At the turn of the century, astronomy was required of every senior in what is now the American University of Beirut, for the reason that “the heavens declare the glory of God”; this was especially appropriate for what was then the Syrian Protestant College. And in the late Middle Ages, astronomy was one of the seven liberal arts, a required part of every basic university education — for much the same reason. Thus, for many centuries, astronomy was considered essential for what every educated person should know. The organizers of this colloquium thought it would be informative to learn more about the historical background to our colloquium and asked if I would speak on the history of astronomy teaching over the ages. I demurred at such an overwhelming topic, which would require a major research program, and have offered instead something about the history of astronomy textbooks, because this subset provides answers to at least some of the broader questions of how astronomy has been taught.

In the earliest studies of close binary evolution (Paczynski 1967; Kippenhahn, Kohl, and Weigert 1967; Plavec, et al. 1968), it was assumed that the total mass and orbital angular momentum of a binary system are conserved during mass transfer. This assumption of convenience actually succeeds quite well in producing model post-mass-transfer binaries which closely resemble classical Algol-type systems, and helium-star binaries such as KS Per and u Sgr as well (Plavec 1973; Schonberner and Drilling 1983). Among longer-period interacting binaries, however, there are strong reasons to believe that these simple assumptions break down. For example, it is well-known that single stars may lose a very substantial fraction of their mass in a stellar wind during ascent of the giant and asymptotic-giant branches (e.g., Kudritzki and Reimers 1978). In addition, many highly-evolved short-period binaries, such as the cataclysmic variables, appear to owe their origins to very long-period progenitors (Paczynski 1976; Ritter 1976; Webbink 1976). These latter systems evidently evolved through a common envelope phase (Paczynski 1976; Meyer and Meyer-Hofmeister 1979), in which the giant progenitor of the present white dwarf devoured its companion star, and ultimately was divested of its envelope by the release of orbital energy as that companion spiralled toward its core.

We have integrated the motion of the four Jovian planets on Myr timescales in fictitious solar systems in which the orbits differ from those of the real solar system. A change of ≲1% in the major axis of any one of the planets from its real value can lead to chaotic motion with a Lyapunov exponent larger than 10-5 yr−1. A survey of fifty solar systems with initial conditions chosen at random from a reasonable probability distribution shows the majority of them to be chaotic.

We have computed a set of models of white dwarfs. The equation of state is the Chandrasekhar (1939) one corrected by Salpeter (1961). It takes into account both the interactions between particles and the effect of non-zero temperature.

The models consist of an isothermal core with 50% of carbon and 50% of oxygen, surrounded by an envelope of population I composition with 70% of hydrogen and 3% of metals by mass. Nuclear energy is liberated by p-p reactions located in a shell at the edge of the isothermal core. Equilibrium models of various masses and luminosities have been built; Table I gives the values of their characteristic parameters. The central temperature-luminosity-mass relation for our models is compared with the Schatzman (1952) one for pure hydrogen envelopes (S), the Hubbard and Wagner (1970) one for Mg core and solar composition envelope models (HW) and the Van Horn (1970) one for carbons models (VH) (Figure 1). At high luminosities there is a sensible departure from the linear relation. Though our models are not evolutionary sequence ones, they fit very well with the sequences calculated by Vila (1966, 1967). The models studied here are of the type expected from the calculation of the evolution of some double systems (Lauterborn, 1970) after the white dwarfs have lost their very diluted envelopes.

Symplectic integrators are numerical integration methods for Hamiltonian systems, which conserves the symplectic 2-form exactly. With use of symplectic integrators there is no secular increase in the error of the energy because of the existence of a conserved quantity closed to the original Hamiltonian. Higher order symplectic integrators are obtained by a composition of 2nd order ones.

We carried out observations of bright optical carbon stars with the ISO SWS, and detected the absorption features of CO, CS, CH, SiS and HCN in N-type and SC-type stars. The CH fundamental bands in 3-4 μm in N-type stars are stronger than those in SC-type stars. On the other hand, the first overtone bands of SiS at 6.6 μm were detected in WZ Cas (SC-type), while none of them were detected in N-type stars. These results can be explained well by the lower C/O ratio in SC-type stars than in N-type stars. The absorption features of HCN (v1, v2 + v3 and v1 − v2) are stronger in SC-type stars than in N-type stars. This fact can be explained by the cooler atmospheres of our SC-type stars due to the lower C/O ratio as well as due to the lower effective temperature, compared with the N-type stars in our sample. The CS bands and the band heads of the CO fundamental bands are weaker in the observed spectra than in those predicted by our model atmospheres. This result cannot be explained by the present model atmosphere and one possible explanation is the contribution by the emission of CO and CS in the outer atmosphere.

It is widely accepted that quasars and other active galactic nuclei (AGN) are powered by accretion of matter onto a central supermassive black hole. While numerical simulations have demonstrated the importance of magnetic fields in generating the turbulence believed necessary for accretion, so far they have not produced the high mass accretion rates required to explain the most powerful sources. We describe new global 3D simulations we are developing to assess the importance of radiation and non-ideal MHD in generating magnetized outflows that can enhance the overall rates of angular momentum transport and mass accretion.

Shortly after the discovery of PSR J1906+0746, some hints of profile variations were already interpreted as first signs of relativistic spin-precession occuring. Using observations from the Nançay, Arecibo and Green Bank Radio Observatories, we report here the measurement of pulse profile and polarimetric variations. Using the Rotating Vector Model, we show that PSR J1906+0746 is likely to be an orthogonal rotator (α ≃ 80°). Fitting our polarimetric data to a precession model, we determined the geometry of the pulsar and found a wide misalignment angle (δ = 89−44+85 deg, 95% C.L.), although the uncertainty is large. Assuming this geometry, we constructed the beam maps of both magnetic poles.

Recent spectroscopic results from the far ultraviolet and X-ray region coupled with infrared observations demonstrate that winds from luminous stars can be warm (300000K) and fast (speeds of several hundred km s—1) linking the hot solar wind to the cool, massive winds of luminous M-type supergiant stars. Hot coronal material (T ∼107 K) appears to be confined near the star, and not expanding in the wind. These new spectra enable a comprehensive picture to be constructed of the presence and character of winds in cool stars.

SigSpec is a new method to compute the significance of the amplitude levels in the frequency domain, based on the false-alarm probability associated with a peak in the amplitude spectrum. The underlying probability density function (PDF) of the amplitude spectrum generated by pure noise may explicitly be derived if treated as frequency and phase-dependent. A comparison of the analytical solution with the results of extensive numerical calculatgions provides excellent agreement. In addition, the SigSpec software has already demonstrated clear advantages compared with the commonly used Fourier methods in various respects. A few examples for ground-based as well as space photometry are presented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Radio jets occur in sources with a wide range of radio luminosities, and in 70% to 80% of nearby radio galaxies. There may be two basic types of large-scale (>1 kpc) jet — B‖-dominated one-sided jets in sources with luminous radio cores, and B⊥-dominated two-sided jets in sources with weak radio cores. The large-scale jets that have been observed at high linear resolution are well collimated within a few kpc of their cores, then flare and recollimate further out. Their brightness-radius evolution is often “subadiabatic”.

A vast increase in the amount of information on cool stars has occurred during the past 3 years starting with the spectroscopy of the brightest objects from the Princeton experiment on Copernicus, the near ultraviolet balloon measurements from BUSS, low dispersion observations in the far ultraviolet from rocket instruments, and most recently, spectra from the International Ultraviolet Explorer satellite (IUE). IUE now gives access to a wide variety of cool stars and stellar systems enabling systematic studies to be made.

Drawing on the most recent material from IUE, we discuss the presence and structure of chromospheres and coronae in single stars of varying gravities, surface temperatures, and activity. Evidence of mass loss and the concurrent presence of a corona are also noted. Binary systems of late-type stars (the RS CVn and W UMa type) are briefly discussed since they display extremes of surface activity. A binary system such as VV Cep containing a late-type star and an early-type companion provides a unique probe of cool extended stellar atmospheres.

The X-ray spectrum of a quiet Sun can be approximated by a 500,000° K Planckian distribution. In the absence of coronal excitation, as evidenced by the intensity of the Fe xiv green line, the X-ray spectrum has a short wave-length limit near 20 A. Coronal activity is accompanied by weak emissions down to wave-lengths as short as 6 A, which appear to be associated with coronal hot spots at temperatures of 2 x 106° K or higher.

During the last 5 years, laboratory experiments relevant to the formation of carbon-bearing molecules in extraterrestrial environments have been performed employing the crossed molecular beam technique and a high intensity source of ground state atomic carbon, C(3Pj). These investigations unraveled for the first time detailed information on the chemical reaction dynamics, involved collision complexes and intermediates, and – most important – reaction products of neutral-neutral reactions. Here, we extend these studies even further, and report on very recent crossed beam experiments of cyano radical, CN(2Σ+), reactions with unsaturated hydrocarbons to form nitriles in extraterrestrial environments and Saturn's moon Titan. Further, preliminary results on reactions of small carbon clusters and with acetylene, ethylene, and methylacetylene to synthesize hydrogen-deficient carbon-bearing molecules are presented.

Luminous Blue Variables (LBV’s) are losing mass at a rate which is higher than in normal stars of the same luminosity. This high mass loss is evident from the occurrence of P Cygni profiles in the visual spectrum, the large numbers of UV lines which are Doppler shifted or show P Cygni profiles and the large IR excess or radio free-free emission. Mass loss from LBV’s is strongly variable on a wide range of timescales from months to centuries and possibly even millenia. During these variations the mass loss may vary from values as low as 10-6 to 10-5 M⊙/yr, when the star is quiet, to outbursts of the type observed in P Cygni in AD 1600 and n Car in 1837 (for reviews see Davidson, 1987; Lamers, 1986, 1987).

We report the results of HI observations of eleven gas-rich SO/SOa galaxies with the Westerbork Synthesis Telescope. The majority of these galaxies have most of their hydrogen outside the optical body, in annular configurations with diameters ~2 times the optical. These outer gas rings are often clumped, incomplete, and in approximately circular motion. They may represent the remnants of primordial, often warped, gas disks; or they may have formed from gas (or dwarf galaxies) accreted recently. Optical spectra could discriminate between these possibilities.

A few objects have filled gas disks, and several have inner HI rings with radii ~0.4 × optical. Two objects have peculiar distributions suggesting, respectively, tidal effects and stripping. However, stripping by intergalactic gas appears not to be a major current process.

An expansion of the source of a great solar microwave burst was observed a little beyond the west limb on March 30, 1969. This expansion is interpreted in terms of diffusion of energetic electrons in a turbulent magnetic field in the flare region. The height of the source is estimated to have been 104 km.

A scanning photoelectric polarimeter of 16 cm aperture that can measure all four Stokes parameters of the visible radiation of the Sun's disk, the Corona, Moon and planets, has been constructed at the Institute for Astronomy and is installed on Mt. Haleakala. It is a two (orthogonal) channel system and uses a rotating λ/4 plate modulator. Photon counting is done by a digital computer that also Fourier analyzes the modulated output of the photomultipliers, and, from the Fourier components, computes the Stokes parameters in real time.

The “Grand Interféromètre à deux Télescopes” (GI2T) is presently the largest operational interferometer operating at visible wavelengths (Labeyrie et al. 1986, Mourard et al. 1991). With two telescopes of 1.5-m aperture and baselines reaching 65 m in the North–South direction, it gives stellar spectra containing interference fringes, which provide high angular resolution measurements in the range of one milliarcsecond.

The GI2T optical combination follows the Michelson principle of output pupil remapping to preserve a constant fringe spacing on the detector for stable and economical spatial sampling. The stellar light is dispersed in order to study the fringes parameters simultaneously with the spectral information. The direction of dispersion is perpendicular to that of the recombined pupils. Due to atmospheric turbulence the instantaneous images contain about 100 speckles. To freeze the atmospheric turbulence a temporal resolution of at least 10 milliseconds is needed.