New measurements of the isotopic composition of helium in the solar wind obtained from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses are presented and compared with earlier SWICS results and previous mass spectrometric determinations of this ratio with the Apollo Solar Wind Composition (SWC) experiment and the Ion Composition Instrument (ICI) on the International Sun Earth Explorer 3 (ISEE 3). The new SWICS data from both the fast and slow solar wind are extrapolated to the photosphere to obtain a representative value of the present-day ratio of 3He/4He = (3.75 ± 0.27) × 10−4 in the Outer Convective Zone (OCZ) of the Sun. After corrections of this ratio for secular changes caused by diffusion, mixing and 3He production by incomplete H-burning (Vauclair 1998), we obtain (D + 3He)/H = (3.6 ± 0.38) × 10−5 for the Protosolar Cloud (PSC). Adopting the Jovian 3He/4He ratio = (1.66 ±0.05) × 10−4 measured by the Galileo Probe mass spectrometer (Mahaffy et al. 1998) as representative for the PSC, we obtain (D/H)protosolar = (1.94 ±0.39) × 10−5. Using results of galactic evolution studies (Tosi 1998, 2000) and the D and 3He abundances in the Protosolar Cloud and the Local Interstellar Cloud (Linsky 1998; Gloeckler &Geiss 1998), we estimate (D/H)primordial = (2.4 − 4.2) × 10−5. This range corresponds to a universal baryon/photon ratio of (5.9−4.2) × 10−10.

It is not straightforward to determine the distribution of supernova remnants (SNRs) in the Galaxy. The two main difficulties are that there are observational selection effects that mean that catalogues of SNRs are incomplete, and distances are not available for most remnants. Here I discuss the selection effects that apply to the latest catalogue of Galactic SNRs. I then compare the observed distribution of ‘bright’ SNRs in Galactic longitude with that expected from models in order to constrain the Galactic distribution of SNRs.

All extraterrestrial particles are heated during their passage through the Earth's atmosphere. The mineral assemblages that form during entry heating can be used to constrain the maximum temperature attained which, in turn, places limits on their entry velocity Entry velocity can be used to discriminate typical cometary IDPs from asteroidal particles.

A common feature of heated IDPs is the presence of magnetite (Mt) rims on the particle surface. These rims range from thin, discontinuous Mt layers on lobes or on small constituent grains within lightly heated IDPs, to thick, continuous, polycrystalline rims that completely surround many strongly heated particles. Petrographic evidence indicates that Mt rims form directly from individual phases in IDPs via oxidation of Fe from the host phases. Our data indicate that the temperature of magnetite formation can range from a minimum of ~600°C (by decarbonation of Fe-bearing carbonates and the breakdown of phyllosilicates) to T > 850°C (decomposition of laihunite). In extreme cases, μm-sized Mt plates armor the surface of partly melted chondritic IDPs. Magnetite rims are more well-developed on hydrated IDPs than on anhydrous particles. The development of magnetite rims correlates with other independent indicators of heating including loss of volatile trace elements and sulfur depletions.

The blazar 3C 279 is one of the strongest extragalactic sources of γ-rays, and is also one of the best studied superluminal radio sources. Definitive testing of models of the broad-band spectral energy distribution, especially in the X-ray and γ-ray regions requires knowledge of the evolution of the spectrum with time. Within the context of the relativistic jet model, multi-wavelength monitoring of the parsec-scale radio jet is also required. We present here the first steps toward such a test, using extensive VLBI monitoring over a 13 year interval at 22 GHz, and γ-ray observations between 1991 and 1996.

Cometary nuclei are often considered to be the most primitive bodies of the solar system. Thus it is particularly important to find out what structural changes may have been brought about as a result of their thermal evolution. Is there reason to believe that the bulk composition of the nucleus of a present-day short-period comet may differ from that of the original planetesimal in the solar nebula? Apart from the development of a non-volatile surface layer (‘dust mantle’), what further depth-dependent differentiation can we expect in such a nucleus? These are the ultimate questions addressed in this paper, and attention is focused on the two most active stages of thermal evolution: the early planetesimal stage with internal heating basically due to radioactive decay, and the recent or present cometary phase with strong external heating due to insolation of the surface.

Supernovae are classified as type I and type II and further subdivided into Ia, Ib, Ic, II-P, II-L, and IIb. The origin of this observational diversity has not been well understood. The recent nearby supernovae SN 1993J and SN 1994I have provided particularly useful material to clarify the supernova — progenitor connection. For a progenitor of type IIb supernova 1993J, we propose that merging of two stars in a close binary is responsible for the formation of a thin H-rich envelope. As a progenitor of type Ic supernova 1994I, we propose a bare C+O star that has lost both its H and He envelope after a common-envelope phase. By generalizing these scenarios, we show that common-envelope evolution in massive close binary stars leads to various degrees of stripping off of the envelope of a massive star. This naturally leads to an explanation of the origin of type II-L, IIn, IIb, Ib, and Ic in a unified manner. The binary hypothesis to explain the diversity of supernovae can be substantiated with new information on SN IIb 1993J and SN Ic 1994I. Model light curves are compared with observations. Since extensive mass loss is essential for the binary scenario, circumstellar interactions are examined for comparison with X-ray observations.

A time sequence of longitudinal magnetograms of two active regions, McMath Regions 9281 and 9760, have indicated magnetic field changes occurring in localized areas with time scales of the order of hours. We believe the observed field changes are evolutionary in nature, rather than related to the occurrence of small flares. Three examples of evolutionary magnetic changes are discussed.

The current status of understanding of the X-ray emission from Seyfert galaxies involves Comptonization of soft photons by hot subrelativistic electrons. After briefly reviewing the early theoretical basis for the presence of hot optically thin plasma in or around accretion disks and the key observations that led to develop the presently popular model of an accretion disk with a hot corona, we summarize recent progress in accretion models that take into account energy dissipation and/or angular momentum transport in the corona. Finally, adopting the simple scheme of a homogeneous plane parallel corona, we discuss in detail the dependence of the X-ray spectrum on the coronal parameters. Despite the strong coupling between optical depth and temperature which determines a spectral shape insensitive to their precise values, moderate spectral changes are possible. The spectral variability patterns can be used as diagnostics for coronal physics and should allow to determine whether the optical depth of the corona is dominated by e+e− pairs.

The study of Earth rotation encompasses the complex nature of orientation changes, the excitation of these changes and their geophysical implications in a broad variety of areas. Studies have embarked on a new era with the advent of highly accurate space geodetic techniques and the increasing availability of complementary geophysical data sets. This paper provides an overview of Earth rotation variations from hours to centuries with a brief discussion of polar motion and nutation results.

Past X-ray observations by ASCA suggest that warm absorbers (O VII and O VIII edges) are apparently rare in high luminosity AGNs (quasars) while they are more common in low luminosity AGNs (Seyferts). However, this could be a selection effect if high luminosity AGNs have mostly narrow absorption lines (with no strong bound free edges), which escaped detection by the low resolution of ASCA. To check this hypothesis we are studying the high-resolution X-ray spectra of quasars from grating spectrometers on board Chandra and XMM-Newton in search for absorption lines. In this contribution we present spectra of three quasars. The spectra show narrow (several hundred km s−1) absorption and emission X-ray lines from H-like and He-like ions of O, Ne, Mg, and other abundant elements. We also detect absorption from iron L-shell lines and iron M-shell unresolved transition array. We present the analysis of MR2251-178 where we find that at least two, and probably three, distinct warm absorbers are needed to explain the high resolution spectrum of this object. We re-analyze the high-resolution X-ray spectrum of PG 1211+143 and suggest that an outflow velocity of ∼3000 km s−1 provides an adequate explanation to these data. We also present preliminary results form the Chandra/HETGS observation of the quasar 4C74.26.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Several areas of stellar observations depend critically on nearly continuous observations of individual objects over very extended periods. Important examples are investigations of stellar oscillations to carry out asteroseismology, and the search for extra-solar planets. To meet this requirement we are establishing the SONG network, consisting of 8 sites with a 1-meter-class telescope with a suitable geographical distribution. These will be optimized for asteroseismology based on Doppler-velocity observations and the characterization of extra-solar planets with photometry, using gravitational microlensing. Funding has been obtained towards the construction of the prototype SONG telescope which will be set up on Tenerife, with first light expected in 2011. The full network will be established in parallel with the tests of the prototype and is planned to be operational in 2014.

Mare ridges often consist of two separate but related features: (1) a broad gentle arch overlain by (2) a sharper, more contorted ridge. Often these sharper, secondary ridges have flowed into craters in the adjacent terrain indicating they are extrusions. Major flows in Mare Imbrium appear to have issued from several prominent mare ridges. These flows show color differences which may be related to their abundance of titanium. The association of flows with mare ridges, the broad arching linked with many ridges and the coincidence of linear ridges with the directions of major fracture patterns in the highlands indicates that arched mare ridges are dike, sill or laccolithic-type intrusions along major fractures. In many cases these intrusions appear to have broken through the surface to form short flows and bulbous lava extrusions. Mare ridges unassociated with arching are probably lava extrusions only.

Mare ridges often take the form of rings indicating that they developed along ring fractures. Several linear mare ridges and mare ridge rings have bright hills situated along them and are considered to be post-mare volcanic hills of more siliceous composition than the maria. Evidence suggests that many of the ring structures are post-mare volcanic ring complexes formed over large igneous masses.

In recent years, an increasing amount of attention is being paid to the gravitational few-body problem and its applications to astrophysical scenarios. Among the main reasons for this renewed interest there is large number of newly discovered exoplanets and the detection of gravitational waves. Here, we present two numerical codes to model three- and few-body systems, called tsunami and okinami. The tsunami code is a direct few-body code with algorithmic regularization, tidal forces and post-Newtonian corrections. okinami is a secular, double-averaged code for stable hierarchical triples. We describe the main methods implemented in our codes, and review our recent results and applications to gravitational-wave astronomy, planetary science and statistical escape theories.

Long–baseline optical interferometry has revolutionised binary star astronomy. This paper reviews some recent binary star work done using the Mark III Stellar Interferometer. For the first time, many spectroscopic binaries, eclipsing binaries, triple systems, and binaries with X-ray sources have had their visual orbit, diameter of the primary component, and color index determined. Also, accurate stellar masses, distances, radii, and effective temperatures have been derived. A preliminary distance to the Hyades cluster has also been determined. In addition, preliminary observations provide evidence of a third body in the binary star system ζ Her, which may resolve an 85-year old discrepancy in astronomy.

The various ways in which compact objects (neutron stars and black holes) can be formed in interacting binary systems are outlined. It is argued that most of the remnants of massive stars (M1 ≳ 10 M⊙) will be runaway pulsars, with space velocities ≳ 100 km/s, i.e.:

1. (i) semi-conservatively evolving massive close binaries (~ 1/3 of all massive stars) after the first SN explosion consist of a massive star and a neutron star; subsequently, after a stage of common-envelope evolution and spiral-in most of these systems are disrupted in the second SN, producing two runaway pulsars, one young and one old.

2. (ii) highly non-conservatively evolving systems (with initial mass ratio q0 ≲ 0.5 and binary periods up to several decades; ≳ 1/3 of all massive stars) will spiral-in during the first phase of mass transfer and are disrupted in the first SN explosion, producing one young runaway pulsar, together with a runaway star of low or moderate mass.

It has been shown in several independent investigations that the multiple-shell phenomenon is prevalent in planetary nebulae. Despite the common classification, the multiple shell planetary nebulae are a heterogeneous group of objects, as testified by the wide variety of their morphologies and physical structures. There are two types of double-shell structures that are seen frequently: one has an inner shell expanding supersonically into a faint, subsonically expanding halo, and the other has a bright attached envelope co-expanding with the inner shell. The physical structures and relative elemental abundances in the shells are reviewed, and their possible formation mechanisms are discussed.

The time during which the temperature of a terrestrial-like planet remains in the liquid water range during the fading of its parent brown dwarf is calculated as a function of brown dwarf mass and planetary semimajor axis using recent models for brown dwarf evolution and two criteria for habitable zone width. Durations of habitability range from 0.5–2 Gyr at a brown dwarf mass of 0.03 M⊙ to 2–10 Gyr at a brown dwarf mass of 0.07 M⊙ for planets within a few Roche radii.

Strong variable radio emission from the bright transient X-ray source GRO J1655-40 (X-ray Nova Scorpii 1994) has been detected at 843 MHz with the Molonglo Observatory Synthesis Telescope (MOST). As the hard X-ray intensity from the 1994 August outburst declined the radio output increased rapidly, reaching a peak of nearly 8 Jy some 12 days after the first X-ray peak. VLBI images obtained at this time showed two main components separating with an apparent transverse velocity > c. The evolution of the radio spectrum suggests that the time delay between X-ray and radio emissions is due, at least in part, to opacity effects associated with this expansion.

We have developed a massively parallel special-purpose computer system for N-body simulations, GRAPE-4 (GRAvity-PipE 4). The GRAPE-4 system is designed for high-accuracy simulations of dense stellar systems. The GRAPE-4 calculates gravitational forces, their derivatives in time and potential energies. It has a hardware for prediction of positions and velocities, which is used for the individual timestep scheme. Using multi-chip module technology, we integrated 1692 chips of 640 megaflops performance. The peak speed of GRAPE-4 is 1.08 teraflops.

We briefly review the traditional classifications of CP stars. The current availability of large numbers of abundances now make it possible to use multivariate techniques, both to supplement traditional classification methods and probe the abundance patterns. We discuss cluster analysis and correlation matrices for sample material. We review the historical resistance to the notion that CP stars were indeed chemically peculiar. Modern work shows that while these objects do indeed have atmospheric anomalies, they are nevertheless chemically peculiar.

Abundance patterns are an important clue to the origin of the abundance peculiarities. We contrast patterns due to nuclear and chemical differentiation processes. The roAp and related stars show vertical as well as horizontal abundance variations, and abnormal line profiles. Photospheric abundances in these stars are surely abnormal (nonsolar), but as long as the models are uncertain the derived abundances will be very crude.

For more than two decades, observations of CP stars in the X-ray and radio regimes have been made with increasing sensitivity and pointing accuracy. We discuss the current evidence linking magnetic and nonmagnetic CP stars to sources of galactic X-rays and radio radiation. There seems no doubt that high energy phenomena are associated with, if not produced by, some CP stars. This circumstance admits the possibility that the release of high energy particles (p's, n's and $\alpha$'s) during such events may initiate nuclear reactions on the surfaces of the CP stars. We briefly reconsider the viability of such processes for producing exotic species like Pm by proton bombardment using recent data for solar and stellar flares.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html