Narrow-band photometry, carried out with filters or spectrum scanners, is useful for measuring molecular bandstrengths and continuum energy distributions in late-type stars. This review emphasizes observations by the writer on three different multicolor photometric systems in the near infrared (0.75 − 4.0 μm); a summary of available data is given. While applications to date have been primarily qualitative (classification, recognition of peculiarities, relative temperatures), future applications are expected to be quantitative (determinations of effective temperatures, luminosities, and abundances) and based upon comparison with synthetic spectra.

Spectroscopic observations at classification dispersion have been obtained for a set of stars having abnormal photometric indices on the Strömgren uvby system. Five of the stars observed have extreme carbon anomalies; two of these spectra are illustrated here.

We show the results of an infrared study of a sample of heavily obscured AGB stars in the LMC. Both carbon-rich and oxygen-rich mass-losing AGB stars can be found at both high and low luminosities, but the percentage of carbon stars decreases with increasing luminosity. The optical depth of the circumstellar envelopes also decreases with increasing luminosity, while the mass-loss rates are (nearly) constant with luminosity. We also show tentative evidence for having found the first post-AGB stars in the LMC.

We have performed a trend analysis of 51 long-period variables (LPVs) of spectral types C, R, N, and S using 90 years of AAVSO data. We studied the periods and amplitudes, as well as the fall time (the time from maximum light to minimum), the rise time (from minimum to maximum), and the magnitudes at maximum and minimum. We also looked for time evolution of period and amplitude in the light curves themselves. The periods are more stable than the other parameters, with longer-period stars more likely to show period fluctuations than shorter-period stars. Fall time and rise time tend to evolve oppositely (mirror evolution), keeping the period fairly constant, whereas magnitude at maximum and minimum often evolve together (parallel evolution). About half of these stars are getting fainter, especially at maximum light, showing a secular dimming of magnitude at maximum; none shows a secular brightening.

Using 75 years of AAVSO data, mean light curve parameters of a sample of 350 long-period M, S and C Mira and semi-regular variable stars have been investigated. We compare M, S and C Mira and semi-regular stars, present a classification of the light curves of LPVs and give discriminant parameters.

Accurate photometry was obtained for all program stars during the 3.3-year HIPPARCOS mission. The final observing program included several hundred Mira (M), long-period semiregular (SR), and irregular (L) variables. A detailed calibration of the aging of the optics allowed the evaluation of very precise magnitudes over the whole range of star colors. Since the time coverage of the satellite observations was not sufficient to describe the behavior of M, SR, or L type variables, smooth curves were fitted statistically to the dense AAVSO observations. These curves were then transformed to the HIPPARCOS system in order to complement the HIPPARCOS photometry and thus produce precise light curves with fuller time coverage, for a set of several hundred late-type variables, including most carbon stars brighter than V = 12.4 at minimum luminosity. A preliminary discussion of the behavior of C stars, as observed from space in the broad Hp band, is given.

Long-term trends in the infrared (JHKL) light curves of various carbon variables are described. Some stars, e.g. the semi-regular variables R Scl and GM CMa, show multiple periodicities; others, particularly the Miras with moderately thick dust-shells, show more erratic long-term changes. The light curves for R For, which have been intensively monitored over 20 years, show a pattern which is reminiscent of that seen for R CrB stars. This pattern is superimposed on regular large-amplitude Mira pulsations. The multi-periodic and erratic behaviour of these stars is compared with the predictions from various models.

It is shown that the historical lightcurve of R CrB contains features that argue against the deep declines being caused by pulsation. As well, recent photoelectric photometry does not show the onset of deep declines occurring at a specific phase of pulsation. The photometry suggests that only one period is present at any time, although this period can drift and/or be replaced by another period. The evidence is strong that the pulsation is radial and obeys relationships found among classical Cepheids.

The evolutionary status and pulsational characteristics of AGB stars in the LMC have been studied. It is found that only those stars with a small mixing-length ratio can fit the observed period-luminosity relation. Strong non-adiabatic effects were found in the outer envelope and must be taken into account in future work.

A brief review is given of the various types of star which are thought to be in the immediate post-AGB stage of evolution. The paper then concentrates on the properties of the RCB stars and particularly on the mass-loss process in these stars. It is suggested that grain formation takes place over the cool regions of giant convection cells in a super-Eddington outflow and in the form of small clouds or puffs. Attention is drawn to observations which suggest that grain formation in the outer atmospheres of Miras and other cool giants may also take place in puffs rather than in spherical shells. Evidence on the long-term variation of the circumstellar dust emission from RCB stars is summarized.

Recent optical spectra of post-AGB stars show the presence of C2, CN, and CH+ originating in the circumstellar shell. We present here new, higher resolution spectra which provide constraints on the physical parameters and information on the line profiles. An empirical curve of growth for the C2 Phillips and CN Red system lines in the spectrum of HD 56126 yields b = 0.050+0.59−0.23 km s−1. CH+ (0,0) emission lines in the spectrum of the Red Rectangle have been resolved with a FWHM ≈ 8.5± 0.8 km s−1. The circumstellar CN lines of IRAS 08005-2356 are resolved into two separate components with a velocity separation of Δv = 5.7 ± 2.0 km s−1. The line profiles of CN of HD 235858 have not been resolved.

Analysis of the chemical compositions of post-AGB stars reveals the following abundance patterns: (i) Post-AGB stars which are extremely underabundant in Fe and other refractory elements, but which have nearly normal abundances of C, N, O, S, and Zn. The depleted refractory elements are locked up in circumstellar dust grains. Formation of dust close to the star, and dust-gas separation and dust-driven mass loss driving out mostly the dust may explain the abundances of these stars. (ii) High-latitude hot post-AGB stars which show an underabundance of carbon, indicating that they left the AGB before the third dredge-up occurred. (iii) Post-AGB stars with overabundances of carbon and s-process elements, indicating that they have gone through the third dredge-up and carbon-star phase on the AGB. The overabundance of Li, Al, C and s-process elements in some post-AGB stars indicate that they have gone through the dredge-up and Hot Bottom Burning nucleosynthesis at the base of the convective envelope. The observed characteristics of post-AGB stars indicate an evolutionary sequence in the transition region from the tip of the AGB into the young planetary nebula stage.

A spectroscopic monitoring of the post-AGB star HD 56126 was performed as regularly as possible over a 14-month interval in order to study atmospheric motions that could be associated with shock wave propagation through the stellar atmosphere. Some spectral features are strongly variable on a timescale of a few days. Radial velocity variations are also good evidence for complex atmospheric dynamics, in agreement with the recently found photometric variability. The data point to a pulsating nature for HD 56126, with a main period of 27.3 days.

The planetary nebula Abell 78 is slightly oval in an Hα image taken with a focal reducer attached to the 2.1-m telescope of San Pedro Mártir Observatory. Jacoby (1979) noted that the morphology of this PN in the [O III] λ5007 line is quite different from that shown on the POSS red plates.

This presentation reviews the role that binaries play in the production of Barium, CH, and S stars. New radial velocity observations confirming the binary nature of subgiant CH stars are also discussed. Evidence is presented that the early R-type carbon stars exhibit no binaries. It is suggested that they were once all binaries, but having small separations, a coalescing companion has caused them to mix near the helium core flash.

Our current understanding of the origin of barium and S stars is briefly reviewed, based on new orbital elements and binary frequencies.

We report the results of monitoring the radial velocities of 31 confirmed Ba dwarfs and CH subgiants, showing that about 27 of them have a variable radial velocity. Therefore, mass transfer in a binary most probably explains their chemical anomalies, as for the Ba giants. The orbital parameters of the 14 systems having sufficient phase coverage are very similar to those of the Ba giants. Whether the CH subgiants and Ba dwarfs may become Ba giants is discussed briefly. Most of the marginal Ba dwarfs listed by Edvardsson et al. (1993) are single, so that their chemical peculiarity, if real, cannot be due to binary evolution.

The observational relation between s-process abundance anomalies and orbital periods for barium stars is discussed and compared with mass-transfer simulations. Recent detailed abundance analyses of a large sample of single-lined long-period binaries provide evidence that all giants with white dwarf companions are likely to have abundance anomalies.

In this contribution we report on our radial-velocity monitoring of optically bright, high-latitude supergiants that appear to be in a post-AGB evolutionary stage. Binarity is a widespread phenomenon among our sample stars. More precisely: all objects with a near-IR excess in their energy distribution turn out to be binaries while the fraction of binaries in our program stars with only a far-IR excess is very small. The orbital periods, the often non-zero eccentricities, and the sometimes large mass functions set strong constraints on the previous evolution in which mass transfer must have been an important ingredient. We have accumulated observational evidence that the presence of a circum-binary dusty disk has an important dynamical and sometimes even chemical influence on the binary and its evolution. Some objects with a high mass function still defy an explanation.

We have monitored velocity variability in nine proto-planetary nebulae (PPN) over a 5 year interval and have monitored light variability in 40 PPN over a 2 year interval. We find all nine of the objects to vary in velocity and almost all of the 40 to vary in light. Three of the objects display a clear periodicity in their velocity variations, and in all three the light varies with the same period as the velocity. Periodic light variations are found in six other objects. We interpret these as due to pulsation in the PPN.