Author name code: rammacher ADS astronomy entries on 2022-09-14 author:"Rammacher, Wolfgang" ------------------------------------------------------------------------ Title: Solar magnetic flux tube simulations with time-dependent ionization Authors: Fawzy, D. E.; Cuntz, M.; Rammacher, W. Bibcode: 2012MNRAS.426.1916F Altcode: 2012arXiv1208.1490F 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. Title: Linear wavelength correlation matrices of photospheric and chromospheric spectral lines. I. Observations vs. modeling Authors: Beck, C. A. R.; Rammacher, W. Bibcode: 2010A&A...510A..66B Altcode: 2009arXiv0909.2224B Context. The process that heats the solar chromosphere is a difficult target for observational studies because the assumption of local thermal equilibrium (LTE) is not valid in the upper solar atmosphere, which complicates the analysis of spectra.
Aims: We investigate the linear correlation coefficient between the intensities at different wavelengths in photospheric and chromospheric spectral lines because the correlation can be determined directly for any spectra from observations or modeling. Waves which propagate vertically through the stratified solar atmosphere affect different wavelengths at different times when the contribution functions for each wavelength peak in different layers. This leads to a characteristic pattern of (non-)coherence of the intensity at various wavelengths with respect to each other which carries information on the physical processes.
Methods: We derived the correlation matrices for several photospheric and chromospheric spectral lines from observations. We separated locations with a significant photospheric polarization signal and thus magnetic fields from those without a polarization signal. For comparison with the observations, we calculated correlation matrices for spectra from simplified LTE modeling approaches, 1-D NLTE simulations, and a 3-D MHD simulation run. We applied the correlation method also to temperature maps at different optical depth layers derived from a LTE inversion of Ca II H spectra.
Results: We find that all photospheric spectral lines show a similar pattern: a pronounced asymmetry of the correlation between line core and red or blue wing. The pattern cannot be reproduced with a simulation of the granulation pattern, but with waves that travel upwards through the formation heights of the lines. The correct asymmetry between red and blue wing only appears when a temperature enhancement occurs simultaneously with a downflow velocity in the wave simulation. All chromospheric spectral lines show a more complex pattern. The 1-D NLTE simulations of monochromatic waves produce a correlation matrix that qualitatively matches the observations near the very core of the Ca II H line. The photospheric signature is well reproduced in the correlation matrix derived from the 3-D MHD simulation.
Conclusions: The correlation matrices of observed photospheric and chromospheric spectral lines are highly structured with characteristic and different patterns in every spectral line. The comparison with matrices derived from simulations and simple modeling suggests that the main driver of the detected patterns are upwards propagating waves. Application of the correlation method to 3-D temperature cubes seems to be a promising tool for a detailed comparison of simulation results and observations in future studies. Title: Simultaneous Maps of the Chromosphere for Ca II H and Ca II 8662 Authors: Rammacher, W.; Schmidt, W.; Hammer, R. Bibcode: 2008ESPM...12.2.40R Altcode: We study chromospheric dynamics by analyzing long (up to 3200 s), high spatial resolution time series of slit spectra of the Ca II H line and the Ca II infrared line at 8662 Angstrom recorded simultaneously near disk center of the Sun with the Echelle Spectrograph of the VTT on Tenerife in June 2007. Fast scans with 6 steps (0.5" per step) were done resulting in small stripes 3.5" wide and 160" long. A scan repetition time of 8 s was reached. These small 2D maps allow us to discover bright points, to follow their horizontal motion, and to associate photospheric objects. Horizontal variations of the intensity with time can be found for both lines and all wavelengths, including cases in which patches of enhanced intensity move rapidly over the entire map, with horizontal velocities of up to 30 km/s.

We study also a series of large x-y-maps (size 160" x 120"), simultaneously recorded for the Ca II H and Ca II 8662 lines. Because of the high spectral resolution we get for both lines 975 wavelength points covering spectral ranges of nearly 4.7 (H) and 10.3 (8662) Angstrom and therefore also 975 large maps for Ca II H as well as Ca II 8662: one X-Y map for each resolved wavelength. Our quasi-monochromatic maps have much narrower contribution functions than the usual filtergrams taken in rather broad spectral regions of the Ca II H & 8662 lines; thus they allow a more precise mapping of features to atmospheric regions of limited height extension. Title: CaII H+K & MgII h+k line Fluxes from Basal Flux Stars Authors: Gadelmavla, D.; Diaa, F.; Stepien, K.; Rammacher, W. Bibcode: 2008ESPM...12..4.2G Altcode: The heating mechanisms of the solar chromosphere are still under discussion. Helpful for this topic is to look for basal flux stars that are similar to the Sun.

The minimum observed CaII H+K & MgII h+k line fluxes from stellar Chromospheres as function of effective temperature Teff are called basal flux lines. It is widely thought that these fluxes are caused by non-magnetic heating of the outer stellar atmospheres. We present numerical calculations of basal fluxes for a variety of stars (G0 - K5) of different metallicity and gravity based on self-consistent time-dependent chromospheric models: Assuming purely acoustic heating we theoretically investigate the differences between the basal flux lines of dwarfs, giants and low metallicity stars and compare them with observations. Since basal flux stars rotate very slowly, they are not supposed to be dominated by magnetic fields and therefore their chromospheres should depend only on the three parameters Teff, gravity g and metallicity Z.

Since our acoustic models also depend only on these three parameters, this Comparison could turn out to be a powerful argument for the reality of the acoustic heating picture. Title: The signature of chromospheric heating in Ca II H spectra Authors: Beck, C.; Schmidt, W.; Rezaei, R.; Rammacher, W. Bibcode: 2008A&A...479..213B Altcode: 2007arXiv0712.2538B Context: The heating process that balances the solar chromospheric energy losses has not yet been determined. Conflicting views exist on the source of the energy and the influence of photospheric magnetic fields on chromospheric heating.
Aims: We analyze a 1-h time series of cospatial Ca II H intensity spectra and photospheric polarimetric spectra around 630 nm to derive the signature of the chromospheric heating process in the spectra and to investigate its relation to photospheric magnetic fields. The data were taken in a quiet Sun area on disc center without strong magnetic activity.
Methods: We have derived several characteristic quantities of Ca II H to define the chromospheric atmosphere properties. We study the power of the Fourier transform at different wavelengths and the phase relations between them. We perform local thermodynamic equilibrium (LTE) inversions of the spectropolarimetric data to obtain the photospheric magnetic field, once including the Ca intensity spectra.
Results: We find that the emission in the Ca II H line core at locations without detectable photospheric polarization signal is due to waves that propagate in around 100 s from low forming continuum layers in the line wing up to the line core. The phase differences of intensity oscillations at different wavelengths indicate standing waves for ν < 2 mHz and propagating waves for higher frequencies. The waves steepen into shocks in the chromosphere. On average, shocks are both preceded and followed by intensity reductions. In field-free regions, the profiles show emission about half of the time. The correlation between wavelengths and the decorrelation time is significantly higher in the presence of magnetic fields than for field-free areas. The average Ca II H profile in the presence of magnetic fields contains emission features symmetric to the line core and an asymmetric contribution, where mainly the blue H2V emission peak is increased (shock signature).
Conclusions: We find that acoustic waves steepening into shocks are responsible for the emission in the Ca II H line core for locations without photospheric magnetic fields. We suggest using wavelengths in the line wing of Ca II H, where LTE still applies, to compare theoretical heating models with observations.

Appendices are only available in electronic form at http://www.aanda.org Title: Simultaneous Observations of Solar Ca II H and Ca II 8662 lines and Numerical Simulation of these lines Authors: Rammacher, Wolfgang; Schmidt, Wolfgang; Hammer, Reiner Bibcode: 2007AN....328..657R Altcode: No abstract at ADS Title: What is Heating the Quiet-Sun Chromosphere? Authors: Wedemeyer-Böhm, S.; Steiner, O.; Bruls, J.; Rammacher, W. Bibcode: 2007ASPC..368...93W Altcode: 2006astro.ph.12627W It is widely believed that the heating of the chromosphere in quiet-Sun internetwork regions is provided by dissipation of acoustic waves that are excited by the convective motions close to the top of the convection zone and in the photospheric overshoot layer. This view lately became challenged by observations suggesting that the acoustic energy flux into the chromosphere is too low, by a factor of at least ten. Based on a comparison of TRACE data with synthetic image sequences for a three-dimensional simulation extending from the top layers of the convection zone to the middle chromosphere, we come to the contradicting conclusion that the acoustic flux in the model provides sufficient energy for heating the solar chromosphere of internetwork regions. The role of a weak magnetic field and associated electric current sheets is also discussed. Title: Observations and Simulations of Ca II H and Ca II 8662 Authors: Rammacher, W.; Schmidt, W.; Hammer, R. Bibcode: 2007ASPC..368..147R Altcode: We study chromospheric dynamics by analyzing long high spatial resolution time series of spectra of the Ca II H line and the Ca II infrared line at 8662 Å, recorded simultaneously near disk center of the sun. The observations were made at the VTT, Tenerife. The time series have a temporal resolution of 3 (8662) and 6 s (H), respectively. After the statistical analysis of the observation results, we used 1-D chromosphere simulation codes to make a series of computations with purely acoustic waves to obtain a time series of synthetic line profiles for Ca II H. A comparison of observational and theoretical results shows profound differences between these model calculations and the observations. A more detailed description of this work is in preparation and will be published in a main astronomy journal. Title: Acoustic Heating of the Solar Chromosphere: Present Indeed and Locally Dominant Authors: Cuntz, M.; Rammacher, W.; Musielak, Z. E. Bibcode: 2007ApJ...657L..57C Altcode: We investigate the physical reality of acoustic heating in the solar chromosphere. Evidence is provided that contrary to previous claims by Fossum & Carlsson, high-frequency acoustic waves are indeed sufficient to heat the nonmagnetic solar chromosphere. This assessment is based on three different lines of evidence, which are (1) a discussion of the inherent problems of the limited sensitivity of TRACE when assessing the three-dimensional solar chromospheric topology, (2) a study of the acoustic chromospheric wave energy flux, and (3) a new look at the heating and emission of chromospheric basal flux stars such as τ Ceti. Title: How Strong is the Dependence of the Solar Chromosphere upon the Convection Zone? Authors: Rammacher, W. Bibcode: 2005ESASP.596E..60R Altcode: 2005ccmf.confE..60R No abstract at ADS Title: On the Validity of Acoustically Heated Chromosphere Models Authors: Ulmschneider, P.; Rammacher, W.; Musielak, Z. E.; Kalkofen, W. Bibcode: 2005ApJ...631L.155U Altcode: Theoretical models of solar and stellar chromospheres heated by acoustic waves have so far been constructed by using time-dependent, one-dimensional, radiation-hydrodynamic numerical codes that are based on the approximation of plane-parallel geometry. The approach seems to be justified by the fact that the chromospheres of most stars extend over very narrow height ranges compared to the stellar radius. It is demonstrated that this commonly used assumption may lead to unrealistic shock mergings, to the artificial formation of unusually strong shocks and the artificial destruction of high-frequency acoustic wave power. Comparing one-dimensional calculations with observations may lead to severe misjudgment about the nature of chromospheric heating. Title: Fast Method for Calculating Chromospheric Ca II and Mg II Radiative Losses Authors: Rammacher, W.; Fawzy, D.; Ulmschneider, P.; Musielak, Z. E. Bibcode: 2005ApJ...631.1113R Altcode: A fast and reasonably accurate method for calculating the total radiative losses by Ca II and Mg II ions for time-dependent chromospheric wave calculations has been developed. The method is based on a two-level atom procedure with pseudo-partial frequency redistribution (pseudo-PRD). The speed of the method is due to scaling of the total losses from single-line results. Acceleration of computation speeds by factors of roughly 102-103 can be achieved. The method is tested against the results from a modified version of the multilevel atom code MULTI. Title: Definition and significance of average temperatures in time-dependent solar chromosphere models Authors: Rammacher, W.; Cuntz, M. Bibcode: 2005A&A...438..721R Altcode: We assess different types of average temperatures in time-dependent solar chromosphere models. They include the conventional definition of mean and median temperature, and a formal definition related to the model-dependent hydrogen ionization degree, referred to as ionization temperature. It is found that the latter is always higher than the mean and median temperatures, except in the photosphere, and that the mean temperatures are always higher than the median temperatures, especially in models with frequency spectra. The most dramatic differences are attained in the topmost portion of one of our models with the ionization temperatures up to a factor 150 higher than the mean and median temperatures. The differences between the mean, median, and ionization temperatures are a direct consequence of nonlinearities (“spikyness”) of the temperatures in the models mostly due to strong shocks. The main results hold for both acoustic and magnetic models despite significant differences in the initial wave energy fluxes, densities, and geometrical settings. Title: Time-dependent ionization in solar magnetic flux tubes Authors: Rammacher, W.; Cuntz, M. Bibcode: 2005ESASP.560..891R Altcode: 2005csss...13..891R No abstract at ADS Title: Acoustic Heating Models for the Basal Flux Star τ Ceti Including Time-dependent Ionization: Results for Ca II and Mg II Emission Authors: Rammacher, W.; Cuntz, M. Bibcode: 2003ApJ...594L..51R Altcode: We present new calculations of chromospheric heating for τ Ceti (G8 V), a star exhibiting an extremely low level of chromospheric activity, thus also referred to as a basal flux star or a flat activity star. Our simulations consider energy deposition by acoustic shocks and also take into account time-dependent (i.e., noninstantaneous) ionization processes of hydrogen, magnesium, and calcium, allowing us to attain a new generation of chromospheric heating models previously obtained for the Sun. We consider both monochromatic waves and acoustic frequency spectra. The latter are calculated using new models of acoustic energy generation based on an extended Kolmogorov spectrum with a modified Gaussian frequency factor. Our models show that the theoretically deduced emergent Ca II and Mg II emission very much agree with observations, adding to the argument that the chromospheres of basal flux stars are predominantly heated by acoustic shocks. Title: Time-dependent Ionization in Dynamic Solar and Stellar Atmospheres. I. Methods Authors: Rammacher, W.; Ulmschneider, P. Bibcode: 2003ApJ...589..988R Altcode: We propose a new numerical method to compute one-dimensional time-dependent wave propagation in stellar atmospheres that incorporates the time-dependent treatment of hydrogen ionization together with an evaluation of radiation losses under departures from local thermodynamic equilibrium (NLTE). The method permits us to calculate acoustic waves and longitudinal magnetohydrodynamic (MHD) tube waves. We have tested the method for the solar atmosphere by calculating the propagation of three types of waves, namely, a monochromatic acoustic wave, a stochastic acoustic wave, and a stochastic longitudinal tube wave. It was found that with a time-dependent treatment of the hydrogen ionization (as well as the Mg ionizations) the degree of ionization (H+/H) and the Mg II/Mg ratio become insensitive to the temperature fluctuations, even in the presence of weak and moderately strong shocks. Only when strong shocks appear do the transition rates become large enough to cause a high correlation between the degree of ionization and the high postshock temperatures. Our calculations show that a mean degree of ionization gets established that increases with height and is very little perturbed by the local temperature fluctuations of the wave. In stochastic calculations, strong shocks appeared periodically (roughly every 3 minutes), which in their postshock regions carried a zone of high or complete ionization. Tests with different numbers of frequency and height points, as well as of the rate of convergence of the Λ-iteration, were performed. Title: Acoustic and magnetic wave heating in stars . I. Theoretical chromospheric models and emerging radiative fluxes Authors: Fawzy, D.; Rammacher, W.; Ulmschneider, P.; Musielak, Z. E.; Stȩpień, K. Bibcode: 2002A&A...386..971F Altcode: We describe a method to construct theoretical, time-dependent, two-component and wave heated chromosphere models for late-type dwarfs. The models depend only on four basic stellar parameters: effective temperature, gravity, metallicity and filling factor, which determines the coverage of these stars by surface magnetic fields. They consist of non-magnetic regions heated by acoustic waves and vertically oriented magnetic flux tubes heated by longitudinal tube waves with contributions from transverse tube waves. Acoustic, longitudinal and transverse wave energy spectra and fluxes generated in stellar convection zones are computed and used as input parameters for the theoretical models. The waves are allowed to propagate and heat both components by shock dissipation. We compute the time-dependent energy balance between the dissipated wave energy and the most prominent chromospheric radiative losses as function of height in the stellar atmosphere. For the flux tube covered stars, the emerging radiative fluxes in the Ca II and Mg II lines are computed by using a newly developed multi-ray radiative transfer method. Title: Acoustic and magnetic wave heating in stars . II. On the range of chromospheric activity Authors: Fawzy, D.; Ulmschneider, P.; Stȩpień, K.; Musielak, Z. E.; Rammacher, W. Bibcode: 2002A&A...386..983F Altcode: In the first paper of this series we developed a method to construct theoretical, time-dependent and two-component chromosphere models for late-type main sequence stars. The models consist of non-magnetic regions heated by acoustic waves and magnetic flux tube regions heated by magnetic tube waves. By specifying the magnetic filling factor, theoretical models of stellar atmospheres with different chromospheric activity can be calculated. Here, these models are used to simulate the emerging Ca II and Mg II chromospheric emission fluxes and compare them with observations. The comparison shows that the wave heating alone can explain most but not all of the observed range of chromospheric activity. In addition, the results obtained clearly imply that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave (e.g., reconnective) heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres. Title: Acoustic and magnetic wave heating in stars . III. The chromospheric emission-magnetic filling factor relation Authors: Fawzy, D.; Stȩpień, K.; Ulmschneider, P.; Rammacher, W.; Musielak, Z. E. Bibcode: 2002A&A...386..994F Altcode: Theoretical chromospheric models described in the two previous papers of this series are used to study the relationship between the chromospheric emission and the filling factor. This theoretically determined relationship shows that the chromospheric emission flux in Ca II (H+K) is approximately proportional to the square root of the magnetic filling factor at the stellar surface. To relate the filling factor to stellar rotation rate, we compare the theoretical fluxes with observations of stars with known rotation period. The comparison shows that the Rossby number is probably a more appropriate measure of the rotation influence on activity of main-sequence stars than the rotation period. Our theoretical Mg II (h+k) and Ca II (H+K) emission fluxes are also found to be well correlated, which is in a good agreement with the observational data. Title: Main Heating Mechanisms in Stellar Atmospheres Authors: Musielak, Z. E.; Fawzy, D.; Ulmschneider, P.; Rammacher, W.; Stepien, K. Bibcode: 2001AAS...19914302M Altcode: 2001BAAS...33.1522M To identify the main heating mechanisms operating in atmospheres of late-type stars, we have constructed purely theoretical, two-component and time-dependent models of stellar chromospheres. Our models depend only on four basic stellar parameters: effective temperature, gravity, metallicity, and filling factor, which determines the coverage of these stars by surface magnetic fields and is treated as a free parameter. They consist of non-magnetic regions heated by acoustic waves and magnetic flux tubes heated by longitudinal and transverse tube waves. At each height in stellar atmospheres, the time-dependent energy balance between the dissipated wave energy and the most prominent radiative losses is calculated. By specifying the filling factor, theoretical models of stellar atmospheres with different chromospheric activity are computed. We have used these models to simulate the emerging Ca II and Mg II chromospheric emission fluxes and compare them with observations. The comparison shows that the wave heating alone can explain most but not all of the observed range of chromospheric activity. In addition, the obtained results clearly imply that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave (e.g., reconnective) heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres. This work was supported by NSF, NATO, DFG, KBN and The Alexander von Humboldt Foundation. Title: Self-Consistent Magnetic/Acoustic Chromosphere Models of Late-Type Stars (CD-ROM Directory: contribs/cuntz1) Authors: Cuntz, M.; Ulmschneider, P.; Rammacher, W.; Musielak, Z. E.; Saar, S. H. Bibcode: 2001ASPC..223..913C Altcode: 2001csss...11..913C No abstract at ADS Title: Two-Component Theoretical Chromosphere Models for K Dwarfs of Different Magnetic Activity: Exploring the Ca II Emission-Stellar Rotation Relationship Authors: Cuntz, M.; Rammacher, W.; Ulmschneider, P.; Musielak, Z. E.; Saar, S. H. Bibcode: 1999ApJ...522.1053C Altcode: We compute two-component theoretical chromosphere models for K2 V stars with different levels of magnetic activity. The two components are a nonmagnetic component heated by acoustic waves and a magnetic component heated by longitudinal tube waves. The filling factor for the magnetic component is determined from an observational relationship between the measured magnetic area coverage and the stellar rotation period. We consider stellar rotation periods between 10 and 40 days. We investigate two different geometrical distributions of magnetic flux tubes: uniformly distributed tubes, and tubes arranged as a chromospheric network embedded in the nonmagnetic region. The chromosphere models are constructed by performing state-of-the-art calculations for the generation of acoustic and magnetic energy in stellar convection zones, the propagation and dissipation of this energy at the different atmospheric heights, and the formation of specific chromospheric emission lines that are then compared to the observational data. In all these steps, the two-component structure of stellar photospheres and chromospheres is fully taken into account. We find that heating and chromospheric emission is significantly increased in the magnetic component and is strongest in flux tubes that spread the least with height, expected to occur on rapidly rotating stars with high magnetic filling factors. For stars with very slow rotation, we are able to reproduce the basal flux limit of chromospheric emission previously identified with nonmagnetic regions. Most importantly, however, we find that the relationship between the Ca II H+K emission and the stellar rotation rate deduced from our models is consistent with the relationship given by observations. Title: Two-Component Chromosphere Models for K Dwarf Stars: The Chromospheric Emission --- Stellar Rotation Relationship Authors: Cuntz, M.; Musielak, Z. E.; Ulmschneider, P.; Rammacher, W.; Saar, S. H. Bibcode: 1998AAS...193.4402C Altcode: 1998BAAS...30.1315C We present two-component theoretical chromosphere models for K dwarf stars with different levels of magnetic activity. The two components are: a nonmagnetic component heated by acoustic waves, and a magnetic component heated by longitudinal tube waves. The filling factor for the magnetic component is determined from an observational relationship between the stellar rotation rate and the measured coverage of stellar surface by magnetic fields. The chromosphere models are constructed by performing state-of-the-art calculations of the generation of acoustic and magnetic energy in stellar convection zones, the propagation and dissipation of this energy at the different atmospheric heights, and the formation of specific chromospheric emission lines, which are then compared to the observational data. In all these steps, the two-component structure of stellar photospheres and chromospheres is fully taken into account. We find that due to the presence of magnetic flux tubes, the heating and chromospheric emission is significantly increased in the magnetic component. The heating and chromospheric emission is found to be the strongest in flux tubes with small spreading factors which are expected to be present in fast rotating stars. For stars with very slow rotation we are able to reproduce the basal flux limit of chromospheric emission previously identified as due to pure acoustic heating. Most importantly, however, we find that the relationship between the Ca II H+K emission and the stellar rotation rate deduced from our models is consistent with the empirical relationship given by observations. Title: Chromospheric Heating and Metal Deficiency in Cool Giants: Theoretical Results versus Observations Authors: Cuntz, M.; Rammacher, W.; Ulmschneider, P. Bibcode: 1994ApJ...432..690C Altcode: We compute acoustic shock wave-heated chromosphere models for moderately cool giant stars which differ greatly in metallicity. Subsequently, we simulate the emerging Mg II k lines assuming partial redistribution. The initial acoustic energy fluxes and the wave periods are taken from acoustic wave generation calculations based on traditional convection zone models. We find that the Mg II and Ca II core emissions are close to the observed basal flux limits which are common for giants and dwarfs. In addition, we find that the Mg II core emission is independent of the metallicity, in agreement with observations. We argue that these results should be considered as further evidence that the basal flux limits are indeed due to acoustic shock heating. The acoustic heating mechanism seems to be dominant in all nonmagnetic nonpulsating late-type stars. Title: An operator splitting method for atmospheres with shocks Authors: Buchholz, B.; Hauschildt, P. H.; Rammacher, W.; Ulmschneider, P. Bibcode: 1994A&A...285..987B Altcode: We develop a fast operator splitting (OS) method to solve spectral line radiative transfer problems in time-dependent hydrodynamic computations with shock discontinuities, assuming complete redistribution. The convergence properties and the results obtained with our method are compared with results obtained using a modified core-saturation method and with the {LAMBDA}-iteration. We find that our operator splitting method is robust, accurate and fast. Title: Acoustic waves in the solar atmosphere. IX - Three minute pulsations driven by shock overtaking Authors: Rammacher, Wolfgang; Ulmschneider, Peter Bibcode: 1992A&A...253..586R Altcode: Computations are presented showing that short-period acoustic waves with periods less than 40 sec can generate, by the process of shock overtaking, 3-min type first-overtone pulsations of the solar chromosphere. It is suggested that 3-min pulsations generated by acoustic waves may be an explanation for the observed Ca II K(2V) cell grains. It is shown that shock overtaking occurs only if the wavelength of the shock wave is small enough, such that the excess speed of the faster moving shock is able to catch up with the slower shock within the chromosphere. It is suggested that the shock overtaking pulsation process, by feeding energy into long-period waves may be very important for the driving of mass loss in red giant stars. Title: Atmospheric Pulsations; Mass Loss Driven by Overtaking Acoustic Shocks Authors: Ulmschneider, P.; Rammacher, W.; Gail, H. -P. Bibcode: 1992ASPC...26..471U Altcode: 1992csss....7..471U No abstract at ADS Title: Effects of Mg II and Ca II ionization on ab-initio solar chromosphere models Authors: Rammacher, W.; Cuntz, M. Bibcode: 1991A&A...250..212R Altcode: Acoustically heated solar chromosphere models are computed considering radiation damping by (non-LTE) emission from H(-) and by Mg II and Ca II emission lines. The radiative transfer equations for the Mg II k and Ca II K emission lines are solved using the core-saturation method with complete redistribution. The Mg II k and Ca II K cooling rates are compared with the VAL model C. Several substantial improvements over the work of Ulmschneider et al. (1987) are included. It is found that the rapid temperature rises caused by the ionization of Mg II are not formed in the middle chromosphere, but occur at larger atmospheric heights. These models represent the temperature structure of the 'real' solar chromosphere much better. This result is a major precondition for the study of ab-initio models for solar flux tubes based on MHD wave propagation and also for ab-initio models for the solar transition layer. Title: Ca- und Mg-Linienbildung in dynamischen, magnetischen Sonnenregionen. Authors: Rammacher, W. Bibcode: 1991cumd.book.....R Altcode: Contents: 1. Einleitung. 2. Die Behandlung der Hydrodynamik. 3. Die Strahlungsbehandlung. 4. Das Verhalten der Mg II-k-Profile. 5. Diskussion der Ca II-K-Profile und Vergleich mit Mg II-k. 6. Linienentstehung und Blau-Rot-Asymmetrie. 7. Zwei-Komponent-Modelle. 8. Vergleich mit den Beobachtungen. Title: Line Simulation of Solar Structures Permeated by Acoustic and MHD-Waves (With 6 Figures) Authors: Rammacher, W. Bibcode: 1991mcch.conf..414R Altcode: No abstract at ADS Title: What Do the Mg II Lines Tell Us About Waves and Magnetic Fields? Authors: Rammacher, W.; Ulmschneider, P. Bibcode: 1989ASIC..263..589R Altcode: 1989ssg..conf..589R No abstract at ADS