KICP Seminars & Colloquia, Fall 2007

Seminar schedule for Fall 2007
September 26, 2007
Wednesday colloquium
William Wester
GammeV - a gamma to milli-eV particle search   [Abstract]
September 28, 2007
Friday noon seminar
Grant Wilson
University of Massachusetts
Millimeter Wavelength Exploration of Submillimeter Galaxies   [Abstract]
October 3, 2007
Astronomy Colloquium
David Weinberg
Ohio State University
Dark Matter and Galaxies   [Abstract]
October 5, 2007
Friday noon seminar
Shirley Ho
Princeton University
What can we do with CMB as a backlight?   [Abstract]
October 10, 2007
Wednesday colloquium
Graham Smith
University of Birmingham
Early Results from the Local Cluster Substructure Survey (LoCuSS)   [Abstract]
October 12, 2007
Friday noon seminar
Michael Kesden
Canadian Institute for Theoretical Astrophysics (CITA)
Testing Dark Matter Forces with Tidal Streams   [Abstract]
October 17, 2007
Astronomy Colloquium
Henk Hoekstra
University of Victoria
Weak Lensing by Large Scale Structure   [Abstract]
October 18, 2007
Astronomy Special Seminar
Ron Wilhelm
Texas Tech
Using RR Lyrae Variable Stars to Probe the Kinematic Signature of the Sagittarius Stream   [Abstract]
October 19, 2007
Friday noon seminar
Kai G Noeske
Harvard-Smithsonian Center for Astrophysics
A New Picture of Star Formation in Field Galaxies since z~1   [Abstract]
October 24, 2007
Wednesday colloquium
Richard J Gaitskell
Brown University
Noble Travails: Noble Liquid Detectors Searching for Particle Dark Matter   [Abstract]
October 26, 2007
Friday noon seminar
David A Rapetti
KIPAC (Stanford/SLAC)
Probing dark energy with X-ray galaxy clusters studies   [Abstract]
October 31, 2007
Astronomy Colloquium
Nick Scoville
California Institute of Technology
Large Scale Structures and Galaxy Evolution in the COSMOS Survey   [Abstract]
November 2, 2007
Friday noon seminar
Beth Willman
Harvard-Smithsonian Center for Astrophysics
The Least Luminous Galaxies in the Universe - A Nearby Window to Cosmology   [Abstract]
November 5, 2007
Open Group seminar
Mustafa Amin
Stanford University
A framework for probing gravity and dark energy on cosmological scales   [Abstract]
November 6, 2007
Open Group seminar
Daniel Ceverino
Stellar Feedback and Galaxy Formation   [Abstract]
November 7, 2007
Astronomy Colloquium
Roger Hildebrand
The University of Chicago
Magnetic Fields in Star-Forming Clouds   [Abstract]
November 9, 2007
Friday noon seminar
Brian F. Gerke
KIPAC, Stanford Linear Accelerator Center
High-redshift Galaxy Groups and Clusters in DEEP2 and Beyond   [Abstract]
November 14, 2007
Astronomy Colloquium
Leo Blitz
University of California, Berkeley
Star Formation and Neutral Gas in Normal Galaxies   [Abstract]
November 16, 2007
Friday noon seminar
Brian W O'Shea
Los Alamos National Lab
Population III stars and the formation of the first protogalaxies   [Abstract]
November 28, 2007
Open Group seminar
Alessandra Silvestri
Syracuse University
Scale-dependent Growth of Structure in Modified Gravity   [Abstract]
November 28, 2007
Wednesday colloquium
Andrea Pocar
Stanford University
The Enriched Xenon Observatory for Double Beta Decay   [Abstract]
November 30, 2007
Friday noon seminar
Katherine J Mack
Princeton University
Constraining early universe relics with radio astronomy   [Abstract]
December 10, 2007
Open Group seminar
Michael D Schneider
UC Davis
Improved statistics for obtaining cosmological parameter constraints from the nonlinear matter powe rspectrum   [Abstract]
December 12, 2007
Wednesday colloquium
Dan Hooper
Hot on the trail of particle dark matter   [Abstract]

  • September 26, 2007 | 3:30 PM | RI 480 | Wednesday colloquium
    GammeV - a gamma to milli-eV particle search
    William Wester, Fermilab

    The GammeV experiment uses a high-power laser and an accelerator magnet for photons to potentially oscillate into new milli-eV mass astroparticles. I will describe how I spent my Summer vacation to set interesting limits for these new class of particles.
  • October 3, 2007 | 3:30 PM | RI 480 | Astronomy Colloquium
    Dark Matter and Galaxies
    David Weinberg, Ohio State University

    I will discuss various aspects of the relation between galaxies and dark matter and more general issues in the theory of galaxy formation, including: disk galaxy scaling relations and the fraction of baryons in galaxies, the relation between satellite galaxies and dark matter substructures, the universality of the relation between central galaxies and dark matter halos,the relative accretion/merger rates of central and satellite galaxies, and the origin of bimodality in the galaxy color distribution and the shape of the galaxy luminosity function. While recent theoretical and observational developments have shed light on many of these issues, many puzzles remain.
  • October 10, 2007 | 3:30 PM | RI 480 | Wednesday colloquium
    Early Results from the Local Cluster Substructure Survey (LoCuSS)
    Graham Smith, University of Birmingham

    Gravitational lensing has long been recognized as a powerful tool for mapping the distribution of dark matter in clusters, and yet until recently, it has only been applied routinely to individual clusters. I will show that recent results are changing this picture; both strong and weak lensing are developing rapidly into tools that can routinely be applied to samples rivaling, for example, those considered by X-ray-only scaling relation studies. I will introduce a new survey, the Local Cluster Substructure Survey (LoCuSS) that is assembling a sample of ~100 clusters with HST, Subaru, Chandra, XMM, SZE and Spitzer data. The overall goal is to study how the recent assembly history of the clusters (as revealed by lensing-based mass maps) influences the baryons trapped in the clusters. After outlining the results that motivated the survey (e.g.structural segregation in the mass-temperature plane), I will present new LoCuSS results on the mass-observable scaling relations and the relationship between cluster merger history and the propoerties and thus evolution of brightest cluster galaxies.
  • October 17, 2007 | 3:30 PM | LASR | Astronomy Colloquium
    Weak Lensing by Large Scale Structure
    Henk Hoekstra, University of Victoria

    Intervening structures in the universe give rise to small distortions in the shapes of distant galaxies. By measuring this tiny coherent signal, we can study the mass distribution in the universe directly, without relying on baryonic tracers. This makes weak lensing by large-scale structures a powerful probe of cosmology. I will review the topic of "cosmic shear" and discuss how the signal is extracted from the data. I will present results from recent surveys, most notably the CFHT Legacy Survey. Finally I will discuss what will be required to significantly improve constraints on the properties of dark energy.
  • October 24, 2007 | 3:30 PM | RI 480 | Wednesday colloquium
    Noble Travails: Noble Liquid Detectors Searching for Particle Dark Matter
    Richard J Gaitskell, Brown University

    Particle dark matter is thought to be the overwhelming majority of the matter in the Universe, dwarfing the contribution from conventional material that we, the earth and the stars, are composed of. However, we still have no direct evidence for the existence of particle dark matter. This may soon change...

    I will report on the latest results from the XENON10 liquid xenon- based detector which began searching for particle dark matter at Gran Sasso in late 2006 ( The experiment has demonstrated ( a world class direct search sensitivity which is a factor 4 better than its current nearest rival (CDMS II). I will discuss some of the details of this experiment.

    I will also discuss some of the other noble liquid target experiments that are also providing competitive sensitivities in the race for the direct detection of particle dark matter. Theoretical estimates, based on supersymmetric models predict dark matter interaction rates from the best sensitivity of existing direct detection experiments of
    ~1 evts/kg/month, down to rates of ~1 evts/100 kg/yr, and below this.
    Current and future noble liquid experiments for dark matter searches, range in scale from 10's kg to tonnes, and are designed to rise to this challenge. The new liquid xenon detector, LUX, which has begun construction, will be 100 times more sensitive than current best search experiments.
  • October 31, 2007 | 3:30 PM | RI 480 | Astronomy Colloquium
    Large Scale Structures and Galaxy Evolution in the COSMOS Survey
    Nick Scoville, California Institute of Technology

    The COSMOS survey is the largest high redshift galaxy evolution survey ever done -- imaging 2 square degrees with all major space-based and ground based observatories. I will describe the key data in the survey and then present recent results on large-scale structures, the dark matter distributions and galaxy evolution.
  • November 7, 2007 | 3:30 PM | RI 480 | Astronomy Colloquium
    Magnetic Fields in Star-Forming Clouds
    Roger Hildebrand, The University of Chicago

    The "strong field" picture of star formation involves a slow drift of neutrals through a magnetic field into the core of a self-gravitating cloud until magnetic support can no longer prevent dynamical collapse. A contrasting "weak field", picture involves support primarily by turbulence with clumps sometimes gaining sufficient mass to become self-gravitating. Attempts to compare observations with theoretical simulations have not been adequate to provide a convincing model.

    I will discus the outlook for measuring relevant properties of the magnetic field such as the angular dispersion, the relative magnitudes of the systematic and turbulent components, and the size of the turbulent eddies.
  • November 14, 2007 | 3:30 PM | RI 480 | Astronomy Colloquium
    Star Formation and Neutral Gas in Normal Galaxies
    Leo Blitz, University of California, Berkeley

    Great strides have been made in galaxy evolution in the last decade through a combination of improved observations, semi-analytic modeling of galaxy evolution, and simulations. Nevertheless, one of the biggest gaps in our knowledge has to do with how stars form on galactic scales. How does the number and distribution of new stars in galaxies get established? How does this change as a function of redshift? What is the role of "feedback," i.e. mass expulsion? How ubiquitous is the IMF? I will take the position that the distribution and state of the interstellar gas is paramount in answering these questions. I will describe several well-known observational facts about the distribution of atomic gas in spiral galaxies that have no agreed upon explanation. We will see that the neutral gas, the atomic plus the molecular, follows an approximate scaling relation. I will discuss the molecular gas depletion time problem in spiral galaxies, and some of the implications for galaxy evolution, and a possible solution. I will show that what determines how the star forming material, the dense molecular gas is formed in galaxies, is hydrostatic pressure, and how this relates to the star formation within them.
  • November 28, 2007 | 3:30 PM | RI 480 | Wednesday colloquium
    The Enriched Xenon Observatory for Double Beta Decay
    Andrea Pocar, Stanford University

    The Enriched Xenon Observatory (EXO) is a project aiming at detecting neutrinoless double beta decays of Xe-136. A xenon-filled time projection chamber (TPC) supplemented with scintillation light readout detects ionising particle interactions within its volume. When candidate events are recorded, the Ba-136 ion daughters will be identified, event by event, by means of optical spectroscopy. This coincidence technique would allow for a measurement of double beta decays virtually immune to external radioactive contaminations. The EXO collaboration is planning on combining these experimental techniques in a ton-scale Xe detector using a phased approach.

    A smaller detector, EXO-200, employing 200 kg of enriched xenon (80% Xe-136) in liquid form within a TPC with scintillation readout and with no Ba identification, is in advanced stage of assembly. Its cryogenic and xenon handling systems are being re-assembled at the Waste Isolation Pilot Plant (WIPP) underground site in New Mexico. The central detector is planned to be installed by early 2008. As a parallel effort to EXO-200, strategies for Ba tagging are being developed in the laboratory.

    I will present the EXO experiment in the context of neutrinoless double beta decay searches and describe the EXO-200 detector in detail, discussing its physics goals, experimental challenges, and schedule. I will also illustrate some of the most promising approaches for tagging single Ba ions produced in a ton-scale Xe detector, show milestone results achieved in laboratory setups, and discuss the EXO timeline for the near future.
  • December 12, 2007 | 3:30 PM | RI 480 | Wednesday colloquium
    Hot on the trail of particle dark matter
    Dan Hooper, Fermilab

    Over seventy years, a body of evidence has steadily grown indicating that much of the Universe's mass is non-luminous. Still today, however, we have not identified what makes up this mysteriously dark substance. Many experimental programs that hope to change this are underway, including deep underground detectors, gamma-ray telescopes, neutrino and anti-matter detectors, as well as particle colliders. Each of these efforts are searching for clues of dark matter's identity. With the new technologies needed to observe these particles rapidly developing, the hunt to discover dark matter's identity is well underway.


  • September 28, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    Millimeter Wavelength Exploration of Submillimeter Galaxies
    Grant Wilson, University of Massachusetts

    Submillimeter galaxies, first detected by the SCUBA instrument in 1998, are thought to be host to some of the most prolific bursts of star formation in the early universe. Notoriously difficult detect at mm-wavelengths and even more difficult to follow-up with other facilities, a comprehensive understanding of this population has remained elusive over the past decade. In this talk I will describe an ongoing program to create and exploit new catalogs of SMGs to provide a new accounting of the star formation history of the early universe. Our work is centered on imaging made with the AzTEC mm-wavelength camera on three telescopes: the JCMT, the ASTE telescope, and the future Large Millimeter Telescope (LMT). I will describe a collection of survey results from the JCMT and ASTE telescopes and conclude with the exciting prospects of first light with AzTEC on the LMT in 2009.
  • October 5, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    What can we do with CMB as a backlight?
    Shirley Ho, Princeton University

    The Cosmic Microwave Background has been providing us with a wealth of information for cosmology. Can we learn more from the CMB apart from its primary anisotropies?

    Here, we are going to present the next frontiers of the CMB: the Integrated Sachs-Wolfe Effect, Weak Lensing of the CMB and Kinetic Sunyaev-Zeldovich effect.

    In order to understand the gravitational potential of the universe, we make use of the ISW effect and weak lensing of CMB via the following
    datasets: WMAP, 2MASS, SDSS photometric LRGs and Quasars and NVSS. We perform a joint analysis of all samples, allowing a reliable covariance matrix to be constructed including all the cross-correlations of different samples, which is necessary for joint cosmological parameter fitting.
    We will present our methodologies, analysis and cosmological results.

    To understand the evolution of electron density of the universe, we utilize the kinetic SZ signature of the CMB. This method is very promising with the upcoming surveys such as SPT. ACT and APEX, as long as we have a galaxy survey such as DES, ADEPT or Panstarrs available.
    We will present our prediction for ACT cross ADEPT correlation and results of the application of this method to the WMAP and SDSS main spectroscopic galaxy sample as a trial example.
  • October 12, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    Testing Dark Matter Forces with Tidal Streams
    Michael Kesden, Canadian Institute for Theoretical Astrophysics (CITA)

    Satellite galaxies can be tidally disrupted as they orbit a more massive host galaxy. If dark matter (DM) experiences a stronger self-attraction than baryons, stars will preferentially gain rather than lose energy during tidal disruption leading to an enhancement in the trailing compared to the leading tidal stream. The Sgr dwarf galaxy, a satellite of our own Milky Way, is seen to have roughly equal streams, challenging models in which DM and baryons accelerate differently by more than 10%. Future observations and a better understanding of DM distribution should allow detection of DM forces only a few percent the strength of gravity.

    BONUS: Binary Black Hole Merger: Symmetry and the Spin Expansion

    We regard binary black hole (BBH) merger as a map from a simple initial state (two well separated Kerr black holes) to a simple final state (a single Kerr black hole with a recoil). By Taylor expanding this map around the spinless case and systematically applying symmetry constraints, we obtain a formalism that is simple, yet remarkably successful at explaining existing BBH simulations.
  • October 19, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    A New Picture of Star Formation in Field Galaxies since z~1
    Kai G Noeske, Harvard-Smithsonian Center for Astrophysics

    The "All Wavelength Extended Groth Strip Survey" (AEGIS) has recently provided a first comprehensive picture of star formation in field galaxies out to z>1.

    (1) Our data showed that star formation histories are a strong function of galaxy mass.
    (2) Star formation evolved predominantly gradually declining, not through an evoloving role of starbursts, placing a tight constraint on the role of major mergers in the evolution of star formation rates.
    (3) The observed mass dependencies of star formation histories imply not only a slower decline, but also a systematically later onset, of star formation in less massive galaxies. These mass dependencies jointly generate the observed "downsizing" phenomena.

    I present a quantitative model that parametrizes the evolution of star formation as a function of mass and redshift. This picture of "normal" star formation provides a testbed for current theoretical concepts of star formation and baryon physics and, for the first time, a baseline against which we can measure the effect of additional processes, quenching or mergers, as a function of galaxy mass and z.
  • October 26, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    Probing dark energy with X-ray galaxy clusters studies
    David A Rapetti, KIPAC (Stanford/SLAC)

    Most of the energy density of the Universe is in the form of dark matter and dark energy, and yet these two components are the most intriguing mysteries in current cosmology. Using two complementary X-ray galaxy clusters studies we present new constraints on the mean matter density of the Universe, dark energy density, normalization of the density fluctuation power spectrum, and dark energy equation of state parameter. First, using Chandra measurements of the X-ray gas mass fraction in 42 hot, X-ray luminous, dynamically relaxed galaxy clusters spanning the redshift range 0.05
  • November 2, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    The Least Luminous Galaxies in the Universe - A Nearby Window to Cosmology
    Beth Willman, Harvard-Smithsonian Center for Astrophysics

    Since 2005, nearly 20 dwarf galaxies have been discovered around the Milky Way and M31 that are 100 times less luminous than any galaxy previously known. These discoveries are changing our understanding of galaxy formation at the lowest luminosities, and are also currently our most direct tracers of the properties of dark matter on small scales. I will present the properties of these new discoveries as a population, such as the spectroscopic observations that appear to confirm their residence within dark matter halos and the imaging that will ultimately reveal their star formation histories. I will also examine the properties of the Willman 1 object in detail to critically assess whether we can functionally distinguish globular clusters from dwarf galaxies at the extremely low luminosities at which future surveys may reveal an abundance of objects. I will discuss the implications of all these results in a cosmological plus galaxy formation context, including resolutions to the 'substructure problem' and predictions for the possible gamma-ray fluxes from annihilating dark matter particles in these tiny galaxies.
  • November 9, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    High-redshift Galaxy Groups and Clusters in DEEP2 and Beyond
    Brian F. Gerke, KIPAC, Stanford Linear Accelerator Center

    Groups and clusters of galaxies, as the largest, most recently formed objects in the universe, carry a great deal of information about the recent history of the cosmos. By studying these systems at a variety of epochs, it is possible to place strong constraints on theories of galaxy formation and on cosmological parameters. With the recent completion of the DEEP2 Galaxy Redshift Survey at z~1, we can now perform detailed studies of galaxy groups and clusters over a wider redshift range than ever before. In this talk I will present evidence that DEEP2 galaxy groups had only recently become suitable environments for shutting off star formation in galaxies. In addition, I will show results suggesting that DEEP2 groups are underluminous in the X-ray band, compared to local systems. I will also discuss an ongoing effort to constrain cosmological parameters by comparing the abundance of groups in DEEP2 to the abundance in the local universe. In particular, I will describe the primary challenges to performing this test reliably, and I will present a realistic plan for overcoming them. Finally, I will briefly mention some important implications of the DEEP2 results for future attempts to constrain cosmology with optical cluster surveys.
  • November 16, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    Population III stars and the formation of the first protogalaxies
    Brian W O'Shea, Los Alamos National Lab

    I use the cosmological adaptive mesh refinement code Enzo to do a suite of high-resolution numerical simulations of Population III protostellar clouds in a cosmological context. These calculations examine the formation of primordial protostellar clouds at a range of redshifts and in differing cosmic "neighborhoods." I find that these cores have a wide variety of accretion rates - varying by over two orders of magnitude - which may have significant implications for the IMF of Population III stars. I then simulate supernovae from the inferred stellar mass range and follow the evolution of the ensuing supernova remnant until the deposition of metal-enriched gas in the next generation of halos, which generally occurs ~50 million years after the original supernova. The dense gas in the core of these "child" halos is typically enriched to metallicities of ~10^-3 solar, which is above the "critical metallicity" at which metal line cooling dominates over molecular cooling, and suggests that the stars in these halos will have a significantly lower mass range than their Population III parents. This metal enrichment is a local phenomenon, and the transition of the universe from primordial to metal-enriched gas will be quite extended.
  • November 30, 2007 | 12:00 PM | LASR Conference Room | Friday noon seminar
    Constraining early universe relics with radio astronomy
    Katherine J Mack, Princeton University

    I will discuss recent work on using future radio astronomy observations to constrain populations of early universe relics. In the first half, I will present a method for constraining the existence of cosmic strings with gravitational lensing surveys. Past radio surveys have already ruled out a portion of the cosmic string parameter space, and future radio telescope arrays such as LOFAR and SKA have the potential to outperform current constraints from pulsar timing and the CMB by up to two orders of magnitude. In the second half, I will discuss the effect of evaporating primordial black holes on the ionization history of the universe, with an emphasis on the limits derivable from future 21-cm observations of high-redshift neutral hydrogen. In addition to giving us insight into the history of structure formation in the universe, 21cm surveys will also allow us to search for exotic physics in the Dark Ages.


    • November 5, 2007 | 2:00 PM | LASR Conference Room | Open Group seminar
      A framework for probing gravity and dark energy on cosmological scales
      Mustafa Amin, Stanford University

      Departures from the flat-LCDM model can occur in the geometry, expansion history and the growth of structure. In addition, the relationship between the non-relativistic matter distribution and metric perturbations depends on the theory of gravity and any additional fields that are present. This provides another means of distinguishing the alternatives to LCDM. I will briefly discuss kinematic constraints on the expansion history. I will then concentrate on our attempt to develop a framework for probing the matter-metric relationship on linear, sub-horizon scales in a scale- dependent manner.
    • November 6, 2007 | 12:15 AM | | Open Group seminar
      Stellar Feedback and Galaxy Formation
      Daniel Ceverino, NMSU

      Although supernova explosions and stellar winds happens at very small scales, they affect the interstellar medium(ISM) and galaxy formation. We use cosmological N-body+Hydrodynamics simulations of galaxy formation, as well as simulations of the ISM to study the effect of stellar feedback on galactic scales. Stellar feedback maintains gas with temperatures above a million degrees. This gas fills bubbles, super-bubbles and chimneys. Our model of feedback, in which 10%-30% of the feedback energy is coming from runaway stars, reproduces this hot gas only if the resolution is better than 50 pc. This is 10 times better than the typical resolution in cosmological simulations of galaxy formation. Only with this resolution, the effect of stellar feedback in galaxy formation is resolved without any assumption about sub-resolution physics. Stellar feedback can regulate the formation of bulges and can shape the inner parts of the rotation curve.
    • November 28, 2007 | 11:00 AM | LASR Conference Room | Open Group seminar
      Scale-dependent Growth of Structure in Modified Gravity
      Alessandra Silvestri, Syracuse University

      A modification of gravity in the low-curvature regime may account for the late-time acceleration of our universe, and is therefore an interesting alternative to Dark Energy. In such models, the modified Einstein equations admit self-accelerated solutions in the presence of negligible matter. At the level of perturbation theory, the modified equations give rise to a richer dynamics for the perturbations to the metric and matter, with predictions for the growth of structure which differ from those in a cosmological constant scenario. I will focus in particular on f(R) theories, showing what could be observable features of such theories in the Large Scale Structure of the universe.
    • December 10, 2007 | 3:00 PM | LASR 152 | Open Group seminar
      Improved statistics for obtaining cosmological parameter constraints from the nonlinear matter powe rspectrum
      Michael D Schneider, UC Davis

      I will describe a statistical framework for using limited numbers of N-body simulations to build a model for the sample variance distribution of the nonlinear matter power spectrum. Our preliminary model retains the common assumption of a multivariate Normal distribution for the power spectrum band powers, but takes full account of the (parameter dependent) power spectrum covariance in the nonlinear regime. This machinery can be used to improve the accuracy of cosmological parameter constraints obtained from galaxy clustering and cosmic shear surveys.


    • October 18, 2007 | 3:15 PM | AAC 123 | Special Seminar
      Using RR Lyrae Variable Stars to Probe the Kinematic Signature of the Sagittarius Stream
      Ron Wilhelm, Texas Tech

      RRLyrae variable stars in the halo of our Galaxy are excellent kinematic tracer probes of halo substructure because the characteristics of their light curves allow them to be identified unambiguously. The problem with using these stars to probe the general halo field is the large amount of telescope time required to confirm variability for a population which is spread out across the entire sky.

      I will present a brand new technique which uses only two epochs of observation, one photometric and one spectroscopic to identify RR Lyrae stars within the Sloan Digital Sky Survey (SDSS)and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). With this technique it is possible to achieve a discovery efficiency of ~85% when compared to published variables within the SDSS. We find similar efficiencies from follow up observations at McDonald observatory and by comparison to SDSS stars with multiple spectroscopic observations.

      The relative purity of the resulting sample allows us to probe the kinematics of the Sagittarius galaxy, tidal stellar stream. I will present new kinematic results for the leading and trailing arms of the Northern Steam which to date have never been explored. These results will ultimately help to place stronger constraints on theoretical models of the stream and on the shape of the Galactic dark matter halo.