Chromospheric activity in 
                
                  
                
                
                  
                    ϵ
                  
                
                $\epsilon$
               Eridani: results from theoretical wave studies

Fawzy, Diaa E.; Cuntz, M.

doi:10.1007/s10509-018-3373-3

Cited by 7 publications

(4 citation statements)

References 51 publications

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“…Generally, higher shock strengths are attained for spectral waves compared to monochromatic waves. This result agrees with previous findings (e.g., Cuntz et al 1998Cuntz et al , 1999Fawzy & Cuntz 2018). Notable differences between the models occur at larger heights, mostly due the impact of dilution of the wave energy flux.…”

Section: Discussionsupporting

confidence: 94%

“…LTWs are constraint by 55 Cnc's stellar parameters, notably its rotation period, which in the framework of our model allows us to describe the photospheric and chromospheric magnetic filling factors; see, e.g., Cuntz et al (1999) for a discussion of the inherent features and limitations of this approach. Previous models for ǫ Eri based on this kind of approach were given by Fawzy & Cuntz (2018). Moreover, we calculated additional models for 55 Cnc that consider the time-dependent energy deposition by transverse tube waves in an approximate manner.…”

Section: Discussionmentioning

confidence: 99%

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Chromospheric Activity in 55 Cancri: I. Results from Theoretical Wave Studies

Fawzy,

Cuntz

2021

Preprint

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We present theoretical models of chromospheric heating for 55 Cancri, an orange dwarf of relatively low activity. Self-consistent, nonlinear and time-dependent ab-initio numerical computations are pursued encompassing the generation, propagation, and dissipation of waves. We consider longitudinal waves operating among arrays of flux tubes as well as acoustic waves pertaining to nonmagnetic stellar regions. Additionally, flux enhancements for the longitudinal waves are also taken into account as supplied by transverse tube waves. The Ca II K fluxes are computed (multi-ray treatment) assuming partial redistribution as well as time-dependent ionization. The self-consistent treatment of time-dependent ionization (especially for hydrogen) greatly impacts the atmospheric temperatures and electron densities (especially behind the shocks); it also affects the emergent Ca II fluxes. Particularly, we focus on the influence of magnetic heating on the stellar atmospheric structure and the emergent Ca II emission, as well as the impact of nonlinearities. Our study shows that a higher photospheric magnetic filling factor entails a larger Ca II emission; however, an increased initial wave energy flux (e.g., associated with mode coupling) is of little difference. Comparisons of our theoretical results with observations will be conveyed in forthcoming Paper II.

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Section: Discussionsupporting

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Chromospheric Activity in 55 Cancri: I. Results from Theoretical Wave Studies

Fawzy,

Cuntz

2021

Preprint

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“…To test this, quantitative agreement between acoustic heating and the lowest empirical values of chromospheric emission have been reported by (e.g.) Mullan and Cheng (1993) and by Fawzy and Stepien (2018). To be quantitative, we note that the phrase "near the basal level" is defined as follows in the study by Mullan and Cheng (1993).…”

Section: Comparison With Theoretical Work: Basal Fluxesmentioning

confidence: 86%

A Transition of Dynamo Modes in M Dwarfs: Narrowing Down the Spectral Range Where the Transition Occurs*

Mullan

Houdebine

2020

ApJ

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Houdebine et al (2017: H17) combined CaII data with projected rotational velocities (v sin i) to construct rotation-activity correlations (RAC) in K-M dwarfs. The RAC slopes were used to argue that a transition between dynamo modes occurs at a spectral type between M2 and M3. H17 suggested that the dynamo transition corresponds to a transition to complete convection (TTCC). An independent study of GAIA data led Jao et al (2018) to suggest that the TTCC sets in near M3.0V, close to the H17 result. However, the changes in a star which cause TTCC signatures in GAIA data might not lead to changes in CaII emission at an identical spectral type: the latter are also affected by magnetic effects which depend on certain properties of convection in the core. Here, we use CaII emission fluxes in a sample of ~600 M dwarfs, and attempt to narrow down the transition from one dynamo mode to another: rather than relying on RAC slopes, we quantify how the CaII emission flux varies with spectral type to identify steps where the flux decreases significantly across a narrow range of spectral types. We suggest that the dynamo mode transition may be narrowed down to between M2.1 and M2.3. This is close to, but earlier than, the TTCC location identified by Jao et al (2018). We suggest that the transition in dynamo mode may be related to the existence of a small convective core which occurs for a finite time interval in certain low mass stars.

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“…For the determination of the magnetic field strength at height z = 0 km, we first compute the maximum allowed field of a void tube assuming the inner gas pressure p i = 0 dyne cm −2 ; this values also known as the equipartition field strength given by p e /8π = B eq taken at 0 km, the photospheric reference height. According to the initial atmospheric model, the resulting equipartition magnetic field strength is given as B eq = 1505 G. A comparison to the solar case, as well as in alignment to previous magneto-acoustic model simulations for other stars (e.g., Fawzy & Cuntz 2018Cuntz et al 2021), we choose a surface magnetic field strength given as 0.85 B eq . Nevertheless, as part of our parameter study of magnetic energy generation based on longitudinal flux-tube waves, we consider a larger set of parameters η = B/B eq , given as 0.75, 0.85, and 0.95.…”

Section: Flux Tubes Modelsmentioning

confidence: 99%

Evolution of solar-type activity: acoustic and magnetic energy generation and propagation in $\beta $ Hydri (G2 IV)

Fawzy

Cuntz

2023

Astrophys Space Sci

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We examine the acoustic and magnetic energy generation and propagation in β Hydri (G2 IV). The underlying motivation for this work is based on the solar, stellar, and galactic relevance of β Hyi (a star in the Southern hemisphere), which is readily understood as a prime example and proxy of the future Sun -thus allowing assessments and analyses of the secular decay of solar activity. Regarding the magnetic energy generation, we consider longitudinal flux tube waves. We also assess acoustic waves. For the acoustic wave energy flux, the difference between the results obtained for β Hyi and the Sun is significantly smaller than typically attained for main-sequence stars, which is largely due to the gravity-dependence of the acoustic energy generation. Furthermore, we study the height-dependent behavior of the magnetic energy flux for different magnetic filling factors corresponding to different flux tube spreadings. Finally, we comment on possible directions of future research.

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Chromospheric activity in ϵ $\epsilon$ Eridani: results from theoretical wave studies

Cited by 7 publications

References 51 publications

Chromospheric Activity in 55 Cancri: I. Results from Theoretical Wave Studies

Chromospheric Activity in 55 Cancri: I. Results from Theoretical Wave Studies

A Transition of Dynamo Modes in M Dwarfs: Narrowing Down the Spectral Range Where the Transition Occurs*

Evolution of solar-type activity: acoustic and magnetic energy generation and propagation in $\beta $ Hydri (G2 IV)

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