We have conducted a survey for molecular outflows toward 71 pre-main-sequence stars using the J = 2 → 1 transition of CO. Outflows were detected and mapped toward 20 of these objects and in an additional six background sources not included in the original survey. The outflow sources range in mass from 0.5 to 30 M⊙, in luminosity from 4 to 1.1 × 105 L⊙, and in age from < 104 to ~ 106 years. In the H-R diagram, the outflow sources form a distinct band running across the top of the diagram.

Roughly half of the observed outflows are bipolar at some level; the rest show a rich variety of morphologies. In addition to the CO (J = 2 → 1) data, we have obtained CO (J = 1 → 0) and 13CO (J = 1 → 0) observations that enable us to estimate the excitation temperature and optical depth in each outflow, leading to the derivation of outflow masses. The observed outflows range in mass from 0.01 to 56 M⊙, in size from < 0.07 to ~ 5 pc, and in age from ~ 103 to 5 × 105 years old.

Simple momentum conservation arguments are then used to derive the mass loss rates necessary to produce the observed outflows. The results range from ~ 10−8 to ~ 10−3 M⊙ yr−1. Correlation of these mass loss rates with other parameters shows that pre-main-sequence mass loss goes as the square root of the bolometric luminosity and as the 1.7 power of the stellar mass. Implications for these findings on the nature of the pre-main-sequence mass loss mechanism, for self-regulated low-mass star formation, and for formation of the terrestrial planets are discussed.

Millimeter wave interferometric images of HL Tau show a clear disk morphology with a nearly keplerian velocity curve. A few a few tenths of a solar mass are in orbit around the star.

In the CO(J=3−2) line we observe a bipolar outflow in V645 Cyg. The physical properties of the neutral flow gas and its geometry put new constraints on the structure of this YSO.

High velocity molecular outflows with bipolar morphology are detected in association with young stellar objects within dense interstellar clouds. Recent observations suggest that the flow could be “confined to a relatively thin, swept-up shell surrounding an evacuated wind cavity” (1). A shell structure characteristic of the wind-cloud interaction had been predicted in earlier theoretical works (see for instance (2)). More recently, models with different (not shell-shaped) geometries were presented, e.g. (3).

We present a model of CO J=1→0 line formation in accelerated bipolar outflows. We find that the integrated intensity maps can be divided into four categories, depending on the view angle and the flow opening angle. We then show that no accurate values of the flow parameters can be derived from the CO observations without careful modelling of the outflow properties.

NGC 3576 (RCW 57) is a very bright optically visible nebula (~10' in size) located near the galactic plane at a distance of 3.6kpc. The region is associated with the HII region G291.28–0.71 (Retallack & Goss), and with a giant molecular cloud of M≃9×104 M⊙ (Cheung et al.1980) The source is reported in the IRAS Small Scale Structure Catalog. From the observed far-IR fluxes we derive a total luminosity of L(FIR)≃7×105 L⊙, suggesting that at least seven possible 07–09 stars could ionize the entire observed region. A cluster of five IR sources and extended 10μm emission were found by Frogel & Persson (1974). IRS 1 is a very compact object (<3'), while IRS 2–5 show diffuse infrared emission. In addition IRS 2, very close to IRS 1, is coincident with the radio emission peak. An H2O maser source and NH3 emission are present in the complex region.

We present multidiaphragm photometry from 1 to 20μm of 1RS 1, IRS 3 and IRS 4 and CVF observations between 2-μm and 8–13μm of IRS 1, collected at the 1m and 3.6m ESO telescopes.

In a region of 0.4 × 0.5 pc around HD 97300 the amount of mass in gas and dust is < 16 M⊙, while the stellar mass is 6–9 M⊙. Thus in this core of a collapsing cloud (Cha T1) several stars have been formed in a very efficient way.

In this work we give a revised distance (250 ± 20 pc) to the star VV Serpentis and its associated dark cloud complex, redetermine its spectral type (= A2e, see also Herbig, 1960, ApJ Suppl. 4, 337), and report on observations of previously unknown associated emission line stars, and of stars with associated reflection nebulosity (R-stars) belonging to the same region.

Intermediate mass (2 < M/M⊙ < 9) pre-main sequence objects, also named Herbig Ae/Be stars, are known to have excess radiation in the near-infrared. From IRAS o bservations it turns out without doubt (quality 3, high S/N radio), that these objects are very strong far-infrared emitters at 12, 25, 60 and often also at 100 μm. The spectral energy distribution, depicted in Fig. 1 for intermediate mass pre-main sequence stars, show clearly this large excess. From the difference curves it is apparent that this excess radiation is most probably caused by several dust shells. Using very simplified methods it is possible to derive the average temperature of the dust shells (see Thé, Wesselius, Tjin A Djie and Steenman, 1986). If the chemical composition of the mixture of the dust grains and their average size are assumed it is also possible to estimate other characteristics like the distance from the central star and the mass of the dust shells (see Thé, Hageman, Westerlund, Tjin A Djie, 1985).

In stars with dense envelopes such as classical Be and T Tauri stars, the near infrared lines of OI have been observed: λ 8446 Å in emission, λ 7772 Å in absorption or in emission (e.g. Polidan and Peters, 1976; Herbig and Soderblom, 1980). In Herbig stars, only low resolution (2-7 Å) material is available on a few objects (Shanin et al. 1975; Andrillat and Swings, 1976).

We discuss new spectroscopic material on 7 T Tauri stars of low to intermediate activity level which have envelopes of low optical thickness and small circumstellar/interstellar extinction. We show that difference plots between the target star and appropriate standards are a powerful tool to probe the stellar envelope structure. In our sample we find 1 object with a P Cyg type, 3 with inverse P Cyg type, and 3 with symmetrical Balmer line profiles. We conclude that the physical processes in these T Tauri stars do not differ qualitatively from the ones found in extremely active ones. In particular, the inverse P Cyg type profiles are not restricted to stars with very opaque envelopes and are possibly a much more common attribute of young stellar objects.

Following the successful modelling of the wind from RU Lupi using data at moderate and high dispersion we report on similar observations of other T Tauri stars where the general pattern of the wind, as deduced from the widths of the emission lines of the various species, seems to be similar.

I discuss a survey of X-ray sources in regions of star formation. The survey has revealed at least 30 low mass PMS, naked T Tauri stars (NTTS) in Tau-Aur, and a comparable number in Oph. I summarize the properties of these stars, and argue that the spectra of the classical T Tauri stars are due to the interaction of an underlying NTTS with a dominant circumstellar environment. I discuss the impact the NTTS are likely to have on our understanding of the PMS evolution of low mass stars.

The variability of the two T Tauri stars RY and RU Lup has been monitored between 1980 and 1984 at both optical and infrared wavelengths. We present here a preliminary analysis of the data and suggest possible mechanisms for the observed variability.

The sources (1) SSV 13 (identified with the IRAS (2) source 03259+3105), SSV 9 (IRAS 03256+3107), SSV 5 (IRAS 03262+3108) were observed photometrically in the JHKL bands with the In-Sb photometer at the Italian IR Telescope (TIRGO, Gornergrat, Switzerland). In addition CVF spectrophotometry between 2.0 and 2.4 μm of SSV 13 was carried out. We present a study of the energy distribution between 1 and 100 μm, including both our photometry and IRAS data.

0.9 μm CCD images and 2.2 μm slit scan observations reveal the double character of the infrared source Serpens - SVS20; the separation, position angle and brightness ratio are 1.″6, 10°, and Δm ≍ 1.6 mag respectively. The southern source is the brightest at both spectral ranges. At 0.9 μm the observed polarization of each component is p = 9.0 %, ⊙ = 155° and p = 10.4 %, ⊙ = 135° for SVS20-South and SVS20-North respectively. These results combined with 2.2 μm polarimetry and JHKLM photometry suggest that both SVS20 sources are in fact low mass, probably PMS, stars.

Using a rapid slit scan technique in the infrared (JHKL), the source GSS 31 (alias EL 22 or Do-Ar 24E), a T Tauri star in the Ophiuchus dark cloud, was discovered to be double at a projected separation of 1.“95±0.”10 (i.e. 320 AU). The position angle is almost exactly north-south. This is the second discovery of its kind, and the first in the southern hemisphere, the only previous case known being T Tauri itself (Dyck et al. 1982, Schwartz et al. 1984). The important point is that we were able to secure infrared photometry separately for both components while for T Tau the separation into two components was model-dependent due to their small separation (0.6). IR-photometry for the joint system GSS 31 had previously been obtained by Grasdalen, Strom & Strom (1973) and Elias (1978), while Chini (1981) obtained UBVRI photometry.

We report here on the complete EINSTEIN survey of Orion within the central 2° x 2° region centered on the Trapezium. We present an X-ray mosaic of the Nebula and a complete X-ray catalog (200 sources) for this very young cluster. In addition, we discuss in detail variability, early-type stars, solar-type stars, and K-M stars.

Spherical NLTE-model photospheres surrounded by envelopes are calculated in order to interpret BN-like objects. Both the existence and the emitted spectra of the HII-region can be understood by such models.

We present accurate positions and near infrared photometry (Table I) of 11 point-like objects in the neighbourhood of GGD objects obtained on the 1.55 m and on the 1.23 m in Teide Obs. and Calar Alto Obs. respectively, in Spain. Several of the near infrared sources are directly associated with the GGD nebulae and/or are candidate for their excitation. In addition some of them seem to be the near infrared counterparts of IRAS sources. We believe, on the basis of their infrared excess, far infrared emission (IRAS), association with nebulosity, coincidence with H2O masers or the fact that in most cases the observed luminosities are higher than those expected for main sequence stars, that most of them (9/12) are young stars embedded in the dark clouds which contain the GGD objects. The loci of the detected sources in an (H-K,K-L) infrared two-colour diagram is the same as that obtained for known pre-main sequence stars, such as T Tauris and Herbig Ae-Be stars, indicating the presence of dust shells with temperatures in the range 800–1500 K. The observed range in luminosity, 10–4600 L⊙, added to other different characteristics found between them, such' as the presence, or absence, of H2O masers, indicates the interest for a detailed study of the infrared sources and related GGD nebulae.