CHIANTI – an atomic database for emission lines

Landi, E.; Landini, M.; Dere, K. P.; Young, Peter R.; Mason, H. E.

doi:10.1051/aas:1999449

Cited by 109 publications

(73 citation statements)

References 35 publications

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“…With five different "noisy" datasets, the stability of the solution against errors in the data can be evaluated. As a further test on the effects due to atomic physics only, we repeated the MCMC determinations using the synthetic intensities calculated with version 2 of the CHIANTI database (Landi et al 1999) and the ion fractions of Mazzotta et al (1998). The atomic data and ion fractions in the two CHIANTI versions are very different, so that the use of CHIANTI V.2 represents a rather bad case of uncertainties in atomic parameters.…”

Section: Methodology Of the Testsmentioning

confidence: 99%

Monte Carlo Markov chain DEM reconstruction of isothermal plasmas

Landi

Reale

Testa

2012

A&A

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Context. Recent studies carried out with SOHO and Hinode high-resolution spectrometers have shown that the plasma in the off-disk solar corona is close to isothermal. If confirmed, these findings may have significant consequences for theoretical models of coronal heating. However, these studies have been carried out with diagnostic techniques whose ability to reconstruct the plasma distribution with temperature has not been thoroughly tested. Aims. In this paper, we carry out tests on the Monte Carlo Markov chain (MCMC) technique with the aim of determining: 1) its ability to retrieve isothermal plasmas from a set of spectral line intensities, with and without random noise; 2) to what extent can it discriminate between an isothermal solution and a narrow multithermal distribution; and 3) how well it can detect multiple isothermal components along the line of sight. We also test the effects of 4) atomic data uncertainties on the results, and 5) the number of ions whose lines are available for the DEM reconstruction. Methods. We first use the CHIANTI database to calculate synthetic spectra from different thermal distributions: single isothermal plasmas, multithermal plasmas made of multiple isothermal components, and multithermal plasmas with a Gaussian DEM distribution with variable width. We then apply the MCMC technique on each of these synthetic spectra, so that the ability of the MCMC technique at reconstructing the original thermal distribution can be evaluated. Next, we add a random noise to the synthetic spectra, and repeat the exercise, in order to determine the effects of random errors on the results. We also we repeat the exercise using a different set of atomic data from those used to calculate synthetic line intensities, to understand the robustness of the results against atomic physics uncertainties. The size of the temperature bin of the MCMC reconstruction is varied in all cases, in order to determine the optimal width. Results. We find that the MCMC technique is unable to retrieve isothermal plasmas to better than Δ log T 0.05. Also, the DEM curves obtained using lines calculated with an isothermal plasma and with a Gaussian distribution with FWHM of log T 0.05 are very similar. Two near-isothermal components can be resolved if their temperature separation is Δ log T = 0.2 or larger. Thus, DEM diagnostics has an intrinsic resolving power of log T = 0.05. Atomic data uncertainties may significantly affect both temperature and peak DEM values, but do not alter our conclusions. The availability of small sets of lines also does not worsen the performance of the MCMC technique, provided these lines are formed in a wide temperature range. Conclusions. Our analysis shows the present limitations in our ability to identify the presence of strictly isothermal plasmas in stellar and solar coronal spectra.

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Section: Methodology Of the Testsmentioning

confidence: 99%

Monte Carlo Markov chain DEM reconstruction of isothermal plasmas

Landi

Reale

Testa

2012

A&A

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“…The method provide estimates of the ratios between element abundances and iron coronal abundance, relative to the solar photospheric ratio. The contribution functions C(T ) of the selected lines were calculated from the atomic physics parameters provided in the CHIANTI version 4.0 database (Landi et al 1999;Dere et al 2001) assuming collisional ionisation equilibrium. Right: ratio G = (i + f )/r of the summed intensities of the OVII intercombination and forbiden lines over the intensity of the recombination line (λ = 21.60 Å) calculated using the CHIANTI database (Dere et al 2001).…”

Section: Abundances and Emission Measure Distributionmentioning

confidence: 99%

X-ray spectroscopy of the W UMa-type binary 44 Bootis

Gondoin¹

2004

A&A

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Abstract. 44 Boo B, a W UMa-type binary system, was observed in June 2001 during one entire revolution period with the XMM−Newton observatory. The count rate in the 0.3 to 2 keV band is constant in average with 5 to 20% count rate increases reminiscent of flares. Spectral fitting of the EPIC spectra indicates a corona configuration with little contribution from quiet regions, similar to the Sun. On the contrary, the (2-9) × 10 6 K temperature range of the "cool" plasma suggests that the active corona around the two companions is densely filled with low-lying loops similar to those found in solar-type active regions. The 44 Boo O VII He-like triplet constrains the electron density to an upper limit n e < 8.6 × 10 10 cm −3 . We argue that this low-lying loop system may be overlaid by larger loops. Magnetic reconnection phenomena in this large loops system may explain the characteristic flare decay time in the light curve that implies loop lengths of about 16 × 10 9 cm. An extended corona around 44 Boo would explain the absence of eclipses in its X-ray light curve. The average element abundance in 44 Boo corona is found to be lower than the solar photospheric value. The spectral analysis indicates enhanced abundances of oxygen and neon relative to iron which suggest an inverse FIP effect. Compared with other active binary systems such as RSCVn or BY Dra, 44 Boo has relatively less material at temperatures higher than 10 7 K and the temperature of its hottest plasma component appears to be lower.

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“…38,39) are no longer valid. Conservation of particles requires that the population n m of level m obeys the time-dependent statistical rate equation…”

Section: Transition Rates For Lines and Continuamentioning

confidence: 99%

Chromospheric Dynamics and Line Formation

Hammer¹,

Ulmschneider²

2007

AIP Conference Proceedings

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Abstract. The solar chromosphere is very dynamic, due to the presence of large amplitude hydrodynamic waves. Their propagation is affected by NLTE radiative transport in strong spectral lines, which can in turn be used to diagnose the dynamics of the chromosphere. We give a basic introduction into the equations of NLTE radiation hydrodynamics and describe how they are solved in current numerical simulations. The comparison with observation shows that one-dimensional codes can describe strong brightenings quite well, but the overall chromospheric dynamics appears to be governed by three-dimensional shock propagation.

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CHIANTI – an atomic database for emission lines

Cited by 109 publications

References 35 publications

Monte Carlo Markov chain DEM reconstruction of isothermal plasmas

Monte Carlo Markov chain DEM reconstruction of isothermal plasmas

X-ray spectroscopy of the W UMa-type binary 44 Bootis

Chromospheric Dynamics and Line Formation

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