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We re-analyzed OJ287 in 120 Very Long Baseline Array (VLBA, MOJAVE) observations (at 15 GHz) covering the time span between Apr. 1995 and Apr. 2017. We find that the radio jet motion over the sky is consistent with a precessing and nutating jet source. The variability of the radio flux-density can be explained by Doppler beaming due to a change in the viewing angle. We suggest that part of the optical emission is due to synchrotron emission related to the jet radiation. We find a strikingly similar scaling for the timescales for precession and nutation as indicated for SS433 with a factor of roughly 50 times longer in OJ287.

To record the spectral lines of stars and nebulae, photographic photometry was routinely used in the early 1900s, to be later replaced by methods employing more advanced detectors. We review the progress of planetary nebular spectroscopic studies, i.e. from the early photographic photometry, through to the 1950s photoelectric scanner observations, and finally to recent charge-coupled-device spectroscopy.

The spectra of gaseous nebulae differed strikingly from those of stars which were well understood since 1922 thanks to the work of Saha. Gaseous nebulae exhibited exotic bright line spectra characterized by strange emissions of unknown origin as well as familiar lines of hydrogen and helium. The strongest lines in most nebulae fell at 4959A and 5007A. They were originally attributed to an unknown element. First came the interpretation of the lines of H.

With strategically important diagnostic lines of, e.g., [O II], [O III] and [S II], secured with the Keck I HIRES, we obtained electron densities and temperatures, while retaining 3-D spatial information for the well-known elliptical nebula NGC 7009: we found that the temperature fluctuations exceeded those reported in the HST imaging study, i.e. Te ~9500 – 11500 K; we also found large velocity dispersions in the [S II] maps (with extremely high density fluctuations, i.e. log Ne = 3.8 – 4.5), but not in the [O II] ones. The [S II] map indicates that this emission is from numerous small-scale blobs of size ~ 1″ spread over a wider region, while [O II] shows no such evidence. The [S II] emission is likely to be due to shock excitation, while the [O II] emission is perhaps due to photoionization.

Determinations of the plasma diagnostics and chemical compositions of planetary nebulae require ultimately high dispersion spectra. For objects of high surface brightness the Hamilton Echelle Spectrograph at Lick Observatory is satisfactory for the region 3650–10100Å which involves the 168th to 56th echelle orders. For a slit width of 640 μm amounting to 1.15 arcsec at the Coude focus, the actual spectral resolution (FWHM) is about 0.2Å at 8850Å. The length of the slit is chosen as 4.0 arcsec. Hyung (1994) & Aller (1994) describe the observing procedure. Since the Hamilton echelle was designed primarily for star-like sources, it is not useful for extended low surface brightness PN. The earlier observations were obtained with an 800 × 800 chip that did not cover the echelle field, so several settings were needed. Later, we used a slower 2048 × 2048 chip which covered the whole field and was somewhat more efficient at longer wavelengths. The program has been completed and definitive measurements have obtained for NGC 2440, NGC 6543, NGC 6741, NGC 6818, NGC 7026, NGC 7662, and Hu 1-2. All of these PN display particularly rich, interesting spectra. Previously observed and published objects include IC 351, IC 418, IC 2149, IC 4997, NGC 6567, NGC 6572, NGC 6790, NGC 6886, NGC 7009, BD +30 3639, & Hubble 12. NGC 6884 is in press. Additional nebulae which are yet to be discussed are IC 4634, IC 4846, IC 5117, NGC 6210, & NGC 6803.

Emission lines arising from transitions in S II have been detected in a wide variety of astronomical sources, including planetary nebulae (Hyung, Keyes & Aller 1995). These transitions are used to derive information on emitting plasmas parameters (Te, Ne) through diagnostic line ratios, although to calculate these quantities reliably, accurate atomic data must be employed, especially for electron impact excitation rates.

Variability of the [OIII]4363/4340 H γ ratio in IC 4007 was established in 1956 by William Liller and L.H. Aller who attributed the changes to a gradual decrease of electron density with time. Subsequent 4363/4340 ratio fluctuations negated this explanation. Ferland pointed out that small changes in the radiative flux of the Planetary nebula nucleus (PNN) could explains the variations. Our pervious study emphasized IUE observations, here we compare high dispersion spectra obtained with the Hamilton Echelle Spectrograph with previous measurements to asses line intensity variations. Emission line variability in PNN spectra as noted by Mendez et al. (1988) and by other for HeII 4686 in NGC 6572 may offer significant clues. PNN 4686 appeared by 1990 in IC 4997. Possibly both of these PNN may be evolving into Wolf-Rayet objects, but this development does not necessarily imply that the nebular excitation will increase with time.

The Hamilton Echelle Spectrograph at the coudé focus of the Shane 3 m telescope at Lick Observatory permits us to obtain high resolution spectra of bright planetary nebulae over the spectral range from 3500á to 10300á. Not only is it possible to separate pairs such as λ 5198, 5200 [NI], 4860 HeII and 4861 HI, but one may secure the profiles of Doppler broadened lines. It appears to be possible to separate the HI and HeI contributions of the 3889 line in Hu 1–2. The nebulae most suitable for observation are those of high surface brightness. NGC 7027 was the first nebula intensively studied with this equipment (Keyes et al. 1990); subsequently we have observed NGC 2440, 6537, 6543, 6567, 6572, 6741, 7009, 7662, IC 351, 418, 2149, 2165, 4634, 4997, 5217, Hb 12, and Hu 1–2. In NGC 7009 we measured line fluxes at the ends of major and minor axes. Small compact objects were centered on the slit; other were observed in the bright ring. These planetary nebulae cover a range in excitation level, chemical composition, and evolutionary status.

To review or attempt to summarize a conference such as this recalls the request our department office once received from a little fourth-grade schoolgirl: “I'm doing a science project on the stars. Tell me all about them on two pages.” We can only try to look at the broad picture and attempt to identify problems that require special emphasis or attention.

The chemical compositions of external galaxies are usually found from their HII regions or composite absorption line spectra of their nuclei. In the Magellanic Clouds, however, individual stars are observable, but objects heretofore studied necessarily have been luminous la supergiants which border on the brink of instability. The image photon counting system on the Anglo-Australian Telescope makes it possible to observe fainter, more stable Ib supergiants. Energy distributions and Balmer line profiles for these stars can be fitted with theoretical predictions by Kurucz. A joint effort by J.E. Ross and B.J. O’Mara of the University of Queensland, Bruce Peterson of the Anglo-Australian Observatory, and a group at the University of California, Los Angeles to analyze three lb supergiants suggests that metals of the iron group are depleted by a factor of 2-3.5 with respect to the normal chemical composition of our own galaxy.

Planetary nebulae constitute a popular field of investigation because they offer a unique opportunity to study the final stages of stellar evolution before a star dies. They supply challenges not only to the stellar evolution expert but also to the spectroscopist, to the student of galactic structure, and to all observers, whether one works in the optical, ultraviolet (UV), infrared (IR) or radio-frequency (r.f.) ranges. They offer insights into properties of dusty, low-density plasmas which may help unravel problems of the interstellar medium (ISM) and quasars. Finally, many are aesthetically beautiful art creations.

The determination of the chemical compositions of gaseous nebulae in general and of planetary nebulae in particular is a difficult undertaking. The zeroth-order approximation is straightforward, the first approximation is challenging, and the second approximation is almost intractable.

The problem of the determination of the chemical compositions of planetary and other gaseous nebulae constitutes one of the most exasperating problems in astrophysics. On the one hand, the problem appears to be conceptually simple – the mechanisms of excitation of the various lines appear to be well understood and the necessary physical parameters can be obtained by quantum mechanical theory. Yet the task is a difficult one and we want to explore some of the significant features.

The atmosphere of a star presents a real challenge to the astronomer or physicist. We can observe but the thinnest skin of the star; yet from the information obtained therefrom we must deduce the star’s temperature, chemical composition, its rotation (if any), the state of agitation in its outer layers, and eventually the surface gravity, total luminosity, mass, and evolutionary stage.

165 planetary nebulae south of +27° declination have been observed with the Parkes 64 m telescope. These nebulae were chosen to include most of those for which Hβ flux densities are available. Radio positions and flux densities (generally with probable errors of only a few millijanskies) obtained from the survey must represent the most reliable and homogeneous radio data currently available for the class of object. The data have been used to obtain distances and optical extinctions for these nebulae.

Although additional surveys with large Schmidt telescopes continue to yield small catches of additional planetaries (Kohoutek) one cannot escape the conclusion that most planetaries available to existing equipment have been detected. Much remains to be done with powerful Schmidt equipment in the southern hemisphere, especially in the Magellanic Clouds. A vast body of photometric and spectroscopic observation needs to be garnered for the numerous faint nebulae so far discovered.Spectroscopic and spectrophotometric studies have been carried out for most bright planetaries (λ < 5800) but much remains to be done in the red and near infrared. Important advances have been made in the far infrared (~10μ) (Gillett, Low, Stein, Woolf) where a number of planetaries seem to show abnormally strong continua. This abnormally intense radiation has been attributed to non-thermal emission, effects of many faint lines, and to thermal emission by dust grains (Krishna Swamy, O’Dell) with perhaps the bulk of the evidence favoring the last-mentioned hypothesis. An increasing number of radio observations from 9·5 mm to 73 cm (Thompson, Colvin, Stanley, LeMarne, Kaftan-Kassim, Babieri and Ficarra, Terzian, L. Aller and Milne, Hughes) all indicate that planetaries are thermal sources.

The theory of radiative and collisional processes in gaseous nebulae makes possible precise predictions of line and continuum intensities as functions of density, electron temperature, and degree of ionization of the emitting gases. It predicts, for example, the relative intensities of successive members of the Balmer series (Balmer decrement), and of corresponding transitions in the Balmer and Paschen series. Hence accurate line intensity measurements are not only of astrophysical interest; they also serve to assess the amount of space absorption.

The central stars of planetary nebulae represent seemingly well-defined late stages of stellar evolution. Theoretical investigations with predictions of evolutionary tracks impose difficult requirements for observational data. Measurements of spectral energy distributions, of colors, and of magnitudes, and spectroscopic observations are all urgently needed.

The present investigation is concerned with the energy distributions in globular clusters. In a sense, energy-distribution measurements are comparable with multi-colour photometry. The chief advantage is that narrower band-passes may be used and the entire spectrum traced, whereas in multi-colour photometry one is limited to effective wavelengths determined by the filter and a rather broad band-pass. On the other hand, broad band-pass photometry often permits one to cover a broader spectral range, and to work much faster. Since the time required for a single observation is much shorter, the observer is less at the mercy of the sky transparency. Hence a greater accuracy can be obtained.

In order to predict emission line and continuum intensities and assess plasma diagnostics for gaseous nebulae, it is necessary to have accurate atomic parameters. In some Instances the requirements for accuracy are very severe. A variety of data is required:1)Coefficients of continuous absorption;2)Direct and dielectronic recombination coefficients;3)Transition probabilities for permitted lines, so we can accurately predict both recombination line intensities and fluorescent phenomena (e.g., OI λ8446);4)Transition probabilities for forbidden and intercombination lines;5)Collision cross sections for levels which give rise to: a)resonance transitions,b)intercombination lines,c)forbidden lines;6)Charge-exchange cross sections.

The thermal radio-frequency emission, Ev, per unit volume per unit frequency interval may be computed (e.g. from equations given by Oster) and compared with the volume emissivity E(Hβ) in the optical Hβ transition.

A knowledge of the quantitative chemical composition of the primordial solar system must underlie all comprehensive studies of its origin and evolution. Usually we take the composition of the surface layers (photosphere) of the Sun as representative of this composition (except perhaps for deuterium, Li, B, and Be).

The nucleus of NGC 2346 (=PK 215 + 3°1; α = 7h06m49.S7, δ = −0°43′29″, 1950) was recently discovered by Kohoutek (1982a,b) to be an eclipsing binary with a deep (~ 2.m2) minimum in the visible and an orbital period of 17.2 ± 0.4 days. We observed NGC 2346 with the IUE on 4 occasions between 1982, Feb. 24 and May 13 and obtained 6 SWP and 4 LWR low dispersion spectrograms. These were taken at different phases, using the large entrance aperture centered on the nucleus.

Electron temperatures of compact gaseous nebulae such as planetaries may be derived from radio-frequency data combined with isophotic contours accurately corrected for resolution effects, from the continuum jump at the Balmer limit and other features of the nebular continuum, and from forbidden line ratios.

The classical Zanstra method compares a H Balmer line or He II λ4686 with flux from a limited region of the planetary nuclear (PNN) spectrum to obtain the central star temperature T(PNN). Long ago it was found that generally T(He II) > T(H I), a result attributed to differing optical depths at the Lyman limits of He II and H I; T(He II) often was regarded as the “real” temperature. Much attention has been paid to discordances between Zanstra temperatures and those found by other means, such as the energy-balance (EB) method. (see e.g., Preite-Martinez and Pottasch 1984).

Data from a survey of 51 planetary nebulae (PN) observed with the image tube scanner on Shane Telescope at Lick Observatory are combined with those for a comparable number of objects previously reported. For nearly all of the PN included in the later program, it was possible to obtain adequately accurate plasma diagnostics and line intensities to derive ionic concentrations for He, N, O, Ne, S, Cl, and Ar. To get ionization correction factors we calculated theoretical nebular models to fit the excitation level and the intensities of individual important lines. Final model parameters include the stellar radius, emergent flux, Fv(*), from Husfeld et al. (1984, Astron. Astrophys., 134, 139), nebular size, the optical depth at the hydrogenic Lyman limit, and chemical abundances. Many PN do not appear to be optically very thick in the Lyman continuum.

Three high-excitation planetary nebulae in the Magellanic Clouds were successfully observed with the International Ultraviolet Explorer. Emission lines as well as nebular and stellar continua were detected. Fluxes in the lines 1550 C IV, 1640 He II, 1663 O III, and 1909 C III were measured in spectra of LMC P40, SMC N2, and SMC N5 obtained with the IUE short wavelength spectrograph; 2422 Ne IV was measured in P40 with the long wavelength spectrograph. The data were analyzed together with groundbased observations by Aller in order to derive ionization models and the nebular abundances of He, C, N, O, S, Ar. The C abundances are as large as those typically found in galactic planetaries, although the interstellar media of the Clouds are notably deficient in C. Thus, the C was synthesized in the progenitor stars and presumably was lifted to the stellar envelopes by convection prior to the ejection of the nebulae. Other planetary nebulae in the Clouds, as well as the planetary nebula in the Fornax galaxy, may be observable with IUE.

Absolute flux distributions in the ultraviolet continua of the central stars of three planetary nebulae of known distances have been derived from observations made with the International Ultraviolet Explorer. The observations confirm the existence of planetary nebulae nuclei with masses of ≈1M⊙ and indicate that the progenitors of the nebulae were carbon stars near the theoretical upper luminosity threshold of Mbol = −6.5. The derived masses, luminosities, and temperatures of the three stars indicate that they are currently on horizontal tracks in the HR diagram and probably have not yet attained their maximum luminosities. The present luminosities (≈ 4 × 104 L⊙) each are well above the Eddington luminosity for an 0.6 Mo star. The derived properties of the stars and associated nebulae (LMC P40, SMC N2, SMC N5) are consistent with a nebular ejection mechanism that involves radiation pressure on carbon grains.

Plasma diagnostics of the active corona require data on transition probabilities and collision cross sections for relevant coronal emission lines. Atomic parameters pertaining to a number of coronal transitions have been derived as follows