Bulletin of the American Physical Society
77th Annual Meeting of the Southeastern Section of the APS
Volume 55, Number 10
Wednesday–Saturday, October 20–23, 2010; Baton Rouge, Louisiana
Session JB: Interstellar Gas and Star Formation |
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Chair: Fabian Heitsch, University of North Carolina at Chapel Hill Room: Nicholson Hall 109 |
Friday, October 22, 2010 3:45PM - 4:15PM |
JB.00001: Herschel Observations of a Newly Discovered UX Ori Star in the Large Magellanic Cloud Invited Speaker: The LMC star, SSTISAGE1C J050756.44--703453.9, was first noticed during a survey of EROS-2 lightcurves for stars with large irregular brightness variations typical of the R Coronae Borealis (RCB) class. However, the visible spectrum showing emission lines including the Balmer and Paschen series as well as many Fe II lines is emphatically not that of an RCB star. This star has all of the characteristics of a typical UX Ori star. It has a spectral type of approximately A2 and has excited an H II region in its vicinity. However, if it is an LMC member, then it is very luminous for a Herbig Ae/Be star. It shows irregular drops in brightness of up to 2 mag, and displays the reddening and ``blueing" typical of this class of stars. Its spectrum, showing a combination of emission and absorption lines, is typical of a UX Ori star that is in a decline caused by obscuration from the circumstellar dust. SSTISAGE1C J050756.44--703453.9 has a strong IR excess and significant emission is present out to 500 \micron. Monte Carlo radiative transfer modeling of the SED requires that SSTISAGE1C J050756.44--703453.9 has both a dusty disk as well as a large extended diffuse envelope to fit both the mid- and far-IR dust emission. This star is a new member of the UX Ori subclass of the Herbig Ae/Be stars and only the second such star to be discovered in the LMC. [Preview Abstract] |
Friday, October 22, 2010 4:15PM - 4:45PM |
JB.00002: Translucent, High-Latitude, Molecular Clouds in the Milky Way Invited Speaker: More than 100 molecular clouds are detected in the lowest rotational transition of carbon monoxide are known to exist at high Galactic latitudes (|b| $>$ 25 degrees; b = 0 degrees lies along the Galactic midplane). For the most part,they represent a population of small insterstellar clouds that are likely the local, high-latitude extension of the molecular distribution detected by the Galactic plane surveys (primarily Giant Molecular Clouds or GMCs). The high Galactic latitude and the thinness of the Galactic disk constrain the bulk of the high-latitude molecular clouds to be nearby (i.e., less than a few hundred parsecs away). The vast majority of these clouds are of the translucent variety, that is, with dust opacities in the range of 1-5 magnitudes and a chemistry that is dominated by photoprocesses rather than collisional reactions. Translucent clouds differ from the more common GMCs and dark molecular clouds in that they seldom form stars and self-gravity plays a significantly lesser role in structuring them. Thus, these clouds may still bear the original signatures of the atomic gas flows that created them. In this case, their formation mechanisms would differ substantially from those thought to apply to GMCs. [Preview Abstract] |
Friday, October 22, 2010 4:45PM - 5:15PM |
JB.00003: Orion's Veil: A Laboratory for Understanding Physical Processes in the Interstellar Medium Invited Speaker: Orion's Veil is a foreground cloud of gas and dust which is directly along the line of sight towards the Orion Nebula, and is the primary cause of extinction seen towards the Nebula. The wealth of spectroscopic data available for the Veil makes it an ideal case-study of physical processes in the Interstellar Medium (ISM). Radio observations (continuum and 21cm absorption) allow us to map the amount of extinction in the Veil, along with a map of the line-of-sight magnetic field. UV and optical absorption data of atoms and H$_{2}$ allow us to determine of abundances of elements in multiple stages of ionization, density, and temperature. In this talk, I will discuss the observations which make the Veil unique. I will also show how, by combining the observational with theoretical calculations using the spectral synthesis code Cloudy, we have determined the distance of the Veil from the ionizing stars of the Orion Nebula, the balance between magnetic, thermal, and gravitational energy in the Veil, the geometry of the Veil, abundances, and many other physical properties in the Veil. Overall, a picture develops of a region within two parsecs of the ionizing stars of Orion, a region dominated by magnetic pressure, and a region where H$_{2}$ molecules are in highly excited rotational/vibrational states. [Preview Abstract] |
Friday, October 22, 2010 5:15PM - 5:45PM |
JB.00004: The Formation of Molecular Clouds: Insights from Numerical Models Invited Speaker: Galactic star formation occurs at a surprisingly low rate. Yet, recent large-scale surveys of dark clouds in the Galaxy show that one rarely finds molecular clouds without young stellar objects, suggesting that star formation should occur rapidly upon molecular cloud formation. This rapid onset challenges the traditional concept of ``slow'' star formation in long-lived molecular clouds. It also imposes strong constraints on the physical properties of the parental clouds, mandating that a cloud's structure and dynamics controlling stellar birth must arise during its formation. This requires a new approach to study initial conditions of star formation, namely addressing the formation of molecular clouds. Taking into account the observational constraints, I will outline the physics of flow-driven molecular cloud formation. I will discuss the relevance and the limitations of this scenario for setting the star formation efficiency in our Galaxy and beyond. [Preview Abstract] |
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