Near-IR imaging polarimetry toward a bright-rimmed cloud: Magnetic field in SFO 74

We have made near-infrared (JHKs) imaging polarimetry of a bright-rimmed cloud (SFO 74). The polarization vector maps clearly show that the magnetic field in the layer just behind the bright rim is running along the rim, quite different from its ambient magnetic field. The direction of the magnetic field just behind the tip rim is almost perpendicular to that of the incident UV radiation, and the magnetic field configuration appears to be symmetric as a whole with respect to the cloud symmetry axis. We estimated the column and number densities in the two regions (just inside and far inside the tip rim) and then derived the magnetic field strength, applying the Chandrasekhar-Fermi method. The estimated magnetic field strength just inside the tip rim, ~90 ?G, is stronger than that far inside, ~30 ?G. This suggests that the magnetic field strength just inside the tip rim is enhanced by the UV-radiation-induced shock. The shock increases the density within the top layer around the tip and thus increases the strength of the magnetic field. The magnetic pressure seems to be comparable to the turbulent one just inside the tip rim, implying a significant contribution of the magnetic field to the total internal pressure. The mass-to-flux ratio was estimated to be close to the critical value just inside the tip rim. We speculate that the flat-topped bright rim of SFO 74 could be formed by the magnetic field effect

High-resolution Near-infrared Observations of a Small Cluster Associated with a Bright-rimmed Cloud in W5

We have carried out near-infrared (IR) observations to examine star formation toward the bright-rimmed cloud SFO 12, of which the main exciting star is O7V star in W5-W. We found a small young stellar object (YSO) cluster of six members embedded in the head of SFO 12 facing its exciting star, aligned along the UV radiation incident direction from the exciting star. We carried out high-resolution near-IR observations with the Subaru adaptive optics (AO) system and revealed that three of the cluster members appear to have circumstellar envelopes, one shows an arm-like structure in its envelope. Our near-IR and L?-band photometry and Spitzer IRAC data suggest that formation of two members at the tip side occurred in advance of other members toward the central part, under our adopted assumptions. Our near-IR data and previous studies imply that more YSOs are distributed in the region just outside the cloud head on the side of the main exciting star, but there is little sign of star formation toward the opposite side. We infer that star formation has been sequentially occurring from the exciting star side to the central part. We examined archival data of far-infrared and CO (J = 3-2) which reveals that, unlike in the optical image, SFO 12 has a head-tail structure which is along the UV incident direction. This suggests that SFO 12 is affected by strong UV from the main exciting star. We discuss the formation of this head-tail structure and star formation there by comparing with a radiation-driven implosion (RDI) model

The discovery based on GLIMPSE data of a protostar driving a bipolar outflow

We report the discovery based on GLIMPSE data of a proto-stellar system driving a bipolar outflow . The bipolar outflow closely resembles the shape of an hourglass in the infrared. The total luminosity of L_total=5507 L_sun, derived from IRAS fluxes, indicates the ongoing formation of a massive star in this region. The spectral energy distribution (SED) of the driving source is fitted with an online SED fitting tool, which results in a spectral index of about 1.2. This, along with the presence of a bipolar outflow, suggests the detection of a Class I protostar. The driving source indicates prominent infrared excesses in color-color diagrams based on archived 2MASS and GLIMPSE data, which is in line with an early evolutionary stage of the system.Comment: 6 pages, 4 figures, accepted for publication in Astronomy & Astrophysic

Balancing resolution and response in computational steering with simulation trails

Computational steering provides many opportunities to gain additional insight into a numerical simulation, for example by facilitating what-if experimentation, detection of unstable situations and termination of uninteresting runs. When performing steering, it is important that steering changes are quickly reflected in the state of the simulation, so that cause and effect are clearly linked. However, this places constraints on the simulation: it must produce data quickly. The resolution of the simulation is often reduced to allow this. These two competing requirements of response and resolution must be balanced in a usable steering system. This paper proposes a technique, simulation trails, that addresses this issue of balance for simulations where the transient solutions are as important as the final state, and applies it to a simulation using the Smoothed Particle Hydrodynamics method from the domain of astrophysics

Direct simulation of meteoroids and space debris flux on LDEF spacecraft surfaces

The meteoroid flux on all faces of the long duration exposure facility (LDEF) is predicted by a direct simulation Monte Carlo (DSMC) model, which for the first time provides a self-consistent method to model the collision behaviour between both meteoroids and debris with oriented spacecraft surfaces. This new model includes the modified Divine's meteoroid population, and Taylor's velocity distribution, to include the effects of planetary shielding and gravitational enhancement by the Earth. Results obtained when only meteroid impact is considered show good agreement with observed data and provide some correlation with previous models. When the space debris population is also included, the total particle flux on different faces of LDEF fits well with the observed measurements. Information concerning Earth shielding, gravity capturing and atmospheric effects can be obtained by comparing the ratio of the number of meteoroids moving towards the Earth to the total number of the meteoroids, obtained from the DSMC model with measured data. Approximately 25% of the meteoroids flux is predicted as not returning into the interplanetary space due to these effects

Exploratory simulation for astrophysics

Exploratory simulation involves the combination of computational steering and visualization at interactive speeds. This presents a number of challenges for large scientific data sets, such as those from astrophysics. A computational model is required such that steering the simulation while in progress is both physically valid and scientifically useful. Effective and appropriate visualization and feedback methods are needed to facilitate the discovery process. Smoothed Particle Hydrodynamics (SPH) techniques are of interest in the area of Computational Fluid Dynamics (CFD), notably for the simulation of astrophysical phenomena in areas such as star formation and evolution. This paper discusses the issues involved with creating an exploratory simulation environment for SPH. We introduce the concepts of painting and simulation trails as a novel solution to the competing concerns of interactivity and accuracy, and present a prototype of a system that implements these new ideas. This paper describes work in progress

Visualization of Smoothed Particle Hydrodynamics for Astrophysics

Scientific visualization still presents a number of challenges. Effective visualization straddles several problem domains - the data structures needed to support visualization of large data sets, rendering techniques for fast and interactive display of this data, and enough understanding of the data involved to construct visualizations that provide real insight into the problem. Data from Smoothed Particle Hydrodynamics simulations is of particular interest, due to its time-dependent, point-based nature and its prevalence in simulation in astrophysics in areas such as star formation and evolution. This paper looks at some of the issues associated with building a useful, usable visualization tool for SPH data from astrophysics, and describes a prototype of such a system. This paper describes work in progress

Simulation trails improve accuracy and efficiency in astrophysical simulations

Harnessing expert user insight into simulations gives a promising technique to reduce computational time and improve efficiency in astrophysical simulations

L. Lewer (Editor) Visualization of Smoothed Particle Hydrodynamics for Astrophysics

Scientific visualization still presents a number of challenges. Effective visualization straddles several problem domains- the data structures needed to support visualization of large data sets, rendering techniques for fast and interactive display of this data, and enough understanding of the data involved to construct visualizations that provide real insight into the problem. Data from Smoothed Particle Hydrodynamics simulations is of particular interest, due to its time-dependent, point-based nature and its prevalence in simulation in astrophysics in areas such as star formation and evolution. This paper looks at some of the issues associated with building a useful, usable visualization tool for SPH data from astrophysics, and describes a prototype of such a system. This paper describes work in progress. 1