα 312 bolometric luminosity is very high with log(L X /L bol ) = −2.9, implying that the corona of LkHα 312 reached the "saturation" level. The X-ray luminosity of the flare peak reaches ∼2% of the stellar bolometric luminosity. The different phases of this flare are finally discussed in the framework of solar flares, which leads to the magnetic loop height from 3.1 × 10 10 to 10 11 cm (0.2-0.5 R , i.e., 0.5-1.3 R ).

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“…7 shows a comparison of its EMD distribution vs. temperature (Method 1) with those of other four G-K stars: the Sun (G2V, Peres et al 2000), κ 1 Ceti (G5V, Telleschi et al 2005), Eri (K2V, Sanz-Forcada et al 2004), andHD 283572 (G2IV, Scelsi et al 2005).…”

Section: τ Boo: a Medium-activity Coronal Sourcementioning

confidence: 99%

Photospheric and coronal abundances in solar-type stars: the peculiar case ofτ Bootis

Maggio

Sanz-Forcada

2011

A&A

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Aims. Chemical abundances in solar-type stars are still a much debated topic in many respects. In particular, planet-hosting stars are known to be metal-rich, but whether or not this peculiarity applies also to the chemical composition of the outer stellar atmospheres is still to be clarified. More in general, coronal and photospheric abundances in late-type stars appear to be different in many cases, but understanding how chemical stratification effects work in stellar atmospheres requires an observational base larger than currently available. Methods. We obtained XMM-Newton high-resolution X-ray spectra of τ Bootis, a well known nearby star with a Jovian-mass close-in planet. We analyzed these data with the aim to perform a detailed line-based emission measure analysis and derive the abundances of individual elements in the corona with two different methods applied independently. We compared the coronal abundances of τ Bootis with published photospheric abundances based on high-resolution optical spectra and with those of other late-type stars with different magnetic activity levels, including the Sun. Results. We find that the two methods provide consistent results within the statistical uncertainties for both the emission measure distribution of the hot plasma and for the coronal abundances, with discrepancies at the 2σ level limited to the amount of plasma at temperatures of 3-4 MK and to the O and Ni abundances. In both cases, the elements for which both coronal and photospheric measurements are available (C, N, O, Si, Fe, and Ni) result systematically less abundant in the corona by a factor 3 or more, with the exception of the coronal Ni abundance which is similar to the photospheric value. Comparison with other late-type stars of similar activity level shows that these coronal/photospheric abundance ratios are peculiar to τ Bootis and possibly related to the characteristic over-metallicity of this planet-hosting star.

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The Sun as an X‐Ray Star. II. Using theYohkoh/Soft X‐Ray Telescope–derived Solar Emission Measure versus Temperature to Interpret Stellar X‐Ray Observations

Cited by 183 publications

References 21 publications

X-ray emitting hot plasma in solar active regions observed by the SphinX spectrometer

X-ray emitting hot plasma in solar active regions observed by the SphinX spectrometer

Chandra observation of an unusually long and intense X-ray flare from a young solar-like star in M 78

Photospheric and coronal abundances in solar-type stars: the peculiar case ofτ Bootis

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