Results from an extensive Einstein stellar survey

Vaiana, G. S.; Cassinelli, J. P.; Fabbiano, G.; Giacconi, R.; Golub, L.; Gorenstein, P.; Haisch, B. M.; Harnden, F. R.; Johnson, H. M.; Linsky, J. L.; Maxson, C. W.; Mewe, R.; Rosner, R.; Seward, F. D.; Topka, K.; Zwaan, C.

doi:10.1086/158797

Cited by 368 publications

(134 citation statements)

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“…This is consistent with the known increase of the f x / f opt ratio for M stars compared to that of earlier spectral types (see e.g. Vaiana et al 1981). We note, however, that some high z QSOs have been identified with Fig.…”

Section: Separating Stellar From Extragalactic Sourcessupporting

confidence: 92%

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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Section: Separating Stellar From Extragalactic Sourcessupporting

confidence: 92%

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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“…Reale & Micela (1998) discussed the X-ray data of the flare and derived a loop half-length of ≈7 × 10 9 cm from the analysis of the flare decay. The first X-ray detections of CN Leo have already been reported from Einstein data (Vaiana et al 1981;Golub 1983), and even during quiescence, it is a relatively strong X-ray source with log L X = 26.97 and 27.01 in the ROSAT All-Sky survey and a second pointed PSPC observation, respectively (Schmitt & Liefke 2004). CN Leo is the only star where persistent but variable optical coronal Fe xiii emission has been confirmed (Schmitt & Wichmann 2001;Fuhrmeister et al 2004).…”

Section: The Active M Dwarf Cn Leomentioning

confidence: 85%

Multiwavelength observations of a giant flare on CN Leonis

Liefke¹,

Fuhrmeister²,

Schmitt³

2010

A&A

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Context. Stellar flares affect all atmospheric layers from the photosphere over chromosphere and transition region up into the corona. Simultaneous observations in different spectral bands allow to obtain a comprehensive picture of the environmental conditions and the physical processes going on during different phases of the flare. Aims. We investigate the properties of the coronal plasma during a giant flare on the active M dwarf CN Leo observed simultaneously with the UVES spectrograph at the VLT and XMM-Newton. Methods. From the X-ray data, we analyze the temporal evolution of the coronal temperature and emission measure, and investigate variations in electron density and coronal abundances during the flare. Optical Fe xiii line emission traces the cooler quiescent corona.Results. Although of rather short duration (exponential decay time τ LC < 5 min), the X-ray flux at flare peak exceeds the quiescent level by a factor of ≈100. The electron density averaged over the whole flare is greater than 5 × 10 11 cm −3 . The flare plasma shows an enhancement of iron by a factor of ≈2 during the rise and peak phase of the flare. We derive a size of <9000 km for the flaring structure from the evolution of the the emitting plasma during flare rise, peak, and decay. Conclusions. The characteristics of the flare plasma suggest that the flare originates from a compact arcade instead of a single loop. The combined results from X-ray and optical data further confine the plasma properties and the geometry of the flaring structure in different atmospheric layers.

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“…In O and early B stars, shocks present in supersonic radiatively driven winds produce heating. Stars of type G and later, on the other hand, have thick convective envelopes with magnetic dynamo activity, much of whose energy is dissipated in the corona (e.g., Vaiana et al 1981). Thick convective envelopes are absent above about 1.5 M , but thin surface convection layers present up to about type A5 appear to be enough to produce modest coronal heating and X ray emission (e.g., Robrade & Schmitt 2010;Günther et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Burn Out or Fade Away? On the X-Ray and Magnetic Death of Intermediate Mass Stars

Drake

Braithwaite²,

Kashyap

et al. 2014

ApJ

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The nature of the mechanisms apparently driving X-rays from intermediate mass stars lacking strong convection zones or massive winds remains poorly understood, and the possible role of hidden, lower mass close companions is still unclear. A 20 ks Chandra HRC-I observation of HR 4796A, an 8 Myr old main sequence A0 star devoid of close stellar companions, has been used to search for a signature or remnant of magnetic activity from the Herbig Ae phase. X-rays were not detected and the X-ray luminosity upper limit was L X 1.3 × 10 27 erg s −1 . The result is discussed in the context of various scenarios for generating magnetic activity, including rotational shear and subsurface convection. A dynamo driven by natal differential rotation is unlikely to produce observable X rays, chiefly because of the difficulty in getting the dissipated energy up to the surface of the star. A subsurface convection layer produced by the ionization of helium could host a dynamo that should be effective throughout the main sequence but can only produce X-ray luminosities of the order 10 25 erg s −1 . This luminosity lies only moderately below the current detection limit for Vega. Our study supports the idea that X-ray production in Herbig Ae/Be stars is linked largely to the accretion process rather than the properties of the underlying star, and that early A stars generally decline in X-ray luminosity at least 100,000 fold in only a few million years.

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Results from an extensive Einstein stellar survey

Cited by 368 publications

References 0 publications

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

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

Multiwavelength observations of a giant flare on CN Leonis

Burn Out or Fade Away? On the X-Ray and Magnetic Death of Intermediate Mass Stars

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