13.1.1.3.3 Trisubstituted p-benzosemiquinones

Ulmschneider, K. B.; Stegmann, H. B.

doi:10.1007/10201292_46

Cited by 34 publications

(55 citation statements)

References 17 publications

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“…The wave energy fluxes and wave energy spectra are calculated following the approach by Musielak et al (1994) and Ulmschneider, Theurer & Musielak (1996); see also Fawzy & Cuntz (2011) for updated results pertaining to a grid of models for a set of mainsequence stars including the Sun. These types of models incorporate a detailed description of the spatial and temporal spectrum of the turbulent flow to obtain adequate results for the frequency integrated acoustic energy fluxes along with the wave frequency spectra; furthermore, they utilize an extended Kolmogorov spectrum with a modified Gaussian frequency factor.…”

Section: Wave Energy Fluxes and Wave Energy Spectramentioning

confidence: 99%

Solar magnetic flux tube simulations with time-dependent ionization

Fawzy

Cuntz

Rammacher

2012

Monthly Notices of the Royal Astronomical Society

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In the present work we expand the study of time-dependent ionization previously identified to be of pivotal importance for acoustic waves in solar magnetic flux tube simulations. We focus on longitudinal tube waves (LTW) known to be an important heating agent of solar magnetic regions. Our models also consider new results of wave energy generation as well as an updated determination of the mixing length of convection now identified as 1.8 scale heights in the upper solar convective layers. We present 1D wave simulations for the solar chromosphere by studying tubes of different spreading as a function of height aimed at representing tubes in environments of different magnetic filling factors. Multilevel radiative transfer has been applied to correctly represent the total chromospheric emission function. The effects of time-dependent ionization are significant in all models studied. They are most pronounced behind strong shocks and in low-density regions, i.e. the middle and high chromosphere. Concerning our models of different tube spreading, we attained pronounced differences between the various types of models, which were largely initiated by different degrees of dilution of the wave energy flux as well as the density structure partially shaped by strong shocks, if existing. Models showing a quasi-steady rise of temperature with height are obtained via monochromatic waves akin to previous acoustic simulations. However, longitudinal flux tube waves are identified as insufficient to heat the solar transition region and corona in agreement with previous studies.

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Section: Wave Energy Fluxes and Wave Energy Spectramentioning

confidence: 99%

Solar magnetic flux tube simulations with time-dependent ionization

Fawzy

Cuntz

Rammacher

2012

Monthly Notices of the Royal Astronomical Society

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“…The pressure fluctuations produced by turbulent motions squeeze the flux tubes and thus generate wave energies. For the current computations, we follow the approach described by Ulmschneider & Musielak (1998) and in Paper I to model turbulent motions by using an extended Kolmogorov turbulent energy spectrum with a modified Gaussian frequency factor (Musielak et al 1994). The computations require specifying the rms velocity fluctuations at a squeezing point as given by u t = v CMax /2, with v CMax being the maximum convective velocity (refer to Paper I for the choice of u t ).…”

Section: Magnetic Flux Tube-convection Zone Interactionmentioning

confidence: 99%

“…A study performed by Ulmschneider & Musielak (1998) has shown that the location of the squeezing point does not affect the generated wave energy fluxes. Based on this result, we fix the location for all our computed cases to τ 5000 = 1.…”

Section: Magnetic Flux Tube-convection Zone Interactionmentioning

confidence: 99%

“…We concentrate here on the mechanical energy production that depends on whether one has a region permeated by magnetic fields or one without fields. For field-free regions where the main heating mechanism is acoustic waves, we have computed the spectra and energy fluxes of these waves for a wide variety of stars of different effective temperatures T eff , gravities log g and metallicities Z m (Ulmschneider, Theurer & Musielak 1996;Ulmschneider et al 1999). Created by turbulence in the stellar convection zone, some waves propagate under a wide range of angles in outward directions, and due to the rapid density decrease near the stellar surface they steepen into shocks above it.…”

Section: Introductionmentioning

confidence: 99%

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Longitudinal magnetic tube wave fluxes in stars of low metallicity

Fawzy

2010

Monthly Notices of the Royal Astronomical Society

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A modified theory of turbulence generation is combined with the magnetohydrodynamic equations to numerically compute the wave energies generated at the base of magnetic flux tubes for stars with effective temperatures ranging from Teff= 3000 to 7000 K, gravity log g= 4.44 and with different metal abundances: solar, 0.1, 0.01 and 0.001 of solar metallicity. The results show that the effect of metallicity is very important for cool stars (Teff < 5500 K). The current numerical approach allows for non‐linear waves with large amplitudes and thus the obtained results for time‐averaged wave energy fluxes are higher than those obtained by the analytical approach. For hot stars the effect is negligible. The computed energy fluxes are essential for constructing theoretical models of the magnetic chromosphere of low‐metallicity stars. The maximum obtained wave energy flux for low‐metallicity stars is about 7.3 × 108 erg cm−2 s−1.

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“…Physically, this might arise because turbulent velocities v t are increased in the lower density tidal bulges. Since generation of acoustic and magnetic wave energy depends on v 8 t (Lighthill 1952;Stein 1967;Musielak et al 1994) and v 6 t (Musielak, Rosner & Ulmschneider 1989;Ulmschneider & Musielak 1998), respectively, even small increases in v t caused by nearby planets will result in significantly enhanced production of non-radiative energy. Tidal amplification of flows, waves and shocks in the outer atmosphere will also lead to increased heating.…”

Section: Introductionmentioning

confidence: 99%

A search for Ca II emission enhancement in stars resulting from nearby giant planets

Saar

Cuntz

2001

Monthly Notices of the Royal Astronomical Society

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We present a search for periodicities (Pchr) in the chromospheric Ca ii infrared triplet emission of several stars (τ Boo, 51 Peg, υ And, ρ1 Cnc, ρ CrB, 70 Vir and GL 876) which may be directly attributable to interaction with close‐in giant planets. Activity enhancements could arise from increased non‐radiative heating and dynamo action in planet‐induced tidal bulges (with Pchr≈Porb/2), or from interactions between the stellar and planetary magnetic fields (with Pchr≈Porb). We compare both Pchr and the phase dependence of the activity with the planetary orbital period Porb, the orbital phase, and models. No significant Pchr or phase dependence attributable to planets can be clearly identified. We place approximate upper limits on the amplitude of any planet‐induced activity. We identify a possible stellar rotation period for GL 876, and support previous period determinations for four other stars. We discuss the results and possible directions of future research.

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13.1.1.3.3 Trisubstituted p-benzosemiquinones

Cited by 34 publications

References 17 publications

Solar magnetic flux tube simulations with time-dependent ionization

Solar magnetic flux tube simulations with time-dependent ionization

Longitudinal magnetic tube wave fluxes in stars of low metallicity

A search for Ca II emission enhancement in stars resulting from nearby giant planets

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