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AstroFest 2011

Columbia University Department of Astronomy and Astrophysics September 16, 2011 9:00 am - 5:15 pm

Breakfast: 9:00-9:30 results and briefly discuss their astrophysical implications. Session 1: 9:30-10:20 Josh Peek David Schiminovich Post-doc, Columbia Astronomy Professor, Columbia Astronomy New insights into the magnetized ISM with A Next Generation Ultraviolet Balloon machine vision Experiment for Mapping the Cosmic Web

There are two existing avenues to interpreting I describe a "next generation" version the diffuse ISM: the theorist’s approach in which the Faint Intergalactic Redshifted Emission real data is interpreted numerically in the con- balloon (FIREBall-2), an ultraviolet instru- text of simulations, and the observer’s approach ment/spectrograph payload designed to detect in which objects are found and categorized by faint Lyman alpha and metal-line emission from eye. We are pioneering a middle way, following the low density intergalactic and circumgalactic the fast-growing science of machine vision to medium. We have recently developed novel extract shape information from complex maps detector technology which—when combined of the diffuse Galactic HI ISM. In this work with other design improvements—should boost we show a proof of concept in which newly our "cosmic web" detection sensitivity by x100 discovered needle-like ISM features can be over the first-generation flight instrument. detected with a machine vision algorithm and shown to be oriented with magnetic fields in the Lia Corrales ISM. Graduate Student, Columbia Astronomy Cosmological X-ray Scattering from Jule Stuetzel Intergalactic Dust Post-doc, Columbia Astronomy X-ray astronomy provides a unique oppor- Laboratory studies of electron driven chemistry tunity to detect and characterize micron scale in molecular clouds “grey” populations of dust, which are missed Our knowledge of molecular clouds and by evaluating the colors of background objects. protoplanetary disks rests in part on under- I will discuss X-ray scattering by dust in a standing the underlying which cosmological context and insights it may yield controls the chemical composition, charge concerning and structure in the balance, spectra and thermal structure of these high-z . environments. Of particular importance is the electron recombination process with molecular Aodh O’Connor ions, known as dissociative recombination Post-doc, Columbia Astronomy (DR). Theoretical calculations of the required rate coefficients are beyond current quantum A new laboratory apparatus to study the cosmic chemical computational capabilities. So far, origins of organic chemistry laboratory measurements are the most reliable way to generate the needed DR data. Here, The cosmic pathway towards is thought to we present a sample of our recent experimental begin in molecular clouds when atomic

1 is “fixed” into , initiating organic Graduate Student, Columbia Astronomy chemistry and the synthesis of complex organic species. We are currently constructing a novel A Search for Wide Double White Dwarfs in merged beams laboratory instrument to study SDSS interactions of neutral atomic C with molecular Wide binaries are typically found by match- ions, with initial investigations focusing on ing the proper motion of stars. I will explain the reaction C + H+ –> CH+ + H . As 3 2 how we have used this technique with SDSS H+ is ubiquitous in both diffuse and dense 3 data to find 81 wide double white dwarfs, more molecular clouds, this reaction is one of the first than tripling the known number of such binaries. steps towards organic chemistry yet presents a significant challenge to measure experimentally. Jason Koglin Erika Hamden Research Scientist, Columbia Astronomy Graduate Student, Columbia Astronomy First results from the ground calibration of the NuSTAR flight optics I will briefly describe a project that aims NuSTAR is a hard X-ray satellite experiment to look for and model the FUV signatures of to be launched in February 2012. Two optics diffuse galactic objects. This project uses the with 10.15 m focal length focus X-rays with GALEX AIS survey in combination with the 100 energies between 5 and 80 keV onto CdZnTe micron dust maps from Schlegel, Finkbeiner, detectors located at the end of a deployable Davis (1998) and surveys of diffuse clouds in the mast. The FM1 and FM2 flight optics were . built and calibrated at Columbia’s Nevis Lab- oratory. We describe initial results from the Jacqueline van Gorkom ground calibration performed at the 163 m long Professor, Columbia Astronomy RaMCaF calibration facility that was custom built for this purpose at Columbia. An EVLA HI Deep Field

Why? Jia Liu Graduate Student, Columbia Astronomy Destry Saul Graduate Student, Columbia Astronomy Search for Super Massive Black Hole Binaries

Pigs in Space (An Update) Aiming to find super massive black hole binaries (BHBs), we did follow-up optical spec- Our search for ultra-compact neutral hydro- trography(using MDM 2.4 meter telescope) of gen clouds near the Galaxy was a success with 21 quasars which showed displaced broad lines over 2000 clouds identified. I will highlight in SDSS spectra. We fitted multiple Gaussians our results and explain how we are separating to the line profile(centering at narrow H-beta the clouds into different populations based on line) and compared MDM and SDSS spectra, observed properties. and found: i) 2 potential BHBs candidates showing binary AGNs signals; ii) 5 objects with Doug Brenner no change(BHBs with long period? Recoiling BH?); and iii) 9 quasars showing comoving Research Scientist, AMNH peaks implying single AGN scenario. The rest Astronomical Entomology or Daddy: ’Why is showed changes but we could not identify them the Sky Blue’ as BHBs. We also test a simple Keplerian BHBs model for 3 long-term monitored objects and In an attempt to entrap a first year student, I rejected 2 of the quasars(3C 390.3, Mrk 668) as will make some upcoming observations at SALT BHBs, and found minimum period of 51 yr for seem like the best thing since ham on rye. 3C 227’s orbit.

Manel Errando 2nd session: 10:35-11:25 Post-doc, Columbia Physics Jeff Andrews The VERITAS gamma-ray observatory VERITAS is an array of four imaging at- are there signatures of the binary in the electro- mospheric Cherenkov telescopes located at the magnetic spectrum? We run hydro-dynamical Fred Lawrence Whipple Observatory (FLWO) simulations of a thin circum-binary gaseous disk in southern Arizona, sensitive to very high to determine this. energy gamma-rays of energies from 100 GeV to 30 TeV. We will describe the research activities of the VERITAS group at Columbia University Kyle Parfrey and Barnard College, which includes studies Graduate Student, Columbia Astronomy of very high energy gamma-ray emission from blazars, pulsars and pulsar wind nebulae, with Magnetospheric reconnection driven by stellar a close synergy with Fermi-LAT. surface twisting

A neutron star’s magnetosphere can be Güneş Şentürk deformed by differential motion of its crust, into Graduate Student, Columbia Physics which the field lines are frozen. Using numerical simulations, we show that this deformation VERITAS Observations of Unidentified can lead to large-scale magnetic reconnection, GeV-Bright FERMI-LAT Targets accompanied by dramatic anti-glitches in the spin-down power. We selected TeV gammaray source candi- dates among unidentified targets from Fermi 1year catalog. We observed these sources with Josh Schroeder VERITAS and had no detection. I will describe Graduate Student, Columbia Astronomy our selection criteria, give VERITAS and MDM results and discuss possible explanations of our A New Way For Stars To Die: Eaten Alive and nondetection. Spit Out.

Is the end-product of stellar evolution either Jennifer Weston a white dwarf, neutron star, and black hole? Graduate Student, Columbia Astronomy Or can stars die in other ways? Can a vicious Observing Iron in Neutron Star Atmospheres neighbor act in nefarious ways to cause a death by wind ablation? I will show evidence that this The densities and pressures in the atmo- such a bizarre scenario may be happening and spheres of neutron stars is considerably higher happening quite frequently to boot! than those in standard stellar atmospheric models. The effect of pressure broadening on iron lines in the resulting spectra should be significant, perhaps even observable within 3rd Session: 11:40-12:30 the next few generations of X-ray telescopes. Detailed understandings of these atomic absorp- Cameron Hummels tion features could provide us with a method to Graduate Student, Columbia Astronomy measure rotation speeds, gravitational accelera- The Search for Flat Rotation Curves tion, and composition of the surface of neutron stars. But exactly what do we need to take into Hydrodynamic computer simulations of galax- account when we look at these features, and can ies in a larger cosmological environment almost we rely on them? all suffer from the angular momentum problem, an unrealistic buildup of material in their cores. Dan D’Orazio There are ways to avoid this spurious build up, Graduate Student, Columbia Astronomy but almost all of them are artificial. Come see what seems to work, and what seems to not, as Accretion onto Supermassive Black Hole well as the future directions for fixing this issue. Binaries?

The coalescence of super-massive black hole Ximena Fernández binaries (SMBHB) may be the loudest source Graduate Student, Columbia Astronomy of gravitational radiation in the universe. We consider SMBHB’s within the astrophysical The Origin and Distribution of Cold Gas in the context of a gas filled galactic nucleus, and ask: Halo of a -sized Galaxy We use a high-resolution simulation to study between gas content and star formation rate the cold gas in the halo of a Milky Way-sized change with stellar mass. We also discuss a galaxy. HI observations of the Milky Way sample of gas-rich . and other nearby spirals have revealed the presence of such gas in the form of clouds and other extended structures, which could be Hugh Crowl evidence for on-going accretion. I will discuss Post-doc, Columbia Astronomy the distribution of the gas at z=0, compare it Color Changing Galaxies in the Virgo Cluster with observations, and comment on its origin. I will show results from a study combining Jana Grcevich SDSS data with data from the VIVA HI study Graduate Student, Columbia Astronomy of the nearby Virgo Cluster. Broadly, it ap- pears that the global colors of spiral galaxies is dictated by the overall HI content. More We do not have a complete census of Local interestingly, it seems that gas stripped from Group dwarf galaxies. I have identified possible relatively far out in the galaxies affects the unknown gaseous Local Group dwarf galaxies overall broadband color. I will also describe via their HI content, a method with compli- constraints on the timescale over which the mentary observational biases to those of optical color transformation takes place. searches. Dwarf candidates are identified by examining a catalog of compact, isolated neutral clouds in the Galactic Arecibo L-band Joo Heon Yoon Feed Array (GALFA-HI) survey Graduate Student, Columbia Astronomy

Ryan Joung Warm IGM in the Virgo Cluster is first studied Post-doc, Columbia Astronomy by Lya absorbers toward background quasars. Overall distribution of warm gas in the Virgo Gas Condensation in the Cluster will be presented. There have been debates about whether or not the hot halo gas of spiral galaxies like the Yuan Li Milky Way can simultaneously cool out and Graduate Student, Columbia Astronomy accrete onto their disks. We examine, using adaptive mesh refinement (AMR) hydrodynamic Simulating the Cooling Flow of Cool-Core simulations of vertically stratified hot halo gas, Clusters the conditions under which clouds can form and condense out of the hot halo medium to We carry out high-resolution adaptive mesh potentially fuel star formation in the gaseous refinement simulation of a cool core cluster, disk. resolving the flow from Mpc scales down to pc scales. We do not (yet) include any heating, focusing instead on the development of the Jenna Lemonias cooling instabilities in order to understand how Graduate Student, Columbia Astronomy gas gets to the supermassive black hole (SMBH) Gas content and star formation in massive at the center of the cluster. We find that, galaxies as the gas cools, the cluster develops a very flat temperature profile, undergoing a global I will present results of the GALEX Arecibo cooling instability only in the central 100 pc of SDSS Survey (GASS), an HI survey of massive the cluster. Outside of this region, the flow is galaxies currently ongoing at Arecibo. When smooth, with no local cooling instabilities, and completed, GASS will produce a statistically naturally produces very little low-temperature representative sample of 1000 massive (M∗ > gas (below a few keV), in agreement with 10 10 M ) local (0.025 < z < 0.05) galaxies with observations. The gas cools and condenses in homogeneously measured HI masses, stellar the very center of the cluster, rapidly forming a masses, and star formation rates. This sample thin accretion disk. Isotropic heat conduction allows us to investigate the interplay between does not affect the result, but we show that it these three quantities. We have constructed is very sensitive to resolution, requiring very bivariate HI mass and star formation rate distri- high mass resolution to correctly reproduce the bution functions that show how the relationship small transition radius. The amount of cold gas produced at the very center grows rapidly Arlin Crotts until a reasonable estimate of the resulting Professor, Columbia Astronomy AGN heating rate (assuming even a moderate accretion efficiency) overwhelms cooling. We Supernova 1987A - The Once and Future Fire argue that this naturally produces a thermostat Supernova 1987A was the nearest supernova which links the cooling of gas out to 100 kpc explosion seen in more than 300 years. It has with the cold gas accretion in the central 100 produced a long line of first time realizations, pc, potentially closing the loop between cooling and is in the process of a new one: the first and heating. supernova remnant seen forming in great detail. Crotts is a member of a consortium to follow the Munier Salem evolution of SNR 1987A. (Several members of this consortium can be seen frequenting the halls Graduate Student, Columbia Astronomy of Pupin.) We will present recent developments Simulating Galactic Cosmic Rays with Enzo of the brightening of the structure that preceded the explosion as it is now being impacted Simulations of quiescent disk galaxies reveal and destroyed by the ejecta from the explo- that thermal pressure support alone cannot sion, and is growing into a hard radiation source. prevent cold gas in the disk from fragment- ing. We modified enzo — an adaptive mesh refinement, grid-based, hydrodynamic code — Mary Putman to include a two-fluid approach to modeling Professor, Columbia Astronomy the interaction between ultra-relativistic cosmic Star Puffs rays and thermal gas. Working with a Milky Way-style quiescent gaseous disk, we found What causes the evolution of a star to result substantial evidence that physically realistic in a puff of neutral hydrogen? What role does levels of pressure can significantly this gas play in fueling a galaxy’s star forma- suppress fragmentation in the disk. tion? New HI observations show correlations between discrete HI clouds and variable AGB stars that impact our understanding of both Lunch and Poster Session: stellar and galaxy evolution. 12:30-1:30 Emily Bowsher The poster titles and participants are listed Visiting Research Assistant, Columbia in the back of this program. Astronomy Component Spectral Types of Brown Dwarf Binaries from Combined-Light and 4th session: 1:30-2:15 Resolved Photometry Jeno Sokoloski Brown dwarf binaries are predominantly Research Scientist, Columbia Astronomy tightly-bound systems, generally resolved through high-resolution imaging. While re- The Kepler Satellite’s View of an Accretion solved photometry allows some characterization Disk of the components of these systems, resolved Gray Kanarek spectroscopy is necessary to study their atmo- spheres in detail. However, such data has been Graduate Student, Columbia Astronomy difficult to obtain due to the tightly-bound A Deep NIR Survey for Galactic WR Stars nature of brown dwarf binaries. Here we present an alternative method of extracting compo- A massive NIR survey for WR stars in the nent spectroscopic information, through the has already contributed 25% of application of a constrained spectral template the currently known Milky Way WR stars. By matching technique. We compare combined- applying a new method of image subtraction to light near-infrared spectra of 19 brown dwarf the same images, along with MIR and NIR color binaries to binary templates drawn from the cuts to improve candidate selection, 40 new SpeX Prism Spectral Libraries, with each Galactic WR stars were discovered this summer template constrained by at least three relative magnitude measurements. For these, we infer the component spectral types and relative JHK of the galactic halo. Future work will focus magnitudes of the binaries. on explicitly including ionization heating and self-gravity of the gas. Or Graur Graduate Student, Tel Aviv University 5th Session: 2:30-3:15 Identifying the Progenitors of Type Ia Supernovae through their Delay-Time Michael Way Distribution Professor, Hunter College/NASA - Goddard/Ames I have recently finished a supernova survey in the Subaru Deep Field, in which we’ve Characterizing 3-D Structure in the Sloan discovered some of the oldest supernovae ever Digital Sky Survey observed. I’m currently part of CLASH, a Using a volume limited slice of the Sloan Dig- 3-year galaxy-cluster survey with HST, during ital Sky Survey we have built three multi-scale which we’ll be looking for even older supernovae. (not just "large-scale") structure catalogs based on three algorithms. The first algorithm is a Marcel Agüeros simple Kernel Density Estimator. The second Professor, Columbia Astronomy and third algorithms rely on an initial Voronoi Tesselation of the data, but then combine the ARAR: An Update Voronoi cells in two unique ways never before used: Bayesian Blocks and Self-Organizing I said it once, I’ll say it again: surprisingly Maps. I will briefly describe the data sets and little is known about the evolution of stellar mention some projects that may be possible rotation and activity in Sun-like stars after they with this unique catalog, although any addi- reach the age of the Hyades, or roughly 0.5 tional ideas will be very welcome. Gyr. We’ve been busy trying to rectify this situation in order to close in on a well- calibrated age-rotation-activity relation (ARAR)... and I Lam Hui will provide a whirlwind tour of our work on Professor, Columbia Physics Praesepe, NGC 752, Alpha Persei, the Pleiades, Astronomical Tests of Gravity and M37. I will discuss some ideas on how to test gravity using red giants and cepheids. Mordecai Mac Low Adjunct Professor, AMNH Xiuyuan Yang Structure of the Diffuse Graduate Student, Columbia Physics Ultraviolet radiation and supernova explo- Impact of Baryons on the Cosmological sions dominate the structure of the diffuse Information in Weak Lensing Peaks interstellar medium. Comparison of obser- vations in X-ray and H-alpha to numerical Recent studies have shown that the number of models using the adaptive mesh refinement code peaks in weak lensing (WL) maps, obtained from Flash revealed notable points of agreement, but large forthcoming surveys such as LSST, will also some discrepancies. X-ray observations contain useful cosmological information. The with XMM of the galactic halo agree in their number of peaks as a function of their height, in surface brightness with the models, but have particular, complements more traditional statis- cooler temperatures. H-alpha observations tics, such as the WL power spectrum, and will with WHAM agree in the peak of the emission tighten constraints on cosmological parameters. measure distribution, but have a narrower width These conclusions were derived from N-body than the models (fewer very low or very high simulations that neglect changes in the lensing emission measure lines of sight). To address potential due to the presence of baryons. Here these discrepancies, we have redone the models we model the effect of baryons, by modifying the including magnetic fields and an extended profiles in ray-tracing N-body domain. Surprisingly, the extended domain simulations by hand, mimicking the cooling and appears to be the more important of these condensation of baryons and star-formation in changes, revealing the very dynamical nature halos. This allows us to study (i) the impact of baryons on the WL peak counts, and (ii) be identifiable via these alternative channels. to asses how much the inferred cosmological Here we explore the reach of current and parameters would be biased if the data were fit planned experiments to address this question. ignoring the baryons. We derive constraints on the rate of GW and HEN bursts per Milky Way equivalent (MWE) galaxy based on independent observations by Matt Turk the initial LIGO and Virgo GW detectors and Post-doc, Columbia Astronomy the partially completed IceCube (40-string) HEN detector. We take into account the Next Generation Simulations of the First Stars blue-luminosity-weighted distribution of nearby in the Universe galaxies, assuming that source distribution Ideas about how the first stars in the universe follows the blue-luminosity distribution. We formed are currently undergoing a transition; then estimate the reach of joint GW+HEN while previous generations of studies have searches using advanced GW detectors and 3 suggested that they formed in isolation and the completed km IceCube detector to probe were massive, recent indications have been that the joint parameter space. We show that the these stars in fact formed in pairs, groups or combination of individual and joint GW+HEN even clusters. I will describe current efforts searches undertaken by advanced detectors will designed to leverage next generation computing already be capable of detecting, constraining or techniques and computational algorithms to excluding, several existing models with one year push forward our understanding of these how of contemporaneous observations. these metal-free stars formed, lived, died and enriched their surroundings. Zoltan Haiman Professor, Columbia Astronomy Ken Miller Forming Billion-Solar-Mass Black Holes in the Post-doc, Columbia Astronomy Early Universe

Forming the first stars: Laboratory studies of The supermassive black holes (SMBHs) the H2 chemistry that led there that are believed to power the bright quasars observed at the highest redshifts (z > 6) have Cooling by H2 molecules led to the formation 9 masses of & few×10 M . How these SMBHs of the first stars. A key reaction forming H2 formed so rapidly, within < 1 Gyr after the during this epoch is the associative detachment , is a challenging unsolved problem in − − reaction H + H –> H2 + e . Uncertainties in cosmology. I will discuss a possible solution, in this reaction have hindered our understanding 8 which the gas collapsing into a ∼ 10 M proto- the formation of structure during this epoch. galaxy at redshift z ∼ 10 remains "warm", avoids We have performed the first energy-resolved 5 fragmenting, and rapidly forms a ∼ 10 M measurement of this AD reaction. Here we BH. Such a heavy seed BH can then (hope- report our results and discuss the cosmological 9 fully) grow leisurely into a ∼ 10 M by z ∼ 6−7. implications of our findings.

Colin McNally Imre Bartos Graduate Student, Columbia Astronomy Graduate Student, Columbia Physics Getting Pedantic about Verification of Observational Constraints on Multi-messenger Numerical Methods for Kelvin-Helmholtz Sources of Gravitational Waves and Instability High-energy Neutrinos During our work on Phurbas (an adaptive It remains an open question to what extent Lagrangian meshless method for magnetohydro- many of the astronomical sources of intense dynamics) we have needed to verify the results bursts of electromagnetic radiation are also of a Kelvin-Helmholtz instability test. The be- strong emitters of non-photon messengers, haviour of both grid codes and Smooth Particle in particular gravitational waves (GWs) and Hydrodynamics has been questioned on this high-energy neutrinos (HENs). Such emission class of problem, which has been of particular would provide unique insights into the physics interest to the cosmology and galaxy formation of the bursts; moreover some suspected classes, communities. One of the major complicating e.g. choked gamma-ray bursts, may in fact only factors has been shortcomings in the design and analysis of tests in the literature. We show We show some preliminary results and indicate how this can be remedied, and present results where this could be used in the future. from a few types of code. In particular this careful testing highlights the poor convergence behaviour of Smooth Particle Hydrodynamics Sebastien Lepine in the subsonic regime. Research Scientist, AMNH Finding planets around nearby stars through microlensing? 6th session: 3:30-4:15 The nearby, high-proper motion star VB 10 will move within just 50 milliarcsecond of Ben Oppenheimer a background star in December of this year. Associated Curator and Professor, AMNH Calculations show that the "encounter" will produce a microlensing event, but it will be too Mike Hahn small to be detected. However, if VB 10 hosts a Post-doc, Columbia Astronomy Jupiter-mass planet on a moderately wide orbit, that planet could produce a high-magnification Observational Evidence for Wave Damping in event, detectable with intensive photometric the Solar Corona at Low Heights monitoring on a 1-meter class telescope.

Non-thermal broadening of spectral lines is believed to be a signature of Alfven waves Michael Allison propagating through the solar corona. This Adjunct Professor, NASA - GISS broadening is proportional to the amplitude Juno and the Search for Primordial – of the waves. For undamped waves, energy New Thoughts Toward a Solar Enriched But conservation implies that the amplitude should Low Relative Humidity Mix of Condensibles in increase with height as the plasma density Jupiter’s Deep Atmosphere decreases. However, our observations show that spectral line widths begin to decrease at heights On August 5, 2011 at 12:25 am EDT, an Atlas below where wave damping is theoretically V thundered into the sky above Cape Canaveral, predicted. This could indicate that Alfven launching Juno toward its multi-orbit tour of waves are damped by transferring energy to Jupiter, to begin in 2016. Our primary objective the solar wind at lower heights than shown by – the measurement of the giant planet’s global current models. water abundance. The on board MWR (a five channel, 1 – 20cm microwave radiometer) has already seen first light and is working perfectly. Andreas Svedin Now the science team has only five years to pre- Graduate Student, Columbia Astronomy pare to interpret pole-to-pole maps of brightness emission originating more than 100km below The hidden variable problem Jupiter’s cloud tops. Among the outstanding What do you do if you have a 3D simulation questions: Why are infrared and Galileo probe of the solar surface and your observation is only measurements of the jovian water abundance a 2D satellite picture and you want to estimate apparently so depleted with respect to the solar the state at all depths. What if you have a solar mixture? Why do VLA measurements show cycle or dynamo model in several statistically an upper tropospheric depletion, but a deeper uncorrelated variables and you only have the super-solar enrichment and differentiation of scalar Sun Spot Number record to constrain below its saturation level? How is your model. Both these are example of the this reminiscent of terrestrial moist convection? hidden variable problem of data assimilation; And why is this so important to both the what to do with the things we have not directly planetary meteorology and the history of the observed. Going beyond the normal paradigm Solar System? Please stand by for a few new of correlation and looking at dynamical consis- thoughts on all this and more! tency we have explored a way to obtain these hidden states, something that appears to be Brandon Horn impossible. The limit, as always, is quality of Graduate Student, Columbia Astronomy our models. This approach can also help us to estimate where our model breaks down, instead Orbital Migration of interacting Planets in of assuming the model error properties upfront. Evolutionary Radiative Turbulent Models Non-isothermal disks have been shown to (relative to Earth), however, points to initial have regions where the net torque on a planet accretion chemistry. Sulfur enrichment may is positive, leading to outward migration of the have resulted from highly reduced accretion planet. When a region with negative torque is conditions, consistent with disk mid-plane directly exterior to this, planets in the inner enrichment in C-rich interplanetary dust, as region migrate outwards and planets in the modeled by Ebel and Alexander (in press). outer region migrate inwards, converging where Observed correlations of Mg/Si and Ca/Si with the torque is zero. We incorporate the torques S/Si may be due to the stability of Mg and Ca from an evolving non-isothermal disk into an sulfides in a reducing mantle. MESSENGER’s N-body simulation, and find that the bodies do orbital geochemical, geological, geophysical, converge to the zero torque region, but effects plasma science, and other results constitute a of neighboring planets prevent the planets diverse set of observations demanding explana- from merging. Though N-body interactions tion. prevent complete merging to form one core, the addition of a weak stochastic force to simulate turbulence in the disk allows for orbit crossings Emily Rice and mergers near the convergence zone. In this Post-doc, AMNH way, it is possible to move from the sub-Earth Young Brown Dwarfs as Analogs mass regime into the 10 Earth mass planetary core regime in 2-3 million years. In the quest to understand the physical properties of late-M and early-L type objects (the lowest mass stars and relatively massive Denton Ebel brown dwarfs), many objects with unusual Curator, AMNH spectral features are yet to be explained. One MESSENGER at Mercury: Implications for class of these objects are thought to be young Planet Formation Hypotheses and their spectral features the result of low surface gravity. Because brown dwarfs cool, The MErcury Surface, Space ENvironment, fade, and shrink with time, they will be hotter, GEochemistry, and Ranging (MESSENGER) brighter, and more inflated than objects of the mission has characterized the abundances of same mass at an older ages. The same evolution major elements and the ratios K/Th and K/U in occurs for gas giant planets, and indeed the surface rocks. One of the goals of the MESSEN- physical properties of and brown GER mission has been to test, by measurement dwarfs can overlap at different evolutionary of surface composition, hypotheses advanced to stages. Therefore young brown dwarfs can be account for Mercury’s anomalously large core crucial tools for understanding the atmospheres mass fraction ( 65%) compared to those for of gas giant exoplanets. I will describe two Earth and Venus ( 30%). One set of hypothe- young brown dwarfs we have recently confirmed ses requires primary chemical or mechanical and characterized and explain how they will fractionation of metal and silicates in the high- advance our understanding of directly-imaged temperature inner annulus of the solar system’s exoplanets. nebular disk where Mercury accreted. Another hypothesis calls for the catastrophic loss of the earliest crust and a substantial fraction of the mantle in a high-velocity impact by a planetary- 7th session: 4:30-5:15 embryo-sized body of unknown composition. MESSENGER’s Gamma-Ray Spectrometer Greg Bryan and X-Ray Spectrometer, respectively, indicate Professor, Columbia Astronomy terrestrial K/Th abundance ratios and high The Baryonic Content of Dwarf Galaxies S/Si ratios. Mercury is thus richer in volatiles than expected for some models, and may have I briefly review the evidence that galaxies are a higher bulk S/Si ratio than Earth. Models missing a substantial fraction of their baryonic for crust and mantle removal do not necessarily mass, focusing particularly on dwarfs. Possible result in volatile depletion in what remains solutions will be discussed and critiqued. I will of the target body; the proposed catastrophic argue that it is difficult to hide much mass impact model for Mercury is less fractionating in a hot, ionized halo around a . of volatiles than the Moon’s likely origin via In addition, although it is generally thought accretion within a volatile-depleted disk of to be easy to eject mass from dwarf systems ejected material. Enrichment of S in Mercury because of their relatively shallow potential well, I will use detailed simulations to show that stars). In this study, we show that the apparent supernovae driven winds have a great deal of contradiction in neutron-capture distributions difficulty in actually doing this. could be explained as the under-sampling of intrinsically-skewed distributions in UFDs. We emphasize that the UFD’s distributions can Kerstin Perez be achieved by simply appealing to stochastic Post-doc, Columbia Astrophysics Laboratory pollution by star clusters that are systemati- cally smaller than those in MW progenitors. The General Antiparticle Spectrometer Hence, there is no need to invoke other complex (GAPS) experiment aims to detect low-energy effects such as primordial abundance signatures, antideuterons that result from dark matter blowout of metals, and/or incomplete mixing. interactions in the galactic halo. This signa- ture, which has essentially zero conventional Lauren Corlies astrophysical background, is predicted by many Graduate Student, Columbia Astronomy models of both supersymmetry and extra- dimensional theories. I will report on the status of the prototype GAPS (pGAPS) balloon exper- Recent observations have revealed that abun- iment, scheduled to launch in spring 2012, which dance differences exist between low metallicity will test many key aspects of the detector design. stars in the Milky Way stellar halo and those in the ultrafaint dwarf galaxies. We take a first look at what role the early environment Maureen Teyssier might have played in in shaping these stellar Graduate Student, Columbia Astronomy populations. I’ll briefly discuss the analytic model of supernova-driven winds that was used Intergalactic Light and the Local Group and present the results. In general, we find Environment that main halo progenitors cross-pollute each other more effectively whereas dwarf galaxy With the advent of repeated all-sky pho- progenitors remain more isolated. Thus, inho- tometric surveys, such as PTF, we should be mogeneous cross-pollution can reasonably be able to find intergalactic supernovae outside appealed to as part of an explanation for these of galaxy clusters. But do we expect this observed differences. population to exist? Predictions for such a population are made through analysis of the Via Lactea II Simulation. Our analysis suggests an Gurtina Besla intergalactic population of wandering stars on Post-doc, Columbia Astronomy 8 the order of 10 M to exist beyond the virial radius of a Milky-Way size dark matter halo — The Importance of Dwarf-Dwarf Galaxy suggesting 0.1% of SNIA could be hostless. This Interactions population is created via dynamical interactions Broadly my research interests focus on the in dark matter halos. evolution of dwarf galaxies in various environ- ments. More specifically, I aim to quantify Duane Lee the relative importance of interactions between dwarf galaxies to their morphological and Graduate Student, Columbia Astronomy kinematic evolution, versus interactions with A Mass-Dependent Yield Origin of massive hosts. In this short talk I’ll show Neutron-Capture Distributions in Ultra-Faint some illustrative examples of interacting dwarfs Dwarfs and comment on their relevance to questions about how dwarf galaxies lose their baryons Chemical abundance data exhibit remarkable and the evolutionary connection between dwarf agreement between the distributions of [α/Fe] irregulars and dwarf spheroidal galaxies. ([(Ti, Ca, Mg)/Fe]) abundance ratios found in stars located in the Milky Way (MW) Halo and ultra-faint dwarf (UFD) galaxies. However, Allyson Sheffield when contrasting the neutron-capture distri- Post-doc, Columbia Astronomy butions [(Sr, Ba)/Fe], the peak of the small Disk Stars in the Halo UFD sample (∼ 20 stars) reveals a statistically- significant negative offset in abundance ratios Where did stars in the halo originate? The when compared to the large MW sample (∼ 1000 detection of stellar streams wrapping around the outer realms of the Galaxy provides smoking- gun evidence that accretion has played an important role in the formation of the halo. However, the possibility also exists that some stars in the halo could have formed in the Galactic disk and subsequently been kicked onto more eccentric and more inclined orbits – rendering these stars members of the inner halo. I will present results from recent work using the chemodynamics of M giants aimed at studying the and nearby halo, and discuss the implications for understanding the origin of stars in the nearby halo.

Christine Simpson Graduate Student, Columbia Astronomy Physics of Dwarf Galaxy Formation

Our standard model of the universe (lamb- daCDM) predicts many more satellite dwarf ha- los around the Milky Way and within the Local Group than we see. The dwarfs we do see ex- hibit many unusual properties and trends such as extreme mass to light ratios and a common mass scale. We have conducted a series of high- resolution, hydrodynamical simulations of a sin- gle cosmological dwarf halo. We have varied the physical prescriptions for reionization and super- nova feedback to understand their relative effects on star formation and gas evolution within the halo. I will describe the results of these simula- tions and their implications for our understand- ing of dwarf galaxies and how they form. Undergraduate Poster Session

Vivienne Baldassare Hunter College Studying Star Formation and AGN Activity in Ultraluminous Infrared Galaxies at z > 1.15

Daniel Feldman CUNY College of Staten Island, Searching for Faint Kuiper Belt Objects in HST Archival Data

Adam Greenberg Columbia University Properties of the Low Density Gas in the Outer Reaches of the NGC 5044

Sam Grunblatt Columbia University Time Resolved Spectroscopy of Bright Bursts from the Soft Gamma Repeater SGR J1550-5418

Kay Hiranaka Hunter College Application of Mie Theory to L Dwarf Spectra

Daniel Horenstein Columbia University Finding the First Stars

Alejandro Núñez Hunter College Application of Stellar Flare Model to Solar Flares

Bryan Terrazas Columbia University Analyzing Data from the Large Hadron Collider (LHC)