A Unified Picture of the First Ionization Potential and Inverse First Ionization Potential Effects

Laming, J. M.

doi:10.1086/423780

Cited by 193 publications

(248 citation statements)

References 56 publications

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“…In spite of many attempts in the past, the only model that is capable of producing either a positive or an inverse FIP effect is the one proposed by Laming (2004Laming ( , 2009). In this model charged ions are subject to a ponderomotive force caused by Alfvén waves propagating through the chromosphere, which may originate either in the corona or in the convection zone.…”

Section: τ Boo: a Medium-activity Coronal Sourcementioning

confidence: 99%

Photospheric and coronal abundances in solar-type stars: the peculiar case ofτ Bootis

Maggio

Sanz-Forcada

2011

A&A

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Aims. Chemical abundances in solar-type stars are still a much debated topic in many respects. In particular, planet-hosting stars are known to be metal-rich, but whether or not this peculiarity applies also to the chemical composition of the outer stellar atmospheres is still to be clarified. More in general, coronal and photospheric abundances in late-type stars appear to be different in many cases, but understanding how chemical stratification effects work in stellar atmospheres requires an observational base larger than currently available. Methods. We obtained XMM-Newton high-resolution X-ray spectra of τ Bootis, a well known nearby star with a Jovian-mass close-in planet. We analyzed these data with the aim to perform a detailed line-based emission measure analysis and derive the abundances of individual elements in the corona with two different methods applied independently. We compared the coronal abundances of τ Bootis with published photospheric abundances based on high-resolution optical spectra and with those of other late-type stars with different magnetic activity levels, including the Sun. Results. We find that the two methods provide consistent results within the statistical uncertainties for both the emission measure distribution of the hot plasma and for the coronal abundances, with discrepancies at the 2σ level limited to the amount of plasma at temperatures of 3-4 MK and to the O and Ni abundances. In both cases, the elements for which both coronal and photospheric measurements are available (C, N, O, Si, Fe, and Ni) result systematically less abundant in the corona by a factor 3 or more, with the exception of the coronal Ni abundance which is similar to the photospheric value. Comparison with other late-type stars of similar activity level shows that these coronal/photospheric abundance ratios are peculiar to τ Bootis and possibly related to the characteristic over-metallicity of this planet-hosting star.

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Section: τ Boo: a Medium-activity Coronal Sourcementioning

confidence: 99%

Photospheric and coronal abundances in solar-type stars: the peculiar case ofτ Bootis

Maggio

Sanz-Forcada

2011

A&A

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“…Although the details are still unclear, it appears that in a magnetic plasma low density environment differential ponderomotive forces, produced by wave heating and dependent on their first ionization potential, can prevent certain ions from migrating across a plasma and resulting in an altered measured chemical abundance (Laming 2004). Whether such a process is actually active in the environment of γ Cas, let alone whether it extends to Ne 9+ ions, must be considered speculative.…”

Section: Abundances and Anomalous Line Strengthsmentioning

confidence: 99%

γCassiopeiae: an X-ray Be star with personality

Oliveira

Smith

Motch

2010

A&A

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An exciting unsolved problem in the study of high energy processes of early type stars concerns the physical mechanism for producing X-rays near the Be star γ Cassiopeiae. By now we know that this source and several "γ Cas analogs" exhibit an unusual hard thermal Xray spectrum, compared both to normal massive stars and the non-thermal emission of known Be/X-ray binaries. Also, its light curve is variable on almost all conceivable timescales. In this study we reanalyze a high dispersion spectrum obtained by Chandra in 2001 and combine it with the analysis of a new (2004) spectrum and light curve obtained by XMM-Newton. We find that both spectra can be fit well with 3-4 optically thin, thermal components consisting of a hot component having a temperature kT Q ∼ 12-14 keV, perhaps one with a value of ∼2.4 keV, and two with well defined values near 0.6 keV and 0.11 keV. We argue that these components arise in discrete (almost monothermal) plasmas. Moreover, they cannot be produced within an integral gas structure or by the cooling of a dominant hot process. Consistent with earlier findings, we also find that the Fe abundance arising from K-shell ions is significantly subsolar and less than the Fe abundance from L-shell ions. We also find novel properties not present in the earlier Chandra spectrum, including a dramatic decrease in the local photoelectric absorption of soft X-rays, a decrease in the strength of the Fe and possibly of the Si K fluorescence features, underpredicted lines in two ions each of Ne and N (suggesting abundances that are ∼1.5-3× and ∼4× solar, respectively), and broadening of the strong Ne X Lyα and O VIII Lyα lines. In addition, we note certain traits in the γ Cas spectrum that are different from those of the fairly well studied analog HD 110432 -in this sense the stars have different "personalities." In particular, for γ Cas the hot X-ray component remains nearly constant in temperature, and the photoelectric absorption of the X-ray plasmas can change dramatically. As found by previous investigators of γ Cas, changes in flux, whether occurring slowly or in rapidly evolving flares, are only seldomly accompanied by variations in hardness. Moreover, the light curve can show a "periodicity" that is due to the presence of flux minima that recur semiregularly over a few hours, and which can appear again at different epochs.

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“…Models of shock heating driven by Alfvén waves also predict high velocities, >100 km s −1 (see, e.g., Antolin et al 2008), while models of Alfvén wave turbulence (van Ballegooijen et al 2011) show non-thermal velocities of 25-35 km s −1 at the tops of loops formed near 1.6 MK (Asgari- Targhi et al 2014). Furthermore, models that attempt to explain the first ionization potential (FIP) effect based on the forces acting on propagating waves suggest velocities on the order of 50-80 km s −1 (Laming 2004(Laming , 2012.…”

Section: Introductionmentioning

confidence: 99%

Measurements of Non-Thermal Line Widths in Solar Active Regions

Brooks

Warren

2016

ApJ

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Spectral line widths are often observed to be larger than can be accounted for by thermal and instrumental broadening alone. This excess broadening is a key observational constraint for both nanoflare and wave dissipation models of coronal heating. Here we present a survey of non-thermal velocities measured in the high temperature loops (1-4 MK) often found in the cores of solar active regions. This survey of Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) observations covers 15 non-flaring active regions that span a wide range of solar conditions. We find relatively small non-thermal velocities, with a mean value of 17.6 ± 5.3 km s −1 , and no significant trend with temperature or active region magnetic flux. These measurements appear to be inconsistent with those expected from reconnection jets in the corona, chromospheric evaporation induced by coronal nanoflares, and Alfvén wave turbulence models. Furthermore, because the observed non-thermal widths are generally small, such measurements are difficult and susceptible to systematic effects.

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A Unified Picture of the First Ionization Potential and Inverse First Ionization Potential Effects

Cited by 193 publications

References 56 publications

Photospheric and coronal abundances in solar-type stars: the peculiar case ofτ Bootis

Photospheric and coronal abundances in solar-type stars: the peculiar case ofτ Bootis

γCassiopeiae: an X-ray Be star with personality

Measurements of Non-Thermal Line Widths in Solar Active Regions

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