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Recently, Brα and Brγ emission was detected in the infrared spectrum of the B0.2V star τ Scorpii, without noticeable emission in Hα (Waters et al. A&A 272,L9-L12, 1993). Here we present simple HI recombination line calculations in the infrared and in the optical that demonstrate that there could be a class of B stars with low-density discs, a factor of 100 lower in density compared to normal Be stars, which may have escaped detection so far.

Two-micron spectra of several helium line stars in the galactic center have been obtained at UKIRT with CGS4. Lines studied include He I 2.058μm, He I 2.113μm, Brγ2.166μm, and Paα1.875μm. He/H in four of the stars is shown to be very overabundant.

We have obtained high-resolution spectra of the CO band-head emission from five young stars. We find a variety of line shapes, and we compare the profiles with those predicted by models of accretion disks and neutral winds. Standard accretion disks are able to reproduce the fluxes, profiles, and optical depths of our sources, with accretion rates of ~ 10-7 M⊙ yr-1. Winds successfully account for the fluxes and profiles provided the wind does not cool adiabatically, but remains hot at least out to where the density is too low to excite CO emission. However, our wind model predicts optically-thin emission, which is inconsistent with low-resolution data. We therefore prefer disks as the origin of the CO band-head emission in young stars.

A protoplanetary nebula is the result of the mass loss that occurs as a red giant star evolves into the core of a planetary nebula. The mass loss produces a cool, massive, and slowly expanding envelope around the dying star. Fast and hot winds, emanating from the central star as it approaches the white dwarf stage, overtake and interact with the more slowly-moving envelope (e.g. Kwok 1982, Ap.J., 258, 280). CRL 2688 is a particularly interesting case of this phenomenon, which we have been studying at the JCMT and the UKIRT.

An important means of studying the unusual activity within the central ~0.15 parsec of the galaxy is to obtain detailed information on the high velocity ionized gas there. This gas was first reported by Hall, Kleinmann, and Scoville (1982), who observed the He I line at 2.06 µm. Subsequent observations of this line and the Br α and Br ɤ lines of H I (4.05 µm and 2.17 µm, respectively) by Geballe et al. (1984, 1987) have defined the coarse spatial and spectral properties more accurately. Briefly, the broad (i.e., |v| > 400 km/s) line emission, as observed at velocity resolutions as high as 400 km/s and angular resolutions as high as 2.5″ (1) extends approximately to +/− 700 km/s (e.g., see Fig. 1), (2) is spatially resolved, with a characteristic dimension of 3″, (3) is centered approximately on IRS 16C, and (4) appears to be due neither to rotational motion nor to a simple radial flow from or onto a single compact object. These properties are difficult to understand in terms of simple models, and point out the necessity for further measurements at higher spectral and spatial resolutions.

A cluster of luminous infrared sources has been found near the Galactic Center. It consists of five identical stars clustered in a compact volume, to be called an IR quintuplet. They are all highly reddened, strongly polarized and associated with deep absorptions of silicate band and CO vibration band. They seem to be a cluster of young stars newly born near the Galactic Center.

IRAS 17516–2525 is a cool object at infrared wavelengths between 1 and 60μm. Spectroscopy in the wavelength ranges 2 – 2.5μm and 3 – 3.5μm shows the presence of Brα, Brγ, Pfγ emission lines and of a weak C2H2 absorption band, all clearly associated with the IRAS source. At the infrared position a faint star with a visual magnitude of about 20 is found.

We present infrared spectral data of a sample of fourteen IRAS sources. The observations include the IRAS Low Resolution Spectra, and ground- based 3μm spectroscopy. The sources have been selected because they have strong emission features at 7.7, 8.6 and 11.3μn in their IRAS-LRS spectra. We have detected in most of them the well-known features at 3.3 and 3.4μm, together, with a plateau at 3.4–3.6μm. Additionally, in two sources observed at higher resolution, new emission features at 3.46, 3.51 and 3.56μm are detected. Together with the 3.40μm feature they arise on top of a broad plateau which clearly emerges above the 3μm continuum. Wings are present on the edges of the 3.3μm feature. The IRAS spectra also reveal an emission plateau above the continuum longward of 11.5μm. Possible interpretations for the new features are suggested and a preliminary analysis of these data is presented in the context of the Polycyclic Aromatic Hydrocarbons hypothesis.

We have obtained preliminary evidence from near infrared observations that “non-variable” OH/IR stars are more related to planetary nebulae than to red giants whereas the reverse is true for “variable” OH/IR stars. We propose that “variable” OH/IR stars evolve into “non-variable” OH/IR stars. This transition is very sharp and takes place in a short time.

The evolution of oxygen-rich Miras and OH/IR stars at the top of the asymptotic giant branch (AGB) is discussed. We assume that all AGB stars with main sequence masses larger than about 0.8 M⊙ start to pulsate at a certain moment. The pulsation occurs simultaneously with, and probably causes a mass loss at a rate orders of magnitude larger than earlier in the stars evolution. From this moment on, the mass loss rate increases continuously until the total stellar envelope is lost. IRAS observations of these Miras and OH/IR stars show a continuous sequence in the F25μm/F12μm ratio that can be interpreted as due to an increase in mass loss. A semi-empirical equation for the mass loss rate is given. Main sequence masses of these stars can be calculated by integrating the mass loss rate over time and by adding the core mass, determined from the stellar luminosity.

In 1985 April, the WC7+abs star WR140 = HD 193793 was observed to have brightened by over two mag. in the infrared owing to the formation of a new dust shell. The growth and evolution of the shell was monitored by infrared observations using UKIRT during the remainder of 1985. Examination of infrared photometry of this star since 1979 and previously published data indicate that the dust formation occurs at intervals of 7.9 years. Phasing the published radial velocities of the absorption line component with this period confirms that it is a member of an eccentric (e = 0.7-0.8) binary system having periastron passage shortly before dust formation. Further evidence of the distortion of the stellar wind from the WC7 component is provided by changes in the P Cygni profile of the C IV lines observed with IUE while the dust was forming. The X-ray spectrum also changed between 1984 and 1985 in becoming significantly “harder” while the non-thermal radio source was extinguished. An interpretation is sought in terms of a model wherein the non-thermal radio and X-ray emission is excited by collision of the WC and O star winds and modulated by the orbital motion. A suitably compressed region of the wind must be advected far enough from the stars to form dust.

High resolution spectra of the 4.64 micron 1–0 R2 line of CO toward infrared sources in the galactic center reveal absorption components identified with features in radio and millimeter wave spectra of molecular lines. They demonstrate that the +20 km/s cloud is situated in front of the Sgr A West and the +50 km/s cloud is behind it. The spectra of IRS 3 and IRS 7 have strong absorptions near +50 km/s, which may originate in the 2 pc radius circumnuclear ring; if so then the western side of the ring lies in front of the galactic center. A less likely interpretation is that these objects, which are only a few arc-seconds from IRS 16, are behind the +50 km/s cloud and, thus, well behind the galactic center.

The profiles of the V=1-0 S(1) line of H2 in the Orion molecular cloud show a variation from the center of the emission region where the profiles are broad and have extended blue wings, to the periphery where the profiles are narrow and have a peak at the velocity of the molecular cloud. These observations can be understood by a model of a radially expanding supersonic flow of gas colliding with the surrounding molecular cloud. It is concluded that the high velocity emission originates in the flow and the low velocity emission originates in the molecular cloud. Density variations in the flow and the surrounding cloud are necessary to explain the detailed line profiles and morphology.

The line profile of the v=1→0 S(1) line of H2 in NGC 2071 is ~100 km s-1 wide (FWZI), and asymmetric; it resembles S(1) profiles seen toward Orion KL. The NGC 2071 region represents the second detection of high velocity H2 emission in a region showing signs of ongoing star formation.

A sample was selected from the IRAS Point Source Catalogue based on the following selection criteria: very red (“cold”) IRAScolours: roughly F25/F12 > 2.5 and F60/F25 < 1.2; and low IR-variability: VAR < 30. These non-variable IR-sources may be stars that have evolved beyond the AGB (Asymptotic Giant Branch); a large fraction (40%) is associated with known planetary nebulae (Van der Veen and Habing, 1987, Astron. Astrophys., in press). To determine the nature of the other 60% additional observations were made mainly in the infrared: 1–13 μm, during 4 observing runs: ESO (La Silla, Chile) in July 1986 and June 1987; UKIRT (Hawaii) in August 1986 and June 1987. A total number of 58 sources was observed. A summary of the observations: --IR broad band photometry at 1.2, 1.6, 2.2, 3.8 and 4.6 μm for all 58 sources. --IR broad band photometry at 8.4, 9.7 and 12.8 μm for 19 sources. --IR small band photometry for 4 sources in the ranges 2–2.5 μm and 3–3.5 μm. --IR spectroscopy for 10 sources in the ranges 2–2.5 μm and 3–3.5 μm. --V,R, I observations (0.55, 0.7 and 0.9 μm);for 5 sources associated with a star of visual magnitude 8–9. These observations were carried out by D. de Winter (Amsterdam) with the 0.5-m ESO telescope at La Silla (Chile). --Walraven photometry (0.32, 0.36, 0.38, 0.43 and 0.54 μm) for 21 stars brighter than V = 15 and within 10″ from the IRAS position. These observations were carried out by M. van Haarlem (Leiden) with the 0.9-m Dutch telescope at La Silla (Chile).