We present a method for the analysis of latitude distribution associated with temperature and/or velocity perturbations of the stellar surface due to non-radial pulsation (NRP) modes in rapidly rotating B stars. The technique is applied together with Fourier Doppler Imaging (FDI) to high resolution and high signal-to-noise ratio spectroscopic observations of ϵ Per. The main advantage of this approach is that it decomposes complex multi-periodic line profile variations into single components, allowing the detailed analysis of each mode separately. We study the 10.6-d−1 frequency that is particularly important for modal analysis of non-radial pulsations in the star.

We analyse evolutionary tracks at young ages for low mass stars with masses m ≤ 1.4 M⊙ and brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages ≲ 1 Myr.

We first review reasons why dark matter is an interesting issue in connection with star clusters. Next we consider to what extent the presence of dark matter is consistent with their dynamics and structure. We review various model-dependent and model-independent methods which have been applied to two well studied clusters, NGC 6397 and 47 Tuc. We suggest that about half of the mass in each object is still unobserved, possibly in the form of a mixture of low-mass stars and white dwarfs.

During Cycle 5 of the HST General Observer program we have been carrying out a “snapshot” survey of central stars of planetary nebulae. The snapshots are short exposures in the V (F555W) and I (F814W) filters, taken with the Wide Field Planetary Camera (WFPC2) during brief scheduling opportunities.

I survey recent theoretical work on the structure of the magnetospheres of rotation-powered pulsars, within the observational constraints set by their observed spindown, their ability to power synchrotron nebulae and their ability to produce beamed collective radio emission, while putting only a small fraction of their energy into incoherent X- and gamma radiation. I find no single theory has yet given a consistent description of the magnetosphere, but I conclude that models based on a dense outflow of pairs from the polar caps, permeated by a lower density flow of heavy ions, are the most promising avenue for future research.

The magnetic structure in the Galactic disk, the Galactic center and the Galactic halo can be delineated more clearly than ever before. In the Galactic disk, the magnetic structure has been revealed by starlight polarization within 2 or 3 kpc of the Solar vicinity, by the distribution of the Zeeman splitting of OH masers in two or three nearby spiral arms, and by pulsar dispersion measures and rotation measures in nearly half of the disk. The polarized thermal dust emission of clouds at infrared, mm and submm wavelengths and the diffuse synchrotron emission are also related to the large-scale magnetic field in the disk. The rotation measures of extragalactic radio sources at low Galactic latitudes can be modeled by electron distributions and large-scale magnetic fields. The statistical properties of the magnetized interstellar medium at various scales have been studied using rotation measure data and polarization data. In the Galactic center, the non-thermal filaments indicate poloidal fields. There is no consensus on the field strength, maybe mG, maybe tens of μG. The polarized dust emission and much enhanced rotation measures of background radio sources are probably related to toroidal fields. In the Galactic halo, the antisymmetric RM sky reveals large-scale toroidal fields with reversed directions above and below the Galactic plane. Magnetic fields from all parts of our Galaxy are connected to form a global field structure. More observations are needed to explore the untouched regions and delineate how fields in different parts are connected.

The Large Synoptic Survey Telescope (LSST; Ivezic et al.2008, http://lsst.org) is a planned, large-aperture, wide-field, ground-based telescope that will survey half the sky every few nights in six optical bands from 320 to 1050 nm. It will explore a wide range of astrophysical questions, ranging from discovering killer asteroids, to examining the nature of dark energy. LSST will produce on average 15 terabytes of data per night, yielding an (uncompressed) data set of 200 petabytes at the end of its 10-year mission. Dedicated HPC facilities (with a total of 320 TFLOPS at start, scaling up to 1.7 PFLOPS by the end) will process the image data in near real time, with full-dataset reprocessing on annual scale. The nature, quality, and volume of LSST data will be unprecedented, so the data system design requires petascale storage, terascale computing, and gigascale communications.

The last two years have seen widespread acceptance of the idea that the Milky Way halo was largely created in an early (8-10 Gyr ago) and massive (>1010Mȯ) merger. The roots of this idea pre-date the Gaia mission, but the exquisite proper motions available from Gaia have made the hypothesis irresistible. We trace the history of this idea, reviewing the series of papers that led to our current understanding.

Over 100 individual and cluster interplanetary dust particles (IDPs) have been analyzed for bulk abundances of 15 elements (C, O, Na, Mg, Al, Si, P, S, K, Ca, Ti, Cr, Mn, Fe, Ni). In general, IDPs have chondritic major element abundances, within a factor of 2 of the CI chondrites, and have carbon contents which average ~2-3 times higher than that of the most primitive, carbon-rich, carbonaceous meteorites (CI). The C-rich material is largely amorphous and is distributed throughout the particle as a matrix surrounding individual grains. The carbonaceous material has either smooth or vesicular texture; the latter texture suggests that volatiles could have been lost by particle heating which occurs during entry through the Earth's atmosphere.

Radiation hydrodynamics simulations have been used to produce numerical models of the convective surface layers of a number of stars, including the Sun and other stars on or above the main-sequence, white dwarfs of type DA, and red supergiants.

While granulation of main-sequence solar-type stars resembles that of the Sun, the convective velocity fields of F-type stars are much more violent and accompanied by strong pulsations. The properties of the thin convection zone(s) of A-type stars differ again (see Fig. 1). In this contribution, the pattern and dynamics of their surface granulation, the photospheric velocity fields and their effect on line profiles are investigated, based on new 3-D models of surface convection in main-sequence A-type stars with $T_{\rm eff}$=8500 K and 8000 K. Furthermore, we will look below the surface to study overshoot and the interaction of the surface convection zone and the deeper helium II convection zone.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present preliminary results from the Hamburg/ESO survey for damped Ly-$\alpha$ (hereafter, DLA) systems. This survey is characterised by (i) good knowledge of the biases affecting the parent QSO survey, and (ii) the brightness and (iii) relatively wide magnitude distribution of the background QSOs. Therefore, it is well–suited to study possible magnitude–dependent biases in DLA surveys, such as the one expected from dust obscuration.

We have systematically searched for damped Lyman-$\alpha$ line candidates in 5 Å, resolution spectra of the 188 QSOs that constitute our statistical sample. These candidates have later been re-observed with UVES at the ESO–Very Large Telescope (VLT) for confirmation and accurate $N(HI)$ measurements. In the redshift range covered by the survey, 19 DLA systems have been discovered. Over the whole survey, we find that the number density $n(z)$ and cosmological density of gas $\Omega_\mathrm{gas}$ have comparable values to the ones obtained by CORALS (Ellison et al. 2001).

However, the number densities of DLA systems $n(z)$ in two sub–samples of equal absorption distance path defined by the magnitude of the background QSOs differ by a factor of $\approx 5$. We estimate that the probability that $n(z)$ is equal in the two sub–samples is $<0.003$. A similar, only slightly less significant difference is found for $\Omega_\mathrm{gas}$.

Recent detailed simulations of Galactic Chemical Evolution have shown that the heavy elements, in particular [Fe/H], are expected to exhibit a weak, or absent, correlation with stellar ages in the early Galaxy due to the lack of efficient mixing of interstellar material enriched by individual Type II supernovae. A promising alternative ‘chronometer’ of stellar ages is suggested, based on the expectation that the light elements Be and B are formed primarily as spallation products of Galactic Cosmic Rays.

This review will discuss various plasma waves and instabilities that have been observed near comets. Comments on nonlinear wave evolution and wave cascading, as well as the role of nonlinear waves in wave-particle interactions, will be made.

Solar spectral irradiance measurements from the NOAA-9 and NOAA-11 SBUV/2 instruments and SSBUV are presented and compared. Inter-instrument solar spectral irradiance differences on the order of 5-10% are observed. Internal comparisons of the SBUV/2 solar data suggest instrument sensitivity changes ranging from less than 1% per year near 400 nm to approximately 5% per year near 200 nm.

The mission-to-mission accuracy of the SSBUV solar spectral irradiance measurements is better than ±2%. Initial results of our investigation into the feasibility of using SSBUV data to maintain the long-term calibration of the SBUV/2 instruments for solar spectral irradiance monitoring are reviewed.

I present a preliminary analysis of IR spectra of five K and M dwarfs and two RS CVn variables. Evidence for significant magnetic flux is found on several stars, a number of which are detected for the first time. Field strengths (B) on the RS CVn variables are lower than in the active dwarfs, consistent with the concept of pressure balance limiting B in stellar photospheres. I compare the results with previous measurements.

Low-mass stars exhibit, at all stages of their evolution, the signatures of complex physical processes that require challenging modelling beyond standard stellar theory. In this review, we focus on lithium depletion in low-mass stars. After disecting the Li dip, we discuss how large scale mixing due to rotation and internal gravity waves may interact to explain this feature. We also briefly discuss the impact that is expected on Population II stars.

Recent observational and theoretical advances concerning astronomical masers in star forming regions are reviewed. Major masing species are considered individually and in combination. Key results are summarized with emphasis on present science and future prospects.

We have digitized and processed the daily K-CaII-line full disk spectroheliograms from the archive of the Kodaikanal Observatory during 1907-1995. The programm has been worked out to determine the boundaries of the bright areas (plages, decayed plages, enhanced network features, K-CaII bright points and so on) with contrast that exceeded a level of the quiet Sun on the given value. About the $1.2\,{\times}\,10^6$ K-CaII active regions of different scales were processed. The coordinates, areas, the tilt and latitude-time distributions of bright features were determined. At the high latitudes the K-CaII bright points form a polar branch of solar activity at the period between the polar magnetic field reversals. This polar activity shows both 11-year's and 22-year's cycles. We found that the polar K-CaII bright point cycles proceed on average 5.5 years the sunspot cycles.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Two mechanisms involving purely dynamical processes can lead to the formation of a bulge after its disc: 1) small bulges (1 – 2 kpc), including box-shaped bulges and mildly triaxial bulges, can result from the formation and destruction of a bar; 2) big bulges (> 2kpc) à la Sombrero can grow following the accretion of small satellites. Fully consistent N-body simulations show that the fraction of galaxy mass accreted in this way needs to be larger than about 5%. Less accretion does not create smaller bulges, but heats the whole disc. These dynamical effects transforming Hubble types from SB to SA and vice-versa over ≈ 1 – 2 Gyr also indicate, by the secular growth of bulges, a general sense of galactic evolution from Sd to Sa.

With the substantial improvements in observational techniques we have to deal with very big databases, consisting of a few positions of an object over a short time span; this is often not enough to compute a preliminary orbit with traditional tools. In this paper we first review a classical method by C.F. Gauss to compute a preliminary orbit for asteroids. This method, followed by a least squares fit to improve the orbit, still today gives successful results when we have at least three separate observations. Then we introduce the basics of a very recent orbit determination theory, that has been thought just to be used with modern sets of data. These data allow us in many cases to know the angular position and velocity of an asteroid at a given time, even though the radial distance and velocity $(r,\dot r)$, needed to compute its full orbit, are unknown. The variables $(r,\dot r)$ can be constrained to a compact set, that we call the admissible region(AR), whose definition requires that the body belongs to the Solar System, that it is not a satellite of the Earth, and that it is not a “shooting star” (i.e. very close and very small). We provide a mathematical description of the AR: its topological properties are surprisingly simple, in fact it turns out that the AR cannot have more than two connected components. A sampling of the AR can be performed by means of a Delaunay triangulation; a finite number of six-parameter sets of initial conditions are thus defined, with each node of the triangulation representing a possible orbit (a virtual asteroid).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html