In the course of its short existence the IRAS database has already proved an incredibly powerful tool for studying the classification of sources -both galactic and extragalactic- in a new and very exciting way. For the first time it is now possible to employ selection criteria based purely on the infrared properties of a complete (to very low intensities) and unbiassed infrared sample - thereby eliminating the selection biases which have critically limited any such previous classifications.

This paper describes further development of the study of a set of IRAS-defined T Tauri stars, located within the Taurus region (taken as the area RA = 4h to 5h; dec = +16° to +31°), and selected from the IRAS point-source catalogue purely on the basis of their [25 m – 12 m] and [60 m – 25 m] colours. The original selection, which is described elsewhere (Harris, 1985) was based on an analysis of the IRAS colours of the known T Tauri stars within the region (found to be tightly defined, and representing blackbody temperatures between about 200 and 300 K, and 100 and 200 K, respectively), and gave the intriguing result that the extended sample, defined purely by these colours, adhered strongly to the geographic clustering found previously both for the known T Tauri stars and for the (presumably very much younger) ‘dense core sources’.

The ρ Oph dark cloud is located at a distance of 160 pc and is known as a site of active formation of low-mass stars. In optical photographs a central core of a ∼ 1° × 1° extent and two thin filamentary elongations of obscuring matter are apparent. The two filaments extend toward the east over ∼ 4° – 10°. The central core has been studied in the 2.6 mm CO lines (e.g., Wilking and Lada, 1980, Ap. J. 224, 698). On the other hand, the two filaments have not yet been mapped in molecular spectra. Interestingly, optical studies revealed that polarization vectors run along these remarkable filaments, suggesting that the magnetic field plays an important role in determining the structure of the filaments.

High spatial resolution infrared observations (mostly at L, some at K) of several young stars in the ρ Oph dark cloud were obtained with the specklegraph at the ESO 3.6m telescope in Chile in July 1985. Sources included EL29, EL21, EL14 and EL9 (Elias 1978, Table 2), and were all measured in two orthogonal directions, W-E (PA=90°) and N-S (PA=180°). Here we shall present visibility functions for EL29 and EL21 and indicate the spatial structure and dimension of these objects. We refer to Elias (1978, p.468/69) for earlier studies of EL29 and EL21.

The Rho Ophiuchi source WL 16 is the second Young Stellar Object (YSO) found to have infrared CO emission bands. IRAS observations show that WL 16 is far less luminous (∼ 14 L⊙) than the first source of infrared CO emission, BN (> 5000 L⊙). Also in contrast to BN, the CO emission from WL 16 represents a significant fraction of the total luminosity. The 2.3 μm first overtone CO emission bands were observed with the Steward Observatory Fourier Transform Spectrometer at the 2.3 m telescope.

We present results of CO, 13CO, and HCN(J = 1-0) observations of L1204 by the 4 m telescope of Nagoya University.

Extensive mapping of the CO and 13CO (J = 1-0) emission of the Bok globule, B361, is reported. The observations were made with the 4-m millimeter-wave telescope of Nagoya University. The mapped area extends over 60'x40′ which includes some filamentary dark clouds: L967, L964, L961, and L960, located to the west of B361.

B335 is now recognized as the smallest isolated star forming region. The detection of a Far-IR source and a bipolar flow were succesful, on the other hand, the distribution of the quiet gas is poorly understood. We are trying to determine the density distribution in B335. As the first step, we have carried out HC3N (J = 5-4 and 4-3) observations of B335. The observations of the J = 5-4 line have revealed a high density core with a 30″-60″ size. The Far-IR source is located just at the center of the core, and the core lies at the center of the bipolar flow. A mean hydrogen molecular density in the core of about 5x104 cm−3 is derived from the line ratio J – 5-4/4-3.

A cometary globule in IC1396 named ”comet tail 6” by Osterbrock (1957), has been observed at CO and 13CO (J = 1-0) lines with a high spatial resolution, 14″, with the 45-m radio telescope at the Nobeyama Radio Observatory. The resolution corresponds to a linear size of 0.05 pc at the distance of 750 pc (Matthews 1979). Two possible pre-main sequence stars, LkHα 349 and LkHα 349/c (Cohen and Kuhi 1979), associated with small nebulosities nestle in the central part of the globule. We have obtained CO and 13CO spectra long NS and EW strips which cross each other at the position of LkHα 349 and have mapped a 1.5′x1.5′ area around the globule center at 13CO. Results from the observations are summarized as follows:

Due to highly sensitive detectors and to the observers' efforts the observations of high galactic latitude clouds (HLC) have been improved in the last few years. The detection of infrared cirrus clouds, which were discovered by the IRAS (Low et al. 1984), strongly stimulated research on HLC. It is generally considered that HLC are small clouds which lie around 100 pc of the Sun (Blitz et al. 1984). This idea is consistent with their small velocity (VLSR) in the CO (λ = 2.6 mm) line.

L1641 is a large dark cloud which extends 6.3 degree2 to the south of the Orion nebula (Lynds 1962). This region contains a reflection nebula, NGC 1999, several emission line stars and Herbig-Haro objects and is thought to be a site of on-going star formation. A CO(J = 1-0) map obtained with the Nagoya 1.5 m telescope (Takano 1983) revealed that CO hot spots extend further to the north by ∼ 30′ from NGC 1999. This suggests that L1641 may contain other regions of recent star formation. Therefore, we have mapped the L1641 cloud to investigate if there are other star-forming regions in it.

B361 is an isolated, round-shaped globule in Cygnus. The results of FIR observations by Keene (1981) indicate that there are no internal heat sources while recent CO observations (Hirano et al. 1987) afford evidence for the existence of a few fragments in the core of the globule.

The L204 dark cloud complex is a highly elongated structure stretching over 4 degrees in declination. Its total mass is 400 M⊙ with the more tenuous sections of the cloud being displaced in right ascension from the more heavily obscured parts.

The CMa R1 association is embedded in a curved region of dark and reflection nebulosity which is part of a larger-scale ring structure of emission nebulosity thought to be a relatively old supernova remnant (Herbst and Assousa 1977, 1978), These investigators and Herbst, Racine, and Warner (1978) have argued that recent star formation in CMa R1 was induced by the supernova. Indeed, data for the emission ring, an associated expanding HI shell, and a nearby runaway star infer an age for the supernova remnant of 3x105 years; consistent with the age of most of the CMa R1 stars.

IR observations with the IRAS satellite have revealed in the galaxy a lot of point-like unidentified sources: they have no optical or radiocontinuum counterpart, and cannot be known stars, nor H II regions. We have undertaken mm-wave observations of a sample of ∼ 100 of these sources with the Bordeaux telescope (beamsize = 4.4′ ∼ IRAS resolution). These sources seem to be associated with protostars or young stars still embedded in molecular clouds. Some of the sources present high-velocity wings, suggesting a bipolar gaseous ejection from the protostar.

Interstellar extinction studies (Chlewicki et al, 1984), as well as IR observations (Sellgren et al, 1983) require the presence in the interstellar medium of a substantial number of small (a≲0.01 μm) dust grains. The temperature of such small grains is subjected, because of their small steady-state energy, to large fluctuations as they absorb photons from the incident radiation, which could prevent the accretion on such grains (Greenberg and Hong, 1974).

We have made a preliminary map of the Horsehead nebula in CO (J=1-0) using the NRO 45-m telescope. The HPBW is 15″, the grid spacing 10″, and the velocity resolution is ∼0.1km/s. Figure 1 shows the integrated intensity with a velocity interval 10-11.5 km/s, which we found represents well the shape of the dark globule of the Horsehead. The coincidence of the CO feature and the dark nebulocity is strikingly well, especially at the sharp edges in the south and in the west (from the neck to the ears). The quality of the data are not satisfactory, though. The typical noise level is 1 K rms in TA, and the accuracies of the pointing and the intensity calibration is rather low due to the bad weather during the observation. Some scanning effects in the intensities can be recognized in Figure 1. One of the reason why the gap obtically seen beneath the jaw is not clear in the CO map may be attributed to the pointing errors.

One of the main difficulties to identify molecular species in space has been raised by the lack of reliable spectroscopic data for various molecules, especially for chemically active free radicals and molecular ions. Some of the free radicals and molecular ions have been fundamental to the study of chemistry in space but they are too active under terrestrial conditions and are hardly produced in concentrations enough for laboratory observations. We have developed a millimeter-wave spectrometer of high sensitivity suitable for observations of transient molecules. It covers the frequency region of 30 to 410 GHz and has the sensitivity enabling us to detect molecules in a concentration of 107 molecules/cm3 (about 30 ppb). This high sensitivity is achieved by a combination of low noise and high power microwave source, low noise detector, and low loss cell in the high frequency region, assisted by a mini-computer. We have studied various diatomic and polyatomic transient species, some of which may have likely astronomical significance. They are H2D+, PO, PO2, HPO, CCO, HCCN, SiN, FeO, and CH3O.

The massive OB stars in our Galaxy form predominantly in the warm giant molecular clouds which constitute the spiral arms. The clouds are subject to a variety of mechanisms which retard or prevent further contraction, but are nevertheless able to form stable “cores”. In the regime of subsonic internal motions, the cores may be regarded as potential protostars. The formation of massive cores, which then form massive stars, may initially be determined by the statistics of fragmentation, but may then be a feedback process, once underway, due to the steep increase of the minimum Jeans' mass with increasing temperature of the surroundings. This concept is the basis for the model of bi-modal star formation, and its implications for the initial mass function and the distribution of massive stars and metallicity gradients in the Galaxy.

The solar and the Orion nebula chemical abundances are discussed; their chemical compositions differ at least in the O/H, He/O and 12C/13C ratios. A review of processes that could be responsible for these differences is presented.