scholarly journals TIME EVOLUTION OF VISCOUS CIRCUMSTELLAR DISKS DUE TO PHOTOEVAPORATION BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET, AND X-RAY RADIATION FROM THE CENTRAL STAR

2009 ◽  
Vol 705 (2) ◽  
pp. 1237-1251 ◽  
Author(s):  
U. Gorti ◽  
C. P. Dullemond ◽  
D. Hollenbach
Keyword(s):  
Time Evolution ◽  
Extreme Ultraviolet ◽  
Circumstellar Disks ◽  
Central Star ◽  
X Ray ◽  
Far Ultraviolet

scholarly journals ORFEUS observation of the central star of NGC 6543

1997 ◽  
Vol 180 ◽  
pp. 136-136
Author(s):  
J. Zweigle ◽  
M. Grewing ◽  
J. Barnstedt ◽  
M. Gölz ◽  
W. Gringel ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Planetary Nebula ◽  
Extreme Ultraviolet ◽  
Wavelength Region ◽  
Central Star ◽  
University Of California ◽  
Satellite Mission ◽  
Ultraviolet Spectrometer ◽  
Far Ultraviolet ◽  
The University

During the ORFEUS-SPAS (Orbiting Retrievable Far and Extreme Ultraviolet Spectrometer on the Shuttle Pallet Satellite) mission STS-51, flown in September 1993, we observed the central star of the planetary nebula NGC 6543 in the far ultraviolet (90 nm to 115 nm) wavelength region using the University of California, Berkeley spectrometer with a spectral resolution of 0.03 nm.

scholarly journals The warm-hot circumgalactic medium around EAGLE-simulation galaxies and its detection prospects with X-ray and UV line absorption

2020 ◽  
Vol 498 (1) ◽  
pp. 574-598 ◽  
Author(s):  
Nastasha A Wijers ◽  
Joop Schaye ◽  
Benjamin D Oppenheimer
Keyword(s):  
Column Density ◽  
Extreme Ultraviolet ◽  
Gas Well ◽  
X Ray ◽  
Filling Phase ◽  
Circumgalactic Medium ◽  
Halo Masses ◽  
Collisional Ionization ◽  
Far Ultraviolet ◽  
Halo Gas

ABSTRACT We use the EAGLE (Evolution and Assembly of GaLaxies and their Environments) cosmological simulation to study the distribution of baryons, and far-ultraviolet (O vi), extreme-ultraviolet (Ne viii), and X-ray (O vii, O viii, Ne ix, and Fe xvii) line absorbers, around galaxies and haloes of mass $\,{M}_{\rm {200c}}= 10^{11}$–$10^{14.5} \, \rm {M}_{\odot}$ at redshift 0.1. EAGLE predicts that the circumgalactic medium (CGM) contains more metals than the interstellar medium across halo masses. The ions we study here trace the warm-hot, volume-filling phase of the CGM, but are biased towards temperatures corresponding to the collisional ionization peak for each ion, and towards high metallicities. Gas well within the virial radius is mostly collisionally ionized, but around and beyond this radius, and for O vi, photoionization becomes significant. When presenting observables, we work with column densities, but quantify their relation with equivalent widths by analysing virtual spectra. Virial-temperature collisional ionization equilibrium ion fractions are good predictors of column density trends with halo mass, but underestimate the diversity of ions in haloes. Halo gas dominates the highest column density absorption for X-ray lines, but lower density gas contributes to strong UV absorption lines from O vi and Ne viii. Of the O vii (O viii) absorbers detectable in an Athena X-IFU blind survey, we find that 41 (56) per cent arise from haloes with $\,{M}_{\rm {200c}}= 10^{12.0}{-}10^{13.5} \, \rm {M}_{\odot}$. We predict that the X-IFU will detect O vii (O viii) in 77 (46) per cent of the sightlines passing $\,{M}_{\star }= 10^{10.5}{-}10^{11.0} \, \rm {M}_{\odot}$ galaxies within $100 \, \rm {pkpc}$ (59 (82) per cent for $\,{M}_{\star }\gt 10^{11.0} \, \rm {M}_{\odot}$). Hence, the X-IFU will probe covering fractions comparable to those detected with the Cosmic Origins Spectrograph for O vi.

scholarly journals New view of the corona of classical T Tauri stars: Effects of flaring activity in circumstellar disks

2019 ◽  
Vol 624 ◽  
pp. A50 ◽  
Author(s):  
S. Colombo ◽  
S. Orlando ◽  
G. Peres ◽  
F. Reale ◽  
C. Argiroffi ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Circumstellar Disks ◽  
Central Star ◽  
Field Configuration ◽  
T Tauri Stars ◽  
Stellar Objects ◽  
X Ray ◽  
T Tauri ◽  
Coronal Activity ◽  
Accretion Rates

Context. Classical T Tauri stars (CTTSs) are young low-mass stellar objects that accrete mass from their circumstellar disks. They are characterized by high levels of coronal activity, as revealed by X-ray observations. This activity may affect the disk stability and the circumstellar environment. Aims. Here we investigate if an intense coronal activity due to flares that occur close to the accretion disk may perturb the stability of the inner disk, disrupt the inner part of the disk, and might even trigger accretion phenomena with rates comparable with those observed. Methods. We modeled a magnetized protostar surrounded by an accretion disk through 3D magnetohydrodinamic simulations. The model takes into account the gravity from the central star, the effects of viscosity in the disk, the thermal conduction (including the effects of heat flux saturation), the radiative losses from optically thin plasma, and a parameterized heating function to trigger the flares. We explored cases characterized by a dipole plus an octupole stellar magnetic field configuration and different density of the disk or by different levels of flaring activity. Results. As a result of the simulated intense flaring activity, we observe the formation of several loops that link the star to the disk; all these loops build up a hot extended corona with an X-ray luminosity comparable with typical values observed in CTTSs. The intense flaring activity close to the disk can strongly perturb the disk stability. The flares trigger overpressure waves that travel through the disk and modify its configuration. Accretion funnels may be triggered by the flaring activity and thus contribute to the mass accretion rate of the star. Accretion rates synthesized from the simulations are in a range between 10−10 and 10−9 M⊙ yr−1. The accretion columns can be perturbed by the flares, and they can interact with each other; they might merge into larger streams. As a result, the accretion pattern can be rather complex: the streams are highly inhomogeneous, with a complex density structure, and clumped.

scholarly journals Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

2020 ◽  
Vol 644 ◽  
pp. A67
Author(s):  
A. G. Sreejith ◽  
L. Fossati ◽  
A. Youngblood ◽  
K. France ◽  
S. Ambily
Keyword(s):  
Extreme Ultraviolet ◽  
Radiation Power ◽  
Optical Observations ◽  
Scaling Relations ◽  
Activity Parameter ◽  
X Ray ◽  
Atmospheric Escape ◽  
Direct Measurements ◽  
Nearby Stars ◽  
Far Ultraviolet

Atmospheric escape is an important factor shaping the exoplanet population and hence drives our understanding of planet formation. Atmospheric escape from giant planets is driven primarily by the stellar X-ray and extreme ultraviolet (EUV) radiation. Furthermore, EUV and longer wavelength UV radiation power disequilibrium chemistry in the middle and upper atmospheres. Our understanding of atmospheric escape and chemistry, therefore, depends on our knowledge of the stellar UV fluxes. While the far-ultraviolet (FUV) fluxes can be observed for some stars, most of the EUV range is unobservable due to the lack of a space telescope with EUV capabilities and, for the more distant stars, due to interstellar medium absorption. Therefore, it becomes essential to have an indirect means for inferring EUV fluxes from features observable at other wavelengths. We present here analytic functions for predicting the EUV emission of F-, G-, K-, and M-type stars from the log R′HK activity parameter that is commonly obtained from ground-based optical observations of the Ca II H&K lines. The scaling relations are based on a collection of about 100 nearby stars with published log R′HK and EUV flux values, the latter of which are either direct measurements or inferences from high-quality FUV spectra. The scaling relations presented here return EUV flux values with an accuracy of about a factor of three, which is slightly lower than that of other similar methods based on FUV or X-ray measurements.

scholarly journals Coherence tomography with broad bandwidth extreme ultraviolet and soft X-ray radiation

2021 ◽  
Vol 127 (4) ◽  
Author(s):  
S. Skruszewicz ◽  
S. Fuchs ◽  
J. J. Abel ◽  
J. Nathanael ◽  
J. Reinhard ◽  
...  
Keyword(s):  
Optical Coherence Tomography ◽  
Near Infrared ◽  
Extreme Ultraviolet ◽  
Infrared Light ◽  
Imaging Method ◽  
Optical Coherence ◽  
Axial Resolution ◽  
Cross Sectional ◽  
X Ray ◽  
Broad Bandwidth

AbstractWe present an overview of recent results on optical coherence tomography with the use of extreme ultraviolet and soft X-ray radiation (XCT). XCT is a cross-sectional imaging method that has emerged as a derivative of optical coherence tomography (OCT). In contrast to OCT, which typically uses near-infrared light, XCT utilizes broad bandwidth extreme ultraviolet (XUV) and soft X-ray (SXR) radiation (Fuchs et al in Sci Rep 6:20658, 2016). As in OCT, XCT’s axial resolution only scales with the coherence length of the light source. Thus, an axial resolution down to the nanometer range can be achieved. This is an improvement of up to three orders of magnitude in comparison to OCT. XCT measures the reflected spectrum in a common-path interferometric setup to retrieve the axial structure of nanometer-sized samples. The technique has been demonstrated with broad bandwidth XUV/SXR radiation from synchrotron facilities and recently with compact laboratory-based laser-driven sources. Axial resolutions down to 2.2 nm have been achieved experimentally. XCT has potential applications in three-dimensional imaging of silicon-based semiconductors, lithography masks, and layered structures like XUV mirrors and solar cells.

scholarly journals Table-top extreme ultraviolet second harmonic generation

2021 ◽  
Vol 7 (21) ◽  
pp. eabe2265
Author(s):  
Tobias Helk ◽  
Emma Berger ◽  
Sasawat Jamnuch ◽  
Lars Hoffmann ◽  
Adeline Kabacinski ◽  
...  
Keyword(s):  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
First Principles ◽  
Extreme Ultraviolet ◽  
Second Harmonic ◽  
High Harmonic ◽  
Electronic Structure Calculations ◽  
Free Electron Lasers ◽  
X Ray ◽  
Structure Calculations

The lack of available table-top extreme ultraviolet (XUV) sources with high enough fluxes and coherence properties has limited the availability of nonlinear XUV and x-ray spectroscopies to free-electron lasers (FELs). Here, we demonstrate second harmonic generation (SHG) on a table-top XUV source by observing SHG near the Ti M2,3 edge with a high-harmonic seeded soft x-ray laser. Furthermore, this experiment represents the first SHG experiment in the XUV. First-principles electronic structure calculations suggest the surface specificity and separate the observed signal into its resonant and nonresonant contributions. The realization of XUV-SHG on a table-top source opens up more accessible opportunities for the study of element-specific dynamics in multicomponent systems where surface, interfacial, and bulk-phase asymmetries play a driving role.

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