Clustering of galaxy clusters in cold dark matter universes

We use very large cosmological N -body simulations to obtain accurate predictions for the two-point correlations and power spectra of mass-limited samples of galaxy clusters. We consider two currently popular cold dark matter (CDM) cosmogonies, a critical density model ( τ CDM) and a flat low density model with a cosmological constant (ΛCDM). Our simulations each use 10⁹ particles to follow the mass distribution within cubes of side 2  h ⁻¹ Gpc ( τ CDM) and 3  h ⁻¹ Gpc (ΛCDM) with a force resolution better than 10⁻⁴ of the cube side. We investigate how the predicted cluster correlations increase for samples of increasing mass and decreasing abundance. Very similar behaviour is found in the two cases. The correlation length increases from     for samples with mean separation     to     for samples with     The lower value here corresponds to τ CDM and the upper to ΛCDM. The power spectra of these cluster samples are accurately parallel to those of the mass over more than a decade in scale. Both correlation lengths and power spectrum biases can be predicted to better than 10 per cent using the simple model of Sheth, Mo & Tormen. This prediction requires only the linear mass power spectrum and has no adjustable parameters. We compare our predictions with published results for the automated plate measurement (APM) cluster sample. The observed variation of correlation length with richness agrees well with the models, particularly for ΛCDM. The observed power spectrum (for a cluster sample of mean separation     ) lies significantly above the predictions of both models.     

On measuring low-degree p-mode frequency splitting with full-disc integrated data

The standard method of measuring rotational splitting from solar full-disc oscillation data, based on maximum-likelihood fitting of multi-Lorentzian profiles to oscillation power spectra, systematically overestimates the splitting. One of the reasons is that the maximum likelihood estimators (MLE) become unbiased only asymptotically as the number of data tends to infinity; for a finite data set they are often biased, inducing a systematic error. In this paper we assess by Monte Carlo simulations the amount of systematic error in the splitting measurement, using artificially generated power spectra. The simulations are carried out for multiplets of degree     2 and 3 with various signal-to-noise ratios, linewidths and observing times. We address the possible use of non-MLE estimators that could provide a smaller or negligible systematic error. The implication for asteroseismology is also discussed.     

Thermal and kinematic corrections to the microwave background polarization induced by galaxy clusters along the line of sight

We derive analytic expressions for the leading-order corrections to the polarization induced in the cosmic microwave background (CMB) owing to scattering of photons off hot electrons in galaxy clusters along the line of sight. For a thermal distribution of electrons with kinetic temperature k _B T _e∼10 keV and bulk peculiar velocity V ∼1000 km s⁻¹, the dominant corrections to the polarization induced by the primordial CMB quadrupole and the cluster peculiar velocity arise from electron thermal motion and are at the level of ∼10 per cent in each case, near the peak of the polarization signal. When more sensitive measurements become feasible, these effects will be significant for the determination of transverse peculiar velocities, and the value of the CMB quadrupole at the cluster redshift, via the cluster polarization route.     

Long,accurate time series measurements of radial velocities of solar-type stars

We have been measuring changes in the radial velocities (RV's) of solar-type stars to search for gravitational perturbations by planets. We transmit violet starlight through a Fabry-Perot etalon interferometer and sense changes in Doppler shift from changes in the fluxes of light on the slopes of stellar absorption lines. Our data now span 6 years. Our observations of the Sun showed earlier that both our technique and the profiles of solar photospheric violet absorption lines can be stable enough to reveal planetary perturbations. We now carry this validation to the spectra of other near-solar-type stars. Annual averages of our RV's of Draconis and Virginis are stable to ±6 m s^–1. The slope of our five-year series of RV's of Bootis A is consistent with the star's well-determined visual astrometric orbit about Bootis B. The Fabry-Perot technique of Doppler shift measurement is fully capable of detecting perturbations due to planets with masses and orbits similar to those of Jupiter.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

Solar and stellar chromospheric contrast

Positions of active regions estimated from observations of the whole solar disk in Caii K _iv during the period 1977–1989 at the Coimbra Astronomical Observatory are compared with the time-dependent latitudinal distribution of background solar magnetic fields and with the latitudinal shifts of boundaries of their polarities. We confirm that the sunspot groups are located near the zonal boundaries between the opposite polarities of the solar background magnetic field during different phases of the two recent consecutive cycles of activity. We demonstrate a probable connection between the increased number of groups and the commencement of poleward migration of zonal boundaries in both hemispheres. But the influence of the dominant convective rolls seems to he still unclear. A new problem of interrelation between the zonal and sector boundaries has also appeared.     

Palomar prime-focus infrared camera (PFIRCAM)

In a joint effort between engineers and scientists at the Jet Propulsion Laboratory and the California Institute of Technology, a near-infrared (0.8–2.6 m) direct imaging system has been developed and integrated into the Caltech Palomar Observatory detector series. The camera system has been tested and operated in a science mode at the prime-focus (f/3.3) of the Hale 5-m Telescope. This paper outlines the system components and performance, including discussion of the detector linearity.     

A Moon orbiting observatory for the measurement of the elemental and isotopic composition in the primary cosmic radiation

We describe a project for the measurement of elemental composition of the primary cosmic radiation to be performed by a space observatory orbiting around the Moon. The absence of atmosphere and the low intrinsic magnetic field of the Moon give access to the very low energy component of the cosmic radiation, allowing the search for rare events.The quest for antinuclei, the determination of the lunar lepton albedo and the abundance measurement of galactic radioactive clocks (Be¹⁰, C¹⁴, Al²⁶) are the major tasks of the ANTARES apparatus (ANTimatter Assessment RESearch).We report details of the instrument design, the expected performance for single detectors, their capability to accomplish the proposed measurements and the characteristics of the space mission.