Time series analysis of the brightness variations of R Aqr is based on 1521 visual observations from the AFOEV database. The statistically significant number of harmonics for the mean phase curve is m = 5. The cycle-to-cycle variations of the phase curve are present. The most stable in phase is the maximum, for which no secular period variations detected, but a secondary cycle of P2 = 3955 ± 50d and amplitude (0.032 ± 0.005)P may be suggested.

We have observed 2 compact PPNe, AFGL 2343 and IRAS 22272+5435, in the CO J=1-0 transition using the Owens Valley interferometer (OVRO), and the NRAO 12-meter telescope. Our observations were made in the low and intermediate resolution configurations of the interferometer and we obtain a synthesized beam (HPBW) of ≃ 4″. We are now modelling both sources using statistical equilibrium/radiative transfer codes. Our objectives are to a) map the distribution and kinematics of the molecular gas at high angular resolution and b) estimate the physical conditions (mass loss rate, temperature, density) in the molecular envelopes, through our models.

The results presented here are from an ongoing mid-infrared imaging study of PPNe and PNe, using MIRAC2 the UA/SAO mid-IR camera. Our 8-21 μm observations have a spatial resolution of about 0.7″ to 1.5″, and a pixel scale of 0.25″/pixel (at UKIRT) or 0.34″/pixel (at IRTF). The high S/N and good spatial sampling in our images of IRAS 22272+5435 and IRAS 07134+1005 allow us to construct temperature and optical depth maps. Using our 11.7μm and 20.6μm images we also construct maps which isolate the 11.3μm (UIR) and 21μm emission features (Justannont et al. 1995). As a second part of this project, we are modelling the dust emission from PPNe and young PNe, using a axisymmetrical radiative transfer code.

With the advent of the IRAS All-Sky Survey a sizeable number of transition objects between the AGB and the PN-phase were found - the Proto Planetary Nebulae (PPN). Oxygen-rich AGB stars often show prominent masers of SiO, H2O, and OH, which are lost during the transition process. The heavy mass loss on the AGB however does not stop abruptly and a new axisymmetric wind develops during the PPN phase. These winds both may host new masers and they can be used to study the changes of the mass loss process after that the stars have stopped their large-amplitude variations on the AGB. Several PPN are known to have OH masers, and at least in one case, HD 101584, the presence of a bipolar outflow could be proven (te Lintel Hekkert et al. 1992). Lewis (1989) found that main-line OH masers become prominent again. I will discuss here conclusions, which can be drawn from observations of H2O masers in PPN.

Sub-arcsecond (0.7″) V and I images have been obtained of 13 new proto-planetary nebulae (PPN). The observations were made with the image-stabilization camera (HRCam) on the 3.6 m Canada-France-Hawaii Telescope. The goal of the program is to study the mass-loss history of the stars and to determine when in the evolution the shaping seen in PN occurs.

We have been carrying out a program of monitoring light and velocity variability in proto-planetary nebulae (PPN). Variability might arise due to binarity or pulsation. Many planetary nebulae display a bipolar shape, and it is suggested that this is caused by binarity. This can be investigated in PPN, particularly by radial velocity studies of those of spectral types F and G. Pulsation is known to exist in other types of post-AGB stars, and can be a means to learn more about the physical properties of the stars. No previous study of a sample of PPN has been published.

The evolution of low- and intermediate-mass stars (about 1 to 8 M⊙) from the asymptotic giant branch (AGB) to the planetary nebulae stage is characterized by intense stellar wind. AGB stars evolve on a very short time scale (several thousand years) via a phase, where the star is hidden from view by a dense dust shell, towards the post-AGB phase (an optically visible star surrounded by a cold dust/gas shell). The observational investigation of these shells is rather difficult due to their small angular extent. However, the resolution of current infrared telescopes is sufficient to resolve the warm dust of the inner part of the envelope.

The shapes of light curves of Mira-type variable stars are analyzed by using the multi–harmonic fit (Andronov 1994). The light curves of 63 stars best covered by the AAVSO observations and published by Mattei (1978) were used. Some correlations between the characteristics of the mean light curves were found.

We have calculated numerical models for intermediate mass stars, following the evolution from the MS to the AGB phase. The sequences have been obtained with the Göttingen hydrodynamical code. The Schwarzschild criterion for convection is used. Mass loss is modeled using the formula proposed by Blöcker:

O-rich circumstellar dust shells that do not exhibit 1612 MHz masers (Lewis 1992), despite appropriate IR colors and 1612 MHz sensitivity, are known as OH/IR star color mimics. Since previous studies of mimics depend on samples with a limited IR spectral type and color range, we use the data collected for poster III-8 to identify the mimics in an all-sky sample of bright IRAS sources with S(25) > 100 Jy and (60-25)μm < 0.0: this expands on Gaylard et al. (1989), and benefits from the greater quantity of maser data now and a wider IR color range.

A complete sample of color selected IRAS sources with S(25) ≥ 2 Jy in the Arecibo sky and(0° ≤ δ ≤ 37°) was examined previously for 1612 MHz masers. The resulting set of OH/IR stars has now been searched for mainline OH masers at Arecibo (Lewis 1997) and for 22 GHz water masers at Effelsberg (Engels & Lewis 1996). The high overall detection rate of 61.6% for the mainlines and 54.8% for water is partly a result of deployed sensitivity, and partly due to the many blue objects in the sample. But the detectability of both masers improves when S(25)> 20 Jy, as the accompanying tables show. Still the bluest objects exhibit higher (usually ≥80%) detection rates, while there is a clear decrease in detections from redder shells: this decrease begins circa (25–12) μm=–0.55 for mainline masers, and abruptly circa (25–12) μm = −0.35 for water. These trends adhere to the descriptive sequence of the chronological scenario for masers in circumstellar shells, though a few proto planetary nebulae and very red OH/IR stars have water masers and a few mainline masers are detected in shells with (25-12) μm ≥ −0.2.

Comparisons between color-color diagrams of OH/IR stars with/out IR flux and/or galactic position constraints show that little of the color dispersion is innate: the most precise colors come from high flux samples away from the Galactic Center. It is advantageous to delineate the color range of O-rich shells by only color selecting objects in the IRAS Point Source Catalog (PSC) with S(25) > 100 Jy, which yields 333 objects. All but 2 of these have published LRS spectra, which often suffice to determine whether an object is carbon or oxygen rich. About 80% of them have been searched for 1612 MHz masers, and ≈70% for SiO, water and/or mainline OH masers. As bright objects, most “oddballs” have been investigated at other wavelengths too. This data, together with information gleaned from a SIMBAD search, was then used to distinguish emission-line, T Tauri and carbon stars from the predominent residuum of O-rich shells.

The moments of 82 maxima and 76 minima are used for the correlation analysis of the characteristics of the individual cycles. 5 not trivial correlations were found. The characteristic time of the secular decrease of the period is |P/P| = (23.4 ± 4.3) · 103 yrs, but decade–scale and cycle–to–cycle variations are also present.

We present full synthesis 12CO J= 1–0 line emission images of three carbon rich evolved stars: CIT 6, AFGL 618 and IRAS 21282+5050. Each of these objects represents a different stage of evolution: CIT 6 is a carbon star still on the AGB, AFGL 618 is a transition object, and IRAS 21282+5050 is a young planetary nebula. Common to all three sources, we find what appears to be two mass loss components: a bright “core” located at the center of the source and a fainter “halo” surrounding the core (see Table below for observed characteristics). We speculate that the bright core was created by a more recent and higher mass loss rate wind than the fainter surrounding halo. However, concrete support for this idea awaits radiative transfer modelling of the 12CO that we are currently pursuing. Our full synthesis data are combined from millimeter interferometry using the Berkeley–Illinois–Maryland millimeter array (BIMA) and single dish maps using the NRAO 12m. We find that full-synthesis imaging, which combines the sensitivity of single dish and the spatial resolution of interferometry, is the only means to reveal such core-halo structures.

We present VLA-A radio continuum at 3.6 cm and H92α observations, and optical long-slit spectra at high spectral and spatial resolution of the compact Planetary Nebulae (PNs) Hu 2-1, IC 4997, IC 5117 and NGC 6884. The radio continuum maps show the subarcsecond structure of the PNs in detail. From the optical spectra, the basic kinematical properties can be deduced. The H92α emission line, spatially and spectrally resolved in IC 5117 and Hu 2-1, allows us to observe the kinematics of the PNs in spatial scales of ∼ 0.3″. By combining the radio and optical data, it is possible to identify the components present in the nebulae, to deduce their spatio-kinematical structure, and to obtain estimates for the electron density and temperature, ionized masses and kinematical ages. All this information permits to impose constraints about the mass ejection processes involved in the formation of PNs and when they have occurred.

Roberts 22 (= AFGL 4104) is a peculiar proto-planetary nebula. Its central star has spectral type A2Ie. An OH maser was detected by Manchester et al. (1969), indicating that the shell is oxygen-rich. However Polycyclic Aromatic Hydrocarbons (PAH) features were observed as well (Allen et al., 1982; Cohen et al., 1993), indicating that carbon rich material is also present. In this poster we present new IR data (images and spectra) of this peculiar star and propose an explanation for this curious behaviour.

We present the first diffraction-limited speckle-masking observations of the bipolar nebula Red Rectangle and of the carbon star IRC+10216. Both objects were observed with the SAO 6 m telescope in the NIR (resolution 0″.092) and the Red Rectangle with the ESO/MPG 2.2 m telescope in the red (resolution 0″.087).

We have performed a parameter study of the spectral evolution of a typical post-AGB star with particular emphasis on the evolution of the IRAS colours. The models are based on the latest evolutionary tracks by Blöcker (1995, A&A 297, 727 and A&A 299, 755), which are used to define the evolutionary rate and the mass loss history of the central star. The resulting model for the post-AGB star is then used to calculate the spectral evolution with the photo-ionization code CLOUDY (Ferland 1993, Univ. of Kentucky, Int. Report), which includes dust in the radiative transfer.

We have observed IRAS 09371+1212 using both narrow and broad band filters. As a result, we note that relative color trends B-V/V-R appear to be inconsistent with both the mean IS reddening law, and the variation deduced for model grains (Robinson et al, 1992). There also appears to be a disparity in the B-V/V-R reddening gradient as between the inner and outer source envelopes—a characteristic which, together with other evidence, may indicate a corresponding evolution in grain properties.

CCD imaging and BVRI photometry of 14 IRAS sources with far-IR colours similar to planetary nebulae and post-AGB stars are presented. Also results of optical and near-IR spectroscopy of 10 of these candidates are given. Based on the spectral energy distribution from 0.4 μm to 100 μm, the sample of program stars are put into two groups. The sources IRAS 08187-1905, IRAS 05238-0626 and IRAS 17086-2403 present similar flux distributions. These three sources have detached cold dust components with dust radii Rd ≈ 1000 R∗. The low infrared variability of theses sources suggests that the intense mass loss has been ceased. All three sources are at high galactic latitude (1>9°) suggesting that these are old low-mass evolved stars. In the IRAS colour-colour diagram of Likkel et al (1991) these sources fall in the region where most of the stars are evolved stars and PNe but without CO detection. This is consistent with at least one source IRAS 17086-2403, in which OH and CO molecular features are not detected. The far-IR excess, non-variability and high latitude of these objects suggest that these are post-AGB supergiants, slowly evolving towards planetary nebula phase.