Cosmological Distance Indicators

We review three distance measurement techniques beyond the local universe: (1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and (3) HI intensity mapping. We describe the principles and theory behind each method, the ingredients needed for measuring such distances, the current observational results, and future prospects. Time-delays from strongly lensed quasars currently provide constraints on \(H_{0}\) with \(<4\%\) uncertainty, and with \(1\%\) within reach from ongoing surveys and efforts. Recent exciting discoveries of strongly lensed supernovae hold great promise for time-delay cosmography. BAO features have been detected in redshift surveys up to \(z\lesssim0.8\) with galaxies and \(z\sim2\) with Ly-\(\alpha\) forest, providing precise distance measurements and \(H_{0}\) with \(<2\%\) uncertainty in flat \(\Lambda\)CDM. Future BAO surveys will probe the distance scale with percent-level precision. HI intensity mapping has great potential to map BAO distances at \(z\sim0.8\) and beyond with precisions of a few percent. The next years ahead will be exciting as various cosmological probes reach \(1\%\) uncertainty in determining \(H_{0}\), to assess the current tension in \(H_{0}\) measurements that could indicate new physics.     

The solar and heliospheric observatory,SOHO — A phase-A project of the European space agency

The Solar and Heliospheric Observatory is designed to address basic questions concerning the Sun and Heliosphere. In this paper our present understanding of coronal heating, solar wind generation and solar oscillations is described. The proposed model SOHO instrument payload is outlined and it is shown how it would contribute to our understanding in the above three fields.     

Solar Surface Magnetism and Irradiance on Time Scales from Days to the 11-Year Cycle

The uninterrupted measurement of the total solar irradiance during the last three solar cycles and an increasing amount of solar spectral irradiance measurements as well as solar imaging observations (magnetograms and photometric data) have stimulated the development of models attributing irradiance variations to solar surface magnetism. Here we review the current status of solar irradiance measurements and modelling efforts based on solar photospheric magnetic fields. Thereby we restrict ourselves to the study of solar variations from days to the solar cycle. Phenomenological models of the solar atmosphere in combination with imaging observations of solar electromagnetic radiation and measurements of the photospheric magnetic field have reached high enough quality to show that a large fraction (at least, about 80%) of the solar irradiance variability can be explained by the radiative effects of the magnetic activity present in the photosphere. Also, significant progress has been made with magnetohydrodynamic simulations of convection that allow us to relate the radiance of the photospheric magnetic structures to the observations.     

Foreword

Space Science Reviews -     

A particle event at 5 AU and 20° southern latitude from measurements with the EPAC instrument on Ulysses

In November 1992, the Ulysses spacecraft observed a multiple solar particle event and a CME event at 5.2 AU and a heliographic latitude of 20° S which were superimposed to the recurrent corotating interacting region. Distinct particle flux increases caused by these events were observed in all energy channels of the EPAC experiment. The experimental findings are discussed.     

Plasma Morphology at Mars. Aspera-3 Observations

A total of about of 400 orbits during the first year of the ASPERA-3 operation onboard the Mars Express spacecraft were analyzed to obtain a statistical pattern of the main plasma domains in the Martian space environment. The environment is controlled by the direct interaction between the solar wind and the planetary exosphere/ionosphere which results in the formation of the magnetospheric cavity. Ionospheric plasma was traced by the characteristic “spectral lines” of photoelectrons that make it possible to detect an ionospheric component even far from the planet. Plasma of solar wind and planetary origin was distinguished by the ion mass spectrometry. Several different regions, namely, boundary layer/mantle, plasma sheet, region with ionospheric photoelectrons, ray-like structures near the wake boundary were identified. Upstream parameters like solar wind ram pressure and the direction of the interplanetary electric field were inferred as proxy from the Mars Global Surveyor magnetic field data at a reference point of the magnetic pile up region in the northern dayside hemisphere. It is shown that morphology and dynamics of the main plasma domains and their boundaries are governed by these factors as well as by local crustal magnetizations which add complexity and variability to the plasma and magnetic field environment.     

Origin, Injection, and Acceleration of CIR Particles: Observations Report of Working Group 6

This report emphasizes new observational aspects of CIR ions revealed by advanced instruments launched on the Ulysses, WIND, SOHO, and ACE spacecraft, and by the unique vantage point of Ulysses which carried out the first survey of Corotating Interaction Region (CIR) properties over a very wide range of heliolatitudes. With this more complete observational picture established, this review is the basis to consider the status of theoretical models on origin, injection, and acceleration of CIR particles reported by Scholer, Mann et al. (1999) in this volume. This revised version was published online in August 2006 with corrections to the Cover Date.     

Observed relation between solar luminosity and radius

We compile measurements of the total solar irradiance S_o made in the period 1967 to 1983 from balloons, rockets, and spacecrafts. These data, when corrected for atmospheric and calibration differences, suggest a systematic increase in S_o of about 0.025% per year. In 1979 and after the ACRIM/SMM and the ERB/NIMBUS data reveal a systematic decrease of about the same magnitude. The period of the early apparent increase embraces a full solar activity cycle of 11 years: hence the effect cannot be that of simple sunspot blocking. This trend of a slow increase followed by a similar decrease is compared with solar diameter measurements obtained from daily meridian transit timings of the Sun made during the same period at the Royal Greenwich Observatory and at the U.S. Naval Observatory. We find in both of these data sets an apparent increase in solar diameter of about 0.03″arc per year during the period of increasing solar irradiance and a weaker suggestion of a similar, subsequent decline. If the apparent trends in diameter and luminosity are real they allow us to estimate the empirical relationship between the two quantities. For this period we find W=ΔlogR/ΔlogL=0.078±0.026.     

Observations of Irradiance Variations

Since November 1978 a complete set of total solar irradiance (TSI) measurements from space is available, yielding a time series of 21 years. From measurements made by different space radiometers (HF on NIMBUS-7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite record of TSI can be compiled. The corrections which are needed for each radiometer, mainly to compensate for degradation, but also for operational influences are described. ACRIM I (1980–1989) and ACRIM II (1992–1995) are taken as reference because their degradation was monitored by inflight comparisons with spare radiometers; since 1996 VIRGO is used as reference. The scale of ACRIM II is adjusted to ACRIM I by comparison with NIMBUS-7 and ERBE. The reliability of this adjustment depends strongly on the stability of the HF and ERBE radiometer during the period of the gap between the ACRIMs which is discussed in detail together with an assessment of the overall precision of the composite.