Weekly Calendar of Events

SEPTEMBER 22 - 26, 2014


Noon: Solar, Stellar, and Planetary Sciences Division Seminar. "On the Magnetic Field Structure of CMEs," Nada Al-Haddad, KU Leuven, Belgium. Pratt Conference Room.

Abstract: The magnetic field configuration in coronal mass ejections (CMEs) has been the subject of a number of recent studies that aimed to understand its morphology through various methods: with different magnetic field fitting and reconstruction codes using in situ measurements at 1 AU, with numerical simulations and with new remote-sensing observations by STEREO and SDO, among others. Here, we present a reference study to different magnetic field models and reconstruction methods through analyzing a list of about 60 events from the CDAW list, using four different magnetic field models and reconstruction techniques. The resulted parameters of the reconstructions, for the events are compared, statistically, as well as in more details for some cases. We also present our study on the ability of multi-spacecraft measurements to determine the structure of a CME's magnetic field. We do so by reconstructing the magnetic field configuration of two simulated CMEs with different magnetic field structures using multi-spacecraft techniques then comparing the results.


1:00 pm: Institute for Theory and Computation (ITC) Seminar. "The Range of Ejected Masses in Type Ia Supernovae," Richard Scalzo, ANU College of Physical and Mathematical Sciences. Pratt Conference Room.


11:00 am: Optical and Infrared Astronomy Division Seminar. "Supernovae as Drivers of Dust Evolution in Galaxies," Tea Temim, NASA/Goddard. Pratt Conference Room.

Abstract: The understanding of interstellar dust is important in many areas of astrophysics, but its nature, origin, and evolution is still poorly understood. The presence of dust in galaxies has a profound effect on their spectral appearance and on the many processes that determine the physical, chemical, and thermal state of their interstellar medium (ISM). Dust is primarily formed in the ejecta of core collapse supernovae (SNe) and mass outflows of evolved stars, and then subsequently destroyed by SN shocks expanding into the surrounding ISM. The amount of dust destruction determines whether a galaxy's dust budget can be balanced by dust formation in stellar sources, or whether dust growth in molecular clouds is required. I will discuss the recent progress on the study of SN-formed dust in supernova remnants, including recent observations of Cas A, SN 1987A, and the Crab Nebula that revealed significant masses of cold dust. I will also present new estimates of dust destruction rates by SNRs in the Magellanic Clouds and discuss their implications for dust evolution models and the origin of interstellar dust in galaxies.

4:30 pm: Joint ITAMP/HQOC Quantum Sciences Seminar. "Photon-Mediated Interactions between Artificial Atoms in One Dimension: Quantum Optics with Superconducting Circuits," Andreas Wallraff, ETH Zurich. Tea served at 4:00 after short student talk by Alex Sushkov. Jefferson 250, Department of Physics, Harvard University.

12:30 pm: High Energy Astrophysics Division Lunch Talk. "Emission-line Diagnostics can Reveal the Origin of Type Ia Supernovae," Tyrone Woods, Max Planck Institute for Astrophysics. Pratt Conference Room.

Abstract: Type Ia supernovae (SNe Ia) have proven vitally important in measuring cosmic distances, yet there remains no consensus model for their progenitors. In the canonical single degenerate (SD) scenario, a white dwarf (WD) grows through nuclear burning of hydrogen accreted from a companion prior to explosion. This suggests that SD progenitors should be extremely luminous sources in the EUV and soft X-ray bands. Recently, we demonstrated that if the SD model is correct, then accreting, nuclear-burning white dwarfs should provide the dominant source of ionizing radiation in early-type galaxies, ~40% of which are known to host extended emission-line nebulae. Therefore, one can search for the presence of any high-temperature SD progenitor population in these galaxies by looking for emission lines characteristic of ionization by very high-temperature (10^5 K - 10^6 K) sources. Using our He II diagnostic, we demonstrate that less than ~10% of the observed SN Ia rate in early-type galaxies can be accounted for by the SD channel. A similar approach can be taken for individual SNe Ia, by searching for fossil nebulae in the vicinity of nearby events, although other, stronger lines may be better suited to the task (e.g [O III] 5007, [O I] 6300).


11:00 am: Institute for Theory and Computation (ITC) Colloquium. "The Chemical Signature of First-Generation Massive Stars," Prof. Timothy Beers, Department of Physics, University of Notre Dame. Pratt Conference Room.

Abstract: Numerical simulations of structure formation in the early Universe predict the formation of stars with masses from (1) several tens to (2) several hundred to several thousand times the solar mass. The recently discovered carbon-enhanced metal- poor (CEMP) star with [Fe/H] < -7.1 and the distinctive light-element pattern of CEMP-no stars (carbon-enhanced stars that do not exhibit neutron-capture element over-abundances) can be associated with the first class of progenitors. However, no clear evidence of supernovae from super-massive stars has yet been found among the chemical compositions of Milky Way stars, the second class of expected progenitors. Until now. After a discussion of the abundance patterns from CEMP-no stars, I report on an analysis of a newly discovered very metal-poor star, SDSS J001820.5-093939.2, which possesses elemental-abundance ratios that differ significantly from any previously known star. This star exhibits low [α-element/Fe] ratios and large contrasts between the abundances of odd and even element pairs, such as Sc/Ti and Co/Ni. Such features have been predicted by model calculations of the nucleosynthesis associated with a pair-instability supernova of a 130-260 solar-mass star, or a core- collapse supernova of an even more massive star. The result suggests that the mass distribution of first-generation stars might extend to 100 solar masses or larger, possibly up to 1000 solar masses.

4:00 pm: Colloquium. "The Increasing Complexity of Exoplanet Atmospheres," Emily Rauscher, University of Michigan. Preceded by tea at 3:30 pm. Phillips Auditorium.

Abstract: While there are now many types of exoplanets that have been discovered, the "hot Jupiter" class remains a focus for observers and theorists alike. This partly because these are inherently interesting objects, completely unlike anything in our solar system, but also because these are the best targets for atmospheric characterization. The atmospheric properties of bright transiting planets are currently being probed by multiple instruments using impressive observational techniques; however, while the data are becoming more constraining, our theoretical picture of these planets is only becoming more complex. This is both because of the recognition of additional physical processes that must be accounted for the in the models, but also because of our increased appreciation of the inherent uncertainties in our models and their input parameters. I will discuss the development of 3D atmospheric models and review our current state of understanding. Based on current and future instrumental capabilities, I will then discuss some of the ways that we can hope to combine multiple types of observations in order to more confidently tease out the detailed physical properties of exoplanets.


12:30 pm: Radio and Geoastronomy Division Weekly Lunch Talk. "Assessing Molecular Outflows and Turbulence in Protostellar Clusters," Adele Plunkett, Yale University. Room M-340, 160 Concord Avenue.

Abstract: Molecular outflows driven by protostellar cluster members likely impact their surroundings and contribute to turbulence, affecting subsequent star formation. I will present interferometer and single-dish millimeter-wavelength observations of molecular outflows in the young protostellar clusters NGC 1333 and Serpens South, probing scales that range from the sizes of cores to clouds. I will show the intricate web of outflow morphologies observed in these regions, characterize the outflow-driving protostellar sources, and reveal several outflow features that were previously unidentified in single-dish observations. In both regions, outflows drive enough energy to sustain turbulence, and in the case of the more evolved NGC 1333, the outflows may counter the gravitational potential energy and eventually disrupt the clump. These active regions provide a framework for an empirical model of clustered star formation at different evolutionary stages, and diagnostics from our observations help to constrain numerical models of outflows. Recent observations with ALMA and other facilities of these and other regions will further our understanding of the role of outflows throughout the star forming process.

The Calendar is prepared by the Web Services Group. Entries may be submitted via email to weekly_cal@cfa.


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