21 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
Odnowa - der Versuch einer Erneuerung 1980/81 d. Ereignisse in Polen im Spiegel von Dokumenten u. Presseberichten: e. kommentierte Materialsammlung
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
On the degeneracy of the tidal Love number<i>k</i><sub>2</sub>in multi-layer planetary models: application to Saturn and GJ 436b
No full textInterior structure models of GJ436b
No full textContext. GJ436b is the first extrasolar planet discovered that resembles
Neptune in mass and radius. Two more are known (HAT-P-11b and Kepler-4b), and many more
are expected to be found in the upcoming years. The particularly interesting property of
Neptune-sized planets is that their mass Mp and radius
Rp are close to theoretical
M − R relations of water planets. Given
Mp, Rp, and equilibrium
temperature, however, various internal compositions are possible.
Aims. A broad set of interior structure models is presented here that
illustrates the dependence of internal composition and possible phases of water occurring
in presumably water-rich planets, such as GJ436b on the uncertainty in atmospheric
temperature profile and mean density. We show how the set of solutions can be narrowed
down if theoretical constraints from formation and model atmospheres are applied or
potentially observational constraints for the atmospheric metallicity
Z1 and the tidal Love
number k2.
Methods. We model the interior by assuming either three layers
(hydrogen-helium envelope, water layer, rock core) or two layers (H/He/H2O
envelope, rocky core). For water, we use the equation of state H2O-REOS based
on finite temperature – density functional theory – molecular dynamics (FT-DFT-MD)
simulations.
Results. Some admixture of H/He appears mandatory for explaining the
measured radius. For the warmest considered models, the H/He mass fraction can reduce to
10-3, still extending over ~0.7R⊕.
If water occurs, it will be essentially in the plasma phase or in the superionic phase,
but not in an ice phase. Metal-free envelope models have
0.02 < k2 < 0.2, and the core mass cannot be
determined from a measurement of k2. In contrast, models with
0.3 < k2 < 0.82 require high metallicities
Z1 < 0.89 in the outer envelope. The uncertainty in
core mass decreases to 0.4Mp, if
k2 ≥ 0.3, and further to 0.2Mp,
if k2 ≥ 0.5, and core mass and Z1
become sensitive functions of k2.
Conclusions. To further narrow the set of solutions, a proper treatment
of the atmosphere and the evolution is necessary. We encourage efforts to observationally
determine the atmospheric metallicity and the Love
number k2
Constraining the interior of extrasolar giant planets with the tidal Love number<i>k</i><sub>2</sub>using the example of HAT-P-13b
No full textContext. Transit and radial velocity observations continuously discover an increasing number of exoplanets. However, when it comes to the composition of the observed planets the data are compatible with several interior structure models. Thus, a planetary parameter sensitive to the planet’s density distribution could help constrain this large number of possible models even further.
Aims. We aim to investigate to what extent an exoplanet’s interior can be constrained in terms of core mass and envelope metallicity by taking the tidal Love number k2 into account as an additional, possibly observable parameter.
Methods. Because it is the only planet with an observationally determined k2, we constructed interior models for the Hot Jupiter exoplanet HAT-P-13b by solving the equations of hydrostatic equilibrium and mass conservation for different boundary conditions. In particular, we varied the surface temperature and the outer temperature profile, as well as the envelope metallicity within the widest possible parameter range. We also considered atmospheric conditions that are consistent with nongray atmosphere models. For all these models we calculated the Love number k2 and compared it to the allowed range of k2 values that could be obtained from eccentricity measurements of HAT-P-13b.
Results. We use the example of HAT-P-13b to show the general relationships between the quantities temperature, envelope metallicity, core mass, and Love number of a planet. For any given k2 value a maximum possible core mass can be determined. For HAT-P-13b we find Mcore < 27 M⊕, based on the latest eccentricity measurement. We favor models that are consistent with our model atmosphere, which gives us the temperature of the isothermal region as ~2100 K. With this external boundary condition and our new k2-interval we are able to constrain both the envelope and bulk metallicity of HAT-P-13b to 1−11 times stellar metallicity and the extension of the isothermal layer in the planet’s atmosphere to 3−44 bar. Assuming equilibrium tidal theory, we find lower limits on the tidal Q consistent with 103−105.
Conclusions. Our analysis shows that the tidal Love number k2 is a very useful parameter for studying the interior of exoplanets. It allows one to place limits on the core mass and estimate the metallicity of a planet’s envelope
WASP-135b : a highly irradiated, inflated hot Jupiter orbiting a G5V star
No full textWe report the discovery of a new transiting planet from the WASP survey. WASP-135b is a hot Jupiter with a radius of 1.30 pm 0.09 Rjup, a mass of 1.90 pm 0.08 Mjup and an orbital period of 1.401 days. Its host is a Sun-like star, with a G5 spectral type and a mass and radius of 0.98 pm 0.06 Msun and 0.96 pm 0.05 Rsun respectively. The proximity of the planet to its host means that WASP-135b receives high levels of insolation, which may be the cause of its inflated radius. Additionally, we find weak evidence of a transfer of angular momentum from the planet to its star.Peer reviewe
Discovery of WASP-65b and WASP-75b: Two hot Jupiters without highly inflated radii
No full textWe report the discovery of two transiting hot Jupiters, WASP-65b (Mpl = 1.55 ± 0.16 MJ; Rpl = 1.11 ± 0.06 RJ), and WASP-75b (Mpl = 1.07 ± 0.05 MJ; Rpl = 1.27 ± 0.05 RJ). They orbit their host star every ∼2.311, and ∼2.484 days, respectively. The planet host WASP-65 is a G6 star (Teff = 5600 K, [Fe/H] = −0.07 ± 0.07, age 8 Gyr); WASP-75 is an F9 star (Teff = 6100 K, [Fe/H] = 0.07 ± 0.09, age ∼ 3 Gyr). WASP-65b is one of the densest known exoplanets in the mass range 0.1 and 2.0 MJ (ρpl = 1.13 ± 0.08 ρJ), a mass range where a large fraction of planets are found to be inflated with respect to theoretical planet models. WASP-65b is one of only a handful of planets with masses of ∼1.5 MJ, a mass regime surprisingly underrepresented among the currently known hot Jupiters. The radius of WASP-75b is slightly inflated (10%) as compared to theoretical planet models with no core, and has a density similar to that of Saturn (ρpl = 0.52 ± 0.06 ρJ). Key words. planetary systems – stars: individual
Defining a positive circumferential resection margin in oesophageal cancer and its implications for adjuvant treatment
No full textA positive circumferential resection margin (CRM) has been associated with a poorer prognosis in oesophageal and oesophagogastric junctional (OGJ) cancer. The College of American Pathologists defines the CRM as positive if tumour cells are present at the margin, whereas the Royal College of Pathologists also include tumour cells within 1 mm of this margin. The relevance of these differences is not clear and no study has investigated the impact of adjuvant therapy. The aim was to identify the optimal definition of an involved CRM in patients undergoing resection for oesophageal or OGJ cancer, and to determine whether adjuvant radiotherapy improved survival in patients with an involved CRM.METHODS:This was a single-centre retrospective study of patients who had undergone attempted curative resection for a pathological T3 oesophageal or OGJ cancer. Clinicopathological variables and distance from the tumour to the CRM, measured to ± 0.1 mm, were correlated with survival.RESULTS:A total of 226 patients were included. Sex (P = 0·018), tumour differentiation (P = 0·019), lymph node status (P < 0·001), number of positive nodes (P < 0·001), and CRM distance (P = 0·042) were independently predictive of prognosis. No significant survival difference was observed between positive CRM 0-mm and 0·1-0·9-mm groups after controlling for other prognostic variables. Both groups had poorer survival than matched patients with a CRM at least 1 mm clear of tumour cells. Among patients with a positive CRM of less than 1 mm, those undergoing observation alone had a median survival of 18·6 months, whereas survival was a median of 10 months longer in patients undergoing adjuvant radiotherapy, but otherwise matched for prognostic variables (P = 0·009).CONCLUSION:A positive CRM of 1 mm or less should be regarded as involved. Adjuvant radiotherapy confers a significant survival benefit in selected patients with an involved CRM
