We investigate gas accretion flow onto a circumplanetary disk from a protoplanetary disk in detail by using high-resolution three-dimensional nested-grid hydrodynamic simulations, in order to provide a basis of formation processes of satellites around giant planets. Based on detailed analyses of gas accretion flow, we find that most of gas accretion onto circumplanetary disks occurs nearly vertically toward the disk surface from high altitude, which generates a shock surface at several scale heights of the circumplanetary disk. The gas that has passed through the shock surface moves inward because its specific angular momentum is smaller than that of the local Keplerian rotation, while gas near the midplane in the protoplanetary disk cannot accrete to the circumplanetary disk. Gas near the midplane within the planet's Hill sphere spirals outward and escapes from the Hill sphere through the two Lagrangian points L 1 and L 2 . We also analyze fluxes of accreting mass and angular momentum in detail and find that the distributions of the fluxes onto the disk surface are well described by power-law functions and that a large fraction of gas accretion occurs at the outer region of the disk, i.e., at about 0.1 times the Hill radius. The nature of power-law functions indicates that, other than the outer edge, there is no specific radius where gas accretion is concentrated. These source functions of mass and angular momentum in the circumplanetary disk would provide us with useful constraints on the structure and evolution of the circumplanetary disk, which is important for satellite formation.

We discuss the origin of HE0107-5240 which, with a metallicity of [Fe/H] = −5.3, is the most iron-poor star yet observed. Its discovery has an important bearing on the question of the observability of first generation stars in our Universe. In common with other stars of very small metallicity (−4 [Fe/H] −2.5), HE0107-5240 shows a peculiar abundance pattern, including large enhancements of C, N, and O, and a more modest enhancement of Na. The observed abundance pattern can be explained by nucleosynthesis and mass transfer in a first generation binary star, which, after birth, accretes matter from a primordial cloud mixed with the ejectum of a supernova. We elaborate the binary a metallicity distribution function for first generation (Pop. III) stars currently burning hydrogen and conclude that HE0107-5240 is a first generation object with a surface affected by accreting interstellar matter polluted with heavy elements. Umeda & Nomoto (2003) adjust parameters in a first generation supernova model in such a way as to produce a C/Fe ratio in the supernova ejectum that agrees with the ratio observed in HE0107-5240 and argue that HE0107-5240 is a second generation object formed from the primordial cloud after it has been mixed with the ejectum of the supernova. A similar scenario is presented by Limongi, Chieffi, & Bonifacio (2003) who argue that the HE0107-5240 abundances can be produced by a combination of two types of supernova ejecta: a normal ejectum consisting of ∼ 0.06M ⊙ of iron and an abnormal ejectum consisting only of products of partial helium burning. Though all extant scenarios address important aspects of the problem, further discussion is warranted of the physics of star formation and of the chemical composition expected in a primordial cloud into which matter ejected by a supernova has been mixed. More importantly, the modifications of surface abundances which HE0107-5240 has suffered during its long life should be elucidated. In particular, the possibility of accretion from an evolved first generation companion which has mixed to its surface products of internal nucleosynthesis should be explored. In this paper, we describe results of such an exploration.A major characteristic of models of extremely metal poor stars is that, although the p-p chain reactions are the dominant source of the stellar luminosity and the main driver of evolution during most of the core hydrogen-burning phase, the CNO cycles play an increasingly important role as evolution progresses beyond the main sequence phase. This is because, as temperatures increase, carbon is produced by the highly temperature-sensitive triple-α reaction and because, at high temperatures, only a small abundance of CNO elements is needed for CNO cycle reactions to become the dominant driver of evolution. This character-

The driving mechanisms of low-and high-velocity outflows in star formation processes are studied using threedimensional resistive MHD simulations. Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we calculate cloud evolution from the molecular cloud core (n c ¼ 10 4 cm À3

The transport of angular momentum by magnetic fields is a crucial physical process in formation and evolution of stars and disks. Because the ionization degree in star forming clouds is extremely low, non-ideal magnetohydrodynamic (MHD) effects such as ambipolar diffusion and Ohmic dissipation work strongly during protostellar collapse. These effects have significant impacts in the early phase of star formation as they redistribute magnetic flux and suppress angular momentum transport by magnetic fields. We perform three-dimensional nested-grid radiation magnetohydrodynamic (RMHD) simulations including Ohmic dissipation and ambipolar diffusion. Without these effects, magnetic fields transport angular momentum so efficiently that no rotationally supported disk is formed even after the second collapse. Ohmic dissipation works only in a relatively high density region within the first core and suppresses angular momentum transport, enabling formation of a very small rotationally supported disk after the second collapse. With both Ohmic dissipation and ambipolar diffusion, these effects work effectively in almost the entire region within the first core and significant magnetic flux loss occurs. As a result, a rotationally supported disk is formed even before a protostellar core forms. The size of the disk is still small, about 5 AU at the end of the first core phase, but this disk will grow later as gas accretion continues. Thus the non-ideal MHD effects can resolve the so-called magnetic braking catastrophe while maintaining the disk size small in the early phase, which is implied from recent interferometric observations.

The evolution of the magnetic field and angular momentum in the collapsing cloud core is studied using three-dimensional resistive MHD nested grid simulations. Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we calculate the cloud evolution from the molecular cloud core (n=10^4 cm^-3) to the stellar core (n \simeq 10^22 cm^-3). The magnetic field strengths at the center of the clouds converge to a certain value as the clouds collapse, when the clouds have the same angular momenta but different strengths of the magnetic fields at the initial state. For 10^12 cm^-3 < n < 10^16 cm^-3, Ohmic dissipation considerably removes the magnetic field from the collapsing cloud core, and the magnetic field lines, which are strongly twisted for n <10^12 cm^-3, is de-collimated. The magnetic field lines are twisted and amplified again for nc > 10^16 cm^-3, because the magnetic field is recoupled with the warm gas. Finally, protostars at their formation epoch have 0.1-1kG of the magnetic fields, which are comparable to observations. The magnetic field strength of protostar slightly depends on the angular momentum of the host cloud. The protostar formed from the slowly rotating cloud core has a stronger magnetic field. The evolution of the angular momentum is closely related to the evolution of the magnetic field. The angular momentum in the collapsing cloud is removed by the magnetic effect. The formed protostars have 0.1-2 days of the rotation period at their formation epoch, which are slightly shorter than the observation. This indicates that the further removal mechanism of the angular momentum such as interaction between the protostar and disk, wind gas or jet is important in further evolution of the protostar.Comment: 39 pages,11 figures, Submitted to ApJ, For high resolution figures see http://www2.scphys.kyoto-u.ac.jp/~machidam/protostar/proto/ms.pd

We report the first three-dimensional radiation magnetohydrodynamic (RMHD) simulations of protostellar collapse with and without Ohmic dissipation.We take into account many physical processes required to study star formation processes, including a realistic equation of state. We follow the evolution from molecular cloud cores until protostellar cores are formed with sufficiently high resolutions without introducing a sink particle. The physical processes involved in the simulations and adopted numerical methods are described in detail.We can calculate only about one year after the formation of the protostellar cores with our direct three-dimensional RMHD simulations because of the extremely short timescale in the deep interior of the formed protostellar cores, but successfully describe the early phase of star formation processes. The thermal evolution and the structure of the first and second (protostellar) cores are consistent with previous one-dimensional simulations using full radiation transfer, but differ considerably from preceding multi-dimensional studies with the barotropic approximation. The protostellar cores evolve virtually spherically symmetric in the ideal MHD models because of efficient angular momentum transport by magnetic fields, but Ohmic dissipation enables the formation of the circumstellar disks in the vicinity of the protostellar cores as in previous MHD studies with the barotropic approximation. The formed disks are still small (less than 0.35 AU) because we simulate only the earliest evolution. We also confirm that two different types of outflows are naturally launched by magnetic fields from the first cores and protostellar cores in the resistive MHD models.

We report Atacama Large Millimeter/submillimeter Array (ALMA) cycle 0 observations of C 18 O (J = 2 − 1), SO (J N = 6 5 − 5 4 ) and 1.3 mm dust continuum toward L1527 IRS, a class 0 solar-type protostar surrounded by an infalling and rotating envelope. C 18 O emission shows strong redshifted absorption against the bright continuum emission associated with L1527 IRS, strongly suggesting infall motions in the C 18 O envelope. The C 18 O envelope also rotates with a velocity mostly proportional to r −1 , where r is the radius, while the rotation profile at the -2innermost radius (∼54 AU) may be shallower than r −1 , suggestive of formation of a Keplerian disk around the central protostar of ∼ 0.3 M ⊙ in dynamical mass. SO emission arising from the inner part of the C 18 O envelope also shows rotation in the same direction as the C 18 O envelope. The rotation is, however, rigid-body like which is very different from the differential rotation shown by C 18 O. In order to explain the line profiles and the position-velocity (PV) diagrams of C 18 O and SO observed, simple models composed of an infalling envelope surrounding a Keplerian disk of 54 AU in radius orbiting a star of 0.3 M ⊙ are examined. It is found that in order to reproduce characteristic features of the observed line profiles and PV diagrams, the infall velocity in the model has to be smaller than the free-fall velocity yielded by a star of 0.3 M ⊙ . Possible reasons for the reduced infall velocities are discussed.

The formation process of circumstellar disks is still controversial because of the interplay of complex physical processes that occurs during the gravitational collapse of prestellar cores. In this study, we investigate the effect of the Hall current term on the formation of the circumstellar disk using threedimensional simulations. In our simulations, all non-ideal effects as well as the radiation transfer are considered. The size of the disk is significantly affected by a simple difference in the inherent properties of the prestellar core, namely whether the rotation vector and the magnetic field are parallel or antiparallel. In the former case, only a very small disk (< 1 AU) is formed. On the other hand, in the latter case, a massive and large (> 20 AU) disk is formed in the early phase of protostar formation. Since the parallel and anti-parallel properties do not readily change, we expect that the parallel and anti-parallel properties are also important in the subsequent disk evolution and the difference between the two cases is maintained or enhanced. This result suggests that the disk size distribution of the Class 0 young stellar objects is bimodal. Thus, the disk evolution can be categorized into two cases and we may call the parallel and anti-parallel systems as Ortho-disk and Para-disk, respectively. We also show that the anti-rotating envelopes against the disk-rotation appear with a size of 200 AU. We predict that the anti-rotating envelope will be found in the future observations.