LSST Corporation

Tucson, AZ, United States

LSST Corporation

Tucson, AZ, United States

Time filter

Source Type

Loebman S.R.,University of Michigan | Ivezic Z.,University of Washington | Quinn T.R.,University of Washington | Bovy J.,Institute for Advanced Study | And 5 more authors.
Astrophysical Journal | Year: 2014

We present robust constraints from the Sloan Digital Sky Survey (SDSS) on the shape and distribution of the dark matter halo within the Milky Way (MW). Using the number density distribution and kinematics of SDSS halo stars, we probe the dark matter distribution to heliocentric distances exceeding 10 kpc and galactocentric distances exceeding 20 kpc. Our analysis utilizes Jeans equations to generate two-dimensional acceleration maps throughout the volume; this approach is thoroughly tested on a cosmologically derived N-body+SPH simulation of a MW-like galaxy. We show that the known accelerations (gradients of the gravitational potential) can be successfully recovered in such a realistic system. Leveraging the baryonic gravitational potential derived by Bovy & Rix, we show that the gravitational potential implied by the SDSS observations cannot be explained, assuming Newtonian gravity, by visible matter alone: the gravitational force experienced by stars at galactocentric distances of 20 kpc is as much as three times stronger than what can be attributed to purely visible matter. We also show that the SDSS data provide a strong constraint on the shape of the dark matter halo potential. Within galactocentric distances of 20 kpc, the dark matter halo potential is well described as an oblate halo with axis ratio ; this corresponds to an axis ratio for the dark matter density distribution. Because of our precise two-dimensional measurements of the acceleration of the halo stars, we can reject several MOND models as an explanation of the observed behavior. © 2014. The American Astronomical Society. All rights reserved..


Green G.M.,Harvard - Smithsonian Center for Astrophysics | Schlafly E.F.,Max Planck Institute for Astronomy | Finkbeiner D.P.,Harvard - Smithsonian Center for Astrophysics | Juric M.,LSST Corporation | And 12 more authors.
Astrophysical Journal | Year: 2014

We present a method to infer reddenings and distances to stars based only on their broad-band photometry, and show how this method can be used to produce a three-dimensional (3D) dust map of the Galaxy. Our method samples from the full probability density function of distance, reddening, and stellar type for individual stars, as well as the full uncertainty in reddening as a function of distance in the 3D dust map. We incorporate prior knowledge of the distribution of stars in the Galaxy and the detection limits of the survey. For stars in the Pan-STARRS 1 (PS1) 3π survey, we demonstrate that our reddening estimates are unbiased and accurate to ∼0.13 mag in E(B-V) for the typical star. Based on comparisons with mock catalogs, we expect distances for main-sequence stars to be constrained to within ∼20%-60%, although this range can vary, depending on the reddening of the star, the precise stellar type, and its position on the sky. A later paper will present a 3D map of dust over the three quarters of the sky surveyed by PS1. Both the individual stellar inferences and the 3D dust map will enable a wealth of Galactic science in the plane. The method we present is not limited to the passbands of the PS1 survey but may be extended to incorporate photometry from other surveys, such as the Two Micron All Sky Survey, the Sloan Digital Sky Survey (where available), and in the future, LSST and Gaia. © 2014. The American Astronomical Society. All rights reserved.


Schlafly E.F.,Max Planck Institute for Astronomy | Green G.,Harvard - Smithsonian Center for Astrophysics | Finkbeiner D.P.,Harvard - Smithsonian Center for Astrophysics | Finkbeiner D.P.,Harvard University | And 18 more authors.
Astrophysical Journal | Year: 2014

We present a map of the dust reddening to 4.5 kpc derived from Pan-STARRS1 stellar photometry. The map covers almost the entire sky north of declination -30° at a resolution of 7′-14′, and is based on the estimated distances and reddenings to more than 500 million stars. The technique is designed to map dust in the Galactic plane, where many other techniques are stymied by the presence of multiple dust clouds at different distances along each line of sight. This reddening-based dust map agrees closely with the Schlegel et al. (SFD) far-infrared emission-based dust map away from the Galactic plane, and the most prominent differences between the two maps stem from known limitations of SFD in the plane. We also compare the map with Planck, finding likewise good agreement in general at high latitudes. The use of optical data from Pan-STARRS1 yields reddening uncertainty as low as 25 mmag E(B-V). © 2014. The American Astronomical Society. All rights reserved.


Slater C.T.,University of Michigan | Bell E.F.,University of Michigan | Schlafly E.F.,Harvard University | Juric M.,Harvard - Smithsonian Center for Astrophysics | And 15 more authors.
Astrophysical Journal | Year: 2013

We use data from the Pan-STARRS1 survey to present a panoramic view of the Sagittarius tidal stream in the southern Galactic hemisphere. As a result of the extensive sky coverage of Pan-STARRS1, the southern stream is visible along more than 60° of its orbit, nearly double the length seen by the Sloan Digital Sky Survey. The recently discovered southern bifurcation of the stream is also apparent, with the fainter branch of the stream visible over at least 30°. Using a combination of fitting both the main-sequence turnoff and the red clump, we measure the distance to both arms of the stream in the south. We find that the distances to the bright arm of the stream agree very well with the N-body models of Law & Majewski. We also find that the faint arm lies ∼5 kpc closer to the Sun than the bright arm, similar to the behavior seen in the northern hemisphere. © 2013. The American Astronomical Society. All rights reserved.


Loebman S.R.,University of Washington | Ivezic Z.,University of Washington | Quinn T.R.,University of Washington | Governato F.,University of Washington | And 3 more authors.
Astrophysical Journal Letters | Year: 2012

We search for evidence of dark matter in the Milky Way by utilizing the stellar number density distribution and kinematics measured by the Sloan Digital Sky Survey (SDSS) to heliocentric distances exceeding 10kpc. We employ the cylindrically symmetric form of Jeans equations and focus on the morphology of the resulting acceleration maps, rather than the normalization of the total mass as done in previous, mostly local, studies. Jeans equations are first applied to a mock catalog based on a cosmologically derived N-body+SPH simulation, and the known acceleration (gradient of gravitational potential) is successfully recovered. The same simulation is also used to quantify the impact of dark matter on the total acceleration. We use Galfast, a code designed to quantitatively reproduce SDSS measurements and selection effects, to generate a synthetic stellar catalog. We apply Jeans equations to this catalog and produce two-dimensional maps of stellar acceleration. These maps reveal that in a Newtonian framework, the implied gravitational potential cannot be explained by visible matter alone. The acceleration experienced by stars at galactocentric distances of 20kpc is three times larger than what can be explained by purely visible matter. The application of an analytic method for estimating the dark matter halo axis ratio to SDSS data implies an oblate halo with q DM = 0.47 ± 0.14 within the same distance range. These techniques can be used to map the dark matter halo to much larger distances from the Galactic center using upcoming deep optical surveys, such as LSST. © 2012. The American Astronomical Society. All rights reserved.


Sesar B.,California Institute of Technology | Ivezic Z.,University of Washington | Scott Stuart J.,Lincoln Laboratory | Morgan D.M.,University of Washington | And 7 more authors.
Astronomical Journal | Year: 2013

We present a sample of ∼5000 RR Lyrae stars selected from the recalibrated LINEAR data set and detected at heliocentric distances between 5 kpc and 30 kpc over ∼8000 deg2 of sky. The coordinates and light curve properties, such as period and Oosterhoff type, are made publicly available. We analyze in detail the light curve properties and Galactic distribution of the subset of ∼4000 type ab RR Lyrae (RRab) stars, including a search for new halo substructures and the number density distribution as a function of Oosterhoff type. We find evidence for the Oosterhoff dichotomy among field RR Lyrae stars, with the ratio of the type II and I subsamples of about 1:4, but with a weaker separation than for globular cluster stars. The wide sky coverage and depth of this sample allow unique constraints for the number density distribution of halo RRab stars as a function of galactocentric distance: it can be described as an oblate ellipsoid with an axis ratio q = 0.63 and with either a single or a double power law with a power-law index in the range -2 to -3. Consistent with previous studies, we find that the Oosterhoff type II subsample has a steeper number density profile than the Oosterhoff type I subsample. Using the group-finding algorithm EnLink, we detected seven candidate halo groups, only one of which is statistically spurious. Three of these groups are near globular clusters (M53/NGC 5053, M3, M13), and one is near a known halo substructure (Virgo Stellar Stream); the remaining three groups do not seem to be near any known halo substructures or globular clusters and seem to have a higher ratio of Oosterhoff type II to Oosterhoff type I RRab stars than what is found in the halo. The extended morphology and the position (outside the tidal radius) of some of the groups near globular clusters are suggestive of tidal streams possibly originating from globular clusters. Spectroscopic follow-up of detected halo groups is encouraged. © 2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


Dindar S.,University of Florida | Ford E.B.,University of Florida | Juric M.,LSST Corporation | Juric M.,University of Arizona | And 5 more authors.
New Astronomy | Year: 2013

We present Swarm-NG, a C++ library for the efficient direct integration of many n-body systems using a Graphics Processing Unit (GPU), such as NVIDIA's Tesla T10 and M2070 GPUs. While previous studies have demonstrated the benefit of GPUs for n-body simulations with thousands to millions of bodies, Swarm-NG focuses on many few-body systems, e.g., thousands of systems with 3...15 bodies each, as is typical for the study of planetary systems. Swarm-NG parallelizes the simulation, including both the numerical integration of the equations of motion and the evaluation of forces using NVIDIA's "Compute Unified Device Architecture" (CUDA) on the GPU. Swarm-NG includes optimized implementations of 4th order time-symmetrized Hermite integration and mixed variable symplectic integration, as well as several sample codes for other algorithms to illustrate how non-CUDA-savvy users may themselves introduce customized integrators into the Swarm-NG framework. To optimize performance, we analyze the effect of GPU-specific parameters on performance under double precision. For an ensemble of 131072 planetary systems, each containing three bodies, the NVIDIA Tesla M2070 GPU outperforms a 6-core Intel Xeon X5675 CPU by a factor of ∼2.75. Thus, we conclude that modern GPUs offer an attractive alternative to a cluster of CPUs for the integration of an ensemble of many few-body systems. Applications of Swarm-NG include studying the late stages of planet formation, testing the stability of planetary systems and evaluating the goodness-of-fit between many planetary system models and observations of extrasolar planet host stars (e.g., radial velocity, astrometry, transit timing). While Swarm-NG focuses on the parallel integration of many planetary systems, the underlying integrators could be applied to a wide variety of problems that require repeatedly integrating a set of ordinary differential equations many times using different initial conditions and/or parameter values. © 2013 Published by Elsevier B.V.


Kantor J.P.,LSST Corporation
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The Large Synoptic Survey Telescope (LSST) program is jointly funded by the NSF, the DOE, and private institutions and donors. From an NSF funding standpoint, the LSST is a Major Research Equipment and Facilities (MREFC) project. The NSF funding process requires proposals and D&D reviews to include activity-based budgets and schedules; documented basis of estimates; risk-based contingency analysis; cost escalation and categorization. "Out-of-the box," the commercial tool Primavera P6 contains approximately 90% of the planning and estimating capability needed to satisfy R&D phase requirements, and it is customizable/configurable for remainder with relatively little effort. We describe the customization/configuration and use of Primavera for the LSST Project Management Control System (PMCS), assess our experience to date, and describe future directions. Examples in this paper are drawn from the LSST Data Management System (DMS), which is one of three main subsystems of the LSST and is funded by the NSF. By astronomy standards the LSST DMS is a large data management project, processing and archiving over 70 petabyes of image data, producing over 20 petabytes of catalogs annually, and generating 2 million transient alerts per night. Over the 6-year construction and commissioning phase, the DM project is estimated to require 600,000 hours of engineering effort. In total, the DMS cost is approximately 60% hardware/system software and 40% labor. © 2012 SPIE.


Oluseyi H.M.,Florida Institute of Technology | Becker A.C.,University of Washington | Culliton C.,Florida Institute of Technology | Furqan M.,Florida Institute of Technology | And 9 more authors.
Astronomical Journal | Year: 2012

We report on a study to determine the efficiency of the Large Synoptic Survey Telescope (LSST) to recover the periods, brightnesses, and shapes of RR Lyrae stars' light curves in the volume extending to heliocentric distances of 1.5 Mpc. We place the smoothed light curves of 30 type ab and 10 type c RR Lyrae stars in 1007 fields across the sky, each of which represents a different realization of the LSST sampling cadences, and that sample five particular observing modes. A light curve simulation tool was used to sample the idealized RR Lyrae stars' light curves, returning each as it would have been observed by LSST, including realistic photometric scatter, limiting magnitudes, and telescope downtime. We report here the period, brightness, and light curve shape recovery as a function of apparent magnitude and for survey lengths varying from 1 to 10years. We find that 10years of LSST data are sufficient to recover the pulsation periods with a fractional precision of 10 -5 for ≥90% of ab stars within ≈360kpc of the Sun in Universal Cadence fields and out to ≈760kpc for Deep Drilling fields. The 50% completeness level extends to ≈600kpc and 1.0Mpc for the same fields, respectively. For virtually all stars that had their periods recovered, their light curve shape parameter φ 31 was recovered with sufficient precision to also recover photometric metallicities to within 0.14 dex (the systematic error in the photometric relations). With RR Lyrae stars' periods and metallicities well measured to these distances, LSST will be able to search for halo streams and dwarf satellite galaxies over half of the Local Group, informing galaxy formation models and providing essential data for mapping the Galactic potential. This study also informs the LSST science operations plan for optimizing observing strategies to achieve particular science goals. We additionally present a new [Fe/H]-φ 31 photometric relation in the r band and a new and generally useful metric for defining period recovery for time domain surveys. © © 2012. The American Astronomical Society. All rights reserved..


Axelrod T.,Steward Observatory | Kantor J.,LSST Corporation | Lupton R.H.,Princeton University | Pierfederici F.,US Space Telescope Science Institute
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The LSST Data Management System is built on an open source software framework that has middleware and application layers. The middleware layer provides capabilities to construct, configure, and manage pipelines on clusters of processing nodes, and to manage the data the pipelines consume and produce. It is not in any way specific to astronomical applications. The complementary application layer provides the building blocks for constructing pipelines that process astronomical data, both in image and catalog forms. The application layer does not directly depend upon the LSST middleware, and can readily be used with other middleware implementations. Both layers have object oriented designs that make the creation of more specialized capabilities relatively easy through class inheritance. This paper outlines the structure of the LSST application framework and explores its usefulness for constructing pipelines outside of the LSST context, two examples of which are discussed. The classes that the framework provides are related within a domain model that is applicable to any astronomical pipeline that processes imaging data. Specifically modeled are mosaic imaging sensors; the images from these sensors and the transformations that result as they are processed from raw sensor readouts to final calibrated science products; and the wide variety of catalogs that are produced by detecting and measuring astronomical objects in a stream of such images. The classes are implemented in C++ with Python bindings provided so that pipelines can be constructed in any desired mixture of C++ and Python. © 2010 SPIE.

Loading LSST Corporation collaborators
Loading LSST Corporation collaborators