Extragalactic masers were discovered more than 20 years ago (Whiteoak & Gardner 1973). It soon became apparent that those extragalactic masers we can detect are intrinsically very powerful and are located in galactic nuclei. The term Megamaser was coined to describe the most luminous OH masers, which are a million times more powerful than any OH masers within our own Galaxy (Baan & Haschick 1984). The same word is nowadays applied to any powerful maser associated with an active galactic nucleus (AGN). Whereas normal Galactic masers would be barely detectable outside the Local Group, megamasers are detectable in principle out to redshifts of z ~ 2 (Baan 1997). The galaxies hosting megamasers in their nuclei are invariably active in some degree: they include ultraluminous infrared galaxies, starbursts and Seyfert galaxies.

The OH megamasers have a distinct parent population of dusty and FIR luminous merger galaxies. Optical, radio and molecular characteristics may be used to further identify the nature of the nuclear activity in the OH megamaser host galaxies. Recent interferometric data on OH megamasers Arp 220 and III Zw35 will be used to discuss the spatial distribution of the OH emission.

JD8 assembled for half-day sessions on August 22 & 23, 1997 in a satisfactory meeting hall. Between 350 and 400 delegates - about 50% larger than anticipated - attended most of the sessions.

The theme of the meeting developed from initial conversations between R. H. Koch and Y. Kondo and was extended by E. F. Guinan. Opinions from the officers of Commissions 27 and 42 were favorable to seeking IAU approval and eventually the co-sponsoring Commissions came on board.

In essence, all the organizing workers recognized that there did not exist a broad recognition that we really do know specific stars whose evolution we have actually perceived and that there are also statistical interpretations (not the conventional isochrones in an HRD or CMD) for ensembles of stars which lead to the same conclusion.

The presentation compiled here is really a distillation of short offerings from the JD participants provided against a deadline which was regrettably close at hand. A full presentation of the meeting Proceedings will appear in The New Astronomy series of Elsevier. E. R. Jewell prepared the final files.

We would like to review the current status of OH megamaser pumping models. Contrary to the quantity and quality of observations of OH megamasers, surprisingly little theoretical modeling has been done on them so far.

This Part of the report contains the summaries of the most affirmative conclusions about recognized evidences for stellar evolution. We would certainly prefer to know that we have actually discovered this or that piece of evidence but it can be equally valuable to know that the present state of knowledge forbids a conclusion of the sort which we wish. Not surprisingly, there are instances for which we are lucky to be able to make only a limiting statement about the matter. So affirmative here really means that a conclusion - positive or negative - has actually been attained. To the layman in stellar evolutionary studies it may be surprising that there exists such a diversity of evolutionary criteria - radiometric, spectrometric, orbital dynamical, spin dynamical - all with a defined time base available at the present day. It may be hoped that some of the conclusions summarized here will make their way routinely into undergraduate texts in the for seeable future and that tools such as the HRD or CMD will not appear as only static snapshots.

The variable post-AGB star FG Sge has provided an unique opportunity to study phenomenon which may be characteristic of the post-PN stage of stellar evolution. FG Sge is the central star in the 36-arcsec PN He 1-5 that over the last 50 yrs has been undergoing rapid evolutionary changes. Most notable are changes in temperature, luminosity, chemical composition and pulsation period. Starting in mid-1992, the star has undergone several large dimming events from which it has yet to recover. These events closely resemble the dimming events commonly observed in R CrB stars which result from dust formation in ejected envelopes. From all the evidence, it now appears that FG Sge has evolved into a R CrB star.

In this paper we first summarize the recent photometric history of the FG Sge from UBVRI photometry obtained during 1990-1997. We then combine these data with earlier photometry to define the star’s light bevavior over the last 100 yrs. The photometry is also combined with available spectroscopic polarimetric, and IR observations. Particlar attention is given to comparing FG Sge’s post-dimming behavior with contemporaneous observations of R CrB itself, also done on the same photometric system.

An analysis of a sample of OH megamaser galaxies is presented. It is shown that the dependence of OH luminosity on FIR (far infrared) luminosity is not quadratic, as previously assumed, but closer to linear. Using a luminosity function of the luminous infrared galaxies, as well as linear relationship between OH and FIR luminosities the expected number of OH megamaser galaxies has been estimated. Spectral energy distributions (SED) of 16 megamaser galaxies have been constructed using multiwavelength (from radio to X-ray) data. The SED of megamasers look closely similar from radio to X-ray. It is shown that the maser amplification coefficient depends both on the OH main line to 60 micron ratio and the main line to 2.2 micron ratio. The OH main lines ratio (f1667/f1665) decreases, while the flux density at 10 micron is increasing.

The peculiar T Tauri type star V1331 Cyg = LkH 120, located in the dark cloud Lynds 984, is a FU Orionis pre-outburst candidate (McMuldroch et al., 1993). This star embedded in circumstellar bright nebulosity is also surrounded by a helix-shaped nebula originated from the star. We obtained a series of speckle images of V1331 Cyg on the standard VBR system on July 18-20, 1994 using the Zeiss 1000 1.0 m telescope of the High Altitude Maydanak Observatory in Uzbekistan. We also used the results of Johnson’s system photometry of V1331 Cyg, made simultaneously at Maydanak Observatory with a 0.6 m reflector. Images were computer processed. Surface photometry of the star and surrounding nebula was made and isophotes were constructed. Fourier analysis of light curves for V1331 Cyg has shown 36.2 day periodic process (Melnikov, priv. comm.) which could be due to the presence of a circumstellar disk. Morphologic analysis revealed a complex fine structure of nebula, consisting of many bright knots and obviously show a jet-like outflow. According to spectral observations (Chavarria K. 1981; Penston & Keavey 1977) the line profiles of V1331 Cyg are P Cyg type only; there are no detections of anti-P Cyg profiles during the last 25 years observations. This indicates a stable mass loss (on average, 10−7 M ⊙/yr) with mean velocities about −410 km/s.

We review correlations between water megamaser emission and other properties of AGN. Galaxies detected as water megamaser emitters tend to be nearer, brighter at mid-infrared and possibly centimeter wavelengths, and more highly inclined than undetected galaxies. Only Seyfert 2s and LINERs (no Seyfert Is) are detected. It is argued that the primary parameter determining whether an active galaxy is detectable as an H2O megamaser is the gas column along our line of sight to the nucleus.

Visual magnitude data in Ptolemy’s Almagest are analysed by comparing them with modern photoelectric magnitudes on the Pogson scale, after taking extinction into account. This result is used to transform Almagest magnitudes to the Pogson scale.

A study is made of changes in the vusual magnitudes of supergiant stars in the Almagest between classical and modern times (an interval of nearly 19 centuries). No evidence is found for any secular changes in the mean brightness of these stars, contrary to the conclusion of Mayer (Observatory 104, 77, 1984). However, it is shown that the Almagest magnitudes for stars in the Milky Way are on average 0.34 Pogson magnitudes too faint and about the Almagest supergiants are affected by this. Finally, some evidence is cited for the visual atmospheric extinction in classical times being significantly less than today. If this is the case, and is not taken into account, it would mimic an apparent supergiant brightening of about 0.1 magnitudes over this time interval.

Twenty-one H2O masers have been identified in the nuclei of active galaxies. The detection rate is about 7 percent. Very Long Baseline Interferometric data of four of these maser systems (NGC 4258, NGC 1068, NGC 4945, and NGC 3079) show evidence of Keplerian disks on a subparsec scale. The best example is NGC 4258. There the masers trace a thin warped disk in nearly perfect circular Keplerian motion. If the apparent thinness is indicative of hydrostatic equilibrium, then the kinetic temperature must be less than 1000K, the magnetic field less than 200 mG, and the mass accretion rate less than about α10-3 M⊙/yr, where a is the viscosity parameter. From direct Zeeman measurements the toroidal magnetic field strength is less than 300 mG. The proper motions of the systemic maser feature imply a distance to the galaxy of 7.3 ± 0.3 Mpc. The high-velocity features show no detectable proper motions or accelerations, which confirms the model of circular Keplerian motion, and puts severe constraints on any alternative model. A feature in the systemic group flared to 20 Jy, offering opportunities to study the physics of the maser emission.

The light curves of luminous stars often show spectacular secular changes which can be connected to stellar evolution. Such events are, e.g. the outbursts of P Cygni in the 17th century and 77 Carinae in the last century. Both stars belong to the Luminous Blue Variables, but these changes are not restricted to blue stars. The light curve of HR 8752 (V509 Cassiopeiae) shows a certain similarity to that of the former two stars. When it was first catalogued in the middle of the 19th century, it had been a 6m star. During 100 years the star showed a secular brightening of lm. A similar yellow hypergiant, p Cassiopeiae produced at least two outbursts this century, though bothhave smaller amplitudes than it is in the case of the LBVs. Moreover, these yellow variables also have an apparently secular colour change: the B − V colour of HR 8752 is decreasing while that of ρ Cassiopeiae is increasing. In both cases evolutionary changes are possible but one cannot exclude other causes.

Besides these well studied stars there are several other yellow hypergiants with promising light curves. One of the most interesting cases seems to be R Puppis, which was discovered to be variable in the last century, but then did not show any appreciable change in the following 70-80 years. In the late 1970s, however, it began to vary once more.

Strong H2O maser emission is detected from active galactic nuclei (AGN) as well as Galactic objects such as star-forming regions and late-type stars. In spite of the widely different luminosities of the different masers, a common pump mechanism seems adequate: neutral collisions at densities of ˜ 108-1010 cm-3 and temperatures of ˜ 250-500 K. The different properties of the various masers can be attributed to geometry. Although disk rotation controls the AGN maser geometry it does not directly determine the dimensions. X-ray radiation and spiral shocks have been suggested as the heating sources of H2O megamasers. Both are capable of explaining the observations, and the radiative scenario seems best understood in terms of chance alignment of standard broad-line-region clouds. It is not yet clear whether these different proposals produce distinct maser signatures.

The discovery of megamasers in nearby active galactic nuclei (AGN) is an unexpected boon for AGN researchers. The most immediate benefit, brought out in observations of NGC4258 (Miyoshi et al 1995, Moran, these proceedings) is that it allows an accurate mass measurement for the central black hole, in this case of 3.6 x 107 M⊙, with unprecedented accuracy. (I shall not belabor the point that we have not proven rigorously that it is a black hole because this is surely on much firmer footing than what follows!) Masers also allow us to discover second order features of the kinematics, specifically that the disk is warped. Thirdly, and this is what I have been asked to review here, it should enable us to choose between several possible accretion modes by treating masers as diagnostic probes of physical conditions in the disk.

We first consider all β Cephei stars for which long-term behavior of their pulsation periods is known from observations. As it turns out, these objects fall into two categories: one consisting of stars with complex period variations, and the other, with a constant and non-negative rate of period change, Ṗ = const ≥ 0. The problem is that stars with Ṗ close to that predicted for the hydrogen-shell burning phases of evolution are over-represented. We then compare the five β Cephei stars which exhibit long-term variations of the pulsation amplitudes and note that in each case the cause may be individual. In one star, 16 (EN) Lac, two different effects are responsible for the observed variation of the amplitudes.

An IAU travel grant is gratefully acknowledged. This work was supported by KBN grant 2P03D01611.

Using all available data, we investigate long-term variations of the amplitudes of the three strongest pulsation modes of 16 (EN) Lac and the period of the strongest mode of ν Eri. We show that in case of 16 (EN) Lac there are feasible explanations of the observed variations. The explanations involve non-linear interaction between pulsation modes (the first two observed modes) and beating between two non-interacting modes (the third observed mode). In case of ν Eri, however, we can only indicate the difficulty of accounting for the long-term period variation.

MJ gratefully acknowledges an IAU travel grant. This work was supported by KBN grant 2P03D01611.

We propose that the observed high-velocity maser emission from circumnuclear disks arises in spiral shocks, which can naturally account for several peculiar findings in the spectrum and spatial distribution of the maser emission.