Heidi Jo Newberg

Georgia State University, Atlanta, Georgia, United States

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Publications (214)537.03 Total impact

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    ABSTRACT: We quantify and correct systematic errors in PPMXL proper motions using extragalactic sources from the first two LAMOST data releases and the Veron-Cetty & Veron Catalog of Quasars. Although the majority of the sources are from the Veron catalog, LAMOST makes important contributions in regions that are not well-sampled by previous catalogs, particularly at low Galactic latitudes and in the south Galactic cap. We show that quasars in PPMXL have measureable and significant proper motions, which reflect the systematic zero-point offsets present in the catalog. We confirm the global proper motion shifts seen by Wu, Ma, & Zhou (2011), and additionally find smaller-scale fluctuations of the QSO-derived corrections to an absolute frame. We average the proper motions of 158,106 extragalactic objects in bins of 3x3 degrees and present a table of proper motion corrections.
    09/2014;
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    ABSTRACT: We present a support vector machine classifier to identify the K giant stars from the LAMOST survey directly using their spectral line features. The completeness of the identification is about 75% for tests based on LAMOST stellar parameters. The contamination in the identified K giant sample is lower than 2.5%. Applying the classification method to about 2 million LAMOST spectra observed during the pilot survey and the first year survey, we select 298,036 K giant candidates. The metallicities of the sample are also estimated with uncertainty of $0.13\sim0.29$\,dex based on the equivalent widths of Mg$_{\rm b}$ and iron lines. A Bayesian method is then developed to estimate the posterior probability of the distance for the K giant stars, based on the estimated metallicity and 2MASS photometry. The synthetic isochrone-based distance estimates have been calibrated using 7 globular clusters with a wide range of metallicities. The uncertainty of the estimated distance modulus at $K=11$\,mag, which is the median brightness of the K giant sample, is about 0.6\,mag, corresponding to $\sim30$% in distance. As a scientific verification case, the trailing arm of the Sagittarius stream is clearly identified with the selected K giant sample. Moreover, at about 80\,kpc from the Sun, we use our K giant stars to confirm a detection of stream members near the apo-center of the trailing tail. These rediscoveries of the features of the Sagittarius stream illustrate the potential of the LAMOST survey for detecting substructures in the halo of the Milky Way.
    The Astrophysical Journal 04/2014; 790(2). · 6.73 Impact Factor
  • The Astrophysical Journal Letters 03/2014; 784(2):L46. · 6.35 Impact Factor
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    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
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    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;
  • Julie Dumas, H. J. Newberg, A. Susser
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    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;
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    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;
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    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;
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    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;
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    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;
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    ABSTRACT: MilkyWay@home is a volunteer computing project that allows people from every country in the world to volunteer their otherwise idle processors to Milky Way research. Currently, more than 25,000 people (150,000 since November 9, 2007) contribute about half a PetaFLOPS of computing power to our project. We currently run two types of applications: one application fits the spatial density profile of tidal streams using statistical photometric parallax, and the other application finds the N-body simulation parameters that produce tidal streams that best match the measured density profile of known tidal streams. The stream fitting application is well developed and is producing published results. The Sagittarius dwarf leading tidal tail has been fit, and the algorithm is currently running on the trailing tidal tail and bifurcated pieces. We will soon have a self-consistent model for the density of the smooth component of the stellar halo and the largest tidal streams. The N-body application has been implemented for fitting dwarf galaxy progenitor properties only, and is in the testing stages. We use an Earth-Mover Distance method to measure goodness-of-fit for density of stars along the tidal stream. We will add additional spatial dimensions as well as kinematic measures in a piecemeal fashion, with the eventual goal of fitting the orbit and parameters of the Milky Way potential (and thus the density distribution of dark matter) using multiple tidal streams.
    12/2013;
  • Yan Xu, Heidi Newberg
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    ABSTRACT: We map the stellar distribution on Hess diagram in the Anti-Center roughly in the boxes 130
    12/2013;
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    ABSTRACT: In its first two observing seasons, the LEGUE (LAMOST Experiment for Galactic Understanding and Exploration; Deng et al., Zhao et al. 2012) survey has obtained ~1.7 million science-quality spectra. We apply corrections to the PPMXL proper motions (PMs; Roeser et al. 2010) as a function of position, as determined from the measured PMs of extragalactic objects discovered in LAMOST spectra (see Fig. 1, left and center panels). LAMOST radial velocities and corrected PMs are used to derive 3D space velocities for ~480,000 F-stars (assuming M V =4 to derive distances). The right panel of Fig. 1 shows the radial component of Galactic cylindrical velocities (V R ) for stars between 7.8
    12/2013;
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    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
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    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
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    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
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    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
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    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
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    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
  • Heidi Jo Newberg
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    ABSTRACT: In determining the distances to stars within the Milky Way galaxy, one often uses photometric or spectroscopic parallaxes. In these methods, the type of each individual star is determined, and the absolute magnitude of that star type is compared with the measured apparent magnitude to determine individual distances. In this paper, we define the term statistical photometric parallax, in which statistical knowledge of the absolute magnitudes of stellar populations is used to determine the underlying density distributions of those stars. This technique has been used to determine the density distribution of the Milky Way's stellar halo and its component tidal streams, using very large samples of stars from the Sloan Digital Sky Survey. Most recently, the volunteer computing platform MilkyWay@home has been used to find the best-fitting model parameters for the density of these halo stars.
    Proceedings of the International Astronomical Union 02/2013; 8(S289):74-81.

Publication Stats

4k Citations
537.03 Total Impact Points

Institutions

  • 2014
    • Georgia State University
      • Department of Physics and Astronomy
      Atlanta, Georgia, United States
  • 2012–2014
    • Chinese Academy of Sciences
      • Shanghai Astronomical Observatory
      Peping, Beijing, China
    • 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
  • 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
  • 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
  • 1993
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States