SEPTEMBER 24 - 28, 2007

MONDAY, SEPTEMBER 24

12 noon: Solar, Stellar, and Planetary Sciences Division Seminar. "Three Problems in Planet Formation: The Kuiper Belt, Hot Jupiters, and Transitional Disks," Ruth Murray-Clay, University of California, Berkeley. Pratt Conference Room.

Abstract: The past 15 years have produced a plethora of observations that address the question of how planetary systems form. I will discuss clues to planet formation in three settings: 1) Nearly a quarter of the ~500 Kuiper belt objects with securely determined orbits are in mean-motion resonance with Neptune. The planet likely captured these KBOs as it scattered planetesimals and migrated outward. Does the noise inherent in migration driven by discrete scattering events interfere with a planet's ability to capture bodies into resonance? 2) About 1 in 5 of the ~200 extrasolar planets discovered to date are hot Jupiters, which likely migrated from their birthplaces to distances less than 0.05 AU from their host stars. Photoionization heating from UV radiation incident on the atmospheres of hot Jupiters drives planetary mass loss in the form of hydrodynamic winds. What are the properties of these winds, and how much mass will a hot Jupiter lose over its lifetime? 3) Approximately 10% of the disks around young stars have inner holes but are still accreting. These transitional disks are likely in the process of dissipating. What drives disk accretion in these systems?

12:30 pm: High Energy Astrophysics Division Lunch Talk. "The Potential for Constraining Dark Energy with X-ray Cluster Mass Fraction Measurements," Dr. David Angelo Rapetti, Stanford University. Phillips Auditorium.

Abstract: We examine the ability of a future X-ray observatory, with capabilities similar to those planned for the Constellation-X mission, to constrain dark energy via measurements of the cluster X-ray gas mass fraction, f_gas. We find that f_gas measurements for a sample of ~500 hot (kT>~5keV), X-ray luminous, dynamically relaxed clusters, to a precision of ~5 per cent, can be used to constrain dark energy with a Dark Energy Task Force (DETF; Albrecht et al. 2006) figure of merit of 20-50. Such constraints are comparable to those predicted by the DETF for other leading, planned 'Stage IV' dark energy experiments. Our analysis uses a Markov Chain Monte Carlo method which fully captures the relevant degeneracies between parameters and facilities the incorporation of priors and systematic uncertainties in the analysis. We explore the effects of such uncertainties, for scenarios ranging from optimistic to pessimistic. We conclude that the f_gas experiment offers a competitive and complementary approach to the other best large, planned dark energy experiments. In particular, the f_gas experiment will provide tight constraints on the mean matter and dark energy densities, with a peak sensitivity at redshifts midway between those of supernovae and baryon acoustic oscillation experiments.

WEDNESDAY, SEPTEMBER 26

12:30 pm: High Energy Astrophysics Division Lunch Talk. "R Aquarii: A Small Binary with Big Ambitions," Drs. Ed Kellogg and Joy Nichols, CfA. Pratt Conference Room.

Abstract: Observations with X-ray and far-UV telescopes and the VLA in the past several years reveal a rich variety of features in the historically well studied but still mysterious symbiotic binary, R Aquarii. We discuss jets, lobes, and spectral features reminiscent of AGN plus detection of a 29 minute period, both from the central region of this fascinating and apparently unique system.

4:00 pm: Initiative in Innovative Computing (IIC) Seminar. "Advances in Advancing Interfaces: Building Semiconductors, Inkjet Plotters, Medical Scanners, and Robotic Devices," James Sethian, Department of Mathematics, University of California, Berkeley and Mathematics Department, Lawrence Berkeley National Laboratory. Preceded by refreshments at 3:45 pm. Room 330, 60 Oxford Street, Cambridge. Event parking is available at the 52 Oxford Street Garage [map]. Please inform the parking attendant you are attending the IIC seminar. (The IIC seminar series schedule is updated often with additional information and seminars.)

Abstract: Propagating interfaces occur in a wide variety of settings, and include ocean waves, burning flames, and material boundaries. Less obvious boundaries are equally important, and include iso-intensity contours in images, handwritten characters, and shapes against boundaries. In addition, problems not thought of as moving interface problems often can be recast as advancing fronts, including finding robotic navigation and finding shortest paths on contorted surfaces. One way to frame moving interface problems is by casting them as solutions to partial differential equations, and this has led to Fast Marching Methods and Level Set Methods. There are some advantages to this view; in particular, they easily accommodate merging boundaries, problems in three dimensions, and very subtle motions of boundaries. In many settings, they been proven valuable. The speaker will try to provide an overview of these approaches, with an eye towards fundamental mathematical ideas and their geometric and algorithmic interpretation. Along the way, we will discuss a large collection of applications, with a particular emphasis on industrial engineering collaborations which have led to robust codes for semiconductor manufacturing, the manufacturing of inkjet plotters for building plasma displays, image segmentation and tracking in cardiac scanners, robotic navigation around obstacles, and seismic imaging in oil recovery.

THURSDAY, SEPTEMBER 27

11:00 am: Science Education Seminar and Open Discussion. Weekly sessions focus on current department programs, literature reviews, and recent trends in science education and assessment. Some sessions feature outside speakers or guests. All members of the CfA community are welcome. Please contact Bruce Ward at bward@cfa, if you wish to attend any session. Phillips Auditorium.

11:00 am: Institute for Theory and Computation (ITC) Colloquium. "Estimating the Spin of the Black Holes in Microquasars from the High Frequency QPOs," Prof. Marek Abramowicz, Göteborg University. Pratt Conference Room.

12:30 pm: Optical and Infrared Astronomy Division Lunch Talk. "Trigger Mechanisms and Evolution of ULIRGs: Local vs z~2," Dr. Kalliope Dasyra, IPAC. Pratt Conference Room.

Abstract: I will summarize results from NIR spectroscopic/imaging programs that aim to understand what triggers ULIRGs and how do they evolve. For the local ULIRGs, I will present a stellar kinematical analysis performed using the long-slit spectrograph ISAAC mounted on the VLT. The low moments of the stellar velocity profiles, extracted from the CO bandheads, indicate that local ULIRGs are typically triggered by mergers of equal-mass, sub-m*, gas-rich galaxies and lead to the formation of moderate-mass ellipticals. The position of ULIRG remnants on the fundamental plane of early-type galaxies is well constrained in comparison with that of remnants of other interaction/merger categories (e.g. LIRGs) and that they are less massive than local Palomar-Green (PG) QSOs. This result implies that only a subsample of the local ULIRGs and PG QSOs are part of the same evolutionary sequence. At redshifts ~2, NICMOS2 images of ULIRGs (discovered by Spitzer) show small fraction of perturbations in contrast to both z~2 submm galaxies and local ULIRGs. This could be attributed to different properties in the stellar/ISM distribution between the two populations. A bulge/disk decomposition of the brightest sources indicates that if bulges are indeed present, they are small. Therefore, at least a non-negligible number of z~2 ULIRGs dynamically differs from their local analogues.

4:00 pm: Colloquium. "Spin and Magnetic Evolution of Millisecond X-ray Pulsars," Dr. Deepto Chakrabarty, MIT. (Anyone wishing to meet with the speaker should contact the host, Prof. Jonathan Grindlay, ext. 5-7204.) Preceded by tea at 3:30 pm. Phillips Auditorium.

Abstract: Accretion-powered and nuclear-powered millisecond pulsars are old neutron stars which have been spun up to rapid rotation by magnetic accretion torques. They are among the most rapidly rotating stars known, with surface velocities of order 0.1c. However, their spin frequency distribution, as observed by the Rossi X-Ray Timing Explorer (RXTE), cuts off sharply above 700 Hz, well below the presumed centrifugal break-up limit for neutron stars. The radio millisecond pulsar population appears to exhibit a similar cutoff. A variety of braking mechanisms might contribute to this cutoff, including magnetic accretion torques, magnetic dipole radiation, and even gravitational radiation from the rapidly rotating neutron star. I will discuss recent progress in exploring and understanding the millisecond pulsar spin distribution.

FRIDAY, SEPTEMBER 28

12:30 pm: Solar, Stellar, and Planetary Sciences Division Seminar. "Hydrogen Lyman Alpha Spectral Line Profiles in Coronal Holes from 1.5 - 6.5 Solar Radii," Raid Suleiman, CfA. Pratt Conference Room.

Abstract: UVCS has made detailed measurements of H I Lyman alpha spectral line profiles in a polar coronal hole at projected heliocentric heights from 3.5 to 6.5 solar radii during 1998 January 5 - 11. Similar polar coronal hole measurements were made during 1998 June 16 - 21. Earlier UVCS observations obtained at 1.5 to 2.5 solar radii are used for comparison. In addition, new measurements are being made for the current phase of the solar cycle. From these measurements we derive 1/e half widths of coronal velocity distributions at the observed heights. The velocity distribution includes all motions contributing to the Doppler shifts along the line of sight (LOS). We also measure absolute intensities that can be used to derive outflow speeds via a Doppler dimming analysis. At large heights in coronal holes, the outflowing coronal plasma becomes nearly collisionless and the ionization balance is believed to become frozen. H I Lyman alpha profile measurements characterize the neutral hydrogen velocity distribution, which at lower heights can also be used to describe the proton distribution. However, in the regions above 3 solar radii, the neutral hydrogen velocity distribution may not be the same as that for the protons because the characteristic time for charge transfer between neutral hydrogen and protons becomes longer than the time it takes for the plasma to flow through a density scale height. Hence, the neutral hydrogen velocity distribution may not be directly affected by transverse wave motion or wave damping. An indication of an adiabatic radial decrease in the neutral hydrogen temperature would indicate a decoupling of the protons and neutral hydrogen, and also indicate the absence of mechanisms that would heat the neutrals. We will compare the observations with the predictions of a theoretical model of the combined electron, proton and neutral hydrogen plasma. Such a comparison could lead to an improved knowledge of the proton heating at these large heights.

12:30 pm: Radio and Geoastronomy Division Lunch Talk. "The Giant Meterwave Radio Telescope and Low Frequency Astronomy," Prof. S. Ananthakrishnan, Pune University, India. Room M-340, 160 Concord Avenue.

Abstract: A description of GMRT is given including the `fun' in commissioning it. It is being currently used for observing a wide variety of objects like Nearby Galaxies, groups of galaxies, HI content of various galaxies, dwarf galaxies and DLA systems, Spitzer survey fields, Abell fields, a mega jet, Pulsar searches, Sun and planets, etc. I will present some samples of these areas.

SAO HUMAN RESOURCES NOTES

Leave Donations Requested

Due to a medical emergency, Donna Coletti of the Library has been approved as a leave donor recipient in the Leave Transfer Program. Any SAO Trust Fund employee who wishes to donate annual leave to Donna should complete a Leave Donor Form and send it to MS17.

Under the Leave Transfer Program, Trust Fund employees may only donate annual leave to other Trust Fund employees and Federal employees may donate annual leave only to other Federal employees. If you should have any questions or are not able to access the form, please contact Anne LeBlanc, ext. 5-7371.

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