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Staff Research
2015 Spring Series

All talks are held on Wednesdays in the STScI John N. Bahcall Auditorium at 3:30 p.m. preceded by tea at 3:15 p.m.

Please direct questions or comments to the colloquium committee . The 2014-15 committee members are Rongmon Bordoloi, Susana Deustua, Peter McCullough and Eileen Meyer.

STScI presents live and archived webcasting of talks and Colloquium Series.

Date Speaker/Title
Feb. 11 Debra Fischer (Yale University)
Title: The Search For 100 Earths
Abstract: The search for exoplanets is motivated by the question of whether life exists elsewhere. This drives our interest in the detection of planets that are similar to our own world: rocky planets with the potential for liquid surface water and plate tectonics; worlds that might harbor life that we can recognize. Importantly, we will need to discover not just a few, but hundreds of these worlds to eventually gain a statistical understanding of whether life is rare, common, or ubiquitous and ground-based telescopes offer an ideal platform for carrying out decade-long surveys. It is critical for follow-up studies (imaging, atmospheric studies) that these planets orbit nearby stars. In this talk, I will discuss how we plan to take what we've learned and push on to the next frontier: our plans for a next generation spectrograph, EXPRES, to carry out a search for 100 Earths with the Discovery Channel Telescope.
Host: John Debes
Feb. 18 Heidi Newberg (Rensselaer Polytechnic Institute)
Title: Rings and Radial Waves in the Disk of the Milky Way
Abstract: I will show that there is an asymmetry in the main sequence star counts on either side of the Galactic plane, as one looks towards the Galactic anticenter. This can be explained if the disk of the Milky Way oscillates up and down. This oscillation provides an explanation for the Monoceros Ring, and also for the TriAndromeda Stream (or Ring). The implication is that the stellar disk extends out to at least 25 kpc from the Galactic center - much farther than the canonical 15 kpc that is typically quoted. The oscillations are aligned with the spiral arms of the Milky Way, and are plausibly consistent with previous predictions for disk ringing due to a Sagittarius dwarf-sized galaxy plunging through the disk.
Host: Susana Deustua
Feb. 25 Christine Chen (Space Telescope Science Institute)
Title: Dusting for Prints of Exoplanetary Systems
Abstract: Debris disks are dusty disks around main sequence stars that are distinguished from proto-planetary disks by their small gas:dust ratios. Without bulk gas to retard the loss of particles against radiation pressure or corpuscular stellar wind and Poynting-Robertson (CPR) drag, circumstellar grains typically possess lifetimes of <10,000 years, significantly shorter than the age of the central star, implying that the grains are replenished from a reservoir. In these systems, unseen planets are presumed to perturb minor bodies such as asteroids or comets into crossing orbits, generating small dust grains that are detected via remote sensing. The Spitzer Space Telescope enabled the discovery and characterization of more than one thousand debris disks for the first time. I will (1) provide an overview of debris disks as planetary systems, (2) describe the time and mass dependent evolution of the mid- to far-infrared properties of debris disks and (3) describe how debris disk properties can be used to constrain the architecture of underlying planetary systems. I will also describe outstanding questions about debris disk evolution that will be addressed using the next generation of ground- and space-based instruments.
Host: I. Neill Reid
Mar. 04 Desika Narayanan (Haverford College)
Title: The Complex Interplay Between Star Formation and Galaxy Evolution at Low and High-Redshift
Abstract: Building a comprehensive picture for the evolution of galaxies from early times through present epoch requires understanding a huge dynamic range of physical processes. With observations ranging from detections of galaxies less than a billion years after the Big Bang to stellar and molecular cloud mass spectra in the Milky Way, the challenge has been to develop a concordance theory for galaxy formation than simultaneously explains this diverse range of observed galaxy properties across cosmic epoch. At the heart of many of the central questions in the astrophysics of galaxy evolution lies the physics of the interstellar medium, and galactic-scale star formation. In this talk, I will describe how understanding the complex interplay between small scale star formation physics and global galaxy evolution processes can lead to considerable insight in long-standing problems in both fields.
Host: Andrew Fox
Mar. 11 Rob Simcoe (Massachusetts Institute of Technology)
Title: Heavy Element Enrichment in Early Intergalactic and Circumgalactic Environments
Abstract: Infrared photometric surveys are discovering numerous quasars at z > 6.5, enabling absorption investigations of neutral Hydrogen and its associated heavy elements at the tail end of the reionization epoch. I will describe the status of my group's ongoing IR and optical spectroscopic surveys targeting metal pollution in the first few Gyr. Beginning with a systematic study of absorption candidates for "cold flows" at z~3, I will move on to describe a 100-sightline survey of circumgalactic MgII pollution with the Magellan/FIRE spectrometer, extending prior optical measurements (restricted to z<2) out to z~6.5. I will also describe our latest constraints on the CIV mass density and intergalactic carbon enrichment at z = 4.5-6.5. Finally, I will outline our first attempt at measuring actual chemical abundances in the z > 7 universe, and discuss their significance for reionization and the formation of the first stars.
Host: Jason Tumlinson
Mar. 25 Claire Max (UC Observatories and University of California – Santa Cruz)
Title: Mergers and Outflows in Nearby Galaxies, Seen with Adaptive Optics
Abstract: TBD.
Host: David Soderblom
Mar. 26 Claudia Alexander (Jet Propulsion Laboratory)
Title: Rosetta: Wild Bounce at Comet Churyumov-Gerasimenko
Abstract: Rosetta is the third cornerstone mission of the European Space Agency's (ESA) Horizon 2000 Programme. It's goals are to examine some of the original material of the solar system with a comprehensive evaluation of the minearologic, isotopic, and organic constituents of a comet; understand how the body works as a machine to absorb and re-radiate energy from the sun; and understand more about the origins of the solar system. In this talk, I'll explain the science background of some of the mysteries of comets including pros and cons about why we think comets might have brought Earth's water, concepts regarding missing nitrogen in the outer solar system, and material the comet is made of (CAIs & IDPs). The talk will include images of the comet's activity, the landing, the 60 hours of time spent on the comet's surface, and an overview of initial findings.
Host: David Neufeld JHU/Peter McCullough
Apr. 01 Sandra Faber (University of California - Santa Cruz); Caroline Hershel Speaker
Title: The Evolution of Star-Forming Galaxies Since z = 2.5 from CANDELS
Abstract: The CANDELS team has recently assembled a comprehensive database of galaxies in the CANDELS fields that combines HST photometry and structure with integrated photometry from a wide array of multiwavelength sources. These data have been used to derive photometric redshifts, rest-frame SEDs, stellar masses, dust absorptions, and star formation rates. At UCSC, we have studied this new database for galaxies below z = 2.5 with the goal of elucidating the simplicity -- or lack of it -- of galactic evolution of star-forming galaxies at mid-to-late cosmic epochs. Star-forming galaxies at these times appear to exhibit only a small number of independent parameters, which can plausibly be linked to properties of their evolving dark-matter halos. However, a puzzle has emerged concerning the relationship between radius and dust corrections, which may force revision to our present dust-correction model.
Host: Susan Kassin
Apr. 08 (No Colloquium: Phase 1 Deadline week)
Apr. 15 Krzystof Gorsk (Jet Propulsion Laboratory)
Title: TBD
Abstract: TBD.
Host: Marc Kamionkowski
Apr. 22 (No Colloquium: Spring Symposium)
Apr. 29 Gary Zank (University of Alabama-Huntsville)
Title: Faltering Steps into the Galaxy
Abstract: Voyager 1 has now entered the interstellar medium, a moment of great historical import. We describe the Voyager 1 magnetic field and energetic particle observations, the initial uncertainty surrounding a possible crossing of the heliopause, and the eventual clarification by the Plasma Waves Analyzer. The interaction of the solar wind and the interstellar medium is complicated by the presence of neutral hydrogen that is coupled via charge exchange to the plasma. We present the current status of theory, models, and simulations, describing the highly non-equilibrated interaction and the underlying physics. We conclude by discussing briefly related interactions of stellar winds with their local environments.
Host: Scott Friedman
May 06 Tyce DeYoung (Michigan State University)
Title: IceCube Observations of High Energy Cosmic Neutrinos
Abstract: The IceCube Neutrino Observatory uses a cubic kilometer of the Antarctic ice cap as the world’s largest neutrino detector. IceCube has observed nearly half a million neutrino events at energies from the GeV to the PeV scale, including a flux of high energy neutrinos from extraterrestrial sources. After introducing the instrument and the data analysis used to isolate these events, we will discuss the current observations, the prospects for identifying the sources of these neutrinos, and the significance of the discovery of this cosmic neutrino flux.
Host: Christine Chen
May 13 Anna Frebel (Massachusetts Institute of Technology)
Title: Hunting the First Generations of Stars and Galaxies
Abstract: The new Australian SkyMapper 1.3m telescope is carrying out a photometric survey of the entire Southern Sky. From using ugriz filter plus an additionally narrow filter placed at the Ca K line at 3933A, stellar parameters can be obtained for all stars observed. This allows for an efficient selection of a variety of stellar types, including metal-poor stars. Recent efforts to search for the most metal-poor stars have indeed delivered a new record holder for the most iron-poor star: no iron lines were detected in the high-resolution follow-up Magellan spectrum and only an upper limit of [Fe/H] <-7.1 could be determined. Contrary to its iron deficiency, the star has a significant amount of carbon. This abundance pattern can be explained with the star being a second-generation star in the universe which formed from a gas cloud enriched by only one PopIII first star. What was the environment in which these early stellar generations formed? A spectroscopic study of the faintest dwarf galaxy Segue 1 has shed light on this question. Given the chemical abundance patterns of some of its only few stars (with metallicities ranging from -4 < [Fe/H] <-1) suggest that this tiny galaxy may be a surviving first galaxy from the early universe. This suggestion is in line with recent age measurements for similar ultra-faint dwarf which showed these galaxies to be single-age stellar systems that are about as old as the universe itself.
Host: David Soderblom
May 20 Philip Chang (University of Wisconsin-Milwaukee)
Title: The Physics and Cosmology of TeV Blazars
Abstract: The universe is teeming with very high energy gamma ray sources (> 100 GeV), but it is generally thought that their impact on the universe is minor at best. On energetic grounds, this assumption seems well-founded because the energy density in TeV photons is 0.2% of that of ionizing photons from quasars. However, as I hope to show in this talk, this is not the case. Rather, the greater efficiency by which TeV photons can be converted to heating in the intergalactic medium (IGM) allows TeV blazars dominate the heating of the IGM at low redshift. I will discuss the nature of this conversion via beam instabilities. I will then discuss how the resultant heating from these TeV sources makes dramatic differences in the formation of structure in the universe. In particular, I will discuss how it gives rise to the inverted temperature-density profile of the IGM, the bimodality of galaxy clusters, the paucity of dwarf galaxies in galactic halos and voids, and some recent work on the non-uniform nature of this heating and the effect of these instabilities on the gamma-ray background.
Host: Eileen Meyer
May 27 Rachel Osten (Space Telescope Science Institute)
Title: Stellar Flares: From Plasma Physics on Stars to Space Weather on Other Worlds
Abstract: The Sun is a star, but of course it is a special one by virtue of its proximity to us; many processes can be studied on the Sun in the kind of detail which is inaccessible in studies of the remote stars. The Sun and cool stars produce flaring eruptions which impact the star itself and the create the particle and radiation environment which planetary companions experience. Multi-wavelength stellar flare studies cement a physical connection with solar flare processes and invite detailed comparisons between the Sun and stars. I will describe recent results on stellar flares which probe the extremities of these events using novel observational techniques, and discuss how these can be used to give context to processes bounding solar flare properties. I will discuss how these studies give insight into space weather and habitability on other worlds, as astronomers expand the realm of potentially habitable worlds.
Host: I. Neill Reid