65 research outputs found
First year growth in the lithodids Lithodes santolla and Paralomis granulosa reared at different temperatures
No full textThe southern king crab, Lithodes santolla Molina, and stone crab, Paralomis granulosa Jacquinot, inhabit the cold-temperate waters of southernmost South America (southern Chile and Argentina), where stocks of both species are endangered by overfishing. Recent investigations have shown that these crabs show life-cycle adaptations to scarcity of food and low temperatures prevailing in subantarctic regions, including complete lecithotrophy of all larval stages and prolonged periods of brooding and longevity. However, growth and development to maturity are slow under conditions of low temperatures, which may explain the particular vulnerability of subpolar lithodids to fisheries. In the present study, juvenile L. santolla and P. granulosa were individually reared in the laboratory at constant temperatures ranging from 3–15 °C, and rates of survival and development through successive instars were monitored throughout a period of about nine months from hatching. When the experiments were terminated, L. santolla had maximally reached juvenile instar IV (at 6 °C), V (9 °C), or VII (15 °C). In P. granulosa the maximum crab instar reached was II (at 3 °C), V (6 °C), V (9 °C), or VII (15 °C). The intermoult period decreased with increasing temperature, while it increased in successively later instars. In consequence, growth rate showed highly significant differences among temperatures (P<0.001). Growth-at-moult was highest at 9 °C. Rates of survival decreased significantly in juvenile P. granulosa with increasing temperature. Only at 15 °C in L. santolla, was a significantly enhanced mortality found compared with lower temperatures. Our results indicate that juvenile stages of L. santolla and P. granulosa are well adapted to 5–10°C, the range of temperatures typically prevailing in subantarctic marine environments. In spite of causing higher mortality rates, higher rearing temperatures (12–15 °C) should accelerate the rates of growth and maturation, which may be favourable for projects aiming at aquaculture or repopulation of overexploited king crab stocks
Low- and high-order gravitational harmonics of rigidly rotating Jupiter
No full textThe Juno Orbiter has provided improved estimates of the even gravitational harmonics J2 to J8 of Jupiter. To compute higher-order moments, new methods such as the concentric Maclaurin spheroids (CMS) method have been developed, which surpass the commonly used theory of figures (ToF) method in accuracy. This progress raises the question whether ToF can still provide a useful service for deriving the internal structure of giant planets in the solar system. In this paper, I apply both the ToF and the CMS method to compare results for polytropic Jupiter and for the physical equation of state H/He-REOS.3-based models. An accuracy in the computed values of J2 and J4 of 0.1% is found to be sufficient in order to obtain the core mass safely within 0.5 M⊕ numerical accuracy and the atmospheric metallicity within about 0.0004. ToF to the fourth order provides that accuracy, while ToF to the third order does not for J4. Furthermore, I find that the assumption of rigid rotation yields J6 and J8 values in agreement with the current Juno estimates, and that higher-order terms (J10 to J18) deviate by about 10% from predictions by polytropic models. This work suggests that ToF 4 can still be applied to infer the deep internal structure of giant planets, and that the zonal winds on Jupiter reach less deep than 0.9 RJ
Composition and fate of short-period super-Earths. The case of CoRoT-7b
No full textAstronomy and Astrophysics, 516, p. id.A20 (2010)International audienc
Patterns of larval growth and chemical composition in the Amazon River prawn, Macrobrachium amazonicum
No full textThe Amazon River prawn, Macrobrachium amazonicum (Heller, 1862), is a target speciesfor regional fisheries in Brazil and a candidate for aquaculture. Under controlled laboratoryconditions (29°C, 10), the larval phase of this species shows variability in the morphology and number of successive stages (mostly 9-10, occasionally 8 to >12). In the most commonly observed developmental pathway (9 stages, taking approximately 20-22 days from hatching to the first juvenile stage), we studied patterns of larval growth in terms of total body length (TL), carapace length (CL), dry mass (W), and elemental composition (carbon, hydrogen, nitrogen; collectively CHN). At hatching, about 12% of late embryonic W, 15-18% of C and H, but only 7% of N were lost, indicating higher losses of lipids and/or carbohydrates than proteins. Significant variability was observed in the initial biomass and elemental composition of newly hatched larvae from 20 different egg batches. This may cause variation in the endotrophic potential of the early stages, as the zoea I of this species is a non-feeding stage, and also the zoea II may still utilize internal energy stores remaining from the egg yolk. Lacking or low larval feeding activity from hatching through stage II coincided with low initial growth. Concomitantly, the proportions of C and H (in % of W) as well as the C:N ratio decreased from hatching through stage IV, indicating a utilization of stored lipids. The percentage of N showed an opposite pattern, reflecting protein synthesis associated with morphogenesis. Size growth showed maximum increments per moult in the late zoeal stages (IIIVI), followed by lower increments in the subsequent decapodid stages (VII-IX). This sigmoidal growth pattern may reflect ontogenetic changes in morphometric relationships. Biomass showed exponential patterns of increase from zoeal stage III throughout later larval development and in the first two juvenile stages. Furthermore, patterns of larval growth in M. amazonicum are characterized as linear relationships between larval W in stage n and that in stage n+1 (Hiattdiagram), between larval size (CL) and biomass (W, C), and between W and either C or N. Using CHN data, we also provide estimates of the protein and lipid contents of larval biomass (ca. 38-46% and 10-12% of W, respectively). High survival, rapid development, and predictable patterns of larval growth support the assumption that M. amazonicum should be a suitable species for production in aquaculture
An exploration of double diffusive convection in Jupiter as a result of hydrogen–helium phase separation
No full textJupiter's atmosphere has been observed to be depleted in helium (Yatm ∼ 0.24), suggesting active helium sedimentation in the interior. This is accounted for in standard Jupiter structure and evolution models through the assumption of an outer, He-depleted envelope that is separated from the He-enriched deep interior by a sharp boundary. Here we aim to develop a model for Jupiter's inhomogeneous thermal evolution that relies on a more self-consistent description of the internal profiles of He abundance, temperature, and heat flux. We make use of recent numerical simulations on H/He demixing, and on layered double diffusive (LDD) and oscillatory double diffusive (ODD) convection, and assume an idealized planet model composed of an H/He envelope and a massive core. A general framework for the construction of interior models with He rain is described. Despite, or perhaps because of, our simplifications made we find that self-consistent models are rare. For instance, no model for ODD convection is found. We modify the H/He phase diagram of Lorenzen et al. to reproduce Jupiter's atmospheric helium abundance and examine evolution models as a function of the LDD layer height, from those that prolong Jupiter's cooling time to those that actually shorten it. Resulting models that meet the luminosity constraint have layer heights of ≈0.1–1 km, corresponding to ≈10 000–20 000 layers in the rain zone between ∼1 and 3–4.5 Mbar. Present limitations and directions for future work are discussed, such as the formation and sinking of He droplets
Estimating the number of planets that PLATO can detect
No full textContext. The PLATO mission is scheduled for launch in 2026. It will monitor more than 245 000 FGK stars of magnitude 13 or brighter for planet transit events. Among the key scientific goals are the detection of Earth-Sun analogs; the detailed characterization of stars and planets in terms of mass, radius, and ages; the detection of planetary systems with longer orbital periods than are detected in current surveys; and to advance our understanding of planet formation and evolution processes.
Aims. This study aims to estimate the number of exoplanets that PLATO can detect as a function of planetary size and period, stellar brightness, and observing strategy options. Deviations from these estimates will be informative of the true occurrence rates of planets, which helps constraining planet formation models.
Methods. For this purpose, we developed the Planet Yield for PLATO estimator (PYPE), which adopts a statistical approach. We apply given occurrence rates from planet formation models and from different search and vetting pipelines for the Kepler data. We estimate the stellar sample to be observed by PLATO using a fraction of the all-sky PLATO stellar input catalog (PIC). PLATO detection efficiencies are calculated under different assumptions that are presented in detail in the text.
Results. The results presented here primarily consider the current baseline observing duration of 4 yr. We find that the expected PLATO planet yield increases rapidly over the first year and begins to saturate after 2 yr. A nominal (2+2) 2-yr mission could yield about several thousand to several tens of thousands of planets, depending on the assumed planet occurrence rates. We estimate a minimum of 500 Earth-size (0.8−1.25 RE) planets, about a dozen of which would reside in a 250–500 days period bin around G stars. We find that one-third of the detected planets are around stars bright enough (V ≤11) for RV-follow-up observations. We find that a 3-yr-long observation followed by 6 two-month short observations (3+1 yr) yield roughly twice as many planets as two long observations of 2 yr (2+2 yr). The former strategy is dominated by short-period planets, while the latter is more beneficial for detecting earths in the habitable zone.
Conclusions. Of the many sources of uncertainties for the PLATO planet yield, the real occurrence rates matters most. Knowing the latter is crucial for using PLATO observations to constrain planet formation models by comparing their statistical yields
An exploration of double diffusive convection in Jupiter as a result of hydrogen–helium phase separation
No full textOn the degeneracy of the tidal Love number
No full textContext. In order to accurately model giant planets, a whole set of
observational constraints is needed. As the conventional constraints for extrasolar
planets like mass, radius, and temperature allow for a large number of acceptable models,
a new planetary parameter is desirable in order to further constrain planetary models.
Such a parameter may be the tidal Love number k2.
Aims. In this paper we aim to study the capability of
k2 to reveal further information about the interior
structure of a planet.
Methods. With theoretical planetary models we investigate how the tidal
Love number k2 responds to the internal density distribution
of a planet. In particular, we demonstrate the effect of the degeneracy of
k2 due to a density discontinuity in the envelope of a
three-layer planetary model.
Results. The effect of a possible outer density discontinuity masks the
effect of the core mass on the Love number k2. Hence, there is
no unique relationship between the Love number k2 and the core
mass of a planet. We show that the degeneracy of k2 with
respect to a layer boundary in the envelope also occurs in existing planets, e.g.
Satur
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