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TUESDAY, APRIL 17

12:30 pm: Institute for Theory and Computation (ITC) Seminar. "The Role of the Environment in Shaping the Nature and Abundance of Dwarf Galaxy Satellites," Prof. Lucio Mayer, ETH. Pratt Conference Room.

Abstract: Dwarf galaxy satellites, in particular the satellites of the Milky Way and M31, have become the testbed of the cold dark matter model at small scales. The missing satellites problem still remains one of the major challenges that the theory is facing. A proper study of the formation and evolution of satellites in galaxy halos, however, requires cosmological hydrodynamical simulations having a resolution that is just starting to become achievable. In the meantime, detailed N-Body+SPH simulations of individual dwarf galaxies evolving within the primary halo remain the best tool to understand the origin of the present-day population of satellites. Here we review a number of works showing how tidal stripping, tidally induced dynamical instabilities, ram pressure stripping and the cosmic ionizing background combine to explain the morphology-density relation, the kinematics, the morphology, gas content, mass-to-light ratios and star formation histories of known dwarf spheroidal satellites within hierarchical structure formation. The redshift of infall of the satellites within the primary halo is a crucial parameter determining many of the final properties of the satellites. The accurate determination of their orbits will allow to test our model. We end by discussing the implications of such environmentally driven evolution on the missing satellites problem.

1:30 pm: Special Seminar. "Rotational Stability of Planets with Lithospheres," Dr. Isamu Matsuyama, Carnegie Institute. EPS Faculty Lounge, Hoffman Lab, 4th Floor.

Abstract: Mass redistribution on the surface and within the interior of planets leads to a reorientation of the rotation pole relative to the surface geography, or true polar wander (TPW), which in turn has implications for long-term climate and habitability. I will discuss a new and general theoretical treatment of TPW for planets with an elastic lithosphere. The theory corrects previous analyses and also extends these studies to take into account the effects of elastic energy and tidal deformation. I will review several recent applications of the new theory, including reassessments of the rotational stability of Mars and the icy satellites of the outer solar system.

2:00 pm: Radio and Geoastronomy Division Special Seminar. "Extrasolar Planetary Systems at High Angular Resolution," Michael Liu, Institute for Astronomy, Hawaii. Room M-340, 160 Concord Avenue.

Abstract:: Detection and characterization of extrasolar planetary systems demand a challenging combination of both high angular resolution and high contrast. New adaptive optics (AO) studies on the largest ground-based telescopes can meet this challenge. We discuss AO studies of the evolution of young debris disks (the extrasolar analogs of the young Kuiper Belt) and of direct detection of young massive planets. For the latter, our team has been selected to carry out an extensive multi-year search to directly image extrasolar planets around other stars using the new high contrast imager NICI at the Gemini-South Telescope. Our NICI Planet-Finding Campaign is expected to be the largest and most sensitive imaging survey to date for massive (~1 Mjup) planets around other stars.

4:00 pm: Graduate Student Research Forum. "Galactic Archaeology: Using Globular Clusters to Understand the Formation and Evolution of Galaxies," Julie Nantais, CfA. Pratt Conference Room.

Abstract: Ancient globular clusters, dating back to the era 10-13 billion years ago when the main bodies of today's galaxies were just coming together, allow us to study the process of galaxy formation right here in the local Universe. I will explain how globular clusters reveal information relevant to galaxy formation history, what we've learned so far about galaxies and their formation histories by studying their globular cluster populations, and the motivation and nature of studying the globular cluster population of the nearby spiral M81.

WEDNESDAY, APRIL 18

12:30 pm: High Energy Astrophysics Division Lunch Talk. "Low-Mass X-ray Binaries and Globular Clusters in Early-Type Galaxies," Dr. Greg Sivakoff, Ohio University. Pratt Conference Room.

Abstract: The sub-arcsecond resolution of the Chandra X-Ray Observatory has resolved the X-ray content of nearby early-type galaxies into low-mass X-ray binaries (LMXBs) and diffuse interstellar gas. Extragalactic low-mass X-ray binaries probe the massive stars formed billions of years ago in early-type galaxies and probe the properties of dense stellar environments (globular clusters). The ~50-200 bright LMXBs per galaxy are an incredible complementary sample to the ~150 active Galactic LMXBs; large LMXB samples reveal general LMXB properties and rare LMXB phenomena. I discuss results from single- and multi-epoch observations of individual galaxies. In particular, I highlight results comparing a sample of eleven early-type Virgo Cluster galaxies with Hubble Space Telescope Advanced Camera for Surveys observations of globular clusters. Finally, I discuss future plans to explore the X-ray content of early-type galaxies.

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) Seminar. "Tracing Magnetic Field with Aligned Dust: Mystery Unveiled," Dr. Alex Lazarian, University of Wisconsin. Pratt Conference Room.

Abstract: Aligned non-spherical dust particles both polarize starlight passing through the dust cloud and emit polarized far infrared and sub-mm radiation. This provides an easy way to study magnetic fields in diffuse interstellar gas, hotbeds of star formation, circumstellar regions and interplanetary medium. The interpretation of the polarization in terms of magnetic field, however, requires the knowledge of the grain alignment theory. This has been the stumbling block for reliable magnetic field tracing since 50s of the previous century. While great minds, e.g. Ed Purcell and Lyman Spitzer worked productively in the field and contributed to it substantially, I shall show that the textbook solutions of the problem of grain alignment are not tenable for most of the interstellar grains. Instead, I shall identify grain helicity, which stems from their irregularity, as a most important component of a successful grain alignment theory. I shall demonstrate a simple analytical model of a helical grain that is able to explain the existing observational data (including the cases when the alignment fails) and thus allow more reliable studies of magnetic fields. I shall discuss a few new condensed matter effects, e.g. magneto-mechanical effects, which have been discovered in the process of the grain alignment research.

12:30 pm: Optical and Infrared Astronomy Division Lunch Talk. "Exploring the Relationship Between Stellar Mass and Planet Formation," John Johnson, University of California, Berkeley. Pratt Conference Room.

Abstract: Over 160 nearby stars are known to harbor planetary companions, and the physical properties of these host stars provide an important link between the planets detected today and the circumstellar environments from which they formed long ago. In particular, determining the relationship between stellar mass and planet occurrence provides an important test of the core accretion model of planet formation, which predicts the fraction of stars with planets increases with stellar mass. To measure the occurrence rate of planets as a function of mass, the I am conducting a precision Doppler survey of intermediate-mass (1.3 to 1.9 Msun) subgiant stars at Lick and Keck Observatories, in conjunction with the California and Carnegie Planet Search. I will discuss how subgiants are ideal proxies of A and F type main-sequence stars in Doppler-based planet searches. I'll also present the latest planet detections from my sample, including several planets orbiting "retired" A stars with masses greater than 1.6 Msun.

4:00 pm: Colloquium. "Clumpy Galaxies in the Early Universe," Prof. Debra Meloy Elmegreen, Vassar College. (Anyone wishing to meet with the speaker should contact the host, Prof. John Huchra, ext. 5-7375.) Preceded by tea at 3:30 pm. Phillips Auditorium.

Abstract: Observations of galaxies out to z~5 in the Hubble Ultra Deep Field reveal unusual clumpy morphologies in addition to spirals and ellipticals. These high redshift galaxies are mostly starburst systems, with star-forming regions 1000 times more massive than in today's galaxies. Many of the clumpy galaxies have thick disks that are half the size of local galaxies and lack bulges and exponential disks; they may grow through merging and accretion, and evolve into today's spirals when the star-forming clumps migrate to the centers or dissolve.

7:30 pm: Monthly Observatory Night for the Public. "From Dust to Planets," Dr. David Wilner, CfA. The lecture will be followed by telescopic observing, weather permitting. No tickets or reservations are necessary; however, seating is to the capacity of the hall. Doors open at 7:00 pm. Phillips Auditorium.

Abstract: Where do the planets come from? How do we explore the early history of our solar system? We can't go back in time, but we can study the "fossil record" of planets, moons, asteroids and comets, and we can observe the dusty disks around distant, young stars where we believe planets are forming right now. David Wilner will discuss what we know (and what we don't know) about planet formation, using dramatic images from the Hubble Space Telescope, the Submillimeter Array, and other state-of-the-art facilities. He will describe the signs of new planets being born and the evidence for debris bombardment that may have important consequences for life on other worlds.

12 noon: Optical and Infrared Astronomy Division Special Lunch Discussion. "Roundtable Discussion of AURA Activities: The NSF Senior Review & the Next Decadal Survey," Prof. John Huchra, CfA. Phillips Auditorium.

Abstract: Each year, as a part of the AURA Annual Meeting, the Member Representatives conduct a round table discussion to air important policy issues, understand more fully the views of our member institutions, and to develop guidance for the AURA Board for the future. The two topics for this year are: 1. Implementation and Impact of the NSF Senior Review. NSF is currently implementing many of the recommendations of the 2006 Senior Review. For AURA, these include a new role as a "national program manager" for GSMT (see here), as well as improvements to NOAO and NSO telescope infrastructure, and attention to optimizing a "community access system" over a range of apertures. The AURA Board seeks advice on how AURA should work with NSF to provide and operate astronomical facilities, to balance the need for cutting-edge telescopes and instruments with community access to 2-8m telescopes, and to leverage the investments from private and public institutions and consortia with NSF operations funding. We also would appreciate advice on how to help NSF/ASTR increase the support funding base. 2. Planning for the Next Decadal Survey. The NRC, AAS, and other organizations have begun planning for the next A&A Decadal Survey, including identifying the "lessons learned" and handling the backlog of missions and facilities from the 2000 study (Astronomy & Astrophysics in the New Millennium). Some obvious suggestions include: mixing science drivers and mission/wavelength themes; obtaining better cost estimates; re-prioritization of carryover projects with new science ideas; creating broader community involvement; producing a unified ranking system of priorities. In our discussion, we hope to focus on AURA-specific actions, such as workshops to define major initiatives in ground-based or space-based astronomy. We may also wish to re-examine current projects that are not yet started or have yet to receive substantial funding from NSF and NASA.

Science Fiction Movie Night: "Star Trek IV: The Voyage Home" drew more new viewers to the series than ever before with its message of caution and hope. A gigantic space probe has parked in Earth orbit, sending out incomprehensible signals that are wreaking havoc with the planet's oceans and atmosphere. When they decode the signals, Kirk and company realize that they must time travel back to the 20th century in hopes of bringing back the creatures the probe is trying to contact. We won't spoil it for you here, other than to say perhaps humans aren't the only intelligent species on the planet. Letıs hope that the message of conservation and stewardship in this film catches on around the world before it's too late.

7:00 pm: "Flash Gordon" episode―Thrilling adventures on the edge of space!

7:15 pm: "Star Trek IV: The Voyage Home" (PG)―The key to saving the future, can be found only in the past.

Sci-Fi Movie Nights are held in the Phillips Auditorium. Doors open at 6:30 pm. No reservations are necessary; however, seating is to the capacity of the auditorium.

Thursday, April 19, 6:00 pm - 7:30 pm: Women, Science and Society Seminar Series. "The Estrogen Elixir: Women and Science in the Making and Unmaking of Hormone Replacement Therapy," Dr. Elizabeth Watkins, Associate Professor in the School of Medicine, University of California, San Francisco. HMS Conference Center, HIM Room, 77 Avenue Louis Pasteur, Boston. A small reception with the guest speaker will follow. Sponsored by the Harvard Graduate Women in Science and Engineering; Graduate School of Arts and Sciences; and Office of the Senior Vice Provost for Faculty Development and Diversity.

Abstract: Dr. Watkins studies interplay between medicine and culture, including the popularization of information about health and medicine and the roles of gender in medicine. Her most recent book, The Estrogen Elixir: A History of Hormone Replacement Therapy in America, tells the story of the use and public perception of estrogen since the 19th century.

Leave Donations Requested

Two SAO Trust Fund employees have been approved to receive leave donations. Due to medical emergencies, Nathalie Martimbeau of the Optical and Infrared Division and Donna Coletti of the Library have been approved as leave donor recipients in the Leave Transfer Program. Any SAO Trust Fund employee who wishes to donate annual leave to Nathalie or 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.

A list of scientists currently visiting the CfA is available here.