A violent outflow of high-velocity gas is one of the first manifestations of the formation of a new star. Such outflows emerge bipolarly from the young object and involve amounts of energy similar to those involved in accretion processes. The youngest (proto-)stellar low-mass objects known to date (the Class 0 protostars) present a particularly efficient outflow activity, indicating that outflow and infall motions happen simultaneously and are closely linked since the very first stages of the star formation processes. This article reviews the wealth of information being provided by large millimeter-wave telescopes and interferometers on the small-scale structure of molecular outflows, as well as the most recent theories about their origin. The observations of highly collimated CO outflows, extremely high velocity (EHV) flows, and molecular “bullets” are examined in detail, since they provide key information on the origin and propagation of outflows. The peculiar chemistry operating in the associated shocked molecular regions is discussed, highlighting the recent highsensitivity observations of low-luminosity sources. The classification schemes and the properties of the driving sources of bipolar outflows are summarized with special attention devoted to the recently identified Class 0 protostars. All these issues are crucial for building a unified theory on the mass-loss phenomena in young stars.

http://web.gps.caltech.edu/classes/ge133/reading/outflows_bachiller_araa.pdf

Bipolar molecular outflows from young stars and protostars

We demonstrate with a minimal example that in Filippov systems (dynamical systems governed by discontinuous but piecewise smooth vector fields) stable periodic motion with sliding is not robust with respect to stable singular perturbations. We consider a simple dynamical system that we assume to be a quasi-static approximation of a higher-dimensional system containing a fast stable subsystem. We tune a system parameter such that a stable periodic orbit of the simple system touches the discontinuity surface: this is the so-called grazing-sliding bifurcation. The periodic orbit remains stable, and its local return map becomes piecewise linear. However, when we take into account the fast dynamics the local return map of the periodic orbit changes qualitatively, giving rise to, for example, period-adding cascades or small-scale chaos.

On a small scale

We present results from high-precision photometric monitoring of several bright early-type stars. The data cover five years and are collected by the STEREO satellite. Stellar types covered are a sample of CP, δ Scuti, and Be-stars. We describe STEREO data and data pipeline developed to produce final light curves. 

We studied long-term variations in the rotational periods of 14 CP stars. With our pipeline, we were able to accurately determine their periods, and hence we investigated any period changes.

The second study concerned Be-stars and looked at the connection between disk structures and non-radial pulsations. STEREO photometric data were supported by spectroscopic information on the Hα line. As a result, we found that, in some cases, variations in emission line properties were connected with changes in pulsation characteristics, and we discussed the consequences of this situation.

In the final study, which involved a sample of δ Scuti stars, STEREO data were used to investigate the stars' pulsational properties and to look for any possible changes in their pulsations. Pulsation constants and modes of the main frequencies were identified, and regular spacings in frequencies were examined. Several cases in which pulsational characteristics changed were also determined, and their consequences were interpreted.

Photometric investigations of several early-type variable stars using the stereo satellite

Considers the study of isotopically anomalous materials in meteorites which is a rapidly developing subdiscipline of astronomy providing primary data on stellar and supernova nucleosynthesis. Several types of presolar circumstellar grains have been analyzed and exhibit wide variations in isotopic signature, probably indicating many stellar sources. Refractory Ca-, Al-rich inclusions (CAIs) are thought to have formed within the solar system but surprisingly preserve a variety of anomaly signatures, one of which points towards a component originating in neutron-rich nuclear statistical equilibrium deep inside one or more supernovae. The uncertain cosmochemical mode of origin of the CAI anomalies, however, remains an important unsolved problem. Barium r-process anomalies provide critical insights because cosmochemically volatile holdups at 137Cs (T12/=30 a) and 135Cs (T12/=2.3 Ma) constrain, respectively, the time of Ba condensation relative to nucleosynthesis and the age of any 'exotic' Ba component at the time of CAI formation approximately 4566 Ma ago. An important frontier for future innovation is the development of mass analysis techniques for ultra-small trace element samples from individual presolar grains and micro-CAIs.

Isotopic astronomy from anomalies in meteorites: recent advances and new frontiers

Temperatures and densities in instellar molecular clouds

On a effectue des comptages d'etoiles couvrant les nuages sombres dont Av>1 mag du complexe Taurus-Auriga-Perseus sur les plaques rouges du Palomar. On discute de la distance du complexe. La masse du complexe de Perseus est ≃7.10 3 M ○. . Pour Taurus, on a obtenu une masse de 6,5-9,5•10 3 M ○. ; elle se trouve en grande partie dans le halo etendu

The Taurus-Auriga-Perseus complex of dark clouds. I: Density structure

Les observations radio, de la raie J = 1 → 0 de 12 CO et 13 CO, et l'imagerie, CCD Hα, I, R et S II, du petit globule ayant des bords brillants de la region H II, IC 1396, sont presentees. Un ecoulement bipolaire associe a une source IRAS est decouvert a partir des donnees radio et la contrepartie optique de la source IR est determinee a partir de l'imagerie. Les caracteristiques du globule sont analysees.

Star formation in a small globule in IC 1396

New HC7N cloudlets in Taurus.

The Bok globule Orion-I-2 have been mapped in the lines of 12 CO, 13 CO, C 18 O, CS, and HCN with the IRAM 30-m radio telescope. These high angular resolution observations reveal a bipolar outflow extending over 40″ (∼2 10 4 AU) associated with an IRAS point source of L(FIR) ∼ 12 L ⊙ . Therefore, these observations show that low-mass star formation can take place in isolated and small Bok globules

The physical structure of the small and isolated cometary globule Orion-I-2

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The Taurus-Auriga-Perseus complex of dark clouds. I: Density structure

Star formation in a small globule in IC 1396

New HC7N cloudlets in Taurus.

The physical structure of the small and isolated cometary globule Orion-I-2