Tidal Constraints Research Articles

A method to constrain the total mass of galaxy groups

We present a simple method to constrain the total mass of groups of galaxies. Tidal theory predicts that a limit to the mass of bound groups of galaxies can be obtained by using the fact that the tidal forces due to the external mass distributions are insufficient to disrupt the groups. To illustrate how the method works, we find tidal limits on the mass of 11 nearby galaxy groups. In most cases, tidal limits placed on these groups show that the mass estimations obtained from methods based either on the application of the virial theorem or moments of the projected mass are underestimated by a factor of ∼2 even if, in many cases, errors are large. Three groups show virial parameters fully concordant with the tidal constraints while two outlier groups show anomalous results. The “irregular” state of the latter suggests that the reliability of the method depends on the physical properties of the test groups, which should match the fundamental assumptions of spherical symmetry and dynamical equilibrium state.

A New Halo‐finding Method forN‐Body Simulations

We have developed a new halo-finding method called the physically self-bound (PSB) group-finding algorithm, which is designed to identify halos located in crowded regions. To demarcate subhalo regions, we introduce the tidal constraint combined with the self-boundedness check. In order to reduce overload and parallel finding, we first divide whole simulation particles into many local particle groups using two distinct methods. One adopts a density mesh used to group particles in connected local overdense cells, and the other applies the friends-of-friends (FoF) algorithm with a linking length (lloc) 0.3 times the mean particle separation. Then we divide each local particle group into several subgroups enclosed by numerous density levels and identify tidally stable and self-bound subhalos around density peaks. Subhalo finding is done on a fine mesh with cell size equal to twice the force resolution. Particles in a density shell that surrounds only one density peak form a subhalo candidate. Particles located in the outer remaining density shells that surround more than one peak become member candidates of one of the subhalos. We determine the membership using the tidal boundary constraint. We have found that the mass function is very insensitive to lloc when lloc ≥ 0.3. At least 40% of subhalos do not seem to collapse to the most massive subhalo in a FoF group when the Press & Schechter collapse model is applied to measure the size of a collapsed structure in the Lagrangian space. We have applied our halo-finding method to a 10243 particle simulation in a ΛCDM model and compare the halo mass functions with those previously found in the literature.

Axially symmetric rotating traversable wormholes

This paper generalizes the static and spherically symmetric traversable wormhole geometry to a rotating axially symmetric one with a time-dependent angular velocity by means of an exact solution. It was found that the violation of the weak energy condition, although unavoidable, is considerably less severe than in the static spherically symmetric case. The radial tidal constraint is more easily met due to the rotation. Similar improvements are seen in one of the lateral tidal constraints. The magnitude of the angular velocity may have little effect on the weak energy condition violation for an axially symmetric wormhole. For a spherically symmetric one, however, the violation becomes less severe with increasing angular velocity. The time rate of change of the angular velocity, on the other hand, was found to have no effect at all. Finally, the angular velocity must depend only on the radial coordinate, confirming an earlier result.

Tidal Constraints on the Masses of Extrasolar Planets

Tidal theory predicts that the orbits of close extrasolar giant planets will circularize on timescales that can be comparable to the ages of those systems. Additionally, planets that are close enough and massive enough can spin up their central stars. Since the eccentricities of extrasolar planet orbits are determined by the radial velocity technique and since stellar rotation rates are observed, or at least derived, limits on the masses of close extrasolar planets can be placed. We find upper limits on the masses of eight extrasolar planets, including limiting the masses of υ And b, HD 75289b, HD 187123b, and 51 Peg b to less than 1.48, 1.21, 0.59, and 0.51 Jupiter masses, respectively. There is a contradiction in the constrained mass of HD 217107b, in that its eccentricity is apparently too high. This anomalously high eccentricity could be real and caused by other planets in that system; or it could be an artifact of fitting a one-orbit solution to multiplanet data. The tidal limits placed on all these extrasolar planets are only as good as the knowledge of the stellar parameters (age, rotation period), which in some cases is not very good; better detailed knowledge of stars hosting planets will be necessary.

Does Titan have an ocean? A review of current understanding of Titan's surface

The nature of Titan's surface has been a fascinating puzzle since the first definitive detection of an atmosphere in 1944. Pre‐Voyager models of the surface based largely on cosmochemistry and the detection of atmospheric methane permitted a range of possibilities from clathrate hydrate to pure methane snow. The Voyager 1 flyby ruled out this last possibility but pointed to a mixed ocean of methane, higher hydrocarbons, and nitrogen about a kilometer in thickness. Subsequent ground‐based radar observations reveal a reflective surface, inconsistent with pure light hydrocarbons. The variation in radar reflectivity from night to night is surprisingly high. Passive radiometry at centimeter wavelengths indicates a surface emissivity distinct from that of the icier Galilean satellites, suggesting that water ice does not dominate the surface either. Observations in the near‐infrared region are consistent with dirty water ice as well as a suite of other materials, including areas of hydrocarbon seas. Reconciling the Voyager, radar and near‐infrared data continue to be a challenge. Possibilities include the following: a hydrocarbon ocean, which is frothy or contains a significant amount of aerosol contaminants, maintained near the surface by stirring; an ocean stored in pore spaces of the ice regolith or in an aquiferlike system; an ocean that is somewhat smaller than estimated from the methane photolysis rate because of impact‐driven chemistry. Models involving significant amounts of dry land exposed above a shallow ocean potentially run afoul of tidal constraints imposed by Titan's nonzero free orbital eccentricity. The Cassini/Huygens mission will investigate the nature of the surface through a variety of techniques and hopefully solve this long‐standing planetary puzzle.

A Motographic Analysis of Foraging Behaviour in Intertidal Chitons (Acanthopleura Spp.)

The behaviour of two intertidal chitons (Mollusca: Polyplacophora) from the western Indian Ocean (Acanthopleura gemmata and A. brevispinosa) and one from the Caribbean Sea (A. granulata) were analyzed in order to assess the spatial and temporal organization of their foraging activity. Individual paths were recorded in the field using a motographic method based on LED-tracking and the speed variation during each excursion used to reveal the places where the animals slowed down or stopped for the purpose of grazing. Foraging segments of each trajectory were selected according to a threshold speed which was individually calibrated. The three species of Acanthopleura exhibited graded foraging strategies of different spatial complexity. Acanthopleura gemmata focused its foraging on a few large feeding sites well separated from its permanent home. Acanthopleura brevispinosa exploited more subdivided feeding grounds not distinctly separated from its rest area. Acanthopleura granulata spreads its grazing activity over many small segments, throughout each excursion. Due to different tidal and diel constraints on their activity the three species allocated different absolute time to foraging, but the fraction of time spent foraging relative to the total excursion was similar in each.

Initial Dilution for Outfall Parallel to Current

Rotary tidal currents or site constraints can result in an outfall diffuser being alined with the current in shallow water. Experiments using a small model laboratory diffuser flume and a much larger scale model in an estuarine channel were used to establish the significant processes causing initial dilution of effluent discharged from a multiport diffuser alined parallel to the ambient current. From considerations of momentum conservation and mixing, and the results of the flume experiments, an expression for the initial dilution in shallow water was obtained and the conditions defining shallow water were established. The results of the field experiments carried out in an estuarine channel were in agreement with the laboratory results and verified the derived expression. A relationship between the initial dilution and the angle between the diffuser and the current was developed from the field studies.

Correlation between digestion rate and feeding frequency in the stomachless teleost, Blennius pholis L.

Foregut emptying in Blennius pholis at 16–18°C is exponential (St=Soe‐Rt; R=0.006 when t is in min and s in mg dry weight). In consequence, the time for the foregut to empty completely varies in proportion to ln (meal size) in a chosen size of fish or to ln (body weight) in different sized fish fed to the same relative amount (% body weight). Appetite returns rapidly in comparison with other species (4–15 h for fish of 0.5−30 g) and, because of the tidal constraints imposed on this littoral fish, voluntarily ingested meals are large (14–9% body weight depending on fish size). Studies on digestion in small, stomachless fish are not adequately made using X‐radiography and must be supported by sequential gut samples after a meal.

Some dynamic aspects of the distribution of planktonic Foraminifera in the western North Atlantic : Cifello R., 1962. J. Mar. Res., 20 (3): 201–213

In the present study we investigate the ecology and distribution of living benthic foraminifera to test the effect of hyper tidal exposure and their suitability as sea level indicators. Within a salt marsh area along the Canche Estuary (northern France), four transects were sampled to see the effects of maximal tidal constraints (shore transects) and minimal tidal constraints (alongshore transects). Multivariate analyses have been performed to determine the correlations between biotic (foraminiferal absolute abundances) and abiotic factors (elevation, grain-size, TOC and total sulphur). For each of the principal benthic foraminiferal species the tolerance to subaerial exposure have been estimated as well. Two distinctive foraminiferal zones have been identified along the vertical tidal gradient: a zone I in the higher part of the salt marsh dominated by agglutinated and porcelaneous taxa, and a zone II in the lower one dominated by hyaline specimens. Hyper tidal exposure constraints the foraminiferal vertical zonation in accordance with the tidal frame. However it does not constitute a threshold parameter able by itself to explain all the faunal variations in the Canche Estuary. For sea level indicators, foraminifera should be considered relative to tidal subaerial exposure rather than to absolute altitude.