Author name code: musielak ADS astronomy entries on 2022-09-14 author:"Musielak, Zdzislaw E." ------------------------------------------------------------------------ Title: Determining Hill Stability of Triple Stellar Systems with Confirmed Exoplanets Authors: Boyle, Lindsey; Rosario-Franco, Marialis; Musielak, Zdzislaw Bibcode: 2021DPS....5321211B Altcode: The universe contains a multitude of stellar systems with configurations that range from single star systems up to sextuplet star systems. A percentage of these multi-star systems contain exoplanets. Out of a total of 35 multi-stellar systems with exoplanets, 33 are triple-star systems. This work aims to provide insight into the dynamics of such systems by determining the topological boundary that forbids close encounters for an infinite time, otherwise known as Hill stability. Motivated by this, we apply the criterion established in Walker (1983) to determine the Hill stability of the triple stellar components by calculating the stability coefficient and comparing it with the semi-major axis coefficient of the system. Additionally, we extend it to corroborate the Hill stability of the planets within. We found 17 triple stellar systems out of the 18 in our sample to be Hill stable. Within these 17 systems, 29 planets are shown to be Hill stable as well.

Cross-listed as presentation #403.02. Title: Spatial variation in the periods of ion and neutral waves in a solar magnetic arcade Authors: Kuźma, B.; Murawski, K.; Musielak, Z. E.; Poedts, S.; Wójcik, D. Bibcode: 2021A&A...652A..88K Altcode: 2021arXiv210509882K Context. We present new insight into the propagation of ion magnetoacoustic and neutral acoustic waves in a magnetic arcade in the lower solar atmosphere.
Aims: By means of numerical simulations, we (a) study two-fluid waves propagating in a magnetic arcade embedded in the partially ionised, lower solar atmosphere and (b) investigate the effect of the background magnetic field configuration on the observed wave-periods.
Methods: We considered a 2D approximation of the gravitationally stratified and partially ionised lower solar atmosphere consisting of ion plus electron and neutral fluids that are coupled by ion-neutral collisions. In this model, the convection below the photosphere causes the excitation of ion magnetoacoustic-gravity and neutral acoustic-gravity waves.
Results: We find that in the solar photosphere, where ions and neutrals are strongly coupled by collisions, ion magnetoacoustic-gravity and neutral acoustic-gravity waves have periods ranging from 250 s to 350 s. In the chromosphere, where the collisional coupling is weak, the wave characteristics strongly depend on the magnetic field configuration. Above the footpoints of the considered arcade, the plasma is dominated by a vertical magnetic field along which ion magnetoacoustic-gravity waves propagate. These waves exhibit a broad range of periods, and the most prominent periods are 180 s, 220 s, and 300 s. Above the main loop of the solar arcade, where mostly horizontal magnetic field lines guide ion magnetoacoustic-gravity waves, the main spectral power reduces to the period of about 180 s, and no longer wave-periods exist.
Conclusions: In photospheric regions, ongoing solar granulation excites a broad spectrum of wave-periods that undergoes complex interactions: mode-coupling, refractions through the inhomogeneous atmosphere, real physical absorption, and conversion of wave power. We found that, in addition, the magnetic arcade configuration with a partially ionised plasma drastically changes the image of wave-periods observed in the upper layers of the chromosphere and corona. Our results agree with recent observational data. Title: New equation of nonrelativistic physics and theory of dark matter Authors: Musielak, Z. E. Bibcode: 2021IJMPA..3650042M Altcode: 2021arXiv210414345M Two infinite sets of Galilean invariant equations are derived using the irreducible representations of the orthochronous extended Galilean group. It is shown that one set contains the Schrödinger equation, which is the fundamental equation for ordinary matter, and the other set has a new asymmetric equation, which is proposed to be the fundamental equation for dark matter. Using this new equation, a theory of dark matter is developed and its profound physical implications are discussed. This theory explains the currently known properties of dark matter and also predicts a detectable gravitational radiation. Title: New cutoff frequency for torsional Alfvén waves propagating along wide solar magnetic flux tubes Authors: Routh, Swati; Musielak, Z. E.; Sundar, M. N.; Joshi, Sai Sravanthi; Charan, Sree Bibcode: 2020Ap&SS.365..139R Altcode: 2020arXiv200803653R An isolated, isothermal, and wide magnetic flux tube embedded either in the solar chromosphere or in the lower solar corona is considered, and the propagation of linear torsional Alfvén waves is investigated. It is shown that the wideness of the tube leads to a new cutoff frequency, which is a local quantity that gives the conditions for the wave propagation at different atmospheric heights. The cutoff is used to establish the ranges of frequencies for the propagating and reflected waves in the solar chromosphere and lower solar corona. The obtained results are compared to those previously obtained for thin magnetic flux tubes and the differences are discussed. Moreover, the results are also compared to some current observational data, and used to establish the presence of propagating waves in the data at different atmospheric heights; this has profound implications on the energy and momentum transfer by the waves in the solar atmosphere, and the role of linear torsional Alfvén waves in the atmospheric heating and wind acceleration. Title: 3D Numerical Simulations of Solar Quiet Chromosphere Wave Heating Authors: Murawski, K.; Musielak, Z. E.; Wójcik, D. Bibcode: 2020ApJ...896L...1M Altcode: Despite numerous observational and theoretical attempts, the heating problem of the solar chromosphere still remains unsolved. We develop a novel 3D two-fluid model that accounts for dynamics of charged species and neutrals, and use it to perform the numerical simulations of granulation driven jets and associated waves in a quiet region of the solar chromosphere. The energy carried by the waves is dissipated through ion-neutral collisions, which are sufficient to balance radiative energy losses and to sustain the quasi-stationary atmosphere whose ion and neutral number densities, ionization fraction, and temperature profiles are relatively close to the observationally based semi-empirical model. Additional verification of our results is provided by a good fit of the numerically predicted waveperiod variations with height to the recent observational data. These observational validations of the numerical results demonstrate that the wave heating problem of a quiet region of the chromosphere may be solved. Title: Orbital Stability of Exomoons and Submoons with Applications to Kepler 1625b-I Authors: Rosario-Franco, Marialis; Quarles, Billy; Musielak, Zdzislaw E.; Cuntz, Manfred Bibcode: 2020AJ....159..260R Altcode: 2020arXiv200506521R An intriguing question in the context of dynamics arises: could a moon possess a moon itself? Such a configuration does not exist in the solar system, although this may be possible in theory. Kollmeier & Raymond determined the critical size of a satellite necessary to host a long-lived subsatellite, or submoon. However, the orbital constraints for these submoons to exist are still undetermined. Domingos et al. indicated that moons are stable out to a fraction of the host planet's Hill radius RH,p, which in turn depend on the eccentricity of its host's orbit. Motivated by this, we simulate systems of exomoons and submoons for 105 planetary orbits, while considering many initial orbital phases to obtain the critical semimajor axis in terms of RH,p or the host satellite's Hill radius RH,sat, respectively. We find that, assuming circular coplanar orbits, the stability limit for an exomoon is 0.40 RH,p and for a submoon is 0.33 RH,sat. Additionally, we discuss the observational feasibility of detecting these subsatellites through photometric, radial velocity, or direct imaging observations using the Neptune-sized exomoon candidate Kepler 1625b-I and identify how stability can shape the identification of future candidates. Title: Wave heating of the solar atmosphere without shocks Authors: Wójcik, D.; Kuźma, B.; Murawski, K.; Musielak, Z. E. Bibcode: 2020A&A...635A..28W Altcode: Context. We investigate the wave heating problem of a solar quiet region and present its plausible solution without involving shock formation.
Aims: We aim to use numerical simulations to study wave propagation and dissipation in the partially ionized solar atmosphere, whose model includes both neutrals and ions.
Methods: We used a 2.5D two-fluid model of the solar atmosphere to study the wave generation and propagation. The source of these waves is the solar convection located beneath the photosphere.
Results: The energy carried by the waves is dissipated through ion-neutral collisions, which replace shocks used in some previous studies as the main source of local heating in quiet regions.
Conclusions: We show that the resulting wave dissipation is sufficient to balance radiative and thermal energy losses, and to sustain a quasi-stationary atmosphere whose averaged temperature profile agrees well with the observationally based semi-empirical model of Avrett & Loeser (2008, ApJS, 175, 229). Title: Partially Ionized Solar Atmosphere: Two-fluid Waves and Their Cutoffs Authors: Wójcik, D.; Murawski, K.; Musielak, Z. E. Bibcode: 2019ApJ...882...32W Altcode: A novel model of the solar atmosphere that accounts for partially ionized plasma is developed and used to study the propagation of magnetoacoustic-gravity waves, which are generated by solar granulation. The model includes neutrals in otherwise ionized plasma and therefore the considered waves are two-fluid waves. Numerical simulations of these waves allow computing their cutoff period and its variations in the solar atmosphere. The results of these computations are compared to the observational data collected by Wiśniewska et al. and Kayshap et al., and a good agreement between the theory and observations is obtained. This first theoretical confirmation of the observational data profoundly shows the importance of effects caused by partially ionized plasma on the behavior of waves in the solar atmosphere, and on the origin of solar chromospheric oscillations. It is also suggested that theoretically predicted differences between the behavior of ions and neutrals can be verified by some currently operating solar missions. Title: Determining Stability Conditions for Submoons Orbiting Exomoon Candidate: Kepler 1625-b-I Authors: Rosario-Franco, Marialis; Quarles, Billy; Musielak, Zdzislaw E.; Cuntz, Manfred Bibcode: 2019DDA....5030309R Altcode: An intriguing question in the context of dynamics arises: Could a moon possess a moon itself? Such a configuration does not exist in the Solar System, although this may be possible in theory; Kollmeier & Raymond (2019) showed the critical size of a satellite necessary to host a long-lived sub-satellite, or submoon. However, the orbital constraints for these submoons to exist are still undetermined, where a critical parameter is how far from the host satellite can these submoons orbit. Previous studies (Domingos et al. 2006) indicate that moons should be stable out to a fraction of the host planet's Hill sphere, which in turn will depend on the eccentricity and inclination of its orbit. Motivated by this, we have performed orbital integrations of the exomoon candidate Kepler 1625-b-I, a Neptune-sized exomoon candidate that orbits the Jovian planet Kepler 1625-b (Teachey & Kipping 2018). In our numerical study, we evaluate the orbital parameters where possible submoons could be stable by varying the eccentricity and inclination of their orbits. Moreover, we provide discussion on the observational consequences of observing these satellites through photometric or radial velocity observations. Title: Cutoff periods of magnetoacoustic waves in the solar atmosphere Authors: Kraśkiewicz, J.; Murawski, K.; Musielak, Z. E. Bibcode: 2019A&A...623A..62K Altcode: We perform numerical simulations of magnetoacoustic waves (MAWs) in the solar atmosphere, which is gravitationally stratified and structured by either vertical or horizontal uniform magnetic fields. These waves are excited by a monochromatic driver that operates in the photosphere. We show that the gradients of the atmospheric parameters lead to filtering of the waves through the solar atmosphere and to variations of the dominant wave period with height. We use these variations to determine a local cutoff period, which shows a good agreement with the previously obtained analytical and numerical results in an isothermal solar atmosphere. In our numerical simulations, the propagation of MAWs in a more realistic model of the solar atmosphere is considered, and the obtained results demonstrate that the waves with periods higher than a local cutoff wave period are strongly reflected and become evanescent with height, while the waves with shorter wave periods are propagating, and may even reach the solar corona. Some of the evanescent waves may also tunnel and reach the atmospheric heights that would not be otherwise accessible to them. An important result of our study is excitation of chromospheric oscillations with periods equal to the period that is comparable to the observed solar chromospheric oscillations. Implications of our theoretical predictions are discussed. Title: Acoustic waves in two-fluid solar atmosphere model: cut-off periods, chromospheric cavity, and wave tunnelling Authors: Wójcik, D.; Murawski, K.; Musielak, Z. E. Bibcode: 2018MNRAS.481..262W Altcode: 2018MNRAS.tmp.2189W We perform numerical simulations of acoustic waves in a two-fluid model of quiet region of the solar atmosphere. The two-fluid model describes partially ionized (non-magnetized) solar plasma, whose main components are neutral atoms, protons, and electrons. The waves are excited by a monochromatic driver, which operates at the bottom of the solar photosphere. Our numerical results show that the driver excites ion and neutral acoustic waves whose propagation is affected by the gravity. As a result, the acoustic waves with periods higher than a local acoustic cut-off period are evanescent, while lower waveperiods are free to reach the solar corona. Acoustic waves, which are evanescent in the photosphere and low chromosphere, tunnel their energy into the upper chromosphere and the transition region. The wave propagation to the solar corona is affected by partial wave reflection that occurs in the transition region, and is responsible for formation of a cavity, where the waves are trapped. Fourier power analysis of temporal characteristic of plasma quantities reveals that a spectrum of various periods is generated. While oscillations traced in ion and neutral velocities look very similar, dynamics of mass densities of ions and neutrals differs a lot. The obtained results clearly show that the two-fluid model provides new insights into the acoustic wave propagation in a more realistic (partially ionized) quiet region of the solar atmosphere. Title: Confined pseudo-shocks as an energy source for the active solar corona Authors: Srivastava, Abhishek Kumar; Murawski, Krzysztof; Kuźma, BlaŻej; Wójcik, Dariusz Patryk; Zaqarashvili, Teimuraz V.; Stangalini, Marco; Musielak, Zdzislaw E.; Doyle, John Gerard; Kayshap, Pradeep; Dwivedi, Bhola N. Bibcode: 2018NatAs...2..951S Altcode: 2018NatAs.tmp..138S The Sun's active corona requires an energy flux of 103 W m-2 to compensate for radiative losses and to maintain its high temperature1. Plasma moves in the corona through magnetic loops2,3, which may be connected with the flows in and around sunspots4-6. Global energizing processes (for example, reconnection) play an important part in heating the corona7-9; however, energy and mass transport may also occur via shocks, waves or flows5,10,11. A full picture and the influence of such localized events, which significantly couple with various layers of the solar upper atmosphere, is still not clear. Using the Interface Region Imaging Spectrograph temporal image data of C uc(ii) 1,330 Å, we observed the presence of pseudo-shocks around a sunspot. Unlike shocks12, pseudo-shocks exhibit discontinuities only in the mass density. A two-fluid numerical simulation reproduces such confined pseudo-shocks with rarefied plasma regions lagging behind them. We find that these pseudo-shocks carry an energy of 103 W m-2, which is enough to locally power the inner corona and also generate bulk flows ( 10-5 kg m-2 s-1), contributing to the localized mass transport. If they are ubiquitous, such energized and bulky pseudo-shocks above active regions could provide an important contribution to the heating and mass transport in the overlying solar corona. Title: Vertical propagation of acoustic waves in the solar internetworkas observed by IRIS Authors: Kayshap, P.; Murawski, K.; Srivastava, A. K.; Musielak, Z. E.; Dwivedi, B. N. Bibcode: 2018MNRAS.479.5512K Altcode: 2018arXiv180701449K; 2018MNRAS.tmp.1776K We investigate the Interface Region Imaging Spectrograph (IRIS) observations of the quiet-Sun (QS) to understand the propagation of acoustic waves in transition region (TR) from photosphere. We selected a few IRIS spectral lines, which include the photospheric (Mn I 2801.25 Å), chromospheric (Mg II k 2796.35 Å), and TR (C II 1334.53 Å), to investigate the acoustic wave propagation. The wavelet cross-spectrum reveals significant coherence (about 70 per cent locations) between photosphere and chromosphere. Few minutes oscillations (i.e. period range from 1.6 to 4.0 min) successfully propagate into chromosphere from photosphere, which is confirmed by dominance of positive phase lags. However, in higher period regime (i.e. greater than ≈4.5 min), the downward propagation dominates is evident by negative phase lags. The broad spectrum of waves (i.e. 2.5-6.0 min) propagates freely upwards from chromosphere to TR. We find that only about 45 per cent locations (out of 70 per cent) show correlation between chromosphere and TR. Our results indicate that roots of 3 min oscillations observed within chromosphere/TR are located in photosphere. Observations also demonstrate that 5 min oscillations propagate downward from chromosphere. However, some locations within QS also show successful propagation of 5 min oscillations as revealed by positive phase lags, which might be the result of magnetic field. In addition, our results clearly show that a significant power, within period ranging from 2.5 to 6.0 min, of solar chromosphere is freely transmitted into TR triggering atmospheric oscillations. Theoretical implications of our observational results are discussed. Title: Dynamics of a Probable Earth-mass Planet in the GJ 832 System Authors: Satyal, S.; Griffith, J.; Musielak, Z. E. Bibcode: 2017ApJ...845..106S Altcode: 2016arXiv160404544S The stability of planetary orbits around the GJ 832 star system, which contains inner (GJ 832c) and outer (GJ 832b) planets, is investigated numerically and a detailed phase-space analysis is performed. Special attention is given to the existence of stable orbits for a planet less than 15 M ⊕ that is injected between the inner and outer planets. Thus, numerical simulations are performed for three and four bodies in elliptical orbits (or circular for special cases) by using a large number of initial conditions that cover the selected phase-spaces of the planet’s orbital parameters. The results presented in the phase-space maps for GJ 832c indicate the least deviation of eccentricity from its nominal value, which is then used to determine its inclination regime relative to the star-outer planet plane. Also, the injected planet is found to display stable orbital configurations for at least one billion years. Then, the radial velocity curves based on the signature from the Keplerian motion are generated for the injected planets with masses 1 M ⊕ to 15 M ⊕ in order to estimate their semimajor axes and mass limits. The synthetic RV signal suggests that an additional planet of mass ≤15 M ⊕ with a dynamically stable configuration may be residing between 0.25 and 2.0 au from the star. We have provided an estimated number of RV observations for the additional planet that is required for further observational verification. Title: Numerical Simulations of Torsional Alfvén Waves in Axisymmetric Solar Magnetic Flux Tubes Authors: Wójcik, D.; Murawski, K.; Musielak, Z. E.; Konkol, P.; Mignone, A. Bibcode: 2017SoPh..292...31W Altcode: 2017arXiv170104594W We numerically investigate Alfvén waves propagating along an axisymmetric and non-isothermal solar flux tube embedded in the solar atmosphere. The tube magnetic field is current-free and diverges with height, and the waves are excited by a periodic driver along the tube magnetic field lines. The main results are that the two wave variables, the velocity and magnetic field perturbations in the azimuthal direction, behave differently as a result of gradients of the physical parameters along the tube. To explain these differences in the wave behavior, the time evolution of the wave variables and the resulting cutoff period for each wave variable are calculated and used to determine regions in the solar chromosphere where strong wave reflection may occur. Title: Why Theory Fails to Reproduce the Observed Variation of Acoustic Cutoff in the Solar Atmosphere? Authors: Musielak, Zdzislaw E.; Murawski, Krzysztof Bibcode: 2017AAS...22932501M Altcode: Recent observational results by Wisniewska et al. (2016) suggest that the acoustic cutoff frequency varies with height within the solar atmosphere, and that the existing theoretical formulas for the cutoff cannot account for the observed variations. Specifically, five formulas for acoustic cutoffs commonly used in helioseismology and asteroseismology failed to reproduce the observations. We present results of both numerical and analytical studies, and discuss improvements that may be applied to the theory in order to fully reproduce the observational results. In addition, we use observational and theoretical results to seismically probe the physical parameters of the background solar atmosphere. Title: Improving Habitability of Earth-sized Proxima Centauri b by an Exomoon Authors: Garza, Sergio; Rosario Franco, Marialis; Davachi, Niyousha; Musielak, Zdzislaw E. Bibcode: 2017AAS...22912005G Altcode: In an unprecedented discovery, an Earth-sized exoplanet was discovered on a stable, low-eccentricity orbit located in the habitable zone of our nearest neighbor, Proxima Centauri. While the exoplanet, called Proxima Centauri b, is located within the region that may support liquid water on its surface, its habitability has been questioned because of dangerous flares generated by the M dwarf host star and also because of possible tidal locking. The main goal of this work is to understand the constraints under which an exomoon can maintain stable orbits around the exoplanet and how its presence can improve the habitability of the exoplanet. We utilize an N-body integrator, REBOUND, which is a software package that can integrate the motion of particles under the influence of gravity, to perform exomoon’s orbital evolution studies. We present the results of numerical simulations of exomoons of different sizes, determine locations of their stable orbits around Proxima Centauri b, and discuss the effects caused by their presence on the exoplanet’s habitability. Title: Effects of exomoon’s magnetic field on generation of radio emissions Authors: Griffith, John; Noyola, Joaquin; Satyal, Suman; Musielak, Zdzislaw E. Bibcode: 2017AAS...22924528G Altcode: In the recent work by Noyola et al. (2014, 2016), a novel technique of detection of exomoons through the radio emissions produced by the magnetic field interactions between exoplanet-exomoon pair is emulated based upon the processes occurring in the Jupiter-Io system. Their calculations have shown that the radio signal from the distant extra-solar planetary systems is detectable by current technology provided that the systems emanating the radio waves are relatively closer, have some form of atmosphere, and have larger exomoons. In this work, we explore the effect of exomoon’s magnetic field on the radio emission processes by considering a hypothetical magnetic exomoon and re-calculating the resulting radio flux. Then, a limit to the exomoon’s magnetic field is proposed based on the signal amplification versus the dampening effect the magnetic field induces on the secondary conditions such as the containment of ions within the exomoon’s magnetic field and the effect of the plasma torus density that co-orbits with the moon. The energy from the exomoon’s magnetic field is expected to amplify the radio signal, hence increasing the probability of detection of the first exomoons. Title: Searching for the First Exomoon in the Radio: A Report on GMRT Data Authors: Rosario-Franco, Marialis; Noyola, Joaquin; Satyal, Suman; Musielak, Zdzislaw E.; Kodilkar, Jitendra Bibcode: 2017AAS...22941502R Altcode: The field of exoplanetary research has undergone a great deal of development and growth. Achievements in theoretical studies and detection techniques have allowed the discovery of over 3,500 exoplanets in ~2,600 planetary systems to date. Despite this great success, the detection of the first exomoon is yet to be achieved. Motivated by this, we have applied a novel radio-detection method, proposed by Noyola et.al (2014, 2016). The technique is based on a planet-moon interaction observed in the Jupiter-Io system, and Io-controlled decametric radio emissions were used to demonstrate how the presence of exomoons around giant planets might be revealed by the same modulation mechanism. Three targets, selected as the best candidates for radio detection, were observed through the Giant Metrewave Radio Telescope (GMRT); located in India. The results of our data analysis will be presented and discussed. Title: Stable Orbits for Exomoons in Earth’s Cousin (Kepler-452b) Orbiting a Sun-like Star Authors: Davachi, Niyousha; Rosario Franco, Marialis; Garza, Sergio; Musielak, Zdzislaw E. Bibcode: 2017AAS...22912006D Altcode: Kepler 452b, also nicknamed Earth’s cousin, was discovered orbiting the habitable zone (HZ) of a G2 Star (Jenkins et al. 2015). This exoplanet is considered a super Earth, with a mass of 5 ± 2 Mass of Earth and a radius of 1.11 Radius of Earth; and is arguably the first rocky, habitable exoplanet to orbit a sun-like star. With a period of 385 days, conditions are prompt to be similar to those of Earth, and while Kepler-452b orbits the HZ of its parent star, its habitability could also be affected by the presence of an exomoon. Motivated by the need to understand conditions of habitability and orbital stability of Kepler-45b, we have performed a series of N-body integrations to examine the possibility of the exoplanet hosting an exomoon(s). Our results give a range of physical parameters leading to stable orbits for exomoons around this habitable super Earth. Title: Randomly driven acoustic-gravity waves in the solar atmosphere: cutoff period and its observational verification Authors: Murawski, K.; Musielak, Z. E. Bibcode: 2016MNRAS.463.4433M Altcode: 2016MNRAS.tmp.1416M We study the propagation of acoustic-gravity waves in the solar atmosphere. The waves are excited by a space- and time-dependent random driver, whose action mimics turbulence in the upper part of the solar convection zone. Our main goal is to find vertical variations of wave periods of these waves and compare the obtained results to the recent observations of Wiśniewska et al. We solve numerically the hydrodynamic equations in the solar atmosphere whose temperature is given by the semi-empirical model of Avrett & Loeser. The obtained numerical results show that wave periods vary along vertical direction in agreement with the recent observational data. We discuss physical consequences of our theoretical results. Title: Variation of Acoustic Cutoff Period with Height in the Solar Atmosphere: Theory versus Observations Authors: Murawski, K.; Musielak, Z. E.; Konkol, P.; Wiśniewska, A. Bibcode: 2016ApJ...827...37M Altcode: 2016arXiv160802748M Recently Wiśniewska et al. demonstrated observationally how the acoustic cutoff frequency varies with height in the solar atmosphere including the upper photosphere and the lower and middle chromosphere, and showed that the observational results cannot be accounted for by the existing theoretical formulas for the acoustic cutoff. In order to reproduce the observed variation of the cutoff with atmospheric height, numerical simulations of impulsively generated acoustic waves in the solar atmosphere are performed, and the spectral analysis of temporal wave profiles is used to compute numerically changes of the acoustic cutoff with height. Comparison of the numerical results with the observational data shows good agreement, which clearly indicates that the obtained results may be used to determine the structure of the background solar atmosphere. Title: Dark Energy and Dark Matter: Current Ideas and Their Implications Authors: Musielak, Zdzislaw E. Bibcode: 2016pas..conf..207M Altcode: Astronomical observations show that our Universe is dominated by Dark Energy (DE) and Dark Matter (DM). Understanding the origin and nature of DE and DM is one of the most challenging and pressing scientific problems of modern science. Elucidating its solution requires new ideas and new approaches. In this paper, standard and non-standard theories to explain DE and DM are reviewed with a special emphasis on recent theoretical developments and their far reaching physical consequences. Title: On the Radio Detection of Multiple-exomoon Systems due to Plasma Torus Sharing Authors: Noyola, J. P.; Satyal, S.; Musielak, Z. E. Bibcode: 2016ApJ...821...97N Altcode: 2016arXiv160301862N The idea of single exomoon detection due to the radio emissions caused by its interaction with the host exoplanet is extended to multiple-exomoon systems. The characteristic radio emissions are made possible in part by plasma from the exomoon’s own ionosphere. In this work, it is demonstrated that neighboring exomoons and the exoplanetary magnetosphere could also provide enough plasma to generate a detectable signal. In particular, the plasma-torus-sharing phenomenon is found to be particularly well suited to facilitate the radio detection of plasma-deficient exomoons. The efficiency of this process is evaluated, and the predicted power and frequency of the resulting radio signals are presented. Title: Observational Evidence for Variations of the Acoustic Cutoff Frequency with Height in the Solar Atmosphere Authors: Wiśniewska, A.; Musielak, Z. E.; Staiger, J.; Roth, M. Bibcode: 2016ApJ...819L..23W Altcode: Direct evidence for the existence of an acoustic cutoff frequency in the solar atmosphere is given by observations performed by using the HELioseismological Large Regions Interferometric DEvice operating on the Vacuum Tower Telescope located on Tenerife. The observational results demonstrate variations of the cutoff with atmospheric heights. The observed variations of the cutoff are compared to theoretical predictions made by using five acoustic cutoff frequencies that have been commonly used in helioseismology and asteroseismology. The comparison shows that none of the theoretical predictions is fully consistent with the observational data. The implication of this finding is far reaching as it urgently requires either major revisions of the existing methods of finding acoustic cutoff frequencies or developing new methods that would much better account for the physical picture underlying the concept of cutoff frequencies in inhomogeneous media. Title: Stability of a planet in the HD 41004 binary system Authors: Satyal, S.; Musielak, Z. E. Bibcode: 2016AN....337..300S Altcode: The Hill stability criterion is applied to analyse the stability of a planet in the binary star system of HD 41004 AB, with the primary and secondary separated by 22 AU, and masses of 0.7 M_⊙ and 0.4 M_⊙, respectively. The primary hosts one planet in an S-type orbit, and the secondary hosts a brown dwarf (18.64 M_J) on a relatively close orbit, 0.0177 AU, thereby forming another binary pair within this binary system. This star-brown dwarf pair (HD 41004 B+Bb) is considered a single body during our numerical calculations, while the dynamics of the planet around the primary, HD 41004 Ab, is studied in different phase-spaces. HD 41004 Ab is a 2.6 M_J planet orbiting at the distance of 1.7 AU with orbital eccentricity 0.39. For the purpose of this study, the system is reduced to a three-body problem and is solved numerically as the elliptic restricted three-body problem (ERTBP). The {Hill stability} function is used as a chaos indicator to configure and analyse the orbital stability of the planet, HD 41004 Ab. The indicator has been effective in measuring the planet's orbital perturbation due to the secondary star during its periastron passage. The calculated Hill stability time series of the planet for the coplanar case shows the stable and quasi-periodic orbits for at least ten million years. For the reduced ERTBP the stability of the system is also studied for different values of planet's orbital inclination with the binary plane. Also, by recording the planet's {ejection time} from the system or {collision time} with a star during the integration period, stability of the system is analysed in a bigger phase-space of the planet's orbital inclination, ≤ 90o, and its semimajor axis, 1.65-1.75 AU. Based on our analysis it is found that the system can maintain a stable configuration for the planet's orbital inclination as high as 65o relative to the binary plane. The results from the Hill stability criterion and the planet's dynamical lifetime map are found to be consistent with each other. Title: Theoretical prediction of chromospheric oscillations in late-type stars Authors: Fawzy, Diaa E.; Musielak, Z. E. Bibcode: 2016Ap&SS.361...23F Altcode: Self-consistent, nonlinear and time-dependent numerical computations of the excitation of chromospheric oscillations in a thin and non-isothermal magnetic flux tube embedded in magnetic-free atmospheres of late-type stars are performed. Longitudinal tube waves are considered and the wave energy spectra and fluxes generated in convective zones of these stars are calculated. The process of filtering the energy carried by longitudinal tube waves is investigated and both the local heating by shock waves as well as the excitation of chromospheric oscillations are studied. Cutoff frequencies of the resulting oscillations are computed numerically at different atmospheric heights in stars of different effective temperatures and gravities, and compared to three analytically derived cutoff frequencies. The obtained results show that the oscillation frequency ranges from 4 mHz for F5V stars to 20 MHz for M0V stars. It is pointed out that this frequency range may be relevant to the recent stellar p-mode observations made by the NASA space mission Kepler. Title: Exomoon Capture in the Restricted 3-Body Problem and the Role of Torque in Mechanical Energy Transfer Authors: Polo Noyola, Joaquin; Rosario Franco, Marialis; Musielak, Zdzislaw Bibcode: 2015IAUGA..2258136P Altcode: The discovery of giant exoplanets in habitable zones has raised the question of how common large habitable exomoons really are in the universe. Several detection techniques for exomoons have been developed; however their effectiveness depends largely on the exomoon’s size. It is commonly believed that large exomoons are primarily created through a capture processes whereby a terran exoplanet becomes gravitationally bounded to a nearby Jovian. The efficiency of this process is investigated within the framework of the restricted 3-body problem. Specifically, we explore how a small particle orbiting a primary mass can be captured by a secondary mass through cumulative perturbations over long periods of time, and concentrate on the transfer of mechanical energy through a gravitational torque from the secondary mass on the small particle about the barycenter. Conditions under which the gravitational torque performs net positive work on the particle are derived, and applied to several astronomical systems known to have giant exoplanets and which have great potential for hosting exomoons. The study is used to assess the existence of large exomoons in these systems. Title: Dynamics of an Earth-Like Planet in GJ 832 System Authors: Satyal, Suman; Griffith, John; Musielak, Zdzislaw Bibcode: 2015IAUGA..2243278S Altcode: The dynamics of planetary orbits around GJ 832 is studied with an emphasis on a potential Earth-like planet. We perform various phase space analyses of GJ 832c (inner planet) and the long-term orbital stability of an Earth-mass planet injected in between the inner and outer (GJ 832b) planets. The stability of the system is defined in terms of the planet’s lifetime during the orbital integration and the phase space maps, displaying the maximum eccentricity, generated in the evolution process. Furthermore, the net deviation in the planet’s initial eccentricity is used to study perturbation in the system. Numerical integrations comprising of three and four bodies in an elliptical orbits (or circular for special cases) are carried out for a large number of initial conditions that incorporates the whole phase space of the existing bodies. Our results show that the orbital elements of the inner planets seem unaffected by addition of the Earth-like planet. Further analysis of the added planet displays stable orbital configuration for the relative orbital inclination up to 40 degrees and semi major axis ranging from 0.2 to 2.2 AU with an exception of few de-stabilizing resonances between the inner and the outer planets. Finally, resonance, including Kozai, among the planets is studied for assertion of the system’s dynamics. Title: Fractal and multifractal analysis of the rise of oxygen in Earth's early atmosphere Authors: Kumar, Satish; Cuntz, Manfred; Musielak, Zdzislaw E. Bibcode: 2015CSF....77..296K Altcode: 2014arXiv1402.3243K The rise of oxygen in Earth's atmosphere that occurred 2.4 to 2.2 billion years ago is known as the Earth's Great Oxidation, and its impact on the development of life on Earth has been profound. Thereafter, the increase in Earth's oxygen level persisted, though at a more gradual pace. The proposed underlying mathematical models for these processes are based on physical parameters whose values are currently not well-established owing to uncertainties in geological and biological data. In this paper, a previously developed model of Earth's atmosphere is modified by adding different strengths of noise to account for the parameters' uncertainties. The effects of the noise on the time variations of oxygen, carbon and methane for the early Earth are investigated by using fractal and multifractal analysis. We show that the time variations following the Great Oxidation cannot properly be described by a single fractal dimension because they exhibit multifractal characteristics. The obtained results demonstrate that the time series as obtained exhibit multifractality caused by long-range time correlations. Title: Nonlinear Wave Coupling of Torsional Alfvén Waves in the Solar Atmosphere Authors: Musielak, Zdzislaw; Murawski, Krzysztof Bibcode: 2015IAUGA..2258447M Altcode: There is strong observational evidence for the existence of torsional Alfvén waves in the solar atmosphere. The waves propagate inside solar magnetic flux tubes and transfer energy to thesolar chromosphere and corona. We present analytical and numerical models that describe theprocess of nonlinear wave coupling, and use them to determine the efficiency of the process andits effect on dissipation of energy carried by the waves. Our numerical models involve the wave propagation along 3D solar magnetic flux tubes, and they are used to identify regions in the solar atmosphere where maximum amounts of the wave energy can be dissipated. By comparing ourresults to the heating rates observed in different parts of the solar atmosphere, are able to determinethe role played by torsional Alfvén waves in the heating of the solar chromospheres and corona Title: Multi-shell Magnetic Twisters as a New Mechanism for Coronal Heating and Solar Wind Acceleration Authors: Murawski, K.; Srivastava, A. K.; Musielak, Z. E.; Dwivedi, B. N. Bibcode: 2015ApJ...808....5M Altcode: We perform numerical simulations of impulsively generated Alfvén waves in an isolated photospheric flux tube and explore the propagation of these waves along such magnetic structure that extends from the photosphere, where these waves are triggered, to the solar corona, and we analyze resulting magnetic shells. Our model of the solar atmosphere is constructed by adopting the temperature distribution based on the semi-empirical model and specifying the curved magnetic field lines that constitute the magnetic flux tube that is rooted in the solar photosphere. The evolution of the solar atmosphere is described by 3D, ideal MHD equations that are numerically solved by the FLASH code. Our numerical simulations reveal, based on the physical properties of the multi-shell magnetic twisters and the amount of energy and momentum associated with them, that these multi-shell magnetic twisters may be responsible for the observed heating of the lower solar corona and for the formation of solar wind. Moreover, it is likely that the existence of these twisters can be verified by high-resolution observations. Title: Theoretical evidence for cutoff frequencies for Alfvén waves propagating in the solar atmosphere Authors: Perera, H. K.; Musielak, Z. E.; Murawski, K. Bibcode: 2015MNRAS.450.3169P Altcode: Propagation of linear Alfvén waves in the isothermal solar atmosphere is investigated numerically and analytically. It is shown that the two wave variables, the velocity and magnetic field perturbations, behave differently and that there is a range of wave frequencies for which the wave behaviour changes from propagating to non-propagating. The so-called transition and turning points corresponding to this change are determined analytically, and their locations in the atmosphere are calculated and verified against the numerical results. The transition and turning points are then used to introduce cutoff frequencies, which are different for different wave variables. The main result of the paper is that there is no one unique cutoff frequency for Alfvén waves but instead a number of cutoff frequencies can be introduced depending upon the method used to define them as well as on the choice of the wave variable used to describe the waves. Relevance of the obtained results to recent observations of Alfvén waves in the solar atmosphere is also briefly discussed. Title: Torsional Alfvén waves in solar magnetic flux tubes of axial symmetry Authors: Murawski, K.; Solov'ev, A.; Musielak, Z. E.; Srivastava, A. K.; Kraśkiewicz, J. Bibcode: 2015A&A...577A.126M Altcode: 2015arXiv150100252M
Aims: Propagation and energy transfer of torsional Alfvén waves in solar magnetic flux tubes of axial symmetry is studied.
Methods: An analytical model of a solar magnetic flux tube of axial symmetry is developed by specifying a magnetic flux and deriving general analytical formulas for the equilibrium mass density and gas pressure. The main advantage of this model is that it can be easily adopted to any axisymmetric magnetic structure. The model is used to numerically simulate the propagation of nonlinear Alfvén waves in such 2D flux tubes of axial symmetry embedded in the solar atmosphere. The waves are excited by a localized pulse in the azimuthal component of velocity and launched at the top of the solar photosphere, and they propagate through the solar chromosphere, the transition region, and into the solar corona.
Results: The results of our numerical simulations reveal a complex scenario of twisted magnetic field lines and flows associated with torsional Alfvén waves, as well as energy transfer to the magnetoacoustic waves that are triggered by the Alfvén waves and are akin to the vertical jet flows. Alfvén waves experience about 5% amplitude reflection at the transition region. Magnetic (velocity) field perturbations that experience attenuation (growth) with height agree with analytical findings. The kinetic energy of magnetoacoustic waves consists of 25% of the total energy of Alfvén waves. The energy transfer may lead to localized mass transport in the form of vertical jets, as well as to localized heating because slow magnetoacoustic waves are prone to dissipation in the inner corona. Title: Numerical simulations of multi-shell plasma twisters in the solar atmosphere Authors: Murawski, K.; Srivastava, A. K.; Musielak, Z. E.; Dwivedi, B. N. Bibcode: 2015arXiv150503793M Altcode: We perform numerical simulations of impulsively generated Alfvén waves in an isolated photospheric flux tube, and explore the propagation of these waves along such magnetic structure that extends from the photosphere, where these waves are triggered, to the solar corona, and analyze resulting magnetic shells. Our model of the solar atmosphere is constructed by adopting the temperature distribution based on the semi-empirical model and specifying the curved magnetic field lines that constitute the magnetic flux tube which is rooted in the solar photosphere. The evolution of the solar atmosphere is described by 3D, ideal magnetohydrodynamic equations that are numerically solved by the FLASH code. Our numerical simulations reveal, based on the physical properties of the multi-shell magnetic twisters and the amount of energy and momentum associated with them, that these multi-shell magnetic twisters may be responsible for the observed heating of the lower solar corona and for the formation of solar wind. Moreover, it is likely that the existence of these twisters can be verified by high-resolution observations. Title: Astronomical constraints on quantum theories of cold dark matter - II. Supermassive black holes and luminous matter Authors: Spivey, S. C.; Musielak, Z. E.; Fry, J. L. Bibcode: 2015MNRAS.448.1574S Altcode: Our previous model of quantum cold dark matter (QCDM) is expanded to include the influence of supermassive black holes located at centres of different galaxies and galactic luminous (baryonic) matter distributions. The inclusion of a black hole to the galactic potential is shown to produce a more concentrated halo with a cuspier core. The addition of a small-scale galactic luminous matter distribution also concentrates the halo, while a large-scale distribution diffuses it; nevertheless, in either case the smooth core of the halo is preserved. Effects caused by including a non-linear scattering term are investigated by solving the Gross-Pitaevskii equation. The obtained results demonstrate that the scattering term produces a rounder and more diffuse density profile. Moreover, adding a sufficiently large black hole in combination with this term results in an even cuspier profile than the black hole alone. As a result of all these additions, our extended QCDM model can be applied to a much larger range of dark matter halo shapes and sizes. Title: Is the Alfvén wave propagation in the solar atmosphere affected by cutoff frequencies or not? Authors: Musielak, Zdzislaw E.; Perera, Harsha K.; Murawski, Krzysztof Bibcode: 2015AAS...22511501M Altcode: The question posed in the title does not have a unique answer. Some researchers argue that the Alfvén wave propagation in the solar atmosphere is cutoff-free, while others claim that it is exactly the opposite! To resolve this longstanding puzzle, we solved numerically the initial-value problem for the Alfvén wave propagation and identified a range of wave frequencies for which the wave's behavior changes from propagating to non-propagating at certain heights in the solar atmosphere. We determined the locations of these heights in the atmosphere and identified them with the so-called transition and turning points, which we use to introduce cutoff frequencies for Alfvén waves. We find that there is not one unique cutoff frequency for Alfvén waves but instead the cutoffs depend on the method used to define them as well as on the choice of the wave variable selected to describe the waves. Our results provide strong theoretical evidence for the existence of the cutoff frequencies for the Alfvén wave propagation in the solar atmosphere. We discuss the relevance of our results to the current observational data. Title: Propagation of acoustic waves in the non-isothermal solar atmosphere Authors: Routh, S.; Musielak, Z. E. Bibcode: 2014AN....335.1043R Altcode: The acoustic cutoff frequency was originally introduced by Lamb in the study of the propagation of acoustic waves in a stratified, isothermal medium. In this paper, we use a new method to generalize Lamb's result for a stratified, non-isothermal medium and obtain the local acoustic cutoff frequency, which describes the propagation of acoustic waves in such a medium. The main result is that the cutoff frequency is a local quantity and that its value at a given atmospheric height determines the frequency acoustic waves must have in order to propagate at this height. Application of this result to specific physical problems like the solar atmosphere is discussed. Title: Numerical Simulations of Impulsively Generated Alfvén Waves in Solar Magnetic Arcades Authors: Chmielewski, P.; Murawski, K.; Musielak, Z. E.; Srivastava, A. K. Bibcode: 2014ApJ...793...43C Altcode: 2014arXiv1408.0855C We perform numerical simulations of impulsively generated Alfvén waves in an isolated solar arcade, which is gravitationally stratified and magnetically confined. We study numerically the propagation of Alfvén waves along the magnetic structure that extends from the lower chromosphere, where the waves are generated, to the solar corona, and analyze the influence of the arcade size and the width of the initial pulses on the wave propagation and reflection. Our model of the solar atmosphere is constructed by adopting the temperature distribution based on the semi-empirical VAL-C model and specifying the curved magnetic field lines that constitute the asymmetric magnetic arcade. The propagation and reflection of Alfvén waves in this arcade is described by 2.5-dimensional magnetohydrodynamic equations that are numerically solved by the FLASH code. Our numerical simulations reveal that the Alfvén wave amplitude decreases as a result of a partial reflection of Alfvén waves in the solar transition region, and that the waves that are not reflected leak through the transition region and reach the solar corona. We also find the decrement of the attenuation time of Alfvén waves for wider initial pulses. Moreover, our results show that the propagation of Alfvén waves in the arcade is affected by the spatial dependence of the Alfvén speed, which leads to phase mixing that is stronger for more curved and larger magnetic arcades. We discuss the processes that affect the Alfvén wave propagation in an asymmetric solar arcade and conclude that besides phase mixing in the magnetic field configuration, the plasma properties of the arcade, the size of the initial pulse, and the structure of the solar transition region all play a vital role in the Alfvén wave propagation. Title: Detection of Exomoons through Observation of Radio Emissions Authors: Noyola, J. P.; Satyal, S.; Musielak, Z. E. Bibcode: 2014ApJ...791...25N Altcode: 2013arXiv1308.4184N In the Jupiter-Io system, the moon's motion produces currents along the field lines that connect it to Jupiter's polar regions. The currents generate and modulate radio emissions along their paths via the electron-cyclotron maser instability. Based on this process, we suggest that such modulation of planetary radio emissions may reveal the presence of exomoons around giant planets in exoplanetary systems. A model explaining the modulation mechanism in the Jupiter-Io system is extrapolated and used to define criteria for exomoon detectability. A cautiously optimistic scenario of the possible detection of such exomoons around Epsilon Eridani b and Gliese 876 b is provided. Title: Fast Magnetic Twister and Plasma Perturbations in a Three-dimensional Coronal Arcade Authors: Murawski, K.; Srivastava, A. K.; Musielak, Z. E. Bibcode: 2014ApJ...788....8M Altcode: 2014arXiv1404.4176M We present results of three-dimensional (3D) numerical simulations of a fast magnetic twister excited above a foot-point of the potential solar coronal arcade that is embedded in the solar atmosphere with the initial VAL-IIIC temperature profile, which is smoothly extended into the solar corona. With the use of the FLASH code, we solve 3D ideal magnetohydrodynamic equations by specifying a twist in the azimuthal component of magnetic field in the solar chromosphere. The imposed perturbation generates torsional Alfvén waves as well as plasma swirls that reach the other foot-point of the arcade and partially reflect back from the transition region. The two vortex channels are evident in the generated twisted flux-tube with a fragmentation near its apex which results from the initial twist as well as from the morphology of the tube. The numerical results are compared to observational data of plasma motions in a solar prominence. The comparison shows that the numerical results and the data qualitatively agree even though the observed plasma motions occur over comparatively large spatio-temporal scales in the prominence. Title: The three-body problem Authors: Musielak, Z. E.; Quarles, B. Bibcode: 2014RPPh...77f5901M Altcode: 2015arXiv150802312M The three-body problem, which describes three masses interacting through Newtonian gravity without any restrictions imposed on the initial positions and velocities of these masses, has attracted the attention of many scientists for more than 300 years. In this paper, we present a review of the three-body problem in the context of both historical and modern developments. We describe the general and restricted (circular and elliptic) three-body problems, different analytical and numerical methods of finding solutions, methods for performing stability analysis and searching for periodic orbits and resonances. We apply the results to some interesting problems of celestial mechanics. We also provide a brief presentation of the general and restricted relativistic three-body problems, and discuss their astronomical applications. Title: Impulsively Generated Linear and Non-linear Alfven Waves in the Coronal Funnels Authors: Chmielewski, P.; Srivastava, A. K.; Murawski, K.; Musielak, Z. E. Bibcode: 2014AcPPA.125..158C Altcode: 2014arXiv1401.2329C We present simulation results of the impulsively generated linear and non-linear Alfvén waves in the weakly curved coronal magnetic flux-tubes (coronal funnels) and discuss their implications for the coronal heating and solar wind acceleration. We solve numerically the time-dependent magnetohydrodynamic equations to find the temporal signatures of the small and large-amplitude Alfvén waves in the model atmosphere of open and expanding magnetic field configuration with a realistic temperature distribution. We compute the maximum transversal velocity of both linear and non-linear Alfvén waves at different heights of the model atmosphere, and study their response in the solar corona during the time of their propagation. We infer that the pulse-driven non-linear Alfvén waves may carry sufficient wave energy fluxes to heat the coronal funnels and also to power the solar wind that originates in these funnels. Our study of linear Alfvén waves shows that they can contribute only to the plasma dynamics and heating of the funnel-like magnetic flux-tubes associated with the polar coronal holes. Title: Reflection and Wave Coupling of Torsional Alfven Waves in 3D Solar Magnetic Flux Tubes Authors: Musielak, Zdzislaw E.; Murawski, K.; Srivastava, A. K. Bibcode: 2014AAS...22311806M Altcode: We simulate numerically propagation of nonlinear torsional Alfven waves in 3D magnetic flux tubes embedded in the solar atmosphere with the VAL-C temperature profile that is smoothly extended into the solar corona. The waves are launched at the top of the solar photosphere and their propagation through the solar chromosphere and transition region to the solar corona is studied. We investigate wave reflection in the solar transition region and nonlinear coupling of torsional Alfven waves to magnetoacoustic waves, and use our numerical results to determine the efficiency of energy transfer by these waves to the solar corona and the role played by nonlinear coupling of the waves in heating of different parts of the solar atmosphere. The obtained results are compared to the recent observational data that supplied evidence for the existence of torsional Alfven waves in the solar atmosphere and to the observationally established heating requirements in different parts of the solar atmosphere. Title: Astronomical constraints on quantum theories of cold dark matter - I. Einasto density profile for galactic haloes Authors: Spivey, S. C.; Musielak, Z. E.; Fry, J. L. Bibcode: 2013MNRAS.428..712S Altcode: 2012MNRAS.tmp...52S Among different models of dark matter, the so-called quantum (or `fuzzy') cold dark matter plays an important role as it allows removing cuspy halo profiles and an abundance of low mass haloes, which are predicted by cold dark matter models but have never been observed. The basic idea of the quantum cold dark matter is the existence of extremely light bosonic particles whose expected masses are of the order of 10-22 eV or even as small as 10-24 eV. With such a small mass, the particle's behaviour in galactic dark matter haloes is described by the Schrödinger equation with a gravitational potential term. In this paper, two previously introduced quantum models of dark matter are reconsidered and the probability densities predicted by these models are compared to the astronomically established density profiles of dark matter haloes of the Milky Way and a dwarf galaxy. By imposing these astronomical constraints on the quantum models, it is shown that the models do reproduce well the Einasto profile with index n ≈ 0.56. However, the models can neither account for the total masses and halo shapes of these two galaxies, nor other galaxies, using the same dark matter elementary particle. Possible improvements of the quantum models that could potentially remove this deficiency are discussed. Title: Global and Local Cutoff Frequencies for Transverse Waves Propagating along Solar Magnetic Flux Tubes Authors: Routh, S.; Musielak, Z. E.; Hammer, R. Bibcode: 2013ApJ...763...44R Altcode: 2013arXiv1301.2736R It is a well-established result that the propagation of linear transverse waves along a thin but isothermal magnetic flux tube is affected by the existence of the global cutoff frequency, which separates the propagating and non-propagating waves. In this paper, the wave propagation along a thin and non-isothermal flux tube is considered and a local cutoff frequency is derived. The effects of different temperature profiles on this local cutoff frequency are studied by considering different power-law temperature distributions, as well as the semi-empirical VAL C model of the solar atmosphere. The obtained results show that the conditions for wave propagation strongly depend on the temperature gradients. Moreover, the local cutoff frequency calculated for the VAL C model gives constraints on the range of wave frequencies that are propagating in different parts of the solar atmosphere. These theoretically predicted constraints are compared to observational data and are used to discuss the role played by transverse tube waves in the atmospheric heating and dynamics, and in the excitation of solar atmospheric oscillations. Title: Pulse-driven non-linear Alfvén waves and their role in the spectral line broadening Authors: Chmielewski, P.; Srivastava, A. K.; Murawski, K.; Musielak, Z. E. Bibcode: 2013MNRAS.428...40C Altcode: 2012MNRAS.tmp....5C; 2012arXiv1207.6507C We study the impulsively generated non-linear Alfvén waves in the solar atmosphere and describe their most likely role in the observed non-thermal broadening of some spectral lines in solar coronal holes. We solve numerically the time-dependent magnetohydrodynamic equations to find temporal signatures of large-amplitude Alfvén waves in the solar atmosphere model of open and expanding magnetic field configuration, with a realistic temperature distribution. We calculate the temporally and spatially averaged, instantaneous transversal velocity of non-linear Alfvén waves at different heights of the model atmosphere and estimate its contribution to the unresolved non-thermal motions caused by the waves. We find that the pulse-driven non-linear Alfvén waves with the amplitude Av = 50 km s- 1 are the most likely candidates for the non-thermal broadening of Si viii λ1445.75 Å line profiles in the polar coronal hole as reported by Banerjee et al. We also demonstrate that the Alfvén waves driven by comparatively smaller velocity pulse with amplitude Av = 25 km s- 1 may contribute to the spectral line width of the same line at various heights in coronal hole broadening. We conclude that the non-linear Alfvén waves excited impulsively in the lower solar atmosphere may be responsible for the observed spectral line broadening in polar coronal holes. This is an important result as it allows us to conclude that such large amplitude and pulse-driven Alfvén waves may indeed exist in solar coronal holes. The existence of these waves may impart the required momentum to accelerate the solar wind. Title: Study of resonances for the restricted 3-body problem Authors: Quarles, B.; Musielak, Z. E.; Cuntz, M. Bibcode: 2012AN....333..551Q Altcode: 2012arXiv1205.0950Q Our aim is to identify and classify mean-motion resonances (MMRs) for the coplanar circular restricted three-body problem (CR3BP) for mass ratios between 0.10 and 0.50. Our methods include the maximum Lyapunov exponent, which is used as an indicator for the location of the resonances, the Fast Fourier Transform (FFT) used for determining what kind of resonances are present, and the inspection of the orbital elements to classify the periodicity. We show that the 2:1 resonance occurs the most frequently. Among other resonances, the 3:1 resonance is the second most common, and furthermore both 3:2 and 5:3 resonances occur more often than the 4:1 resonance. Moreover, the resonances in the coplanar CR3BP are classified based on the behaviour of the orbits. We show that orbital stability is ensured for high values of resonance (i.e., high ratios) where only a single resonance is present. The resonances attained are consistent with the previously established resonances for the solar system, i.e., specifically, in regards to the asteroid belt. Previous work employed digital filtering and Lyapunov characteristic exponents to determine stochasticity of the eccentricity, which is found to be consistent with our usage of Lyapunov exponents as an alternate approach based on varying the mass ratio instead of the eccentricity. Our results are expected to be of principal interest to future studies, including augmentations to observed or proposed resonances, of extra-solar planets in binary stellar systems. Title: Habitability of Earth-mass Planets and Moons in the Kepler-16 System Authors: Quarles, B.; Musielak, Z. E.; Cuntz, M. Bibcode: 2012ApJ...750...14Q Altcode: 2012arXiv1201.2302Q We demonstrate that habitable Earth-mass planets and moons can exist in the Kepler-16 system, known to host a Saturn-mass planet around a stellar binary, by investigating their orbital stability in the standard and extended habitable zone (HZ). We find that Earth-mass planets in satellite-like (S-type) orbits are possible within the standard HZ in direct vicinity of Kepler-16b, thus constituting habitable exomoons. However, Earth-mass planets cannot exist in planetary-like (P-type) orbits around the two stellar components within the standard HZ. Yet, P-type Earth-mass planets can exist superior to the Saturnian planet in the extended HZ pertaining to considerably enhanced back-warming in the planetary atmosphere if facilitated. We briefly discuss the potential detectability of such habitable Earth-mass moons and planets positioned in satellite and planetary orbits, respectively. The range of inferior and superior P-type orbits in the HZ is between 0.657-0.71 AU and 0.95-1.02 AU, respectively. Title: The stability of the suggested planet in the ν Octantis system: a numerical and statistical study Authors: Quarles, B.; Cuntz, M.; Musielak, Z. E. Bibcode: 2012MNRAS.421.2930Q Altcode: 2012arXiv1201.2313Q; 2012MNRAS.tmp.2692Q We provide a detailed theoretical study aimed at the observational finding about the ν Octantis binary system that indicates the possible existence of a Jupiter-type planet in this system. If a prograde planetary orbit is assumed, it has earlier been argued that the planet, if existing, should be located outside the zone of orbital stability. However, a previous study by Eberle & Cuntz concludes that the planet is most likely stable if assumed to be in a retrograde orbit with respect to the secondary system component. In the present work, we significantly augment this study by taking into account the observationally deduced uncertainty ranges of the orbital parameters for the stellar components and the suggested planet. Furthermore, our study employs additional mathematical methods, which include monitoring the Jacobi constant, the zero velocity function and the maximum Lyapunov exponent. We again find that the suggested planet is indeed possible if assumed to be in a retrograde orbit, but it is virtually impossible if assumed in a prograde orbit. Its existence is found to be consistent with the deduced system parameters of the binary components and of the suggested planet, including the associated uncertainty bars given by observations. Title: Atmospheric oscillations in late-type stars - I. Non-linear response to excitation by acoustic wave energy spectra Authors: Fawzy, Diaa E.; Musielak, Z. E. Bibcode: 2012MNRAS.421..159F Altcode: The main aim of this paper is to perform first self-consistent numerical computation of the response of stellar atmospheres to the propagation of acoustic waves specified by realistic acoustic wave energy spectra. In the numerical approach, stellar atmospheres are stratified, non-isothermal and plane-parallel, and only their magnetic-free regions are considered. The resulting atmospheric heating is calculated and the time sequence of atmospheric velocities computed by a time-dependent hydrodynamic numerical code is analysed. All computations are done adiabatically and Fourier analysis is used in order to determine the oscillatory properties of stellar atmospheres. The numerical approach is supplemented by an analytical treatment in which three different local acoustic cut-off frequencies are selected from the literature; their values in the stellar atmospheric models are calculated and compared to the numerical results. The theoretical results obtained clearly show that atmospheric oscillations do exist in late-type stars and that their origin and physical properties are similar to those observed in the solar atmosphere. The oscillation frequency of stellar atmospheric oscillations ranges from 7.5 mHz for F5V stars to 16.0 mHz for M0V stars. The relevance of this theoretically predicted range of stellar oscillation in solar-like stars to the recent data obtained by the NASA space mission Kepler is discussed. Title: The stability of the suggested planet in the ν Octantis system: a numerical and statistical study Authors: Quarles, Billy; Cuntz, Manfred; Musielak, Zdzislaw Bibcode: 2012APS..TSS.C1003Q Altcode: Exoplanets in binary systems have received heightened interest by the scientific community. Especially with the recent detection of a circumbinary planet of Kepler-16b (Doyle et al. 2011)[Science 333, 1602] planets in binary systems have warranted second and even third glances. The system of ν Octantis has been a system of great controversy since the suggested planet in this system (Ramm et al. 2009)[MNRAS 394, 1695] appears to be located beyond its theoretical stability limit. In order to resolve this controversy we seek to determine whether the proposed planet can exist in the context of current stability theory. We have performed detailed simulations by exploiting the uncertainty measurements to determine the short and long-term stability of a prograde starting configuration. However to follow up on the previous results by Eberle & Cuntz (2010)[ApJ 721, L168], we have investigated the hypothesis of a retrograde orbit in more detail by considering a larger set of possible initial conditions to determine the possibility of a retrograde configuration with respect to the motion of the binary system. We will show that a retrograde configuration is preferred by both stability considerations with respect to the maximum Lyapunov exponent and numerical statistical considerations. Title: On The Existence Of Earth-like Planets In The Circumbinary System Kepler-16 Authors: Quarles, Billy L.; Musielak, Z. E.; Cuntz, M. Bibcode: 2012AAS...21911003Q Altcode: The newly discovered circumbinary system Kepler-16 contains a pair of low-mass stars and a Saturn-mass planet (Doyle et al. 2011) [Science 333, 1602]. A truly fascinating problem is to explore whether Earth-like planets can exist in the habitable zone (HZ) of this unique system. The HZ of this system is mainly due to the primary star and extends from 0.36 AU to 0.71 AU. We have performed extensive numerical studies of long-term orbital stability of Earth-like planets in this HZ by considering both S-type and P-type planetary orbits. The semi-major axis for S-type orbits has been determined as 0.0675 ± 0.0039 AU from the stellar primary. This distance is well inside the inner limit of habitability where the influence of the runaway greenhouse effect becomes important. Consequently, the existence of a habitable Earth-like planet in an S-type orbit is highly unlikely. However it appears possible that such a planet can exist in a P-type orbit inside the HZ thus providing a realistic possibility for long-term evolution of life in this type of system. The obtained results are of special interest because they can assist in the selection process of system candidates in future terrestrial planet search missions. Title: Astronomical Constraints on Quantum Cold Dark Matter Authors: Spivey, Shane; Musielak, Z.; Fry, J. Bibcode: 2012AAS...21911202S Altcode: A model of quantum (`fuzzy') cold dark matter that accounts for both the halo core problem and the missing dwarf galaxies problem, which plague the usual cold dark matter paradigm, is developed. The model requires that a cold dark matter particle has a mass so small that its only allowed physical description is a quantum wave function. Each such particle in a galactic halo is bound to a gravitational potential that is created by luminous matter and by the halo itself, and the resulting wave function is described by a Schrödinger equation. To solve this equation on a galactic scale, we impose astronomical constraints that involve several density profiles used to fit data from simulations of dark matter galactic halos. The solutions to the Schrödinger equation are quantum waves which resemble the density profiles acquired from simulations, and they are used to determine the mass of the cold dark matter particle. The effects of adding certain types of baryonic matter to the halo, such as a dwarf elliptical galaxy or a supermassive black hole, are also discussed. Title: Case studies of habitable Trojan planets in the system of HD 23079 Authors: Eberle, J.; Cuntz, M.; Quarles, B.; Musielak, Z. E. Bibcode: 2011IJAsB..10..325E Altcode: 2011arXiv1104.3092E We investigate the possibility of habitable Trojan planets in the HD 23079 star-planet system. This system consists of a solar-type star and a Jupiter-type planet, which orbits the star near the outer edge of the stellar habitable zone in an orbit of low eccentricity. We find that in agreement with previous studies Earth-mass habitable Trojan planets are possible in this system, although the success of staying within the zone of habitability is significantly affected by the orbital parameters of the giant planet and by the initial condition of the theoretical Earth-mass planet. In one of our simulations, the Earth-mass planet is captured by the giant planet and thus becomes a habitable moon. Title: The instability transition for the restricted 3-body problem. III. The Lyapunov exponent criterion Authors: Quarles, B.; Eberle, J.; Musielak, Z. E.; Cuntz, M. Bibcode: 2011A&A...533A...2Q Altcode: 2011arXiv1106.5062Q
Aims: We establish a criterion for the stability of planetary orbits in stellar binary systems by using Lyapunov exponents and power spectra for the special case of the circular restricted 3-body problem (CR3BP). The criterion augments our earlier results given in the two previous papers of this series where stability criteria have been developed based on the Jacobi constant and the hodograph method.
Methods: The centerpiece of our method is the concept of Lyapunov exponents, which are incorporated into the analysis of orbital stability by integrating the Jacobian of the CR3BP and orthogonalizing the tangent vectors via a well-established algorithm originally developed by Wolf et al. The criterion for orbital stability based on the Lyapunov exponents is independently verified by using power spectra. The obtained results are compared to results presented in the two previous papers of this series.
Results: It is shown that the maximum Lyapunov exponent can be used as an indicator for chaotic behaviour of planetary orbits, which is consistent with previous applications of this method, particularly studies for the Solar System. The chaotic behaviour corresponds to either orbital stability or instability, and it depends solely on the mass ratio μ of the binary components and the initial distance ratio ρ0 of the planet relative to the stellar separation distance. Detailed case studies are presented for μ = 0.3 and 0.5. The stability limits are characterized based on the value of the maximum Lyapunov exponent. However, chaos theory as well as the concept of Lyapunov time prevents us from predicting exactly when the planet is ejected. Our method is also able to indicate evidence of quasi-periodicity.
Conclusions: For different mass ratios of the stellar components, we are able to characterize stability limits for the CR3BP based on the value of the maximum Lyapunov exponent. This theoretical result allows us to link the study of planetary orbital stability to chaos theory noting that there is a large array of literature on the properties and significance of Lyapunov exponents. Although our results are given for the special case of the CR3BP, we expect that it may be possible to augment the proposed Lyapunov exponent criterion to studies of planets in generalized stellar binary systems, which is strongly motivated by existing observational results as well as results expected from ongoing and future planet search missions. Title: Detection of Moons around Giant Extrasolar Planets Authors: Musielak, Dora; Musielak, Z. E. Bibcode: 2011AAS...21731805M Altcode: 2011BAAS...4331805M The fact that Jupiter's radio emission is affected by the presence of its moon Io has been know for many years and extensively studied both observationally and theoretically. Since Io moves inside the Jovian magnetic field, its motion produces currents along the field lines that connect the moon to the Jupiter's polar regions, where the radio emission is modulated by the currents. It has been suggested that such modulation of planetary radio emission may reveal the presence of moons around giant planets in extrasolar planetary system. With the first indirect observational evidence for extrasolar planetary magnetic fields, and with the promise of detecting more such cases by the upcoming new observations, we seriously consider the idea and determine the required physical conditions for such detection to take place. The results of our study will be used to select the most promising candidates for detection of moons around giant planets in currently known extrasolar planetary systems. Title: Lyapunov Exponent Criterion for Stability of Planetary Orbits in Binary Systems Authors: Musielak, Zdzislaw E.; Quarles, B.; Eberle, J.; Cuntz, M. Bibcode: 2011AAS...21741505M Altcode: 2011BAAS...4341505M The existence of planets in stellar binary systems is now well-confirmed by many observations. Stability of planetary orbits in these systems has extensively been studied and some attempts have been made to establish stringent stability criteria for the orbits. In this paper, we contribute to the ongoing work on the stability criteria in binary systems by introducing a Lyapunov exponent criterion. We have computed the Lyapunov exponents, the Lyapunov dimension and the time series spectra for planets in binary system. The obtained results demonstrate when a system becomes unstable by orbital energy criterion and the method of Lyapunov exponents provides a quantitative classification scale to characterize the instability. By applying the maximum Lyapunov exponent to the parameter space, which covers mass and distance ratios for the considered binary systems, we determined regions of stability and used the time series spectra and the Lyapunov dimension to illustrate the reasons behind the stability. Specific applications of the criterion to binary systems with known planets will also be discussed. Title: The great oxidation of Earth's atmosphere Authors: Musielak, Zdzislaw E.; Cuntz, Manfred; Roy, Dipanjan Bibcode: 2010HiA....15..680M Altcode: A simplified model of the Earth's atmosphere consisting of three nonlinear differential equations with a driving force was developed by Goldblatt et al. (2006). They found a steady-state solution that exhibits bistability and identified its upper value with the great oxidation of the Earth's atmosphere. Noting that the driving force in their study was a step function, it is the main goal of this paper to investigate the stability of the model by considering two different more realistic driving forces. The stability analysis is performed by using Lyapunov exponents. Our results show that the model remains stable and it does not exhibit any chaotic behavior. Title: Orbital stability of Earth-type planets in stellar binary systems Authors: Eberle, Jason; Cuntz, Manfred; Musielak, Zdzislaw E. Bibcode: 2010HiA....15..691E Altcode: An important factor in estimating the likelihood of life elsewhere in the Universe is determining the stability of a planet's orbit. A significant fraction of stars like the Sun occur in binary systems which often has a considerable effect on the stability of any planets in such a system. In an effort to determine the stability of planets in binary star systems, we conducted a numerical simulation survey of several mass ratios and initial conditions. We then estimated the stability of the planetary orbit using a method that utilizes the hodograph to determine the effective eccentricity of the planetary orbit. We found that this method can serve as an orbital stability criterion for the planet. Title: Linear Alfvén waves in the solar atmosphere Authors: Murawski, K.; Musielak, Z. E. Bibcode: 2010A&A...518A..37M Altcode:
Aims: We aim to analytically and numerically explore small-amplitude Alfvén waves in the solar atmosphere.
Methods: We transform the wave equations to obtain the cutoff-frequency and wave travel time for strictly linear Alfvén waves. The wave equations are solved numerically to find out spatial and temporal signatures of the waves.
Results: The analytical predictions are verified by numerically solving the wave equations for linear Alfvén waves. The waves are impulsively generated and their characteristics and behavior in the solar atmosphere are investigated by the numerical simulations. The derived cutoff-frequency is used to determine regions in the solar atmosphere where strong reflection occurs for Alfvén waves of different frequencies.
Conclusions: The numerical results reveal that impulsively generated small-amplitude waves exhibit characteristic spatial and temporal signatures which agree with the predictions of the analytical theory. Title: The origin of cutoff frequencies for torsional tube waves propagating in the solar atmosphere Authors: Hammer, R.; Musielak, Z. E.; Routh, S. Bibcode: 2010AN....331..593H Altcode: Torsional waves supported by magnetic flux tubes have long been thought to bear a high potential for supplying energy and momentum to the upper solar atmosphere, thereby contributing to its heating and to the driving of dynamic events like spicules. This hope rested on the belief that their propagation is not impeded by cutoff restrictions, unlike longitudinal and kink waves. We point out that this applies only to thin, isothermal tubes. When they widen in the chromosphere, and as a result of temperature gradients, cutoff restrictions arise. We compare them to recent observational reports of such waves and of vortex motions and find that their long period components are already affected by cutoff restrictions. An observational strategy is proposed that should permit the derivation of better information on vortex flows from off-center observations with next generation telescopes. Title: Temperature Gradients in the Solar Atmosphere and the Origin of Cutoff Frequency for Torsional Tube Waves Authors: Routh, S.; Musielak, Z. E.; Hammer, R. Bibcode: 2010ApJ...709.1297R Altcode: Fundamental modes supported by a thin magnetic flux tube embedded in the solar atmosphere are typically classified as longitudinal, transverse, and torsional waves. If the tube is isothermal, then the propagation of longitudinal and transverse tube waves is restricted to frequencies that are higher than the corresponding global cutoff frequency for each wave. However, no such global cutoff frequency exists for torsional tube waves, which means that a thin and isothermal flux tube supports torsional tube waves of any frequency. In this paper, we consider a thin and non-isothermal magnetic flux tube and demonstrate that temperature gradients inside this tube are responsible for the origin of a cutoff frequency for torsional tube waves. The cutoff frequency is used to determine conditions for the wave propagation in the solar atmosphere, and the obtained results are compared to the recent observational data that support the existence of torsional tube waves in the Sun. Title: Generation and Propagation of Torsional Tube Waves in the Solar Atmosphere Authors: Musielak, Zdzislaw E.; Routh, S.; Hammer, R. Bibcode: 2010AAS...21532204M Altcode: 2010BAAS...42..324M Recent observational evidence for the existence of torsional tube waves in the solar atmosphere (e.g., Bonet et al. 2008; Jess et al. 2009) has triggered theoretical work on the generation and propagation of these waves. We modify our previous theory of generation of torsional tubes waves by the solar turbulent convection and compute the resulting the wave energy spectra and fluxes. We also demonstrate that tube thickness and temperature gradients lead to the origin of cutoff frequencies for torsional tube waves. Using the cutoffs, we calculate a range of frequencies corresponding to the propagating waves and compare it to that given by the observations. We use the obtained result to discuss the role of torsional tube waves in heating of the solar atmosphere. This work is supported by NSF under grant ATM-0538278. Title: Orbital Stability of Earth-Type Planets in Binary Systems Authors: Eberle, J.; Cuntz, M.; Musielak, Z. E. Bibcode: 2009ASPC..420..357E Altcode: 2007arXiv0712.3266E About half of all known stellar systems with Sun-like stars consist of two or more stars, significantly affecting the orbital stability of any planet in these systems. Here we study the onset of instability for an Earth-type planet that is part of a binary system. Our investigation makes use of previous analytical work allowing to describe the permissible region of planetary motion. This allows us to establish a criterion for the orbital stability of planets that may be useful in the context of future observational and theoretical studies. Title: The Great Oxidation of Earth's Atmosphere: Contesting the Yoyo Model Via Transition Stability Analysis Authors: Cuntz, M.; Roy, D.; Musielak, Z. E. Bibcode: 2009ApJ...706L.178C Altcode: A significant controversy regarding the climate history of the Earth and its relationship to the development of complex life forms concerns the rise of oxygen in the early Earth's atmosphere. Geological records show that this rise occurred about 2.4 Gyr ago, when the atmospheric oxygen increased from less than 10-5 present atmospheric level (PAL) to more than 0.01 PAL and possibly above 0.1 PAL. However, there is a debate whether this rise happened relatively smoothly or with well-pronounced ups and downs (the Yoyo model). In our study, we explore a simplified atmospheric chemical system consisting of oxygen, methane, and carbon that is driven by the sudden decline of the net input of reductants to the surface as previously considered by Goldblatt et al. Based on the transition stability analysis for the system equations, constituting a set of non-autonomous and non-linear differential equations, as well as the inspection of the Lyapunov exponents, it is found that the equations do not exhibit chaotic behavior. In addition, the rise of oxygen occurs relative smoothly, possibly with minor bumps (within a factor of 1.2), but without major jumps. This result clearly argues against the Yoyo model in agreement with recent geological findings. Title: Novel explanation for the shape of the lenticular galaxy bulge and its implication for red spiral galaxy evolution Authors: Schachar, R. A.; Liao, G. G.; Kirby, R. D.; Kamangar, F.; Musielak, Z. E.; Rosensteel, G. Bibcode: 2009A&A...505..613S Altcode: Aims: According to Hubble's classification scheme, lenticular galaxies represent an intermediate evolutionary step between elliptical and spiral galaxies. This evolutionary path predicts that the aspect ratios of both lenticular and spiral galaxies should be smaller than the aspect ratios of their E6 or E7 elliptical predecessors. In contradiction to this prediction, observation has demonstrated that the aspect ratio of lenticular galaxies is larger than its immediate elliptical predecessor. In this paper, we suggest a novel explanation for this inconsistency.
Methods: The approach described in this paper is primarily based on analytical methods; however, some numerical methods are also used.
Results: Our idea comes from theoretical and experimental results, which show that a small increase in the equatorial diameter of an oblate spheroid with an aspect ratio ≤0.6 surprisingly causes its minor axis to also increase. We demonstrate that the same phenomenon occurs in the isodensity contours of elliptical galaxies given by Miyamoto & Nagai (Miyamoto M., & Nagai R., 1975, PASJ, 27, 533) and in a Maclaurin spheroidal mass in response to the gravitational force generated by a circumferential equatorial disk.
Conclusions: The result of this paper is our explanation for the transformation of a disky elliptical galaxy into a lenticular galaxy which in response to rotation and equatorial diameter expansion evolves into a red spiral galaxy. This evolutionary path is consistent with the common environmental location of disky ellipticals, lenticular and red spiral galaxies and explains why elliptical galaxies are generally ≤E4. The proposed evolutionary path is opposite to the generally accepted formation of lenticular galaxies from the merger of spiral galaxies. Title: Propagation of Waves in Solar Non-Isothermal Atmosphere Authors: Routh, Swati; Musielak, Z.; Hammer, R. Bibcode: 2009SPD....40.1001R Altcode: Fundamental modes supported by a thin and isothermal magnetic flux tube embedded in the solar atmosphere are typically identified as longitudinal, transverse and torsional waves. The propagation of longitudinal and transverse tube waves is restricted to frequencies that are higher than the corresponding global cutoff frequency for each wave. No such global cutoff frequency exists for torsional tube waves, which means that the flux tube supports torsional tube waves of any frequency. The situation becomes different when a 'wide’ and isothermal flux tube is concerned; in this case, a cutoff frequency for torsional tube waves arises naturally and it becomes a local quantity. Since the solar atmosphere is not isothermal, the effects of different temperature gradients on the cutoff are investigated. A method to determine these effects is presented and applied to specific models of solar magnetic flux tubes. An interesting result is that the resulting cutoff frequency is a local quantity in the model, and that its value at a given height determines the frequency that transverse and torsional tube waves must have in order to be propagating at this height. The obtained results are applied to the VAL C model of the solar atmosphere. Title: The instability transition for the restricted 3-body problem. I. Theoretical approach Authors: Eberle, J.; Cuntz, M.; Musielak, Z. E. Bibcode: 2008A&A...489.1329E Altcode: Aims: We study the onset of orbital instability for a small object, identified as a planet, that is part of a stellar binary system with properties equivalent to the restricted three body problem.
Methods: Our study is based on both analytical and numerical means and makes use of a rotating (synodic) coordinate system keeping both binary stars at rest. This allows us to define a constant of motion (Jacobi's constant), which is used to describe the permissible region of motion for the planet. We illustrate the transition to instability by depicting sets of time-dependent simulations with star-planet systems of different mass and distance ratios.
Results: Our method utilizes the existence of an absolute stability limit. As the system parameters are varied, the permissible region of motion passes through the three collinear equilibrium points, which significantly changes the type of planetary orbit. Our simulations feature various illustrative examples of instability transitions.
Conclusions: Our study allows us to identify systems of absolute stability, where the stability limit does not depend on the specifics or duration of time-dependent simulations. We also find evidence of a quasi-stability region, superimposed on the region of instability, where the planetary orbits show quasi-periodic behavior. The analytically deduced onset of instability is found to be consistent with the behavior of the depicted time-dependent models, although the manifestation of long-term orbital stability will require more detailed studies. Title: Spicules: Energetics and the Role of Magnetic Waves Authors: Hammer, R.; Musielak, Z. E.; Routh, S.; Nesis, A. Bibcode: 2008ESPM...12.3.11H Altcode: The class of spicule-like processes comprises a variety of phenomena that were given different names, depending on how and where on the Sun they can be observed - including (classical limb) spicules, macrospicules, FUV spicules, mottles, fibrils, and the "type II spicules" recently discovered with Hinode. The relationships between these phenomena are not fully clarified. We point out that the reported observed properties cannot all be reconciled with a single driving mechanism. Indeed, many different mechanisms have been suggested in the past, all with some success. We argue that this was ultimately possible because the observed properties are consistent with an approximate equipartition between enthalpy, kinetic energy, and presumably also magnetic energy. One of the most popular driving mechanisms of the last few years invokes the guiding of global p-mode oscillations along magnetic field lines that are sufficiently inclined against the vertical, so that the cutoff frequency for longitudinal waves drops below the excitation frequency. We show that in such a situation transverse, and perhaps also torsional, waves are much more promising, because of their weaker cutoff restrictions even for the small inclinations that are typical for limb spicules. Indeed there is now growing observational evidence for transverse waves. We point out the need to understand better the cutoff properties of various kinds of magnetic waves. Title: Local Cutoff Frequencies for Transverse Waves Propagating Along Thin and Non-Isothermal Magnetic Flux Tubes Authors: Musielak, Z. E.; Subramaniam, S.; Routh, S.; Hammer, R. Bibcode: 2008ESPM...12.3.25M Altcode: Propagation of transverse waves along thin magnetic flux tubes embedded in an isothermal atmosphere is affected by the cutoff frequency, which is a global quantity that restricts the wave propagation to only those frequencies that are higher than the cutoff. Since the solar atmosphere is not isothermal, the effects of different temperature gradients on the cutoff are investigated. A method to determine these effects is presented and applied to specific models of solar magnetic flux tubes. An interesting result is that the resulting cutoff frequency is a local quantity in the model, and that its value at a given height determines the frequency that transverse tube waves must have in order to be propagating at this height. The obtained results are applied to the solar atmospheric oscillations. Title: Orbital stability of planets in binary systems: A new look at old results Authors: Eberle, J.; Cuntz, M.; Musielak, Z. E. Bibcode: 2008IAUS..249..507E Altcode: 2007IAUS..249..507E; 2007arXiv0712.3239E About half of all known stellar systems with Sun-like stars consist of two or more stars, significantly affecting the orbital stability of any planet in these systems. This observational evidence has prompted a large array of theoretical research, including the derivation of mathematically stringent criteria for the orbital stability of planets in stellar binary systems, valid for the “coplanar circular restricted three-body problem”. In the following, we use these criteria to explore the validity of results from previous theoretical studies. Title: Stability of planetary orbits in binary systems Authors: Musielak, Z. E.; Cuntz, M.; Marshall, E. A.; Stuit, T. D. Bibcode: 2008A&A...480..573M Altcode: No abstract at ADS Title: Waves in Inclined Solar Magnetic Flux Tubes Authors: Routh, Swati; Musielak, Z.; Hammer, R. Bibcode: 2007AAS...211.8001R Altcode: 2007BAAS...39..870R The solar chromosphere shows numerous needle-shaped extensions into the overlying corona, in which plasma shoots up at high speeds. These phenomena are variously called spicules, mottles, or dynamic fibrils, depending on where and how they are observed on the Sun. Many different explanations have been suggested for how these phenomena might be generated in the dynamic solar atmosphere. The currently most popular suggestion is that global solar oscillations propagate as longitudinal waves along magnetic flux tubes. These long-period waves suffer from a cutoff restriction, but if the flux tubes are sufficiently inclined to the vertical they can propagate nevertheless. We will analyze the cutoff behavior of longitudinal and also other wave modes, namely kink flux tube waves inside these inclined tubes and show that they have better chances to transport energy upward. Such waves must therefore be taken into account in order to understand spicules.

This work is supported by NSF grant ATM 05-38278 Title: Conditions for Propagation of Torsional Waves in Solar Magnetic Flux Tubes Authors: Routh, S.; Musielak, Z. E.; Hammer, R. Bibcode: 2007SoPh..246..133R Altcode: Propagation of torsional waves along isothermal and initially-untwisted magnetic-flux tubes embedded in the solar atmosphere is studied analytically. Conditions for wave propagation along thin and wide magnetic-flux tubes are determined, and it is shown that the propagation along thin tubes is cutoff free; however, for wide tubes the propagation is affected by a cutoff frequency. A method to determine the cutoff frequency is presented and applied to a specific model of solar magnetic flux tubes. An interesting result is that the cutoff frequency is a local quantity in the model and that its value at a given height determines the frequency that torsional tube waves must have to propagate at this height. Title: Stringent Criteria for Stable and Unstable Planetary Orbits in Stellar Binary Systems Authors: Cuntz, M.; Eberle, J.; Musielak, Z. E. Bibcode: 2007ApJ...669L.105C Altcode: The existence of planets in stellar binary (and higher order) systems has now been confirmed by many observations. The stability of planetary orbits in these systems has been extensively studied, but no precise stability criteria have so far been introduced. Therefore, there is an urgent need for developing stringent mathematical criteria that allow us to precisely determine whether a planetary orbit in a binary system is stable or unstable. In this Letter, such criteria are defined using the concept of Jacobi's integral and Jacobi's constant. These criteria are used to contest previous results on planetary orbital stability in binary systems. Title: Propagation Characteristics of Waves in Solar Magnetic Flux Tubes Authors: Hammer, Reiner; Musielak, Zdzislaw E.; Routh, Swati Bibcode: 2007AN....328..704H Altcode: No abstract at ADS Title: The Multiple Time Scales of Solar Granulation Authors: Hammer, Reiner; Musielak, Zdzislaw E.; Nesis, Anastasios; Routh, Swati; Schleicher, Helmold Bibcode: 2007AN....328..703H Altcode: No abstract at ADS Title: Cutoff-free Propagation of Torsional Alfvén Waves along Thin Magnetic Flux Tubes Authors: Musielak, Z. E.; Routh, S.; Hammer, R. Bibcode: 2007ApJ...659..650M Altcode: 2007astro.ph..1720M Propagation of torsional Alfvén waves along magnetic flux tubes has been extensively studied for many years, but no conclusive results regarding the existence of a cutoff frequency for these waves have been obtained. The main purpose of this paper is to derive new wave equations that describe the propagation of linear torsional Alfvén waves along thin and isothermal magnetic flux tubes and to use these wave equations to demonstrate that the torsional wave propagation is not affected by any cutoff frequency. It is also shown that this cutoff-free propagation is independent of the different choices of coordinate system and wave variables adopted in previous studies. A brief discussion of the implications of this cutoff-free propagation of torsional tube waves on theories of wave heating of the solar and stellar atmospheres is also given. 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: Case Studies of the Restricted Three Body Problem Authors: Eberle, Jason; Cuntz, Manfred; Musielak, Zdzislaw Bibcode: 2006APS..TSF.P1005E Altcode: Are we alone in the universe? Nobody can give an answer yet. However, one step on the way to find out is to inquire how many planets in the universe could harbor life. An important feature a planet should have for life to exist is that the planet shouldn't crash into the star or fly off into interstellar space. In regard to our own solar system this is a non-issue as all planets are known to have orbited the Sun for billons of years. The unfortunate truth is that most planets don't have it as nice as Earth does. In fact, about half of all known stellar systems harbor two or more stars, thus affecting orbital stability of any planets in the systems. It is found that when a system harbors two stars, the planet may orbit one or both stars, depending on the physical conditions, or may even be kicked out of the neighborhood of the stars completely, and lost in space forever. In this poster, we provide detailed case studies for planets in binary systems. Title: Role of analyticity and covariance in determining laws of mechanics Authors: Fry, John; Musielak, Zdzislaw; Swift, L. D. Bibcode: 2006APS..TSFOT2006F Altcode: We impose two postulates for state functions in our universe and use them to obtain dynamical equations of mechanics for isolated elementary particles. The first postulate is that the state function is analytic on its carrier space. The second postulate is that any equation defining the state function must be written in covariant form for the metric of its carrier space. This implies Wigner's definition of an elementary particle, which we adopt. Using a Minkowski metric we obtain equations for isolated elementary particles which resemble the Dirac and Klein-Gordon equations. We introduce a quantum action operator and observe that the state function must be an eigenfunction of the operator. It must have eigenvalue to obtain the quantum theory of our universe. We identify the origin of Hamilton's principle for quantum systems as a consequence of the first two postulates and the definition of a particle. Dynamical equations in non-relativistic and classical limits will also be discussed. 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: Atmospheric Oscillations in White Dwarfs: A New Indicator of Chromospheric Activity Authors: Musielak, Z. E.; Winget, D. E.; Montgomery, M. H. Bibcode: 2005ApJ...630..506M Altcode: A new type of oscillation, the so-called atmospheric oscillations resulting from the response of stellar atmospheres to propagating acoustic waves, must be present in white dwarfs with chromospheric activity. Since these oscillations exist only in atmospheres with an outward temperature increase, they can be used as a new indicator of chromospheric activity in white dwarfs. Theoretical predictions of periods and amplitudes of the oscillations are given for selected DA and DB stars. The best candidates for detection of these oscillations are also identified. Title: Stability of planetary orbits in binary systems Authors: Musielak, Z. E.; Cuntz, M.; Marshall, E. A.; Stuit, T. D. Bibcode: 2005A&A...434..355M Altcode: Stability of S-type and P-type planetary orbits in binary systems of different mass and separation ratios is investigated. Criteria for stable, marginally stable and unstable planetary orbits are specified. These criteria are used to determine regions of stability of planetary orbits in different binary systems with Jupiter-type planets. The obtained results show that the regions of stability for S-type orbits depend on the distance ratio between the star and planet, and the stellar companions, in the range of 0.22 and 0.46, depending on the mass ratio. For P-type orbits, the regions of stability also depend on that distance ratio, in the range of 1.75 and 2.45, again depending on the the mass ratio. Applications of these results to three observed binary systems with giant planets, namely, τ Boo, HD 195019 and GJ 86, show that the orbits of the giant planets in those systems can be classified as stable, as expected. Title: Heating of Stellar Chromospheres and Transition Regions Authors: Musielak, Z. E. Bibcode: 2004IAUS..219..437M Altcode: 2003IAUS..219E..45M To explain the heating of stellar chromospheres and transition regions two classes of heating mechanisms have been considered: (1) dissipation of acoustic and magnetic waves generated in stellar convection zones; and (2) dissipation of currents generated by photospheric motions of surface magnetic fields. I will review both classes of heating mechanisms and discuss recent results which demonstrate that theoretical models of stellar chromospheres based on the wave heating (1) can explain the ""basal flux"" and the observed Ca II emission in most stars but cannot account for the observed Mg II emission in active stars. I will also present theoretical arguments which 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 (2)heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres and transition regions. Title: Torsional magnetic tube waves in stellar convection zones. I. Analysis of wave generation and application to the Sun Authors: Noble, M. W.; Musielak, Z. E.; Ulmschneider, P. Bibcode: 2003A&A...409.1085N Altcode: An analytic approach to the generation of torsional magnetic tube waves in stellar convection zones is presented. The waves are produced in a thin, vertically oriented magnetic flux tube embedded in a magnetic field-free, turbulent and compressible external medium and are excited by external turbulent flows. A theory for this interaction is developed and used to compute the wave energy spectra and fluxes carried by torsional tube waves in the solar atmosphere. We find that these tube waves have a characteristic cutoff frequency. Title: Atmospheric oscillations in solar magnetic flux tubes. II. Excitation by transverse tube waves and random pulses Authors: Musielak, Z. E.; Ulmschneider, P. Bibcode: 2003A&A...406..725M Altcode: The response of an exponentially diverging magnetic flux tube embedded in an isothermal solar atmosphere to the propagation of transverse tube waves and random transverse pulses generated in the solar convection zone is studied analytically. General solutions are presented and applied to solar flux tubes located in the interior region and at the boundary of supergranulation cells. It is shown that the period of the free oscillations driven by transverse waves and pulses ranges from 7 to 10 min for the considered values of the tube magnetic field, and that these oscillations decay in time as t-3/2. Since the observational signatures of these transverse oscillations are hard to detect, we also consider the generation of longitudinal tube waves by nonlinear mode coupling and the excitation of free atmospheric oscillations by longitudinal waves. Our results show that the basic properties of oscillations driven by transverse and longitudinal tube waves are different. While transverse waves excite oscillations with 7-10 min periods, oscillations by longitudinal waves have periods near 3 min. This is consistent with the observed 3-min oscillations inside the supergranule cells but inconsistent with the 7-min oscillations observed in the chromospheric network. We suggest that an explanation of the observed 7-min oscillations might be found by taking into account a more realistic structure of flux tubes located in the magnetic network. Title: Chandra Observations of Magnetic White Dwarfs and Their Theoretical Implications Authors: Musielak, Z. E.; Noble, M.; Porter, J. G.; Winget, D. E. Bibcode: 2003ApJ...593..481M Altcode: Observations of cool DA and DB white dwarfs have not yet been successful in detecting coronal X-ray emission, but observations of late-type dwarfs and giants show that coronae are common for these stars. To produce coronal X-rays, a star must have dynamo-generated surface magnetic fields and a well-developed convection zone. There is some observational evidence that the DA star LHS 1038 and the DB star GD 358 have weak and variable surface magnetic fields. It has been suggested that such fields can be generated by dynamo action, and since both stars have well-developed convection zones, theory predicts detectable levels of coronal X-rays from these white dwarfs. However, we present analysis of Chandra observations of both stars showing no detectable X-ray emission. The derived upper limits for the X-ray fluxes provide strong constraints on theories of formation of coronae around magnetic white dwarfs. Another important implication of our negative Chandra observations is the possibility that the magnetic fields of LHS 1038 and GD 358 are fossil fields. Title: Atmospheric oscillations in solar magnetic flux tubes. I. Excitation by longitudinal tube waves and random pulses Authors: Musielak, Z. E.; Ulmschneider, P. Bibcode: 2003A&A...400.1057M Altcode: The response of exponentially spreading magnetic flux tubes embedded in an isothermal solar atmosphere to the propagation of longitudinal tube waves and random pulses produced in the solar convection zone is studied analytically. General solutions are presented and applied to solar tube models. It is shown that free atmospheric oscillations inside these flux tubes are generated with oscillation periods near 3 min, which are essentially identical to the oscillation periods observed in the interior regions of supergranulation cells. The observed oscillations are therefore consistent with processes in magnetic tubes as well as in nonmagnetic regions. Stochastic perpetual excitation is expected to keep these flux tube oscillations present at all times. These oscillations are inconsistent with the observed 7-min oscillations in the chromospheric network. Title: Mechanisms of Chromospheric and Coronal Heating (Invited review) Authors: Ulmschneider, P.; Musielak, Z. Bibcode: 2003ASPC..286..363U Altcode: 2003ctmf.conf..363U No abstract at ADS Title: On the Generation of Flux-Tube Waves in Stellar Convection Zones. IV. Longitudinal Wave Energy Spectra and Fluxes for Stars with Nonsolar Metallicities Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P. Bibcode: 2002ApJ...573..418M Altcode: In the previous papers of this series, we developed an analytical method describing the generation of longitudinal tube waves in stellar convection zones and used it to compute the wave energy spectra and fluxes for late-type stars with the solar metal abundance (Population I). We now extend these calculations to Population II stars with effective temperatures ranging from Teff=2500 to 10,000 K, gravities logg=3-5, and with three different metal abundances: 1/10, 1/100, and 1/1000 of solar metallicity. The obtained results are valid for a single magnetic flux, and they show that the effects of metallicity are important only for cool stars with Teff<6000 K and that the amount of the generated wave energy decreases roughly by an order of magnitude for every decrease of the metallicity by an order of magnitude. The maximum wave energy flux generated in Population II stars is 7×108 ergs cm-2 s-1, and it is practically the same for stars of different gravities and metallicities. The computed spectra and fluxes can be used to construct theoretical models of magnetic regions in chromospheres of Population II stars. Title: Orbital Stability of Terrestrial Planets inside the Habitable Zones of Extrasolar Planetary Systems Authors: Noble, M.; Musielak, Z. E.; Cuntz, M. Bibcode: 2002ApJ...572.1024N Altcode: We investigate orbital stability of terrestrial planets inside the habitable zones of three stellar systems, i.e., 51 Peg, 47 UMa, and HD 210277, with recently discovered giant planets. These systems have similar habitable zones; however, their giant planets have different masses and significantly different orbital parameters. It is shown that stable orbits of terrestrial planets exist in the entire habitable zone of 51 Peg as well as in the inner part of the habitable zone of 47 UMa, but no stable orbits are found in the habitable zone of HD 210277. The obtained results allow us to draw general conclusions on the existence of stable orbits in the habitable zones of newly found extra-solar planetary systems. 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: Torsional Tube Waves in the Solar Atmosphere Authors: Noble, M.; Musielak, Z. E. Bibcode: 2002AAS...200.8803N Altcode: 2002BAAS...34..789N Recent results presented by Ulmschneider et al. (2001) imply that the energy carried by acoustic waves and magnetic (longitudinal and transverse) tube waves from the solar convection zone to the solar atmosphere is insufficient to heat the uppermost chromospheric layers, the transition region and corona. Since torsional tube waves are not included in their study, we have developed a theory of generation of these waves in the solar convection zone and use it to compute the resulting wave energy spectra and fluxes. We show the dependence of these spectra and fluxes on the strength of the magnetic field and various models of the solar convection zone, and discuss the role played by torsional tube waves in the heating of different layers of the solar atmosphere. This work is supported by NSF under grant ATM-0087184, NATO under grant CRG-910058 and The Alexander von Humboldt Foundation. Title: Excitation of transverse magnetic tube waves in stellar convection zones. II. Wave energy spectra and fluxes Authors: Musielak, Z. E.; Ulmschneider, P. Bibcode: 2002A&A...386..606M Altcode: The wave energy spectra and fluxes for transverse magnetic tube waves generated in stellar convection zones are computed by using the analytical method developed in the previous paper of this series. The main physical process responsible for the generation of these waves is shaking of a thin and vertically oriented magnetic flux tube by the external turbulent convection. The approach includes the correlation effects, which occur when the tube is shaken over a significant fraction of its length, but is limited to linear waves. The calculations are performed for population I stars with effective temperatures ranging from Teff = 2000 K to 10 000 K, and with gravities log g = 3-5. It is shown that the fluxes carried by linear transverse waves along a single flux tube are approximately one order of magnitude higher than those carried by linear longitudinal tube waves. The obtained results can be used to construct theoretical models of stellar chromospheres and winds. Title: Excitation of transverse magnetic tube waves in stellar convection zones . III. Effects of metallicity on wave energy spectra and fluxes Authors: Musielak, Z. E.; Ulmschneider, P. Bibcode: 2002A&A...386..615M Altcode: In the previous two papers of this series, we developed an analytical method describing the generation of transverse tube waves in stellar convection zones and used it to compute the wave energy spectra and fluxes for late-type stars with the solar metal abundance (population I stars). We now extend these calculations to population II stars with effective temperatures ranging from Teff = 2500 K to 10 000 K, gravities log g = 3 - 5, and with three different metal abundances: 1/10, 1/100 and 1/1000 of solar metallicity. The obtained results are valid only for a single magnetic flux tube and they show that the effects of metallicity are important only for cool stars with Teff < 6000 K and that the amount of the generated wave energy decreases roughly by an order of magnitude for every decrease of the metallicity by an order of magnitude. The maximum wave energy flux generated in population II stars is 3 x 109 erg cm-2 s-1 and it is practically the same for stars of different gravities and metallicities. Title: Chromospheric Heating Authors: Musielak, Z. E. Bibcode: 2002AAS...200.5302M Altcode: 2002BAAS...34..729M It is now well-established that the Sun and all other late-type stars show chromospheric activity, which is typically identified with the presence of emission in the cores of Ca II and Mg II spectral lines. This activity varies significantly for a given spectral type and a star is more active when a larger portion of its surface is covered by magnetic fields. For stars of very low activity, a minimum core emission flux ("basal flux") has been observed. To explain the required heating and the observed range of activity, two classes of heating mechanisms have been considered: (1) dissipation of acoustic and magnetic waves generated in stellar convection zones; and (2) dissipation of currents generated by photospheric motions of surface magnetic fields. I will review both classes of heating mechanisms and discuss recent results which demonstrate that theoretical models of stellar chromospheres based on the wave heating (1) can explain the "basal flux" and the observed Ca II emission in most stars but cannot account for the observed Mg II emission in active stars. I will also present theoretical arguments which 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 (2) heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres in active stars. This work was supported by NSF under grant ATM-0087184, NATO under grant CRG-910058 and The Alexander von Humboldt Foundation. 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: Orbital Stability of Earth-like Planets in Stellar Habitable Zones Authors: Noble, M.; Musielak, Z. E.; Cuntz, M. Bibcode: 2001AAS...199.0310N Altcode: 2001BAAS...33.1304N Long-term orbital stability of Earth-like planets in stellar habitable zones (HZs) is necessary for the evolution of any form of life. It is then interesting to ask whether Earth-like planets can exist in stable orbits around single stars with giant planets and in multiple stellar systems? The main conclusion from previous studies is that orbits of terrestrial planets in the HZs of 70 Vir, ρ CrB and 47 UMa are stable over the length of time required for the biological evolution, however, no long-term stability was found for Gl 876 and υ And. We have investigated orbital stability of terrestrial planets inside the HZs of three stellar systems, 51 Peg, 47 UMa and HD 210277, with known giant planets. The chosen systems have similar HZs, however, their planets have significantly different masses and orbital parameters. It is shown that stable orbits of terrestrial planets exist in the entire HZ of 51 Peg and in the inner part of the HZ of 47 UMa, but no stable orbits are found in the HZ of HD 210277. In addition, we have studied stability of orbits of Earth-like planets in one binary system (ζ Her) and in one triple system (ξ UMa). The obtained results allow us to draw general conclusions on the existence of stable orbits in the HZs of newly detected extra-solar planetary systems. This work was supported by NSF, NATO and The Alexander von Humboldt Foundation. Title: Habitability and Orbital Stability of Terrestrial Planets around 47 UMa Authors: Cuntz, M.; Noble, M.; Musielak, Z. E. Bibcode: 2001AAS...199.3305C Altcode: 2001BAAS...33R1356C We investigate the orbital stability and habitability of terrestrial planets around 47 UMa. This planetary system shows striking similarities to the Solar System by hosting two Jupiter-mass planets in nearly circular orbits at distances where respectable giant planets should be present and with its inner region free of gas giants. Orbits of terrestrial planets at different positions in the habitable zone (HZ) of 47 UMa are simulated numerically taking into account an updated definition of habitability. We show that habitable planets can in principle exist in the inner part of the HZ of 47 UMa, but not in its outer part owing to gravitational disturbances by the inner giant planet. Our study, which has meanwhile been extended to other stars as well, allows general conclusions about the existence of habitable planets around host stars, which may assist in the selection process of system candidates for future terrestrial planet search missions. Title: Wave Heating and Range of Stellar Activity in Late-Type Dwarfs Authors: Ulmschneider, P.; Fawzy, D.; Musielak, Z. E.; Stępień, K. Bibcode: 2001ApJ...559L.167U Altcode: Theoretical time-dependent and two-component chromospheric models for late-type dwarfs are constructed based on acoustic and magnetic wave heating mechanisms. The models are used to predict the theoretical range of chromospheric activity for these stars. Comparison of this range with the one established observationally shows that the wave heating alone can explain most but not all of the observed range of stellar activity. Title: Magnetic wave energy fluxes for late-type stars. I. Longitudinal tube waves Authors: Ulmschneider, P.; Musielak, Z. E.; Fawzy, D. E. Bibcode: 2001A&A...374..662U Altcode: The wave energy fluxes carried by longitudinal tube waves along thin vertical magnetic flux tubes embedded in atmospheres of late-type stars are computed. The main physical process responsible for the generation of these waves is the nonlinear time-dependent response of the flux tubes to continuous and impulsive external turbulent pressure fluctuations, which are represented here by an extended Kolmogorov spatial and modified Gaussian temporal energy spectrum. Both the wave energy fluxes and spectra are calculated for population I stars with effective temperatures ranging from Teff = 3500 K to 7000 K, and with gravities in the range log g = 3-5. The obtained results show that the computed wave energy may significantly contribute to the enhanced heating observed in magnetic regions of late-type stars. Title: Excitation of transverse magnetic tube waves in stellar convection zones. I. Analytical approach Authors: Musielak, Z. E.; Ulmschneider, P. Bibcode: 2001A&A...370..541M Altcode: Analytical treatment of the excitation of transverse magnetic tube waves in stellar convection zones is presented. The waves are produced by the interaction between thin and vertically oriented magnetic flux tubes embedded in stellar convection zones and the external turbulent motions. A general theory describing this interaction is developed and used to compute the wave energy spectra and fluxes for the Sun. 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: Analyzing the Effects of Planets and Brown Dwarfs on Stellar Chromospheric and Coronal Activity (CD-ROM Directory: contribs/cuntz2) Authors: Cuntz, M.; Musielak, Z. E.; Saar, S. H. Bibcode: 2001ASPC..223.1528C Altcode: 2001csss...11.1528C No abstract at ADS Title: Time-dependent analytical solutions for MHD surface waves propagating in a compressible plasma Authors: Musielak, Z. E.; Huang, P.; Ulmschneider, P. Bibcode: 2000A&A...362..359M Altcode: The propagation of linear MHD surface waves in a compressible plasma with a discontinuous interface in the magnetic field and temperature is considered. The initial perturbation is applied only to a vorticity line, which is located on the RHS of the discontinuity. Two different surface waves exist in this model, one associated with the vorticity line and the other confined to the discontinuity. Time-dependent analytical solutions for the wave velocity perturbations are obtained for both surface waves by applying Laplace transforms. The solutions are used to investigate the effects caused by compressibility on the propagation of these waves. It is shown that the compressibility effects are most important in the vicinity of the vorticity line and at the magnetic interface, and that they affect differently the behavior of the surface waves. Title: a Search for Coronal X-Rays from White Dwarfs by Chandra Authors: Musielak, Zdzislaw Bibcode: 2000cxo..prop..541M Altcode: 2000chan.prop..410M; 2000cxo..prop..410M Observations of DA and DB white dwarfs have not been successful in detecting coronal X-ray emission, but observations of late-type dwarfs and giants show that coronae are common for these stars. To produce coronal X-rays, a star has to have a well-developed convection zone and a dynamo-generated magnetic field. There is strong evidence that the DB star GD 358 and the DA star LHS 1038 have weak and variable surface magnetic fields. Theory suggests that these fields are generated by dynamo action, and that both stars have well-developed convection zones. These stars are among the most promising white dwarf candidates for having coronal X-ray emission at level detectable by CHANDRA. Its discovery would confirm the existence of a new class of objects with convection-dynamo driven X-rays. Title: On the Generation of Flux-Tube Waves in Stellar Convection Zones. III. Longitudinal Tube Wave-Energy Spectra and Fluxes for Late-Type Stars Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P. Bibcode: 2000ApJ...541..410M Altcode: The wave-energy spectra and fluxes for longitudinal tube waves generated in stellar convection zones are computed by using analytical methods developed in the two previous papers of this series. The main physical process responsible for the generation of these waves is the interaction between a thin and vertically oriented magnetic flux tube and the external turbulent convection. The spatial component of the turbulent convection is represented by an extended Kolmogorov turbulent energy spectrum, and its temporal component by a modified Gaussian frequency factor. The calculations are performed for Population I stars with effective temperatures ranging from Teff=2000 K to 10,000 K, and with gravities logg=3-5. The obtained results can be used to construct theoretical models of magnetic regions in stellar chromospheres. Title: On Stellar Activity Enhancement Due to Interactions with Extrasolar Giant Planets Authors: Cuntz, Manfred; Saar, Steven H.; Musielak, Zdzislaw E. Bibcode: 2000ApJ...533L.151C Altcode: We present a first attempt to identify and quantify possible interactions between recently discovered extrasolar giant planets (and brown dwarfs) and their host stars, resulting in activity enhancement in the stellar outer atmospheres. Many extrasolar planets have masses comparable to or larger than Jupiter and are within a distance of 0.5 AU, suggesting the possibility of their significant influence on stellar winds, coronae, and even chromospheres. Beyond the well-known rotational synchronization, the interactions include tidal effects (in which enhanced flows and turbulence in the tidal bulge lead to increased magnetoacoustic heating and dynamo action) and direct magnetic interaction between the stellar and planetary magnetic fields. We discuss relevant parameters for selected systems and give preliminary estimates of the relative interaction strengths. Title: On the Origin and Evolution of Stellar Chromospheres, Coronae and Winds Authors: Musielak, Z. E. Bibcode: 2000STIN...0038209M Altcode: This grant was awarded by NASA to The University of Alabama in Huntsville (UAH) to construct state-of-the-art, theoretical, two-component, chromospheric models for single stars of different spectral types and different evolutionary status. In our proposal, we suggested to use these models to predict the level of the "basal flux", the observed range of variation of chromospheric activity for a given spectral type, and the decrease of this activity with stellar age. In addition, for red giants and supergiants, we also proposed to construct self-consistent, purely theoretical wind models, and used these models to investigate the origin of "dividing lines" in the H-R diagram. In the following, we describe our completed work. We have accomplished the first main goal of our proposal by constructing first purely theoretical, time-dependent and two-component models of stellar chromospheres.1 The models require specifying only three basic stellar parameters, namely, the effective temperature, gravity and rotation rate, and they take into account non-magnetic and magnetic regions in stellar chromospheres. The non-magnetic regions are heated by acoustic waves generated by the turbulent convection in the stellar subphotospheric layers. The magnetic regions are identified with magnetic flux tubes uniformly distributed over the entire stellar surface and they are heated by longitudinal tube waves generated by turbulent motions in the subphotospheric and photospheric layers. The coverage of stellar surface by magnetic regions (the so-called filling factor) is estimated for a given rotation rate from an observational relationship. The constructed models are time-dependent and are based on the energy balance between the amount of mechanical energy supplied by waves and radiative losses in strong Ca II and Mg II emission lines. To calculate the amount of wave energy in the non-magnetic regions, we have used the Lighthill-Stein theory for sound generation. 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: Acoustic wave energy fluxes for late-type stars. II. Nonsolar metallicities Authors: Ulmschneider, P.; Theurer, J.; Musielak, Z. E.; Kurucz, R. Bibcode: 1999A&A...347..243U Altcode: Using the Lighthill-Stein theory with modifications described by Musielak et al. (1994), the acoustic wave energy fluxes were computed for late-type stars with the solar metal abundance (population I stars) by Ulmschneider et al. (1996). We now extend these computations to stars with considerably lower metal content (population II stars with 1/10 to 1/1000 of solar metallicity) and find that the acoustic fluxes calculated for stars of different spectral types and different luminosities are affected differently by the metallicity. It is found that the Hertzsprung-Russel diagram can be subdivided into three domains (labeled I, II and III) representing a different dependence of the generated acoustic fluxes on the stellar metal abundance. For the high T_eff stars of domain I there is no dependence of the generated acoustic fluxes on metallicity. In domain III are stars with low T_eff. Here the generated acoustic fluxes are lowered roughly by an order of magnitude for every decrease of the metal content by an order of magnitude. Finally, domain II represents the transition between the other two domains and the generated acoustic fluxes strongly depend on T_eff. The boundaries between the domains I and II, and II and III can be defined by simple relationships between stellar effective temperatures and gravities. Title: Numerical simulations of nonlinear MHD body and surface waves in magnetic slabs Authors: Huang, P.; Musielak, Z. E.; Ulmschneider, P. Bibcode: 1999A&A...342..300H Altcode: The behavior of MHD waves propagating in magnetically structured plasmas has been extensively investigated in the literature. In most of these studies, the wave treatment was restricted to the linear regime. This paper presents the results of time-dependent and nonlinear numerical simulations of MHD body and surface waves propagating along magnetic slabs. Both longitudinal and transverse waves are computed, and the wave behavior in the linear and nonlinear regime is compared. Two physical processes are investigated in detail. The first is the energy leakage from the magnetic slab to the field-free external medium. It is found that the energy leakage is 62% for transverse slab waves, which means that the efficiency of energy transfer along the slab by these waves is significantly reduced. The second process is the excitation of MHD waves in two adjacent magnetic slabs by large amplitude acoustic waves from the external medium. The slabs have physical parameters typical for photospheric magnetic flux tubes. It is shown that only 1-3% of the energy carried by these acoustic waves is transferred to the slabs, and that the efficiency of this process strongly depends on the location of the slabs relative to the source of acoustic waves and on the amplitude of these waves. Both physical processes are important for the problem of heating of magnetically structured regions in the solar and stellar atmospheres. Title: The Generation of Longitudinal Tube Waves in Late Type Stars Authors: Fawzy, D. E.; Musielak, Z. E.; Ulmschneider, P. Bibcode: 1999RoAJ....9S.149F Altcode: The aim of the present work is to compute the generated nonlinear tube wave energy fluxes carried by longitudinal waves as a result of the interaction between a vertically directed thin magnetic flux tube and the turbulent medium in the stellar convection zone of late type stars. The computations are based on work by Ulmschneider and Musielak (1998). The current computations are for stars of gravities log g = 3,4,5 and temperature range from Teff = 3500 to 7000 K. Title: Acoustic wave propagation in the solar atmosphere. III. Analytic solutions for adiabatic wave excitations Authors: Sutmann, G.; Musielak, Z. E.; Ulmschneider, P. Bibcode: 1998A&A...340..556S Altcode: The response of an isothermal solar type atmosphere to adiabatic excitations by various small amplitude acoustic disturbances is studied analytically. Both continuous and pulse excitations are discussed. It is shown that wavetrains of random pulses may be responsible for the excitation of the 3-min solar oscillations. Title: Theoretical Models of Stellar Chromospheres Authors: Musielak, Z. E.; Cuntz, M.; Ulmschneider, P. Bibcode: 1998AAS...193.2204M Altcode: 1998BAAS...30.1283M To identify the basic physical processes that underlie stellar chromospheric activity, we have taken a novel theoretical approach and constructed first purely theoretical, two-component and time-dependent models of stellar chromospheres. Our models require specifying only four basic stellar parameters, namely, the effective temperature, gravity, metallicity and rotation rate, and they take into account non-magnetic and magnetic regions in stellar chromospheres. The non-magnetic regions are heated by acoustic waves generated by the turbulent convection in the stellar subphotospheric layers. The magnetic regions are identified with magnetic flux tubes uniformly distributed over the entire stellar surface and are heated by longitudinal tube waves generated by turbulent motions in the subphotospheric and photospheric layers. The coverage of stellar surface by magnetic regions (the so-called filling factor) is estimated for a given rotation rate from an observational relationship. The constructed models are based on the energy balance between the amount of mechanical energy supplied by waves and radiative losses in strong Ca II and Mg II emission lines. We have already used our chromospheric models to predict the level of ``basal flux'' and the decrease of chromospheric activity with stellar rotation in selected late-type dwarfs. We present these new results and discuss how to include stellar transition regions, coronae and winds in our models. Title: On Wave Processes in the Solar Atmosphere Authors: Musielak, Z. E. Bibcode: 1998STIN...9945903M Altcode: This grant was awarded by NASA/MSFC to The University of Alabama in Huntsville (UAH) to investigate the physical processes responsible for heating and wind acceleration in the solar atmosphere, and to construct theoretical, self-consistent and time-dependent solar wind models based on the momentum deposition by finite amplitude and nonlinear Alfven waves. In summary, there are three main goals of the proposed research: (1) Calculate the wave energy spectra and wave energy fluxes carried by magnetic non- magnetic waves. (2) Find out which mechanism dominates in supplying the wave energy to different parts of the solar atmosphere. (3) Use the results obtained in (1) and (2) to construct theoretical, self-consistent and time- dependent models of the solar wind. We have completed the first goal by calculating the amount of non-radiative energy generated in the solar convection zone as acoustic waves and as magnetic tube waves. To calculate the amount of wave energy carried by acoustic waves, we have used the Lighthill-Stein theory for sound generation modified by Musielak, Rosner, Stein & Ulmschneider (1994). The acoustic wave energy fluxes for stars located in different regions of the Hertzsprung-Russell (H-R) diagram have also been computed. The wave energy fluxes carried by longitudinal and transverse waves along magnetic flux tubes have been calculated by using both analytical and numerical methods. Our analytical approach is based a theory developed by Musielak, Rosner & Ulmschnelder and Musielak, Rosner, Gall & Ulmschneider, which allows computing the wave energy fluxes for linear tube waves. A numerical approach has been developed by Huang, Musielak & Ulmschneider and Ulmschneider & Musielak to compute the energy fluxes for nonlinear tube waves. Both methods have been used to calculate the wave energy fluxes for stars located in different regions of the HR diagram (Musielak, Rosner & Ulmschneider 1998; Ulmschneider, Musielak & Fawzy 1998). Having obtained the wave energy fluxes for acoustic and magnetic tube waves, we have investigated the behavior of these waves in the solar and stellar atmospheres. The results of our extensive studies have been published in many papers and presented at numerous scientific meetings. In these studies we have investigated different aspects of propagation of acoustic and magnetic waves, the efficiency of energy transfer along magnetic structures in the solar atmosphere, and behavior of Alfven waves in stgeady and expanding solar and stellar atmospheres. Recently, we have used some of these results to construct first purely theoretical, two component and time-dependent models of solar and stellar chromospheres. Finally, to address the third goal, we have constructed first fully theoretical, self-consistent and time dependent wind models based on the momentum deposition by non-linear Alfven waves. The full set of single-fluid MHD equations with the background flow has been solved by using a modified version of the ZEUS MHD code. The constructed wind models are radially symmetric with the magnetic field decreasing radially and the initial outflow is described by the standard Parker wind solution. In contrast to previous studies, no assumptions regarding wave linearity, wave damping, and wave-flow interaction are made; the models thus naturally account for the backreaction of the wind on the waves as well as for the nonlinear interaction between different types of MHD waves. The models have been used to explain the origin of fast speed streams in solar coronal holes. The obtained results clearly demonstrate that the momentum deposition by Alfven waves in the solar wind can be sufficient to explain the origin of fast stream components of the solar wind. The range of wave amplitudes required to obtain the desired results seems to be in good agreement with recent 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: On the generation of nonlinear magnetic tube waves in the solar atmosphere. II. Longitudinal tube waves Authors: Ulmschneider, P.; Musielak, Z. E. Bibcode: 1998A&A...338..311U Altcode: The nonlinear time-dependent response to external pressure fluctuations acting on a thin vertical magnetic flux tube embedded in the solar atmosphere is investigated numerically. The continuous and impulsive fluctuations are imposed on the tube at different atmospheric heights and the resulting longitudinal tube wave energy fluxes are calculated for an observationally established range of velocity amplitudes and tube magnetic fields. The obtained results show that typical wave energy fluxes carried by nonlinear longitudinal tube waves are of the order of 2*10(8) erg/cm(2) s, which is roughly a factor of 30 less than the flux for transverse waves. In contrast to our linear analytical results the generated nonlinear longitudinal tube wave fluxes can be up to an order of magnitude higher. Title: Self-Consistent and Time-Dependent Magnetohydrodynamic Chromosphere Models for Magnetically Active Stars Authors: Cuntz, Manfred; Ulmschneider, Peter; Musielak, Zdzislaw E. Bibcode: 1998ApJ...493L.117C Altcode: We present self-consistent and time-dependent MHD heating models for chromospheres of magnetically active stars. We investigate the propagation and dissipation of longitudinal flux-tube waves in K2 V stars with different rotation rates implying different photospheric and chromospheric magnetic filling factors. These filling factors are critical for determining the number of flux tubes on the stellar surface and the spreading of the tubes with height, which is relevant for the propagation and dissipation of the magnetic energy as well as the generated radiative emission losses. The filling factors used in this Letter are estimated using a relationship between the photospheric values for B0f0 and Prot in accord with very recent magnetic field measurements by Rüedi et al. We also consider revised computations of magnetic energy fluxes by Ulmschneider & Musielak generated by turbulent motions. Our models show increased shock strengths and energy dissipation rates in stars of faster rotation because of the narrower spreading of the tubes. This also leads to increased chromospheric emission, particularly in Mg II in stars of faster rotation. We consider these results as a first step toward a theoretical derivation of chromospheric emission--stellar rotation relationships for stars of different masses and evolutionary status. Title: Reflection Coefficient and Non-WKB Effects for Alfven Waves Propagating in the Solar Wind Authors: Krogulec, M.; Musielak, Z. E. Bibcode: 1998AcA....48...77K Altcode: The propagation of Alfven waves in spherically symmetric, isothermal solar wind models with two different temperatures T_0=2.85 times 10^6 K and T_0=8.2 times 10^5 K is considered. The steady-state Alfven wave equations are solved numerically and the resulting reflection coefficient and non-WKB effects are calculated. The obtained results show that the reflection coefficient is practically zero in the high-temperature wind model, where wave reflection and non-WKB effects are essentially absent, and that it can also be zero in the low-temperature model, where wave reflection and non-WKB effects are present. A physical explanation of these results is given. Title: MHD Waves and Turbulence in the Solar Wind Authors: Musielak, Z. E. Bibcode: 1998asct.conf..339M Altcode: No abstract at ADS Title: Acoustic and MHD Wave Energy Fluxes for Late-Type Stars Authors: Musielak, Z. E.; Cuntz, M.; Ulmschneider, P.; Theurer, J.; Kurucz, R. Bibcode: 1997AAS...191.1206M Altcode: 1997BAAS...29.1228M The vast amount of observational data collected at wavelengths ranging from X-rays to radio waves have indicated the ubiquity of stellar chromospheres among late-type stars. In addition, there is growing observational evidence for inhomogeneous and locally strong magnetic fields in stellar atmospheres. It is reasonable to assume that stellar magnetic inhomogeneities may be similar to the `flux tube' structures observed in the solar atmosphere outside sunspots. If so, two distinct components of stellar chromospheres must be recognized, namely, non-magnetic component, where acoustic waves are responsible for the heating, and magnetic component, where MHD tube waves supply energy for the heating. To construct theoretical models of stellar chromospheres (see paper by Cuntz et al. presented at this meeting), it is necessary to know the amount of non-radiative energy generated in stellar convective zones and carried by acoustic and MHD tube waves through stellar photospheres. In this paper, we discuss the correct status of computing acoustic and MHD wave energy fluxes for the Sun and late-type dwarfs. Our calculations are based on grey LTE mixing-length convection zone models and both linear and non-linear theories of wave generation are used. New acoustic and MHD wave energy fluxes are presented for stars of population I and II in the range of effective temperatures T_eff 2000 - 10000 K and gravities log g = 1 - 8. The turbulent flow field is represented by an extended Kolmogorov spatial and modified Gaussian temporal energy spectrum. The mixing-length parameter is varied in the range alpha = 1 - 2. We find that the obtained acoustic wave energy strongly depend on stellar chemical composition and that MHD fluxes show wide variations for a given spectral type, variations which can be attributed to changes in the stellar flux tube filling factor. We discuss the range of the filling factor for which the calculated MHD fluxes may account for the observed levels of chromospheric activity. Title: Self-Consistent and Time-Dependent MHD Heating Models for Chromospheres of Magnetically Active Stars Authors: Cuntz, M.; Musielak, Z. E.; Ulmschneider, P. Bibcode: 1997AAS...191.1205C Altcode: 1997BAAS...29.1228C We present self-consistent and time-dependent MHD heating models for chromospheres of magnetically active stars. We investigate the propagation and dissipation of longitudinal flux tube waves in K2V stars with different rotation rates implying different photospheric and chromospheric magnetic filling factors. These filling factors are critical for determining the number of flux tubes on the stellar surface and the spreading of the tubes with height, which is relevant for the propagation and dissipation of the magnetic energy. The photospheric filling factors are estimated using a relationship between the magnetic field strength B_o multiplied by the photospheric magnetic filling factor f_o and the stellar rotation P_rot in accord with very recent magnetic field measurements. We also consider revised computations for the initial magnetic energy fluxes generated by turbulent motions (Ulmschneider & Musielak 1997, A&A, submitted). Our models show increased shock strengths and energy dissipation rates in stars of faster rotation due to the narrower spreading of the tubes. This also leads to increased chromospheric emission particularly in Mg II in stars of faster rotation. We consider these results as a first step toward a theoretical derivation of chromospheric emission --- stellar rotation relations for stars of different masses and evolutionary status. Title: On the Origin and Evolution of Stellar Chromospheres, Coronae and Winds Authors: Musielak, Z. E. Bibcode: 1997STIN...9731037M Altcode: The final report discusses work completed on proposals to construct state-of-the-art, theoretical, two-component, chromospheric models for single stars of different spectral types and different evolutionary status. We suggested to use these models to predict the level of the "basal flux", the observed range of variation of chromospheric activity for a given spectral type, and the decrease of this activity with stellar age. In addition, for red giants and supergiants, we also proposed to construct self-consistent, purely theoretical, chromosphere-wind models, and investigate the origin of "dividing lines" in the H-R diagram. In the report, we list the following six specific goals for the first and second year of the proposed research and then describe the completed work: (1) To calculate the acoustic and magnetic wave energy fluxes for stars located in different regions of the H-R diagram; (2) To investigate the transfer of this non-radiative energy through stellar photospheres and to estimate the amount of energy that reaches the chromosphere; (3) To identify major sources of radiative losses in stellar chromospheres and calculate the amount of emitted energy; (4) To use (1) through (3) to construct purely theoretical, two-component, chromospheric models based on the local energy balance. The models will be constructed for stars of different spectral types and different evolutionary status; (5) To explain theoretically the "basal flux", the location of stellar temperature minima and the observed range of chromospheric activity for stars of the same spectral type; and (6) To construct self-consistent, time-dependent stellar wind models based on the momentum deposition by finite amplitude Alfven waves. Title: A Study of Magnetic Complexity Using HURST`S Rescaled Range Analysis Authors: Adams, M.; Hathaway, D. H.; Stark, B. A.; Musielak, Z. E. Bibcode: 1997SoPh..174..341A Altcode: A fractal analysis using the classical Hurst method has been applied to artificial data, simulated sunspot magnetic field data, and to data acquired with NASA/Marshall Space Flight Center's vector magnetograph. The main goals of this study are to quantify the complexity of an active region and to determine if significant changes in complexity are associated with flare activity. We tested the analysis using three basic types of two-dimensional synthetic data: (1) data composed of gaussians with various types of superimposed features, (2) random data, and (3) synthetic sunspots created from a basic, simple configuration on which are placed increasingly smaller structures. Our results confirm that the Hurst method of analysis is sensitive to the presence of large-scale structures within a two-dimensional image. When the large-scale structure has been removed, the value of the Hurst exponent is inversely proportional to increasing complexity in the image. The Hurst exponent of magnetograph data with the large-scale structure of the sunspot removed, shows a tantalizing variation in the shear parameter five minutes prior to a flare. Title: Self-consistent and Time-dependent Solar Wind Models Authors: Ong, K. K.; Musielak, Z. E.; Rosner, R.; Suess, S. T.; Sulkanen, M. E. Bibcode: 1997ApJ...474L.143O Altcode: We describe the first results from a self-consistent study of Alfvén waves for the time-dependent, single-fluid magnetohydrodynamic (MHD) solar wind equations, using a modified version of the ZEUS MHD code. The wind models we examine are radially symmetrical and magnetized; the initial outflow is described by the standard Parker wind solution. Our study focuses on the effects of Alfvén waves on the outflow and is based on solving the full set of the ideal nonlinear MHD equations. In contrast to previous studies, no assumptions regarding wave linearity, wave damping, and wave-flow interaction are made; thus, the models naturally account for the back-reaction of the wind on the waves, as well as for the nonlinear interaction between different types of MHD waves. Our results clearly demonstrate when momentum deposition by Alfvén waves in the solar wind can be sufficient to explain the origin of fast streams in solar coronal holes; we discuss the range of wave amplitudes required to obtained such fast stream solutions. Title: Acoustic wave energy fluxes for late-type stars. Authors: Ulmschneider, P.; Theurer, J.; Musielak, Z. E. Bibcode: 1996A&A...315..212U Altcode: We revisit the problem of acoustic wave generation by turbulent convection in late-type stellar atmospheres. Using the Lighthill-Stein theory with modifications described in our recent paper Musielak et al. (1994ApJ...423..474M), we compute both acoustic frequency spectra and total acoustic fluxes on basis of grey LTE mixing-length convection zone models for population I stars, in the range of effective temperatures T_eff_=2000-10000K and gravities logg=0-8. The turbulent flow field is represented by an extended Kolmogorov spatial and modified Gaussian temporal energy spectrum. The mixing-length parameter was varied in the range α=1-2. Particularly for M-dwarf stars we find large discrepancies between our fluxes and those of Bohn (1981 (Ph.D. Thesis, Univ. Wuerzburg, Germany), 1984A&A...130..202B). Except for very cool dwarf stars our total fluxes are well reproduced by the simple Lighthill-Proudmann formula already developed in the 1950's. Title: Alfvén wave resonances and flow induced by nonlinear Alfvén waves in a stratified atmosphere Authors: Stark, B. A.; Musielak, Z. E.; Suess, S. T. Bibcode: 1996AIPC..382..153S Altcode: A nonlinear, time-dependent, ideal MHD code has been developed and used to compute the flow induced by nonlinear Alfvén waves propagating in an isothermal, stratified, plane-parallel atmosphere. The code is based on characteristic equations solved in a Lagrangian frame. Results show that resonance behavior of Alfvén waves exists in the presence of a continuous density gradient and that the waves with periods corresponding to resonant peaks exert considerably more force on the medium than off-resonance periods. If only off-peak periods are considered, the relationship between the wave period and induced longitudinal velocity shows that short period WKB waves push more on the background medium than longer period, non-WKB, waves. The results also show the development of the longitudinal waves induced by finite amplitude Alfvén waves. Wave energy transferred to the longitudinal mode may provide a source of localized heating. Title: On Complexity of Solar Magnetic Fields Authors: Musielak, Z. E. Bibcode: 1996alab.rept.....M Altcode: Observational data collected by solar magnetographs from different places around the world seem to clearly indicate that the onset of flares is related to the structure of sunspot magnetic fields. The simple, but not necessarily always valid, rule is that the more complex the structure of the field the more flares are produced. Until now, estimates of the magnetic field complexity were mostly subjective. An important problem is how to quantify the field complexity by using rigorous methods of data analysis. In the completed research we have used several fractal techniques to address the problem. We have adopted the well=-known concept of fractal dimension, to quantify the field complexity and to search for temporal variations of this complexity. We have calculated the fractal dimension for a chosen magnetic field data set acquired by the NASA/MSFC vector magnetograph and searched for temporal changes in the computed fractal dimension which may be related to the onset of solar flares. The analysis was performed on magnetic field data collected from solar active regions that showed different levels of flare activity as well as from non-flaring regions. Title: Propagation of MHD Body and Surface Waves in Magnetically Structured Regions of the Solar Atmosphere Authors: Wu, S. T.; Xiao, Y. C.; Musielak, Z. E.; Suess, S. T. Bibcode: 1996SoPh..163..291W Altcode: The fact that magnetically structured regions exist in the solar atmosphere has been known for a number of years. It has been suggested that different kinds of magnetohydrodynamic (MHD) waves can be efficiently damped in these regions and that the dissipated wave energy may be responsible for the observed enhancement in radiative losses. From a theoretical point of view, an important task would be to investigate the propagation and dissipation of MHD waves in these highly structured regions of the solar atmosphere. In this paper, we study the behavior of MHD body and surface waves in a medium with either a single or double (slab) magnetic interface by use of a nonlinear, two-dimensional, time-dependent, ideal MHD numerical model constructed on the basis of a Lagrangean grid and semi-implicit scheme. The processes of wave confinement and wave energy leakage are discussed in detail. It is shown that the obtained results depend strongly on the type of perturbations imposed on the interface or slab and on the plasma parameter, β. The relevance of the obtained results to the heating problem of the upper parts of the solar atmosphere is also discussed. Title: New acoustic wave energy computations for late-type stars Authors: Theurer, J.; Ulmschneider, P.; Musielak, Z. Bibcode: 1996ASPC..109..169T Altcode: 1996csss....9..169T No abstract at ADS Title: Generation of Linear and Nonlinear Magnetic Tube Waves in the Solar Atmosphere Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P. Bibcode: 1996mpsa.conf..427M Altcode: 1996IAUCo.153..427M No abstract at ADS Title: ROSAT Pointed Observations of Cool Magnetic White Dwarfs Authors: Musielak, Z. E.; Porter, J. G.; Davis, J. M. Bibcode: 1995ApJ...453L..33M Altcode: Observational evidence for the existence of a chromosphere on the cool magnetic white dwarf GD 356 has been reported. In addition, there have been theoretical speculations that cool magnetic white dwarfs may be sources of coronal X-ray emission. This emission, if it exists, would be distinct from the two types of X-ray emission (deep photospheric and shocked wind) that have already been observed from hot white dwarfs. We have used the PSPC instrument on ROSAT to observe three of the most prominent DA white dwarf candidates for coronal X-ray emission: GD 356, KUV 2316+123, and GD 90. The data show no significant emission for these stars. The derived upper limits for the X-ray luminosities provide constraints for a revision of current theories of the generation of nonradiative energy in white dwarfs. Title: Klein-Gordon Equation and the Local Critical Frequency for Alfven Waves Propagating in an Isothermal Atmosphere Authors: Musielak, Z. E.; Moore, R. L. Bibcode: 1995ApJ...452..434M Altcode: A Klein-Gordon equation approach developed by Musielak, Fontenla, and Moore for assessing reflection of Alfvén waves in a smoothly nonuniform medium is reexamined. In this approach, the local critical frequency for strong reflection is simply found by transforming the wave equations into their Klein-Gordon forms and then choosing the largest positive coefficient of the zeroth-order term to be the square of the local critical frequency. In this paper, we verify this approach for a particular atmosphere and show that the local critical frequency can be alternatively defined by using the turning-point property of Euler's equation. Our results are obtained specifically for steady state, linear Alfvén waves in an isothermal atmosphere with constant gravity and uniform vertical magnetic field. The upward Alfvén waves (those above the wave source) are standing waves and the downward waves (those below the wave source) are propagating waves. We demonstrate that for any given wave frequency both upward and downward waves have the same turning point or critical height. This height is determined by the condition ω = ΩA = VA/2H, where VA is the Alfvén velocity and H is the scale height; ΩA can be taken as the local critical frequency for strong reflection for the upward waves and as the local critical frequency for free propagation for the downward waves. Our turning-point analysis also yields another interesting result: for our particular model atmosphere the magnetic field perturbation wave equation yields the local critical frequency but the velocity-perturbation wave equation does not. Thus, for this model atmosphere, we find that the Klein-Gordon equation approach of Musielak, Fontenla, and Moore is correct in (1) its choice of the magnetic-field-perturbation wave equation for finding the local critical frequency, and (2) its assumption that the upward and downward waves have the same critical frequency. Title: On the physical processes underlying the existence and origin of X-ray and mass loss 'dividing lines' for cool giants and supergiants Authors: Musielak, Z. E. Bibcode: 1995alab.rept.....M Altcode: The necessity of magnetic confinement for hot coronal material and the large reflection efficiency for Alfven waves in cool exponential atmospheres are considered. The joint problem is addressed, namely, how one can account for the coincidence of the relatively sudden onset of large mass loss rates with the equally sudden disappearance of emission associated with high temperature (greater than 106 K) plasma emitting X-rays as one moves along the giant and supergiant branches in the H-R diagram. A model is constructed for the transition from solar-like coronal and transition region behavior to strong, cool mass outflows as evolved stars move across the locus of 'dividing lines' in the H-R diagram. This model favors Alfven waves as a main source of heating the atmospheres to coronal temperatures and as a source of the wind acceleration. Analytical and numerical methods are used to investigate reflection and trapping of linear and nonlinear Alfven waves in highly inhomogeneous and expanding stellar atmospheres. Title: On the Generation of Flux-Tube Waves in Stellar Convection Zones. II. Improved Treatment of Longitudinal Tube Wave Generation Authors: Musielak, Z. E.; Rosner, R.; Gail, H. P.; Ulmschneider, P. Bibcode: 1995ApJ...448..865M Altcode: We have previously considered the generation of purely longitudinal magnetohydrodynamic tube waves by external turbulent convection and derived general formulas for the source function and for the wave energy fluxes. In this paper, we present an improved treatment of the generation of such tube waves, based on a more sophisticated description of the turbulence and more refined calculations. These improvements allow us to compute and discuss in greater detail the spectra and fluxes of longitudinal tube waves generated in the solar convective zone. Title: Magnetospheric filter effect for Pc 3 Alfvén mode waves Authors: Zhang, X.; Comfort, R. H.; Gallagher, D. L.; Green, J. L.; Musielak, Z. E.; Moore, T. E. Bibcode: 1995JGR...100.9585Z Altcode: We present a ray-tracing study of the propagation of Pc 3 Alfvén mode waves originating at the dayside magnetopause. This study reveals interesting features of a magnetospheric filter effect for these waves. Pc 3 Alfvén mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index, show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O+ block the waves. When the O+ concentration is removed from the plasma composition, the barriers caused by the O+ no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30-mHz or lower frequency Alfvén waves can be guided to low altitudes agrees with ground-based power spectrum observations at high latitudes. Title: Alfven wave resonances and flow induced by non-linear Alfven waves in a stratified atmosphere Authors: Stark, B. A.; Musielak, Z. E.; Suess, S. T. Bibcode: 1995sowi.confR..66S Altcode: A nonlinear, time-dependent, ideal MHD code has been developed and used to compute the flow induced by nonlinear Alfven waves propagating in an isothermal, stratified, plane-parallel atmosphere. The code is based on characteristic equations solved in a Lagrangian frame and is highly accurate. Results show that resonance behavior of Alfven waves exists in the presence of a continuous density gradient and that the waves with periods corresponding to resonant peaks exert considerably more force on the medium than off-resonance periods; this leads to enhanced flow. If only off-peak periods are considered, the relationship between the wave period and induced longitudinal velocity shows that short period WKB waves push more on the background medium than longer period, non-WKB, waves. The results also show the development of the longitudinal waves produced by the finite amplitude of the Alfven waves. The longitudinal wave becomes strong as the Alfven wave relative amplitude grows above 10 percent and will lead to strong damping of the Alfven waves. Title: On the generation of nonlinear magnetic tube waves in the solar atmosphere. Authors: Huang, P.; Musielak, Z. E.; Ulmschneider, P. Bibcode: 1995A&A...297..579H Altcode: The nonlinear time-dependent response to purely transverse shaking of a thin vertical magnetic flux tube embedded in the solar atmosphere is investigated numerically. The shaking is imposed on the tube at different heights in the solar atmosphere and the resulting magnetic wave energy fluxes are calculated for the observationally established range of velocity amplitudes and tube magnetic fields. The obtained results clearly demonstrate that typical wave energy fluxes carried by nonlinear transverse tube waves are of the order of 10^9^erg/cm2/s. This, in contrast to previous analytical studies, seems to indicate that there is enough wave energy to account for the enhanced heating observed in the chromospheric network, and that magnetic tube waves may also play some role in the heating of other regions of the solar atmosphere. Title: Evolution of the Fractal Dimension in a Flaring Active Region Authors: Adams, M.; Hathaway, D. H.; Musielak, Z. E. Bibcode: 1995SPD....26.1016A Altcode: 1995BAAS...27..980A No abstract at ADS Title: On the Origin of ``Dividing Lines'' for Late-Type Giants and Supergiants Authors: Rosner, R.; Musielak, Z. E.; Cattaneo, F.; Moore, R. L.; Suess, S. T. Bibcode: 1995ApJ...442L..25R Altcode: We show how a change in the nature of the stellar dyanmo can lead to a transition in the topological character of stellar magnetic fields of evolved stars, from being mainly closed on the blueward side of the giant tracks in the Hertzsprung-Russell (H-R) diagram to being mainly open on their redward side. If such a topological transition occurs, then these stars naturally segregate into two classes: those having hot coronae on the blueward side, and those having massive cool winds on the redward side, thus leading naturally to the so-called dividing lines. Title: Klein-Gordon Equations for Acoustic Waves and Their Applications in Helioseismology Authors: Neergaard, L. F.; Musielak, Z. E.; Hathaway, D. H. Bibcode: 1995SPD....26..401N Altcode: 1995BAAS...27..954N No abstract at ADS Title: Klein-Gordon Equation and Reflection of Alfvén Waves Authors: Musielak, Z. E.; Moore, R. L. Bibcode: 1995SPD....26..910M Altcode: 1995BAAS...27R.975M No abstract at ADS Title: Self-Consistent Models of the Solar Wind Accelerated by Alfvén Waves Authors: Ong, K. K.; Krogulec, M.; Musielak, Z. E. Bibcode: 1995SPD....26..904O Altcode: 1995BAAS...27..973O No abstract at ADS Title: Propagating Alfven Waves, Intermittent Magnetic Levitation, and Coronal Heating in Coronal Holes Authors: Moore, R. L.; Musielak, Z. E.; Krogulec, M.; Suess, S. T. Bibcode: 1995SPD....26..908M Altcode: 1995BAAS...27Q.975M No abstract at ADS Title: Reflection of Alfvén waves in the solar wind Authors: Krogulec, M.; Musielak, Z. E.; Suess, S. T.; Nerney, S. F.; Moore, R. L. Bibcode: 1994JGR....9923489K Altcode: We have revisited the problem of propagation of toroidal and linear Alfvén waves formulated by Heinemann and Olbert (1980) to compare WKB and non-WKB waves and their effects on the solar wind. They considered two solar wind models and showed that reflection is important for Alfvén waves with periods of the order of one day and longer and that non-WKB Alfvén waves are no more effective in accelerating the solar wind than WKB waves. There are several recently published papers that seem to indicate that Alfvén waves with periods of the order of several minutes should be treated as non-WKB waves and that these non-WKB waves exert a stronger acceleration force than WKB waves. The purpose of this paper is to study the origin of these discrepancies by performing parametric studies of the behavior of the waves under a variety of different conditions. In addition, we want to investigate two problems that have not been addressed by Heinemann and Olbert, namely, calculate the efficiency of Alfvén wave reflection by using the reflection coefficient and identify the region of strongest wave reflection in different wind models. To achieve these goals, we investigated the influence of temperature, electron density distribution, wind velocity,and magnetic field strength on the waves.

The obtained results clearly demonstrate that Alfvén wave reflection is strongly model dependent and that the strongest reflection can be expected in the models with the base temperatures higher than 106 K and with the base densities lower than 7 × 107 cm-3. In these models as well as in the models with lower temperatures and higher densities, Alfvén waves with periods as short as several minutes have negligible reflection so that they can be treated as WKB waves; however, for Alfvén waves with periods of the order of one hour or longer reflection is significant, requiring a non-WKB treatment. We also show that non-WKB, linear Alfvén waves are always less effective in accelerating the plasma than WKB Alfvén waves. Finally, it is evident from our results that the region of strongest wave reflection is usually located at the base of the models and hence that interpretation of wave reflection based solely on the reflection coefficient can be misleading. Title: The Role of Alfven Waves in Solar Wind Acceleration Authors: Krogulec, M.; Musielak, Z. E.; Suess, S. T.; Nerney, S. F.; Moore, R. L. Bibcode: 1994AAS...185.9206K Altcode: 1994BAAS...26.1472K The fact that Alfven waves may play a significant role in the energy balance in solar coronal holes has been known for a number of years. A special attention has been given to these waves because they can transfer energy to large distances and deposit efficiently momentum in the background medium. It has been shown that non-WKB effects are important for Alfven waves with periods of the order of one day and longer, and that non-WKB Alfven waves are no more effective in acceleration of the solar wind than WKB waves. There are, however, some recently published papers which seem to indicate that Alfven waves with periods of the order of several minutes should be treated as non-WKB waves and that these waves exert a stronger acceleration force than WKB waves. To investigate the origin of these discrepancies, we have performed a series of parametric studies of the behavior of the waves under a variety of different conditions in solar coronal holes. The obtained results demonstrate that both Alfven wave reflection and the acceleration force due to the waves are strongly model dependent. The strongest reflection can be expected in models with the base temperatures higher than 10(6) K and with the base densities lower than 7 times 10(7) cm(-3) . However, the strongest acceleration force is expected in the models with the weakest reflection. This clearly indicates that linear non-WKB Alfven waves are always less effective in accelerating the plasma than WKB Alfven waves. Implications of this result for the heating in solar coronal holes and for the acceleration of the solar wind will be discussed. Title: Fractal Techniques Applied to a Flaring Active Region Authors: Adams, Mitzi; Musielak, Z. E. Bibcode: 1994AAS...185.9203A Altcode: 1994BAAS...26.1472A Fractal techniques have been used extensively to characterize data from the fields of atmospheric physics, geophysics, astrophysics, and recently to identify fractal clusters in sunspot penumbrae and solar active regions. Using data acquired with NASA/Marshall Space Flight Center's vector magnetograph, we apply fractal techniques to identify temporal changes of the Hurst coefficient by applying Hurst's modified ``Range over Standard Deviation" analysis to 30 sets of data taken at five minute intervals. These data were obtained over a period of three hours, during which time one of two M-class flares occured. To determine the correlation with solar flares, we compare the evolution of Hurst coefficients from this active region (NOAA AR 6659) June 10, 1991 to a simple, non-flaring sunspot (NOAA AR 6484). Title: Klein-Gordon Equation and Reflection of Alfven Waves Authors: Musielak, Z. E.; Moore, R. L. Bibcode: 1994AAS...18512106M Altcode: 1994BAAS...26.1520M It is of some interest to know the physical conditions that lead to efficient reflection of Alfven waves in the solar and stellar atmospheres. The problem seems to be important because these waves may play some role in non-radiative heating of the solar and stellar chromosphere and coronae, and may also be responsible for acceleration of the solar and cool massive stellar winds. A significant effort has been made by a number of authors to understand the behavior of these waves in highly inhomogeneous stellar atmospheres. The simplest treatment of the problem seems to be the so-called Klein-Gordon equation approach, which allows obtaining local critical frequencies by transforming the wave equations into their Klein-Gordon forms and then choosing the largest positive coefficient to be the square of the local critical frequency. In this paper, we show that the local critical frequency can be alternatively defined by using the turning-point property of Euler's equation. Our results are obtained specifically for Alfven waves propagating in an isothermal atmosphere with constant gravity and uniform vertical magnetic field. We demonstrate that Alfven waves in the upper (above the wave source) part of our model always form a standing wave pattern and that the waves in the lower (below the wave source) part of the model are always propagating (but partially reflected) waves. We also show that the turning point for the upward and downward waves is located at the height where the condition omega = Omega_A is satisfied and that Omega_A = V_A / 2 H, where V_A is the Alfven velocity and H is the scale height, can be taken as a local critical frequency because the waves undergo strong reflection in this region of the atmosphere where omega <= Omega_A . By applying our turning-point analysis to the Alfven wave equations for the velocity and magnetic field perturbation, we obtain an interesting result: for our particular model atmosphere the magnetic-field-perturbation wave equation yields the local critical frequency but the velocity-perturbation wave equation does not. A physical interpretation of the obtained results will be given. Title: Limits to Extensions of Burgers Equation Authors: Nerney, Steven; Schmahl, Edward J.; Musielak, Z. E. Bibcode: 1994solv.int.11005N Altcode: The vector Burgers equation is extended to include pressure gradients and gravity. It is shown that within the framework of the Cole-Hopf transformation there are no physical solutions to this problem. This result is important because it clearly demonstrates that any extension of Burgers equation to more interesting physical situations is strongly limited. Title: On the physics of waves in the solar atmosphere: Wave heating and wind acceleration Authors: Musielak, Z. E. Bibcode: 1994alab.reptQ....M Altcode: New calculations of the acoustic wave energy fluxes generated in the solar convective zone have been performed. The treatment of convective turbulence in the sun and solar-like stars, in particular, the precise nature of the turbulent power spectrum has been recognized as one of the most important issues in the wave generation problem. Several different functional forms for spatial and temporal spectra have been considered in the literature and differences between the energy fluxes obtained for different forms often exceed two orders of magnitude. The basic criterion for choosing the appropriate spectrum was the maximal efficiency of the wave generation. We have used a different approach based on physical and empirical arguments as well as on some results from numerical simulation of turbulent convection. Title: On the origin and evolution of stellar X-ray emission Authors: Musielak, Z. E. Bibcode: 1994pas..conf...41M Altcode: No abstract at ADS Title: On Sound Generation by Turbulent Convection: A New Look at Old Results Authors: Musielak, Z. E.; Rosner, R.; Stein, R. F.; Ulmschneider, P. Bibcode: 1994ApJ...423..474M Altcode: We have revisited the problem of acoustic wave generation by turbulent convection in stellar atmospheres. The theory of aerodynamically generated sound, originally developed by Lighthill and later modified by Stein to include the effects of stratification, has been used to estimate the acoustic wave energy flux generated in solar and stellar convection zones. We correct the earlier computations by incorporating an improved description of the spatial and temporal spectrum of the turbulent convection. We show the dependence of the resulting wave fluxes on the nature of the turbulence, and compute the wave energy spectra and wave energy fluxes generated in the Sun on the basis of a mixing-length model of the solar convection zone. In contrast to the previous results, we show that the acoustic energy generation does not depend very sensitively on the turbulent energy spectrum. However, typical total acoustic fluxes of order FA = 5 x 107 ergs/sq cm/s with a peak of the acoustic frequency spectrum near omega = 100 mHz are found to be comparable to those previously calculated. The acoustic flux turns out to be strongly dependent on the solar model, scaling with the mixing-length parameter alpha as alpha3.8. The computed fluxes most likely constitute a lower limit on the acoustic energy produced in the solar convection zone if recent convection simulations suggesting the presence of shocks near the upper layers of the convection zone apply to the Sun. Title: On the physics of waves in the solar atmosphere: Wave heating and wind acceleration Authors: Musielak, Z. E. Bibcode: 1994STIN...9425264M Altcode: This paper presents work performed on the generation and physics of acoustic waves in the solar atmosphere. The investigators have incorporated spatial and temporal turbulent energy spectra in a newly corrected version of the Lighthill-Stein theory of acoustic wave generation in order to calculate the acoustic wave energy fluxes generated in the solar convective zone. The investigators have also revised and improved the treatment of the generation of magnetic flux tube waves, which can carry energy along the tubes far away from the region of their origin, and have calculated the tube wave energy fluxes for the sun. They also examine the transfer of the wave energy originated in the solar convective zone to the outer atmospheric layers through computation of wave propagation and dissipation in highly nonhomogeneous solar atmosphere. These waves may efficiently heat the solar atmosphere and the heating will be especially significant in the chromospheric network. It is also shown that the role played by Alfven waves in solar wind acceleration and coronal hole heating is dominant. The second part of the project concerned investigation of wave propagation in highly inhomogeneous stellar atmospheres using an approach based on an analytic tool developed by Musielak, Fontenla, and Moore. In addition, a new technique based on Dirac equations has been developed to investigate coupling between different MHD waves propagating in stratified stellar atmospheres. Title: Fractal dimension: a predictor for solar flares. Authors: Adams, M.; Musielak, Z. E.; Jaenisch, H. M. Bibcode: 1994BAAS...26..794A Altcode: No abstract at ADS Title: ROSAT observations of cool magnetic white dwarfs. Authors: Musielak, Z. E.; Davis, J. M.; Porter, J. G.; Trimble, V. L. Bibcode: 1994BAAS...26R.792M Altcode: No abstract at ADS Title: Propagation characteristics of Pc 3 compressional waves generated at the dayside magnetopause Authors: Zhang, X.; Comfort, R. H.; Musielak, Z. E.; Moore, T. E.; Gallagher, D. L.; Green, J. L. Bibcode: 1993JGR....9815403Z Altcode: New, three-dimensional ray tracing of Pc 3 compressional waves from the magnetosheath reveals that the magnetosphere can present a major propagation barrier to the penetration of these waves to the plasmasphere. This barrier is the ion-ion cutoff between the He+ and O+ gyroresonances. As a result of the frequency-dependent location of this cutoff, the magnetosphere behaves like a filter for Pc 3 compressional waves, and only low-frequency components of Pc 3 compressional waves can penetrate to inner magnetosphere. Results are in agreement with previous satellite observations. This ``filter action'' strongly depends on the relative concentration of He+ and O+ and is therefore sensitive to solar and magnetic activity. Ray-tracing results are based on a cold plasma dispersion relation, a semi-empirical model of plasma density, and the Mead-Fairfield magnetic field model. Title: On the physics of waves in the solar atmosphere: Wave heating and wind acceleration Authors: Musielak, Z. E. Bibcode: 1993alab.reptS....M Altcode: This paper presents work performed on the generation and physics of acoustic waves in the solar atmosphere. The investigators have incorporated spatial and temporal turbulent energy spectra in a newly corrected version of the Lighthill-Stein theory of acoustic wave generation in order to calculate the acoustic wave energy fluxes generated in the solar convective zone. The investigators have also revised and improved the treatment of the generation of magnetic flux tube waves, which can carry energy along the tubes far away from the region of their origin, and have calculated the tube energy fluxes for the sun. They also examine the transfer of the wave energy originated in the solar convective zone to the outer atmospheric layers through computation of wave propagation and dissipation in highly nonhomogeneous solar atmosphere. These waves may efficiently heat the solar atmosphere and the heating will be especially significant in the chromospheric network. It is also shown that the role played by Alfven waves in solar wind acceleration and coronal hole heating is dominant. The second part of the project concerned investigation of wave propagation in highly inhomogeneous stellar atmospheres using an approach based on an analytic tool developed by Musielak, Fontenla, and Moore. In addition, a new technique based on Dirac equations has been developed to investigate coupling between different MHD waves propagating in stratified stellar atmospheres. Title: Excitation of Nonlinear Magnetic Flux Tube Waves in the Solar Atmosphere Authors: Huang, P.; Musielak, Z. E.; Ulmschneider, P. Bibcode: 1993BAAS...25.1213H Altcode: No abstract at ADS Title: The Heating of Solar Coronal Holes by Means of Non-Linear Alfven Wave Coupling Authors: Stark, B.; Musielak, Z. E.; Suess, S. T.; Ulmschneider, P. Bibcode: 1993BAAS...25R1212S Altcode: No abstract at ADS Title: The Cutoff Frequency for Fast-Mode Magnetohydrodynamic Waves in an Isothermal Atmosphere with a Uniform Horizontal Magnetic Field Authors: Stark, B. A.; Musielak, Z. E. Bibcode: 1993ApJ...409..450S Altcode: This study analytically examines conditions for reflection of MHD fast-mode waves propagating upward in an isothermal atmosphere. A new method of transforming the linearized wave equation into Klein-Gordon form is utilized to calculate a local cutoff (critical) frequency for these waves. This critical frequency determines the height in the atmosphere at which reflection dominates and above which wave propagation is effectively cut off. Comparison of our results to those previously obtained shows that earlier calculations of the critical frequency for MHD fast mode waves were done incorrectly. The results may be helpful in explaining the short-period end of the spectrum of the solar global p-mode oscillations. They may also be important in studies of wave propagation and wave trapping in highly magnetized stellar atmospheres. Title: On the Heating Mechanism of Coronal Holes Authors: Hammer, R.; Moore, R. L.; Musielak, Z. E.; Suess, S. T. Bibcode: 1993ASSL..183..587H Altcode: 1993pssc.symp..587H No abstract at ADS Title: On reflection of Alfven waves in the solar wind Authors: Krogulec, M.; Musielak, Z. E.; Suess, S. T.; Moore, R. L.; Nerney, S. F. Bibcode: 1993STIN...9530582K Altcode: We have revisited the problem of propagation of toroidal and linear Alfven waves formulated by Heinemann and Olbert (1980) to compare WKB and non-WKB waves and their effects on the solar wind. They considered two solar wind models and showed that reflection is important for Alfven waves with periods of the order of one day and longer, and that non-WKB Alfven waves are no more effective in accelerating the solar wind than WKB waves. There are several recently published papers which seem to indicate that Alfven waves with periods of the order of several minutes should be treated as non-WKB waves and that these non-WKB waves exert a stronger acceleration force than WKB waves. The purpose of this paper is to study the origin of these discrepancies by performing parametric studies of the behavior of the waves under a variety of different conditions. In addition, we want to investigate two problems that have not been addressed by Heinemann and Olbert, namely, calculate the efficiency of Alfven wave reflection by using the reflection coefficient and identify the region of strongest wave reflection in different wind models. To achieve these goals, we investigated the influence of temperature, electron density distribution, wind velocity and magnetic field strength on the waves. The obtained results clearly demonstrate that Alfven wave reflection is strongly model dependent and that the strongest reflection can be expected in models with the base temperatures higher than 106 K and with the base densities lower than 7 x 107 cm-3. In these models as well as in the models with lower temperatures and higher densities, Alfven waves with periods as short as several minutes have negligible reflection so that they can be treated as WKB waves; however, for Alfven waves with periods of the order of one hour or longer reflection is significant, requiring a non-WKB treatment. We also show that non-WKB, linear Alfven waves are always less effective in accelerating the plasma than WKB Alfven waves. Finally, it is evident from our results that the region of strongest wave reflection is usually located at the base of the models, and hence that interpretation of wave reflection based solely on the reflection coefficient can be misleading. Title: On Sound Generation by Turbulent Convection: A New Look at Old Results Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Gail, P.; Wang, A. Bibcode: 1992AAS...181.9403M Altcode: 1992BAAS...24.1269M No abstract at ADS Title: A New Way to Convert Alfven Waves into Heat in Solar Coronal Holes: Intermittent Magnetic Levitation Authors: Moore, R. L.; Hammer, R.; Musielak, Z. E.; Suess, S. T.; An, C. -H. Bibcode: 1992ApJ...397L..55M Altcode: In our recent analysis of Alfven wave reflection in solar coronal holes, we found evidence that coronal holes are heated by reflected Alfven waves. This result suggests that the reflection is inherent to the process that dissipates these Alfven waves into heat. We propose a novel dissipation process that is driven by the reflection, and that plausibly dominates the heating in coronal holes. Title: On the physics of waves in the solar atmosphere: Wave heating and wind acceleration Authors: Musielak, Z. E. Bibcode: 1992STIN...9233947M Altcode: In the area of solar physics, new calculations of the acoustic wave energy fluxes generated in the solar convective zone was performed. The original theory developed was corrected by including a new frequency factor describing temporal variations of the turbulent energy spectrum. We have modified the original Stein code by including this new frequency factor, and tested the code extensively. Another possible source of the mechanical energy generated in the solar convective zone is the excitation of magnetic flux tube waves which can carry energy along the tubes far away from the region. The problem as to how efficiently those waves are generated in the Sun was recently solved. The propagation of nonlinear magnetic tube waves in the solar atmosphere was calculated, and mode coupling, shock formation, and heating of the local medium was studied. The wave trapping problems and evaluation of critical frequencies for wave reflection in the solar atmosphere was studied. It was shown that the role played by Alfven waves in the wind accelerations and the coronal hole heating is dominant. Presently, we are performing calculations of wave energy fluxes generated in late-type dwarf stars and studying physical processes responsible for the heating of stellar chromospheres and coronae. In the area of physics of waves, a new analytical approach for studying linear Alfven waves in smoothly nonuniform media was recently developed. This approach is presently being extended to study the propagation of linear and nonlinear magnetohydrodynamic (MHD) waves in stratified, nonisothermal and solar atmosphere. The Lighthill theory of sound generation to nonisothermal media (with a special temperature distribution) was extended. Energy cascade by nonlinear MHD waves and possible chaos driven by these waves are presently considered. Title: A Regularization Method for Extrapolation of Solar Potential Magnetic Fields Authors: Gary, G. A.; Musielak, Z. E. Bibcode: 1992ApJ...392..722G Altcode: The mathematical basis of a Tikhonov regularization method for extrapolating the chromospheric-coronal magnetic field using photospheric vector magnetograms is discussed. The basic techniques show that the Cauchy initial value problem can be formulated for potential magnetic fields. The potential field analysis considers a set of linear, elliptic partial differential equations. It is found that, by introducing an appropriate smoothing of the initial data of the Cauchy potential problem, an approximate Fourier integral solution is found, and an upper bound to the error in the solution is derived. This specific regularization technique, which is a function of magnetograph measurement sensitivities, provides a method to extrapolate the potential magnetic field above an active region into the chromosphere and low corona. Title: Intermittent Magnetic Levitation and Heating by Alfven Waves in Solar Coronal Holes Authors: Moore, R. L.; Hammer, R.; Musielak, Z. E.; Suess, S. T.; An, C. -H. Bibcode: 1992AAS...180.5506M Altcode: 1992BAAS...24R.819M No abstract at ADS Title: ROSAT guest investigator program (AO-1). On a search for coronal X ray emissions from white dwarfs Authors: Musielak, Z. E. Bibcode: 1992STIN...9413171M Altcode: We have suggested that cool magnetic white dwarfs may be sources of X-ray coronal emission and proposed several prominent candidates for this emission. One of these candidates (EG 250) was approved for the C-category observation by the National and International Committee and was observed by ROSAT on April 17, 1991. Unfortunately, the granted exposure time (1071 s) was much shorter than that which was required by theoretical predictions to observe coronal X-ray emission from this object. The tape containing the data was send to us in November 1991. Since then we have analyzed the data visiting the ROSAT Science Center at NASA Goddard Space Flight Center. The analysis of the data taken during this short observation show, as expected, no X-rays. It is our hope that EG 250 will be observed again during the AO-2 phase of pointed observations, as 10,000 s of observing time was granted to V. Trimble for the C-category observation of this star. We have a close contact with Dr. Trimble regarding this matter. Because our all targets (GD 90, KUV 2316-123 and GD 356) proposed for the observation during the AO-2 phase of pointed observations have been approved by the National and International Committee, we have installed the required software at NASA/MSFC to be able to carry out the data analysis in Huntsville. Two of our targets have already been observed (KUV 2316-123 was observed on Dec. 3, 1991 with 10,000 s of the exposure time, and GD 356 was observed on Jan 4, 1992 with 5,000 s of the exposure time). We just received the data and will begin the analysis soon. The results of our analysis will be reported to the scientific community by publishing papers in the Astrophysical Journal Letters. Our intention is to submit a paper when the analysis of the data taken during AO2 is completed. The data taken during the observation of EG 250 will be a part of this paper. Title: Why the Winds from Late-Type Giants; Supergiants are Cool Authors: Moore, R. L.; Musielak, Z. E.; An, C. -H.; Rosner, R.; Suess, S. T. Bibcode: 1992ASPC...26..464M Altcode: 1992csss....7..464M No abstract at ADS Title: Heating of solar coronal holes by reflected Alfven waves Authors: Moore, R. L.; Musielak, Z. E.; Suess, S. T.; An, C. -H. Bibcode: 1992MmSAI..63..777M Altcode: As a continuation of the work of Moore et al. (1991), who found evidence that coronal holes are heated by Alfven waves that are reflected back down within the coronal holes, this paper shows that to demonstrate this evidence, it is only necessary to consider a subset of the Moore et al. models, namely, those having radial magnetic field. Using these models, it is shown that the Alfven velocity is not constant in the atmosphere of coronal holes, but changes with height (or radius), causing downward reflection of all upward Alfven waves of sufficiently long wavelength (or period). Title: Heating of solar and stellar chromospheres and coronae by MHD waves Authors: Musielak, Z. E. Bibcode: 1992HiA.....9..665M Altcode: No abstract at ADS Title: Klein-Gordon equation and reflection of Alfvén waves in nonuniform media Authors: Musielak, Z. E.; Fontenla, J. M.; Moore, R. L. Bibcode: 1992PhFlB...4...13M Altcode: A new analytical approach is presented for assessing the reflection of linear Alfven waves in smoothly nonuniform media. The general one-dimensional case in Cartesian coordinates is treated. It is shown that the wave equations, upon transformation into the form of the Klein-Gordon equation, display a local critical frequency for reflection. At any location in the medium, reflection becomes strong as the wave frequency descends past this characteristic frequency set by the local nonuniformity of the medium. This critical frequecy is given by the transformation as an explicit function of the Alfven velocity and its first and second derivatives, and hence as an explicit spatial function. The transformation thus directly yields, without solution of the wave equations, the location in the medium at which an Alfven wave of any given frequency becomes strongly reflected and has its propagation practically cut off. Title: Alfven wave reflection and heating in coronal holes - Theory and observation Authors: Suess, S. T.; Moore, R. L.; Musielak, Z. E.; An, C. -H. Bibcode: 1992sws..coll..117S Altcode: We present evidence for significant reflection of Alfven waves in an isothermal, hydrostatic model corona and that heating in coronal holes is provided by Alfven waves. For Alfven waves with periods of 5 min, upward propagating waves are reflected if the temperature is less than 10 exp 6 K, but escape into the solar wind if the temperature is greater than 10 exp 6 K. This sensitive temperature dependence may provide the self-limiting mechanism that has been suspected to exist because the reflected waves result in heating which raises the temperature which, in turn, decreases the reflection. The reflection occurs mostly inside of about 6 solar radii, depending on temperature, wave period, and magnetic field strength and geometry. The importance of this process has often been overlooked due to a poor choice of coronal Alfven speed and temperature. SOHO is well-suited to measure whether the required properties for reflection exist. Solar Probe, however, is the only definitive experiment to show if the waves actually exist to the degree necessary. Title: Heating of solar and stellar chromospheres and coronae by MHD waves Authors: Musielak, Z. E. Bibcode: 1992MmSAI..63..635M Altcode: The two general classes of models that deal with the required heating of stellar chromospheres and coronae assume that outer stellar atmospheres are heated by hydrodynamic or by magnetohydrodynamic (MHD) waves and that these waves are generated by turbulent motions in the stellar convection zones. This paper considers the types of MHD waves and the source of these waves in stars like sun, the efficiency of the generation of MHD waves, and the manner of propagation and energy dissipation of MHD waves. It is shown that the basic criteria for the validity of any theory of MHD wave heating must account for the mean level of heating observed in stellar chromospheres and coronae, and for the range of radiative losses observed for a given spectral type. It is also required that the MHD wave heating theory accounts for the existence of inhomogeneities in stellar atmospheres. The results obtained indicate that magnetic tube waves might supply enough energy for the chromospheric and coronal heating and might also account for the observed range of variations of stellar radiative losses for a given spectral type. Title: Alfven Wave Trapping, Network Microflaring, and Heating in Solar Coronal Holes Authors: Moore, R. L.; Musielak, Z. E.; Suess, S. T.; An, C. -H. Bibcode: 1991ApJ...378..347M Altcode: Fresh evidence that much of the heating in coronal holes is provided by Alfven waves is presented. This evidence comes from examining the reflection of Alfven waves in an isothermal hydrostatic model coronal hole with an open magnetic field. Reflection occurs if the wavelength is as long as the order of the scale height of the Alfven velocity. For Alfven waves with periods of about 5 min, and for realistic density, magnetic field strength, and magnetic field spreading in the model, the waves are reflected back down within the model hole if the coronal temperature is only slightly less than 1.0 x 10 to the 6th K, but are not reflected and escape out the top of the model if the coronal temperature is only slightly greater than 1.0 x 10 to the 6th K. Because the spectrum of Alfven waves in real coronal holes is expected to peak around 5 min and the temperature is observed to be close to 1.0 x 10 to the 6th K, the sensitive temperature dependence of the trapping suggests that the temperature in coronal holes is regulated by heating by the trapped Alfven waves. Title: Why the Winds from Late-Type Giants and Supergiants are Cool Authors: Moore, R. L.; Musielak, Z. E.; An, C. -H.; Rosner, R.; Suess, S. T. Bibcode: 1991BAAS...23Q1385M Altcode: No abstract at ADS Title: On the Generation of Magnetic Tube Waves in the Solar Convection Zone Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Gail, P. Bibcode: 1991BAAS...23.1442M Altcode: No abstract at ADS Title: On Reflection of Fast Mode Waves in the Solar Atmosphere Authors: Stark, B. A.; Musielak, Z. E. Bibcode: 1991BAAS...23.1442S Altcode: No abstract at ADS Title: Magnetic Confinement, Alfven Wave Reflection, and the Origins of X-Ray and Mass-Loss ``Dividing Lines'' for Late-Type Giants and Supergiants Authors: Rosner, R.; An, C. -H.; Musielak, Z. E.; Moore, R. L.; Suess, S. T. Bibcode: 1991ApJ...372L..91R Altcode: A simple qualitative model for the origin of the coronal and mass-loss dividing lines separating late-type giants and supergiants with and without hot, X-ray-emitting corona, and with and without significant mass loss is discussed. The basic physical effects considered are the necessity of magnetic confinement for hot coronal material on the surface of such stars and the large reflection efficiency for Alfven waves in cool exponential atmospheres. The model assumes that the magnetic field geometry of these stars changes across the observed 'dividing lines' from being mostly closed on the high effective temperature side to being mostly open on the low effective temperature side. Title: On the generation of magnetic tube waves in the solar convection zone. Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Gail, P. Bibcode: 1991BAAS...23.1037M Altcode: No abstract at ADS Title: A Regularization Method for the Extrapolation of Solar Magnetic Fields Authors: Gary, G. A.; Musielak, Z. Bibcode: 1991BAAS...23.1031G Altcode: No abstract at ADS Title: Critical Frequencies and Reflection of Fast Mode Waves in an Isothermal Atmosphere Authors: Stark, B. A.; Musielak, Z. E. Bibcode: 1991BAAS...23.1060S Altcode: No abstract at ADS Title: On the Generation of Magnetic Tube Waves in the Solar Convection Zone Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Gail, P. Bibcode: 1991BAAS...23Q1037M Altcode: No abstract at ADS Title: Propagation of nonlinear longitudinal-transverse waves along magnetic flux tubes in the solar atmosphere. I - Adiabatic waves Authors: Ulmschneider, P.; Zaehringer, K.; Musielak, Z. E. Bibcode: 1991A&A...241..625U Altcode: The nonlinear time-dependent response to purely transverse foot point shaking of a vertical magnetic flux tube in the solar atmosphere was studied. The adiabatic calculations show the generation of a longitudinal wave mode which has twice the frequency of the transverse wave. The amplitude of the longitudinal wave increases with the wave period and with the magnitude of the shaking. Due to the action of centrifugal forces significant lifting of the tube gas was found. A forced oscillator type resonance occurs which depends on the tube length. Title: Recent Developments in Theories of Wave Generation (With 5 Figures) Authors: Musielak, Z. E. Bibcode: 1991mcch.conf..369M Altcode: No abstract at ADS Title: Magnetic Confinement, Alfvén Wave Reflection, and the Origin of X-ray and Mass Loss "Dividing Lines" Authors: An, C. -H.; Rosner, R.; Musielak, Z. E.; Moore, R. L.; Suess, S. T. Bibcode: 1991mcch.conf..445A Altcode: No abstract at ADS Title: Reflection of Alfvén Waves and Heating in Solar Coronal Holes (With 1 Figure) Authors: Moore, R. L.; Musielak, Z. E.; Suess, S. T.; An, C. -H. Bibcode: 1991mcch.conf..435M Altcode: No abstract at ADS Title: Conditions for Vertical Propagation of Magnetoacoustic Waves in an Isothermal Atmosphere Authors: Musielak, Z. E. Bibcode: 1990ApJ...351..287M Altcode: The propagation of magnetoacoustic waves in an isothermal atmosphere with constant gravity and uniform magnetic field of an arbitrary direction is considered. The conditions for the vertical propagation of these waves are determined by characteristic frequencies that arise in the MHD wave equation which is considered here in the limit of low-beta plasma. The obtained steady state solutions to the wave equation describe the behavior of fast and slow magnetoacoustic waves and allow defining the characteristic frequencies that separate domains of wave frequency where the sinusoidal and nonsinusoidal wave solutions are found. The particular problem of dependence of the characteristic frequencies on the density gradient as well as on the strength and direction of the uniform magnetic field are discussed. The obtained results may have important consequences on the behavior of magnetoacoustic waves in stellar atmospheres and may be found useful in studying stellar p-mode oscillations. Title: Reflection and Trapping of Alfven Waves in a Spherically Symmetric Stellar Atmosphere Authors: An, C. -H.; Suess, S. T.; Moore, R. L.; Musielak, Z. E. Bibcode: 1990ApJ...350..309A Altcode: Alfven wave propagation in a spherically symmetric isothermal and stratified stellar atmosphere are analzyed using a time-dependent MHD numerical model. Particular consideration is given to wave reflection and the resultant trapping of the wave due to a peak in the Alfven speed in the atmosphere. Resonance frequencies in the trapping region and the effect of trapping on Alfven wave pressure force and propagation are examined. The data reveal that Alfven wave trapping has a potentially important role in accelerating winds from cool stars. Title: Effect of Radiative Transfer on Convection in the Deep Photosphere of Late-Type Dwarfs Authors: Fontenla, J. M.; Musielak, Z. E.; Moore, R. L. Bibcode: 1990ASPC....9...82F Altcode: 1990csss....6...82F A method is proposed to eliminate the compressional instability of a shallow layer in the upper part of stellar convective zones in standard mixing-length models. By equating the radiative cooling time of mixing eddies to their convective turnover time, the effective sizes of the eddies are assumed to be the smallest of those which are not eliminated by radiative transfer. Computations of the models with this assumption leads to smooth temperature profiles in the previously unstable layers and reductions of the convective velocity above its maximum value. Title: Generation of Transverse Magnetic Tube Waves and X-Ray Emissions from Late-Type Dwarfs Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P. Bibcode: 1990ASPC....9...79M Altcode: 1990csss....6...79M The X-ray emissions observed in late-type stars are shown to be associated with transverse magnetic tube waves generated in stellar convective zones. The heating theory is examined to insure that it accounts for the mechanical energy flux associated with the wide range of X-ray emissions for each spectral type, and the inhomogeneous and locally strong magnetic fields in stellar atmospheres. The values of the free parameters from the wave-heating model developed agree with observational data, and the tube waves can account for the observed X-ray emissions of F, G, and K dwarfs. Title: Longitudinal-Transverse Magnetic Tube Waves in the Solar Atmosphere Authors: Ulmschneider, P.; Musielak, Z. Bibcode: 1990ASPC....9..116U Altcode: 1990csss....6..116U The propagation of nonlinear adiabatic magnetohydrodynamic waves in a thin magnetic flux tube is studied. The waves are excited by purely transverse shaking. Due to nonlinear coupling there is a significant energy transfer to the longitudinal wave. This transfer is largest for long period waves and increases with the shaking amplitude. Lifting of the tube mass is found due to the increased swaying with height. Title: A Mechanism for the Increase in Stellar Wind Mass Loss from Giants across the Dividing Line Authors: An, C. H.; Musielak, Z. E.; Rosner, R.; Moore, R. L.; Suess, S. T. Bibcode: 1990ASPC....9...70A Altcode: 1990csss....6...70A No abstract at ADS Title: Why DA and DB White Dwarfs Do Not Show Coronal Activity and p-Mode Oscillations Authors: Musielak, Z. E.; Fontenla, J. M. Bibcode: 1989ApJ...346..435M Altcode: The problems of nonradiative heating of outer atmospheric layers and p-mode oscillations in white dwarfs caused by acoustic waves generated in convective zones are discussed. These effects have been studied by calculating the cutoff periods for adiabatic and isothermal waves propagating in atmospheres of DA and DB stars with Teff greater than or equal 20,000 K and log g = 6-9. The obtained cutoff periods are approximately bounded by 0.01 and 40 sec for high- and low-gravity white dwarfs, respectively. Expected amplitudes of p-mode oscillations corresponding to trapped acoustic waves with small angular wave numbers are estimated, indicating that the amplitudes could be observed as Doppler shifts of spectral lines which might be detectable if adequate spectral resolution were available. The luminosity variations corresponding to these amplitudes are unlikely to be observable when all damping processes are accounted for. Results also indicate that the present theory of convection predicts some irregularities in the behavior of physical parameters. Title: Reflection and trapping of transient Alfven waves propagating in an isothermal atmosphere with constant gravity and uniform magnetic field Authors: An, C. -H.; Musielak, Z. E.; Moore, R. L.; Suess, S. T. Bibcode: 1989ApJ...345..597A Altcode: A time-dependent linear magnetohydrodynamic numerical model was used to investigate the propagation of Alfven waves in an isothermal and stratified atmosphere with constant gravity and uniform vertical magnetic field. Results show that the Alfven wave transit time for the wave source to infinity is finite and that the wave exhibits continuous partial reflection which becomes total reflection as the front approaches infinity. The total reflection causes the waves to be trapped in the cavity that extends from the wave source to infinity and in which the wave energy is stored. The results suggest that the reflection of Alfven waves (of sufficiently long period) from the outer corona is an intrinsic phenomenon for any stellar atmosphere stratified by gravity and an open magnetic field, and that, therefore, such waves may be trapped in the stellar atmosphere. Title: Alfven Speed and Heating in Solar Coronal Holes Authors: Moore, R. L.; An, C. H.; Suess, S. T.; Musielak, Z. E. Bibcode: 1989BAAS...21.1180M Altcode: No abstract at ADS Title: Propagating and Nonpropagating Compression Waves in an Isothermal Atmosphere with Uniform Horizontal Magnetic Field Authors: Musielak, Z. E.; An, C. -H.; Moore, R. L.; Suess, S. T. Bibcode: 1989ApJ...344..478M Altcode: Full analytical solutions to the wave equations for steady vertical compression waves in an isothermal hydrostatic atmosphere with a uniform horizontal magnetic field are presented. It is shown that, in the steady state approach, the behavior of upward waves and downward waves is very different. It is shown that the finding of Thomas (1983), indicating that the cutoff frequency for vertically propagating magnetoacoustic waves in an isothermal atmosphere with a horizontal magnetic field is the same for isothermal atmosphere with no magnetic field, is true only for the downward waves. Title: Do Any White Dwarfs Have X-ray Coronae? Authors: Musielak, Z. E.; Fontenla, J. M.; Moore, R. L. Bibcode: 1989BAAS...21.1222M Altcode: No abstract at ADS Title: MHD surface waves in high- and low-beta plasmas. Part 1. Normal-mode solutions Authors: Musielak, Z. E.; Suess, S. T. Bibcode: 1989JPlPh..42...75M Altcode: Since the first paper by Barston (1964) on electrostatic oscillations in inhomogeneous cold plasmas, it has been commonly accepted that all finite layers with a continuous profile in pressure, density and magnetic field cannot support normal surface waves but instead the waves always decay through phase mixing (also called resonant absorption). Here we reanalyse the problem by studying a compressible current sheet of a general structure with rotation of the magnetic field included. We find that all inhomogeneous layers considered in the high-β plasma limit do not support normal modes. However, in the limit of a low-β plasma there are some cases when normal-mode solutions are recovered. The latter means that the process of resonant absorption is not common for all inhomogeneous layers. Title: The generation of MHD waves by forced turbulence in a weakly magnetized fluid Authors: Rosner, R.; Musielak, Z. E. Bibcode: 1989A&A...219L..27R Altcode: The effect of the fluctuating buoyancy force on wave generation in a weakly magnetized plasma is considered. As expected, the efficiency of MHD wave generation is enhanced by including this force. However, it remains true that the observed variation of coronal emission at fixed spectral type cannot be accounted for by a wave generation process of the type discussed here. Title: Wave energy leakage and heating of white dwarf atmospheres. Authors: Fontenla, J. M.; Musielak, Z. E. Bibcode: 1989BAAS...21.1021F Altcode: No abstract at ADS Title: The Role of Alfven Wave Trapping in the Acceleration of Stellar Winds from Late-Type Giants and Supergiants Authors: An, C. -H.; Musielak, Z. E.; Rosner, R.; Suess, S. T.; Moore, R. L. Bibcode: 1989BAAS...21..792A Altcode: No abstract at ADS Title: Reflection and Trapping of Alfven Waves in Coronal Holes Authors: An, C. -H.; Suess, S. T.; Moore, R. L.; Musielak, Z. E. Bibcode: 1989BAAS...21..844A Altcode: No abstract at ADS Title: Can Magnetic Tube Waves Account for X-ray Emissions Observed from Late-Type Dwarfs Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P. Bibcode: 1989BAAS...21..796M Altcode: No abstract at ADS Title: Subphotospheric Excitation of Alfven Waves and Their Role in the Solar Atmosphere Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Moore, R. L. Bibcode: 1989BAAS...21R.830M Altcode: No abstract at ADS Title: Propagation of Nonlinear Longitudinal-Transverse Waves Along Magnetic Flux Tubes in the Solar Atmosphere Authors: Ulmschneider, P.; Zahringer, K.; Musielak, Z. E. Bibcode: 1989BAAS...21..844U Altcode: No abstract at ADS Title: Alfven Wave Trapping and Heating in Coronal Holes Authors: Moore, R. L.; An, C. -H.; Suess, S. T.; Musielak, Z. E. Bibcode: 1989BAAS...21Q.830M Altcode: No abstract at ADS Title: Interaction Between Forced Turbulent Flow Field and Intense Magnetic Flux Tubes Authors: Rosner, R.; Musielak, Z. E.; Ulmschneider, P. Bibcode: 1989BAAS...21..844R Altcode: No abstract at ADS Title: On the Generation of Flux Tube Waves in Stellar Convection Zones. I. Longitudinal Tube Waves Driven by External Turbulence Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P. Bibcode: 1989ApJ...337..470M Altcode: The source functions and the energy fluxes for wave generation in magnetic flux tubes embedded in an otherwise magnetic field-free, turbulent, and compressible fluid are derived. The calculations presented here assume that the tube interior is not itself turbulent, e.g., that motions within the flux tube are due simply to external excitation. Specific results for the generation of longitudinal tube waves are presented. Title: Surface waves on a generalized current sheet. Authors: Suess, S. T.; Musielak, Z. E. Bibcode: 1989GMS....54..413S Altcode: 1989opss.conf..413S; 1989sspp.conf..413S The authors extend the theory for MHD surface waves in a non-isothermal layer of finite thickness in two different examples. The first is a tangential "discontinuity" in which the magnetic field undergoes a rotational change in direction parallel to the layer with no change in amplitude. The second is a sheet pinch across which the field undergoes a change in amplitude with no rotation or reversal. Bound, normal mode surface wave solutions are found to be supported by both the sheet pinch and tangential discontinuities in which the field vector undergoes a limited rotation of less that 90°. However, field rotation does not always remove singularities in the wave equations and wave decay through mode coversion can then occur. Title: Magnetohydrodynamic Bending Waves in a Current Sheet Authors: Musielak, Z. E.; Suess, S. T. Bibcode: 1988ApJ...330..456M Altcode: The physical properties of MHD bending waves in an isothermal, compressible, low-beta, three-dimensional current sheet of finite thickness in which the magnetic field direction and strength varies are considered. The case of the wavenumber (k) to circular frequency ratio being greater than the Alfven velocity outside the layer (VA) corresponds to one-sided surface waves, and it is suggested that the heliospheric current sheet ripples are not this type of bending wave. The case of k/omega of less than VA describes the interaction of freely and obliquely propagating MHD waves with the layer, while the case of k/omega = VA describes an Alfven wave propagating parallel to but having no interaction with the layer. Title: On the Generation of Magnetohydrodynamic Waves in a Stratified and Magnetized Fluid. II. Magnetohydromagnetic Energy Fluxes for Late-Type Stars Authors: Musielak, Z. E.; Rosner, R. Bibcode: 1988ApJ...329..376M Altcode: Magnetohydrodynamic (MHD) wave energy fluxes for late-type stars are calculated, using previously obtained formulae for the source functions for the generation of MHD waves in a stratified, but otherwise uniform, turbulent atmosphere; the magnetic fields in the wave generation region are assumed to be homogeneous. In contradiction to previous results, it is shown that in this uniform magnetic field case there is no significant increase in the efficiency of MHD wave generation, at least within the theory's limits of applicability. The major results are that the MHD energy fluxes calculated for late-type stars are less than those obtained for compressible modes in the magnetic field-free case, and that these MHD energy fluxes do not vary enough for a given spectral type to explain the observed range of UV and X-ray fluxes from such stars. It is therefore concluded that MHD waves in stellar atmospheres with homogeneous magnetic fields in the wave generation region cannot explain the observed stellar coronal emissions; if such MHD waves are responsible for a significant component of stellar coronal heating, then nonuniform fields within the generation region must be appealed to. Title: Trapping of Magnetoacoustic Waves in an Isothermal Atmosphere Authors: Musielak, Z. E.; Moore, R. L.; Suess, S. T. Bibcode: 1988BAAS...20..683M Altcode: No abstract at ADS Title: Magnetic Modulation of the Short-Period Cutoff for Solar Global p-Mode Oscillations Authors: Moore, R. L.; Musielak, Z. E. Bibcode: 1988BAAS...20Q.684M Altcode: No abstract at ADS Title: Interaction of Freely and Obliquely Propagating MHD Wave Trains with the Heliospheric Current Sheet Authors: Suess, S. T.; Musielak, Z. E. Bibcode: 1988BAAS...20S.714S Altcode: No abstract at ADS Title: A Numerical MHD Simulation Model for the Study of Flux Tube Waves Authors: Xiao, Y. C.; Wu, S. T.; Musielak, Z. E.; Suess, S. T. Bibcode: 1988BAAS...20..716X Altcode: No abstract at ADS Title: Generation of MHD Waves by Convective Turbulence Authors: Rosner, R.; Musielak, Z. E. Bibcode: 1988BAAS...20..715R Altcode: No abstract at ADS Title: Wave Energy in White Dwarf Atmospheres. I. Magnetohydrodynamic Energy Spectra for Homogeneous DB and Layered DA Stars Authors: Musielak, Zdzislaw E. Bibcode: 1987ApJ...322..234M Altcode: The radiative damping of acoustic and MHD waves that propagate through white dwarf photospheric layers is studied, and other damping processes that may be important for the propagation of the MHD waves are calculated. The amount of energy remaining after the damping processes have occurred in different types of waves is estimated. The results show that lower acoustic fluxes should be expected in layered DA and homogeneous DB white dwarfs than had previously been estimated. Acoustic emission manifests itself in an enhancement of the quadrupole term, but this term may become comparable to or even lower than the dipole term for cool white dwarfs. Energy carried by the acoustic waves is significantly dissipated in deep photospheric layers, mainly because of radiative damping. Acoustically heated corona cannot exist around DA and DB white dwarfs in a range T(eff) = 10,000-30,000 K and for log g = 7 and 8. However, relatively hot and massive white dwarfs could be exceptions. Title: Theoretical Energy Spectrum for Solar p-Modes Authors: Musielak, Z. E. Bibcode: 1987BAAS...19.1132M Altcode: No abstract at ADS Title: Excitation of Solar p-Modes by Monopole and Dipole Sources of Acoustic Waves Authors: Musielak, Z. E. Bibcode: 1987BAAS...19..934M Altcode: No abstract at ADS Title: On the Generation of Magnetohydrodynamic Waves in a Stratified and Magnetized Fluid. I. Vertical Propagation Authors: Musielak, Z. E.; Rosner, R. Bibcode: 1987ApJ...315..371M Altcode: The generation of MHD waves by turbulent motions in a stratified medium with an embedded uniform magnetic field, a topic which is relevant to the study of the solar atmosphere, is considered. Both compressible and incompressible MHD waves are treated in a one-dimensional approach; however, the direction of the background magnetic field is permitted to vary in an arbitrary direction. Theoretical expressions for MHD energy fluxes are obtained as a function of wave frequency and multipole coefficients. It is shown that monopole, dipole, and quadrupole emissions are responsible for the generation of the compressible components of the fast and slow modes. However, the incompressible components and the Alfven modes can be generated by the dipole emission only. Specific results obtained for special magnetic field geometries are discussed for the fast and slow modes. Title: MHD Wave Energy Fluxes for Late-Type Dwarfs Authors: Rosner, R.; Musielak, Z. E. Bibcode: 1987LNP...291...69R Altcode: 1987csss....5...69R We calculate the efficiency of MHD wave generation by turbulent motions in the stratified stellar atmospheres of late-type main sequence stars, under the assumption that the embedded magnetic fields are uniform. In contradiction with previous results, we show that there is no significant increase in the efficiency of wave generation because of the presence of magnetic fields, at least within the theory's limits of applicability. Thus, we show that MHD energy fluxes for late-type stars whose surface magnetic fields are uniform are less than those obtained for acoustic waves in a magnetic field-free atmosphere, and do not vary enough for a given spectral type in order to explain observed UV and X-ray fluxes. Thus, our results show that MHD energy fluxes obtained if stellar surface magnetic fields are uniform cannot explain the observed stellar coronal emissions. Title: Magnetic Flux Tubes as Sources of Wave Generation Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P. Bibcode: 1987LNP...291...66M Altcode: 1987csss....5...66M Because solar (and, most likely, stellar) surface magnetic fields are highly inhomogeneous, and show concentration into `flux tube' structures, the wave energy generated in stellar convection zones may be largely carried away by flux tube waves, which then become important sources for the heating of the outer atmospheric layers. We report calculations for longitudinal tube waves generated in magnetic flux tubes embedded in an otherwise magnetic field-free, turbulent, and stratified medium; we find that such waves are generated by dipole emission, and that the generation efficiency is a strong function of the magnetic field strength. We also present wave flux calculations for magnetic flux tubes embedded in the solar convective zone; the main result is that the longitudinal tube wave fluxes are at least 2 orders of magnitude too low to play a significant role in the heating of the solar chromosphere. Title: Generation of flux tube waves in stellar convection zones. 1: Longitudinal tube waves Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P. Bibcode: 1987STIN...8824561M Altcode: The source functions and the energy fluxes are derived for wave generation in magnetic flux tubes embedded in an otherwise magnetic- field free, turbulent, and compressible fluid. Specific results for the generation of longitudinal tube waves are presented. Title: Fine-Scale Waves on the Heliospheric Current Sheet Authors: Musielak, Z. E.; Suess, S. T. Bibcode: 1987sowi.conf..340M Altcode: No abstract at ADS Title: Relationship between directions of wave and energy propagation for cold plasma waves Authors: Musielak, Zdzislaw E. Bibcode: 1986JPlPh..36..341M Altcode: The dispersion relation for plasma waves is considered in the ‘cold’ plasma approximation. General formulae for the dependence of the phase and group velocities on the direction of wave propagation with respect to the local magnetic field are obtained for a cold magnetized plasma. The principal cold plasma resonances and cut-off frequencies are defined for an arbitrary angle and are used to establish basic regimes of frequency where the cold plasma waves can propagate or can be evanescent. The relationship between direction of wave and energy propagation, for cold plasma waves in hydrogen atmosphere, is presented in the form of angle diagrams (angle between group velocity and magnetic field versus angle between phase velocity and magnetic field) and polar diagrams (also referred to as ‘Friedrich's diagrams’ ) for different directions of wave propagation. Morphological features of the diagrams as well as some critical angles of propagation are discussed. Title: Efficiency of Flux Tube Wave Generation in Late Type Stars Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Bohn, H. U. Bibcode: 1986BAAS...18.1002M Altcode: No abstract at ADS Title: Heating of intense magnetic flux tubes by magnetohydrodynamic waves Authors: Musielak, Z.; Bielicz, E. Bibcode: 1983IAUS..102..413M Altcode: Theoretical models of intense magnetic flux tubes embedded in the photospheres of late-type stars have been calculated. Magnetohydrodynamic waves generated in the convective zone are radiatively damped in the lower part of the flux tube and then dissipated. The authors discuss how the presence of flux tubes in stellar photospheres influences the temperature minimum and the chromospheric activity. They suggest a possible interpretation of the Wilson-Bappu effect in stars with strong chromospheric activity. Title: Physical processes determining the structure of stellar chromospheres. II Authors: Musielak, Z. Bibcode: 1983PoAst..30..269M Altcode: Observational data pertaining to physical processes in stellar chromospheres are presented, and correlations between chromospheric and other atmospheric parameters are examined. The development of models of the solar chromosphere and stellar chromospheres is described, the models being based on the balance between radiative losses and dissipated mechanical energy. Questions relating to the inhomogeneity of the theoretical models and evolution effects are considered. Title: Physical processes determining the structure of stellar chromospheres. I Authors: Musielak, Z. Bibcode: 1982PoAst..30..123M Altcode: The principal sources of radiative losses in the chromospheres of F, G, and K stars are indicated, with particular attention given to the hydrogen continuum and intense and faint lines formed by different elements. Mechanisms of the heating of stellar chromospheres are examined, with emphasis on heating via the dissipation of acoustic and magnetohydrodynamic waves. Title: Generation of magnetohydrodynamic waves in white dwarfs Authors: Musielak, Z. Bibcode: 1982AcA....32..233M Altcode: Mechanical energy fluxes generated in H-rich and He-rich convective zones of white dwarfs were calculated for a wide range of effective temperatures. In these computations the author assumes that convection and turbulent spectrum are independent of the magnetic field. The presence of the magnetic field causes an important change in the generation of an acoustic flux in the convective zone and introduces new energy carrying modes - the #agnetohydrodynamic waves. New estimates of the mechanical energy fluxes give significantly higher values than those previously given for the white dwarf. Consequently, the author predicts higher X-ray luminosities that should be observed with the present-day techniques. It is also shown that the mechanism of X-ray generation plays a negligible role in the white dwarf companion in a cataclysmic binary system. Title: Waves in stellar atmospheres. II - Heating of flux tubes by magnetohydrodynamic waves Authors: Bielicz, E.; Musielak, Z. Bibcode: 1982AcA....32..251B Altcode: The authors assume that the active regions are closely connected with the presence of intense magnetic flux tubes. They also consider the changes of flux tube models in the upper photosphere which are caused by propagation and dissipation of magnetohydrodynamic waves. The presence of a magnetic field leads to a higher value of temperature minimum and to the increase of chromospheric activity in the flux tube. The treatment of energy balance in a strong magnetic field is presented. Title: Connection between chromospheric activity of F, G, K type stars and their magnetic field Authors: Musielak, Z.; Bielicz, E. Bibcode: 1982AcA....32..263M Altcode: The appearance of bright emission in the cores of strong resonance lines is used to define active regions in the solar chromosphere. In the present study, attention is given to the dependence of chromospheric activity on the number of the intense magnetic flux tubes. It is suggested that the strong chromospheric activity found in the case of some stars can be caused by the appearance of a greater number of flux tubes in these stars. Theoretical inhomogeneous models of chromospheres are considered along with aspects of chromospheric activity in dwarfs and giants, and the Wilson-Bappu effect. The interpretation of the Wilson-Bappu relation provided for stars with strong chromospheric activity indicates the important role of flux tubes in explanation of the strong activity. Title: Theoretical models of homogeneous chromospheres for main sequence stars. Authors: Musielak, Z. Bibcode: 1982A&A...105...23M Altcode: It is shown that the structure of the chromosphere is determined by three parameters: (1) the dissipating wave period; (2) the energy flux spectrum provided to the chromosphere; and (3) the magnetic field; where these parameters are mutually dependent, with the greatest dependency being between the energy flux spectrum value and the magnetic field. The analysis presented demonstrates that it is impossible to reconstruct the semi-empirical models considered when short-period waves are adopted for heating. The range of energy flux spectrum values given is from 10 million erg/sq cm per sec, for the case of stars cooler than the sun, to 100 million erg/sq cm per sec for the case of stars that are hotter. The results contradict theoretical estimates of convective zone-generated mechanical energy flux, especially for cooler stars. It is concluded that the strength of the average magnetic field determines the division of stars into those with weak, and those with strong, chromospheric activity. Title: Chromospheres of F, G, K type stars. VIII. Energy balance in transition region. Authors: Prominski, M.; Musielak, Z.; Sikorski, J. Bibcode: 1982AcA....32..111P Altcode: Radiative losses, thermal conductivity from the corona, the convective energy flux, and the dissipation, refraction, and reflection of MHD waves are calculated for known empirical and theoretical models of the transition region for the quiet and active (flare) sun and Epsilon Eri. Emissions of bound-free and free-free transitions for hydrogen and helium and bound-bound transitions for more than 350 of the strongest lines identified in that region are allowed for in computing the radiative losses. It is confirmed that some mechanisms for heating from below are required to form the lower layers of the transition region. It is believed that thermal conductivity may compensate radiative losses only for the upper part of the transition region of the quiet sun model. Title: Chromospheres of F, G, K Type Stars. VII. Upper Chromosphere and Transition Region Authors: Musielak, Z. E.; Sikorski, J. Bibcode: 1981AcA....31..494M Altcode: Basing on detailed energy balance between radiative losses and amount of mechanical energy (with different flux spectra) we made an attempt to reconstruct conditions for the formation of transition region chromosphere-corona. We confirmed that the shape of mechanical energy spectrum may be different for stars with different effective temperatures and we found that the gradient of microturbulence velocity in the chromosphere has a significant influence on formation of the transition region. Calculations show that transition regions are present in main sequence stars and absent for alpha Boo and alpha Tau, in agreement with observations. Title: Chromospheres of F G K Type Stars - Part Seven - Upper Chromosphere and Transition Region Authors: Musielak, Z.; Sikorski, J. Bibcode: 1981AcA....31..493M Altcode: No abstract at ADS Title: Waves in stellar atmospheres. I. Heating of upper photosphere by short period acoustic waves. Authors: Bielicz, E.; Musielak, Z.; Sikorski, J. Bibcode: 1981AcA....31...51B Altcode: Theoretical models of upper photosphere and low chromosphere for ten main sequence stars are calculated. Short period acoustic waves generated in the convective zone are radiatively damped in the lower photosphere and then converted into weak shocks which heat the medium by dissipation processes. The obtained models are compared with semiempirical ones. It is shown that the temperature minimum region can be reconstructed using acoustic fluxes different from those predicted by the Lighthill-Proudman and mixing length theories, especially for cool stars. Title: Chromospheres of F, G, K type stars. IV - The zone model of heating Authors: Musielak, Z.; Sikorski, J. Bibcode: 1980AcA....30..167M Altcode: The paper proposes the so called 'zone model' of heating in which the chromosphere is divided into three regions corresponding to dissipation of energy by acoustic, fast, and slow plus Alfven waves, respectively. A phenomenological chi parameter is introduced simulating a development of wave into shock over a finite distance. The influence of magnetic field, wave period, and chi parameter on the amount of dissipated energy is investigated for known semiempirical chromospheric models. Title: Chromospheres of F, G K type stars. V. Radiative losses in spectral lines. Authors: Glebocki, R.; Musielak, Z.; Sikorski, J. Bibcode: 1980AcA....30..259G Altcode: Radiative losses in weak and strong lines are compared with losses in continua. In spite of large number of weak lines (more than 20,000 in visible region) their total energy losses are small in comparison to losses in continua. Title: Chromospheres of F, G, K type stars. VI - Theoretical homogeneous models of solar chromosphere Authors: Musielak, Z.; Sikorski, J. Bibcode: 1980AcA....30..479M Altcode: Theoretical models of the chromosphere were developed on the basis of the energy balance between radiative losses and the amount of dissipated mechanical energy. The influence of boundary conditions in the temperature minimum as well as that of free parameters is examined. Particular attention is given to the effect of the dissipating-wave period, the amount of mechanical energy provided for dissipation, and the magnetic field strength on the resulting model. The influence of these parameters on the Mg II h and k line profiles is also discussed. It is shown that the monochromatic wave approximation cannot explain the structure of the highest layers of the chromosphere. Title: Chromospheres of F, G, K type stars. III. Dissipation of mechanical energy by waves of acoustic, fast and slow modes. Authors: Musielak, Z.; Sikorski, J. Bibcode: 1979AcA....29..609M Altcode: Mechanisms of dissipation of acoustic, fast and slow mode waves were applied for five F, G, K type stars with known semiempirical models of chromospheres and the sun. The rates of dissipation of energy for constant and variable period waves with geometrical height were calculated. The total amount as well as variations with height of dissipated energy are compared with the radiative losses which were obtained in a previous paper. It is concluded that heating of the chromosphere only by the acoustic waves is an oversimplification. The regions where various magnetohydrodynamic waves should be applied are discussed. Title: Chromospheres of F, G, K type stars. II - Radiative losses in continuum Authors: Musielak, Z.; Sikorski, J. Bibcode: 1979AcA....29..381M Altcode: Radiative losses for six F, G, K type stars with known semi-empirical models of the chromospheres and for the sun are calculated. The total losses as well as the variation of the radiative loss with height are discussed. Calculated radiative fluxes are compared with predicted values of mechanical energy supplied in the form of acoustic waves by the convective zone. In some cases considerable discrepancies between these fluxes are found. Title: Physical properties of asteroids. Part II. Authors: Musielak, Z. Bibcode: 1978PoAst..25..161M Altcode: No abstract at ADS Title: Physical properties of asteroids. Part I. Authors: Musielak, Z. Bibcode: 1977PoAst..25..115M Altcode: The paper reviews some of the more important methods of observing asteroids and studying their physical properties. The principles of photoelectric observations are examined. Examples of light curves are discussed. The dependence of brightness on phase angle and the variation of color indices are also considered.