Wilhelm

Avrett, Robert; Bernal, José Domingo Arias

doi:10.2307/40085204

Cited by 3 publications

(3 citation statements)

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“…(2) over the second, but across the ALC7 chromosphere it is simply a resonancescattering line with a source function decline like all others in Fig. 1 Since the ALC7 chromosphere is near-isothermal there is good resemblance to the classic demonstration of two-level scattering by Avrett (1965), except that ε is not constant. The outward S decline from such scattering (" √ ε law") causes a dark line core which is often called "self-absorption" in ultraviolet spectroscopy.…”

Section: Alc7: Eb Diagnostics In 1d Se Modelingmentioning

confidence: 97%

Hαfeatures with hot onsets

Rutten

2016

A&A

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Ellerman bombs are transient brightenings of the wings of the Balmer lines that uniquely mark reconnection in the solar photosphere.They are also bright in strong Ca ii and ultraviolet lines and in ultraviolet continua, but they are not visible in the optical continuum and the Na i D and Mg i b lines. These discordant visibilities invalidate all published Ellerman bomb modeling. I argue that the assumption of Saha-Boltzmann lower-level populations is informative to estimate bomb-onset opacities for these diverse diagnostics, even and especially for Hα, and employ such estimates to gauge the visibilities of Ellerman bomb onsets in all of them. They constrain Ellerman bomb formation to temperatures 10 000−20 000 K and hydrogen densities around 10 15 cm −3 . Similar arguments likely hold for Hα visibility in other transient phenomena with hot and dense onsets.

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Section: Alc7: Eb Diagnostics In 1d Se Modelingmentioning

confidence: 97%

Hαfeatures with hot onsets

Rutten

2016

A&A

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“…trum of the reflected radiation. The energy separation between the emission peaks can reach many Doppler widths (see Avrett 1965, Avrett & Hummer 1965, Sect. 6.4 of Ivanov 1973and Mihalas 1978.…”

Section: Formation Of the Cyclotron Linementioning

confidence: 99%

A Reflection Model for the Cyclotron Lines in the Spectra of X-Ray Pulsars

Poutanen

Mushtukov

Suleimanov

et al. 2013

ApJ

149

155

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Cyclotron resonance scattering features observed in the spectra of some X-ray pulsars show significant changes of the line energy with the pulsar luminosity. At high luminosities, these variations are often associated with the onset and growth of the accretion column, which is believed to be the origin of the observed emission and of the cyclotron lines. However, this scenario inevitably implies a large gradient of the magnetic field strength within the line-forming region, which makes the formation of the observed line-like features problematic. Moreover, the observed variation of the cyclotron line energy is much smaller than could be anticipated for the corresponding luminosity changes. We argue here that a more physically realistic situation is that the cyclotron line forms when the radiation emitted by the accretion column is reflected from the neutron star surface, where the gradient of the magnetic field strength is significantly smaller. Here we develop a reflection model and apply it to explain the observed variations of the cyclotron line energy in a bright X-ray pulsar V 0332+53 over a wide range of luminosities.

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“…The relative intensity between the core peaks of Mg ii H & K lines, are more prominent and easier to analyse than H & K cores of Ca ii in C25 and C26. Following Avrett (2012) the relative difference between Mg ii H & K core lines indicates an averaged stellar outflow.…”

Section: Mg II H and K Linementioning

confidence: 99%

Far beyond the Sun − II. Probing the stellar magnetism of the young Sun ι Horologii from the photosphere to its corona

Amazo-Gómez

Alvarado‐Gómez

Poppenhaeger

et al. 2023

Monthly Notices of the Royal Astronomical Society

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A comprehensive multi-wavelength campaign has been carried out to probe stellar activity and variability in the young Sun-like star ι-Horologii. We present the results from long-term spectropolarimetric monitoring of the system by using the ultra-stable spectropolarimeter/velocimeter HARPS at the ESO 3.6-m telescope. Additionally, we included high-precision photometry from the NASA Transiting Exoplanet Survey Satellite (TESS) and observations in the far- and near-ultraviolet spectral regions using the STIS instrument on the NASA/ESA Hubble Space Telescope (HST). The high-quality dataset allows a robust characterisation of the star’s rotation period, as well as a probe of the variability using a range of spectroscopic and photometric activity proxies. By analyzing the gradient of the power spectra (GPS) in the TESS lightcurves we constrained the faculae-to-spot driver ratio ($\rm S_{fac}/S_{spot}$) to 0.510±0.023, which indicates that the stellar surface is spot dominated during the time of the observations. We compared the photospheric activity properties derived from the GPS method with a magnetic field map of the star derived using Zeeman-Doppler imaging (ZDI) from simultaneous spectropolarimetric data for the first time. Different stellar activity proxies enable a more complete interpretation of the observed variability. For example, we observed enhanced emission in the HST transition line diagnostics C iv and C iii, suggesting a flaring event. From the analysis of TESS data acquired simultaneously with the HST data, we investigate the photometric variability at the precise moment that the emission increased and derive correlations between different observables, probing the star from its photosphere to its corona.

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Wilhelm

Cited by 3 publications

References 0 publications

Hαfeatures with hot onsets

Hαfeatures with hot onsets

A Reflection Model for the Cyclotron Lines in the Spectra of X-Ray Pulsars

Far beyond the Sun − II. Probing the stellar magnetism of the young Sun ι Horologii from the photosphere to its corona

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