Planet formation models: the interplay with the planetesimal disc

According to the sequential accretion model, giant planet formation is based first on the formation of a solid core which, when massive enough, can gravitationally bind gas from the nebula to form the envelope. In order to trigger the accretion of gas, the core has to grow up to several Earth masses before the gas component of the protoplanetary disc dissipates. We compute the formation of planets, considering the oligarchic regime for the growth of the solid core. Embryos growing in the disc stir their neighbour planetesimals, exciting their relative velocities, which makes accretion more difficult. We compute the excitation state of planetesimals, as a result of stirring by forming planets, and gas-solid interactions. We find that the formation of giant planets is favoured by the accretion of small planetesimals, as their random velocities are more easily damped by the gas drag of the nebula. Moreover, the capture radius of a protoplanet with a (tiny) envelope is also larger for small planetesimals. However, planets migrate as a result of disc-planet angular momentum exchange, with important consequences for their survival: due to the slow growth of a protoplanet in the oligarchic regime, rapid inward type I migration has important implications on intermediate mass planets that have not started yet their runaway accretion phase of gas. Most of these planets are lost in the central star. Surviving planets have either masses below 10 ME or above several Jupiter masses. To form giant planets before the dissipation of the disc, small planetesimals (~ 0.1 km) have to be the major contributors of the solid accretion process. However, the combination of oligarchic growth and fast inward migration leads to the absence of intermediate mass planets. Other processes must therefore be at work in order to explain the population of extrasolar planets presently known.Comment: Accepted for publication in Astronomy and Astrophysic

CHEOPS performance for exomoons: The detectability of exomoons by using optimal decision algorithm

Many attempts have already been made for detecting exomoons around transiting exoplanets but the first confirmed discovery is still pending. The experience that have been gathered so far allow us to better optimize future space telescopes for this challenge, already during the development phase. In this paper we focus on the forthcoming CHaraterising ExOPlanet Satellite (CHEOPS),describing an optimized decision algorithm with step-by-step evaluation, and calculating the number of required transits for an exomoon detection for various planet-moon configurations that can be observable by CHEOPS. We explore the most efficient way for such an observation which minimizes the cost in observing time. Our study is based on PTV observations (photocentric transit timing variation, Szab\'o et al. 2006) in simulated CHEOPS data, but the recipe does not depend on the actual detection method, and it can be substituted with e.g. the photodynamical method for later applications. Using the current state-of-the-art level simulation of CHEOPS data we analyzed transit observation sets for different star-planet-moon configurations and performed a bootstrap analysis to determine their detection statistics. We have found that the detection limit is around an Earth-sized moon. In the case of favorable spatial configurations, systems with at least such a large moon and with at least Neptune-sized planet, 80\% detection chance requires at least 5-6 transit observations on average. There is also non-zero chance in the case of smaller moons, but the detection statistics deteriorates rapidly, while the necessary transit measurements increase fast. (abridged)Comment: 32 pages, 14 figures, accepted for publication in PAS

Astronomical spectrograph calibration with broad-spectrum frequency combs

Broadband femtosecond-laser frequency combs are filtered to spectrographically resolvable frequency-mode spacing, and the limitations of using cavities for spectral filtering are considered. Data and theory are used to show implications to spectrographic calibration of high-resolution, astronomical spectrometers

The match/mismatch hypothesis and the feeding success of fish larvae in ice-covered southeastern Hudson Bay

We studied the synchronism between the seasonal occurrence of fish larvae and their prey in ice-covered southeastern Hudson Bay, Canada, in spring 1988, 1989 and 1990. Arctic cod #Boreogadus saida and sand lance #Ammodytes sp. larvae hatched several weeks before ice break-up and fed primarily on copepod nauplii. The timing of 50% yolk resorption was the same every year (11 to 18 May for Arctic cod and 5 to 11 June for sand lance) but the availability of copepod nauplii varied substantially between years, both in magnitude (7-fold) and timing (4 to 6 wk). Interannual differences in the under-ice abundance of nauplii were linked to variations in the abundance of female cyclopoid copepods, and appeared unrelated to the timing of the ice-algal or phytoplankton blooms. Interannual differences (2- to 4-fold) in the feeding success of fish larvae (percent feeding incidence at length and mean feeding ratio at length) were related to the availability of copepod nauplii. Consistent with the match/mismatch hypothesis, the fixity of the spawning season in relation to a variable cycle of prey abundance accounted for the observed variations in feeding success and apparent growth (length at date) of fish larvae. Yet, in this particular ecosystem, a match or mismatch between Arctic cod or sand lance larvae and their prey may depend more on the dynamics of cyclopoid copepods during the previous winter than on the timing of the spring algal blooms. (Résumé d'auteur

Cognitive impairment in individuals with insomnia : clinical significance and correlates

Study Objectives: The aims of this study were to (1) investigate the nature of cognitive impairment in individuals with insomnia, (2) document their clinical significance, (3) examine their correlates, and (4) explore differences among individuals with insomnia with and without cognitive complaints. Design: Participants underwent 3 consecutive nights of polysomnography. On the morning following the third night, they completed a battery of questionnaires and neuropsychological tests. Participants: The sample included 25 adults with primary insomnia (mean age: 44.4 ± 11.5 y, 56% women) and 16 controls (mean age: 42.8 ± 12.9 y, 50% women) matched for sex, age, and education. Intervention: N/A. Measurement and Results: Participants completed neuropsychological tests covering attention, memory, working memory, and executive functions, as well as questionnaires assessing the subjective perception of performance, depression, anxiety, fatigue, sleepiness, and hyperarousal. There were significant group differences for the attention and episodic memory domains. Clinically significant deficits were more frequent in the insomnia group. Within the insomnia group, individuals with cognitive complaints exhibited significantly poorer performance on a larger number of neuropsychological variables. All impaired aspects of performance were significantly associated with either subjective or objective sleep continuity, and some were also independently related to sleep microstructure (i.e., relative power for alpha frequencies) or selected psychological variables (i.e., beliefs or arousal). Conclusions: These findings suggest clinically significant alterations in attention and episodic memory in individuals with insomnia. Objective deficits were more pronounced and involved more aspects of performance in a subgroup of individuals with cognitive complaints. These deficits appear associated with sleep continuity, and may also be related to sleep microstructure and dysfunctional beliefs

Femtosecond frequency comb measurement of absolute frequencies and hyperfine coupling constants in cesium vapor

We report measurements of absolute transition frequencies and hyperfine coupling constants for the 8S_{1/2}, 9S_{1/2}, 7D_{3/2}, and 7D_{5/2} states in ^{133}Cs vapor. The stepwise excitation through either the 6P_{1/2} or 6P_{3/2} intermediate state is performed directly with broadband laser light from a stabilized femtosecond laser optical-frequency comb. The laser beam is split, counter-propagated and focused into a room-temperature Cs vapor cell. The repetition rate of the frequency comb is scanned and we detect the fluorescence on the 7P_{1/2,3/2} -> 6S_{1/2} branches of the decay of the excited states. The excitations to the different states are isolated by the introduction of narrow-bandwidth interference filters in the laser beam paths. Using a nonlinear least-squares method we find measurements of transition frequencies and hyperfine coupling constants that are in agreement with other recent measurements for the 8S state and provide improvement by two orders of magnitude over previously published results for the 9S and 7D states.Comment: 14 pages, 14 figure

Impact of Groundwater Flow on Permafrost Degradation and Transportation Infrastructure Stability

INE/AUTC 13.0