A survey of the Monoceros OB1 dark cloud has been made for molecular outflows and young stellar objects. In all, nine molecular outflows and thirty far-infrared sources were identified in a portion of the cloud composed of about 3 x 10⁴ M(⊙)of material. Statistical arguments suggest that 90% of the far-infrared sources actually are young stellar objects embedded in the cloud. If the star formation rate in the Mon OB1 cloud is roughly constant with time then molecular outflows in the cloud should be able to support it against collapse due to gravity. This suggests that the birthrate of outflows in the solar neighborhood is very high. In fact, regardless of considerations of cloud support, the large number of outflows identified in the Mon OB1 cloud and the propensity of the youngest stellar objects in the cloud to be associated with outflows suggest that outflows have a high birthrate in the solar neighborhood and are part of a common stage in early stellar evolution. The young stellar objects identified in the cloud can be fit into a spectral classification system. In fact, in terms of spectral slopes, far-infrared luminosity, and source size the properties of the objects are consistent with expectations if the system represents an evolutionary sequence. It is also found that the outflow phase in early stellar evolution tends to occur at about the time that young stellar objects lose a large fraction of their circumstellar envelopes. As a result it seems likely that outflows play an important role in sweeping out the circumstellar gas around many young stellar objects and may, in fact, play an important part in the evolutionary transition between the protostellar and stellar stages of evolution.

We present a near-infrared study of the stars forming in the ρ Ophiuchi dark cloud and a mid- to far-infrared study of their environment. We determine that the total cloud luminosity matches that of the known embedded sources, ruling out the existence of a numerous but faint low mass embedded population. IRAS and optically thin C¹⁸O column density data are used to evaluate dust grain sizes and compositions via competing grain models. Radiative modleing shows that a standard power law distribution of graphite and silicate grains is responsible for IRAS 60 and 100 μm band emissions. These grains are heated to about one tenth of the cloud's depth in the core region. Their optical depths closely follow molecular column density structure, but these grains are considerably colder than the molecular gas. We detect 481 sources in the J,H, or K bands in a 0.184 deg.² survey region in the cloud. Approximately 79% of the embedded 3 band (JHK) detected sources have near-infrared color indices greater than the local background population, suggesting that many of these objects are in pre-main-sequence evolutionary phases. The reddest of these sources are grouped in a high column and spatial density area within the survey region. Sources in this area have a normal power-law K luminosity function which is consistent with a theoretical model of a standard mass function and an age of 10⁵ yr. Sources exterior to this area have a luminosity function with an excess of intermediate luminosity sources that significantly differs from the luminosity function of the interior region. We interpret this non-standard luminosity function and the wide range of source reddenings in this peripheral region to be indicators of a considerable age (10⁶ yr) or age spread among sources there. We estimate that the cloud's star formation efficiency is currently greater than or equal to 25%. These newly discovered young stellar sources provide a statistically significant sample for studies of the cloud's embedded population and support established ideas of bound cluster formation and star formation bursts within the cloud.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

We present new HST/WFC3-IR narrow-band [Fe II] images of protostellar jets in the Carina Nebula. Combined with five previously published sources, we have a sample of 18 jets and two Herbig-Haro (HH) objects. All of the jets we targeted with Wide-Field Camera 3 (WFC3) show bright infrared [Fe II] emission, and a few Ha candidate jets are confirmed as collimated outflows based on the morphology of their [Fe II] emission. Continuum-subtracted images clearly separate jet emission from the adjacent ionization front, providing a better tracer of the collimated jet than Ha and allowing us to connect these jets with their embedded driving sources. The [Fe II] 1.64 mu m/Ha flux ratio measured in the jets is greater than or similar to 5 times larger than in the adjacent ionization fronts. The low-ionization jet core requires high densities to shield Fe+ against further ionization by the FUV radiation from O-type stars in the H II region. High jet densities imply high mass-loss rates, consistent with the intermediate-mass driving sources we identify for 13 jets. The remaining jets emerge from opaque globules that obscure emission from the protostar. In many respects, the HH jets in Carina look like a scaled-up version of the jets driven by low-mass protostars. Altogether, these observations suggest that [Fe II] emission is a reliable tracer of dense, irradiated jets driven by intermediate-mass protostars. We argue that highly collimated outflows are common to more massive protostars, and that they suggest the outflow physics inferred for low-mass stars formation scales up to at least similar to 8 M-circle dot.

Texte remanié de: Th. doct.--Sciences de l'éducation--Tours, 2003. Titre de soutenance : Quarante ans d'enseignement technique en Afrique. / Bibliogr. p. 243-246.

Thèse de doctorat : Informatique : Villeurbanne, INSA : 2002. / Thèse : 2002ISAL0047. Titre provenant de l'écran-titre. Bibliogr. p.191-202.

Thèse de doctorat : Sciences de l'éducation : Lyon 2 : 1998. / Titre provenant de l'écran-titre. Bibliogr.

Thesis (S.T.M.)--Dallas Theological Seminary, 2003. / Includes bibliographical references (leaves [68]-78).

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