X-ray spectroscopy of stars

Güdel, M.; Nazé, Yaël

doi:10.1007/s00159-009-0022-4

Cited by 278 publications

(300 citation statements)

References 375 publications

(685 reference statements)

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“…Following this activity-dependence scenario (see e.g. Güdel & Nazé 2009), an abundance ratio Ne/Fe ∼ 0.25 (with respect to the photospheric value) is expected for Sun-like stars, while Ne/Fe ∼ 5-10 in very active stars. An intermediate activity star with an EMD similar to those of τ Boo, Eri, and κ 1 Cet, should display Ne/Fe ∼ 1.…”

Section: τ Boo: a Medium-activity Coronal Sourcementioning

confidence: 83%

“…For the solar corona, and in particular in long-lived coronal structures, the composition of the plasma appears enriched with elements having low first ionization potentials (FIP < 10 eV) by about a factor 4, on average, with respect to photospheric values (Feldman & Laming 2000). In other stars a more complex behavior has been observed (Güdel & Nazé 2009), with a tendency for the low-FIP elements (including iron) to become depleted with respect to the high-FIP elements (neon in particular) in extremely active RS CVn-type and Algol-type binaries. Several theoretical explanations have been proposed, but our understanding is still largely driven by the observations, which indicate a dependence of the coronal/photospheric abundance ratios on the stellar magnetic activity level (Robrade et al 2008) or on the spectral type (Wood & Linsky 2010).…”

Section: Introductionmentioning

confidence: 99%

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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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Section: τ Boo: a Medium-activity Coronal Sourcementioning

confidence: 83%

Section: Introductionmentioning

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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“…In a colliding wind binary, variations of the flux, correlated with orbital phase, are expected to arise from changes in the separation (in eccentric systems) and/or in the absorbing column (when the winds are different). Indeed, such variations have been observed in several systems (for a review, see Güdel & Nazé 2009). In HD 191612, the previous observations, taken before periastron, revealed a 20% change in reddening-corrected flux (see Table 2) for a phase difference Δφ orb of only 0.12, corresponding to a change in separation of 36%.…”

Section: X-ray Datamentioning

confidence: 96%

New findings on the prototypical Of?p stars

Nazé¹,

ud‐Doula

Spano

et al. 2010

A&A

111

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Aims. In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken. These multiwavelength studies revealed the peculiar properties of these objects (in the X-rays as well as in the optical): magnetic fields, periodic line profile variations, recurrent photometric changes. However, many questions remain unsolved.Methods. To clarify some of the properties of the Of?p stars, we have continued their monitoring. A new xmm-Newton observation and two new optical datasets were obtained. Results. Additional information about the prototypical Of?p trio has been found. HD 108 has now reached its quiescent, minimumemission state for the first time in 50-60 yr. The échelle spectra of HD 148937 confirm the presence of the 7d variations in the Balmer lines and reveal similar periodic variations (though of lower amplitudes) in the He i λ 5876 and He ii λ 4686 lines, underlining its similarities with the other two prototypical Of?p stars. The new xmm-Newton observation of HD 191612 was taken at the same phase in the line modulation cycle, but at a different orbital phase from previous data. It clearly shows that the X-ray emission of HD 191612 is modulated by the 538d period and not by the orbital period of 1542d -it is thus not of colliding-wind origin. The phenomenon responsible for the optical changes appears also at work in the high-energy domain. There are problems however: our MHD simulations of the wind magnetic confinement predict both a harder X-ray flux of a much larger strength than what is observed (the modelled differential emission measure peaks at 30-40 MK, whereas the observed one peaks at 2 MK) and narrow lines (hot gas moving with velocities of 100-200 km s −1 , whereas the observed full width at half maximum is ∼2000 km s −1 ).

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“…In most cases, two thermal components are required to satisfactorily represent the observed energy distribution (see a recent review in Güdel & Nazé 2009). X-ray studies of open clusters and field stars of different ages led to a relatively coherent picture linking stellar rotation rates, overall X-ray luminosity and X-ray temperatures.…”

Section: X-ray Active Starsmentioning

confidence: 99%

Cross-correlation of the 2XMMi catalogue with Data Release 7 of the Sloan Digital Sky Survey

Pineau

Motch

Carrera

et al. 2011

A&A

102

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The Survey Science Centre of the XMM-Newton satellite released the first incremental version of the 2XMM catalogue in August 2008. Containing more than 220 000 X-ray sources, the 2XMMi was at that time the largest catalogue of X-ray sources ever published and thus constitutes an unprecedented resource for studying the high-energy properties of various classes of X-ray emitters such as AGN and stars. Thanks to the high throughput of the EPIC cameras on board XMM-Newton accurate positions, fluxes, and hardness ratios are available for a substantial fraction of the X-ray detections. The advent of the 7th release of the Sloan Digital Sky Survey offers the opportunity to cross-match two major surveys and extend the spectral energy distribution of many 2XMMi sources towards the optical bands. This implies building extensive homogeneous samples with a statistically controlled rate of spurious matches and completeness. We here present a cross-matching algorithm based on the classical likelihood ratio estimator. The method developed has the advantage of providing true probabilities of identifications without resorting to heavy Monte-Carlo simulations. Over 30,000 2XMMi sources have SDSS counterparts with individual probabilities of identification higher than 90%. At this threshold, the sample has only 2% spurious matches and contains 77% of all expected SDSS identifications. Using spectroscopic identifications from the SDSS DR7 catalogue supplemented by extraction from other catalogues, we build an identified sample from which the way the various classes of X-ray emitters gather in the multi dimensional parameter space can be analysed and later used to design a source classification scheme. We illustrate the interest of this clean source sample by investigating two scientific use cases. In the first example we show how these multi-wavelength data can be used to search for new QSO2s. Although no specific range of observed properties allows us to efficiently identify Compton Thick QSO2s, we show that the prospects are much better for Compton Thin AGN2 and discuss several possible multi-parameter selection strategies. In a second example, we confirm the hardening of the mean X-ray spectrum with increasing X-ray luminosity on a sample of over 500 X-ray active stars and reveal that on average X-ray active M stars display bluer g − r colour indexes than less active ones. Although this catalogue of 2XMM-SDSS sources cannot be used directly for statistical studies, it nevertheless represents an excellent starting point to select well defined samples of X-ray-emitting objects.

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X-ray spectroscopy of stars

Cited by 278 publications

References 375 publications

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

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

New findings on the prototypical Of?p stars

Cross-correlation of the 2XMMi catalogue with Data Release 7 of the Sloan Digital Sky Survey

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