The presence of a diffuse stellar component in galaxy clusters has been established by a number of observational works in recent years. In this contribution I summarize our results (Zibetti et al. 2005) obtained by stacking SDSS images of 683 clusters, selected with the maxBCG algorithm at 0.2 < z < 0.3. Thanks to our large sample (≳30 times larger than any other sample of individually observed clusters so far) and the advantages of image stacking applied to SDSS images, we are able to measure the systematic properties of the intracluster light (ICL) with very high accuracy.

We find that the average surface brightness of the ICL ranges between 26 and 32 mag arcsec−2, and constantly declines from 70 kpc cluster-centric distance (i.e. distance from the BCG) to 700 kpc. Interestingly, the fraction of diffuse light over the total light (including galaxies), monotonically declines from ~ 50 to ≲ 5% over the same range of distances, thus showing that the ICL is more easily produced close to the bottom of a cluster's potential well. On the other hand, clusters lacking a bright BCG, hardly build up a large amount of intracluster stellar component. The link between the growth of the BCG and the ICL is also suggested by the strong degree of alignment between these two components which is observed in clusters where the BCG displays a significant elongation. With the additional fact that the colors of the ICL are consistent with those of galaxies, all this appears to be evidence for intracluster stars being stripped from galaxies that suffer very strong tidal interactions in the center of clusters and eventually merge into the BCG.

Our measurements also show that intracluster stars are a minor component of a cluster's baryonic budget, representing only ~ 10% of the total optical emission within 500 kpc.

Finally, we discuss some open issues that emerge from a comparison of the present results with other observations and recent theoretical modeling.

The objective of the passive seismic experiment is to measure vibrations of the lunar surface produced by all natural and artificial sources of seismic energy and to use these data to deduce the internal structure and constitution of the Moon, the nature of tectonic processes which may be active within the Moon, the rate of strain energy release for the lunar body, and the numbers and masses of meteroroids striking the lunar surface. The instrument used is also capable of measuring changes in gravity and tidal tilts which occur in its vicinity. To accomplish these objectives, seismic data must be combined with data from laboratory measurements of the physical and chemical properties of surface rocks, and many other geophysical and geochemical measurements. Thus far, we have had the opportunity to record data from two lunar seismic stations which were installed by the astronauts during Apollo missions 11 and 12. The combined recording time from these stations is presently over 9 months, but there was no overlap to permit recording the same event at two stations. Results from the analysis of these data have been presented by the seismic experiment team in five previous papers.

In addition to revealing spherical harmonic degrees, $\ell$, of excited modes, pulsational amplitudes and phases from multicolour photometry and radial velocity data yield valuable constraints on stellar atmospheric parameters and on subphotospheric convection. Multiperiodic pulsators are of particular interest because each mode yields independent constraints. We present an analysis of data on the twelve modes observed in FG Vir.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

HERMES is a new high-resolution multi-object spectrograph on the Anglo Australian Telescope. The primary science driver for HERMES is the GALAH survey, GALactic Archaeology with HERMES. We are planning a spectroscopic survey of about a million stars, aimed at using chemical tagging techniques to reconstruct the star-forming aggregates that built up the disk, the bulge and halo of the Galaxy. This project will benefit greatly from the stellar distances and transverse motions from the Gaia mission.

The stability diagrams in the “pericentric distance — eccentricity” plane of initial data are built and analyzed for Kepler-38, Kepler-47, and Kepler-64 (PH1). This completes a survey of stability of the known up to now circumbinary planetary systems, initiated by Popova & Shevchenko (2013), where the analysis was performed for Kepler-16, 34, and 35. In the diagrams, the planets appear to be “embedded” in the fractal chaos border; however, I make an attempt to measure the “distance” to the chaos border in a physically consistent way. The obtained distances are compared to those given by the widely used numerical-experimental criterion by Holman & Wiegert (1999), who employed smooth polynomial approximations to describe the border. I identify the resonance cells, hosting the planets.

Euclid enables the exploration of large sky areas with diffraction limited resolution in the optical and near-infrared, and is sensitive enough to detect targets at cosmological distances. This combination of capabilities gives Euclid a clear advantage over telescope facilities with larger apertures, both on ground and in space. The decision to mount in the NISP instrument one extra grism for the wavelength range 0.92-1.3 μm with a spectral resolution of R ≈260 makes possible a rest-frame UV survey of the early Universe in the redshift range 6.5 < z < 9.7. Euclid’s standard imaging with VIS in the 0.55-0.9 μm band and with NISP in the Y, J, H bands provide complementary photometry for further target identification and characterization. Euclid is a suitable facility to discover and map the spatial distribution of rare high-redshift targets and to collect statistically relevant samples, in particular of high redshift Lyα emitters and QSOs, which can be used as signposts of the cosmic structures. The Euclid surveys are also a starting point for deeper follow up observations of the individual high-z objects. We present the Euclid mission and discuss the detectability of high-z objects to probe the epoch of ionization.

The Problem of Chemical Identification of the interstellar dust grains has vexed astronomers for over three decades. The earliest evidence for the mere presence of interstellar dust was deduced from the observation of stars (via star counts) in the Milky Way. The best presently available clues for possible chemical identification are spectroscope data, particularly the diffuse (hitherto unidentified) interstellar absorption lines. This paper is concerned primarily with a discussion of new theoretical interpretations of the spectroscopic data.

Much related information on the dust grains was obtained from observations of space reddening, its wavelength dependence, and from interstellar polarization. Furthermore, correlation of space reddening and the strength of some of the diffuse lines is important to the discussion of possible chemical identification of the dust.

The zone of bright stars inclined 20° to the galactic plane, pointed out by John Herschel (1847) and by Gould (1874,1879), is generally referred to as Gould’s Belt. This General Assembly is well timed. With the splendour of the centre of the Milky Way in the zenith in the early hours of the night anyone who comes out of the city-lights of Sydney can try to convince himself of the reality of this phenomenon.

Shapley and Cannon (1922, 1924) showed that the concentration towards Gould’s Belt is very pronounced for the brighter B. stars, while the fainter ones are highly concentrated towards the galactic plane. Their results indicated the radius of this local system to be of the order of 500 pc. The motions of the B. stars brighter than a magnitude of about 5m.5 are characterized by the K-effect, which thus seems to be a property of this local Gould Belt system.

We present our earlier measurement of the coronal fields above a sunspot in the active region, NOAA #4741, which was obtained using microwave spectroscopy from the Owens Valley Radio Observatory (OVRO) in a form that allows comparison with theoretical models. Our empirical results for the coronal fields are compared with several theoretical models in order to understand the magnetic structure of a static sunspot. It is found that the presence of transverse pressure gradients should be considered to get a satisfactory fit.

A statistical analysis of the UHURU catalogue of X-ray sources leads to the following conclusions. If the weak sources are omitted, there is a strong concentration to low galactic latitude but the absence of a strong background and the presence of some strong sources at low galactic longitude indicate an appreciable number of sources of luminosity L ∼ 104L⊙ in the vicinity of the ‘nuclear bulge’. This region generally suggests ‘stellar population II’ and therefore stars of small mass. However, there is some suggestion of a second class of sources, distributed in the galactic plane like ‘stellar population I’ and suggesting large stellar masses.

There are three possible types of simple X-ray spectra, (a) optically thin bremsstrahlung, (b) black-body spectrum, and (c) power-law spectra. In this talk only theoretical models for type (a) are reviewed, including accretion, rotation and vibration for a white dwarf star and cocoons around a neutron star.

Some 6 km. of high-speed (Brush) records of the solar radio radiation at 200 Mc./s. made at Cornell University by Ch. L. Seeger in 1949 and 1950 have been kindly put at our disposal. They were made with a paper speed of 0·5 cm./sec., sometimes with 2·5 cm./sec. The response time of the recording pen was 0s·02. Some records have been made simultaneously at 205 Mc./s. and at 200 Mc./s. This paper gives some results of a discussion of these records. The properties that were studied are: the clustering tendencies among the radio-pips, their band-widths, the echo-phenomena and the duration of the pips.

We outline the results of numerical experiments on low SNR interferometer data. We confirm several theoretical analyses of the effect of averaging on visibility amplitude and closure phase data. However the triple product method for estimating the closure phase, which is useful in optical interferometry, does not provide a significant improvement over existing practice in radio interferometry. We introduce a way of using the triple product to estimate visibility amplitudes from arrays dominated by a single large telescope.

The large light curve changes of XY UMa, observed in the last 20 yr, are interpreted as stellar starspot activity of the primary component of this binary.

Central to any analysis of dynamical systems, or large scale motion, is the interpretation of redshifts of galaxies as classical Doppler velocity shifts. This is a testable assumption and for many years evidence has accumulated that is inconsistent with the assumption. Here we review recent evidence suggesting systematic radial dependence and temporal variation of redshifts.

Single, random, close encounters of long-period comets with Jupiter are studied. In contrast to earlier work, Jupiter's orbit is taken to be elliptical, but this has no effect on the rate of capture into short-period orbits and neither does it influence the distribution of longitudes of perihelion.

Dust formation by Wolf-Rayet stars is a powerful diagnostic of exceptional activity in their winds. Observed behaviour ranges from stars which make dust continually (e.g., WR 104, WC9d+B0.5V) to those which make dust for short episodes at periodic intervals (e.g., WR 140, WC7pd+04-5). In both examples, dust formation is related to colliding WR and OB stellar winds in binary orbits. We have been using IR photometry primarily from the SAAO and ESO and spectroscopy with ISO-sws to investigate systems having intermediate properties (WR 98a, WC8-9vd+?) or more complex behaviour (WR 48a, WC8ed+?).

Observations over the past 20 yrs or so are reviewed, with emphasis on recent high spatial resolution observations. The results lend support to earlier ideas on the propagation of type III electron streams through coronal regions of weak magnetic field strength but have not as yet settled the question whether the electrons propagate along the axes of coronal streamers. Several important burst properties appear to be significantly affected by ray scattering on small-scale size density irregularities in the corona.

We discuss the origin of hot hydrogen-deficient post-AGB stars. Evidence is growing that the “born-again AGB star scenario” as a consequence of a late He shell flash cannot explain the diverse observations. Analyses of the stars and their associated planetary nebulae suggest that the H-deficiency is not formed during the second post-AGB phase but already while the star is still on the AGB. There are even hints that the H-deficiency can occur before the first departure from the AGB.

The ζ Herculis system is one of the closest well-kown binaries. A tentative modelling shows that though the brighter star is easily described with a mass compatible with the observed one and an age of approximately 3.4 billion years, difficulties arise for the secondary, which plea for more precise observations.

A computer model for isolated disks of stars is used to study the self-consistent motion of large numbers of point masses as they move in the plane of the galactic disk. The Langley Research Center's CDC 6600 computers are used to integrate the equations of motion for systems containing from 50000 to 200000 stars. The results are presented in the form of a motion picture.