81 research outputs found
Stellar activity and planetary atmosphere evolution in tight binary star systems
Context. In tight binary star systems, tidal interactions can significantly
influence the rotational and orbital evolution of both stars, and therefore
their activity evolution. This can have strong effects on the atmospheric
evolution of planets that are orbiting the two stars.
Aims. In this paper, we aim to study the evolution of stellar rotation and of
X-ray and ultraviolet (XUV) radiation in tight binary systems consisting of two
solar mass stars and use our results to study planetary atmosphere evolution in
the habitable zones of these systems.
Methods. We have applied a rotation model developed for single stars to
binary systems, taking into account the effects of tidal interactions on the
rotational and orbital evolution of both stars. We used empirical
rotation-activity relations to predict XUV evolution tracks for the stars,
which we used to model hydrodynamic escape of hydrogen dominated atmospheres.
Results. When significant, tidal interactions increase the total amount of
XUV energy emitted, and in the most extreme cases by up to factor of 50.
We find that in the systems that we study, habitable zone planets with masses
of 1~M can lose huge hydrogen atmospheres due to the extended high
levels of XUV emission, and the time that is needed to lose these atmospheres
depends on the binary orbital separation.For some orbital separations, and when
the stars are born as rapid rotators, it is also possible for tidal
interactions to protect atmospheres from erosion by quickly spinning down the
stars. For very small orbital separations, the loss of orbital angular momentum
by stellar winds causes the two stars to merge. We suggest that the merging of
the two stars could cause previously frozen planets to become habitable due to
the habitable zone boundaries moving outwards.Comment: Accepted for publication by A&
Escape of the martian protoatmosphere and initial water inventory
Latest research in planet formation indicate that Mars formed within a few
million years (Myr) and remained a planetary embryo that never grew to a more
massive planet. It can also be expected from dynamical models, that most of
Mars' building blocks consisted of material that formed in orbital locations
just beyond the ice line which could have contained ~0.1-0.2 wt. % of H2O. By
using these constraints, we estimate the nebula-captured and catastrophically
outgassed volatile contents during the solidification of Mars' magma ocean and
apply a hydrodynamic upper atmosphere model for the study of the soft X-ray and
extreme ultraviolet (XUV) driven thermal escape of the martian protoatmosphere
during the early active epoch of the young Sun. The amount of gas that has been
captured from the protoplanetary disk into the planetary atmosphere is
calculated by solving the hydrostatic structure equations in the protoplanetary
nebula. Depending on nebular properties such as the dust grain depletion
factor, planetesimal accretion rates and luminosities, hydrogen envelopes with
masses >=3x10^{19} g to <=6.5x10^{22} g could have been captured from the
nebula around early Mars. Depending of the before mentioned parameters, due to
the planets low gravity and a solar XUV flux that was ~100 times stronger
compared to the present value, our results indicate that early Mars would have
lost its nebular captured hydrogen envelope after the nebula gas evaporated,
during a fast period of ~0.1-7.5 Myr. After the solidification of early Mars'
magma ocean, catastrophically outgassed volatiles with the amount of ~50-250
bar H2O and ~10-55 bar CO2 could have been lost during ~0.4-12 Myr, if the
impact related energy flux of large planetesimals and small embryos to the
planet's surface lasted long enough, that the steam atmosphere could have been
prevented from condensing. If this was not the case... (continued)Comment: 47 pages, 10 figures, 3 tables, submitted to PS
A case study for the formation of stanene on a metal surface
The discovery and realization of graphene as an ideal two-dimensional (2D) material has triggered extensive efforts to create similar 2D materials with exciting spin-dependent properties. Here, we report on a novel Sn 2D superstructure on Au(111) that shows similarities and differences to the expected electronic features of ideal stanene. Using spin- and angle-resolved photoemission spectroscopy, we find that a particular Sn/Au superstructure reveals a linearly dispersing band centered at the Γ-point and below the Fermi level with antiparallel spin polarization and a Fermi velocity of vF ≈ 1×106 m/s, the same value as for graphene. We attribute the origin of the band structure to the hybridization between the Sn and the Au orbitals at the 2D Sn-Au interface. Considering that free-standing stanene simply cannot exist, our investigated structure is an important step towards the search of useful stanene-like overstructures for future technological applications
A two-columns formalism for time-dependent modelling of stellar convection. I. Description of the method
Despite all advances in multi-dimensional hydrodynamics, investigations of
stellar evolution and stellar pulsations still depend on one-dimensional
computations. The present work devises an alternative to the mixing length
theory or turbulence models usually adopted for the modelling of convective
transport in such studies. Assuming that the largest convective patterns
generate the majority of convective transport, the convective velocity field is
described using two parallel radial columns to represent up- and downstream
flows. Horizontal exchange in the form of fluid flow and radiation over their
connecting interface couples the two columns and allows a simple circulating
motion. The main parameters of this convective description have a
straightforward geometrical meaning, namely the diameter of the columns
(corresponding to the size of the convective cells) and the ratio of cross
section between up- and downdrafts. For this geometrical setup, the
time-dependent solution of the equations of radiation hydrodynamics is computed
from an implicit scheme which has the advantage of being not affected by the
Courant-Friedrichs-Lewy time step limit. In order to demonstrate the approach,
results for the example of convection zones in Cepheids are presented
The context of chemical communication driving a mutualism
Recent work suggests that Drosophila and Saccharomyces yeasts may establish a mutualistic association, and that this is driven by chemical communication. While individual volatiles have been implicated in the attraction of D. melanogaster, the semiochemicals affecting the behavior of the sibling species D. simulans are less well characterised. Here, we comprehensively scrutinize a broad range of volatiles produced by attractive and repulsive yeasts to experimentally evaluate the chemical nature of communication between these species. When grown in liquid or on agar-solidified grape juice, attraction to S. cerevisiae was primarily driven by 3-methylbutyl acetate (isoamyl acetate) and repulsion by acetic acid, a known attractant to D. melanogaster (also known as vinegar fly). Using T-maze choice tests and synthetic compounds we show that these responses were strongly influenced by compound concentration. Moreover, the behavioral response is further impacted by the chemical context of the environment. Thus, chemical communication between yeasts and flies is complex, and is not simply driven by the presence of single volatiles, but modulated by compound interactions. The ecological context of chemical communication needs to be taken into consideration when testing for ecologically realistic responses
Quantifying variation in the ability of yeasts to attract Drosophila melanogaster
Yeasts that invade and colonise fruit significantly enhance the volatile chemical diversity of this ecosystem. These modified bouquets are thought to be more attractive to Drosophila flies than the fruit alone, but the variance of attraction in natural yeast populations is uncharacterised. Here we investigate how a range of yeast isolates affect the attraction of female D. melanogaster to fruit in a simple two choice assay comparing yeast to sterile fruit. Of the 43 yeast isolates examined, 33 were attractive and seven repellent to the flies. The results of isolate-versus-isolate comparisons provided the same relative rankings. Attractiveness varied significantly by yeast, with the strongly fermenting Saccharomyces species generally being more attractive than the mostly respiring non-Saccharomyces species (P = 0.0035). Overall the habitat (fruit or other) from which the isolates were directly sampled did not explain attraction (P = 0.2352). However, yeasts isolated from fruit associated niches were more attractive than those from non-fruit associated niches (P = 0.0188) regardless of taxonomic positioning. These data suggest that while attractiveness is primarily correlated with phylogenetic status, the ability to attract Drosophila is a labile trait among yeasts that is potentially associated with those inhabiting fruit ecosystems. Preliminary analysis of the volatiles emitted by four yeast isolates in grape juice show the presence/absence of ethanol and acetic acid were not likely explanations for the observed variation in attraction. These data demonstrate variation among yeasts for their ability to attract Drosophila in a pattern that is consistent with the hypothesis that certain yeasts are manipulating fruit odours to mediate interactions with their Drosophila dispersal agent. © 2013 Palanca et al
Pheromonal Cues Deposited by Mated Females Convey Social Information about Egg-Laying Sites in Drosophila Melanogaster
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