The nearest, youngest groups of stars to the Sun provide important samples of age-dated stars for studying circumstellar disk evolution, imaged exoplanets, and brown dwarfs. I briefly comment on the status of the known stellar groups within 100 pc: β Pic, AB Dor, UMa, Car-Near, Tuc-Hor and β Tuc nucleus, Hyades, Col, TW Hya, Car, Coma Ber, 32 Ori, η Cha, and χ1 For. I also discuss some poorly characterized groups and “non-groups.” Grades for 2015 of Pass, Satisfactory, or Fail are assigned to the groups for the purposes of age-dating stars and brown dwarfs. I speculate that Tuc-Hor could have provided a supernova ~60 pc away ~2.2 Myr ago which showered the Earth with traces of 60Fe-bearing dust.

In the seventies of the last century the EPM ephemerides (Ephemerides of Planets and the Moon) of IAA RAS originated and have been developed since that time. These ephemerides are based upon relativistic equations of motion of celestial bodies and light rays and upon relativistic time scales. The updated model of EPM2008 includes the new values of planet masses and other constants, the improved dynamical model with adding Trans–Neptunian Objects and the expanded database (1913–2008). More than 260 parameters have been determined while improving the planetary part of EPM2008 to 550000 observations. EPM2008 have been oriented to ICRF by including into the total solution the VLBI data of spacecraft near the planets. The real uncertainty of EPM ephemerides has been checked by comparison with the JPL's DE ephemerides. Some estimates of the post–model parameters have been obtained: |1−β| < 0.0002, |1−γ| < 0.0002, /G = (−5.9±4.4) ⋅ 10−14 per year, the statistic zero corrections to the planet perihelion advances.

Convection and turbulence in stellar atmospheres have a significant effect on the emergent flux from A-type stars. The recent theoretical advancements in convection modelling have proven to be a challenge to the observers to obtain measurements with sufficient precision and accuracy to permit discrimination between the various predictions.

A discussion of the current observational techniques used to evaluate the various convection theories is presented. These include filter photometry, spectrophotometry, hydrogen lines, and metal lines. The results from these techniques are given, along with the successes and limitations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Cool gas in the heart of the hot solar chromosphere betrays itself through anomalously strong absorptions of 4.7 μm CO lines at the extreme limb, and off-limb emissions. The origin of the “cool clouds” is thought to be a thermal instability driven by the CO itself. Questions concerning the pervasiveness and detailed structure of the “thermally-bifurcated” zones are being addressed through stigmatic spectroscopy of the solar CO bands with the NSO McMath-Pierce telescope. Here, I report recent progress, and implications for surface thermal inhomogeneities on other stars.

The radio spectrum is a finite and increasingly precious resource for astronomical research, as well as for other spectrum users. Keeping the frequency bands used for radio astronomy as free as possible of unwanted Radio Frequency Interference (RFI) is crucial. The aim of spectrum management, one of the tools used towards achieving this goal, includes setting regulatory limits on RFI levels emitted by other spectrum users into the radio astronomy frequency bands. This involves discussions with regulatory bodies and other spectrum users at several levels – national, regional and worldwide. The global framework for spectrum management is set by the Radio Regulations of the International Telecommunication Union, which has defined that interference is detrimental to radio astronomy if it increases the uncertainty of a measurement by 10%. The Radio Regulations are revised every three to four years, a process in which four organisations representing the interests of the radio astronomical community in matters of spectrum management (IUCAF, CORF, CRAF and RAFCAP) participate actively. The current interests and activities of these four organisations range from preserving what has been achieved through regulatory measures, to looking far into the future of high frequency use and giant radio telescope use.

Voids form a prominent aspect of the Megaparsec distribution of galaxies and matter. Not only do they represent a key constituent of the Cosmic Web, they also are one of the cleanest probes and measures of global cosmological parameters. The shape and evolution of voids are highly sensitive to the nature of dark energy, while their substructure and galaxy population provides a direct key to the nature of dark matter. Also, the pristine environment of void interiors is an important testing ground for our understanding of environmental influences on galaxy formation and evolution. In this paper, we review the key aspects of the structure and dynamics of voids, with a particular focus on the hierarchical evolution of the void population. We demonstrate how the rich structural pattern of the Cosmic Web is related to the complex evolution and buildup of voids.

The MACHO data base has been used to examine light curves of all red giant stars brighter than Mbol ∼ −2 in a 0.5° × 0.5° area of the LMC bar. Periods, often multiple, have been searched for in all stars found to be variable. Five distinct period-luminosity sequences have been found on the low mass (M ≲ 2.25M⊙) giant branch. Comparison of observed periods, luminosities and period ratios with theoretical models identifies Miras unambiguously as radial fundamental mode pulsators, while semi-regular variables can be pulsating in the 1st, 2nd or 3rd overtone, or even the fundamental. All these variables lie on just 3 of the 5 distinct sequences, and they all appear to be on the AGB.

The fourth sequence contains red giants on the first giant branch (FGB) or at the red end of the core-helium burning loops of intermediate mass stars (M ≳ 2.25M⊙). The light curves of these stars strongly suggest that they are contact binaries, and they make up ∼0.5% of stars within 1 mag. of the FGB tip. Stars on the fifth sequence show semi-regular, eclipse-like light curves. The light curves and periods of these stars suggest that they are in semi-detached binaries, transfering mass to an invisible companion via a stellar wind or Roche lobe overflow. They make up ∼25% of AGB stars. If the existence of these red giant contact and semi-detached binaries is confirmed, then extant theories of binary star evolution will require substantial modification.

The Two Micron All Sky Survey (2MASS) provides an unprecedented, uniform photometric data set for large samples of AGN discovered at other wavelengths, and also forms the basis to search for previously unknown, obscured AGN. We present the results of a highly efficient near infrared color-based AGN survey using 2MASS that has already discovered 485 new, red AGN and QSOs. The extrapolated surface density of the 2MASS red AGN is ~0.57 deg~−2 for Ks≤15.5 mag. The ratio of Type 1 to Type 2 AGN among the newly discovered objects is 4:1, similar to proportions found in X-ray and deep ISO surveys, but the inverse of that found in IRAS surveys. The median redshift of the the new 2MASS red AGN sample is z<0.22, and all but three have z<0.7. The color distribution, polarization and X-ray properties data suggest that most of the 2MASS-discovered AGN are red because of obscuration by dust in and around their nuclei.

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a large-scale, near-infrared (H-band), high-resolution (R ~ 30,000), high S/N (≳100) spectroscopic survey of Milky Way stellar populations. APOGEE will operate from 1.51–1.68μm, a region that includes useful absorption lines from at least fifteen chemical species including α, odd-Z, and iron peak elements. The APOGEE instrument has a novel design featuring 300 science fibers feeding light to a mosaiced VPH grating and a six-element camera encased in a liquid nitrogen-cooled cryostat. A three year bright-time observing campaign will enable APOGEE to observe approximately 100,000 red giants across the Galactic bulge, disk and halo.

I can compute arbitrary-abundance models and spectra at high resolution using millions of atomic and diatomic molecular lines. Examples are given for Sakurai’s object and for a λBoo star. I am continuing to improve the input line data.

Comets are among the most primitive bodies of the solar system, and their chemical composition is rich in information on the protosolar nebula and its possible connection with interstellar cloud chemistry. Comets are also a source of light atoms and, possibly, prebiotic organic molecules for the early Earth. We know better and better the abundances of cometary volatiles through spectroscopy, mainly at infrared and radio wavelengths. Another crucial component of cometary matter – organic refractories – is still poorly characterized, however.

We summarize here the $\sim$30 abundances and $\sim$20 upper limits obtained on cometary volatiles and highlight a few species and problems: ethylene glycol, NS, HNC/HCN, $^{14}$N/$^{15}$N, the origin of CN, CS$_{2}$, PAHs, and H$_{2}$O. Comet-to-comet variations and comet internal heliocentric variations can now be studied, and cometary comas can be mapped with a variety of techniques. We list a number of temperature indicators, for they can help understand the relation between IS and cometary matters, which present both a global similarity but also marked differences, such as the high ethylene glycol content of comets.

We conclude by outlining a few key problems to be addressed by future ground-based and space instruments or by cometary sample analysis. For many species, we stress that laboratory data are missing on spectroscopy, photodissociation and collisions with H$_{2}$O.

Sanduleak (1971) has listed five stars, not apparently associated with planetary nebulae, which show very strong 0 VI 3811,34 å emission. He pointed out that two of them are in the Magellanic Clouds and have absolute magnitudes comparable to those of classical (Population I) Wolf-Rayet stars. 0 VI emission is know to occur in some classical Wolf-Rayet stars, but not with the extreme strength shown by the Sanduleak stars. We have obtained absolute optical spectrophotometry (3100–7400å) of all five of these stars, using the UCL Image Photon Counting System and RGO Spectrograph on the Anglo-Australian Telescope. Figure 1 shows their relative flux distributions. Inspection shows that Sand 1 is very lightly reddened, Sand 2 and 3 have intermediate reddening, and Sand 4 and 5 are heavily reddened. IUE ultraviolet spectrophotometry has been obtained of the first three stars; Sand 4 and 5 are too heavily reddened for IUE spectra to be feasible.

Skylab has demonstrated the dominant role of magnetic fields in the solar atmosphere. The solar wind is not a necessary consequence of the pressure imbalance between the hot corona and the interplanetary medium. High speed solar windstreams are originating in coronal holes where coronal density and temperature are less than in the quiet sun. Older models of the solar wind invoke heat conduction from the hot corona as the prime energy source for the solar wind. However in coronal holes the energy supplied by heat conduction is less than in the ordinary sun while the high speed windstreams require an amount of energy which cannot be supplied by conduction alone.

An X-ray burst is a sudden increase (rise time of order seconds) of the X-ray brightness of an X-ray source, which after reaching its peak decays, generally within a minute. The sky distribution of X-ray burst sources indicates that they are galactic objects (see Fig. 1); their concentration to the direction of the galactic center tells us that they lie at typical distances of ∼ 8 kpc, with corresponding peak luminosities of order 1038 erg s−1. The X-ray and optical properties of the persistent emission of X-ray burst sources show that they are low-mass X-ray binaries, in which mass is transferred from a rather normal low-mass (< 1 M⊙) star to a neutron star. The persistent emission is caused by the conversion of kinetic energy of the transferred matter into heat, at a rate of ∼ GM/R (∼ 0.1c2) per gram of accreted matter. The bursts are caused by unstable thermonuclear burning of material that has accumulated on the neutron star (‘thermonuclear flash’).

The global properties of X-ray bursts, in particular their dependence on the mass accretion rate, are fairly well understood. Different from the case of γ-ray bursts (see the contributions by Fishman, Hartmann and Kouveliotou to this Colloquium) the relevant question about X-ray bursts is not ‘What are they?’, but rather ‘What use are they?’. As we will argue here, X-ray bursts may provide us information on the mass and radius of a neutron star. This usefulness of X-ray bursts derives from the fact that the burst emission originates from the surface of the neutron star, unlike the persistent emission caused by mass accretion, of which we only know that it comes from the neutron star’s near vicinity.

The Astronomical Unit is one of the most basic units of astronomy: the scale of the solar system. Yet its long and colorful history is sprinkled liberally with incorrect descriptions and mis-quoted definitions – today as much as ever. Over the last half century, the accuracy of the au determinations has improved dramatically: optical (triangulation) methods have given way to modern electronic observations, high-speed computers, and dedicated efforts to improve planetary ephemerides. Typical uncertainties in the value of the au have decreased from many tens of thousands of kilometers to the present level of only a few meters. With the solar system providing a very clean, undisturbed dynamical model, the ephemerides have been used for a variety of exotic physical tests: alternative theories of gravitation, $d({\rm G})/dt$, $d({\rm au})/dt$, etc. In the beginning of this modern era, the author happened to be a witness to a couple of rather key events; more lately, a participant. A couple of these personal experiences are related.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A review of microwave and radio-frequency spectral lines which might possibly be detected by the techniques of radio astronomy is attempted here. Brief discussions of this type have already been given by several authors [1, 2, 3, 4]. However, the present treatment is somewhat more complete than previously published material, and has the advantage of more recent information about certain transition frequencies. It includes a general discussion of types of spectra which might be found, expected intensities, and some characteristics and known frequencies of the lines which may be of interest in radio astronomy.

The SkyView virtual observatory provides a single, simple interface where users can retrieve images of the sky at all wavelengths from the radio through gamma rays. Below we discuss how SkyView works and how it represents a new paradigm in astronomical data archives. Users get to SkyView over the WorldWideWeb at http://skyview.gsfc.nasa.gov. Within a few moments they can have high-quality images from ground- or satellite-based surveys.

We give a brief review on the present status of our research of A-F pulsating components of semi-detached Algol-type systems. We suggest a new asteroseismic approach for estimating the evolutionary stage of the mass-accreting components of Algols during rapid and slow mass-transfer phases, asynchronization and differential rotation.

We show radio continuum observations of the WR ring nebulae around WR 101 and WR 113 obtained using the VLA and H i 21 cm line data of the interstellar bubble around the O type stars BD +24° 3866 and BD+25° 3952 obtained with the DRAO Synthesis Telescope. We review previous radio continuum and H i line results toward WR and O-type stars.