Effective Collision Strengths for Fine‐Structure Transitions in S
                    <scp>i</scp>

Tayal, S. S.

doi:10.1086/421908

Cited by 12 publications

(9 citation statements)

References 23 publications

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“…S i S i is a new addition to the database. We have included effective collision strengths from Tayal (2004). gf and E1 A-values have been obtained from Zatsarinny & Bartschat (2006).…”

Section: S-like Ionsmentioning

confidence: 99%

CHIANTI – An atomic database for emission lines. Version 8

Zanna

Dere

Young

et al. 2015

A&A

436

407

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We present version 8 of the CHIANTI database. This version includes a large amount of new data and ions, which represent a significant improvement in the soft X-ray, extreme UV (EUV) and UV spectral regions, which several space missions currently cover. New data for neutrals and low charge states are also added. The data are assessed, but to improve the modelling of low-temperature plasma the effective collision strengths for most of the new datasets are not spline-fitted as previously, but are retained as calculated. This required a change of the format of the CHIANTI electron excitation files. The format of the energy files has also been changed. Excitation rates between all the levels are retained for most of the new datasets, so the data can in principle be used to model highdensity plasma. In addition, the method for computing the differential emission measure used in the CHIANTI software has been changed.

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“…S i S i is a new addition to the database. We have included effective collision strengths from Tayal (2004). gf and E1 A-values have been obtained from Zatsarinny & Bartschat (2006).…”

Section: S-like Ionsmentioning

confidence: 99%

CHIANTI – An atomic database for emission lines. Version 8

Zanna

Dere

Young

et al. 2015

A&A

436

407

View full text Add to dashboard Cite

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“…While the electron density, n e , is expected to be much lower than for hydrogen, n H , it has larger collisional de-excitation rates. Electron collision rates are available for S I from Tayal (2004) and Fe II from Bautista et al (2015, and Priv Comm), S+H collision rates can be estimated using the O+H rates of Lique et al (2018), and Fe+H rates are given by Hollenbach & McKee (1989). Using the thermodynamic models of Rodgers & Glassgold (1991), Harper et al (2001), or Harper et al (2017b) (where the gas temperatures are reduced close to the star) both lines are formed predominantly above the critical densities (i.e., thermalized) when T gas > 500 K. If Fe II and S I and are dominant ionization states, then the ratio of [Fe II] 25.99 µm and [S I] 25.25 µm fluxes, would be ≤ 4.5 in the optically thin limit, and lower, ∼ 1.5, when allowing for optical depth effects.…”

Section: [Fementioning

confidence: 99%

SOFIA-EXES Observations of Betelgeuse during the Great Dimming of 2019/2020

Harper

DeWitt²,

Richter³

et al. 2020

ApJL

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In 2019 October Betelgeuse began a decline in V-band brightness that went beyond the minimum expected from its quasi-periodic ∼ 420 day cycle, becoming the faintest in recorded photometric history. Observations obtained in 2019 December with VLT/SPHERE (Montargès 2020) have shown that the southern half of the star has become markedly fainter than in 2019 January indicating that a major change has occurred in, or near, the photosphere. We present SOFIA-EXES high spectral-resolution observations of [Fe II] 25.99 µm and [S I] 25.25 µm emission lines from Betelgeuse obtained during the unprecedented 2020 February V-band brightness minimum to investigate potential changes in the circumstellar flow. These spectra are compared to observations obtained in 2015 and 2017 when the V magnitude was typical of brighter phases. We find only very small changes in the gas velocities reflected by either of the line profiles, no significant changes in the flux to continuum ratios, and hence no significant changes in the [Fe II]/[S I] flux ratios. There is evidence that absorption features have appeared in the 2020 continuum. The Alfvén wave-crossing time from the upper-photosphere is sufficiently long that one would not expect a change in the large scale magnetic field to reach the circumstellar [Fe II] and [S I] line forming regions, 3 < R(R * ) < 20. However, the light-crossing time is of order a few hours and a reduction in luminosity may reduce the dust-gas heating rate and [O I] 63.19 µm emission which has contributions from R > 20R * , where significant circumstellar oxygen-rich dust is observed.

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“…We use CHIANTI version 8 to predict the S I emissivities. Notably, Table 3 of Tayal (2004) mislabels the collision strengths from levels 1 and 3 to levels 4 and 5, and we have corrected the corresponding data file. We find an S:Ca abundance ratio of 29±7.…”

Section: Chemical Abundancesmentioning

confidence: 99%

iPTF15eqv: Multiwavelength Exposé of a Peculiar Calcium-rich Transient

Milisavljevic

Patnaude

Raymond

et al. 2017

ApJ

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The progenitor systems of the class of "Ca-rich transients" is a key open issue in time domain astrophysics. These intriguing objects exhibit unusually strong calcium line emissions months after explosion, fall within an intermediate luminosity range, are often found at large projected distances from their host galaxies, and may play a vital role in enriching galaxies and the intergalactic medium. Here we present multi-wavelength observations of iPTF15eqv in NGC 3430, which exhibits a unique combination of properties that bridge those observed in Ca-rich transients and Type Ib/c supernovae. iPTF15eqv has among the highest [Ca II]/[O I] emission line ratios observed to date, yet is more luminous and decays more slowly than other Ca-rich transients. Optical and near-infrared photometry and spectroscopy reveal signatures consistent with the supernova explosion of a 10 M star that was stripped of its H-rich envelope via binary interaction. Distinct chemical abundances and ejecta kinematics suggest that the core collapse occurred through electron capture processes. Deep limits on possible radio emission made with the Jansky Very Large Array imply a clean environment (n 0.1 cm −3 ) within a radius of ∼ 10 17 cm. Chandra X-ray Observatory observations rule out alternative scenarios involving tidal disruption of a white dwarf by a black hole, for masses > 100 M . Our results challenge the notion that spectroscopically classified Ca-rich transients only originate from white dwarf progenitor systems, complicate the view that they are all associated with large ejection velocities, and indicate that their chemical abundances may vary widely between events.

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Effective Collision Strengths for Fine‐Structure Transitions in S i

Cited by 12 publications

References 23 publications

CHIANTI – An atomic database for emission lines. Version 8

CHIANTI – An atomic database for emission lines. Version 8

SOFIA-EXES Observations of Betelgeuse during the Great Dimming of 2019/2020

iPTF15eqv: Multiwavelength Exposé of a Peculiar Calcium-rich Transient

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