Author name code: cuntz
ADS astronomy entries on 2022-09-14
author:"Cuntz, Manfred"
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Title: Evolution of Solar-type Activity: A Brief Study of Ca II
Emission in Beta Hydri (G2 IV)
Authors: Cuntz, Manfred; Fawzy, Diaa E.
Bibcode: 2022RNAAS...6..147C
Altcode:
We present results about the decrease of stellar activity for stars
like the Sun evolving toward the subgiant stage. Specifically, we
examine two-component chromosphere models (acoustic and magnetic)
for β Hydri (G2 IV) based on detailed time-dependent simulations
while focusing on Ca II emission. We convey models for two different
photospheric magnetic filling factors.
Title: Study of chemically peculiar stars - I. High-resolution
spectroscopy and K2 photometry of Am stars in the region of M44
Authors: Joshi, Santosh; Trust, Otto; Semenko, E.; Williams, P. E.;
Lampens, P.; De Cat, P.; Vermeylen, L.; Holdsworth, D. L.; García,
R. A.; Mathur, S.; Santos, A. R. G.; Mkrtichian, D.; Goswami, A.;
Cuntz, M.; Yadav, A. P.; Sarkar, M.; Bhatt, B. C.; Kahraman Aliçavuş,
F.; Nhlapo, M. D.; Lund, M. N.; Goswami, P. P.; Savanov, I.; Jorissen,
A.; Jurua, E.; Avvakumova, E.; Dmitrienko, E. S.; Chakradhari, N. K.;
Das, M. K.; Chowdhury, S.; Abedigamba, O. P.; Yakunin, I.; Letarte,
B.; Karinkuzhi, D.
Bibcode: 2022MNRAS.510.5854J
Altcode: 2021arXiv211014275J
We present a study based on the high-resolution spectroscopy and K2
space photometry of five chemically peculiar stars in the region of
the open cluster M44. The analysis of the high-precision photometric
K2 data reveals that the light variations in HD 73045 and HD 76310
are rotational in nature and caused by spots or cloud-like co-rotating
structures, which are non-stationary and short-lived. The time-resolved
radial velocity measurements, in combination with the K2 photometry,
confirm that HD 73045 does not show any periodic variability on
time-scales shorter than 1.3 d, contrary to previous reports in the
literature. In addition to these new rotational variables, we discovered
a new heartbeat system, HD 73619, where no pulsational signatures are
seen. The spectroscopic and spectropolarimetric analyses indicate that
HD 73619 belongs to the peculiar Am class, with either a weak or no
magnetic field, considering the 200-G detection limit of our study. The
least-squares deconvolution profiles for HD 76310 indicate a complex
structure in its spectra, suggesting that this star is either part of
a binary system or surrounded by a cloud shell. When placed in the
Hertzsprung-Russell diagram, all studied stars are evolved from the
main sequence and situated in the δ Scuti instability strip. This
work is relevant for further detailed studies of chemically peculiar
stars, for example on inhomogeneities (including spots) in the absence
of magnetic fields and the origin of the pulsational variability in
heartbeat systems.
Title: Orbital Stability of Planet-hosting Triple-star Systems
according to Hill: Applications to Alpha Centauri and 16 Cygni
Authors: Boyle, Lindsey; Cuntz, Manfred
Bibcode: 2021RNAAS...5..285B
Altcode:
In this study we investigate aspects of orbital stability for the Alpha
Centauri and 16 Cygni systems. They are planet-hosting triple star
systems of highly hierarchic nature. For each system, orbital stability
of the outlying stellar component and the observed exoplanet(s)
are explored through assessing Hill stability. Orbital stability is
identified for all components, including the observed system planets.
Title: Updated studies on exomoons in the HD 23079 system
Authors: Jagtap, O.; Quarles, B.; Cuntz, M.
Bibcode: 2021PASA...38...59J
Altcode: 2021arXiv211010013J
We re-evaluate the outer edge of orbital stability for possible
exomoons orbiting the radial velocity planet discovered in the HD 23079
system. In this system, a solar-type star hosts a Jupiter-mass planet
in a nearly circular orbit in the outer stellar habitable zone. The
outer stability limit of exomoons is deduced using N-body and tidal
migration simulations considering a large range of initial conditions,
encompassing both prograde and retrograde orbits. In particular, we
extend previous works by evaluating many values in the satellite mean
anomaly to identify and exclude regions of quasi-stability. Future
observations of this system can make use of our results through a
scale factor relative to the currently measured minimum mass. Using a
constant time lag tidal model (Hut 1981), we find that plausible tidal
interactions within the system are insufficient to induce significant
outward migration toward the theoretical stability limit. While current
technologies are incapable of detecting exomoons in this system,
we comment on the detectability of putative moons through Doppler
monitoring within direct imaging observations in view of future
research capacities.
Title: Chromospheric activity in 55 Cancri: II. Theoretical wave
studies versus observations
Authors: Cuntz, Manfred; Schröder, Klaus-Peter; Fawzy, Diaa E.;
Ridden-Harper, Andrew R.
Bibcode: 2021MNRAS.505..274C
Altcode: 2021MNRAS.tmp.1242C; 2021arXiv210414684C
In this study, we consider chromospheric heating models for 55
Cancri in conjunction with observations. The theoretical models,
previously discussed in Paper I, are self-consistent, non-linear,
and time-dependent ab-initio computations encompassing the generation,
propagation, and dissipation of waves. Our focus is the consideration
of both acoustic waves and longitudinal flux tube waves amounting to
two-component chromosphere models. 55 Cancri, a K-type orange dwarf,
is a star of low activity, as expected by its age, which also implies
a relatively small magnetic filling factor. The Ca II K fluxes are
computed (multi-ray treatment) assuming partial redistribution
and time-dependent ionization. The theoretical Ca II H+K fluxes
are subsequently compared with observations. It is found that for
stages of lowest chromospheric activity the observed Ca II fluxes are
akin, though not identical, to those obtained by acoustic heating,
but agreement can be obtained if low levels of magnetic heating -
consistent with the expected photospheric magnetic filling factor -
are considered as an additional component; this idea is in alignment
with previous proposals conveyed in the literature.
Title: Chromospheric activity in 55 Cancri - I. Results from
theoretical wave studies
Authors: Fawzy, Diaa E.; Cuntz, Manfred
Bibcode: 2021MNRAS.502.5075F
Altcode: 2021arXiv210110871F; 2021MNRAS.tmp..296F
We present theoretical models of chromospheric heating for 55
Cancri, an orange dwarf of relatively low activity. Self-consistent,
non-linear, and time-dependent ab initio numerical computations are
pursued encompassing the generation, propagation, and dissipation of
waves. We consider longitudinal waves operating among arrays of flux
tubes as well as acoustic waves pertaining to non-magnetic stellar
regions. Additionally, flux enhancements for the longitudinal
waves are also taken into account as supplied by transverse
tube waves. The Ca II K fluxes are computed (multi-ray treatment)
assuming partial redistribution as well as time-dependent ionization
(TDI). The self-consistent treatment of TDI (especially for hydrogen)
greatly impacts the atmospheric temperatures and electron densities
(especially behind the shocks); it also affects the emergent Ca II
fluxes. Particularly, we focus on the influence of magnetic heating
on the stellar atmospheric structure and the emergent Ca II emission,
as well as the impact of non-linearities. Our study shows that a higher
photospheric magnetic filling factor entails a larger Ca II emission;
however, an increased initial wave energy flux (e.g. associated with
mode coupling) is of little difference. Comparisons of our theoretical
results with observations will be conveyed in forthcoming Paper II.
Title: Space Science as a Context for Science Education
Authors: Lopez, Ramon E.; Ambrose, B. S.; Bailey, J. M.; Benson,
A. G.; Cid, X. C.; da Costa, E., Jr.; Cuntz, Manfred; Jaafari, F.;
Vieyra, R. E.; Willoughby, S. D.
Bibcode: 2020inte.confE...1L
Altcode:
Over the past few years, our team has been developing instructional
materials that use space science as the context for teaching basic
and advanced physics concepts in university courses. The purpose of
this project is to capitalize on the proven strong interest that high
school students worldwide have in space science, with the expectation
that university science and engineering students will maintain that
high level of interest. We have conducted surveys of student interest
in using space science to teach basic and advanced science concepts
at a university in the United States, and at several universities in
Brazil, and we find that university students majoring in various areas
of science and engineering have a strong interest in space science. We
will report on our survey of student interest, as well as some of the
materials that we have developed and the design process for these
materials, which incorporate findings and pedagogical structure
determined by physics education research.
Title: Theoretical studies of comets in the 55 Cancri system
Authors: Dvorak, Rudolf; Loibnegger, Birgit; Cuntz, Manfred
Bibcode: 2020MNRAS.496.4979D
Altcode: 2020MNRAS.tmp.1868D; 2020arXiv200601711D
We present orbital integrations for various Jupiter family comets
(JFCs) in the 55 Cancri system. This star is known to possess
(at least) five planets with masses ranging from super-Earth to
Jupiter-type. Furthermore, according to observational constraints,
there is a space without planets between ∼0.8 and ∼5.7 au, offering
the principal possibility of habitable terrestrial planets, including
long-term orbital stability. Hence, there is a stark motivation for
the study of comets in the 55 Cnc system noting that comets are viewed
a viable candidate mechanism for the delivery of water to Earth-type
planets located in stellar habitable zones. However, our study shows
that the duration of stability of JFC analogues in the 55 Cnc system is
much shorter compared to comets in the Solar system owing to profound
differences in the planetary structure of the systems. For example,
between planet 55 Cnc-f and 55 Cnc-d, the comets do not undergo close
cometary encounters akin to the Earth and Mars in the Solar system
as the planetary masses in the 55 Cnc system are much larger than
in the Solar system and therefore the comets are much less orbitally
stable. Nevertheless, we expect an increased number of comet-planet
encounters as well as cometary collisions in the 0.8/5.7 au gap. Future
observations and additional theoretical studies are required to shed
light on the possibility of habitable terrestrial planets in the 55 Cnc
system, including the possible role(s) of exocomets in the facilitation
of planetary habitability.
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: When more is less: The P-type binary habitability paradox
Authors: Cuntz, Manfred; Wang, Zhaopeng
Bibcode: 2020AN....341..402C
Altcode:
In the case of single stars, larger stellar luminosities always entail
larger habitable zones (HZs). If the stellar luminosity is increased,
the HZs are established at larger stellar distances, and their
widths are broader. However, studies have shown that this behavior
is not necessarily the case for P-type HZs of binary systems. In
some of those systems, the width of the circumbinary HZ is smaller
(or even nonexisting) than the width of the primary's HZ if they
are considered a single star—an obvious paradox considering that
the total luminosity of the binary is always larger than that of the
system's primary. Here, we present a tutorial study of this behavior
for theoretical main-sequence stars with the combined masses of the
stellar components equal to two solar masses. The planetary climate
models are chosen in correspondence to the general HZ. The paradox
is found to occur for systems of relatively unequal stellar masses
(or luminosities) or in systems where the separation distances or
eccentricities of the stellar components are relatively large.
Title: On the dynamics of comets in extrasolar planetary systems
Authors: Dvorak, Rudolf; Loibnegger, Brigit; Cuntz, Manfred
Bibcode: 2020tnss.book..331D
Altcode: 2019arXiv190306910D
Since very recently, we acquired knowledge on the existence of comets
in extrasolar planetary systems. The formation of comets together
with planets around host stars now seems evident. As stars are often
born in clusters of interstellar clouds, the interaction between
the systems will lead to the exchange of material at the edge of the
clouds. Therefore, almost every planetary system should have leftover
remnants as a result of planetary formation in the form of comets at
the edges of those systems. These Oort clouds around stars are often
disturbed by different processes (e.g., Galactic tides, passing
stars, etc.), which consequently scatter bodies from the distant
clouds into the system close to the host star. Regarding the solar
system, we observe this outcome in the form of cometary families. This
knowledge supports the assumption of the existence of comets around
other stars. In the present work, we study the orbital dynamics
of hypothetical exocomets, based on detailed computer simulations,
in three star-planet systems, which are: HD 10180, 47 UMa, and HD
141399. These systems host one or more Jupiter-like planets, which
change the orbits of the incoming comets in characteristic ways.
Title: Dead zones of classical habitability in stellar binary systems
Authors: Moorman, S. Y.; Wang, Z.; Cuntz, M.
Bibcode: 2020Ap&SS.365...10M
Altcode: 2020arXiv200101754M
Although habitability, defined as the general possibility of hosting
life, is expected to occur under a broad range of conditions,
the standard scenario to allow for habitable environments is often
described through habitable zones (HZs). Previous work indicates that
stellar binary systems typically possess S-type or P-type HZs, with the
S-type HZs forming ring-type structures around the individual stars and
P-type HZs forming similar structures around both stars, if considered
a pair. However, depending on the stellar and orbital parameters of the
system, typically, there are also regions within the systems outside
of the HZs, referred to as dead zones (DZs). In this study, we will
convey quantitative information on the width and location of DZs for
various systems. The results will also depend on the definition of
the stellar HZs as those are informed by the planetary climate models.
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: Can planets exist in the habitable zone of 55 Cancri?
Authors: Satyal, Suman; Cuntz, Manfred
Bibcode: 2019PASJ...71...53S
Altcode: 2019PASJ..tmp...45S; 2019arXiv190209613S
The aim of our study is to explore the possible existence of Earth-mass
planets in the habitable zone of 55 Cancri, an effort pursued based on
detailed orbital stability simulations. This star is known to possess
(at least) five planets with masses ranging between super-Earth and
Jupiter-type. Additionally, according to observational constraints,
there is a space without planets between ∼0.8 au and ∼5.7 au,
and it is noted that the inner part of this gap largely coincides
with 55 Cnc's habitable zone—a sincere motivation for the search
of potentially habitable planets. It has previously been argued that
terrestrial habitable planets are able to exist in the 55 Cnc system,
including a planet at ∼1.5 au. We explore this possibility through
employing sets of orbital integrations and assuming an integration
time of 50 Myr. We found that the possibility of Earth-mass planets
in the system's habitable zone strongly depends on the adopted system
parameters, notably the eccentricity of 55 Cnc-f, which is controversial
as both a high value (e ∼ 0.32) and a low value (e ∼ 0.08) have
previously been deduced. In the case where the low value, the more
plausible and most recent value, is adopted (together with other updates
for the system parameters), Earth-mass planets would be able to exist
in the gap between 1.0 au and 2.0 au, thus implying the possibility of
habitable system planets. Thus, 55 Cnc should be considered a favorable
target for future habitable planet search missions.
Title: Massive Star Formation in the Infrared: Further Analysis of
the SOFIA SOMA Survey
Authors: Dingler, Ryne S.; Cuntz, Manfred
Bibcode: 2019RNAAS...3...87D
Altcode: 2019RNAAS...3f..87D
No abstract at ADS
Title: S-type and P-type Habitable Zones of Stellar Binary Systems:
Effect of the Planetary Mass
Authors: Wang, Zhaopeng; Cuntz, Manfred
Bibcode: 2019RNAAS...3...70W
Altcode: 2019RNAAS...3e..70W
No abstract at ADS
Title: Reconstructing Extreme Space Weather From Planet Hosting Stars
Authors: Airapetian, Vladimir; Adibekyan, V.; Ansdell, M.; Alexander,
D.; Barklay, T.; Bastian, T.; Boro Saikia, S.; Cohen, O.; Cuntz,
M.; Danchi, W.; Davenport, J.; DeNolfo, G.; DeVore, R.; Dong, C. F.;
Drake, J. J.; France, K.; Fraschetti, F.; Herbst, K.; Garcia-Sage,
K.; Gillon, M.; Glocer, A.; Grenfell, J. L.; Gronoff, G.; Gopalswamy,
N.; Guedel, M.; Hartnett, H.; Harutyunyan, H.; Hinkel, N. R.; Jensen,
A. G.; Jin, M.; Johnstone, C.; Kahler, S.; Kalas, P.; Kane, S. R.;
Kay, C.; Kitiashvili, I. N.; Kochukhov, O.; Kondrashov, D.; Lazio, J.;
Leake, J.; Li, G.; Linsky, J.; Lueftinger, T.; Lynch, B.; Lyra, W.;
Mandell, A. M.; Mandt, K. E.; Maehara, H.; Miesch, M. S.; Mickaelian,
A. M.; Mouschou, S.; Notsu, Y.; Ofman, L.; Oman, L. D.; Osten, R. A.;
Oran, R.; Petre, R.; Ramirez, R. M.; Rau, G.; Redfield, S.; Réville,
V.; Rugheimer, S.; Scheucher, M.; Schlieder, J. E.; Shibata, K.;
Schnittman, J. D.; Soderblom, David; Strugarek, A.; Turner, J. D.;
Usmanov, A.; Van Der Holst, B.; Vidotto, A.; Vourlidas, A.; Way, M. J.;
Wolk, Scott J.; Zank, G. P.; Zarka, P.; Kopparapu, R.; Babakhanova,
S.; Pevtsov, A. A.; Lee, Y.; Henning, W.; Colón, K. D.; Wolf, E. T.
Bibcode: 2019BAAS...51c.564A
Altcode: 2019astro2020T.564A; 2019arXiv190306853A
The goal of this white paper is to identify and describe promising key
research goals to aid the theoretical characterization and observational
detection of ionizing radiation from quiescent and flaring upper
atmospheres of planet hosts as well as properties of stellar coronal
mass ejections (CMEs) and stellar energetic particle (SEP) events.
Title: S-type and P-type Habitability in Stellar Binary Systems: A
Comprehensive Approach. III. Results for Mars, Earth, and Super-Earth
Planets
Authors: Wang, Zh.; Cuntz, M.
Bibcode: 2019ApJ...873..113W
Altcode: 2019arXiv190111171W
In Papers I and II, a comprehensive approach was utilized for
the calculation of S-type and P-type habitable regions in stellar
binary systems for both circular and elliptical orbits of the binary
components. This approach considered a joint constraint, including
orbital stability for possible system planets and a habitable region,
determined by the stellar radiative energy fluxes (“radiative
habitable zone” RHZ). Specifically, the stellar S-type and
P-type RHZs are calculated based on the solution of a fourth-order
polynomial. However, in concurrent developments, mostly during 2013
and 2014, important improvements have been made in the computation
of stellar habitable zones for single stars based on updated climate
models given by R. K. Kopparapu and collaborators. These models entail
considerable changes for the inner and outer limits of the stellar
habitable zones. Moreover, regarding the habitability limit given
by the runaway greenhouse effect, notable disparities were identified
between Earth, Mars, and super-Earth planets due to differences in their
atmospheric models, thus affecting their potential for habitability. It
is the aim of this study to compute S-type and P-type habitable regions
of binaries in response to the updated planetary models. Moreover,
our study will also consider improved relationships between effective
temperatures, radii, and masses for low-luminosity stars.
Title: The habitable zone of Kepler-16: impact of binarity and
climate models
Authors: Moorman, S. Y.; Quarles, B. L.; Wang, Zh.; Cuntz, M.
Bibcode: 2019IJAsB..18...79M
Altcode: 2018arXiv180206856M
We continue to investigate the binary system Kepler-16, consisting
of a K-type main-sequence star, a red dwarf and a circumbinary
Saturnian planet. As part of our study, we describe the system's
habitable zone based on different climate models. We also report
on stability investigations for possible Earth-mass Trojans while
expanding a previous study by B. L. Quarles and collaborators given in
2012. For the climate models, we carefully consider the relevance of the
system's parameters. Furthermore, we pursue new stability simulations
for the Earth-mass objects starting along the orbit of Kepler-16b. The
eccentricity distribution as obtained prefers values close to circular,
whereas the inclination distribution remains flat. The stable solutions
are distributed near the co-orbital Lagrangian points, thus enhancing
the plausibility that Earth-mass Trojans might be able to exist in
the Kepler-16(AB) system.
Title: Exocomets in the 47 UMa System: Theoretical Simulations
Including Water Transport
Authors: Cuntz, Manfred; Loibnegger, Birgit; Dvorak, Rudolf
Bibcode: 2018AJ....156..290C
Altcode: 2018arXiv181109579C
Motivated by ongoing discoveries of features (most likely) attributable
to exocomets in various systems, this study examines the dynamics
of possible comets around 47 UMa. Based on the assumption that most
systems hosting planets should also harbor leftovers from planet
formation processes, comets are thus also expected to exist in the
system of 47 UMa. This system is known to host three Jupiter-type
planets; however, based on stability analyses, additional terrestrial
planets in stable orbits might also be able to exist, including planets
in 47 UMa’s habitable zone (HZ). Furthermore, we also consider a
possible “Hilda”-planet. The aim of our study is to explore the
interaction of exocomets with the Jupiter-type planets in the system
and examine the probability of cometary collisions with the planets,
including possible Earth-mass planets located in the HZ. Moreover,
we investigate the transport of water onto the Earth-mass planets,
including quantitative estimates. It is found that most Earth-mass
planets would be able to receive some water, but much less than is
currently present on Earth. We also checked if the comets form families,
but no families were found. Finally, the capture of comets in close
orbits and the possibility that small clouds formed when comets come
too close to the star and disintegrate are also part of our work.
Title: Chromospheric activity in ɛ Eridani: results from theoretical
wave studies
Authors: Fawzy, Diaa E.; Cuntz, M.
Bibcode: 2018Ap&SS.363..152F
Altcode:
This work discusses theoretical models of chromospheric heating for ɛ
Eridani by shock waves. Self-consistent, nonlinear and time-dependent
ab-initio numerical computations for the excitation of the atmosphere
(i.e., arrays of flux tubes) are pursued based on waves generated in
stellar convective zones. Based on previous studies the magnetic filling
factor is estimated according to the stellar rotational period, although
general models are described as well. The Ca II H+K fluxes are computed
assuming partial redistribution (PRD). Time-dependent ionization
notably affects the resulting Ca II fluxes, as expected. The emergent
Ca II H+K fluxes are based on two-component models, consisting of a
dominant magnetic component (as given by longitudinal tube waves) and a
subordinate acoustic component. The Ca II fluxes as obtained are smaller
by about a factor of 2 than those given by observations. Possible
reasons for this discrepancy include (1) inherent limitations of our
theoretical approach as it is based on 1-D rather than 3-D modelling
and/or (2) the existence of additional heating processes in ɛ Eridani
(a young star) not included here.
Title: Exploring Extreme Space Weather Factors of Exoplanetary
Habitability
Authors: Airapetian, V. S.; Adibekyan, V.; Ansdell, M.; Cohen, O.;
Cuntz, M.; Danchi, W.; Dong, C. F.; Drake, J. J.; Fahrenbach, A.;
France, K.; Garcia-Sage, K.; Glocer, A.; Grenfell, J. L.; Gronoff,
G.; Hartnett, H.; Henning, W.; Hinkel, N. R.; Jensen, A. G.; Jin,
M.; Kalas, P.; Kane, S. R.; Kobayashi, K.; Kopparapu, R.; Leake, J.;
López-Puertas, M.; Lueftinger, T.; Lynch, B.; Lyra, W.; Mandell,
A. M.; Mandt, K. E.; Moore, W. B.; Nna-Mvondo, D.; Notsu, Y.; Maehara,
H.; Yamashiki, Y.; Shibata, K.; Oman, L. D.; Osten, R. A.; Pavlov,
A.; Ramirez, R. M.; Rugheimer, S.; Schlieder, J. E.; Schnittman,
J. D.; Shock, E. L.; Sousa-Silva, C.; Way, M. J.; Yang, Y.; Young,
P. A.; Zank, G. P.
Bibcode: 2018arXiv180303751A
Altcode:
It is currently unknown how common life is on exoplanets, or how long
planets can remain viable for life. To date, we have a superficial
notion of habitability, a necessary first step, but so far lacking an
understanding of the detailed interaction between stars and planets
over geological timescales, dynamical evolution of planetary systems,
and atmospheric evolution on planets in other systems. A planet mass,
net insolation, and atmospheric composition alone are insufficient
to determine the probability that life on a planet could arise
or be detected. The latter set of planetary considerations, among
others, underpin the concept of the habitable zone (HZ), defined
as the circumstellar region where standing bodies of liquid water
could be supported on the surface of a rocky planet. However, stars
within the same spectral class are often treated in the same way in HZ
studies, without any regard for variations in activity among individual
stars. Such formulations ignore differences in how nonthermal emission
and magnetic energy of transient events in different stars affect the
ability of an exoplanet to retain its atmosphere.In the last few years
there has been a growing appreciation that the atmospheric chemistry,
and even retention of an atmosphere in many cases, depends critically
on the high-energy radiation and particle environments around these
stars. Indeed, recent studies have shown stellar activity and the
extreme space weather, such as that created by the frequent flares and
coronal mass ejections (CMEs) from the active stars and young Sun, may
have profoundly affected the chemistry and climate and thus habitability
of the early Earth and terrestrial type exoplanets. The goal of this
white paper is to identify and describe promising key research goals
to aid the field of the exoplanetary habitability for the next 20 years.
Title: On the Dynamics of Comets in Extrasolar Planetary Systems
Authors: Dvorak, R.; Loibnegger, B.; Cuntz, M.
Bibcode: 2018tss..confE...1D
Altcode:
Since very recently, we acquired knowledge on the existence of comets
in extrasolar planetary systems. The formation of comets together
with planets around host stars now seems evident. As stars are often
born in clusters of interstellar clouds, the interaction between
the systems will lead to the exchange of material at the edge of the
clouds. Therefore, almost every planetary system should have leftover
remnants as a result of planetary formation in form of comets at the
edges of those systems. These Oort clouds around stars are often
disturbed by different processes (e.g., galactic tides, passing
stars, etc.), which consequently scatter bodies from the distant
clouds into the system close to the host star. Regarding the Solar
System, we observe this outcome in the form of cometary families. This
knowledge supports the assumption of the existence of comets around
other stars. In the present work, we study the orbital dynamics
of hypothetical exocomets, based on detailed computer simulations,
in three star-planet systems, which are: HD 10180, 47 UMa, and HD
141399. These systems host one or more Jupiter-like planets, which
change the orbits of the incoming comets in characteristic ways.
Title: The Mass-Luminosity Relation for a Refined Set of Late-K/M
Dwarfs
Authors: Cuntz, Manfred; Wang, Zhaopeng
Bibcode: 2018RNAAS...2...19C
Altcode: 2018RNAAS...2a..19C
No abstract at ADS
Title: Fitting Formulae and Constraints for the Existence of S-type
and P-type Habitable Zones in Binary Systems
Authors: Wang, Zhaopeng; Cuntz, Manfred
Bibcode: 2017AJ....154..157W
Altcode: 2017arXiv171003273W
We derive fitting formulae for the quick determination of the existence
of S-type and P-type habitable zones (HZs) in binary systems. Based
on previous work, we consider the limits of the climatological HZ in
binary systems (which sensitively depend on the system parameters)
based on a joint constraint encompassing planetary orbital stability
and a habitable region for a possible system planet. Additionally,
we employ updated results on planetary climate models obtained
by Kopparapu and collaborators. Our results are applied to four
P-type systems (Kepler-34, Kepler-35, Kepler-413, and Kepler-1647)
and two S-type systems (TrES-2 and KOI-1257). Our method allows us
to gauge the existence of climatological HZs for these systems in a
straightforward manner with detailed consideration of the observational
uncertainties. Further applications may include studies of other
existing systems as well as systems to be identified through future
observational campaigns.
Title: Case Studies of Exocomets in the System of HD 10180
Authors: Loibnegger, Birgit; Dvorak, Rudolf; Cuntz, Manfred
Bibcode: 2017AJ....153..203L
Altcode: 2017arXiv171202386L
The aim of our study is to investigate the dynamics of possible comets
in the HD 10180 system. This investigation is motivated by the discovery
of exocomets in various systems, especially β Pictoris, as well as
in at least 10 other systems. Detailed theoretical studies about the
formation and evolution of star-planet systems indicate that exocomets
should be quite common. Further observational results are expected in
the foreseeable future, in part, due to the availability of the Large
Synoptic Survey Telescope. Nonetheless, the solar system represents the
best studied example for comets, thus serving as a prime motivation for
investigating comets in HD 10180 as well. HD 10180 is strikingly similar
to the Sun. This system contains six confirmed planets and (at least)
two additional planets subject to final verification. In our studies,
we consider comets of different inclinations and eccentricities and
find an array of different outcomes such as encounters with planets,
captures, and escapes. Comets with relatively large eccentricities are
able to enter the inner region of the system facing early planetary
encounters. Stable comets experience long-term evolution of orbital
elements, as expected. We also tried to distinguish cometary families
akin to our solar system, but no clear distinction between possible
families was found. Generally, theoretical and observational studies of
exoplanets have a large range of ramifications, involving the origin,
structure, and evolution of systems as well as the proliferation
of water and prebiotic compounds to terrestrial planets, which will
increase their chances of being habitable.
Title: Climatological and ultraviolet-based habitability of possible
exomoons in F-star systems
Authors: Sato, S.; Wang, Zh.; Cuntz, M.
Bibcode: 2017AN....338..413S
Altcode: 2015arXiv150302560S
The identification of conditions suitable for life is considered a key
element of modern-day astronomy, astrophysics, and astrobiology. This
research encompasses the environments of stars of different spectral
types and evolutionary status. In this article, we focus on the
possibility of habitable moons in selected F-star systems. We explore
the astrobiological significance of F-type stars of spectral type
between F5 V and F9.5 V, which possess Jupiter-type planets within
or close to their climatological habitable zones. These planets,
or at least a subset of those, may also possess rocky exomoons,
which potentially offer habitable environments. Our work considers
eight selected systems. The Jupiter-type planets in these systems are
in notably differing orbits with eccentricities between 0.08 (about
Mars) and 0.72. We consider the stellar UV environments provided
by the photospheric stellar radiation, which allows us to compute
the UV habitable zones for the systems. Following previous studies,
deoxyribonucleic acid (DNA) is taken as a proxy for carbon-based
macromolecules following the paradigm that extraterrestrial biology
might be based on hydrocarbons. We found that the damage inflicted on
DNA is notably different for the range of systems studied, and also
varies according to the orbit of the Jupiter-type planet, especially
for systems of high ellipticity, as expected. Furthermore, the UV
levels in the CLI-HZs of the F-type stars are generally more severe
than for the solar environment, except for regions beyond the outer
limits of the general habitable zones. Particular emphasis was placed
on locations akin to Earth-equivalent (i.e., homeothermic) positions
in the Solar System. The general conditions of habitability in F-star
systems are also affected by the rapidness of stellar evolution;
nonetheless, based on previous research on the origin of life on Earth,
a generally favorable assessment about the overall possibility of
life around F-type stars can be conveyed. For some systems studied
here, excessive values of damage are attained if compared to today's
Earth or during the Archean eon. Considering that the detection of
exomoons around different types of stars will remain challenging
in the foreseeable future, we view our work also as an example and
template for investigating the combined requirements of climatological
and UV-based habitability for exosolar objects. Further studies for
systems of stars with other spectral types and/or other evolutionary
status will be considered as part of our future research.
Title: The Secret Lives of Cepheids: δ Cep—The Prototype of a
New Class of Pulsating X-Ray Variable Stars
Authors: Engle, Scott G.; Guinan, Edward F.; Harper, Graham M.; Cuntz,
Manfred; Remage Evans, Nancy; Neilson, Hilding R.; Fawzy, Diaa E.
Bibcode: 2017ApJ...838...67E
Altcode: 2017arXiv170206560E
From our Secret Lives of Cepheids program, the prototype Classical
Cepheid, δ Cep, is found to be an X-ray source with periodic
pulsation-modulated X-ray variations. This finding complements our
earlier reported phase-dependent FUV-UV emissions of the star that
increase ∼10-20 times with highest fluxes at ∼ 0.90{--}0.95φ
, just prior to maximum brightness. Previously δ Cep was found as
potentially X-ray variable, using XMM-Newton observations. Additional
phase-constrained data were secured with Chandra near X-ray
emission peak, to determine if the emission and variability were
pulsation-phase-specific to δ Cep and not transient or due to a
possible coronally active, cool companion. The Chandra data were
combined with prior XMM-Newton observations, and were found to very
closely match the previously observed X-ray behavior. From the combined
data set, a ∼4 increase in X-ray flux is measured, reaching a peak
{L}{{X}} = 1.7 × 1029 erg s-1 near
0.45ϕ. The precise X-ray flux phasing with the star’s pulsation
indicates that the emissions arise from the Cepheid and not from a
companion. However, it is puzzling that the maximum X-ray flux occurs
∼0.5ϕ (∼3 days) later than the FUV-UV maximum. There are several
other potential Cepheid X-ray detections with properties similar to
δ Cep, and comparable X-ray variability is indicated for two other
Cepheids: β Dor and V473 Lyr. X-ray generating mechanisms in δ Cep
and other Cepheids are discussed. If additional Cepheids are confirmed
to show phased X-ray variations, then δ Cep will be the prototype of
a new class of pulsation-induced X-ray variables.
Title: The Habitable Zone of the Binary System Kepler-16
Authors: Moorman, Sarah; Cuntz, Manfred
Bibcode: 2017AAS...22943323M
Altcode:
We report on the current results and envisioned future work from our
study of the binary star system Kepler-16, which consists of a K-type
main-sequence star and an M dwarf as well as a circumbinary Saturnian
planet, Kepler-16b. We focus on the calculation of the location and
extent of the habitable zone while considering several criteria for both
the inner and outer boundaries previously given in the literature. In
particular, we investigate the impact of the two stellar components
(especially Kepler-16A) as well as of the system’s binarity regarding
the provision of circumbinary habitability. Another aspect of our work
consists in a careful assessment of how the extent of the system’s
habitable zone is impacted by the relative uncertainties of the
stellar and system parameters. Finally, we comment on the likelihood of
habitable objects in the system by taking into account both radiative
criteria and the need of orbital stability.
Title: About K Dwarfs - Investigating the Goldilocks Stars of
Exobiology
Authors: Cuntz, Manfred; Guinan, Edward F.
Bibcode: 2017AAS...22923006C
Altcode:
In this study, we argue that stars between spectral type late-G and
mid-K (with a maximum at early-K), i.e., orange dwarfs, are expected
to provide the best conditions for the development and sustainability
of life, including advanced life forms. Though our study is mostly
theoretical, observational data are considered as fit. Our analysis
considers a variety of stellar properties, including (1) the frequency
of the various types of stars, (2) the speed of stellar evolution their
lifetimes, (3) the size of the stellar climatological habitable zones
(CLI-HZs), (4) the strengths and persistence of their magnetic dynamo
generated X-ray--UV emissions, and (5) the frequency and severity
of (super-)flares; both (4) and (5) greatly reduce the suitability
of M-type dwarfs to host life-bearing planets. M-type dwarfs are
numerous, having long lifetimes, but their narrow CLI-HZs and
hazards from magnetic activity make them less suitable for hosting
exolife. Therefore, we argue that K-dwarfs should be rightfully
considered "Goldilocks" stars, thus deserving heightened attention in
future observational and theoretical studies.
Title: A New Method for the Quick Determination of S-Type and P-Type
Habitable Zones in Binary Systems
Authors: Wang, Zhaopeng; Cuntz, Manfred
Bibcode: 2017AAS...22941304W
Altcode:
More than 3500 exoplanets have been confirmed nowadays, including a very
large number of planets discovered by the Kepler mission. Additional
exoplanets are expected to be found by ongoing missions as, e.g.,
K2 as well as future missions such as TESS. Exoplanets, especially
terrestrial planets, located in stellar habitable zones are drawing
great attention from the community and the public at large due
to their potential for hosting alien life - a prospect that makes
the adequate determination of stellar habitable zones an important
goal of exoplanetary research. In the local Galactic neighborhood,
binary systems occur relatively frequently. Thus, it is the aim of
my presentation to offer a method for the quick determination for the
existence of habitable zones in binaries. Therefore, fitting formulas
for binary habitable zones regarding both S-type and P-type star-planet
configurations are provided. Based on previous work in the literature,
a joint constraint regarding radiative habitable zones and planetary
orbital stability limits is used. Models of stellar habitable zones
utilize updated computations for planetary climate models as given
by Kopparapu et al. (2013, 2014) [ApJ 765, 131; ApJL 787, L29]. Cases
studies showing the quality of the fit formulas, as well as applications
to observed systems, are presented as well.
Title: Fitting Formulas For Determining The Existence Of S-Type And
P-Type Habitable Zones In Binary Systems: First Results
Authors: Wang, Zhaopeng; Cuntz, Manfred
Bibcode: 2016csss.confE...7W
Altcode: 2016arXiv160907238W
We present initial work about attaining fitting formulas for the
quick determination of the existence of S-type and P-type habitable
zones in binary systems. Following previous work, we calculate
the limits of the climatological habitable zone in binary systems
(which sensitively depend on the system parameters) based on a joint
constraint encompassing planetary orbital stability and a habitable
region for a possible system planet. We also consider updated results
on planetary climate models previously obtained by Kopparapu and
collaborators. Fitting equations based on our work are presented for
selected cases.
Title: About Exobiology: The Case for Dwarf K Stars
Authors: Cuntz, M.; Guinan, E. F.
Bibcode: 2016ApJ...827...79C
Altcode: 2016arXiv160609580C
One of the most fundamental topics of exobiology concerns the
identification of stars with environments consistent with life. Although
it is believed that most types of main-sequence stars might be able
to support life, particularly extremophiles, special requirements
appear to be necessary for the development and sustainability of
advanced life forms. From our study, orange main-sequence stars,
ranging from spectral type late-G to mid-K (with a maximum at early
K), are most promising. Our analysis considers a variety of aspects,
including (1) the frequency of the various types of stars, (2) the
speed of stellar evolution in their lifetimes, (3) the size of the
stellar climatological habitable zones (CLI-HZs), (4) the strengths
and persistence of their magnetic-dynamo-generated X-ray-UV emissions,
and (5) the frequency and severity of flares, including superflares;
both (4) and (5) greatly reduce the suitability of red dwarfs to host
life-bearing planets. The various phenomena show pronounced dependencies
on the stellar key parameters such as effective temperature and mass,
permitting the assessment of the astrobiological significance of various
types of stars. Thus, we developed a “Habitable-Planetary-Real-Estate
Parameter” (HabPREP) that provides a measure for stars that are most
suitable for planets with life. Early K stars are found to have the
highest HabPREP values, indicating that they may be “Goldilocks”
stars for life-hosting planets. Red dwarfs are numerous, with long
lifetimes, but their narrow CLI-HZs and hazards from magnetic activity
make them less suitable for hosting exolife. Moreover, we provide
X-ray-far-UV irradiances for G0 V-M5 V stars over a wide range of ages.
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: BinHab: A Numerical Tool for the Calculation of S/P-Type
Habitable Zones in Binary Systems
Authors: Cuntz, M.; Bruntz, R.
Bibcode: 2015csss...18..845C
Altcode: 2014arXiv1409.3449C
The aim of this contribution is to introduce the numerical tool BinHab,
a publicly accessible code, available at The University of Texas at
Arlington, that allows the calculation of S-type and P-type habitable
zones of general binary systems.
Title: Atmospheric Heating and Wind Acceleration in Cool Evolved Stars
Authors: Airapetian, Vladimir S.; Cuntz, Manfred
Bibcode: 2015ASSL..408..123A
Altcode: 2014arXiv1406.6238A
A chromosphere is a universal property of stars of spectral type later
than ∼ F5. Evolved K and M giants and supergiants, including the
ζ Aur binaries, show extended and highly turbulent chromospheres,
which develop into slow massive winds. The associated continuous mass
loss has a significant impact on stellar evolution, and thence on the
chemical evolution of galaxies. Yet despite the fundamental importance
of those winds in astrophysics, the question of their origin(s) remains
unsolved. What mechanisms heat a chromosphere? What is the role of the
chromosphere in the formation of stellar winds? This chapter provides
a review of the observational requirements and theoretical approaches
for modelling chromospheric heating and the acceleration of winds in
single cool, evolved stars and in eclipsing binary stars, including
physical models that have recently been proposed. It describes the
successes that have been achieved so far by invoking acoustic and MHD
waves to provide a physical description of plasma heating and wind
acceleration, and discusses the challenges that still remain.
Title: S-type and P-type Habitability in Stellar Binary Systems:
A Comprehensive Approach. II. Elliptical Orbits
Authors: Cuntz, M.
Bibcode: 2015ApJ...798..101C
Altcode: 2014arXiv1409.3796C
In the first paper of this series, a comprehensive approach has been
provided for the study of S-type and P-type habitable regions in stellar
binary systems, which was, however, restricted to circular orbits of
the stellar components. Fortunately, a modest modification of the method
also allows for the consideration of elliptical orbits, which of course
entails a much broader range of applicability. This augmented method is
presented here, and numerous applications are conveyed. In alignment
with Paper I, the selected approach considers a variety of aspects,
which comprise the consideration of a joint constraint including
orbital stability and a habitable region for a possible system planet
through the stellar radiative energy fluxes ("radiative habitable
zone"; RHZ). The devised method is based on a combined formalism for
the assessment of both S-type and P-type habitability; in particular,
mathematical criteria are deduced for which kinds of systems S-type and
P-type habitable zones are realized. If the RHZs are truncated by the
additional constraint of orbital stability, the notation of ST-type and
PT-type habitability applies. In comparison to the circular case, it is
found that in systems of higher eccentricity, the range of the RHZs is
significantly reduced. Moreover, for a considerable number of models,
the orbital stability constraint also reduces the range of S-type and
P-type habitability. Nonetheless, S-, P-, ST-, and PT-type habitability
is identified for a considerable set of system parameters. The method
as presented is utilized for BinHab, an online code available at The
University of Texas at Arlington.
Title: A Joint Approach to the Study of S-Type and P-Type Habitable
Zones in Binary Systems: New Results in the View of 3-D Planetary
Climate Models
Authors: Cuntz, Manfred
Bibcode: 2015AAS...22541501C
Altcode:
In two previous papers, given by Cuntz (2014a,b) [ApJ 780, A14 (19
pages); arXiv:1409.3796], a comprehensive approach has been provided
for the study of S-type and P-type habitable zones in stellar binary
systems, P-type orbits occur when the planet orbits both binary
components, whereas in case of S-type orbits, the planet orbits only
one of the binary components with the second component considered
a perturbator. The selected approach considers a variety of aspects,
including (1) the consideration of a joint constraint including orbital
stability and a habitable region for a possible system planet through
the stellar radiative energy fluxes; (2) the treatment of conservative
(CHZ), general (GHZ) and extended zones of habitability (EHZ) [see
Paper I for definitions] for the systems as previously defined for
the Solar System; (3) the provision of a combined formalism for the
assessment of both S-type and P-type habitability; in particular,
mathematical criteria are devised for which kind of system S-type
and P-type habitability is realized; and (4) the applications of
the theoretical approach to systems with the stars in different
kinds of orbits, including elliptical orbits (the most expected
case). Particularly, an algebraic formalism for the assessment of
both S-type and P-type habitability is given based on a higher-order
polynomial expression. Thus, an a prior specification for the presence
or absence of S-type or P-type radiative habitable zones is - from
a mathematical point of view - neither necessary nor possible, as
those are determined by the adopted formalism. Previously, numerous
applications of the method have been given encompassing theoretical
star-panet systems and and observations. Most recently, this method
has been upgraded to include recent studies of 3-D planetary climate
models. Originally, this type of work affects the extent and position
of habitable zones around single stars; however, it has also profound
consequence for the habitable regions in binary systems (both S-type
and P-type), the topic of the intended presentation.
Title: Habitability around F-type stars
Authors: Sato, S.; Cuntz, M.; Guerra Olvera, C. M.; Jack, D.;
Schröder, K. -P.
Bibcode: 2014IJAsB..13..244S
Altcode: 2013arXiv1312.7431S
We explore the general astrobiological significance of
F-type main-sequence stars with masses between 1.2 and 1.5
M ⊙. Special consideration is given to stellar
evolutionary aspects due to nuclear main-sequence evolution. DNA
is taken as a proxy for carbon-based macromolecules following
the paradigm that extraterrestrial biology may be most likely
based on hydrocarbons. Consequently, the DNA action spectrum is
utilized to represent the impact of the stellar ultraviolet (UV)
radiation. Planetary atmospheric attenuation is taken into account
based on parameterized attenuation functions. We found that the
damage inflicted on DNA for planets at Earth-equivalent positions
is between a factor of 2.5 and 7.1 higher than for solar-like stars,
and there are intricate relations for the time-dependence of damage
during stellar main-sequence evolution. If attenuation is considered,
smaller factors of damage are obtained in alignment to the attenuation
parameters. This work is motivated by earlier studies indicating that
the UV environment of solar-type stars is one of the most decisive
factors in determining the suitability of exosolar planets and exomoons
for biological evolution and sustainability.
Title: S-type and P-type Habitability in Stellar Binary Systems:
A Comprehensive Approach. I. Method and Applications
Authors: Cuntz, M.
Bibcode: 2014ApJ...780...14C
Altcode: 2013arXiv1303.6645C
A comprehensive approach is provided for the study of both S-type
and P-type habitability in stellar binary systems, which in principle
can also be expanded to systems of higher order. P-type orbits occur
when the planet orbits both binary components, whereas in the case of
S-type orbits, the planet orbits only one of the binary components with
the second component considered a perturbator. The selected approach
encapsulates a variety of different aspects, which include: (1) the
consideration of a joint constraint, including orbital stability and
a habitable region for a putative system planet through the stellar
radiative energy fluxes ("radiative habitable zone"; RHZ), needs to be
met; (2) the treatment of conservative, general, and extended zones of
habitability for the various systems as defined for the solar system and
beyond; (3) the provision of a combined formalism for the assessment
of both S-type and P-type habitability; in particular, mathematical
criteria are presented for the kind of system in which S-type and
P-type habitability is realized; (4) applications of the attained
theoretical approach to standard (theoretical) main-sequence stars. In
principle, five different cases of habitability are identified, which
are S-type and P-type habitability provided by the full extent of the
RHZs; habitability, where the RHZs are truncated by the additional
constraint of planetary orbital stability (referred to as ST- and
PT-type, respectively); and cases of no habitability at all. Regarding
the treatment of planetary orbital stability, we utilize the formulae
of Holman & Wiegert as also used in previous studies. In this work,
we focus on binary systems in circular orbits. Future applications will
also consider binary systems in elliptical orbits and provide thorough
comparisons to other methods and results given in the literature.
Title: Nonmagnetic Heating in Evolved Stars
Authors: Cuntz, Manfred
Bibcode: 2013giec.conf30201C
Altcode:
Outer atmospheric heating in evolved stars, notably giant and
supergiant stars, is a topic of great interest as it is linking
observable atmospheric phenomena to physical processes of the stellar
interior, associated with convection, rotation, and the evolution of
stellar angular momentum. Within the last decade considerable emphasis
has rightfully been placed on deciphering various types of magnetic
processes; however, this does not imply that nonmagnetic processes
are of abridged relevance. It is therefore the purpose of my talk
to elaborate on the significance of nonmagnetic heating processes by
considering both convective and pulsational phenomena, which are found
to occur on numerous spatial and temporal scales. Emphasis is placed
on observational as well as theoretical findings of the recent past.
Title: On the Possibility of Habitable Moons in the System of HD
23079: Results from Orbital Stability Studies
Authors: Cuntz, M.; Quarles, B.; Eberle, J.; Shukayr, A.
Bibcode: 2013PASA...30...33C
Altcode: 2013arXiv1304.1157C
The aim of our study is to investigate the possibility of habitable
moons orbiting the giant planet HD 23079b, a Jupiter-mass planet,
which follows a low-eccentricity orbit in the outer region of
HD 23079's habitable zone. We show that HD 23079b is able to host
habitable moons in prograde and retrograde orbits, as expected, noting
that the outer stability limit for retrograde orbits is increased by
nearly 90% compared with that of prograde orbits, a result consistent
with previous generalised studies. For the targeted parameter space,
it was found that the outer stability limit for habitable moons varies
between 0.05236 and 0.06955 AU (prograde orbits) and between 0.1023 and
0.1190 AU (retrograde orbits), depending on the orbital parameters of
the Jupiter-type planet if a minimum mass is assumed. These intervals
correspond to 0.306 and 0.345 (prograde orbits) and 0.583 and 0.611
(retrograde orbits) of the planet's Hill radius. Larger stability limits
are obtained if an increased value for the planetary mass mp
is considered; they are consistent with the theoretically deduced
relationship of m 1/3 p . Finally, we compare
our results with the statistical formulae of Domingos, Winter, &
Yokoyama, indicating both concurrence and limitations.
Title: Solar magnetic flux tube simulations with time-dependent
ionization
Authors: Fawzy, D. E.; Cuntz, M.; Rammacher, W.
Bibcode: 2012MNRAS.426.1916F
Altcode: 2012arXiv1208.1490F
In the present work we expand the study of time-dependent ionization
previously identified to be of pivotal importance for acoustic waves
in solar magnetic flux tube simulations. We focus on longitudinal tube
waves (LTW) known to be an important heating agent of solar magnetic
regions. Our models also consider new results of wave energy generation
as well as an updated determination of the mixing length of convection
now identified as 1.8 scale heights in the upper solar convective
layers. We present 1D wave simulations for the solar chromosphere by
studying tubes of different spreading as a function of height aimed
at representing tubes in environments of different magnetic filling
factors. Multilevel radiative transfer has been applied to correctly
represent the total chromospheric emission function. The effects of
time-dependent ionization are significant in all models studied. They
are most pronounced behind strong shocks and in low-density regions,
i.e. the middle and high chromosphere. Concerning our models of
different tube spreading, we attained pronounced differences between
the various types of models, which were largely initiated by different
degrees of dilution of the wave energy flux as well as the density
structure partially shaped by strong shocks, if existing. Models
showing a quasi-steady rise of temperature with height are obtained
via monochromatic waves akin to previous acoustic simulations. However,
longitudinal flux tube waves are identified as insufficient to heat the
solar transition region and corona in agreement with previous studies.
Title: Application of the Titius-Bode Rule to the 55 Cancri System:
Tentative Prediction of a Possibly Habitable Planet
Authors: Cuntz, Manfred
Bibcode: 2012PASJ...64...73C
Altcode: 2011arXiv1107.5038C
Following the notion that the Titius-Bode rule (TBR) may also be
applicable to some extrasolar planetary systems, although this number
could be relatively small, it is applied to 55 Cancri, which is a G-type
main-sequence star currently known to host five planets. Following
a concise computational process, we tentatively identified four new
hypothetical planetary positions, given as 0.081, 0.41, 1.51, and 2.95
AU from the star. The likelihood that these positions are occupied by
real existing planets is significantly enhanced for the positions of
1.51 and 2.95 AU in view of previous simulations on planet formation and
planetary orbital stability. For example, Raymond, Barnes, and Gorelick
(2008,
ApJ, 689, 478) argued that additional planets would be possible
between 55 Cnc f and 55 Cnc d, which would include planets situated
at 1.51 and 2.95 AU. If two additional planets are assumed to exist
between 55 Cnc f and 55 Cnc d, the deduced domains of stability would
be given as 1.3-1.6 and 2.2-3.3 AU. The possible planet near 1.5 AU
appears to be located at the outskirts of the stellar habitable zone,
which is, however, notably affected by the stellar parameters as well
as the adopted model of circumstellar habitability. We also computed
the distance of the next possible outer planet in the 55 Cnc system,
which, if existing, is predicted to be located between 10.9 and 12.2 AU,
which is consistent with orbital stability constraints. The inherent
statistical significance of the TBR was evaluated following a method by
Lynch (2003,
MNRAS, 341, 1174). Yet it is up to future planetary search missions
to verify or falsify the applicability of the TBR to the 55 Cnc system,
and to obtain information on additional planets, if existing.
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: Basal chromospheric flux and Maunder Minimum-type stars:
the quiet-Sun chromosphere as a universal phenomenon
Authors: Schröder, K. -P.; Mittag, M.; Pérez Martínez, M. I.;
Cuntz, M.; Schmitt, J. H. M. M.
Bibcode: 2012A&A...540A.130S
Altcode: 2012arXiv1202.3314S
Aims: We demonstrate the universal character of the quiet-Sun
chromosphere among inactive stars (solar-type and giants). By
assessing the main physical processes, we shed new light on some common
observational phenomena.
Methods: We discuss measurements of the
solar Mt. Wilson S-index, obtained by the Hamburg Robotic Telescope
around the extreme minimum year 2009, and compare the established
chromospheric basal Ca II K line flux to the Mt. Wilson S-index data
of inactive ("flat activity") stars, including giants.
Results:
During the unusually deep and extended activity minimum of 2009, the Sun
reached S-index values considerably lower than in any of its previously
observed minima. In several brief periods, the Sun coincided exactly
with the S-indices of inactive ("flat", presumed Maunder Minimum-type)
solar analogues of the Mt. Wilson sample; at the same time, the solar
visible surface was also free of any plages or remaining weak activity
regions. The corresponding minimum Ca II K flux of the quiet Sun and
of the presumed Maunder Minimum-type stars in the Mt. Wilson sample
are found to be identical to the corresponding Ca II K chromospheric
basal flux limit.
Conclusions: We conclude that the quiet-Sun
chromosphere is a universal phenomenon among inactive stars. Its
mixed-polarity magnetic field, generated by a local, "fast" turbulent
dynamo finally provides a natural explanation for the minimal soft
X-ray emission observed for inactive stars. Given such a local dynamo
also works for giant chromospheres, albeit on longer length scales,
i.e., l ∝ R/g, with R and g as stellar radius and surface gravity,
respectively, the existence of giant spicular phenomena and the
guidance of mechanical energy toward the acceleration zone of cool
stellar winds along flux-tubes have now become traceable.
Title: Planet-Induced Emission Enhancements in HD 179949: Results
from McDonald Observations
Authors: Gurdemir, L.; Redfield, S.; Cuntz, M.
Bibcode: 2012PASA...29..141G
Altcode: 2012arXiv1202.3612G
We monitored the Ca II H and K lines of HD 179949, a notable star in the
southern hemisphere, to observe and confirm previously identified planet
induced emission (PIE) as an effect of star-planet interaction. We
obtained high resolution spectra (R~53000) with a signal-to-noise
ratio S/N >~50 in the Ca II H and K cores during 10 nights of
observation at the McDonald Observatory. Wide-band echelle spectra
were taken using the 2.7-m telescope. Detailed statistical analysis
of Ca II K revealed fluctuations in the Ca II K core attributable
to planet induced chromospheric emission. This result is consistent
with previous studies by Shkolnik et al. (2003). Additionally, we were
able to confirm the reality and temporal evolution of the phase shift
of the maximum of star-planet interaction previously found. However,
no identifiable fluctuations were detected in the Ca II H core. The Al
I λ3944Å line was also monitored to gauge if the expected activity
enhancements are confined to the chromospheric layer. Our observations
revealed some variability, which is apparently unassociated with
planet-induced activity.
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: 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: VizieR Online Data Catalog: Chromospheric Mg II h+k flux of
evolved stars (Perez+, 2011)
Authors: Perez Martinez, M. I.; Schroder, K. -P.; Cuntz, M.
Bibcode: 2012yCat..74140418P
Altcode:
Of a total of 177 cool G, K and M giants and supergiants, we measured
the MgII h+k line emission of extended chromospheres in high-resolution
(LWR) International Ultraviolet Explorer (IUE) spectra by using the IUE
final data archive at the Space Telescope Science Institute (STScI)
and derived the respective stellar surface fluxes. They represent
the chromospheric radiative energy losses presumably related to basal
heating by the dissipation of acoustic waves, plus a highly variable
contribution due to magnetic activity. (1 data file).
Title: Habitability of super-Earth planets around main-sequence stars
including red giant branch evolution: models based on the integrated
system approach
Authors: Cuntz, M.; von Bloh, W.; Schröder, K. -P.; Bounama, C.;
Franck, S.
Bibcode: 2012IJAsB..11...15C
Altcode: 2011arXiv1107.5714C
In a previous study published in Astrobiology, we focused on the
evolution of habitability of a 10 M⊕ super-Earth
planet orbiting a star akin to the Sun. This study was based on a
concept of planetary habitability in accordance with the integrated
system approach that describes the photosynthetic biomass production
taking into account a variety of climatological, biogeochemical and
geodynamical processes. In the present study, we pursue a significant
augmentation of our previous work by considering stars with zero-age
main-sequence masses between 0.5 and 2.0 M⊙ with special
emphasis on models of 0.8, 0.9, 1.2 and 1.5 M⊙. Our
models of habitability consider geodynamical processes during the
main-sequence stage of these stars as well as during their red
giant branch evolution. Pertaining to the different types of stars,
we identify the so-called photosynthesis-sustaining habitable zone
(pHZ) determined by the limits of biological productivity on the
planetary surface. We obtain various sets of solutions consistent with
the principal possibility of life. Considering that stars of relatively
high masses depart from the main-sequence much earlier than low-mass
stars, it is found that the biospheric lifespan of super-Earth planets
of stars with masses above approximately 1.5 M⊙ is always
limited by the increase in stellar luminosity. However, for stars
with masses below 0.9 M⊙, the lifespan of super-Earths
is solely determined by the geodynamic timescale. For central star
masses between 0.9 and 1.5 M⊙, the possibility of life
in the framework of our models depends on the relative continental
area of the super-Earth planet.
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: The basal chromospheric Mg II h+k flux of evolved stars:
probing the energy dissipation of giant chromospheres
Authors: Pérez Martínez, M. Isabel; Schröder, K. -P.; Cuntz, M.
Bibcode: 2011MNRAS.414..418P
Altcode: 2011arXiv1102.4832P
Of a total of 177 cool G, K and M giants and supergiants, we measured
the Mg II h+k line emission of extended chromospheres in high-resolution
(LWR) International Ultraviolet Explorer (IUE) spectra by using the IUE
final data archive at the Space Telescope Science Institute (STScI)
and derived the respective stellar surface fluxes. They represent
the chromospheric radiative energy losses presumably related to
basal heating by the dissipation of acoustic waves, plus a highly
variable contribution due to magnetic activity. Thanks to the
large sample size, we find a very well defined lower limit, the
basal chromospheric Mg II h+k line flux of cool giant chromospheres,
as a function of Teff. A total of 16 giants were observed
several times, over a period of up to 20 yr. Their respective minimal
Mg II h+k line fluxes confirm the basal flux limit very well because
none of their emissions dips beneath the empirically deduced basal
flux line representative for the overall sample. Based on a total
of 15-22 objects with very low Mg II h+k emission, we find as limit
? (cgs units; based on the B-V relation). Within its uncertainties,
this is almost the same relation as has been found in the past
for the geometrically much thinner chromospheres of main-sequence
stars. But any residual dependence of the basal flux on the surface
gravity is difficult to determine, since especially among the G-type
giants there is a large spread of the individual chromospheric Mg II
fluxes, apparently due to revived magnetic activity. However, it can
be stated that over a gravity range of more than 4 orders of magnitude
(main-sequence stars to supergiants), the basal flux does not appear
to vary by more than a factor of 2. These findings are in good
agreement with the predictions by previous hydrodynamic models of
acoustic wave propagation and energy dissipation, as well as with
earlier empirical determinations. Finally, we also discuss the idea
that the ample energy flux of the chromospheric acoustic waves in a
cool giant may yield, as a by-product, the energy flux required by its
cool wind (i.e. non-dust-driven, 'Reimers-type' mass-loss), provided
a dissipation mechanism of a sufficiently long range is operating.
Title: Habitability of the Goldilocks planet Gliese 581g: results
from geodynamic models
Authors: von Bloh, W.; Cuntz, M.; Franck, S.; Bounama, C.
Bibcode: 2011A&A...528A.133V
Altcode: 2011arXiv1102.3926V
Aims: In 2010, detailed observations have been published that
seem to indicate another super-Earth planet in the system of Gliese 581,
which is located in the midst of the stellar climatological habitable
zone. The mass of the planet, known as Gl 581g, has been estimated to
be between 3.1 and 4.3 M⊕. In this study, we investigate
the habitability of Gl 581g based on a previously used concept that
explores its long-term possibility of photosynthetic biomass production,
which has already been used to gauge the principal possibility of
life regarding the super-Earths Gl 581c and Gl 581d.
Methods:
A thermal evolution model for super-Earths is used to calculate the
sources and sinks of atmospheric carbon dioxide. The habitable zone
is determined by the limits of photosynthetic biological productivity
on the planetary surface. Models with different ratios of land/ocean
coverage are pursued.
Results: The maximum time span for
habitable conditions is attained for water worlds at a position of about
0.14 ± 0.015 AU, which deviates by just a few percent (depending on
the adopted stellar luminosity) from the actual position of Gl 581g,
an estimate that does however not reflect systematic uncertainties
inherent in our model. Therefore, in the framework of our model
an almost perfect Goldilock position is realized. The existence of
habitability is found to critically depend on the relative planetary
continental area, lending a considerable advantage to the possibility of
life if Gl 581g's ocean coverage is relatively high.
Conclusions:
Our results are another step toward identifying the possibility of life
beyond the Solar System, especially concerning super-Earth planets,
which appear to be more abundant than previously surmised.
Title: Generation of longitudinal flux tube waves in theoretical
main-sequence stars: effects of model parameters
Authors: Fawzy, D. E.; Cuntz, M.
Bibcode: 2011A&A...526A..91F
Altcode: 2010arXiv1009.4174F
Aims: We compute the wave energy fluxes carried by longitudinal
tube waves along vertically oriented thin magnetic fluxes tubes
embedded in the atmospheres of theoretical main-sequence stars
based on stellar parameters deduced by Kurucz and Gray. In addition,
we present a fitting formula for the wave energy flux based on the
governing stellar and magnetic parameters.
Methods: A modified
theory of turbulence generation based on the mixing-length concept
is combined with the magneto-hydrodynamic equations to numerically
account for the wave energies generated at the base of magnetic flux
tubes.
Results: The results indicate a stiff dependence of
the generated wave energy on the stellar and magnetic parameters
in principal agreement with previous studies. The wave energy flux
FLTW decreases by about a factor of 1.7 between G0 V and
K0 V stars, but drops by almost two orders of magnitude between K0
V and M0 V stars. In addition, the values for FLTW are
significantly higher for lower in-tube magnetic field strengths. Both
results are consistent with the findings from previous studies.
Conclusions: Our study complements existing descriptions of magnetic
energy generation in late-type main-sequence stars. Our results will
be helpful for calculating theoretical atmospheric models for stars
of different levels of magnetic activity.
Title: On the ejection of Earth-mass planets from the habitable
zones of the solar twins HD 20782 and HD 188015
Authors: Yeager, K. E.; Eberle, J.; Cuntz, M.
Bibcode: 2011IJAsB..10....1Y
Altcode:
We provide a detailed statistical study of the ejection of fictitious
Earth-mass planets from the habitable zones of the solar twins HD 20782
and HD 188015. These systems possess a giant planet that crosses into
the stellar habitable zone, thus effectively thwarting the possibility
of habitable terrestrial planets. In the case of HD 188015, the orbit
of the giant planet is essentially circular, whereas in the case of HD
20782, it is extremely elliptical. As starting positions for the giant
planets, we consider both the apogee and perigee positions, whereas
the starting positions of the Earth-mass planets are widely varied. For
the giant planets, we consider models based on their minimum masses as
well as models where the masses are increased by 30%. Our simulations
indicate a large range of statistical properties concerning the ejection
of the Earth-mass planets from the stellar habitable zones. For example,
it is found that the ejection times for the Earth-mass planets from
the habitable zones of HD 20782 and HD 188015, originally placed at
the centre of the habitable zones, vary by a factor of ~200 and ~1500,
respectively, depending on the starting positions of the giant and
terrestrial planets. If the mass of the giant planet is increased
by 30%, the variation in ejection time for HD 188015 increases to a
factor of ~6000. However, the short survival times of any Earth-mass
planets in these systems are of no surprise. It is noteworthy, however,
that considerable differences in the survival times of the Earth-mass
planets are found, which may be relevant for establishing guidelines
of stability for systems with less intrusive giant planets.
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 Advection of Supergranules by the Sun's Axisymmetric Flows
Authors: Hathaway, David H.; Williams, Peter E.; Dela Rosa, Kevin;
Cuntz, Manfred
Bibcode: 2010ApJ...725.1082H
Altcode: 2010arXiv1008.4385H
We show that the motions of supergranules are consistent with a model
in which they are simply advected by the axisymmetric flows in the
Sun's surface shear layer. We produce a 10 day series of simulated
Doppler images at a 15 minute cadence that reproduces most spatial
and temporal characteristics seen in the SOHO/MDI Doppler data. Our
simulated data have a spectrum of cellular flows with just two
components—a granule component that peaks at spherical wavenumbers
of about 4000 and a supergranule component that peaks at wavenumbers
of about 110. We include the advection of these cellular components
by the axisymmetric flows—differential rotation and meridional
flow—whose variations with latitude and depth (wavenumber) are
consistent with observations. We mimic the evolution of the cellular
pattern by introducing random variations to the phases of the spectral
components at rates that reproduce the levels of cross-correlation as
functions of time and latitude. Our simulated data do not include any
wave-like characteristics for the supergranules yet can reproduce the
rotation characteristics previously attributed to wave-like behavior. We
find rotation rates which appear faster than the actual rotation rates
and attribute this to projection effects. We find that the measured
meridional flow does accurately represent the actual flow and that
the observations indicate poleward flow to 65°-70° latitude with
equatorward countercells in the polar regions.
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: Stellar Imager (SI): developing and testing a predictive
dynamo model for the Sun by imaging other stars
Authors: Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska,
Margarita; Kraemer, Steve; Lyon, Richard; Mozurkewich, David;
Airapetian, Vladimir; Adams, John C.; Allen, Ronald J.; Brown, Alex;
Bruhweiler, Fred; Conti, Alberto; Christensen-Dalsgaard, Joergen;
Cranmer, Steve; Cuntz, Manfred; Danchi, William; Dupree, Andrea; Elvis,
Martin; Evans, Nancy; Giampapa, Mark; Harper, Graham; Hartman, Kathy;
Labeyrie, Antoine; Leitner, Jesse; Lillie, Chuck; Linsky, Jeffrey L.;
Lo, Amy; Mighell, Ken; Miller, David; Noecker, Charlie; Parrish, Joe;
Phillips, Jim; Rimmele, Thomas; Saar, Steve; Sasselov, Dimitar; Stahl,
H. Philip; Stoneking, Eric; Strassmeier, Klaus; Walter, Frederick;
Windhorst, Rogier; Woodgate, Bruce; Woodruff, Robert
Bibcode: 2010arXiv1011.5214C
Altcode:
The Stellar Imager mission concept is a space-based UV/Optical
interferometer designed to resolve surface magnetic activity and
subsurface structure and flows of a population of Sun-like stars,
in order to accelerate the development and validation of a predictive
dynamo model for the Sun and enable accurate long-term forecasting of
solar/stellar magnetic activity.
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: On the Reality of the Suggested Planet in the ν Octantis
System
Authors: Eberle, J.; Cuntz, M.
Bibcode: 2010ApJ...721L.168E
Altcode:
The aim of this study is to explore an enigmatic finding about the
ν Octantis binary system that indicates the possible existence of a
Jupiter-type planet even though the planet seems to be located outside
the zone of orbital stability. We perform a detailed analysis of
orbital stability based on previous studies that carefully considers
the ν Octantis system parameters including their observationally
deduced uncertainties. In our analysis, we confront the probability
distribution of the parameter space of the system with the requirements
of planetary orbital stability. Our results indicate that the suggested
planet, if in a prograde orbit with respect to the motion of the
binary components, is virtually impossible. However, the estimated
probability of existence for a planet in a retrograde orbit is nearly
60%, an estimate that encapsulates the probability distribution of
the mass ratio of the stellar components. This estimate increases
if a relatively low stellar mass ratio (within the error bars) is
assumed. The principal possibility of a planet in a retrograde orbit is
also consistent with long-term orbital stability simulations pursued
as part of our study. Thus, the existence of the suggested planet in
the ν Octantis system constitutes a realistic possibility.
Title: The instability transition for the restricted 3-body
problem. II. The hodograph eccentricity criterion
Authors: Eberle, J.; Cuntz, M.
Bibcode: 2010A&A...514A..19E
Altcode:
Aims: We present a new method that allows identifying the
onset of orbital instability, as well as quasi-periodicity and
multi-periodicity, for planets in binary systems. This method is
given for the special case of the circular restricted 3-body problem
(CR3BP).
Methods: Our method relies on an approach given by
differential geometry that analyzes the curvature of the planetary
orbit in the synodic coordinate system. The centerpiece of the method
consists in inspecting the effective (instantaneous) eccentricity of the
orbit based on the hodograph in rotated coordinates and in calculating
the mean and median values of the eccentricity distribution.
Results: Orbital stability and instability can be mapped by numerically
inspecting the hodograph and/or the effective eccentricity of the
orbit in the synodic coordinate system. The behavior of the system
depends solely on the mass ratio μ of the binary components and
the initial distance ratio ρ_0 of the planet relative to the stellar
separation distance noting that the stellar components move on circular
orbits. Our study indicates that orbital instability occurs when the
median of the effective eccentricity distribution exceeds unity. This
instability criterion can be compared to other criteria, including
those based on Jacobi's integral and the zero-velocity contour of the
planetary orbit.
Conclusions: The method can be used during
detailed numerical simulations and in contrast to other methods such as
methods based on the Lyapunov exponent does not require a piece-wise
secondary integration of the planetary orbit. Although the method has
been deduced for the CR3BP, it is likely that it can be expanded to
more general cases.
Title: Biological damage due to photospheric, chromospheric and
flare radiation in the environments of main-sequence stars
Authors: Cuntz, Manfred; Guinan, Edward F.; Kurucz, Robert L.
Bibcode: 2010IAUS..264..419C
Altcode: 2009arXiv0911.1982C
We explore the biological damage initiated in the environments of F, G,
K, and M-type main-sequence stars due to photospheric, chromospheric
and flare radiation. The amount of chromospheric radiation is, in
a statistical sense, directly coupled to the stellar age as well
as the presence of significant stellar magnetic fields and dynamo
activity. With respect to photospheric radiation, we also consider
detailed synthetic models, taking into account millions or hundred of
millions of lines for atoms and molecules. Chromospheric UV radiation is
increased in young stars in regard to all stellar spectral types. Flare
activity is most pronounced in K and M-type stars, which also has the
potential of stripping the planetary atmospheres of close-in planets,
including planets located in the stellar habitable zone. For our
studies, we take DNA as a proxy for carbon-based macromolecules,
guided by the paradigm that carbon might constitute the biochemical
centerpiece of extraterrestrial life forms. Planetary atmospheric
attenuation is considered in an approximate manner.
Title: Astrobiology in the Environments of Main-Sequence Stars:
Effects of Photospheric Radiation
Authors: Cuntz, M.; Gurdemir, L.; Guinan, E. F.; Kurucz, R. L.
Bibcode: 2009ASPC..420..253C
Altcode: 2007arXiv0712.3260C
We explore if carbon-based macromolecules (such as DNA) in the
environments of stars other than the Sun are able to survive the effects
of photospheric stellar radiation, such as UV-C. Therefore, we focus
on main-sequence stars of spectral types F, G, K, and M. Emphasis
is placed on investigating the radiative environment in the stellar
habitable zones. Stellar habitable zones are relevant to astrobiology
because they constitute circumstellar regions in which a planet of
suitable size can maintain surface temperatures for water to exist in
fluid form, thus increasing the likelihood of Earth-type life.
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 Advection of Supergranules by Large-Scale Flows
Authors: Hathaway, D. H.; Williams, P. E.; Cuntz, M.
Bibcode: 2009ASPC..416..495H
Altcode: 2010arXiv1003.4210H
We produce a 10-day series of simulated Doppler images at a 15-minute
cadence that reproduces the spatial and temporal characteristics seen
in the SoHO/MDI Doppler data. Our simulated data contains a spectrum
of cellular flows with but two necessary components—a granule
component that peaks at wavenumbers of about 4000 and a supergranule
component that peaks at wavenumbers of about 110. We include the
advection of these cellular components by a differential rotation
profile that depends on latitude and wavenumber (depth). We further
mimic the evolution of the cellular pattern by introducing random
variations to the amplitudes and phases of the spectral components at
rates that reproduce the level of cross-correlation as a function of
time and latitude. Our simulated data do not include any wave-like
characteristics for the supergranules yet can accurately reproduce
the rotation characteristics previously attributed to wave-like
characteristics.
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: A method for the treatment of supergranulation advection by
giant cells
Authors: Williams, P. E.; Cuntz, M.
Bibcode: 2009A&A...505.1265W
Altcode:
Aims: We present a new method for the treatment of the advection of
solar supergranulation by giant cells, a large-scale analogue to
the observed property of granule advection by supergranules.
Methods: The proposed method is derived from a description of
solar convection via spherical harmonics and spectral coefficients,
allowing the investigation of the influence of a giant cell component
on a realistic supergranule signal.
Results: We show that a
supergranule pattern derived from real data, as well as a simplified
test signal, can be advected by a giant cell component of various
sizes.
Conclusions: The identified behaviour is in analogy to
observed supergranulation patterns, including those based on MDI
Dopplergrams, which show wavelike supergranulation patterns, even
after the removal of the geometric projection effect. Our method is
an important step towards the construction of future models involving
supergranule flow patterns advected by a giant cell flow. Nevertheless,
additional efforts are required to obtain a final verification of giant
cells as a separate component of the solar photospheric convection
spectrum. New address: NASA Goddard Space Flight Center,
Greenbelt, MD 20771, USA.
Title: Habitability of Super-Earth Planets Around Other Suns: Models
Including Red Giant Branch Evolution
Authors: von Bloh, W.; Cuntz, M.; Schröder, K. -P.; Bounama, C.;
Franck, S.
Bibcode: 2009AsBio...9..593V
Altcode: 2008arXiv0812.1027V
The unexpected diversity of exoplanets includes a growing number of
super-Earth planets, i.e., exoplanets with masses of up to several
Earth masses and a similar chemical and mineralogical composition as
Earth. We present a thermal evolution model for a 10 Earth-mass planet
orbiting a star like the Sun. Our model is based on the integrated
system approach, which describes the photosynthetic biomass production
and takes into account a variety of climatological, biogeochemical,
and geodynamical processes. This allows us to identify a so-called
photosynthesis-sustaining habitable zone (pHZ), as determined by the
limits of biological productivity on the planetary surface. Our model
considers solar evolution during the main-sequence stage and along the
Red Giant Branch as described by the most recent solar model. We obtain
a large set of solutions consistent with the principal possibility
of life. The highest likelihood of habitability is found for "water
worlds." Only mass-rich water worlds are able to realize pHZ-type
habitability beyond the stellar main sequence on the Red Giant Branch.
Title: On the Validity of the "Hill Radius Criterion" for the Ejection
of Planets from Stellar Habitable Zones
Authors: Cuntz, M.; Yeager, K. E.
Bibcode: 2009ApJ...697L..86C
Altcode:
We challenge the customary assumption that the entering of an Earth-mass
planet into the Hill radius (or multiples of the Hill radius) of a
giant planet is a valid criterion for its ejection from the star-planet
system. This assumption has widely been used in previous studies,
especially those with an astrobiological focus. As intriguing examples,
we explore the dynamics of the systems HD 20782 and HD 188015. Each
system possesses a giant planet that remains in or crosses into the
stellar habitable zone, thus effectively thwarting the possibility of
habitable terrestrial planets. In the case of HD 188015, the orbit of
the giant planet is almost circular, whereas in the case of HD 20782,
it is extremely elliptical. Although it is found that Earth-mass planets
are eventually ejected from the habitable zones of these systems, the
"Hill Radius Criterion" is identified as invalid for the prediction
of when the ejection is actually occurring.
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: Habitability of super-Earths: Gliese 581c & 581d
Authors: von Bloh, W.; Bounama, C.; Cuntz, M.; Franck, S.
Bibcode: 2008IAUS..249..503V
Altcode: 2007arXiv0712.3219V; 2007IAUS..249..503V
The unexpected diversity of exoplanets includes a growing number of
super-Earth planets, i.e., exoplanets with masses smaller than 10 Earth
masses. Unlike the larger exoplanets previously found, these smaller
planets are more likely to have similar chemical and mineralogical
composition to the Earth. We present a thermal evolution model for
super-Earth planets to identify the sources and sinks of atmospheric
carbon dioxide. The photosynthesis-sustaining habitable zone (pHZ) is
determined by the limits of biological productivity on the planetary
surface. We apply our model to calculate the habitability of the two
super-Earths in the Gliese 581 system. The super-Earth Gl 581c is
clearly outside the pHZ, while Gl 581d is at the outer edge of the
pHZ. Therefore, it could at least harbor some primitive forms of life.
Title: First observation of planet-induced X-ray emission: The system
HD 179949
Authors: Saar, S. H.; Cuntz, M.; Kashyap, V. L.; Hall, J. C.
Bibcode: 2008IAUS..249...79S
Altcode: 2007IAUS..249...79S; 2007arXiv0712.3270S
We present the first observation of planet-induced stellar X-ray
activity, identified for the HD 179949 system, using Chandra /
ACIS-S. The HD 179949 system consists of a close-in giant planet
orbiting an F9 V star. Previous ground-based observations already showed
enhancements in Ca II K in phase with the planetary orbit. We find an
30% increase in the X-ray flux over quiescent levels coincident with the
phase of the Ca II enhancements. There is also a trend for the emission
to be hotter at increased fluxes, confirmed by modeling, showing the
enhancement at 1 keV compared to 0.4 keV for the background star.
Title: Astrobiological effects of F, G, K and M main-sequence stars
Authors: Cuntz, M.; Gurdemir, L.; Guinan, E. F.; Kurucz, R. L.
Bibcode: 2008IAUS..249..203C
Altcode: 2007arXiv0712.3257C; 2007IAUS..249..203C
We focus on the astrobiological effects of photospheric radiation
produced by main-sequence stars of spectral types F, G, K, and M. The
photospheric radiation is represented by using realistic spectra, taking
into account millions or hundred of millions of lines for atoms and
molecules. DNA is taken as a proxy for carbon-based macromolecules,
assumed to be the chemical centerpiece of extraterrestrial life
forms. Emphasis is placed on the investigation of the radiative
environment in conservative as well as generalized habitable zones.
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: The habitability of super-Earths
Authors: von Bloh, W.; Bounama, C.; Cuntz, M.; Franck, S.
Bibcode: 2008EAS....33..275V
Altcode:
The unexpected diversity of exoplanets includes a growing number of
super Earth-planets, i.e. exoplanets with masses smaller than 10
Earth masses and a similar chemical and mineralogical composition
like Earth. We present a thermal evolution model for a super-Earth to
calculate the sources and sinks of atmospheric carbon dioxide. The
photosynthesis-sustaining habitable zone (pHZ) is determined by the
limits of biological productivity on the planetary surface. We apply the
model to calculate the habitability of super-Earths in Gliese 581. The
super-Earth Gl 581c is clearly outside the pHZ while Gl 581d at the
outer edge of the pHZ could at least harbor some primitive life forms.
Title: The habitability of super-Earths in Gliese 581
Authors: von Bloh, W.; Bounama, C.; Cuntz, M.; Franck, S.
Bibcode: 2007A&A...476.1365V
Altcode: 2007arXiv0705.3758V
Aims:The planetary system around the M star Gliese 581 consists of a
hot Neptune (Gl 581b) and two super-Earths (Gl 581c and Gl 581d). The
habitability of this system with respect to the super-Earths is
investigated following a concept that studies the long-term possibility
of photosynthetic biomass production on a dynamically active planet.
Methods: A thermal evolution model for a super-Earth is used to
calculate the sources and sinks of atmospheric carbon dioxide. The
habitable zone is determined by the limits of photosynthetic life on the
planetary surface. Models with different ratios of land / ocean coverage
are investigated.
Results: The super-Earth Gl 581c is clearly
outside the habitable zone, since it is too close to the star. In
contrast, Gl 581d is a tidally locked habitable super-Earth near the
outer edge of the habitable zone. Despite the adverse conditions on this
planet, at least some primitive forms of life may be able to exist on
its surface. Therefore, Gl 581d is an interesting target for the planned
TPF/Darwin missions to search for biomarkers in planetary atmospheres.
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: Solar Rossby Wave ``Hills'' Identified as Supergranules
Authors: Williams, P. E.; Hathaway, D. H.; Cuntz, M.
Bibcode: 2007ApJ...662L.135W
Altcode:
We explore the nature of ``hills'' observed on the solar surface
that had previously been attributed to Rossby waves. We investigate
the solar hills phenomenon by analyzing the output from a synthetic
model based solely on the observed solar photospheric convection
spectrum. We show that the characteristics of these hills can be
explained by the corrugation of the surface produced by the radial
flows of the convection. The hills in our simulations are dominated
by supergranules, a well-known component of solar convection. Rossby
waves have been predicted to exist within the Sun and may play an
important role in the dynamics of the solar interior, including the
Sun's differential rotation and magnetic dynamo. Our study suggests,
however, that the hills observed at the solar limb do not confirm the
existence of solar Rossby waves.
Title: A critical test of empirical mass loss formulas applied to
individual giants and supergiants
Authors: Schröder, K. -P.; Cuntz, M.
Bibcode: 2007A&A...465..593S
Altcode: 2007astro.ph..2172S
To test our new, improved Reimers-type mass-loss relation, given by
Schröder & Cuntz in 2005 (ApJ, 630, L73), we take a look at the
best studied galactic giants and supergiants - particularly those with
spatially resolved circumstellar shells and winds, obtained directly
or by means of a companion acting as a probing light source. Together
with well-known physical parameters, the selected stars provide the
most powerful and critical observational venues for assessing the
validity of parameterized mass-loss relations for cool winds not
driven by molecules or dust. In this study, star by star, we compare
our previously published relation with the original Reimers relation
(1975, Mem. Roy. Soc. Liège 6. Ser. 8, 369), the Lamers relation
(1981, ApJ, 245, 593), and the two relations by de Jager and his group
(1988, A&AS, 72, 259; 1990, A&A, 231, 134). The input data,
especially the stellar masses, have been constrained using detailed
stellar evolution models. We find that only the relationship by
Schröder & Cuntz agrees, within the error bars, with the observed
mass-loss rates for all giants and supergiants.
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: Living with a dM Star: Evolution over Time of Dynamo: Generated
X-ray UV Emissions and Effects on Hosted Planets
Authors: Guinan, Edward F.; Engle, S. G.; DeWarf, L. E.;
Schulze-Makuch, D.; Cuntz, M.; Zellem, R. T.; Pettiford, V.
Bibcode: 2006AAS...209.0604G
Altcode: 2006BAAS...38..901G
We report on a multi-frequency study of dM stars with ages from <30
Myr to 13 Gyr. The goals are to understand the magnetic activity,
coronal physics, and XUV spectral irradiances of dM stars with
widely different rotations, ages, and widely different levels of
XUV emissions. Because of the large number of dM stars (>70% of
all stars), and their very long lifetimes, there should be numerous
dM stars hosting planets. Thus dM stars are attractive targets of
extrasolar planet search missions such as COROT, Kepler, SIM, and
Darwin/TPF. The habitable zones (HZs) around dM stars are close to the
host star (HZ 0.05-0.40 AU) making the hypothetical HZ planet strongly
influenced by stellar flares, winds, and plasma ejection events that are
frequent in dM stars. Also, with the long-lifetimes of dM-stars of >
20-Gyr, it might be possible for life on a HZ-planet to be much more
evolved than ourselves. Of particular interest is the determination
of XUV emission flux evolution with time. This is because of the
critical roles that XUV coronal and chromospheric emissions play in
the photoionization and photochemical evolution (and possible erosion)
of planetary atmospheres and ionospheres. We have used ROSAT, ASCA, XMM
and Chandra X-ray observations and combined these with EUV, and FUV-UV
data (from EUVE, FUSE and IUE or HST) to form XUV spectral irradiance
tables of dM stars covering a wide range of ages and XUV fluxes. These
results are critical to the studies of XUV radiation of dM-stars and
its effects on the environments of possible hosted extrasolar planets
and on the possible origin and evolution of extraterrestrial life on
such planets. The initial results of this study will be presented and
discussed. This research is supported by grants from NASA/FUSE
and NSF which we gratefully acknowledge.
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: Supergranules -- The True Nature of Solar Rossby Hills?
Authors: Williams, Peter; Cuntz, Manfred; Hathaway, David
Bibcode: 2006APS..TSF.P1002W
Altcode:
Supergranulation is a well established component of solar convection
and visible on the solar surface as cellular structures. The convective
upflow within a supergranule cell overshoots the equilibrium solar
surface creating a corrugated surface. The hills associated with these
upflows have been detected as they pass over the solar limb. Their
discovery was initially attributed to Rossby waves, arising from r-mode
oscillations in the Sun where the Coriolis force acts as a restoring
force on internal gravity waves. We analyze these hills by producing an
artificial height map derived from the radial component of supergranule
Doppler velocity data constructed from the spectral components of a
synthetic photospheric convection spectrum. We are able to show that
the observed signals leading to the detection of these solar hills can
be modeled by applying the same methods that lead to the Rossby wave
`discovery', prompting the conclusion that the corrugation has its
origins in supergranulation.
Title: Rossby 'Hills' Identified as Supergranule Manifestations
Authors: Williams, Peter E.; Hathaway, D. H.; Cuntz, M.
Bibcode: 2006SPD....37.3002W
Altcode: 2006BAAS...38S.256W
Rossby waves have been well established as oceanographic and atmospheric
features on Earth in which the Coriolis force acts as a restoring force
on internal gravity waves. Rossby waves have also been predicted to
exist as "r-mode oscillations" on rotating stars and the Sun. Recently,
reports have claimed that such phenomena exist as low amplitude,
long wavelength features - "hills" - on the surface of the Sun by
analyzing spatial and temporal signatures of the solar limb from the MDI
instrument on SOHO. We have used simulated data to conduct a similar
analysis of the limb and discovered that the reported signatures can
be obtained by considering only the supergranule convection pattern.
Title: Supergranule Superrotation Identified as a Projection Effect
Authors: Hathaway, D. H.; Williams, P. E.; Cuntz, M.
Bibcode: 2006ApJ...644..598H
Altcode:
Previous measurements of the rotation rate of the supergranule
Doppler velocity pattern revealed surprising characteristics: (1) the
pattern rotates faster than the plasma at the surface, and, at each
latitude, it rotates faster than the plasma at any level below the
surface (superrotation), (2) larger cells rotate more rapidly than
smaller cells, and (3) faster rotation rates are found when using
cross-correlation techniques with larger time lags between Doppler
images. We simulate the supergranulation velocity pattern using a
spectrum for the cellular flows that matches the observed spectrum,
but we keep the pattern unchanged and rotating rigidly. Our simulation
shows that the superrotation and its dependence on cell size can be
largely reproduced by projection effects on the line-of-sight Doppler
velocity signal. The remaining variation in rotation rate with cell
size can be attributed to cells smaller than supergranules extending
through shallower layers that have slower rotation rates.
Title: The Supergranule Super-Rotation Illusion
Authors: Hathaway, David H.; Williams, P.; Cuntz, M.
Bibcode: 2006SPD....37.3001H
Altcode: 2006BAAS...38..256H
Peculiar aspects of the rotation rate of the supergranules have been
noted for over 20 years now. This has culminated in recent reports
suggesting that the supergranules have wave-like characteristics and
propagate prograde at a rate that exceeds that of the plasma anywhere
below the surface. We have simulated supergranules that rotate at a rate
that is independent of position or size and find that they appear to
rotate at a more rapid rate. This super-rotation of the supergranules
is seen in both cross-correlation and Fourier analyses of the Doppler
velocity pattern. The amplitude of the rotation excess as a function of
size matches that seen in the Fourier analyses of MDI data. The source
of this rotation excess is identified with the effect of projecting
velocity signals into the line-of-sight. We conclude that supergranules
are merely advected by the flow in the near-surface shear layer and that
their apparent super-rotation does not indicate wave-like properties.
Title: Life without Carbon?
Authors: Cuntz, Manfred; Williams, Peter E.
Bibcode: 2006Mercu..35c..12C
Altcode:
Carbon is the centerpiece of all life on Earth and one of the
most abundant elements in the Solar System and Sun-like stars. Yet
alien biochemistries and one's choice of a definition of life offer
possibility for other forms of life.
Title: Solar Coronal Plumes: Theoretical Concepts and Results
Authors: Cuntz, Manfred
Bibcode: 2006aogs....2...21C
Altcode:
In the following, I describe the status of theoretical research on
solar coronal plumes. Emphasis is placed on the relevance of slow
magnetosonic waves, considering results from 1D, 2D, and analytical
magnetohydrodynamic models, in addition to results from empirical models
and observations. Theoretical models, taking into account the combined
effects of plume spreading, heat conduction, and radiative damping,
have shown that the waves nonlinearly steepen as they propagate,
resulting in the formation of shocks at relatively low coronal
heights. Consequently, slow magnetosonic waves are relevant for the
energy budget at most heights, even though they do not constitute a
solely operating energy supply mechanism.
Title: A New Version of Reimers' Law of Mass Loss Based on a Physical
Approach
Authors: Schröder, K. -P.; Cuntz, M.
Bibcode: 2005ApJ...630L..73S
Altcode: 2005astro.ph..7598S
We present a new semiempirical relation for the mass loss of cool
stellar winds, which so far has frequently been described by ``Reimers'
law.'' Originally, this relation was based solely on dimensional scaling
arguments without any physical interpretation. In our approach, the wind
is assumed to result from the spillover of the extended chromosphere,
possibly associated with the action of waves, especially Alfvén waves,
which are used as guidance in the derivation of the new formula. We
obtain a relation akin to the original Reimers law, but which includes
two new factors. They reflect how the chromospheric height depends
on gravity and how the mechanical energy flux depends, mainly, on
the effective temperature. The new relation is tested and sensitively
calibrated by modeling the blue end of the horizontal branch of globular
clusters. The most significant difference from mass-loss rates predicted
by the Reimers relation is an increase by up to a factor of 3 for
luminous late-type (super)giants, in good agreement with observations.
Title: Definition and significance of average temperatures in
time-dependent solar chromosphere models
Authors: Rammacher, W.; Cuntz, M.
Bibcode: 2005A&A...438..721R
Altcode:
We assess different types of average temperatures in time-dependent
solar chromosphere models. They include the conventional definition
of mean and median temperature, and a formal definition related to the
model-dependent hydrogen ionization degree, referred to as ionization
temperature. It is found that the latter is always higher than the
mean and median temperatures, except in the photosphere, and that the
mean temperatures are always higher than the median temperatures,
especially in models with frequency spectra. The most dramatic
differences are attained in the topmost portion of one of our models
with the ionization temperatures up to a factor 150 higher than the
mean and median temperatures. The differences between the mean, median,
and ionization temperatures are a direct consequence of nonlinearities
(“spikyness”) of the temperatures in the models mostly due to strong
shocks. The main results hold for both acoustic and magnetic models
despite significant differences in the initial wave energy fluxes,
densities, and geometrical settings.
Title: 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: Time-dependent ionization in solar magnetic flux tubes
Authors: Rammacher, W.; Cuntz, M.
Bibcode: 2005ESASP.560..891R
Altcode: 2005csss...13..891R
No abstract at ADS
Title: Exploring the use of VO to diagnose spot properties on M dwarfs
Authors: O'Neal, D.; Saar, S. H.; Neff, J. E.; Cuntz, M.
Bibcode: 2005ESASP.560..853O
Altcode: 2005csss...13..853O
No abstract at ADS
Title: Habitability and Stability of Orbits for Earth-Like Planets
in the Extrasolar System 47 UMa
Authors: Franck, Siegfried; von Bloh, Werner; Bounama, Christine;
Cuntz, Manfred
Bibcode: 2004ASPC..316..149F
Altcode:
No abstract at ADS
Title: Further Results of TiO-Band Observations of Starspots
Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H.; Cuntz,
Manfred
Bibcode: 2004AJ....128.1802O
Altcode:
We present measurements of starspot parameters (temperature and filling
factor) on five highly active stars, using absorption bands of TiO, from
observations made between 1998 March and 2001 December. We determined
starspot parameters by fitting TiO bands using spectra of inactive G and
K stars as proxies for the unspotted photospheres of the active stars
and spectra of M stars as proxies for the spots. For three evolved
RS CVn systems, we find spot filling factors between 0.28 and 0.42
for DM UMa, 0.22 and 0.40 for IN Vir, and 0.31 and 0.35 for XX Tri;
these values are similar to those found by other investigators using
photometry and Doppler imaging. Among active dwarfs, we measured a lower
spot temperature (3350 K) for EQ Vir than found in a previous study of
TiO bands, and for EK Dra a lower spot temperature (~3800 K) than found
through photometry. For all active stars but XX Tri, we achieved good
phase coverage through a stellar rotational period. We also present
our final, extensive grid of spot and nonspot proxy stars. This
paper includes data taken at McDonald Observatory of the University
of Texas at Austin.
Title: Properties of longitudinal flux tube waves. III. Wave
propagation in solar and stellar wind flows
Authors: Cuntz, M.; Suess, S. T.
Bibcode: 2004A&A...424.1003C
Altcode:
We discuss the analytic properties of longitudinal tube waves taking
into account ambient wind flows. This is an extension of the studies
of Papers I and II, which assumed a mean flow speed of zero and also
dealt with a simplified horizontal pressure balance. Applications
include the study of longitudinal flux tube waves in stars with
significant mass loss and the heating and dynamics of plumes in the
solar wind. Slow magnetosonic waves, also called longitudinal waves,
have been observed in solar plumes and are likely an important source of
heating. We show that the inclusion of ambient wind flows considerably
alters the limiting shock strength as well as the energy damping length
of the waves.
Title: Properties of longitudinal flux tube waves. II. Limiting
shock strength behavior
Authors: Cuntz, M.
Bibcode: 2004A&A...420..699C
Altcode:
We extend our previous work on analytic evaluations of properties
of longitudinal tube waves to waves propagating in gravitational
atmospheres. We derive an expression for the limiting shock strength
and discuss the behavior of the shock strength in tubes of different
geometry. It is found that a height-independent value for the
limiting strength is attained for constant cross-section tubes and
exponential tubes, whereas for wine-glass tubes the limiting shock
strength increases with height due to the increase of the tube
cross section. The limiting shock strength is well reproduced by
time-dependent simulations. The derived limiting shock strength as
well as the energy dissipation rate of the waves show significant
similarities to acoustic waves. The limiting shock strength allows
to estimate the heating potential of waves in the absence of detailed
time-dependent computations.
Title: Dynamical Habitability in the Extrasolar Planetary Systems
47 UMa and 55 Cnc
Authors: Franck, S.; Bounama, C.; von Bloh, W.; Cuntz, M.
Bibcode: 2004DDA....35.0101F
Altcode: 2004BAAS...36..849F
We investigate whether Earth-like planets could on principle exist
on stable orbits in the habitable zone of extrasolar planetary
systems. Such a configuration is described as dynamically habitable. Our
definition of habitability does not just depend on the parameters of
the central star, but also on the properties of the planetary climate
model. In particular, habitability is linked to the photosynthetic
activity of the planet, which in turn depends on the planetary
atmospheric carbon dioxide concentration, and is thus strongly
influenced by the planetary geodynamics. This leads to additional
spatial and temporal limitations of habitability, as the HZ becomes
narrower with time due to the persistent decrease of the planetary
carbon dioxide concentration. To estimate the orbital stability
of hypothetical terrestrial planets, recent studies investigating
the effects of the giant planets in such systems, have been taken
into account. The system 47 UMa has been identified to host two
Jupiter-mass planets at respectable distances from the host star,
which has properties very similar to those of our Sun, including
mass, effective temperature, spectral type, and metallicity. The star
55 Cnc has an outer planetary companion orbiting at about Jupiter
distance and two inner giant planets at very small orbits. We show
that the existence of a dynamically habitable Earth-like planet is
principally possible in both systems (Cuntz et al. 2003, von Bloh et
al. 2003). This likelihood depends critically on the percentage of the
planetary land/ocean coverage (Franck et al. 2003) and is significantly
increased for planets with a high percentage of ocean surface (water
worlds). Cuntz, M., von Bloh, W., Bounama, C., and Franck,
S. 2003. Icarus 162, 214. Franck, S., Cuntz, M., von Bloh, W.,
and Bounama, C. 2003. Int. J. Astrobiology 2(1), 35. Von Bloh,
W., Cuntz, M., Franck, S., and Bounama, C. 2003. Astrobiology 3(4), 681.
Title: Coronal X-Ray Spectroscopy of Solar Analogs
Authors: Telleschi, A.; Güdel, M.; Arzner, K.; Briggs, K.; Audard,
M.; Ness, J. -U.; Mewe, R.; Raassen, A. J.; Skinner, S. L.; Cuntz,
M.; Saar, S.
Bibcode: 2004IAUS..219..930T
Altcode: 2003IAUS..219E.203T
We present an X-ray study of a series of solar-mass main-sequence stars
with different ages based on data from XMM-Newton and Chandra. This
investigation aims at a closer understanding of the physical mechanisms
of heating and mass transport in magnetically active stars. All targets
are proxies of the Sun that essentially differ only in their rotation
periods and hence in the efficiency of the magnetic dynamo. We present
a spectral analysis that constrains the average elemental composition
and the thermal structure of the coronae at different stages of
their evolution. Further we use the He-like line triplets to derive
characteristic coronal densities and investigate the time variability
in the X-ray light curves. We discuss implications for models related
to heating physics and coronal structure.
Title: Stellar Activity Enhancement by Planets: Theory and
Observations
Authors: Saar, S. H.; Cuntz, M.; Shkolnik, E.
Bibcode: 2004IAUS..219..355S
Altcode: 2003IAUS..219E.119S
Many of the newly discovered exoplanets are apparently gas giants
in close proximity to their parent stars. They therefore raise
tides on their host stars and (if similar to Jupiter) will likely
have substantial magnetospheres which can interact with stellar
fields. Both tidal and magnetospheric interactions can enhance
stellar activity levels. An initial search for such planet-induced
activity using the Ca II IR triplet found no signal but recently
a more sensitive study using the Ca II H and K lines has uncovered
evidence for planet-enhanced emission on HD 179949 and hints of it
in other systems. The phase dependence of the enhanced emission for
HD 179949 suggests a magnetospheric interaction. We discuss a simple
model for this interaction the implications of this possible detection
for diagnosing exoplanetary magnetospheres and future observations.
Title: On the Possibility of Earth-Type Habitable Planets in the 55
Cancri System
Authors: von Bloh, W.; Cuntz, M.; Franck, S.; Bounama, C.
Bibcode: 2003AsBio...3..681V
Altcode:
We discuss the possibility of Earth-type planets in the planetary
system of 55 Cancri, a nearby G8 V star, which is host to two, possibly
three, giant planets. We argue that Earth-type planets around 55 Cancri
are in principle possible. Several conditions are necessary. First,
Earth-type planets must have formed despite the existence of the
close-in giant planet(s). In addition, they must be orbitally stable
in the region of habitability considering that the stellar habitable
zone is relatively close to the star compared to the Sun because of 55
Cancri's low luminosity and may therefore be affected by the close-in
giant planet(s). We estimate the likelihood of Earth-type planets
around 55 Cancri based on the integrated system approach previously
considered, which provides a way of assessing the long-term possibility
of photosynthetic biomass production under geodynamic conditions.
Title: Shock Formation and Energy Dissipation of Slow Magnetosonic
Waves in Coronal Plumes
Authors: Cuntz, M.; Suess, S. T.
Bibcode: 2003csss...12..624C
Altcode:
We study the shock formation and energy dissipation of slow
magnetosonic waves in coronal plumes. The wave parameters and the
spreading function of the plumes as well as the base magnetic field
strength are given by empirical constraints mostly from SOHO/UVCS. Our
models show that shock formation occurs at low coronal heights, i.e.,
within 1.3 R<SUB<⊙, depending on the model parameters. In
addition, following analytical estimates, we show that scale height
of energy dissipation by the shocks ranges between 0.15 and 0.45
R⊙. This implies that shock heating by slow magnetosonic
waves is relevant at most heights, even though this type of waves is
apparently not a solely operating energy supply mechanism.
Title: Acoustic Heating Models for the Basal Flux Star τ Ceti
Including Time-dependent Ionization: Results for Ca II and Mg
II Emission
Authors: Rammacher, W.; Cuntz, M.
Bibcode: 2003ApJ...594L..51R
Altcode:
We present new calculations of chromospheric heating for τ Ceti (G8
V), a star exhibiting an extremely low level of chromospheric activity,
thus also referred to as a basal flux star or a flat activity star. Our
simulations consider energy deposition by acoustic shocks and also
take into account time-dependent (i.e., noninstantaneous) ionization
processes of hydrogen, magnesium, and calcium, allowing us to attain a
new generation of chromospheric heating models previously obtained for
the Sun. We consider both monochromatic waves and acoustic frequency
spectra. The latter are calculated using new models of acoustic energy
generation based on an extended Kolmogorov spectrum with a modified
Gaussian frequency factor. Our models show that the theoretically
deduced emergent Ca II and Mg II emission very much agree with
observations, adding to the argument that the chromospheres of basal
flux stars are predominantly heated by acoustic shocks.
Title: On the possibility of earth-type habitable planets around
47 UMa
Authors: Cuntz, Manfred; von Bloh, Werner; Bounama, Christine;
Franck, Siegfried
Bibcode: 2003Icar..162..214C
Altcode:
We investigate whether Earth-type habitable planets can in principle
exist in the planetary system of 47 UMa. The system of 47 UMa
consists of two Jupiter-size planets beyond the outer edge of the
stellar habitable zone, and thus resembles our own Solar System most
closely compared to all exosolar planetary systems discovered so
far. Our study of habitability deliberately follows an Earth-based
view according to the concept of Franck and colleagues, which assumes
the long-term possibility of photosynthetic biomass production under
geodynamic conditions. Consequently, a broad variety of climatological,
biogeochemical, and geodynamical processes involved in the generation of
photosynthesis-driven life conditions is taken into account. The stellar
luminosity and the age of the star/planet system are of fundamental
importance for planetary habitability. Our study considers different
types of planetary continental growth models and takes into account a
careful assessment of the stellar parameters. In the event of successful
formation and orbital stability, two subjects of intense research, we
find that Earth-type habitable planets around 47 UMa are in principle
possible! The likelihood of those planets is increased if assumed that
47 UMa is relatively young (≲6 Gyr) and has a relatively small stellar
luminosity as permitted by the observational range of those parameters.
Title: The habitable zone of Earth-mass planets around 47 UMa:
results for land and water worlds
Authors: Franck, S.; Cuntz, M.; von Bloh, W.; Bounama, C.
Bibcode: 2003IJAsB...2...35F
Altcode:
In a previous paper, we showed that Earth-type habitable planets around
47 UMa are in principle possible if a distinct set of conditions is
warranted. These conditions include that the Earth-type planets have
successfully formed and are orbitally stable and, in addition, that
the 47 UMa star-planet system is relatively young ([less, similar]6
Gyr). We now extend this study by considering Earth-like planets
with different land/ocean coverages. This study is again based on the
so-called integrated system approach, which describes the photosynthetic
biomass production taking into account a variety of climatological,
biogeochemical and geodynamical processes. This approach implies a
special characterization of the habitable zone defined for a distinct
type of planet. We show that the likelihood of finding a habitable
Earth-like planet on a stable orbit around 47 UMa critically depends
on the percentage of the planetary land/ocean coverage. The likelihood
is significantly increased for planets with a very high percentage of
ocean surface ("water worlds").
Title: Can Earth-Type Habitable Planets Exist Around 47 UMa?
Authors: Cuntz, M.; von Bloh, W.; Bounama, C.; Franck, S.
Bibcode: 2003ASPC..294..221C
Altcode:
We explore whether the existence of Earth-type habitable planets is
in principle possible in the planetary system of 47 UMa. Our analysis
assumes that Earth-type planets have successfully formed and are
orbitally stable. Our study of habitability deliberately follows an
Earth-based view while investigating the long-term possibility of
photosynthetic biomass production. Here the stellar luminosity and
the age of star/planet system are of fundamental importance for the
existence of planetary habitability. We find that the likelihood of
Earth-type habitable planets is increased if assumed that 47 UMa is
relatively young (less than about 6 Gyr) and has a relatively small
stellar luminosity.
Title: The habitable zone of Earth-like planets around 47 UMa
Authors: von Bloh, Werner; Cuntz, Manfred; Bounama, Christine;
Franck, Siegfried
Bibcode: 2002ESASP.518..413V
Altcode: 2002eab..conf..413V
The system of 47 UMa consists of two Jupiter-size planets beyond
the outer edge of the stellar habitable zone, and thus resembles our
own Solar System rather closely. The habitability of this system for
Earth-like planets is investigated following a concept, which assumes
the long-term possibility of photosynthetic biomass production under
geodynamic conditions. In particular, the stellar luminosity and
the age of the star/planet system are of fundamental importance for
planetary habitability. Our study coniders different types of planetary
continental growth models. In ths event of successful formation, we
find that Earth-like habitable planets around 47 UMa are in principle
possible.
Title: Chromospheres, flares and exoplanets
Authors: Cuntz, M.; Shkolnik, E.
Bibcode: 2002AN....323..387C
Altcode:
An interesting and unexpected aspect of stars and planets is whether
close-in giant planets are able to noticeably increase chromospheric
and coronal emission. Cuntz, Saar & Musielak (2000) presented
theoretical evidence that this might indeed be the case. They
distinguished between gravitational (tidal) and magnetic interaction,
with the latter depending on the stellar and planetary magnetic field
strengths and the star-planet distance. Magnetic interaction should
manifest itself in increased activity, akin to well-known flaring events
between interacting RS CVn binaries, but at much smaller scales. It
should also result in an abundance of spots and plagues in the vicinity
of the sub-binary point. In the following, we summarize the status of
theoretical results and observational verifications.
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: 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: What can HST-GHRS Fe II observations of α Orionis (M2 Iab)
tell us about short-period heating?
Authors: Cuntz, M.; Harper, G. M.; Bennett, P. D.
Bibcode: 2001A&A...376..154C
Altcode:
Cuntz (\cite{Cuntz97}) suggested that apparent velocity shifts in Fe II
emission lines observed in Betelgeuse (alpha Orionis: M2 Iab) indicate
that non-magnetic wave modes are relevant for the heating and dynamics
of alpha Ori's chromosphere. This claim was based on the similarity
of computed stochastic velocities in 1-D short-period acoustic wave
models and velocity shifts in profile fits to Fe II emission lines
(Carpenter & Robinson \cite{Carpenter97}), which is now identified
as coincidental. While acoustic waves may indeed be important for the
heating and dynamics of alpha Ori's chromosphere, the interpretation
of the Fe II emission line profiles does not provide evidence for this
possibility. The line formation of optically thick scattering lines
in an extended outflow makes Fe II emission lines poorly suited as a
diagnostic for small-scale structure in hydrodynamical models. Better
diagnostics include electron density sensitive, low opacity lines
such as C II]. In the view of these findings, we discuss directions of
future research. Based on observations made with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555.
Title: A search for Ca II emission enhancement in stars resulting
from nearby giant planets
Authors: Saar, S. H.; Cuntz, M.
Bibcode: 2001MNRAS.325...55S
Altcode:
We present a search for periodicities (Pchr) in the
chromospheric Caii infrared triplet emission of several stars
(τ Boo, 51 Peg, υ And, ρ1 Cnc, ρ CrB, 70 Vir and
GL 876) which may be directly attributable to interaction with
close-in giant planets. Activity enhancements could arise from
increased non-radiative heating and dynamo action in planet-induced
tidal bulges (with Pchr~Porb/2), or from
interactions between the stellar and planetary magnetic fields (with
Pchr~Porb). We compare both Pchr
and the phase dependence of the activity with the planetary orbital
period Porb, the orbital phase, and models. No significant
Pchr or phase dependence attributable to planets can be
clearly identified. We place approximate upper limits on the amplitude
of any planet-induced activity. We identify a possible stellar rotation
period for GL 876, and support previous period determinations for
four other stars. We discuss the results and possible directions of
future research.
Title: Shock Formation of Slow Magnetosonic Waves in Coronal Plumes
Authors: Cuntz, Manfred; Suess, Steven T.
Bibcode: 2001ApJ...549L.143C
Altcode:
We investigate the height of shock formation in coronal plumes for
slow magnetosonic waves. The models take into account plume geometric
spreading, heat conduction, and radiative damping. The wave parameters
as well as the spreading functions of the plumes and the base magnetic
field strength are given by empirical constraints mostly from the Solar
and Heliospheric Observatory/Ultraviolet Coronagraph Spectrometer. Our
models show that shock formation occurs at low coronal heights, i.e.,
within 1.3 Rsolar, depending on the wave parameters. The
shock formation is calculated using the well-established wave-breaking
condition given by the intersection of C+ characteristics
in the space-time plane. Our models show that shock heating by slow
magnetosonic waves is expected to be relevant at most heights in solar
coronal plumes, although slow magnetosonic waves are most likely not
a solely operating energy supply mechanism.
Title: Understanding the Role of Binarity on Mass Loss and Atmospheric
Structure in Detached Systems (CD-ROM Directory: contribs/brown1)
Authors: Brown, A.; Harper, G.; Bennett, P. D.; Baade, R.; Kirsch,
T.; Schröder, K. -P.; Dumm, T.; Cuntz, M.
Bibcode: 2001ASPC..223..411B
Altcode: 2001csss...11..411B
No abstract at ADS
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: Experimental results from a grazing incidence x-ray
interferometer
Authors: Joy, Marshall K.; Shipley, Ann F.; Cash, Webster C.; Carter,
James M.; Zissa, David E.; Cuntz, Manfred
Bibcode: 2000SPIE.4012..270J
Altcode:
A prototype grazing incidence interferometer has been built and tested
at EUV and X-ray wavelengths using a 120 meter long vacuum test facility
at Marshall Space Flight Center. We describe the design and construction
of the interferometer, the EUV and x-ray sources and detector systems,
and compare the interferometric fringe measurements with theoretical
predictions.
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: Properties of longitudinal flux tube waves. I. Shock amplitude
relations
Authors: Cuntz, M.
Bibcode: 1999A&A...350.1100C
Altcode:
We derive relations between the pressure, density, magnetic field
strength, velocity, and other quantities across shocks for the
case of longitudinal tube waves. Due to the extreme coupling of the
Rankine-Hugoniot relations for this type of waves, these relationships
cannot be given separately as function of a given shock strength M_s,
contrary to the case of acoustic waves. In case of weak shocks, however,
those relationships can successfully be decoupled and evaluated. In
this paper, the analytic expansion for these amplitude relations are
given. We also compare our analytical results with numerical results
for shocks of small and moderately large strength. Comparisons are
given for cases with different values of plasma-beta .
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: Erratum: "A generalized version of the Rankine-Hugoniot
relations including ionization, dissociation, radiation and related
phenomena" [Astron. Astrophys., Vol. 280, No. 1, p. 195 - 200
(Dec 1993)].
Authors: Nieuwenhuijzen, H.; de Jager, C.; Cuntz, M.; Lobel, A.;
Achmad, L.
Bibcode: 1999A&A...343..661N
Altcode:
No abstract at ADS
Title: Two-Component Chromosphere Models: Observations versus
Simulations
Authors: Cuntz, M.
Bibcode: 1999ASPC..158..273C
Altcode: 1999ssa..conf..273C
No abstract at ADS
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: 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: The heating of solar magnetic flux tubes. I. Adiabatic
longitudinal tube waves
Authors: Fawzy, Diaa E.; Ulmschneider, P.; Cuntz, M.
Bibcode: 1998A&A...336.1029F
Altcode:
We study the formation of shocks and shock heating by adiabatic
longitudinal tube waves in solar magnetic flux tubes of different
shape. Monochromatic waves with periods between 20 and 160 s and
energy fluxes ranging from 1* 10(7) to 1* 10(9) erg cm(-2) s(-1) were
considered. It is found that the tube shape is of critical importance
for the heating of flux tubes. Constant cross-section tubes show
large heating, whereas exponentially spreading tubes show little or no
heating at all. In tubes of intermediate shapes (``wine-glass tubes"),
the heating is essentially restricted to those regions, where the tube
has attained its maximum diameter. This finding is in good agreement
with the observation that the chromospheric network can still be seen
well above the canopy height. In tubes of lower field strength, the
shock formation is delayed and heating is reduced.
Title: Basal Heating in Main-Sequence Stars and Giants: Results from
Monochromatic Acoustic Wave Models
Authors: Buchholz, Bernd; Ulmschneider, Peter; Cuntz, Manfred
Bibcode: 1998ApJ...494..700B
Altcode:
We calculate time-dependent models of acoustically heated chromospheres
for main-sequence stars between spectral type F0 V and M0 V and for
two giants of spectral type K0 III and K5 III assuming monochromatic
waves. The hydrodynamic equations are solved together with the radiative
transfer and statistical equilibrium equations to investigate the
propagation of acoustic waves into the chromospheric regions. The
emergent radiation in Mg II h + k and Ca II H + K is calculated and
compared with observations. We find good agreement, over nearly 2
orders of magnitude, between the time-averaged emission in these
lines and the observed basal flux emission, which had been suspected
to be due to nonmagnetic (i.e., acoustic) heating operating in all
late-type stars. The height dependence of the acoustic energy flux
can be explained by the limiting strength property of the acoustic
shocks and is consistent with that found in models of quiet solar
regions. We also confirm the validity of the Ayres scaling law,
which has originally been derived for semiempirical chromosphere
models and is thus independent of assumptions about the chromospheric
heating mechanism. Our results strongly support the idea that the
``basal heating'' of chromospheres of late-type stars as revealed
by the frequency-integrated Mg II and Ca II line emission is fully
attributable to the dissipation of acoustic wave energy.
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: UV Spectroscopy of alpha Ori (M2 Iab) and Implications
Regarding Heating Mechanisms
Authors: Cuntz, M.
Bibcode: 1998ASPC..143..356C
Altcode: 1998sigh.conf..356C
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: Chromospheric velocity fields in α Orionis (M2 Iab) generated
by stochastic shocks.
Authors: Cuntz, M.
Bibcode: 1997A&A...325..709C
Altcode:
I present results from recent ab-initio models for the formation
and time-dependent behavior of outer atmospheric flows in α Ori
(M2 Iab) produced by stochastic shock waves. Stochastic shocks are
a natural consequence of acoustic energy generation due to stellar
convection. The wave models show distinct episodes of momentum and
energy deposition produced by strong shocks generated by merging
of shocks in the stochastic wave field. It is found that sub- and
supersonic inflows and outflows are generated at different atmospheric
heights as function of the wave parameters adopted. The flow velocities
given by the models encompass the velocity range revealed by the Fe
II emission line components given by recent GHRS data (Carpenter &
Robinson 1997ApJ...479..970C). This result is evidence that nonmagnetic
wave modes are relevant for the heating and dynamics of the outer
atmosphere of α Ori and possibly other M-type supergiants as well,
although it does not preclude the possibility that magnetic heating
may be equally or more important.
Title: Acoustic wave propagation in the solar
atmosphere. IV. Nonadiabatic wave excitation with frequency spectra.
Authors: Theurer, J.; Ulmschneider, P.; Cuntz, M.
Bibcode: 1997A&A...324..587T
Altcode: 1997astro.ph..3106T
We study the response of the solar atmosphere to excitations
by large amplitude acoustic waves with radiation damping now
included. Monochromatic adiabatic waves, due to unbalanced heating,
generate continuously rising chromospheric temperature plateaus in
which the low frequency resonances quickly die out. All non-adiabatic
calculations lead to stable mean chromospheric temperature distributions
determined by shock dissipation and radiative cooling. For non-adiabatic
monochromatic wave excitation, a critical frequency ν_cr_~1/25Hz
is confirmed, which separates domains of different resonance
behaviour. For waves of ν<ν_cr_, the resonances decay, while for
waves of ν>ν_cr_ persistent resonance oscillations occur, which
are perpetuated by shock merging. Excitation with acoustic frequency
spectra produces distinct dynamical mean chromosphere models where the
detailed temperature distributions depend on the shape of the assumed
spectra. The stochasticity of the spectra and the ongoing shock merging
lead to a persistent resonance behaviour of the atmosphere. The acoustic
spectra show a distinct shape evolution with height such that at great
height a pure 3min band becomes increasingly dominant. With our Eulerian
code we did not find appreciable mass flows at the top boundary.
Title: Stochastic Processes and the Origin of Stellar Winds
Authors: Cuntz, M.; Dorfi, E. A.
Bibcode: 1997cwh..conf..485C
Altcode: 2006mslp.conf..485C
No abstract at ADS
Title: Short-Term Chromospheric Variability in alpha Tauri (K5 III):
Results from IUE Time Series Observations
Authors: Cuntz, Manfred; Deeney, Bryan D.; Brown, Alexander; Stencel,
Robert E.
Bibcode: 1996ApJ...464..426C
Altcode:
We evaluate time series observations of chromospheric lines (Mg II, Mg
I, and C II) for the K giant α Tau obtained using the IUE LWP camera at
high dispersion. These observations cover a time span of about 2 weeks
in 1994 February-March and were designed to resolve variations occurring
within hours, days, and weeks. We consider the observational results in
relation to theoretical acoustic heating models, motivated by the fact
that αTau may exhibit a basal (i.e., minimum) level of chromospheric
activity. The data reveal flux variations between the extremes of 8%
in Mg II h + k and 15% in each emission component. These variations
occur on timescales as short as 8 hr but not on timescales longer than
∼3 days. For the h and k components, flux variations occurring on a
timescale as short as 1.5 hr are also found. These changes are often
not correlated (and are sometimes even anticorrelated), leading to
remarkable differences in the h/k ratios. We argue that these results
are consistent with the presence of strong acoustic shocks, which
can lead to variable Mg II line emission when only a small number of
strong shocks are propagating through the atmosphere. We deduce the
electron density in the C II] λ2325 line formation region to be log
Ne ≃ 9.0, in agreement with previous studies. Our data
provide evidence that the Mg II basal flux limit for K giants might
be a factor of 4 higher than suggested by Rutten et al.
Title: Chromospheric heating in late-type stars: evidence for magnetic
and nonmagnetic surface structure
Authors: Cuntz, M.
Bibcode: 1996IAUS..176..393C
Altcode:
No abstract at ADS
Title: Generation of Mass Loss in K Giants: The Failure of Global
Oscillation Modes and Possible Implications
Authors: Sutmann, G.; Cuntz, M.
Bibcode: 1995ApJ...442L..61S
Altcode:
It is a well-established observational result that many inactive
K stars show global oscillation modes, which lead to low-amplitude
photospheric velocity variations. It is the purpose of this paper to
investigate whether these modes are relevant to the outer atmospheric
dynamics, including the generation of mass loss. We find that this
is not the case as most of these modes remain evanescent ('mode
trapping'). Nonlinear effects are negligible as the wave amplitudes
remain very small. The failure of these modes to produce mass loss
(as well as the failure of acoustic modes previously studied) should be
considered as strong evidence that the mass loss in these stars cannot
be initiated by a nonmagnetic process. This result is of particular
interest as the chromospheric heating in most of these stars seems to
be fully attributable to acoustic energy dissipation.
Title: Short-term Mg II flux variations in α Tauri (K5 III):
results from recent IUE data sets
Authors: Cuntz, M.; Deeney, B. D.; Brown, A.; Stencel, R. E.
Bibcode: 1995IAUS..176P.162C
Altcode:
No abstract at ADS
Title: The CO/SiO Radiative Instability in Cool Star Atmospheres
Revisited
Authors: Cuntz, M.; Muchmore, D. O.
Bibcode: 1994ApJ...433..303C
Altcode:
We revisit the formation of radiative instabilities in cool star
atmospheres and compare our results with those given by Muchmore, Nuth,
& Stencel. We have considered the combined influence of CO and SiO
molecules and have computed models for a grid of effective temperatures
and geometrical dilution factors for the stellar radiation. Our
results are based on the analysis of the energy balance of gas
elements with prescribed thermodynamic properties. Our results show
that radiative instabilities are most likely primarily caused by CO,
whereas SiO is expected to play only a minor role, except when the CO
density is reduced compared to Local Thermodynamic Equilibrium (LTE)
values or the CO band can be assumed to be optically thick. The onset
of radiative instabilities is expected to be strongly modified when
dynamic phenomena such as stochastic shocks are present. Our results
provide strong evidence that dust formation can most likely occur via
a radiative instability alone. Therefore, we present a revised version
of the Muchmore et al. dust formation paradigm, which also considers
hydrodynamic cooling. The new paradigm is particularly relevant in
cases where dust is formed relatively close to the stellar photosphere.
Title: Chromospheric Heating and Metal Deficiency in Cool Giants:
Theoretical Results versus Observations
Authors: Cuntz, M.; Rammacher, W.; Ulmschneider, P.
Bibcode: 1994ApJ...432..690C
Altcode:
We compute acoustic shock wave-heated chromosphere models for moderately
cool giant stars which differ greatly in metallicity. Subsequently, we
simulate the emerging Mg II k lines assuming partial redistribution. The
initial acoustic energy fluxes and the wave periods are taken from
acoustic wave generation calculations based on traditional convection
zone models. We find that the Mg II and Ca II core emissions are
close to the observed basal flux limits which are common for giants
and dwarfs. In addition, we find that the Mg II core emission is
independent of the metallicity, in agreement with observations. We
argue that these results should be considered as further evidence that
the basal flux limits are indeed due to acoustic shock heating. The
acoustic heating mechanism seems to be dominant in all nonmagnetic
nonpulsating late-type stars.
Title: The shock strength in super- and hypergiant atmospheres
derived from microturbulence data
Authors: Nieuwenhuijzen, H.; de Jager, C.; Cuntz, M.
Bibcode: 1994A&A...285..595N
Altcode:
This study is based on evidence that small-scale motions, observed
as microturbulent line broadening, in the atmospheres of super- and
hypergiants can possibly be interpreted as fields of shock waves moving
outwards through the atmosphere. We derive values for the average shock
strength M_1_ for a number of well-observed stars. We found that the
value of M_1_ increases strongly with stellar luminosity, suggesting
that shock wave pressure is relevant for the stability limit of most
evolved stars (Humphreys-Davidson Limit) and for stellar evolution
calculations. Our results however apply only to those stars in which
photospheric shock wave patterns exist. For some stars we studied the
dependence of M_1'_ on the Rosseland optical depths τ_R_ and we found
that M_1'_(τ_R_) does not change very much. We compared the energy
fluxes associated with the shocks with acoustic energy fluxes given
by Bohn and with radiative energy losses from the chromospheres (only
possible for cool giants and supergiants). We found that these fluxes
are compatible for cool stars. The energy fluxes of Bohn cannot be
used for super- and hypergiants with T_eff_ > 6500 K as all these
stars are lacking convection zones.
Title: Short-Term Variability of Luminous K Stars: A Test Case of
Hydrodynamic Modelling
Authors: Cuntz, Manfred
Bibcode: 1994iue..prop.4766C
Altcode:
We propose to obtain time series spectra of chromospheric diagnostics
(Mg II, Mg I) on short timescales (< days) using the LWP camera at
high dispersion, together with supporting ground-based data. We have
selected three bright, but representative "coronal", "non-coronal",
and "hybrid" stars: beta Gem (K0 III), alpha Tau (K5 III), and iota Aur
(K3 II). We aim to gain insight into the mechanism(s) responsible for
chromospheric heating and mass loss, by studying the time-dependent
behavior of the various chromospheric diagnostics on timescales which
are important both from theoretical studies of chromospheric heating
(including the interpretation of recent C II] 2325 A observations
with GHRS) and from previous photospheric observational work. Our
observations will be tested against existing ab-initio models. We
are convinced that only new observations capable to deduce the
timescales of chromospheric line variabilities can provide insight
into the dominant chromospheric heating and mass loss mechanism(s) in
these stars. Although many IUE spectra exist for our target stars, no
data address the short-term variability of the Ca II, Mg II, Mg I and
H-alpha chromospheric and wind diagnostics simultaneously. Obtaining
simultaneous observations of these lines is the only way to test key
predictions from our theoretical models.
Title: Radiative Instabilities in Cool Star Atmospheres: Effects
due to CO and SiO Molecules
Authors: Cuntz, M.; Muchmore, D. O.
Bibcode: 1994ASPC...64..611C
Altcode: 1994csss....8..611C
No abstract at ADS
Title: Effects of Metallicity on Chromospheric Emission in Cool
Giants: Results from Acoustic Wave Models
Authors: Cuntz, M.; Ulmschneider, P.
Bibcode: 1994ASPC...64..368C
Altcode: 1994csss....8..368C
No abstract at ADS
Title: A generalized version of the Rankine-Hugoniot relations
including ionization, dissociation and related phenomena
Authors: Nieuwenhuijzen, H.; de Jager, C.; Cuntz, M.; Lobel, A.;
Achmad, L.
Bibcode: 1993A&A...280..195N
Altcode:
For purposes of computing shocks in stellars atmospheres and winds we
have developed a generalized version of the Rankine-Hugoniot relations
including ionization, dissociation, radiation and related phenomena such
as excitation, rotation and vibration of molecules. The new equations
are given in analytical form. They are valid as long as the internal
energy E, the total pressure P, and the first adiabatic coefficient
gamma1 can be evaluated. However, we have not treated shock
structures. In the case of non-LTE we have to employ an approximation
for gamma1 because in that case no definition exists. Our new
version of the Rankine-Hugoniot relations can easily be used for many
purposes including ab-initio modeling. In our derivation we introduce
a parameter gammaH, which is definded as the ratio of the
enthalpy H (sometimes called heat function w) to the internal energy
E (sometimes called U). Using this parameter we solve the equations
for changing mu and (d(natural log P)/d(natural log rho))ad
identically equal to gamma1 on both sides of the shock. Both
gammaH and gamma1, and also mu are functions
of pressure P and temperature T. We present: (1) the derivation,
(2) examples of gamma1 (P,T) and gammaH (P,T)
which include/exclude ionization and radiation, and (3) as an example
the differences in post-shock parameters as function of the pre-shock
temperature for the case with ionization and without radiation.
Title: Chromospheric Heating by Acoustic Shocks: A Confrontation of
GHRS Observations of alpha Tauri (K5 III) with AB Initio Calculations
Authors: Judge, P. G.; Cuntz, M.
Bibcode: 1993ApJ...409..776J
Altcode:
We compare ab initio calculations of semiforbidden C II line profiles
near 2325 A with recently published observations of the inactive red
giant Alpha Tau (K5 III) obtained using the GHRS on board the Hubble
Space Telescope. Our one-dimensional, time-dependent calculations assume
that the chromosphere is heated by stochastic acoustic shocks generated
by photospheric convection. We calculate various models using results
from traditional (mixing length) convection zone calculations as input
to hydrodynamical models. The semiforbidden C II line profiles and
ratios provide sensitive diagnostics of chromospheric velocity fields,
electron densities, and temperatures. We identify major differences
between observed and computed line profiles which are related to
basic gas dynamics and which are probably not due to technical
modeling restrictions. If the GHRS observations are representative
of chromospheric conditions at all epochs, then one (or more) of
our model assumptions must be incorrect. Several possibilities are
examined. We predict time variability of semiforbidden C II lines for
comparison with observations. Based upon data from the IUE archives,
we argue that photospheric motions associated with supergranulation
or global pulsation modes are unimportant in heating the chromosphere
of Alpha Tau.
Title: Line Profile Variations in M Giants: Clues to Mass-Loss and
Chromospheric Heating Mechanisms
Authors: Judge, P. G.; Luttermoser, D. G.; Neff, D. H.; Cuntz, M.;
Stencel, R. E.
Bibcode: 1993AJ....105.1973J
Altcode:
Analysis is presented of time-series, high dispersion spectra of
the Mg II, k, Ca II H, and K lines of the semiregular giants Rho Per
(M4 II-III, periodicity of about 50 days), R Lyr (M5 III, period of
about 46 days), and g Her (M6 III, period of about 90 days). The fine
error sensor on the IUE satellite and ground based UBV photometry was
used to relate line profile variations to photospheric variations. The
above mentioned stars were selected to study the relative importance
of convective motions and global stellar pulsations in determining
the structure of the outer atmospheres. Small amplitude changes, but
substantial changes in the profiles of Mg II and Ca II lines were
detected. It is contended that the observed variability is due to
changes in chromospheric conditions and not variations within the
circumstellar shell. The picture of a steady state chromosphere,
which is modulated on long time scales, is corroborated by these
observations. Localized heating is found in g Her.
Title: Propagation of Radial Pulsation Modes in the Outer Atmosphere
of Arcturus: First results
Authors: Cuntz, M.
Bibcode: 1993npsp.conf..283C
Altcode: 1993IAUCo.139..283C
No abstract at ADS
Title: The Search for Acoustically-Driven Mass-Loss in Evolved Stars
Authors: Stencel, R. E.; Brown, A.; Carpenter, K. G.; Cuntz, M.;
Judge, P.
Bibcode: 1992AAS...181.3603S
Altcode: 1992BAAS...24.1175S
Recent ab-initio calculations of stochastic stellar wind models by
Cuntz (1992 in Cool Stars VII, ASP Conf. Ser. 26, p.383) have proven
remarkably robust in predicting observed chromospheric flow patterns
including possible variabilities with time in selected cool, evolved
stars. The calculations solve the equations of hydrodynamics using
the method of characteristics and assume: (i) saw-tooth shock wave
profiles, and (ii) wave periods were changed stochastically while
keeping the wave amplitudes constant (see Cuntz 1990 Ap.J. 349,
p.141). Among the results of fitting chromospheric flow velocities is
the implication that the permitted range of acoustic wave periods for
a given star is constrained. We made use of the IUE satellite during
August and September 1992 to repeatedly observe two stars, the yellow
giant Aldebaran (K5 III) and the red supergiant, Betelgeuse (M2 Iab),
in order to sample variations in their atmospheres on timescales of ~
10(4) to ~ 10(6) seconds, which bracket the predicted mean acoustic wave
periods for these objects. In particular, we obtained deep exposures
in order to measure density-sensitive line ratios within the C II]
intercombination features near 2325A (cf. Lennon et al. 1985 Ap.J. 294,
p.200) to test the hypothesis that density fluctuations could be
measured as a consequence of these acoustic waves. The results of
these observations will be presented and discussed in terms of the
number and amplitude of acoustic waves contributing to chromospheric
heating and mass loss from these stars, as well as the wave origins in
the evolving oscillatory structure of these stellar interiors. We are
pleased to acknowledge IUE--NASA grant NAG5-2103 for partial support
of this effort.
Title: Stochastic stellar wind models: evolved stars.
Authors: Cuntz, Manfred
Bibcode: 1992ASPC...26..383C
Altcode: 1992csss....7..383C
The author presents several remarkable observational and semiempirical
results for individual cool giants and supergiants (in particular for
α Ori), which show that stochastic stellar wind flows are an extremely
important feature in these stars. He shows that the status of proposed
theoretical models is very poor due to the fact that appropriate
models must simultaneously take into account a broad variety of
physical processes which are strongly coupled and, furthermore,
not well understood. He presents ab-initio models for the formation
and time-dependent behavior of stochastic stellar wind flows in the
chromosphere of α Ori produced by the propagation and interaction of
stochastic shocks.
Title: A stellar evolution paradigm based on specific mass loss and
feedback modes.
Authors: Cuntz, Manfred; Stencel, Robert E.
Bibcode: 1992ASPC...26..451C
Altcode: 1992csss....7..451C
The authors present a new paradigm for stellar evolution which deals
with a detailed treatment of mass loss and feedback modes. The
paradigm is presented as a logical diagram which describes the
respective dependencies of atmospheric properties relevant to mass
loss generation. (orig.)
Title: A new paradigm of stellar evolution including detailed mass
loss processes
Authors: Cuntz, M.; Stencel, R. E.
Bibcode: 1992iesh.conf..182C
Altcode:
No abstract at ADS
Title: Stellar wind flows in M-type supergiants produced by stochastic
shock waves
Authors: Cuntz, M.
Bibcode: 1992iesh.conf..133C
Altcode:
No abstract at ADS
Title: Chromospheric heating in cool stars
Authors: Cuntz, M.
Bibcode: 1992sccw.conf....3C
Altcode:
No abstract at ADS
Title: Effects of Mg II and Ca II ionization on ab-initio solar
chromosphere models
Authors: Rammacher, W.; Cuntz, M.
Bibcode: 1991A&A...250..212R
Altcode:
Acoustically heated solar chromosphere models are computed considering
radiation damping by (non-LTE) emission from H(-) and by Mg II and Ca
II emission lines. The radiative transfer equations for the Mg II k
and Ca II K emission lines are solved using the core-saturation method
with complete redistribution. The Mg II k and Ca II K cooling rates
are compared with the VAL model C. Several substantial improvements
over the work of Ulmschneider et al. (1987) are included. It is
found that the rapid temperature rises caused by the ionization of
Mg II are not formed in the middle chromosphere, but occur at larger
atmospheric heights. These models represent the temperature structure
of the 'real' solar chromosphere much better. This result is a major
precondition for the study of ab-initio models for solar flux tubes
based on MHD wave propagation and also for ab-initio models for the
solar transition layer.
Title: What Can Observations of Giants and Supergiant Stars Tell Us
About Chromospheric and Coronal Heating?
Authors: Cuntz, M.; Stencel, R. E.
Bibcode: 1991mcch.conf..206C
Altcode:
No abstract at ADS
Title: Wave pressure in stellar atmospheres due to shock wave trains.
Authors: Gail, H. P.; Cuntz, M.; Ulmschneider, P.
Bibcode: 1990A&A...234..359G
Altcode:
Analytic expressions for the wave pressure of propagating shock wave
trains in stellar atmospheres or winds are derived. Applications to
weak shocks and stronger shocks with sawtooth profiles are discussed
in detail. The shocks are treated as discontinuities. The results
provide insight in the momentum balance of time-dependent stellar wind
flows. The analytic expressions can be used as an independent test of
hydrodynamic codes.
Title: On the Generation of Mass Loss in Cool Giant Stars Due to
Propagating Shock Waves
Authors: Cuntz, Manfred
Bibcode: 1990ApJ...353..255C
Altcode:
This paper investigates mass loss in late-type giant stars produced
by propagating shock waves, assuming both monochromatic waves and
acoustic frequency spectra. In monochromatic wave computations, the
wave period is varied by a factor of 50. The wave models show that
short-period waves produced in stellar convective zones do not play any
direct role in generating the observed mass loss, except for episodic
mass-loss events. However, these waves are important for heating stellar
chromospheres. Continuous mass-loss solutions are obtained when the
wavelengths are comparable to or larger than a stellar radius. In the
case of Arcturus, a mass-loss rate between 10 to the -10th and 10 to
the -11th solar mass/yr is found, and the final flow speed of the wind
is larger than 40 km/s, which are close to the observed values.
Title: Stochastic Shock Waves as a Candidate Mechanism for the
Formation of the He i lambda 10830 Line in Cool Giant Stars
Authors: Cuntz, Manfred; Luttermoser, Donald G.
Bibcode: 1990ApJ...353L..39C
Altcode:
The question of whether strong shocks produced in time-dependent
stochastic wave models can explain the formation of the He I 10830-A
line in cool giant stars is examined. The research is based on the
ab initio chromosphere model for Arcturus by Cuntz (1987), showing
that a stochastic distribution of wave periods leads to overtaking
and merging of shocks, which occasionally produce very strong shocks
with temperatures larger than 40,000 K in the postshock regions. These
temperatures can easily produce a significant population in the 2s 3S
state by electron collisional excitation. The 10830-A line occurs in
absorption when the densities in the shocks exceed 10 million/cu cm.
Title: Chromospheric Extents Predicted by Time-dependent Acoustic
Wave Models
Authors: Cuntz, Manfred
Bibcode: 1990ApJ...349..141C
Altcode:
Theoretical models for chromospheric structures of late-type giant
stars are computed, including the time-dependent propagation of acoustic
waves. Models with short-period monochromatic shock waves as well as a
spectrum of acoustic waves are discussed, and the method is applied to
the stars Arcturus, Aldebaran, and Betelgeuse. Chromospheric extent,
defined as the monotonic decrease with height of the time-averaged
electron densities, are found to be 1.12, 1.13, and 1.22 stellar radii
for the three stars, respectively; this corresponds to a time-averaged
electron density of 10 to the 7th/cu cm. Predictions of the extended
chromospheric obtained using a simple scaling law agree well with those
obtained by the time-dependent wave models; thus, the chromospheres
of all stars for which the scaling law is valid consist of the same
number of pressure scale heights.
Title: How Consistent are Ab-Initio Models of Giant Star Chromospheres
with Observations
Authors: Cuntz, M.; Judge, P. G.
Bibcode: 1990ASPC....9...61C
Altcode: 1990csss....6...61C
No abstract at ADS
Title: The Hei LAMBDA10830 Line in Arcturus Produced by Stochastic
Shocks
Authors: Cuntz, Manfred; Luttermoser, Donald G.
Bibcode: 1990ASPC....9..142C
Altcode: 1990csss....6..142C
An investigation is conducted as to whether strong shocks produced in
time-dependent stochastic wave models can explain the formation of the
He I 10830 line in a cool giant star like Arcturus. The exploratory
research is based on the work of Cuntz (1987) who found that stochastic
waves lead to overtaking and merging of shocks producing occasionally
very strong shocks with temperatures larger than 40,000 K in the
postshock regions.
Title: Radiative Transfer in ab-initio Chromospheric Models
Authors: Cuntz, M.; Judge, P. G.
Bibcode: 1989BAAS...21Q1101C
Altcode: 1989BAAS...21.1101C
No abstract at ADS
Title: Generation of Extended Chromospheres and Mass Loss of Late-Type
Giant Stars due to Acoustic Shock Waves
Authors: Cuntz, Manfred
Bibcode: 1989PASP..101..560C
Altcode:
No abstract at ADS
Title: Inhomogeneous Chromospheric Structures in the Atmosphere of
Arcturus Generated by Acoustic Wave Propagation
Authors: Cuntz, M.; Muchmore, D.
Bibcode: 1989ASIC..263..547C
Altcode: 1989ssg..conf..547C
No abstract at ADS
Title: Time-dependent effects of acoustic wave heating and molecular
coolingin the outer atmosphere of Arcturus.
Authors: Cuntz, M.; Muchmore, D.
Bibcode: 1989A&A...209..305C
Altcode:
The propagatiion of acoustic waves is studied in the outer atmosphere
of Arcturus where radiation damping by CO and SiO molecules occurs. The
dynamical effects generated by periodic and nonperiodic wave models are
studied. If the shock strength is larger than 2.35, a hot chromospheric
feature with a temperature similar to the semiempirical model of Ayres
and Linsky (1975) is generated. The development of this feature leads
to a time and height dependent separation between molecule dominated
atmospheric layers and chromospheric structures.
Title: A hydrodynamic code for the treatment of late-type stellar
wind flowsbased on the method of characteristics.
Authors: Cuntz, M.; Ulmschneider, P.
Bibcode: 1988A&A...193..119C
Altcode:
The authors describe a time-dependent eulerian hydrodynamic code
based on the method of characteristics which allows the computation
of radiating stellar wind flows in tube-like structures on late-type
stars. The treatment of boundaries under sub- and supersonic
conditions is discussed as is the introduction of shock waves into the
atmosphere. Ionization is taken into account. For test and application
the authors study the behaviour to approach limiting shock strength.
Title: Generation of extended chromospheres and mass loss of late-type
giantstars due to acoustic shock waves.
Authors: Cuntz, M.
Bibcode: 1988gecm.book.....C
Altcode:
The author investigates the generation of extended chromospheres and
mass loss of late-type giant stars due to acoustic shock waves. Effects
of both monochromatic waves and acoustic frequency spectra are
studied. Short period acoustic wave calculations show that a persistent
wave energy flux can produce an extended chromosphere. If monochromatic
shock waves are used no appreciable mass loss is generated. However,
in the case of wave models with stochastically changing wave periods
episodic mass loss occurs. This behaviour is caused by overtaking and
merging of shocks.