NOVEMBER 5 - 9 2007

MONDAY, NOVEMBER 5

12 noon: Joint Solar, Stellar, and Planetary Sciences/Optical and Infrared Astronomy Seminar. "Are M Dwarfs Good Targets for Planet Searches and Do We Care?" Dr. Angelle Tanner, Jet Propulsion Laboratory. Pratt Conference Room.

Abstract: Here I illustrate the advantages and disadvantages of focusing different types of planet searches on M dwarfs. Ideally, these stars are good targets for both radial velocity (RV) and astrometric searches since their reduced mass results in larger signals, however, they have not been the focus of the original long term RV programs due to their being faint and associated with large photospheric variability. Since observing techniques have matured, there are now both radial velocity and astrometric programs devoted to searching for planets, with three RV planetary systems discovered to date and the first astrometrically detected planet around an M dwarf soon to come. Those planets around M dwarfs have some of the lowest masses discovered to date (< 20 MJ/sini). Ironically, the fact that M dwarfs are faint makes them ideal targets for both transit and direct imaging programs due to improved contrast levels between the star and planet. Larger telescopes and improvements in high contrast and imaging capabilities are making M dwarfs more viable targets for direct imaging and transit surveys. It is believed that a dedicated transit M dwarf survey could result in the detection of superEarths. In addition to the observational arguments, I will address the theoretical expectations for the population of planets around M dwarfs given current planet formation models. The observed frequency of planets around M dwarfs can distinguish core accretion or disk instability as the dominant planet formation mechanism around low mass stars. Finally, I will discuss the potential for detecting terrestrial mass planets around the nearest M dwarfs with SIM PlanetQuest.

TUESDAY, NOVEMBER 6

2:30 pm: Institute for Theory and Computation (ITC) Seminar. "'Exciting' Dark Matter and the 511 keV Line," Prof. Douglas Finkbeiner, CfA. Phillips Auditorium.

Abstract: Weakly-interacting massive particles (WIMPs) are the leading candidate for particle dark matter, and have been invoked to explain excess GeV gamma-rays, high-energy positrons, and even excess microwaves in the inner Milky Way. Until now, however, there has been no connection between these weak scale (mass of ~ 300 GeV) WIMPs and the 511 keV e+e- annihilation radiation from the inner Milky Way.Neal Weiner and I have proposed a WIMP candidate with an "excited state" 1-2 MeV above the ground state (known as "exciting" dark matter, XDM). This state may be collisionally excited and decays by e^+e^- pair emission. Such a particle converts WIMP kinetic energy into pairs, which in turn could produce a substantial fraction of the 511 keV line observed by INTEGRAL/SPI in the inner Milky Way. Only a small fraction of the WIMPs are above threshold, and that fraction drops sharply with Galactocentric radius, naturally yielding a radial cutoff, as observed. Even if the scattering probability in the inner kpc is << 1% per Hubble time, enough power is available to produce the number of pairs per second observed. I will specify the parameters required to explain the INTEGRAL result, and discuss other observational consequences of this model, including our recent consideration of BBN Lithium abundance.

WEDNESDAY, NOVEMBER 7

12:30 pm: High Energy Astrophysics Division Lunch Talk. "Measuring the Growth of Structure with Multi-Wavelength Surveys of Galaxy Clusters," Dr. Neelima Sehgal, Rutgers University. Pratt Conference Room.

Abstract: Current and near-future galaxy cluster surveys at a variety of wavelengths may provide a promising way to obtain precision measurements of structure growth over cosmic time. This in turn would serve as an important precision probe of cosmology. However, to realize the full potential of these surveys, systematic uncertainties in cluster mass estimates and sample selection must be well understood. This work follows two different approaches to understand these uncertainties. 1.) X-ray and weak-lensing mass estimates are compared for shear-selected galaxy clusters in the Deep Lens Survey (DLS) to study possible biases in using cluster baryons or weak-lensing shear as tracers of the cluster dark matter. Results are presented for four galaxy clusters that comprise the top-ranked shear-selected system in the DLS. 2.) Cluster sample selection is investigated in the context of upcoming arcminute-resolution millimeter-wavelength surveys. Large-area, realistic simulations of the microwave sky are constructed and cluster detection is simulated using a multi-frequency Wiener filter to separate the galaxy clusters, via their Sunyaev-Zel'dovich (SZ) signals, from other contaminating microwave signals.

4:00 pm: Initiative in Innovative Computing (IIC) Seminar. "Geospatial Technology - its Values and Challenges," Wendy Guan, Director of GIS Research Services, Center for Geographic Analysis, Harvard University and, Peter Bol, Charles H. Carswell Professor of East Asian Languages and Civilizations; Associate of the Leverett House Senior Common Room, Harvard University. 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: Location matters, not only in geography but also in other sciences and humanities. Geospatial technology helps us investigate and communicate in the spatial domain. The field enjoyed a rapid growth in recent years. Peter Bol and Wendy Guan will talk about why spatial thinking is critical to just about any discipline, what the geospatial technology offers to non-geography researchers, what the driving forces are in its recent boom, and what challenges it faces going forward.

THURSDAY, NOVEMBER 8

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. "Mergers of Dark Matter Halos and Galaxies in Lambda-CDM Cosmology," Prof. Chung-Pei Ma, University of California, Berkeley. Pratt Conference Room.

Abstract: In a cold dark matter universe, galaxies and their host dark matter halos gain mass primarily through mergers with other galaxies. Having an accurate description of the mergers of dark matter haloes is therefore a key first step in understanding galaxy formation and growth. I will describe recent analyses of merger trees constructed from the Millennium simulation and present a nearly universal formula for the merger rates of dark matter halos over a broad range of masses and redshifts. The connection to galaxy mergers, the Press-Schechter model, and the Smoluchowski coagulation equation will be discussed.

12:30 pm: Optical and Infrared Astronomy Division Lunch Talk. "The Nature of Spitzer 24um-Bright Sources," Dr. Anna Sajina, IPAC. Pratt Conference Room.

Abstract: I will present the status of our ongoing program to study z~1-3 Spitzer-selected ULIRGs as part of which we have obtained ~250 Spitzer IRS spectra. I will focus on the analysis of a sample of ~50 24um-bright and red sources (F24>0.9mJy). The decomposition of their IRS mid-IR spectra into their principal contributors (PAH, continuum and extinction) revealed that most of our sources are composite starburst/AGN systems. In addition, I will present the analysis of their far-IR and radio SEDs (from MIPS70um,160um, MAMBO1.2mm, VLA20cm, and GMRT610MHz data). Our analysis suggests that many of our sources host heavily obscured AGN with quasar-scale luminosities. This is especially obvious for our radio-loud sub-sample. Lastly, I will present early results on the analysis of a 150 source flux-limited sample (F24>0.9mJy).

4:00 pm: Colloquium. Cecilia Payne-Gaposchkin Lecture: "HI Cosmology in the Local Universe with ALFALFA," Prof. Martha Haynes, Cornell University. (Anyone wishing to meet with the speaker should contact the host, Prof. Charles Alcock, ext. 5-7100.) Preceded by tea at 3:30 pm. Phillips Auditorium.

Abstract: The Arecibo Legacy Fast ALFA (ALFALFA) survey is an on-going second generation blind extragalactic HI survey exploiting Arecibo's superior sensitivity, angular resolution and digital technology to conduct a census of the local HI universe over a cosmologically significant volume. When complete in 4-5 years, ALFALFA will detect more than 25,000 extragalactic HI line sources out to z~0.06, and its catalog will be especially useful in synergy with wide area surveys conducted at other wavelengths. ALFALFA is detecting HI masses as low as 10**6 solar masses and as high as 10**10.8 solar masses with positional accuracies typically better than 20 arcsec, allowing immediate identification of the most probable optical counterpart to each HI detection. In the region of the Virgo cluster of galaxies, a number of optically dark HI sources have been found. These all lie in the outskirts of the cluster and could be "harassment" or tidal debris, the result of high speed gravitational encounters. First ALFALFA results already indicate, in agreement with the suggestions of previous, more limited studies, that there is not a cosmologically significant population of optically dark but HI rich galaxies. However, the majority of ALFALFA detections are too optically faint or of low surface brightness to have been included in previous targeted HI surveys. ALFALFA promises a wealthy dataset for the exploration of many issues in near-field cosmology and galaxy evolution studies, setting the stage for future extension of these investigations to higher redshifts with the Square Kilometer Array.

SAO HUMAN RESOURCES NOTES

2008 Federal and Trust Fund Open Season

Open Season for Federal and Trust Fund employees will be held from November 12 through December 10, 2007. Open Season is the time during which you can enroll in a health plan sponsored by the Smithsonian and/or change plans or coverage type (individual to family or vice versa).

SAO will sponsor a joint 2008 Federal and Trust Fund Open Season Health Fair on Monday, November 5, 2007, at Cambridge Discovery Park, Room 385, from 10 am to 12:30 pm. Representatives from the major Federal carriers and the Trust Fund medical and dental carriers will be available to answer questions on plan coverage and other healthcare-related products and services. Health plan brochures and 2008 premium rates will be available at the health fair.

You will receive more detailed Open Season information in the mail later this month. If you have questions, please contact Anne LeBlanc,ext. 5-7371, or Linda McDonald, ext. 6-7605.

Combined Federal Campaign

You are invited to participate in the Combined Federal Campaign (CFC) of Eastern Massachusetts. The mission of the CFC is to support and promote philanthropy through a program that is employee-focused, cost-efficient, and effective in providing employees the opportunity to improve the quality of life for all. Federal and non-Federal employees may use payroll deduction, cash, or check to make pledges.

All organizations listed in the CFC brochure have met the stringent application guidelines outlined by the Office of Personnel Management. For more information please refer to http://www.opm.gov/cfc/. For a complete list of the local, national, and international charities please refer to the 2007 CFC brochure of Eastern Massachusetts, which can be accessed at the following website http://www.cfceasternmass.org/.

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.

Job Vacancies

An online listing of all current SAO job openings is available. For more information, please call Human Resources, ext. 5-7371, or view your nearest bulletin board.