The ESA astrometric mission Gaia, due for launch in late 2011, will observe a very large number of asteroids (~ 350,000 down to the magnitude 20), most from the main belt, with an unprecedented positional precision (at the sub-milliarcsecond level). Such high-precision astrometry will enable to considerably improve the orbits of a large number of objects, and also to determine the masses of the largest asteroids by analyzing their gravitational pull during close encounters with smaller ones. A global solution involving simultaneously all the perturbers and the smaller targets should yield about hundred masses with a precision better than 30 percent. The knowledge of these masses will be a rich source of information on the physics of main-belt asteroids and will increase the accuracy of modern solar system ephemerides. We outline the principle of the mathematical method based on variational equations developed to solve for the orbital parameters and the masses of the largest bodies. Calculations have been performed by taking into account realistic simulation of the Gaia observations such as geometry, time sequence, magnitude and by considering possible close approaches among 350,000 asteroids. We give a list of asteroids whose mass can be estimated along with its formal precision.

A study of the distribution of OH gas in the central region of the nearby active starburst galaxy M82 has confirmed two previously known bright masers and revealed several new main line masers. Three of these are seen only at 1665 MHz, one is detected only at 1667 MHz, while the rest are detected in both lines. Observations covering both the 1665 and 1667 MHz lines, conducted with both the Very Large Array (VLA) and the Multi-Element Radio Linked Interferometer Network (MERLIN), have been used to accurately measure the positions and velocities of these features. This has allowed a comparison with catalogued continuum features in the starburst such as HII regions and supernova remnants, as well as known water and satellite line OH masers. Most of the main line masers appear to be associated with known HII regions although the two detected only at 1665 MHz are seen along the same line of sight as known supernova remnants.

We present parsec-resolution spectral-line VLBI data for two epochs separated by 15 months as a precise new probe of the innermost regions of the nearby Ultraluminous Infrared Galaxy (ULIRG) Arp 220. This galaxy hosts a powerful starburst, with an associated supernova (SN) rate of order 4/yr. An extensive population of compact continuum sources interpreted as radio supernovae (RSNe) and young supernova remnants (SNR) has been imaged. We show here that many of the supernova-related radio continuum point sources exhibit clear evidence of OH absorption or maser emission in the intervening gas, and as such provide us with a sampling of conditions along very narrow and specific lines of sight through the nuclear environment. The OH gas along these lines of sight exhibits velocity dispersions of up to several tens of km/sec, and that in some cases, multiple distinct concentrations of masing gas at different radial velocities can be discerned. There is evidence for variability in the OH properties on ~1yr timescales. Our results are discussed in the context of the overall OH megamaser properties of Arp 220.

We examine the photometric and structural properties of early-type galaxies derived from the ACS Virgo and Fornax Cluster Surveys, supplementing these data with previously published or newly reanalysed data for additional early-type galaxies in Virgo, Fornax and the Local Group. As we have noted elsewhere, Sérsic models are found to provide accurate representations of the observed brightness profiles on scales greater than a few percent of the effective radius, Re. On smaller scales, the brightness profiles of bright (MB ≳ −20) galaxies show central deficits with respect to the inward extrapolation of the Sérsic models; fainter galaxies usually show central excesses. Fainter than MB ≈ −20, we find a continuity in the photometric and structural scaling relations: i.e., between absolute magnitude, central surface brightness, Sérsic index, effective radius, and the surface brightness measured at, and averaged within, the effective radius. There is no evidence for a “dwarf/giant dichotomy” — a conclusion consistent with a number of recent studies but contrary to some earlier claims.

The transformation between the International Terrestrial Reference System (ITRS) and the Geocentric Celestial Reference system (GCRS) is an essential part of the models to be used when dealing with Earth's rotation or when computing directions of celestial objects in various systems. The 2000 and 2006 IAU resolutions on reference systems have modified the way the Earth orientation is expressed and adopted high accuracy models for expressing the relevant quantities for the transformation from terrestrial to celestial systems. First, the IAU 2000 Resolutions have refined the definition of the astronomical reference systems and transformations between them and adopted the IAU 2000 precession-nutation. Then, the IAU 2006 Resolutions have adopted a new precession model that is consistent with dynamical theories and have addressed definition, terminology or orientation issues relative to reference systems and time scales that needed to be specified after the adoption of the IAU 2000 resolutions. These in particular provide a refined definition of the pole (the Celestial intermediate pole, CIP) and the origin (the Celestial intermediate origin, CIO) on the CIP equator as well as a rigorous definition of sidereal rotation of the Earth. These also allow an accurate realization of the celestial intermediate system linked to the CIP and the CIO that replaces the classical celestial system based on the true equator and equinox of date. This talk explains the changes resulting from the joint IAU 2000/2006 resolutions and reviews the consequences on the concepts, nomenclature, models and conventions in fundamental astronomy that are suitable for modern and future realizations of reference systems. Realization of the celestial intermediate reference system ensuring a micro-arc-second accuracy is detailed.

At the IAU 26th GA held in Prague in 2006, a new precession model (P03) was recommended and adopted to replace the old one, IAU1976 precession model. This new P03 model is to match the IAU2000 nutation model that is for anelastic Earth model and was adopted in 2003 to replace the previous IAU1980 model. However, this IAU2000 nutation model is also not a perfect one for our complex Earth, as stated in the resolution of IAU nutation working group. The Earth models in the current nutation theories are idealized and too simple, far from the real one. They suffer from several geophysical factors: the an-elasticity of the mantle, the atmospheric loading and wind, the oceanic loading and current, the atmospheric and oceanic tides, the (lateral) heterogeneity of the mantle, the differential rotation between the inner core and the mantle, and various couplings between the fluid outer core and its neighboring solids (mantle and inner core). In this paper, first we give a very brief review of the current theoretical studies of non-rigid Earth nutation, and then focus on the couplings near the core-mantle boundary and the inner core-outer core boundary, including the electro-magnetic, viscous, topographic, and gravitational couplings. Finally, we outline some interesting future studies.

The 6dF Galaxy Survey provides a very large sample of galaxies with reliable measurements of Lick line indices and velocity dispersions. This sample can be used to explore the correlations between mass and stellar population parameters such as age, metallicity and [α/Fe]. Preliminary results from such an analysis are presented here, and show that age and metallicity are significantly anti-correlated for both passive and star-forming galaxies. Passive galaxies have strong correlations between mass and metallicity and between age and α-element over-abundance, which combine to produce a downsizing relation between age and mass. For old passive galaxies, the different trends of M/L with mass and luminosity in different passbands result from the differential effect of the mass–metallicity relation on the luminosities in each passband. Future work with this sample will examine the Fundamental Plane of bulge-dominated galaxies and the influence of environment on relations between stellar population parameters and mass.

Arp 220 is a nearby system in final stages of galaxy merger with powerful ongoing star-formation at and surrounding the two nuclei. Arp 220 was detected in HI absorption and OH Megamaser emission and later recognized as the nearest ultra-luminous infrared galaxy also showing powerful molecular and X-ray emissions. In this paper we review the available radio and mm-wave observational data of Arp 220 in order to obtain an integrated picture of the dense interstellar medium that forms the location of the powerful star-formation at the two nuclei.

Using the Millennium Galaxy Catalogue we quantify the dependency of the disc and bulge luminosity functions on galaxy inclination. Using a contemporary dust model we show that our results are consistent with galaxy discs being optically thick in their central regions (). As a consequence the measured B-band fluxes of bulges can be severely attenuated by 50% to 95% depending on disc inclination. We argue that a galaxy's optical appearance can be radically transformed by simply removing the dust, e.g. during cluster infall, with mid-type galaxies becoming earlier, redder, and more luminous. Finally we derive the mean photon escape fraction from the integrated galaxy population over the 0.1 μm to 2.1 μm range, and use this to show that the energy of starlight absorbed by dust (in our model) is in close agreement with the total far-IR emission.

Luminous, extragalactic OH masers are excellent tracers of merger triggered, intense star formation in Ultra Luminous Infrared Galaxies (ULIRGs). As such, they are tracers of high density regions in the centers of active galaxies. From high resolution imaging of the 1667 MHz emission in a small sample of OH megamaser galaxies, the general consensus is that most of the maser emission arises in thick, circumnuclear structures. Here we summarize the current work on OH megamasers, and present the preliminary results on VLA observations of the 1720 MHz satellite line in III Zw 35, Mrk 231 and Arp 220. We also briefly mention ongoing work on investigating the nature of the high molecular gas density environment in a sample of ULIRGs, using CO (J=3–2) observations. A subset of the ULIRG sample harbors OH megamaser emission, and is therefore suited for comparing gas properties between ULIRGs with and without OH megamaser emission.

Deep-space laser ranging will be ideal for testing relativistic gravity, and mapping the solar-system to an unprecedented accuracy. ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD I are such missions. ASTROD I is a mission with a single spacecraft; it is the first step of ASTROD with 3 spacecraft. In this talk, after a brief review of ASTROD and ASTROD I, we concentrate on the precision of solar astrodynamics that can be achieved together with implications on astrometry and reference frame ties. The precise planetary ephemeris derived from these missions together with second post-Newtonian test of relativistic gravity will serve as a foundation for future precise astrometry observations. Relativistic frameworks are discussed from these considerations.

The nuclei of ULIRGs harbor massive young stars, an accreting central black hole, or both. Results are presented for molecular gas that is exposed to X-rays (1–100 keV, XDRs) and far-ultraviolet radiation (6–13.6 eV, PDRs). Attention is paid to species like HCO+, HCN, HNC, OH, H2O and CO. Line ratios of HCN/HCO+ and HNC/HCN discriminate between PDRs and XDRs. Very high J (>10) CO lines, observable with HIFI/Herschel, discriminate very well between XDRs and PDRs. In XDRs, it is easy to produce large abundances of warm (T > 100 k) H2O and OH. In PDRs, only OH is produced similarly well.

Since VLBI techniques produce a microarcsecond positional accuracy of celestial objects, tests of GR using radio sources as probes of a gravitational field have been made. We present the results from two recent tests using the VLBA: in 2005, the measurement of the classical solar deflection; and in 2002, the measurement of the retarded gravitational deflection associated with Jupiter. The deflection experiment measured γ to an accuracy of 3 × 10−4; the Jupiter experiment measured the retarded term to 20% accuracy. The controversy over the interpretation of the retarded term is summarized.

We have used the BzK-selection to identify a composite population of passive, and star-forming galaxies at redshifts 1.4 ≤ z ≤ 2.5 from the Great Observatories Origins Deep Survey (GOODS). Using an unprecedented large sample of galaxies in this redshift range, we characterize the morphological diversity through the analysis of the surface-brightness profile shapes for 171 galaxies with passive SEDs, and 1068 star-forming galaxies. We find that the z ~ 2 galaxies display a wide range of morphologies, from spheroidals to disk-like. Interestingly, the galaxies with passively-evolving SEDs predominantly have steep profiles as seen for the classical bulges at low redshifts, although they are very compact with re < 3 kpc. The star-forming galaxies on the other hand exhibit mostly disk-like and merger morphologies, and have sizes comparable to their low−z counterparts. Our results emphasize the need for an unbiased selection in order to reveal the morphological diversities, and range of galaxy properties at high redshifts.

We present results on the stellar populations of 232 quiescent galaxies in the Shapley Supercluster, based on spectroscopy from the AAOmega spectrograph at the AAT. The key characteristic of this survey is its coverage of many low-luminosity objects (σ ~ 50 kms−1), with high signal-to-noise (~45 Å−1). Balmer-line age estimates are recovered with ~25% precision even for the faintest sample members. We summarize the observations and absorption line data, and present correlations of derived ages and metallicities with mass and luminosity. We highlight the strong correlation between age and α-element abundance ratio, and the anti-correlation of age and metallicity at fixed mass, which is shown to extend into the low-luminosity regime.

According to a revised schedule of the Russian Space Agency, in October 2008 the 10 m space telescope RadioAstron will be launched in a high eccentric orbit around the Earth. Acting together with ground based radio telescopes, the VLBI interferometer with a ground-space arm will operate. The interferometer will have extraordinary angular resolution of a few microarcsecond (μas) at the shortest wavelength (1.35 cm). Since typical angular scales for gravitational microlensing are at the μas level for cosmological locations of sources and microlenses, in principle there is a chance to resolve microimages and (or) at least, detect astrometrical shift of bright point like images. In particular, gravitationally lensed systems, such as B1600+434, where in radio band a signature of microlensing is found, look suitable for direct observations of microlensing, since microlensing with the RadioAstron interferometer may be detected in the future (considering its high angular resolution and a relatively high sensitivity and assuming a ground support by the advanced radio telescopes).

We model the OH megamaser emission from the luminous infrared galaxy IIIZw35 as arising from a narrow rotating starburst ring of radius 22 pc enclosing a mass of 7×106M⊙. We show how both the compact and apparently diffuse maser emission from this ring can arise from a single phase of unsaturated maser clouds amplifying background radio continuum. The masering clouds are estimated to have a diameter of <0.7 pc and internal velocity dispersion of ∽20 kms−1. We find that the clouds are neither self-gravitating nor pressure confined, and they could be magnetically confined or freely expanding. Their dispersal lifetimes may set the vertical thickness of the ring. For an estimated internal density of 3×103cm−3, cloud masses are of order 24 M⊙. The observed spectral features and velocity gradients indicate that the clouds must be outflowing and escaping the nucleus. The cloud mass outflow rate is estimated to be 0.8 M⊙yr−1, while the star formation rate is ∽19 M⊙yr−1. Associated ionised gas, possibly generated from dissipated clouds, provides free-free absorption along the source axis, explaining the observed East-West asymmetries. We show that the clumpiness of a maser medium can have a dramatic effect on what is observed even in a relatively low gain OH megamaser. Specifically, in IIIZw35 our clumpy maser model naturally explains the large line to continuum ratios, the large 1667MHz:1665MHz line ratios and the wide velocity dispersions seen in the compact maser spots. Other astrophysical masers showing both compact and apparently diffuse emission might be explained by similar clumpy structures.

The observed molecular properties of a sample of FIR-luminous and OH megamaser (OH-MM) galaxies have been investigated. The ratio of high and low-density tracer lines is found to be determined by the progression of the star formation in the system. The HCO+/HCN and HCO+/HNC line ratios are good proxies for the density of the gas, and PDR and XDR sources can be distinguished using the HNC/HCN line ratio. The properties of the OH-MM sources in the sample can be explained by PDR chemistry in gas with densities higher than 105.5cm−3, confirming the classical OH-MM model of IR pumped amplification with (variable) low gains.

General relativistic deflection of light by mass, dipole, and quadrupole moments of gravitational field of a moving massive planet in the Solar system is derived in the approximation of the linearized Einstein equations. All terms of the order of 1 μas and larger are taken into account, parameterized, and classified in accordance with their physical origin. We discuss the observational capabilities of the near-future optical and radio interferometers for detecting the Doppler modulation of the radial deflection, and the dipolar and quadrupolar light-ray bending by Jupiter and Saturn.

There is now good agreement between the various methods of estimating the space density of the star-formation rate (SFRD) at low redshifts (z < 1), with uncertainties around 30–50%. However, the situation at higher redshifts remains much less clear, with uncertainties in the SFRD, due to e.g. poorly known dust absorption corrections, of as much as 300–500%. Radio emission from star-forming galaxies is unaffected by absorption and scales linearly with star-formation rate, thus the radio luminosity of star-forming galaxies provides an excellent independent, unbiased measure of their star-formation rate. The current deepest ‘blank field’ radio surveys (reaching <10 μJy rms at 1.4 GHz) are sensitive enough to detect starburst galaxies out to z ~ 3, and so potentially offer an excellent way to measure the SFRD. Indeed, modelling of the sub-mJy source counts requires an additional population of faint steep spectrum objects, that are very likely to be starburst galaxies.