523 research outputs found
Predicting radio emission from the newborn hot Jupiter V830 Tau and its host star
Magnetised exoplanets are expected to emit at radio frequencies analogously
to the radio auroral emission of Earth and Jupiter. We predict the radio
emission from V830 Tau b, the youngest (2 Myr) detected exoplanet to date. We
model the host star wind using 3DMHD simulations that take into account its
surface magnetism. With this, we constrain the local conditions around V830 Tau
b that we use to then compute its radio emission. We estimate average radio
flux densities of 6 to 24mJy, depending on the assumed radius of the planet
(one or two Rjupiter). These radio fluxes are present peaks that are up to
twice the average values. We show here that these fluxes are weakly dependent
(a factor of 1.8) on the assumed polar planetary magnetic field (10 to 100G),
opposed to the maximum frequency of the emission, which ranges from 18 to
240MHz. We also estimate the thermal radio emission from the stellar wind. By
comparing our results with VLA and VLBA observations of the system, we
constrain the stellar mass-loss rate to be <3e-9 Msun/yr, with likely values
between ~1e-12 and 1e-10 Msun/yr. The frequency-dependent extension of the
radio-emitting wind is around ~ 3 to 30 Rstar for frequencies in the range of
275 to 50MHz, implying that V830 Tau b, at an orbital distance of 6.1 Rstar,
could be embedded in the regions of the host star's wind that are optically
thick to radio wavelengths, but not deeply so. Planetary emission can only
propagate in the stellar wind plasma if the frequency of the cyclotron emission
exceeds the stellar wind plasma frequency. For that, we find that for planetary
radio emission to propagate through the host star wind, planetary magnetic
field strengths larger than ~1.3 to 13 G are required. The V830 Tau system is a
very interesting system for conducting radio observations from both the
perspective of radio emission from the planet as well as from the host star's
wind.Comment: A&A, in pres
Learning about Quantum Gravity with a Couple of Nodes
Loop Quantum Gravity provides a natural truncation of the infinite degrees of
freedom of gravity, obtained by studying the theory on a given finite graph. We
review this procedure and we present the construction of the canonical theory
on a simple graph, formed by only two nodes. We review the U(N) framework,
which provides a powerful tool for the canonical study of this model, and a
formulation of the system based on spinors. We consider also the covariant
theory, which permits to derive the model from a more complex formulation,
paying special attention to the cosmological interpretation of the theory
On the environment surrounding close-in exoplanets
Exoplanets in extremely close-in orbits are immersed in a local
interplanetary medium (i.e., the stellar wind) much denser than the local
conditions encountered around the solar system planets. The environment
surrounding these exoplanets also differs in terms of dynamics (slower stellar
winds, but higher Keplerian velocities) and ambient magnetic fields (likely
higher for host stars more active than the Sun). Here, we quantitatively
investigate the nature of the interplanetary media surrounding the hot Jupiters
HD46375b, HD73256b, HD102195b, HD130322b, HD179949b. We simulate the
three-dimensional winds of their host stars, in which we directly incorporate
their observed surface magnetic fields. With that, we derive mass-loss rates
(1.9 to 8.0 /yr) and the wind properties at the
position of the hot-Jupiters' orbits (temperature, velocity, magnetic field
intensity and pressure). We show that these exoplanets' orbits are
super-magnetosonic, indicating that bow shocks are formed surrounding these
planets. Assuming planetary magnetic fields similar to Jupiter's, we estimate
planetary magnetospheric sizes of 4.1 to 5.6 planetary radii. We also derive
the exoplanetary radio emission released in the dissipation of the stellar wind
energy. We find radio fluxes ranging from 0.02 to 0.13 mJy, which are
challenging to be observed with present-day technology, but could be detectable
with future higher sensitivity arrays (e.g., SKA). Radio emission from systems
having closer hot-Jupiters, such as from tau Boo b or HD189733b, or from nearby
planetary systems orbiting young stars, are likely to have higher radio fluxes,
presenting better prospects for detecting exoplanetary radio emission.Comment: 15 pages, 5 figures, accepted to MNRA
A mixed latent class Markov approach for estimating labour market mobility with multiple indicators and retrospective interrogation
Measurement errors can induce bias in the estimation of transitions, leading to erroneous conclusions about labour market dynamics. Traditional literature on gross flows estimation is based on the assumption that measurement errors are uncorrelated over time. This assumption is not realistic in many contexts, because of survey design and data collection strategies. In this work, we use a model-based approach to correct observed gross flows from classification errors with latent class Markov models. We refer to data collected with the Italian Continuous Labour Force Survey, which is cross-sectional, quarterly, with a 2-2-2 rotating design. The questionnaire allows us to use multiple indicators of labour force conditions for each quarter: two collected in the first interview, and a third collected one year later. Our approach provides a method to estimate labour market mobility, taking into account correlated errors and the rotating design of the survey. The best-fitting model is a mixed latent class Markov model with covariates affecting latent transitions and correlated errors among indicators; the mixture components are of mover-stayer type. The better fit of the mixture specification is due to more accurately estimated latent transitions
How can weedy rice stand against abiotic stresses? a review
Weedy rice is one of the most common weeds in rice cultivation in many rice areas throughout the world and it is able to cause significant yield reductions. Weedy rice is characterized by a high biological diversity that permits different populations to be identified on the basis of their morphological and physiological traits. This variability contributes to its success in different environments and allows different abiotic stresses, which are intensified by climate change, to be faced. Taller plants, enhanced tillering, seed shattering and the presence of red pericarp, variable hull coloration and awn morphology, linked to a deeper seed dormancy, are some of the traits that help weedy rice to spread in changing environments. The higher phenotypic plasticity and genetic variability of weedy rice make it more able to cope with temperature variations, intermittent water availability, soil salinity, drought conditions and increased CO2 concentrations than cultivated rice. As these abiotic stresses will become more frequent in the future, weedy rice competitiveness may be higher, with a spread of infestations. Thus, the control of weedy rice should be based on an integration of different preventive and agronomic techniques, a sensible use of herbicides and the use of suitable rice varieties
M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets
We perform three-dimensional numerical simulations of stellar winds of
early-M dwarf stars. Our simulations incorporate observationally reconstructed
large-scale surface magnetic maps, suggesting that the complexity of the
magnetic field can play an important role in the angular momentum evolution of
the star, possibly explaining the large distribution of periods in field dM
stars, as reported in recent works. In spite of the diversity of the magnetic
field topologies among the stars in our sample, we find that stellar wind
flowing near the (rotational) equatorial plane carries most of the stellar
angular momentum, but there is no preferred colatitude contributing to mass
loss, as the mass flux is maximum at different colatitudes for different stars.
We find that more non-axisymmetric magnetic fields result in more asymmetric
mass fluxes and wind total pressures (defined as the sum of
thermal, magnetic and ram pressures). Because planetary magnetospheric sizes
are set by pressure equilibrium between the planet's magnetic field and , variations of up to a factor of in (as found in the
case of a planet orbiting at several stellar radii away from the star) lead to
variations in magnetospheric radii of about 20 percent along the planetary
orbital path. In analogy to the flux of cosmic rays that impact the Earth,
which is inversely modulated with the non-axisymmetric component of the total
open solar magnetic flux, we conclude that planets orbiting M dwarf stars like
DT~Vir, DS~Leo and GJ~182, which have significant non-axisymmetric field
components, should be the more efficiently shielded from galactic cosmic rays,
even if the planets lack a protective thick atmosphere/large magnetosphere of
their own.Comment: 16 pages, 9 figures, to appear in MNRA
Star-planet magnetic interaction and activity in late-type stars with close-in planets
Late-type stars interact with their close-in planets through their coronal
magnetic fields. We introduce a theory for the interaction between the stellar
and planetary fields focussing on the processes that release magnetic energy in
the stellar coronae. We consider the energy dissipated by the reconnection
between the stellar and planetary magnetic fields as well as that made
available by the modulation of the magnetic helicity of the coronal field
produced by the orbital motion of the planet. We estimate the powers released
by both processes in the case of axisymmetric and non-axisymmetric, linear and
non-linear force-free coronal fields finding that they scale as v_r (B_s)^(4/3)
(B_p)^(2/3) (R_p)^2, where v_r is the relative velocity between the stellar and
planetary fields, B_s the mean stellar surface field, B_p the planetary field
at the poles, and R_p the radius of the planet. A chromospheric hot spot or a
flaring activity phased to the orbital motion of the planet are found only when
the stellar field is axisymmetric. In the case of a non-axisymmetric field, the
time modulation of the energy release is multiperiodic and can be easily
confused with the intrinsic stellar variability. We apply our theory to the
systems with some reported evidence of star-planet magnetic interaction finding
a dissipated power at least one order of magnitude smaller than that emitted by
the chromospheric hot spots. The phase lags between the planets and the hot
spots are reproduced by our models in all the cases except for upsilon And. In
conclusion, the chromospheric hot spots rotating in phase with the planets
cannot be explained by the energy dissipation produced by the interaction
between stellar and planetary fields as considered by our models and require a
different mechanism.Comment: 16 pages, 3 figures, accepted by Astronomy and Astrophysic
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