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Most stars form in rich clusters and therefore in close proximity to massive stars, that strongly affect their environment by ionizing radiation, winds, and supernova explosions. Due to the relatively large distances of massive star forming regions, detailed studies of these feedback effects require very high sensitivity a nd angular resolution. The latest generations of large telescopes have now made studies of the full (i.e. high- and low-mass) stellar populations of distant (D > 2 kpc) star forming regions feasible, and can provide high enough angular resolution to reveal the small-scale structure of their clouds. In this paper, I present first results of a recent deep multi-wa velength study of the Great Nebula in Carina. The Carina Nebula contains some of the most massive and luminous stars in our Galaxy and is an ideal site to study in detail the physics of violent massive star formation and the resulting feedback effects, i.e. cloud dispersal and triggering of star formation. With a distance of 2.3 kpc, it constitutes our best bridge betwee n nearby regions like Orion and the much more massive, but also more distant extragalactic starburst systems like 30 D oradus. Our new X-ray and infrared data reveal, for the first time, the low-mass stellar population in the Carina Nebula, and allo w us to study the ages, mass function, and disk properties of the young stars. With sub-mm observations we also probed the morphology of the cold dusty molecular clouds throughout the complex and obtained new insight into the interaction between massive stars and clouds. These observational data will be compared to detailed numerical radiation-hydrodynamic simulations of the effects of stellar feedback on molecular cloud dynamics and turbulence. This will show how ionizing radiation and stellar winds disperse the clouds and trigger the formation of a new generation of stars.

We found 36 emission lines in the spectrum of the planetary nebula NGC 2438, and we determined its exc. class to be about 6–7. The nebular RVhel = 60.3 ± 3.6 km/s (5 spectra) is in agreement with RVhel = 60.8 ± 4.0 km/s of 4 cluster stars (10 spectra). We conclude that contrary to earlier statements the nebula is probably associated with the cluster.

— The 26Al/27Al ratio in a large number of calcium-aluminum inclusions (CAIs) is a rather uniform 5 × 10−5, whereas in chondrules the ratio is either undetectable or has a much lower value; the simplest interpretation of this is that there was an interval of a few million years between the times that these two meteoritic constituents formed stable solids. The present investigation was undertaken as an exploration of the physics of the processes in the solar nebula during and after the accumulation of the Sun. Understanding the time scales of events in this nebular model, to see if this would cast light on this apparent CAI to chondrule time interval, was the major motivation for the exploration. There were four stages in the history of the solar nebula; in stage 1, a fragment of an interstellar molecular cloud collapsed to form the Sun and solar nebula; in stage 2, the nebula was in approximate steady state balance between infall from the cloud and accretion onto the Sun and was in its FU Orionis accumulation stage; in stage 3, the Sun had been mainly accumulated and there was a slow residual mass flow into the Sun while it was in its classical T Tauri stage; and in stage 4, the nebula had finished accreting material onto the Sun (now a weak-lined T Tauri star) and was in a static condition with no significant dissipation or motions, other than removal at the inner edge due to the T Tauri solar wind and photoevaporation beyond 9 astronomical units (AU). It is found that the energy source keeping the nebula warm during stages 3 and 4 is recombination of ionized H in the ionized bipolar jets and the T Tauri coronal expansion solar wind. The parameters of the heating model were adjusted to locate the ice sublimation line at 5.2 AU. In this work, a nebular model is used with a surface density of 4.25 × 103 gm/cm2 at 1 AU and a variation with radial distance as the inverse first power. Under normal conditions in the nebula, there is a negative pressure gradient that provides partial radial support for the gas, which thus circles the Sun more slowly than large solid objects do. Large objects undergo a slow inward spiral due to the gas drag; very small objects move essentially with the gas but have a slow inward drift; and intermediate objects (e.g., 1 m) have a fairly large inward drift velocity that traverses the full radial extent of the nebula in considerably less than the CAI to chondrule time interval. Such objects are thus lost unless they can grow rapidly to larger sizes. Near the inner edge (bow) of the nebula during stage 4, the pressure gradient becomes positive, creating a narrow zone of zero gas drag toward which solids drift from both directions, facilitating planetesimal formation in the inner solar nebula. Recent theoretical and experimental results on sticking probabilities of solids show that icy surfaces have the best sticking properties, but icy interstellar grains can only stick together when subjected to impact velocities of less than 2000 cm/sec. However, if the solid objects are very underdense, then a collision leads to interpenetration and many points at which the small constituent grains can adhere to one another, and thus coagulation becomes possible for such underdense objects. Simulations were made of such coagulation in the outer solar nebula, and it was found that the central plane of the nebula quickly becomes filled with meter-sized and larger bodies that rapidly accumulated near the top of the nebula and rapidly descended; in a few thousand years this quickly leads to gravitational instabilities that can form planetesimals. These processes led to the rapid formation of Jupiter in the nebula (and the slightly less rapid formation of the other giant planets). The early formation of Jupiter opens an annular gap in the nebula, and thus a second region is created in the nebula with zero gas drag. It is concluded that CAIs were formed at the end of stage 2 of the nebula history and moved out into the nebula for long-term storage, and that most chondrules were formed by magnetic reconnection flares in the bow region of the nebula during stage 4, several million years later. Carbonaceous meteorites should be formed on the far side of the Jovian gap, with the chondrules being heated by flares on the early Jupiter irradiating materials in the nearby zone of zero gas drag, and they should have essentially the same 26Al ages as the CAIs (this will be very hard to confirm owing to scarcity of Al mineral phases in these chondrules).

Spectra of the Orion Nebula with a long slit (7' and 3' in the sky) and with exposures to the appearance of the visual continuum have been obtained for several positions in the field including, in particular, areas of low surface brightness. The variation of the ratio q = intensity of Balmer emission / intensity of continuous emission is studied. This ratio changes generally rather irregularly along the length of the slit and also from position to position. The spatial variation of q is generally small with the exception of the center of the nebula, where it is particularly high. The variation of the ratio q can be seen with a much higher surface resolution than in the spectra, when comparing monochromatic photographs taken in H α + [NII] with those taken in the continuum between the stronger emission lines. Within the larger part of the field of the nebula it is possible to distinguish between surface structures typical of the continuous emission and those typical of the hydrogen line emission. The persistence of this differentiation in many areas below the Balmer discontinuity as well as above Hα in the near infrared proves that for the subareas with the stronger continuum the continuous emission must be predominantly scattered light for the entire wavelength range from the ultraviolet to the near infrared. This criterion cannot be applied to areas where there exist no clear differences in the surface structure of the two types of emission. A determination of the Balmer and Paschen discontinuity may possibly lead to a decision.

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