CHIANTI – An atomic database for emission lines. Version 8

Zanna, G. Del; Dere, K. P.; Young, Peter R.; Landi, E.; Mason, H. E.

doi:10.1051/0004-6361/201526827

Cited by 432 publications

(416 citation statements)

References 124 publications

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“…We determine a lower limit for n e by assuming that the absorbers exist sufficiently far from the SMBH for the recombination time to be much shorter than the ionization time of the gas, and that the gas is not too highly ionized relative to C iv and Si iv [i.e., n e > ∼ 1/(α rec ∆t), where α rec is the recombination-rate coefficient and ∆t is an upper limit for the BAL-variability timescale (see Table 5); see Capellupo et al 2013 andGrier et al 2015 for details]. We calculate α rec using the chianti atomic database version 8.0 (Dere et al 1997;Del Zanna et al 2015) with a nominal BAL-outflow temperature of 20 000 K; the coefficients for C iv and Si iv are 1.5 × 10 −11 and 1.7 × 10 −11 cm 3 s −1 , respectively, and we adopt the average value for our calculation. The recombination rate used in combination with the average measured timescale of ∆t ≤ 3.04 yr for pristine BAL disappearance and emergence thus yields an electrondensity lower limit of n e > ∼ 650 cm −3 .…”

Section: Bal Outflows Undergoing Ionization Changesmentioning

confidence: 99%

Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

McGraw

Brandt

Grier

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate broad absorption line (BAL) disappearance and emergence using a 470 BAL-quasar sample over ≤ 0.10-5.25 rest-frame years with at least three spectroscopic epochs for each quasar from the Sloan Digital Sky Survey. We identify 14 disappearing BALs over ≤ 1.73-4.62 rest-frame years and 18 emerging BALs over ≤ 1.46-3.66 rest-frame years associated with the C iv λλ1548,1550 and/or Si iv λλ1393,1402 doublets, and report on their variability behavior. BAL quasars in our dataset exhibit disappearing/emerging C iv BALs at a rate of 2.3 +0.9 −0.7 and 3.0 +1.0 −0.8 per cent, respectively, and the frequency for BAL to non-BAL quasar transitions is 1.7 +0.8 −0.6 per cent. We detect four re-emerging BALs over ≤ 3.88 rest-frame years on average and three re-disappearing BALs over ≤ 4.15 rest-frame years on average, the first reported cases of these types. We infer BAL lifetimes along the line of sight to be nominally < ∼ 100-1000 yr using disappearing C iv BALs in our sample. Interpretations of (re-)emerging and (re-)disappearing BALs reveal evidence that collectively supports both transverse-motion and ionization-change scenarios to explain BAL variations. We constrain a nominal C iv/Si iv BAL outflow location of < ∼ 100 pc from the central source and a radial size of > ∼ 1×10 −7 pc (0.02 au) using the ionization-change scenario, and constrain a nominal outflow location of < ∼ 0.5 pc and a transverse size of ∼0.01 pc using the transverse-motion scenario. Our findings are consistent with previous work, and provide evidence in support of BALs tracing compact flow geometries with small filling factors.

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Section: Bal Outflows Undergoing Ionization Changesmentioning

confidence: 99%

Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

McGraw

Brandt

Grier

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…The CHIANTI synthetic flare spectrum (Dere et al 1997;Del Zanna et al 2015) indicates that, even in the absence of photopumping, the Ne ix 82.76Å transition should dominate the emission feature observed by Acton et al (1985), contributing at least 50 per cent to the total line flux, with Fe xx and Fe xxii providing the main blending transitions. Furthermore, the Acton et al flare spectrum also contains the Ne ix 1s 2 1 S 0 -1s2p 1 P 1 resonance line at 13.45Å and 1s 2 1 S 0 -1s2s 3 S 1 forbidden line at 13.70Å.…”

Section: Resultsmentioning

confidence: 99%

“…A synthetic solar flare spectrum calculated with the latest version (8.0.1) of the CHIANTI database (Dere et al 1997;Del Zanna et al 2015) with the coronal abundances of Schmelz et al (2012) indicates that Ne ix makes a contribution of less than 1 per cent to the total line flux in both instances, while solar flare observations confirm that the features are due to Fe xiv (Bhatia et al 1994) and O iv (Widing 1982). In the case of the 81.58Å transition, the predicted enhancement is too small to detect the feature, even under optimal conditions.…”

Section: Resultsmentioning

confidence: 99%

X-ray line coincidence photopumping in a solar flare

Keenan

Poppenhaeger

Mathioudakis

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Line coincidence photopumping is a process where the electrons of an atomic or molecular species are radiatively excited through the absorption of line emission from another species at a coincident wavelength. There are many instances of line coincidence photopumping in astrophysical sources at optical and ultraviolet wavelengths, with the most famous example being Bowen fluorescence (pumping of O iii 303.80Å by He ii), but none to our knowledge in X-rays. However, here we report on a scheme where a He-like line of Ne ix at 11.000Å is photopumped by He-like Na x at 11.003Å, which predicts significant intensity enhancement in the Ne ix 82.76Å transition under physical conditions found in solar flare plasmas. A comparison of our theoretical models with published X-ray observations of a solar flare obtained during a rocket flight provides evidence for line enhancement, with the measured degree of enhancement being consistent with that expected from theory, a truly surprising result. Observations of this enhancement during flares on stars other than the Sun would provide a powerful new diagnostic tool for determining the sizes of flare loops in these distant, spatially-unresolved, astronomical sources.

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“…In our work we used the Q(T ) obtained by interpolating the values from the curve given by CHIANTI (Del Zanna et al 2015). For the simulations, the bottom of the box was located in the chromosphere, with 49.0 Mm in the x and y directions, and it extended 40.0 Mm in the vertical direction (z) up to the lower corona.…”

Section: Methodsmentioning

confidence: 99%

Nonlocal heat flux effects on temperature evolution of the solar atmosphere

Silva

Santos

Büchner

et al. 2018

A&A

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Context. Heat flux is one of the main energy transport mechanisms in the weakly collisional plasma of the solar corona. There, rare binary collisions let hot electrons travel over long distances and influence other regions along magnetic field lines. Thus, the fully collisional heat flux models might not describe transport well enough since they consider only the local contribution of electrons. The heat flux in weakly collisional plasmas at high temperatures with large mean free paths has to consider the nonlocality of the energy transport in the frame of nonlocal models in order to treat energy balance in the solar atmosphere properly. Aims. We investigate the impact of nonlocal heat flux on the thermal evolution and dynamics of the solar atmosphere by implementing a nonlocal heat flux model in a 3D magnetohydrodynamic simulation of the solar corona. Methods. We simulate the evolution of solar coronal plasma and magnetic fields considering both a local collision dominated and a nonlocal heat flux model. The initial magnetic field is obtained by a potential extrapolation of the observed line-of-sight magnetic field of AR11226. The system is perturbed by moving the plasma at the photosphere. We compared the simulated evolution of the solar atmosphere in its dependence on the heat flux model. Results. The main differences for the average temperature profiles were found in the upper chromosphere/transition region. In the nonlocal heat transport model case, thermal energy is transported more efficiently to the upper chromosphere and lower transition region and leads to an earlier heating of the lower atmosphere. As a consequence, the structure of the solar atmosphere is affected with the nonlocal simulations producing on average a smoother temperature profile and the transition region placed about 500 km higher. Using a nonlocal heat flux also leads to two times higher temperatures in some of the regions in the lower corona. Conclusions. The results of our 3D MHD simulations considering nonlocal heat transport supports the previous results of simpler 1D two-fluid simulations. They demonstrated that it is important to consider a nonlocal formulation for the heat flux when there is a strong energy deposit, like the one observed during flares, in the solar corona.

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CHIANTI – An atomic database for emission lines. Version 8

Cited by 432 publications

References 124 publications

Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

X-ray line coincidence photopumping in a solar flare

Nonlocal heat flux effects on temperature evolution of the solar atmosphere

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