We present results of stratification analyses for Mg, Si, Ca, Cr and Fe in the atmospheres of two Cr-type sharp-lined peculiar stars HD 133792 and HD 204411. Even in the absence of strong magnetic fields their atmospheres are stable which is confirmed by zero microturbulence. Both stars are slightly evolved, their $\log g \approx 3.5$, whereas their effective temperatures are 9200 and 8400 K, respectively. We find a moderate Cr and Fe stratification. However the abundances of these elements do not fall below the solar value throughout the atmosphere. Si and Ca are strongly stratified, in particular in HD 133792, with large underabundances in the outer atmospheric layers. Abundance stratifications derived for weakly magnetic Ap stars are compared with the empirically determined stratification in the atmospheres of strongly magnetic Ap stars in the same temperature range.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The spherical aberration in the primary mirror of the Hubble Space Telescope causes more than 80% of the light from a point source to be spread into a halo of radius of 2–3 arcsec. The point spread function (PSF) is both time variant (resulting from spacecraft jitter and desorption of the secondary mirror support structure) and space variant (owing to the Cassegrain repeater optics in the Wide Field / Planetary Camera). A variety of image restoration algorithms have been utilized on HST data with some success, although optimal restorations require better modeling of the PSF and the development of efficient restoration algorithms that accommodate a spacevariant PSF. The first HST servicing mission (December 1993) will deploy a corrective optics system for the Faint Object Camera and the two spectrographs and a second generation WF/PC with internal corrective optics. As simulations demonstrate, however, the restoration algorithms developed now for aberrated images will be very useful for removing the remaining diffraction features and optimizing dynamic range in post-servicing mission data.

Silicon and especially carbon bound-free absorptions considerably reduce the emergent flux in the ultraviolet for stars near spectral type A0 (Teff = 10000 K). An overabundance of silicon and/or an underabundance of carbon can affect the Balmer discontinuity and the Paschen continuum by a few per cent at most. However, the abundances of these ultraviolet absorbers will have little effect on the temperature distribution calculated for a star if the model is chosen to match the visual spectrum. An examination of the ultraviolet spectrum of Sirius shows that still more opacity is needed; part of this absorption can be supplied by line blanketing.

Radial Velocity follow-up is essential to establish or exclude the planetary nature of a transiting companion as well as to accurately determine its mass. Here we present some elements of an efficient Doppler follow-up strategy, based on high-resolution spectroscopy, devoted to the characterization of transiting candidates. Some aspects and results of the radial velocity follow-up of the CoRoT space mission are presented in order to illustrate the strategy used to deal with the zoo of transiting candidates.

Spectroheliogram movies of magnetic, velocity, and intensity fields have been obtained in a wide variety of spectral lines. The time resolution was typically 10–30 s. Some of the lines used were: CN λ 3883; CaI λ 6103; FeI λ 4071; FeI λ 5434; FeII λ 4924; CaII λ 3934; CaII λ 8542.

We investigate the stellar angular momentum of galaxies across the Hubble sequence from the CALIFA survey. The distribution of CALIFA elliptical and lenticular galaxies in the λRe - εe diagram is consistent with that shown by the Atlas3D survey. Our data, however, show that the location of spiral galaxies in this diagram is significantly different. We have found two families of spiral galaxies with particularly peculiar properties: (a) spiral galaxies with much higher λRe values than any elliptical and lenticular galaxy; (b) low-mass spiral galaxies with observed λRe values much lower than expected for their apparent flattening. We use these two families of objects to argue that (1) fading alone cannot explain the transformation of spiral to lenticular galaxies, and (2) that those low-mass spiral galaxies are in fact dark matter dominated, which explains the unusually low angular momentum.

Globular clusters produce orders of magnitude more millisecond pulsars per unit mass than the Galactic disk. Since the first cluster pulsar was uncovered 20 years ago, at least 138 have been identified – most of which are binary millisecond pulsars. Because their origins involve stellar encounters, many of the systems are exotic objects that would never be observed in the Galactic disk. Examples include pulsar-main sequence binaries, extremely rapid rotators (including the current record holder), and millisecond pulsars in highly eccentric orbits. These systems are allowing new probes of the interstellar medium, the equation of state of material at supra-nuclear density, the masses of neutron stars, and globular cluster dynamics.

The HARPS search for low-mass extrasolar planets has been ongoing for more than 4 years, targeting originally about 400 bright FGK dwarfs in the solar neighbourhood. The published low-mass planetary systems coming from this survey are fully confirmed by subsequent observations, which demonstrate the sub-m/s long-term stability reached by HARPS. The complex RV curves of these systems have led us to focus on a smaller sample of stars, accumulating more data points per star. We perform a global search in our data to assess the existence of the large population of ice giants and super-Earths predicted by numerical simulations of planet formation. We indeed detect about 45 candidates having minimum masses below 30 M⊕ and orbital periods below 50 days. These numbers are preliminary since the existence of these objects has to be confirmed by subsequent observations. However, they indicate that about 30% of solar-type stars may have such close-in, low-mass planets. Some emerging properties of this low-mass population are presented. We finally discuss the prospects for finding transiting objects among these candidates, which may possibly yield the first nearby, transiting super-Earth.

Inclusions of one type of meteorite enclosed in another have been found in several gas-rich meteorites, unequilihrated chondrites and mesosiderites. The inclusions in all but one case are chondritic; a majority are mineralogically and isotopically similar to carbonaceous chondrites. These meteorite mixtures most probably resulted from collisions among asteroids.

The cosmic microwave background (CMB) provides us with our most direct observational window to the early universe. Observations of the temperature and polarization anisotropies in the CMB have played a critical role in defining the now-standard cosmological model. In this contribution we review some of the basics of CMB science, highlighting the role of observations made with ground-based and balloon-borne Antarctic telescopes. Most of the ingredients of the standard cosmological model are poorly understood in terms of fundamental physics. We discuss how current and future CMB observations can address some of these issues, focusing on two directly relevant for Antarctic programmes: searching for gravitational waves from inflation via B-mode polarization, and mapping dark matter through CMB lensing.

We present an extensive summary of the position, redshift, and flux data on the secure, multiply imaged, quasar and radio lenses. It includes neither the less-promising (in the opinion of the author) lens candidates nor the cluster lenses (which are too hard to reduce to short tables of numbers). A broader listing of suggested lenses and also of the cluster lenses is available at (see Pospieszalskia-Surdej et al. in this volume): http://www.stsci.edu/ftp/stsci/library/grav_lens/grav_lens.html

Among the 50 discovered extrasolar planets orbiting main-sequence solar type stars only three are confirmed to be in a binary star system. However, the majority of stars seem to form in binary or even multiple stellar systems. Standard planet formation scenarios consider the creation of planets or planetary systems only for isolated solitary stars. The presence of a companion creates tidal torques on the protoplanetary disk, which may influence the formation process of planets in disks. In this contribution the consequences of the companion's perturbation on the formation scenario of planets is briefly discussed.

Gaia is an ambitious space astrometry mission of ESA with a main objective to map the sky in astrometry and photometry down to a magnitude 20 by the end of the next decade. Given its extreme astrometric accuracy and the repeated observations over five years, the observation modelling is done in a fully relativistic framework and several tests of General Relativity or of its extensions can be carried out during the data processing. The paper presents an overview of the current activities in this area and of the expected performances.

Cepheid variables provide a key to understanding the structure and distance of the Magellanic Clouds, as well as providing accurate reddenings there. Recent major observing programs have continually expanded the data base of photometry and velocities. It is important to try to reconcile the plethora of Cepheid data into a consonant picture of the three-dimensional spatial structure of the Clouds and to compare in a consistent manner the bulk Cloud distance moduli found by several photometric methods.

We started (sub-)millimeter continuum and line studies of entire molecular cloud complexes located at intermediate distances from the Sun (1–3 kpc). Such an unbiased approach allows to identify and characterize the earliest phases of high-mass stars overlooked by IRAS or MSX. Our complete MAMBO-2 surveys of the Cygnus X and NGC 7538 complexes reveal a large population of ${\sim} 0.1$ pc-size massive young stellar objects (MYSOs) harboring high-mass infrared-quiet protostars. The determination of the nature of all the new millimeter sources is still in progress but we have already collected evidence that the infrared-quiet (or class 0-like) protostellar phase might last as long as the better-known infrared-bright protostellar phase. Besides, our complete census of MYSOs fails to discover the high-mass analogues of pre-stellar dense cores. We propose that the observed lower-density pre-stellar clumps (${>} 1$ pc) rapidly concentrate and collapse as also found in the kinematical studies of other prominent clumps. Indeed, CS and HCO$^+$ mappings in W43 and Cygnus X suggest global supersonic contraction with inward velocities of several km s−1 on parsec scales. Our work and similar studies of entire star-forming complexes will thus definitively contribute to a better knowledge of the earliest phases of high-mass star formation.

Detection of intrinsic solar variability on the total flux level was made using results from the first Active Radiometer Irradiance Monitor (ACRIM) experiment, launched on the Solar Maximum Mission (SMM) in early 1980. ACRIM I, specifically designed to start the high precision total solar irradiance database as part of the U.S. Climate Research Program, produced high precision results throughout the 9.75 years of the Solar Maximum Mission. The second ACRIM experiment was flown aboard the Space Shuttle as part of the NASA/ESA Spacelab 1 Mission in late 1983. Its primary function has been to provide a comparison with ACRIM I that could be used to relate its observations with future satellite solar monitors, should they and ACRIM I fail to overlap in time. The second ACRIM satellite solar monitoring experiment (ACRIM II) has provided high precision total solar irradiance observations since its launch as part of the Upper Atmosphere Research Satellite (UARS) mission in late 1991 and continues at present. The shuttle ACRIM instrumentation has been flown on the ATLAS 1 and 2 missions in 1992 and 1993, providing comparisons with the UARS/ACRIM II.

The determination of effective temperatures of very hot central stars (Teff > 70 000 K) by model atmosphere analyses of optical H and He line profiles is afflicted with considerable uncertainty, primarily due to the lack of neutral helium lines. Ionization balances of metals, accessible only with UV lines, allow more precise temperature estimates. The potential of iron lines is pointed out. At the same time iron and other metal abundances, hardly investigated until today, may be derived from UV spectra. We describe recent HST spectroscopy performed for this purpose.

A search for iron lines in FUV spectra of the hottest H-deficient central stars (PG1159-type, Teff >100000 K) taken with FUSE was unsuccessful. The derived deficiency is interpreted in terms of iron depletion due to n-capture nucleosynthesis in intershell matter, which is now exposed at the stellar surface as a consequence of a late He shell flash.

In an attempt to summarize the present knowledge on the general magnetic field (gmf) of the Sun we pointed out the fine structure and the statistical nature of the gmf as one of its most important properties. The dipole-like behaviour of the mean polar field strengths is combined sometimes (since 1964) with a bias of the S-polarity flux for both poles. Highly uneven distribution of gmf with latitude and longitude, the disappearance of gmf at the South pole for months, and short period, almost synchronous at both poles, variations in the sign of gmf are pointed out. The fluctuations with time of the mean magnetic field of the Sun seen as a star (as well as mf at different latitudes) shows periodicity connected with the rotation of the Sun and very close agreement with the fluctuations of the interplanetary field (sector structure). The effect of faster rotation of N-polarities as compared with S-polarities as well as the bias of mean solar as well as interplanetary S-polarity fields are also pointed out. The possibility of short time-scale (hours) intrinsic changes in the local pattern of gmf is demonstrated.

Observational constraints on the form of the high-mass stellar IMF are reviewed. The evidence includes star counts in the solar neighborhood, individual and composite star clusters, and nearby galaxies, and arguments based on integrated light and chemical evolution modeling. There is no convincing evidence for any systematic variations of the shape of the high-mass IMF. However, the various determinations are very uncertain, and do not allow any firm estimate of the logarithmic slope of the upper IMF; the appropriate value is somewhere between −1.3 and −2.3, with region-to-region variations smaller than about ±0.5. A number of lines of evidence suggest that the lower mass limit or mode mass of the IMF increases with increasing star formation rate, reaching perhaps 10–15 m⊙ in some starburst galaxies. It is also possible that the upper mass limit depends on metallicity, based on variations in excitation conditions of HII regions.