The development of millimeter and submillimeter spectroscopy has allowed astronomers to probe the cold, dense component of the interstellar medium. This medium, primarily composed of gas in molecular form, is gravitationally bound into relatively distinct clouds that are sites of star formation within our Galaxy. The most ubiquitous tracers of these molecular clouds are the rotational transitions of carbon monoxide. Observations of CO emission have been commonly used to estimate the size, temperature, mass, and density of molecular clouds; in addition, the spectral line profiles can be used to study the internal dynamics of these clouds. Although the sound speed within molecular clouds is only about 0.2 km s−1, observed CO line widths are more typically 1 to 5 km s−1. Thus, the internal dynamics of molecular clouds are characterized by supersonic gas motions whose nature is poorly understood.

The mm/sub-mm dust emission from bipolar outflow sources is discussed. In nearby outflows the stars driving the flows appear point like and unresolved, i.e. apparent angular sizes < 7” (i.e. 700AU at lOOpc). The spectra are surprisingly flat, suggesting that the dust emission is affected by temperature and density gradients or that the dust surrounding these stars differs from that of the general interstellar medium. If the spectra are characterized with a conventional dust emissivity index, our sample gives an average value of 1.1, rather than the figure of 2, which is usually claimed at these wavelengths for dust in molecular clouds. The total dust and gas masses associated with these stars are a few tenths of a solar mass for nearby low luminosity sources and the gas densities are >107 cm−3, if the gas is in a shell, and the densities could be much higher if the gas densities fall off as a function of radius, or if the mass is distributed in a disk. These masses correspond to extremely high extinctions, which are not observed, and we therefore argue that the mass distribution must be anisotropic, most likely as an inclined disk surrounding the star. Hence, stars driving outflows are surrounded by a dense disk, possibly an accretion disks and/or collimating disk. If these stars are compared to the more evolved T Tauri stars, we find that the difference in disk mass could account for the mass loss observed in these stars. Because of the high gas densities in the disk, most commonly used molecular lines will be optically thick, and molecular observations should be done in rare isotopes and high density tracers in order to yield reliable results of gas densities and gas dynamics.

We observed with the VLA(D) the (J,K) = (1,1) and (2,2) inversion transition lines of ammonia toward two regions with molecular outflow: AFGL 2591 and Monoceros R2.

We have made aperture synthesis observations of CS(J=l-0, 2-1) and NH3(1,1) lines and 49, 98, and 110 GHz continuum in NGC2071-1RS with the Nobeyama Millimeter Array. Wfe have obtained maps of these lines and continuum maps with 2”. 7-20” resolution, ffe have found that dense molecular gas has a disk structure with a radial scale ranging 0.01 pc - 0.1 pc and has a ring-like structure with expanding motion at the central 5000 AU region. We also have found that there exists double dust continuum sources which are separated by 2500 AU in projection and are apparently located at the inner edges of the ring. Our observational results suggest that the disk of molecular gas has a central hole formed by wind and UV radiation from a central young stellar object, the central part is expanding, and that dust continuum emission comes from tangential parts of the shock compressed ring (r~1300 AU, M(H2)~ 21-34 Mo, and n(H2)~ 109) at the most inner side of the disk structure. The other possible model of the dust continuum sources is a binary system of self-luminous young stellar objects.

The environment of the young stellar object IRS5 in L1551 dark cloud is a representative of the “protostellar disk and outflow” systems found in star forming regions. The bipolar molecular outflow there was discovered as the first of its kind a decade ago (Snell, Loren, and Plambeck 1980). Its location in the sky, that is, its proximity (160 pc), isolation, and its almost edge-on inclination have favored the observation in great detail. IRS5 is thought to have the spectral type G - K (Mundt et al. 1985) similar to the Sun, with its dominant activity in the stellar wind, and not in the UV radiation as in massive protostars. The blueshifted and redshifted outflow lobes are clearly resolved into a pair of shell structures. The successive studies, mostly in CO lines, have led to a model of the outflow in which the molecular material is accelerated at the edge of a cavity evacuated by the protostellar wind (e.g. Uchida et al. 1987, Rainey et al. 1987, Moriarty-Schieven and Snell 1988).

The flow that results from stationary supersonically converging conical streams is studied by means of two dimensional numerical calculations. Convcrgency leads to a “colimator” conical shock and this to the formation of an underexpanded hydrodynamical jet. The properties of the conical shock and of the collimated stream are summarized for a variety of initial conditions. The resultant jets are followed to large distances (≥ 7.5X1017 cm) away from the injection point, and are shown to develop a complicated structure that eventually approaches a stationary state. Stationary features such as crossing shocks are shown to evolve from working surface shocks, left behind the head of the jet to ensure self-collimation of the beam matter.

Outflows from young stars in many cases show evidence for collimation. For example, bipolar molecular outflows are sometimes quite well collimated (see, e. g., Snell 1982), and stellar jets and Herbig-Haro objects show an even higher degree of collimation (see, e. g., Mundt 1987).

After a brief introductory discussion of the statistics of known Herbig-Haro (HH) objects we present a survey of recent spectroscopic results in the ultraviolet, the optical and the near infrared range (the latter mostly in connection with H2 observations). We emphasize the importance of the use of spatially resolved line profiles (position-velocity diagrams) in the optical range for the purpose of testing hydrodynamic models of HH objects. Such observations have now been supplemented by the measurement of spatially dependent intensity ratios for a large number of optical lines ~200 in HH 1) and of some ultraviolet lines (including fluorescent H2 lines) which are very useful for diagnostic purposes. The relevance and importance of spectroscopy and imaging in the infrared H2 lines is discussed.

High mass post-main-sequence nebulae are characterised by a set of unusual, and in certain cases extreme physical characteristics, including large outflow velocities (cf. Phillips and Mampaso, 1988a), extremely compact high emission measure cores (Phillips and Mampaso, 1988b), a high incidence of bipolar morphology (Peimbert and Torres Peimbert, 1982), and evidence for anomalously high levels of shock excited H2 S(l) emission towards both the source cores (Phillips et al 1983, 1985) and nebular peripheries (Zuckerman and Gatley, 1988). The large central star masses also predispose these sources to rapid evolution within the H-R plane (perhaps one or two orders of magnitude more rapid than for typical PN (Schonberner 1981, 1983), and the acquisition of stellar temperatures T* > 105 K, giving rise to correspondingly high levels of nebular excitation.

Using the IRAM 30-m telescope in August and December 1988, we have discovered the first molecular outflow in the central part (L1688) of the nearby ρ Ophiuchi dark cloud. This outflow, found in the J = 2 — 1 line of 12CO near the cloud core A, is an extreme case, weak (outflow mass-loss rate ≈ 5 x 10−8M⊙yr−1) and highly collimated (lenght to width ratio > 14), which explains why it has escaped previous detections with smaller telescopes. The high-velocity molecular gas is hot and optically thin, making the J = 2 — 1 line of 12CO ≈ 3-4 times stronger than the J = 1 — 0 line. Unexpectedly, this outflow does not appears to be driven by any of the embedded near-IR sources known in this region previous deep VLA surveys of the cloud (André, Montmerle, and Feigelson, 1987; Stine et al., 1988; André et al., in prep.). The outflow exciting source is thus probably a very low-luminosity ((L < 0.1L⊙) young stellar object. Using the 30-m equipped with the MPIfIR bolometer, we have very recently found (March 1989) that this object is the strongest continuum point source of L1688 at 1.3 mm. By analogy with L1551-IRS5 and HL Tau, the radio properties of this source suggest that it possesses a weak, possibly collimated, ionized wind and a relatively massive, cold circumstellar disk (Mdisk ≈0.1M⊙).

Three new objects have been found, when carrying out a survey of IRAS sources with colours like planetary nebulae, via low resolution spectroscopy. IRAS 14592-6311 and IRAS 07173-1733 are bright cometary nebulae, showing metal line emission very similar to V1331 Cyg (LkHα 120), which is the prototype of a certain number of T Tauri stars. They present strong P-Cygni profiles and some other peculiar characteristics. IRAS 14592-6311 is associated with a molecular cloud at a distance of 2.9 kpc, while IRAS 07173-1733 is located at the edge of the dark cloud KHAV 201. In the case of IRAS 05506+2414, it presents a bipolar structure with Herbig-Haro emission characteristics in one of the lobes, produces by shocked gas, and is located near Orion.

I present preliminary results from a small mm/submm continuum survey, mostly photometry (1.1mm, 800µm, 450µm and 350µm), but also some mapping at 800µm of Herbig Ae/Be stars and a few peculiar stars. These observations were commenced on the 15m JCMT submillimetre telescope on Mauna Kea, Hawaii.

We have obtained high spectral resolution observations of a number of Herbig-Haro (HH) objects in the H2 v=1-0 S(1) line at 2.12μm. Objects observed included HH1/2, HH7-11, HH19, HH32A, HH40, and HH43, all associated with jet-like features or collimated optical outflows. Here we present velocity-resolved 2.12μm spectroscopy for HH40 (an HH-objects moving close to the line of sight) an for HH43B (an HH-object moving close to the plane of the sky). The full set of observations including interpretation is given in Zinnecker et al. (1989). We also present high spatial resolution H2 2.12μm images of HH40 and HH43. The 2.12μm H2 line profiles were obtained with the UKIRT infrared Fabry-Perot system (effective resolution 30-35 km/s) using a diaphragm of diameter 11” for both HH40 and HH43. The H2 images were obtained with the IR-array imager at the CTIO 1.5m telescope through a narrowband filter centred on the v=1-0 S(1) line. The IR-camera used had 58x62 pixels and a resolution of 0.9”/pixel. The exposure time was 2x120sec and 5x60sec for HH40 and HH43, respectively. The images are sky subtracted, but not fiat fielded, and should be viewed as preliminary test images.

UV spectra of H-H 7 & 11 (L1450, NGC1333) and H-H 29 (L1551) have been observed with both the IUE long- and short- wavelength cameras. These data were obtained using long (≤ 12 hours) exposure shifts over a period of three years. As expected, the S/N quality of the raw data is relatively poor and a special IUE extraction procedure has been developed within the MIDAS environment to deal with this problem. The data on H-H 7 & 11 confirm the very low excitation state of these objects, although the absence of Lyman band H2 line emission is somewhat enigmatic. The continuum emission from HH 29 reveals considerable structure which is inconsistent with a pure 2-photon model for this source. The interpretation of these results are discussed in the light of conflicting optical data.

In order to better understand the outflow phenomenon in young, high mass stars, the three sources S87, LkHα101, and S106 were chosen for closer study. High spatial resolution (5” millimeter line 13CO (J=1→0) and CS (J=2→1) maps of these sources were obtained with the Owens Valley Radio Observatory’s (OVRO) millimeter array at 0.15 and 3.0 km s-1 resolutions, respectively.

Observed stellar jets have the following characteristics : a high degree of collimation, a structure of bright, quasi-periodic knots, a very low excitation spectrum (red [S II] to Hα line ratios of 1-10). Assuming that the latter are indicative of the structure of a supersonic jet, we have made a detailed prediction of the emission line spectrum within each radiating knot using the multi-purpose code MAPPINGS which includes all the atomic processes important in low velocity shocks. The structure (density, temperature, ionization) of the stationary, supersonic, nonadiabatic stellar jet was computed separately using a hydrodynamical code developed by A. Raga. An initially overpressured supersonic jet tries to adjust its pressure to the environmental pressure. In this process of pressure adjustment, a series of expansion fans and incident/reflected shock pairs are formed along the jet. We associate the emission from the recombination region behind these crossing shocks with the knots observed in stellar jets. We find that the calculated emission spectrum is of remarkably low excitation.

We present the results of a study of the sodium ionization and excitation in the winds of low-luminosity, pre-main-sequence stars. Line profiles for the Nal doublet at 5990,5986 Åare discussed and compared with the observations for those T Tauri stars with P-Cygni profiles. We find that the observed shape of the lines put significative constraints on the rate of mass-loss (M ≥ 3 x 10-8M⊙/yr).

The molecular discs around Young Stellar Objects can be detected through high spatial and spectral resolution observations of their position-velocity diagrams. By mapping a high lying transition of a density-tracing molecule (e.g. HON, HCO+, NH3), the lines should be optically thin and we can expect to see the signature of rotation of the protostellar accretion disc. We present single-dish observations of the S106 system which show evidence for the presence of such a rotating disc. We also discuss a simple disc model which predicts the form of the resulting 1-v diagram. With high quality data, we should be able to do the inverse problem that of recovering the disc properties from the 1-v diagram. We discuss approaches to this inverse problem both by a Singular Value Decomposition (least-squares) method, and by a Maximum Entropy Method.

Using the 37-m telescope of the Haystack Observatory, we observed the (J,K)=(1,1) ammonia transition towards the suspected exciting sources of twelve regions with molecular or optical outflows: L1448, L1455, L1524 (Haro 6-10), RNO 43, HH 34, HH 38,43, Haro 4-255 FIR, NGC 2264 (HH 14-4,6), L43, R CrA, HH 32a (AS353A), and V1331 Cyg. We detected and mapped ammonia emission in nine of these regions.

This work is based upon α(16)A(9)-photometry fot 2 Planets, 11 Wolf-Rayet stars and 7 Planetary Nebulae. The results show anomalous α(16) and A(9)-indices for these objects. Thus, they are photometrically peculiar in this system. The main results are:

1) Callisto, Jupiter IV, shows ot(16) and A(9)-indices which can be considered as excellent representatives of solar type stars (G2 V).

2) Uranus and Neptune have anomalous A(9)-index, because of a spectral feature in absorption around λ 7805 Å, most likely due to a carbon compound. Thus, they are off the main sequence in the a(16)A(9)-array.

3) The Hα-line is possibly stronger in Uranus (marginal) and Neptune than in the Sun.

4) Wolf-Rayet stars have anomalous α(16)-inder, because of an extremely wide He II-line (λ 6560 Å), lack of hydrogen and the presence of spectral emission features that fall in the continuum used to determine this index.

5) Most WC stars have anomalous A(9)-index, because the presence of spectral emission features in the short wavelength continuum that defines this index.

6) Some W-R stars show variations in the strength of He II-line (λ 6560 Å).

7) Most WC stars are separated from WN stars in the α(16)A(9)-array.

8) Planetary Nebulae have anomalous α(16)-index, because the continuum around the hydrogen line is probably contaminated by [N II]-lines at λ 6548 Å and λ 6583 Å.

9) Planetary Nebulae have anomalous A(9)-index, because the short wavelength continuum is heavily contaminated by the [Ar III]-line at λ 7751 Å.

10) Planetary Nebulae lie far apart from all kind of stellar objects in the α(16)A(9)-diagram.