The fundamental feature of the evolution of the central star of planetary nebulae (CPN) is the cooling of the core towards a white dwarf. The basic observations were made by O'Dell (1963), Seaton (1966), and Harman and Seaton (1964); namely, they discovered a correlation between the linear size of the nebula and the position of the CNP in the HR diagram. Typical values for the velocity of expansion are 10–30 km/sec and the largest size observed for a nebula is ∼0.6 pc and hence the lifetime is 2–6 × 104 years. From a theoretical point of view the important fact about the Harman-Seaton sequence (HS) is the implication on the evolution of the central star. The star first heats up, L and Te increase, then L decreases. But Te keeps increasing until finally Te decreases also (shown schematically in Figure 2). Thus the HS is an evolutionary sequence and not a locus of stars.

We present results of a search for variable stars in the young open cluster NGC 2244. As a result we have found many eclipsing systems and pulsating stars, some of which are multiperiodic. Here we show only a few examples.

We have constructed two types of analytical models for an isothermal filamentary cloud supported mainly by magnetic tension. The first one describes an isolated cloud while the second considers filamentary clouds spaced periodically. The filamentary clouds are assumed to be highly flattened in both the models. The former is proved to be the asymptotic limit of the latter in which each filamentary cloud is much thinner than the distance to the neighboring filaments. These models show that the mass to flux ratio is crucial for the magnetohydrodynamical equilibrium. The upper bound for the line density, i.e., the mass per unit length, is proportional to the magnetic flux. The mass to flux ratio is slightly larger than the critical value, (2 \pi \sqrt{G}$2 \pi \sqrt{G}$)−1, in the first model and lower in the second model. The first model is unstable against fragmentation and the wavelength of the fastest growing mode is several times longer than the cloud diameter. The second model is likely to be unstable only when the mass to flux ratio is supercritical.

We present here starburst models based on the most recent grids of stellar evolutionary tracks obtained by the Geneva group. These new models, computed with enhanced mass loss rates during the main sequence and the Wolf-Rayet WNL phases, very well reproduce the luminosities, surface abundances and statistics of WR stars (Maeder & Meynet 1994). This change of the mass loss rates considerably affects the way the WR stars, born in a starburst's episode, are distributed among the different WR subtypes. We compare the theoretical predictions with recent observations and conclude that: (1) to reproduce the high observed ratios of WNL to O-type stars, a flat IMF seems to be required; and (2) the models which reproduce the best the observed characteristics of WR stars, i.e., those computed with an enhanced mass loss rate, can also account for the observed properties of the WR populations observed in starbursts. Moreover, the possible presence of numerous WC stars found in the low metallicity He2-10 A starburst by Vacca and Conti (1992), can only be accounted for when the high mass loss rate stellar models are used.

Optical spectra and images in the main optical emission lines were obtained for 21 type I planetary nebulae (PNe). IR images directed towards the detection of shocked molecular hydrogen were secured in 17 of these objects. No evidence of shocked H2 could be found in A 14 and Sh 2-71, and its existence needs to be confirmed in JnEr 1 and M 1-57. Bipolarity is obvious in most of these sources. A 24, JnEr 1 and M 3-5 may be bipolars seen nearly pole-on. The chemical composition of nearly half of these objects indicates that third dredge-up episodes may have occured in their progenitor star. The presence of shock waves in the ionized component is inferred in 9 PNe, where the temperature ratio T(O+2)/T(N+) is large and the Hα/[S II]6724 line ratio small, a typical combination in shock excited plasmas. A larger sample of type I PNe shows that small Hα/[S II]6724 line ratios are usually associated with large temperature ratios.

Recent high-resolution observations have pointed out that prominences are made of small threads (also named fibrils) piled up to form the body of the prominence. These fine structures also seem to support their own oscillatory modes, while their effect on the global modes of the prominences are less certain. We study the effect of adding a smooth transition layer between the prominence material and the corona along the magnetic field line, since previous studies have considered a jump in density in this interface. Then we compare the results with previous models and check that these transition layers do not affect significantly the periods of the modes.

With modern large scale spectroscopic surveys, such as the SDSS and LSS-GAC, Galactic astronomy has entered the era of millions of stellar spectra. Taking advantage of the huge spectroscopic database, we propose to use a “standard pair" technique to a) Estimate multi-band extinction towards sightlines of millions of stars; b) Detect and measure the diffuse interstellar bands in hundreds of thousands SDSS and LAMOST low-resolution spectra; c) Search for extremely faint emission line nebulae in the Galaxy; and d) Perform photometric calibration for wide field imaging surveys. In this contribution, we present some results of applying this technique to the SDSS data, and report preliminary results from the LAMOST data.

In 1980, Feissel et al. identified a quasi–cyclic variation of 55 days in the irregularities of the Earth Rotation (ER) later detected in the Atmospheric Angular Momentum (AAM) (Langley et al., 1981). The purpose of this work is to analyse whether the causes of this cycle could lie in the physical processes of the Sun. The Wolf Numbers (WN) are used as parameters of the solar activity. Their spectral analysis over the period 1967–1985 shows such a component at 51 days. Analysis of three other periods, among which is the MERIT campaign, confirms it as well as during low or increasing solar activity periods.

It has been proposed to the U.S. National Aeronautics and Space Administration that optical retro-reflector packages be placed on the lunar surface under either the Surveyor or Apollo Programs. Methods for measuring the range to the reflectors with an expected accuracy of 15 cm have been presented. The new technique is briefly discussed, and an analysis of the determination of geocentric longitude is given, indicating a potential uncertainty of 0·25 × 10−3s of time.

The notion of the local Macroscopic Volume Element (MVE) is introduced in order to facilitate the application of hydro-dynamical methods of treating internal motions in stellar systems and in particular in our Galaxy. The MVE must characterize the properties of the stellar system in a given point within the system. Hence the diameter of the MVE must be taken as small as possible; it must, however, contain a sufficiently large number of stars in order that the laws of statistics might be applied. The greater is the local star density the smaller can be made the size of the MVE.

Modern catalogues of nearby stars by Gliese (1969) and Woolley et al. (1970) afford a good collection of data for a determination of local characteristics of the Galaxy in the immediate neighbourhood of the Sun. In the first section we discuss such characteristics as the local stellar density, the local luminosity function and the influence of observational selection upon them. In the second section we consider the local solar motion and the effect of the asymmetry of stellar motions. The responsibility for the content of paragraph 1 lies primarily upon T. A. Agekjan while that for paragraph 2 upon K. F. Ogorodnikov. We both are indebted to G. V. Ishkhanov and to L. V. Chuvicova for substantial help in numerical computations.

The analysis of the available data about spectral observations of nucleus and gas velocity field in NGC 1275 leads to a conclusion on the presence in the nucleus of several spatially separated variable sources responsible for a complex variable emission in Hβ and [OIII] lines profiles.

We report on the current status of the HI redshift survey in the Pisces-Perseus supercluster and present results based on a sample of approximately 4700 redshifts known in the 6h by 45° region of the sky dominated by the supercluster. In particular we derive density contrasts between voids and high density regions and discuss the existence of a luminosity bias between galaxies that reside in regions of different local density. Such a bias is not the consequence of the well-known pattern of morphological type segregation, but results from a difference in the shape of the luminosity function of galaxies in high and low density regions. Bright galaxies tend to be relatively less abundant, and faint ones relatively more so, in low density environments.

Recent years have seen dramatic progress in the study of the core and nuclear properties of galaxies. The structure of the cores has been shown to vary methodically with global and nuclear properties, as cores respond to the mechanisms by which galaxies form/evolve. The dynamical centers of galaxies have been found capable of hosting two seemingly disparate objects: supermassive black holes (SBHs) and compact stellar nuclei. In a drastic departure from previous beliefs, it has been discovered that both structures are common: galaxies lacking SBHs and/or stellar nuclei are the exception, rather than the norm. This review explores the connection between cores, SBHs and stellar nuclei in early-type galaxies, as revealed by the ACS Virgo Cluster Survey.

Astronomy in Brazil grew to around 500 astronomers in the last 30 years and is producing around 200 papers per year in refereed journals. Brazilian astronomers are participating in several international collaborations and the development of instrumentation is on the rise.

On the basis of the Second Byurakan Survey (SBS) we have produced the largest and most homogeneous new complete samples of faint Markarian galaxies, Sy galaxies and bright QSOs. The General Catalogue of the SBS Survey, which is completed and prepared for publication, contains the data for more than 3600 objects, half of which are star-like objects while the other half are galaxies. Nearly 2500 slit spectra were obtained for about 2100 SBS objects. 561 new QSOs and AGNs in the magnitude range 15.5 < B < 19.5 with redshifts 0.0 < z <3.2 were spectroscopically confirmed. A sample of 17 BLL has been isolated as well.

The volume for reliable investigation of faint Markarian UVX galaxies has been extended out to a distance of about ~ 500 Mpc, more than 50 times deeper than in the FBS. Faint Markarian UVX galaxies from the SBS survey comprise ~ 12% of field galaxies, slightly greater than in the First Markarian survey; ~ 10% of them (~ 120) turned out to be Sy galaxies.

A complete sample of faint (B ≤ 17.0, z ≤ 0.1) Sy galaxies has been constructed. In the spatial volume with radius of about 500 Mpc, the relative number of AGNs is 1.2% of field galaxies. One of the most complete and representative samples of bright QSOs (~ 130) in the magnitude range 15.7 < B ≤ 17.5 with redshifts 0.3 ≤ z ≤ 2.2 has been constructed as well.

The objects in the combined complete sample of SBS Sy galaxies and QSOs might be roughly divided into two groups: classical Sy galaxies and QSOs in agreement with the previous classification scheme and nonclassical SyG and QSOs for which the existing classification scheme is not sufficient for their classification. The presence of narrow line QSOs (NLQSOs) or so-called QSO II type objects is established. There is a continuous transition of all properties between all types of Sy galaxies and QSOs, from Liners through Sy2, NLSyls, BLSyl to NLQSOs and BLQSOs.

Preliminary results from the Multiwavelength AGN Survey (MWAGN) in X-ray, Radio and IR wavebands in the SBS area are presented. The MWAGN survey in the SBS area shows that the ROSAT or FIRST surveys by themselves cannot represent the whole AGN/QSO sample. The ROSAT Bright sources along with the FIRST sources comprise only 25% of the whole SBS QSO sample. The IRAS survey is effective for a redshift less than z < 0.05. All classical Sy2s but only ~ 50% of classical Syls are IRAS sources. Luminous and Ultraluminous IRAS SBS AGNs comprise ~ 25% of the whole AGN sample. The greater part of SBS AGN/QSOs are neither ROSAT nor FIRST nor IRAS LIG or ULIG sources. They are optically emitting AGN/QSOs.

The multiwavelength “complete” sample of bright QSOs in the SBS area allows us to conclude that the fast evolution of bright QSOs is more likely the result of a selection effect than the result of fast cosmological evolution. The LogN-B relation for these QSOs reduces to the value LogN − B = 0.67 ± 0.005.

A direct empirical estimate of the effect of overlapping images is obtained from the MWAGN survey. The effect of overlap comprises ~ 5% for QSOs brighter than B ≤ 17.0 and ~ 10% for QSOs brighter than B ≤ 17.5.

Strong radio emissions are associated with solar flares. It seems worth while, therefore, to examine whether radio emission associated with flares and eruptions in nonstable stars could be observed. The first problem in this respect is establishing the threshold of sensitivity necessary to receive anything during an eruption or a flare; the second one is naturally fixing the duration of the radio emission, which can be much shorter in a given wavelength than the optical emission.

The Solar Wind Generation Experiment consists of a UV Coronal Spectrometer (UVCS) provided by the Harvard-Smithsonian Center for Astrophysics and a White Light Coronagraph (WLC) of the High Altitude Observatory. The instruments are similar to those flown together on three sounding rocket flights [1,2,3] but they have enhanced capabilities to take advantage of Spartan’s 27 hour observing period. The two instruments comprise a payload for Spartan 2, which is a self-contained instrument carrier that provides on-board data storage, power, thermal control, sun pointing and an observing program sequencer. Spartan is launched and deployed by the Shuttle and spends about 27 orbits in a detached mode before it is recovered and returned to the ground for data tape retrieval and post-flight instrument calibration.

Projected rotational velocities for 67 B, A, and early-F stars have been determined. Some of these stars are early-type, radial-velocity standard candidates. The spectra of seven stars show metallic lines with composite profiles that consist of a narrow component near the center of a broad component, suggesting that they may be shell stars or binaries.

We systematically search for discrete absorption events in the vast archive of the Rossi X-ray Timing Explorer. This includes dozens of nearby type I and Compton-thin type II AGN and covers timescales from days to over a decade for individual objects. We are sensitive to discrete absorption events due to clouds of full-covering, neutral or mildly-ionized gas with columns 1022−25 cm−2 transiting the line of sight. We detect 13 eclipse events in 8 objects, roughly tripling the number of previously published events from this archive. Despite sensitivity to events with NH up to 1024−25 cm−2, we measured no Compton-thick eclipses in our sample. Peak column densities span 2.5–19 × 1022 cm−2. Event durations span hours to months. We infer the clouds distances from the black hole, assuming Keplerian motion, to span 0.2–80 × 104 Schwarzschild radii. We find no statistically significant difference between the individual cloud properties of type I and II objects. The presence of eclipses in both type Is and IIs argues against sharp-edged cloud distributions. The type II AGN show a level of “base-line” X-ray absorption that is consistent with being constant over timescales from 0.6 to 8.4 yr. This can either be explained by a homogeneous medium, or by X-ray-absorbing clouds that each have NH ≪ 1022 cm−2. Considering the “selection function” of the monitoring, we derive the probability of cloud occultation events. Finally, we derive the first X-ray statistical constraints for clumpy-torus models.