Results are presented from a wide area, high resolution HI synthesis survey of the outer regions of the nearby M81 group, where internal (galactic) and external (group-related) evolution processes can be studied simultaneously in great detail. The survey encompasses the star forming dwarf galaxies M81dwA, UGC4483, and HoII, where evidence of ram pressure stripping was recently discovered. The data do not reveal any intergalactic HI, but the outer parts of HoII are reminiscent of tidal tails. We argue however that those structures are equally consistent with the latest ram pressure models including cooling. The case for a hot intergalactic medium in this poor, spiral-only group is thus still open. The survey also puts tight constraints on possible counterparts to the local high velocity cloud population in an external group, reaching a 3σ column density of 1019 atom cm−2 and a 6σ limiting mass of 1.5 × 105M⊙.

The shapes of light curves and of radial velocity curves are two main predictions of the hydrodynamical models of Cepheids. Of the two, the velocity curves are more robust numerically and therefore, more suitable for comparison with the observations. In this report, we present accurate Fourier parameters for an extensive set of classical Cepheid velocity curves. Published radiative models reproduce the observations very well, with only small discrepancies present. We estimate the center of the ω2 = 2ω0 resonance to occur at Pr = 9.947 ± 0.051 day

Major properties of the solar atmosphere and wind are not understood. The energy distribution of the solar atmosphere perturbations, over nearly ten orders of magnitude in energy, is close (within one order of magnitude) to a power-law of index -2, even though there is no agreement on the detailed shape. There is no agreed explanation of the origin of the solar wind, either, nor of the fact that the total wind energy flux is independent of speed, latitude, and phase of solar cycle, with an average base flux of 70 W/m$^2$ – a figure that is similar for a number of other cool stellar winds, and is close to the total observed energy flux of solar atmosphere perturbations. A major theoretical difficulty is that both coronal heating and wind production depend fundamentally on the heat flux, and the solar atmosphere is not collisional enough for classical transport theory to hold. Heat transport thus behaves non classically and the particle velocity distributions may have significant high energy tails, which should dramatically affect coronal heating and solar wind acceleration, in a way that is outside the scope of standard MHD.

We present initial results from a survey of the Orion A and B molecular clouds made with the InfraRed Array Camera (IRAC) onboard the Spitzer Space Telescope. This survey encompasses a total of 5.6 square degrees with the sensitivity to detect objects below the hydrogen burning limit at an age of 1 Myr. These observations cover a number of known star forming regions, from the massive star forming clusters in the Orion Nebula and NGC 2024, to small groups of low mass stars in the L1641. We combine the IRAC photometry with photometry from the 2MASS point source catalog and use the resulting seven band data to identify stars with infrared excesses due to dusty disks and envelopes. Using the presence of an infrared excess as an indicator of youth, we show the distribution of young stars and protostars in the two molecular clouds. We find that roughly half of the stars are found in dense clusters surrounding the two regions of recent massive star formation in the Orion clouds, NGC 2024 and the Orion Nebula.

We analyze the properties of quasar variability using repeated SDSS imaging data in five UV-to-far red photometric bands, accurate to 0.02 mag, for ∼13,000 spectroscopically confirmed quasars. The observed time lags span the range from 3 hours to over 3 years, and constrain the quasar variability for rest-frame time lags of up to two years, and at rest-frame wavelengths from 1000Å to 6000Å. We demonstrate that ∼66,000 SDSS measurements of magnitude differences can be described within the measurement noise by a simple function of only three free parameters. The addition of POSS data constrains the long-term behavior of quasar variability and provides evidence for a turn-over in the structure function. This turn-over indicates that the characteristic time scale for optical variability of quasars is of the order 1 year.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

An investigation of strong magnetic fields associated with flares was made with the 61 cm vacuum telescope and spectroheliograph at the San Fernando Observatory. Magnetograms of the longitudinal component of the field were made daily during the period of September 25–29, 1969. Observations were also made during this same period of the enhanced radio emission at 3.3 mm wavelength. On September 27 an importance class 3 or 4 flare occurred in the region studied. Total magnetic flux was determined for September 25, 26, 28 and 29 for the region which included the flare. In an area of about 190 arc s by 250 arc s the flux values for these dates were respectively 2.4, 2.5, 2.2 and 2.8 × 1022 Mx. Following the flare of September 27 the flux decreased significantly. Magnetic energy change in the region of the flare can be determined if an appropriate height is known. Following Howard and Severny (Astrophys. J. 137, 1242, 1963) a height of 109 cm was used. This yields a value of 5 × 1031 ergs for the decrease of magnetic energy in the longitudinal component of the field.

We surveyed all stars in Taurus (3h 45m < α < 4h 15m, 15° < δ < 35°) for multiplicity which are contained in the Herbig-Bell catalogue of young stars and have a 2 micron brightness of K ≤ 9.5 mag. This sample consists of 106 stellar systems (single or multiple), of which 43 are double or multiple according to the criteria of our survey, i.e. with separations of ≈0″.2 ≤ d ≤ 10″. Of these, 23 binaries are new detections found in this survey. The resulting degree of multiplicity, 43/106 = 41±6%, is higher than found for main-sequence stars. Provided that the period distribution is the same for young stars as on the main sequence, our result implies that the vast majority of stars are born in binary or multiple systems.

In a galaxy, chemical enrichment takes place in an inhomogeneous fashion, and the Galactic Halo is one of the places where the inhomogeneous effects are imprinted and can be constrained from observations. I show this using my chemodynamical simulations of Milky Way type galaxies. The scatter in the elemental abundances originate from radial migration, merging/accretion of satellite galaxies, local variation of star formation and chemical enrichment, and intrinsic variation of nucleosynthesis yields. In the simulated galaxies, there is no strong age-metallicity relation. This means that the most metal-poor stars are not always the oldest stars, and can be formed in chemically unevolved clouds at later times. The long-lifetime sources of chemical enrichment such as asymptotic giant branch stars or neutron star mergers can contribute at low metallicities. The intrinsic variation of yields are important in the early Universe or metal-poor systems such as in the Galactic halo. The carbon enhancement of extremely metal-poor (EMP) stars can be best explained by faint supernovae, the low [α/Fe] ratios in some EMP stars naturally arise from low-mass (~ 13 - 15M⊙) supernovae, and finally, the [α/Fe] knee in dwarf spheroidal galaxies can be produced by subclasses of Type Ia supernovae such as SN 2002cx-like objects and sub-Chandrasekhar mass explosions.

Although the extragalactic nature of 3C 48 and other quasi stellar radio sources was discussed as early as 1960 by John Bolton and others, it was rejected largely because of preconceived ideas about what appeared to be unrealistically high radio and optical luminosities. Not until the 1962 occultations of the strong radio source 3C 273 at Parkes, which led Maarten Schmidt to identify 3C 273 with an apparent stellar object at a redshift of 0.16, was the true nature understood. Successive radio and optical measurements quickly led to the identification of other quasars with increasingly large redshifts and the general, although for some decades not universal, acceptance of quasars as the very luminous nuclei of galaxies.

Curiously, 3C 273, which is one of the strongest extragalactic sources in the sky, was first cataloged in 1959 and the magnitude 13 optical counterpart was observed at least as early as 1887. Since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions which were measured primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded identification until the series of lunar occultation observations led by Cyril Hazard. Although an accurate radio position had been obtained earlier with the OVRO interferometer, inexplicably 3C 273 was initially misidentified with a faint galaxy located about an arc minute away from the true quasar position.

We present optical high-resolution spectroscopy of AM Her and QQ Vul. Making use of indirect imaging techniques (Doppler and Roche tomography), we are able to make details visible, which a model of these systems has to be able to account for. Especially the emission line data cannot be explained by current models of polars.

Spectral analyses of 70 yr of ILS-IPMS data on the variation of latitude are discussed from the point of view of the confidence limits that can be placed on statistical estimates. The available data cannot be used to support the existence of two resonant frequencies in the Chandler wobble, nor are the latter required to remove an anomaly in the value of Q for wobble as long as the oceans cannot be dismissed as an energy sink.

In the framework of Euler flows, I present simulations of wind accretion in well separated binaries for three different cases: Cygnus X-3, a high mass X-ray binary (see e.g. Schmutz et al. 1996), ζ Aurigae, a system showing strong atmospheric eclipse effects (see e.g. Griffin et al. 1990), and the generic barium star model of Theuns and Jorissen (1993), which is recomputed here with a different numerical method (a MUSCL-type integrator, incorporated in our AMRCART code). These simulations represent a first, small sample out of the large parameter space of wind accretion in separated binaries (see Table 1).

On the orbital scale, the vorticity of the flow is due to the orbital motion of the stars. It is particularly large for the case where the wind velocity is comparable to the orbital speed of the stars (see Fig. 1). In the vicinity of the accreting star, the vorticity is determined by the accretion process. With two strong vortices above and below the accretor (with respect to the orbital plane), the flow resembles the flow out of a bath tub. On a smaller scale, one finds even more vorticity: The flow is highly turbulent. Such turbulence and the shear flows in the large scale vortices cannot be well captured by an Euler flow model. A next step of improvement would be the use of an appropriate MHD turbulence model.

Massive black holes (MBHs) are nowadays recognized as integral parts of galaxy evolution. Both the approximate proportionality between MBH and galaxy mass, and the expected importance of feedback from active MBHs in regulating star formation in their host galaxies point to a strong interplay between MBHs and galaxies. MBHs must form in the first galaxies and be fed by gas in these galaxies, with continuous or intermittent inflows that, at times, can be larger than the Eddington rate. Feedback from supernovae and from the MBHs themselves modulates the growth of the first MBHs. While current observational data only probe the most massive and luminous MBHs, the tip of the iceberg, we will soon be able to test theoretical models of MBH evolution on more “normal” MBHs: the MBHs that are indeed relevant in building the population that we observe in local galaxies, including our own Milky Way.

Observed Be stars are considered to be interacting binaries undergoing mostly case B mass exchange. Their observed properties can be explained satisfactorily as the consequences of different modes of mass transfer. Suggestions for further observational and theoretical studies to verify or to disprove the hypothesis presented here are briefly outlined.

Traditionally, a simulation of a dense stellar system required choosing an initial model, running an integrator, and analyzing the output. Almost all of the effort went into writing a clever integrator that could handle binaries, triples and encounters between various multiple systems efficiently. Recently, the scope and complexity of these simulations has increased dramatically, for three reasons: 1) the sheer size of the data sets, measured in Terabytes, make traditional ‘awking and grepping’ of a single output file impractical; 2) the addition of stellar evolution data brings qualitatively new challenges to the data reduction; 3) increased realism of the simulations invites realistic forms of ‘SOS’: Simulations of Observations of Simulations, to be compared directly with observations. We are now witnessing a shift toward the construction of archives as well as tailored forms of visualization including the use of virtual reality simulators and planetarium domes, and a coupling of both with budding efforts in constructing virtual observatories. This review describes these new trends, presenting Starlab as the first example of a full software environment for realistic large-scale simulations of dense stellar systems.

I review progress in interpreting the opposition effect and negative linear polarization observed for solar system dust particles. The so–called coherent backscattering mechanism has recently been introduced to explain the observations. However, fundamental difficulties in theoretical modeling still prevent quantitative interpretation. I also review some of the key observations that questioned the hitherto widely accepted mutual–shadowing explanation for the opposition effect. I summarize previous theoretical and experimental work on the opposition effect and negative polarization.

The B-type Subdwarf BD-07°3477 has been found to be an eclipsing binary with a period of about 2h48m. A preliminary analysis of the light curve reveals the system to be fully detached. It appears to be similar in many respects to the O-Subdwarf binary AA Dor which is thought to be the remnant of a system which has undergone a common envelope phase of evolution.

Plates of planetary nebulae taken in October 1965 and June 1967 with the 100-inch and 60-inch telescopes on Mount Wilson are compared with photographs taken with the same instruments 40 or more years previously, to determine the amount of angular motion of material outward from the central stars. Densitometer tracings of the nebulae yield values of , the radial motion in seconds of arc per century for condensations (filaments, rings, etc.) as well as for the edges of the visible material. Preliminary data are presented for NGC 2392, 6818 and 7662. For NGC 2392 and NGC 7662 distances are derived.

We present new results on RR Lyrae stars and anomalous Cepheids in the Draco dwarf spheroidal galaxy. We have increased the number of double-mode RR Lyrae stars and found three new anomalous Cepheids. With period-magnitude and period-amplitude diagrams, we discuss the Oosterhoff classification of Draco. Contradictory results were found in that Draco appears to contain both Oosterhoff I and II type RR Lyrae populations.