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We have studied the peculiar environment around a ULX in NGC 4559 (with Lx ≈ 2 x 1040 erg s–1 and MBH ≳ 50M⊙). The X-ray source is located near the rim of a young (age < 30 Myr), large (diameter ≈ 700 pc) ring-like star forming complex possibly triggered by the impact of a dwarf satellite galaxy through the gas-rich outer disk of NGC 4559. We speculate that galaxy interactions (including the infall of high-velocity clouds and satellites on a galactic disk) and low-metallicity environments offer favourable conditions for the formation of compact remnants more massive than “standard” X-ray binaries, and accreting from a massive Roche-lobe filling companion.
This document is the final Phase A Science Report of the Australian LYMAN Science Working Group, and describes in detail the scientific objectives, technical feasibility, and engineering implementation of the LYMAN mission as developed in the Australian studies.
We present an overview of the survey for radio emission from active stars that has been in progress for the last six years using the observatories at Fleurs, Molonglo, Parkes and Tidbinbilla. The role of complementary optical observations at the Anglo-Australian Observatory, Mount Burnett, Mount Stromlo and Siding Spring Observatories and Mount Tamborine are also outlined. We describe the different types of star that have been included in our survey and discuss some of the problems in making the radio observations.
The preliminary results of EXOSAT and contemporaneous optical observations of E1405−451 (V834 Cen) in 1985 and 1986 are presented. In the latter of the two observations the soft X-ray light curve was observed to be quite different to that seen in all previous observations, but similar to the optical light curve and the new soft X-ray light curve of E2003+225. A phase shift of the broad soft X-ray eclipse was also observed. The hard X-ray and optical light curves have also undergone small changes.
White light simultaneous photometry and linear and circular polarimetry is presented for the AM Her variable ST LMi. Linear polarization evident throughout the faint phase is tentatively attributed to electron scattering from gas in the accretion column at heights greater than 5Rwd above the surface. The values of inclination and magnetic colatitude are revised to take into account the height and extent of the cyclotron emitting region which are also determined. A model of two closely connected emitting regions is proposed to account for the asymmetries observed in the light curve and polarization data for this and other AM Her systems. The cyclotron and hard x-ray emitting regions are found to be coincident, which eliminates the region above the shock as the source of polarized light. The shock height is found to be too low and the soft x-ray flux too large for the standard radiative shock model to apply.
We present simultaneous multiwavelength observations of the intermediate polar PQ Gem (Mason et al. 1992) obtained on 1993 February 18 and 19 using the Hatfield Polarimeter on UKIRT.
The data are folded on the 13.9 m spin period in Fig. 1. The light curves are double peaked at long wavelengths, with dips at phase ~ 0.15 and phase ~0.65, but almost sinusoidal in the U and B bands where the phase ~0.65 dip is absent. The percentage of circular polarisation also varies with the spin cycle, most notably in the I band, with both positive and negative excursions. The peaks in the positive and negative polarisation occur at phase ~ 0.15 and phase ~ 0.65 respectively, approximately coincident with the two intensity dips.
We apply a new method of eclipse mapping to the light curves of eclipsing polars. The technique aims to locate the bright emission associated with the accretion stream, using a technique that makes the fewest prior assumptions about the location of the accretion stream material. We have obtained data of EP Dra and HU Aqr with the S-Cam 2 superconducting tunnel junction camera using the William Herschel Telescope. The location of emission regions in both systems show that previously assumed trajectories are consistent with those found using our technique. Most of the emission is located in a region where we expect material to be confined to magnetic field lines, particularly for HU Aqr, while there appears to be a lack of emission from where we conventionally expect material to follow a ballistic trajectory from the L1 point.
The Optical Monitors are small optical telescopes which will fly on board of the X-ray satellites SPECTRUM-X-GAMMA (JET-X experiment) and XMM. Their main scientific applications are the simultaneous observations (imaging) in the optical and UV band of the optical counterparts of X-ray sources, with limiting magnitudes of about mv=22 (JET-X) and 24 (XMM). The OMs are developed in order to perform also serendipitous observations with high photometric precision of bright stars falling in the field of view, which should allow the detection of stellar microvariability at a level better than 10−5. The main characteristics of the instruments are presented and the problems to be solved in order to reach the scientific goals are briefly discussed.
Gaia's Radial Velocity Spectrometer (RVS) has been operating in routine phase for over one year since initial commissioning. RVS continues to work well but the higher than expected levels of straylight reduce the limiting magnitude. The end-of-mission radial-velocity (RV) performance requirement for G2V stars was 15 km s−1 at V = 16.5 mag. Instead, 15 km s−1 precision is achieved at 15 < V < 16 mag, consistent with simulations that predict a loss of 1.4 mag. Simulations also suggest that changes to Gaia's onboard software could recover ~0.14 mag of this loss. Consequently Gaia's onboard software was upgraded in April 2015. The status of this new commissioning period is presented, as well as the latest scientific performance of the on-ground processing of RVS spectra. We illustrate the implications of the RVS limiting magnitude on Gaia's view of the Milky Way's halo in 6D using the Gaia Universe Model Snapshot (GUMS).
A large amount (5 × 1010 M⊙) of hot gas is thought to exist in an extended (≈ 200 kpc) hot diffuse halo around the Milky Way. We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation of this gravitationally bound systems in this external environment. Ram pressure, Kelvin-Helmholtz and Rayleigh- Taylor instabilities, and tidal forces are accounted for separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment, useful in observational applications as well as theoretical interpretations of numerical results. We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system, thus investigating the detectability limits and relevance of these different effects for future observational projects. The theoretical framework developed has direct applications to the cases of our MW system as well as dwarf galaxies in galaxy clusters or any primordial gas-rich star cluster of stars orbiting within its host galaxy.
We compare the stellar motion around a spiral arm created in two different scenarios, transient/co-rotating spiral arms and density-wave-like spiral arms. We generate Gaia mock data from snapshots of the simulations following these two scenarios using our stellar population code, SNAPDRAGONS, which takes into account dust extinction and the expected Gaia errors. We compare the observed rotation velocity around a spiral arm similar in position to the Perseus arm, and find that there is a clear difference in the velocity features around the spiral arm between the co-rotating spiral arm and the density-wave-like spiral arm. Our result demonstrates that the volume and accuracy of the Gaia data are sufficient to clearly distinguish these two scenarios of the spiral arms.
We present the initial performance of the Gaia Radial Velocity Spectrometer, providing an overview of its performance, which is essentially nominal in terms of spectral resolution, throughput and operation, except for the presence of unexpectedly high levels of scattered background. This is mainly Solar in origin, and reduces the limiting magnitude for radial velocity measurements by ∼1 magnitude to V ∼ 16. Radial velocity calibration accuracies are compliant with requirements.
Euclid is the next ESA mission devoted to cosmology. It aims at observing most of the extragalactic sky, studying both gravitational lensing and clustering over ~15,000 square degrees. The mission is expected to be launched in year 2020 and to last six years. The sheer amount of data of different kinds, the variety of (un)known systematic effects and the complexity of measures require efforts both in sophisticated simulations and techniques of data analysis. We review the mission main characteristics, some aspects of the the survey and highlight some of the areas of interest to this meeting.
The lack of radial velocity data in the Hipparcos catalogue was considered a significant
deficiency, so when Gaia was conceived, a spectrometer was a core constituent of its
payload. The Gaia Radial Velocity Spectrometer faced a number of design challenges, in
particular set by the need to balance kinematic and astrophysical capability. We present
an overview of the evolution of the instrument to its present form, identifying the
competing technical, performance and programmatic factors which have shaped it.
During the five years of the mission, the Gaia spectrograph, the Radial Velocity
Spectrometer (RVS) will repeatedly survey the celestial sphere down to magnitude
V ~ 17–18. This talk presents: (i) the system which is currently developed within
the Gaia Data Processing and Analysis Consortium (DPAC) to reduce and calibrate the
spectra and to derive the radial and rotational velocities, (ii) the RVS expected
performances and (iii) scientific returns.
The ESA space astrometry mission Gaia will measure the positions, parallaxes and proper motions of the 1 billion brightest stars on the sky. Expected accuracies are in the 7–25 μas range down to 15 mag and sub-mas accuracies at the faint limit (20 mag). The astrometric data are complemented by low-resolution spectrophotometric data in the 330–1000 nm wavelength range and, for the brighter stars, radial velocity measurements. The scientific case covers an extremely wide range of topics in galactic and stellar astrophysics, solar system and exoplanet science, as well as the establishment of a very accurate, dense and faint optical reference frame. With a planned launch around 2012 and an (extended) operational lifetime of 6 years, final results are expected around 2021. We give a brief overview of the science goals of Gaia, the overall project organisation, expected performance, and some key technical features and challenges.
Gaia is an ESA cornerstone mission which will observe some billion stars in the galaxy enabling micro-arcsec astrometric catalogues to be constructed. In addition Gaia will produce high quality photometric and spectroscopic catalogues.
The data processing tasks are large and complex. A European consortium has been formed - the Gaia Data Processing and Analysis Consortium (DPAC). This paper describes the form of the UK Gaia Data Flow System Project contribution to the DPAC.
One of the principal restraints on the productivity of sheep in Less Favoured Areas of the EC is the small size of the native breeds which can only produce light finished carcases. The experiment reported here forms part of a collaborative study made between centres in Spain, Greece (Zygoyiannis, Stamataris and Katsaounis, 1993) and Great Britain (Friggens, Kyriazakis, Shanks and McClelland, 1993) aimed at assessing and comparing the potential and feed intake capacity of nine lesser known, small-sized European sheep breeds.
In previous work (Cropper et al.), we examined the U.S. Environmental Protection Agency's (EPA's) decision to cancel or continue the registration of pesticides that went through its Special Review process between 1975 and 1989. Our focus in that paper was on the final decision (Notice of Final Determination) issued by the EPA at the end of the rule-making process. Specifically, we asked whether this decision could be explained by the reported risks and benefits associated with pesticide use, and by the comments of special-interest groups that were entered in the public docket.