Heidi Jo Newberg

Georgia State University, Atlanta, Georgia, United States

Are you Heidi Jo Newberg?

Claim your profile

Publications (212)525.43 Total impact

  • The Astrophysical Journal Letters 03/2014; 784(2):L46. · 6.35 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We report the first hypervelocity star (HVS) discovered from the LAMOST spectroscopic survey. It is a B-type star with a heliocentric radial velocity about 620 km/s, which projects to a Galactocentric radial velocity component of ~477 km/s. With a heliocentric distance of ~13 kpc and an apparent magnitude of ~13 mag, it is the nearest and brightest HVS currently known. With a mass of ~9Msun, it is very similar to HVS HE 0437-5439 in its stellar properties; the two stars are the most massive HVSs known so far. The star is clustered on the sky with many other known HVSs, with the position suggesting a possible connection to Galactic center structures. With the current poorly-determined proper motion, a Galactic center origin of this HVS remains consistent with the data at the 2-3sigma level. We discuss the potential of the LAMOST survey to discover a large statistical sample of HVSs of different types.
    The Astrophysical Journal Letters 01/2014; 785(2). · 6.35 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: MilkyWay@home is a 0.5 petaFLOPS volunteer computer platform that is currently measuring the spatial density of stars in the spheroid (including tidal tails of dwarf galaxies), and runs n-body simulations of dwarf galaxy tidal disruptions to compare with observations. MilkyWay@home is a very powerful engine for optimizing model parameters, using differential evolution and particle swarm techniques that were specifically adapted to our highly asynchronous and heterogeneous environment, in which each potentially best set of parameters is sent out to one of about 20,000 volunteer computers worldwide that are available at any given time. The results are returned in a few seconds or a few days or even weeks from some processors. We have already fit the spatial density of stars in the Sagittarius dwarf tidal tails using the method of statistical photometric parallax, applied to photometry for turnoff stars in the Sloan Digital Sky Survey Data Release 8 (SDSS DR8). We will soon characterize the entire volume covered by SDSS DR8. We currently compare N-body simulations (including both stars and dark matter) of dwarf galaxy tidal disruption to the measured spatial density of stars along a tidal stream, to optimize the dwarf galaxy size, mass, mass-to-light ratio, and disruption time. We are building a system that will be capable of fitting additional parameters, including: Milky Way potential (including dark matter), orbital parameters, and multiple disrupting dwarf galaxies. We will also include other observational constraints including radial velocities, distance to stream, and width of stream, all as a function of position. This research is funded by the National Science Foundation grant AST 10-09670.
    01/2014;
  • [show abstract] [hide abstract]
    ABSTRACT: We are improving the current spatial density profile for the Sagittarius dwarf tidal stream and other tidal streams in the Milky Way halo, using new color corrections to the Sloan Digital Sky Survey and a new statistical model for main sequence turnoff stars absolute magnitude distribution. Using the MilkyWay@home distributed computing platform, we implement a method of maximum likelihood to fit a model to both tidal streams and a smooth component of the halo. With this technique, we currently have one of the most accurate descriptions for part of the Sagittarius dwarf tidal stream’s spatial density profile as well as a spatial density profile for part of a second (bifurcated) stream near the Sagittarius dwarf tidal stream, whose origins are not well understood. Along with fitting the width, positions, and orientations of the previously mentioned streams, we also have found that the smooth component of the Milky Way halo is oblate. Using these results, we hope to run N-body simulations of the dwarf galaxy tidal disruption that created the tidal debris to constrain the dark matter profile of the Milky Way galaxy. This research was funded by NSF grant AST 10-09670 and the Rensselaer Center for Open Source Software (RCOS).
    01/2014;
  • [show abstract] [hide abstract]
    ABSTRACT: We use maximum likelihood estimation (MLE) to find the best parameters for the mass, size, and mass/light ratio of dwarf galaxies that are the progenitors of tidal streams. An N-body simulation, including both dark matter and stars, is run for each set of candidate parameters. The distribution of stars in the resulting tidal stream is compared to either a simulated tidal stream with known progenitor properties, or observations of stars in a tidal stream. Massively parallelized sets of n-body simulations using the BOINC computing project, MilkyWay@Home, allow probing of an extensive likelihood surface. We show evidence that this approach is feasible, and report the results of initial trials on real streams. This research is supported by NSF grant AST AST 10-09670.
    01/2014;
  • Julie Dumas, H. J. Newberg, A. Susser
    [show abstract] [hide abstract]
    ABSTRACT: We test a particular theory of dark matter, in which dark matter axions form ring "caustics" in the plane of the Milky Way. According to this theory, cold collisionless dark matter particles with angular momentum flow in and out of the Milky Way as it forms. These flows form caustic rings (at the positions of the rings, the density of the flow is infinite) at the locations of closest approach to the Galactic center. We show that the caustic ring dark matter theory reproduces a roughly logarithmic halo, with large perturbations near the rings. We show that the theory can reasonably match the known Galaxy rotation curve. We explore the effects of the caustic rings on dwarf galaxy tidal disruption using N-body simulations. Tidally disrupted galaxies are stripped apart by the gravitational forces of the Milky Way, leaving both leading and trailing streams of stars. We compare the results of the model with observations of tidal streams.
    01/2014;
  • [show abstract] [hide abstract]
    ABSTRACT: This project involves analyzing data directly off the footprint of the Sloan Digital Sky Survey in order to find the progenitor of the Orphan tidal stream. This stream of stellar debris, known to span distances 20 to 47 kpc from the Sun, is believed to be the remnants of a small dwarf galaxy that is largely disrupted. Images were obtained in the vicinity of this stream from the MOSAIC1.1 camera on the 4-meter Mayall telescope at the Kitt Peak National Observatory. The region observed covers 11 square degrees of sky, approximately 7 square degrees of which have no SDSS data. The area outside the SDSS was selected to explore the increase in density of Orphan stars in this location, discussed in Newberg et al. 2010. The positions and magnitudes of stars outside of the SDSS were calculated and calibrated with both data from the SDSS itself, as well as the USNOB-1 catalog. The resulting Orphan candidates selected from this catalog were used to explore the stellar densities along this stream, providing insight into the nature of its progenitor. This research was supported by NSF grant AST 09-37523.
    01/2014;
  • [show abstract] [hide abstract]
    ABSTRACT: We characterize the spatial properties of the Sagittarius dwarf galaxy tidal debris, both primary and secondary (bifurcated) tidal tails, in the south Galactic cap. The Sagittarius dwarf galaxy is currently being ripped apart by tidal forces from the Milky Way galaxy. The spatial density of turnoff stars from the Sloan Digital Sky Survey Data Release 8 are fit using statistical photometric parallax with half a petaFLOPS of computing power from the MilkyWay@home volunteer computing platform. The secondary tail appears to be significantly wider than the originally detected primary tail. These results are compared with the leading tidal tail stream density measured in the north Galactic cap. This research was funded by NSF grant AST 10-09670.
    01/2014;
  • [show abstract] [hide abstract]
    ABSTRACT: We find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the mid-plane as well as azimuthally. These findings are based on LAMOST spectroscopic velocities for a sample of ~400,000 F-type stars, combined with proper motions from the PPMXL catalog for which we have derived corrections to the zero points based in part on spectroscopically discovered galaxies and QSOs from LAMOST. In the region within 2 kpc outside the Sun's radius and +/-2 kpc from the Galactic midplane, we show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior. We discuss this in the context of other recent findings, and conclude that we are likely seeing the signature of vertical disturbances to the disk due to an external perturbation.
    The Astrophysical Journal 09/2013; 777(1). · 6.73 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: We trace the Cetus Polar Stream (CPS) with blue horizontal branch (BHB) and red giant stars (RGBs) from Data Release 8 of the Sloan Digital Sky Survey (SDSS DR8). Using a larger dataset than was available previously, we are able to refine the measured distance and velocity to this tidal debris star stream in the south Galactic cap. Assuming the tidal debris traces the progenitor's orbit, we fit an orbit to the CPS and find that the stream is confined between ~24-36 kpc on a rather polar orbit inclined 87 degrees to the Galactic plane. The eccentricity of the orbit is 0.20, and the period ~700 Myr. If we instead matched N-body simulations to the observed tidal debris, these orbital parameters would change by 10% or less. The CPS stars travel in the opposite direction to those from the Sagittarius tidal stream in the same region of the sky. Through N-body models of satellites on the best-fitting orbit, and assuming that mass follows light, we show that the stream width, line-of-sight depth, and velocity dispersion imply a progenitor of at least 10^8 solar masses. However, the density of stars along the stream requires either a disruption time on the order of one orbit, or a stellar population that is more centrally concentrated than the dark matter. We suggest that an ultra-faint dwarf galaxy progenitor could reproduce a large stream width and velocity dispersion without requiring a very recent deflection of the progenitor into its current orbit. We find that most Cetus stars have metallicities of -2.5 < [Fe/H] < -2.0, similar to the observed metallicities of the ultra-faint dwarfs. Our simulations suggest that the parameters of the dwarf galaxy progenitors, including their dark matter content, could be constrained by observations of their tidal tails through comparison of the debris with N-body simulations.
    The Astrophysical Journal 08/2013; 776(2). · 6.73 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: A total of $\sim640,000$ objects from LAMOST pilot survey have been publicly released. In this work, we present a catalog of DA white dwarfs from the entire pilot survey. We outline a new algorithm for the selection of white dwarfs by fitting S\'ersic profiles to the Balmer H$\beta$, H$\gamma$ and H$\delta$ lines of the spectra, and calculating the equivalent width of the CaII K line. 2964 candidates are selected by constraining the fitting parameters and the equivalent width of CaII K line. All the spectra of candidates are visually inspected. We identify 230 (59 of them are already in Villanova and SDSS WD catalog) DA white dwarfs, 20 of which are DA white dwarfs with non-degenerate companions. In addition, 128 candidates are classified as DA white dwarf/subdwarfs, which means the classifications are ambiguous. The result is consistent with the expected DA white dwarf number estimated based on the LEGUE target selection algorithm.
    The Astronomical Journal 07/2013; 146(2). · 4.97 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: The LAMOST spectroscopic survey for Galactic structure and evolution has been in operation since October 2012, following a one-year pilot survey. The pilot survey produced a data release containing over 600,000 stellar spectra. By cross-checking with a large time series photometric database of RR Lyrae stars in high Galactic latitude regions, we found a total number of 157 stars that have been observed with LAMOST. In this sample, we successfully captured three RR Lyrae stars in the fast expansion phase, all of them showing significant hypersonic shock wave features in the spectra. By fitting the H{\alpha} line shape, we determine that the emission features seen within the broader H{\alpha} absorption line suggest hypersonic relative motions in the atmospheres of these three objects. With a further LAMOST survey of millions of stars, we will capture a large sample of RR Lyrae stars in their hypersonic expansion phase, and therefore provide a large database for the study of the internal structure and pulsation mechanism of RR Lyrae stars.
    New Astronomy 06/2013; · 1.85 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We measure the spatial density of F turnoff stars in the Sagittarius dwarf tidal stream, from Sloan Digital Sky Survey (SDSS) data, using statistical photometric parallax. We find a set of continuous, consistent parameters that describe the leading Sgr stream's position, direction, and width for 15 stripes in the North Galactic Cap, and 3 stripes in the South Galactic Cap. We produce a catalog of stars that has the density characteristics of the dominant leading Sgr tidal stream that can be compared with simulations. We find that the width of the leading (North) tidal tail is consistent with recent triaxial and axisymmetric halo model simulations. The density along the stream is roughly consistent common disruption models in the North, but possibly not in the South. We explore the possibility that one or more of the dominant Sgr streams has been mis-identified, and that one or more of the `bifurcated' pieces is the real Sgr tidal tail, but we do not reach definite conclusions. If two dwarf progenitors are assumed, fits to the planes of the dominant and `bifurcated' tidal tails favor an association of the Sgr dwarf spheroidal galaxy with the dominant Southern stream and the `bifurcated' stream in the North. In the North Galactic Cap, the best fit Hernquist density profile for the smooth component of the stellar halo is oblate, with a flattening parameter q = 0.53, and a scale length of r_0 = 6.73. The Southern data for both the tidal debris and the smooth component of the stellar halo do not match the model fits to the North, although the stellar halo is still overwhelmingly oblate. Finally, we verify that we can reproduce the parameter fits on the asynchronous Milkyway@home volunteer computing platform.
    The Astronomical Journal 04/2013; 145(6). · 4.97 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We report the kinematic discovery of the Pisces Stellar Stream (PSS), at Galactic longitude of roughly l=135 degrees and longitude between -39 < b < -36 deg. We originally identified this halo substructure from velocities of red giant branch stars in Sloan Digital Sky Survey (SDSS) Data Release 8, and confirmed its presence in turnoff stars from SDSS photometric data. The PSS is a narrow, kinematically cold tidal stream, with a velocity dispersion of 8 km/s. Its metallicity is [Fe/H]=-2.2, with ~0.3 dex dispersion. The color-magnitude signature of the stream turnoff, combined with our measured metallicity, places the PSS at a distance of 35+/-3 kpc. The Pisces Stellar Stream is the same as the previously announced "Triangulum stream" and part of the proposed "stream a". We rule out an association of the PSS with other previously known Milky Way substructures in the same region of the sky.
    The Astrophysical Journal Letters 02/2013; 765(2). · 6.35 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: We explore disk kinematics using the Large Sky Area Area Mulit-Object Fiber Spectroscopic Telescope (LAMOST) pilot survey. Spectra for 484,185 stars with magnitudes 10 to 18 were released after being observed using the Guo Shou Jing Telescope in the pilot survey. Because the majority of the stars with sufficient signal-to-noise for velocity measurements are bright, we focus our study on the Milky Way disk. We show the local kinematics of the disk using these stars, which show gradients in the radial and rotational motion along with longitudinal asymmetries. Funding for this project has been provided by The NASA/NY Space Grant, NSF grant AST 10-09670, NSF grant AST 09-37523 and NSFC grants 10973015 and 11061120454.
    01/2013;
  • Kathleen Grabowski, M. Newby, H. J. Newberg
    [show abstract] [hide abstract]
    ABSTRACT: We use techniques of Newby et al. (2011) that established a mean magnitude of Mg=4.18 ± 0.008 for F-turnoff (FTO) stars in globular clusters within the Milky Way halo to analyze two globular clusters in the Southern Galactic Cap. Data from the two clusters, Palomar 13 and Whiting 1, recently became available in Data Release 8 (DR8) of the Sloan Digital Sky Survey (SDSS). Based on a histogram of the magnitude distribution, we find that the mean magnitude of FTO stars in Palomar 13 is Mg=4.46 ± 0.26 and the mean magnitude of FTO stars in Whiting 1 is Mg=4.11 ± 0.30. We confirm that the observed distribution of stars in these two clusters is consistent wiht the predictions of Newby et al.(2011), even though the two clusters are more distant than previously studied, and Whiting 1 is younger and more metal-rich than other globular clusters studied in this manner. We confirm previous results that indicate Whiting 1 is within the Sagittarius dwarf tidal stream, while Palomar 13 is not. This research was supported by NSF grant AST 10-09670.
    01/2013;
  • [show abstract] [hide abstract]
    ABSTRACT: In statistical photometric parallax, the knowledge of the distribution of absolute magnitudes of a population of stars is used to statistically determine the density distribution of that population, even though the distance to each individual star cannot be determined. We use a maximum likelihood technique and the 0.5 PetaFLOPS MilkyWay@home volunteer computing platform to calculate the density of the leading tidal tail of the Sagittarius dwarf Galaxy using Sloan Digital Sky Survey data from Data Release 7. While the width and position of the leading tidal, as a function of angular distance for the Sgr dwarf, are a good match to the Law & Majewski (2010) triaxial halo model, there is some deviation in the density along the leading tidal tail. We compare the orbital planes of the dominant leading and trailing tidal tails of Sgr, as well as the orbital planes of the bifurcated pieces, and conclude that it is not obvious which or how many of these tidal streams is associated with the Sgr dwarf galaxy. This research was supported by NSF grant AST 10-09670.
    01/2013;
  • Samantha Scibelli, H. J. Newberg, B. Yanny
    [show abstract] [hide abstract]
    ABSTRACT: We visually compared Sloan Digital Sky Survey (SDSS) spectra of 12,113 objects with that are bluer than (g-r)0 = -0.25 with the templates to which they were matched in SDSS DR7. It was determined that 1203 of these spectra were misclassified. Most of the misclassified stars are rarer types for which template spectra were not available, including DB white dwarf stars, binary stars, and ‘featureless’ spectra. The featureless spectra have high proper motions, indicating that they are likely subdwarfs in the Milky Way. We present a census of the types of misclassified blue stars observed, including their locations in (u-g)0 vs. (g-r)0 and g0 vs. (g-r)0 diagrams. Of the 1203 misclassified stars, 559 were previously classified in rare object catalogs, while 629 had yet to be classed before this research. We recommend that future SDSS data releases should include additional templates to match these rarer types of stars.This research was supported by NSF grant AST 10-09670.
    01/2013;
  • [show abstract] [hide abstract]
    ABSTRACT: The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also named the Guo Shou Jing Telescope) pilot survey ran from October 2011 to April 2012, and spectra of nearly 500,000 stars have been released. Radial velocities from the spectra can be combined with proper motions and magnitudes to calculate 3 dimensional positions and velocities. We attempt to separate components of the Milky Way based on measured velocities and metallicities using LAMOST pilot survey spectra. We use QSOs and galaxies to measure zero point offsets in PPMXL proper motions as a function of position on the sky at low Galactic latitudes. This research was supported by NSF grants AST 10-09670 and AST 09-37523, and NSFC grants 10973015 and 11061120454.
    01/2013;
  • [show abstract] [hide abstract]
    ABSTRACT: The Guo Shoujing Telescope (GSJT, formerly LAMOST) pilot survey started in October 2011 and will run through April 2012. We report on the footprint and selection algorithms for the stellar portion of the survey (LEGUE).
    08/2012;

Publication Stats

3k Citations
525.43 Total Impact Points

Institutions

  • 2014
    • Georgia State University
      • Department of Physics and Astronomy
      Atlanta, Georgia, United States
  • 2001–2014
    • Rensselaer Polytechnic Institute
      • • Department of Physics, Applied Physics, and Astronomy
      • • Department of Computer Science
      Troy, New York, United States
  • 2013
    • American Museum of Natural History
      • Division of Physical Sciences
      New York City, New York, United States
  • 2012
    • China West Normal University
      Shun’tsin, Sichuan, China
    • Northeast Institute of Geography and Agroecology
      • Shanghai Astronomical Observatory
      Peping, Beijing, China
    • CUNY Graduate Center
      New York City, New York, United States
    • Chinese Academy of Sciences
      • Shanghai Astronomical Observatory
      Peping, Beijing, China
  • 1996–2009
    • Fermi National Accelerator Laboratory (Fermilab)
      • Experimental Astrophysics Department
      Batavia, Illinois, United States
  • 2008
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 2005–2008
    • University of Sussex
      • Astronomy Centre
      Brighton, England, United Kingdom
  • 2000–2006
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States
    • University of Washington Seattle
      • Department of Astronomy
      Seattle, Washington, United States
  • 2004
    • University of Colorado at Boulder
      • Center for Astrophysics and Space Astronomy
      Boulder, Colorado, United States
  • 2003
    • University of Michigan
      • Department of Physics
      Ann Arbor, Michigan, United States
  • 2002
    • University of Chicago
      • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States