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[show abstract]
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ABSTRACT: We present a sample of ~5,000 RR Lyrae stars selected from the recalibrated
LINEAR dataset and detected at heliocentric distances between 5 kpc and 30 kpc
over ~8,000 deg^2 of sky. The coordinates and light curve properties, such as
period and Oosterhoff type, are made publicly available. 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. The number density distribution of halo RRab
stars as a function of galactocentric distance can be described as an oblate
ellipsoid with the 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. Using a 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 is suggestive of tidal streams
possibly originating from globular clusters. Spectroscopic followup of detected
halo groups is encouraged.
05/2013;
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[show abstract]
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ABSTRACT: The Apache Point Survey of Transit Lightcurves of Exoplanets (APOSTLE)
observed 10 transits of XO-2b over a period of three years. We present
measurements which confirm previous estimates of system parameters like the
normalized semi-major axis (a/R_{*}), stellar density (\rho_{*}), impact
parameter (b) and orbital inclination (i_{orb}). Our errors on system
parameters like a/R_{*} and \rho_{*} have improved by ~40% compared to previous
best ground-based measurements. Our study of the transit times show no evidence
for transit timing variations and we are able to rule out co-planar companions
with masses \ge 0.20 \mearth\ in low order mean motion resonance with XO-2b. We
also explored the stability of the XO-2 system given various orbital
configurations of a hypothetical planet near the 2:1 mean motion resonance. We
find that a wide range of orbits (including Earth-mass perturbers) are both
dynamically stable and produce observable TTVs. We find that up to 51% of our
stable simulations show TTVs that are smaller than the typical transit timing
errors (~20 sec) measured for XO-2b, and hence remain undetectable.
04/2013;
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[show abstract]
[hide abstract]
ABSTRACT: We present transit observations of the WASP-2 exoplanet system by the Apache
Point Survey of Transit Lightcurves of Exoplanets (APOSTLE) program. Model
fitting to these data allows us to improve measurements of the hot-Jupiter
exoplanet WASP-2b and its orbital parameters by a factor of ~2 over prior
studies; we do not find evidence for transit depth variations. We do find
reduced chi^2 values greater than 1.0 in the observed minus computed transit
times. A sinusoidal fit to the residuals yields a timing semi-amplitude of 32
seconds and a period of 389 days. However, random rearrangements of the data
provide similar quality fits, and we cannot with certainty ascribe the timing
variations to mutual exoplanet interactions. This inconclusive result is
consistent with the lack of incontrovertible transit timing variations (TTVs)
observed in other hot-Jupiter systems. This outcome emphasizes that unique
recognition of TTVs requires dense sampling of the libration cycle (e.g.
continuous observations from space-based platforms). However, even in systems
observed with the Kepler spacecraft, there is a noted lack of transiting
companions and TTVs in hot-Jupiter systems. This result is more meaningful, and
indicates that hot-Jupiter systems, while they are easily observable from the
ground, do not appear to be currently configured in a manner favorable to the
detection of TTVs. The future of ground-based TTV studies may reside in
resolving secular trends, and/or implementation at extreme quality observing
sites to minimize atmospheric red noise.
01/2013;
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[show abstract]
[hide abstract]
ABSTRACT: The Apache Point Survey of Transit Lightcurves of Exoplanets (APOSTLE)
observed eleven transits of TrES-3b over two years in order to constrain system
parameters and look for transit timing and depth variations. We describe an
updated analysis protocol for APOSTLE data, including the reduction pipeline,
transit model and Markov Chain Monte Carlo analyzer. Our estimates of the
system parameters for TrESb are consistent with previous estimates to within
the 2\sigma\ confidence level. We improved the errors (by 10--30%) on system
parameters like the orbital inclination ($i_{\text{orb}}$), impact parameter
(b) and stellar density (\rho$_{\star}$) compared to previous measurements. The
near-grazing nature of the system, and incomplete sampling of some transits,
limited our ability to place reliable uncertainties on individual transit
depths and hence we do not report strong evidence for variability. Our analysis
of the transit timing data show no evidence for transit timing variations and
our timing measurements are able to rule out Super-Earth and Gas Giant
companions in low order mean motion resonance with TrES-3b.
11/2012;
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John J. Ruan,
Scott F. Anderson,
Chelsea L. MacLeod, Andrew C. Becker,
T. H. Burnett,
James R. A. Davenport,
Zeljko Ivezic,
Christopher S. Kochanek,
Richard M. Plotkin,
Branimir Sesar,
J. Scott Stuart
[show abstract]
[hide abstract]
ABSTRACT: We investigate the use of optical photometric variability to select and
identify blazars in large-scale time-domain surveys, in part to aid in the
identification of blazar counterparts to the ~30% of gamma-ray sources in the
Fermi 2FGL catalog still lacking reliable associations. Using data from the
optical LINEAR asteroid survey, we characterize the optical variability of
blazars by fitting a damped random walk model to individual light curves with
two main model parameters, the characteristic timescales of variability (tau),
and driving amplitudes on short timescales (sigma). Imposing cuts on minimum
tau and sigma allows for blazar selection with high efficiency E and
completeness C. To test the efficacy of this approach, we apply this method to
optically variable LINEAR objects that fall within the several-arcminute error
ellipses of gamma-ray sources in the Fermi 2FGL catalog. Despite the extreme
stellar contamination at the shallow depth of the LINEAR survey, we are able to
recover previously-associated optical counterparts to Fermi AGN with E > 88%
and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r <
8'. We find that the suggested radio counterpart to Fermi source 2FGL
J1649.6+5238 has optical variability consistent with other gamma-ray blazars,
and is likely to be the gamma-ray source. Our results suggest that the
variability of the non-thermal jet emission in blazars is stochastic in nature,
with unique variability properties due to the effects of relativistic beaming.
After correcting for beaming, we estimate that the characteristic timescale of
blazar variability is ~3 years in the rest-frame of the jet, in contrast with
the ~320 day disk flux timescale observed in quasars. The variability-based
selection method presented will be useful for blazar identification in
time-domain optical surveys, and is also a probe of jet physics.
09/2012;
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[show abstract]
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ABSTRACT: We present follow-up observations and analysis of the recently discovered
short period low-mass eclipsing binary, SDSS J001641-000925. With an orbital
period of 0.19856 days, this system has one of the shortest known periods for
an M dwarf binary system. Medium-resolution spectroscopy and multi-band
photometry for the system are presented. Markov chain Monte Carlo modeling of
the light curves and radial velocities yields estimated masses for the stars of
M1 = 0.54 +/- 0.07 Msun and M2 = 0.34 +/- 0.04 Msun, and radii of R1 = 0.68 +/-
0.03 Rsun and R2 = 0.58 +/- 0.03 Rsun respectively. This solution places both
components above the critical Roche overfill limit, providing strong evidence
that SDSS J001641-000925 is the first verified M-dwarf contact binary system.
Within the follow-up spectroscopy we find signatures of non-solid body rotation
velocities, which we interpret as evidence for mass transfer or loss within the
system. In addition, our photometry samples the system over 9 years, and we
find strong evidence for period decay at the rate of dP/dt ~8 s/yr. Both of
these signatures raise the intriguing possibility that the system is in
over-contact, and actively losing angular momentum, likely through mass loss.
This places SDSS J001641-000925 as not just the first M-dwarf over-contact
binary, but one of the few systems of any spectral type known to be actively
undergoing coalescence. Further study SDSS J001641-000925 is on-going to verify
the nature of the system, which may prove to be a unique astrophysical
laboratory.
06/2012;
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Michael Solontoi,
Zeljko Ivezic,
Mario Juric, Andrew C. Becker,
Lynne Jones,
Andrew A. West,
Steve Kent,
Robert H. Lupton,
Mark Claire,
Gillian R. Knapp,
Tom Quinn,
James E. Gunn,
Donald P. Schneider
[show abstract]
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ABSTRACT: We present the ensemble properties of 31 comets (27 resolved and 4
unresolved) observed by the Sloan Digital Sky Survey (SDSS). This sample of
comets represents about 1 comet per 10 million SDSS photometric objects.
Five-band (u,g,r,i,z) photometry is used to determine the comets' colors,
sizes, surface brightness profiles, and rates of dust production in terms of
the Af{\rho} formalism. We find that the cumulative luminosity function for the
Jupiter Family Comets in our sample is well fit by a power law of the form N(<
H) \propto 10(0.49\pm0.05)H for H < 18, with evidence of a much shallower fit
N(< H) \propto 10(0.19\pm0.03)H for the faint (14.5 < H < 18) comets. The
resolved comets show an extremely narrow distribution of colors (0.57 \pm 0.05
in g - r for example), which are statistically indistinguishable from that of
the Jupiter Trojans. Further, there is no evidence of correlation between color
and physical, dynamical, or observational parameters for the observed comets.
02/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present the first rates of flares from M dwarf stars in both red optical
and near infrared (NIR) filters. We have studied ~50,000 M dwarfs from the SDSS
Stripe 82 area, and 1,321 M dwarfs from the 2MASS Calibration Scan Point Source
Working Database that overlap SDSS imaging fields. We assign photometric
spectral types from M0 to M6 using (r-i) and (i-z) colors for every star in our
sample. Stripe 82 stars each have 50-100 epochs of data, while 2MASS
Calibration stars have ~1900 epochs. From these data we estimate the observed
rates and theoretical detection thresholds for flares in eight photometric
bands as a function of spectral type. Optical flare rates are found to be in
agreement with previous studies, while the frequency per hour of NIR flare
detections is found to be more than two orders of magnitude lower. An excess of
small amplitude flux increases in all bands exhibits a power-law distribution,
which we interpret as the result of flares below our detection thresholds. In
order to investigate the recovery efficiency for flares in each filter, we
extend a two-component flare model into the NIR. Quiescent M0-M6 spectral
templates were used with the model to predict the photometric response of
flares from u to Ks. We determine that red optical filters are sensitive to
flares with u-band amplitudes >2 mag, and NIR filters to flares with delta
u>4.5 mag. Our model predicts that M0 stars have the best color-contrast for
J-band detections, but M4-M6 stars should show the highest rate of NIR flares
with amplitudes of delta J ~0.01 mag. Characterizing flare rates and
photometric variations at longer wavelengths is important for predicting the
signatures of M dwarf variability in next-generation surveys, and we discuss
their impact on surveys such as LSST.
02/2012;
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Chelsea L. MacLeod,
Zeljko Ivezic,
Branimir Sesar,
Wim de Vries,
Christopher S. Kochanek,
Brandon C. Kelly, Andrew C. Becker,
Robert H. Lupton,
Patrick B. Hall,
Gordon T. Richards,
Scott F. Anderson,
Donald P. Schneider
[show abstract]
[hide abstract]
ABSTRACT: We provide a quantitative description and statistical interpretation of the
optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS)
has obtained repeated imaging in five UV-to-IR photometric bands for 33,881
spectroscopically confirmed quasars. About 10,000 quasars have an average of 60
observations in each band obtained over a decade along Stripe 82 (S82), whereas
the remaining ~25,000 have 2-3 observations due to scan overlaps. The observed
time lags span the range from a day to almost 10 years, and constrain quasar
variability at rest-frame time lags of up to 4 years, and at rest-frame
wavelengths from 1000A to 6000A. We publicly release a user-friendly catalog of
quasars from the SDSS Data Release 7 that have been observed at least twice in
SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it
to analyze the ensemble properties of quasar variability. Based on a damped
random walk (DRW) model defined by a characteristic time scale and an
asymptotic variability amplitude that scale with the luminosity, black hole
mass, and rest wavelength for individual quasars calibrated in S82, we can
fully explain the ensemble variability statistics of the non-S82 quasars such
as the exponential distribution of large magnitude changes. All available data
are consistent with the DRW model as a viable description of the optical
continuum variability of quasars on time scales of ~5-2000 days in the rest
frame. We use these models to predict the incidence of quasar contamination in
transient surveys such as those from PTF and LSST.
12/2011;
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James Annis,
Marcelle Soares-Santos,
Michael A. Strauss, Andrew C. Becker,
Scott Dodelson,
Xiaohui Fan,
James E. Gunn,
Jiangang Hao,
Zeljko Ivezic,
Sebastian Jester,
Linhua Jiang,
David E. Johnston,
Jeffrey M. Kubo,
Hubert Lampeitl,
Huan Lin,
Robert H. Lupton,
Gajus Miknaitis,
Hee-Jong Seo,
Melanie Simet,
Brian Yanny
[show abstract]
[hide abstract]
ABSTRACT: We present details of the construction and characterization of the coaddition
of the Sloan Digital Sky Survey Stripe 82 \ugriz\ imaging data. This survey
consists of 275 deg$^2$ of repeated scanning by the SDSS camera of $2.5\arcdeg$
of $\delta$ over $-50\arcdeg \le \alpha \le 60\arcdeg$ centered on the
Celestial Equator. Each piece of sky has $\sim 20$ runs contributing and thus
reaches $\sim2$ magnitudes fainter than the SDSS single pass data, i.e. to
$r\sim 23.5$ for galaxies. We discuss the image processing of the coaddition,
the modeling of the PSF, the calibration, and the production of standard SDSS
catalogs. The data have $r$-band median seeing of 1.1\arcsec, and are
calibrated to $\le 1%$. Star color-color, number counts, and psf size vs
modelled size plots show the modelling of the PSF is good enough for precision
5-band photometry. Structure in the psf-model vs magnitude plot show minor psf
mis-modelling that leads to a region where stars are being mis-classified as
galaxies, and this is verified using VVDS spectroscopy. As this is a wide area
deep survey there are a variety of uses for the data, including galactic
structure, photometric redshift computation, cluster finding and cross
wavelength measurements, weak lensing cluster mass calibrations, and cosmic
shear measurements.
11/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We describe photometric recalibration of data obtained by the asteroid survey LINEAR. Although LINEAR was designed for astrometric discovery of moving objects, the data set described here contains over 5 billion photometric measurements for about 25 million objects, mostly stars. We use Sloan Digital Sky Survey (SDSS) data from the overlapping ~10,000 deg2 of sky to recalibrate LINEAR photometry and achieve errors of 0.03 mag for sources not limited by photon statistics with errors of 0.2 mag at r ~ 18. With its 200 observations per object on average, LINEAR data provide time domain information for the brightest four magnitudes of the SDSS survey. At the same time, LINEAR extends the deepest similar wide-area variability survey, the Northern Sky Variability Survey, by 3 mag. We briefly discuss the properties of about 7000 visually confirmed periodic variables, dominated by roughly equal fractions of RR Lyrae stars and eclipsing binary stars, and analyze their distribution in optical and infrared color-color diagrams. The LINEAR data set is publicly available from the SkyDOT Web site.
The Astronomical Journal 11/2011; 142(6):190. · 4.03 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We describe photometric recalibration of data obtained by the asteroid survey
LINEAR. Although LINEAR was designed for astrometric discovery of moving
objects, the dataset described here contains over 5 billion photometric
measurements for about 25 million objects, mostly stars. We use SDSS data from
the overlapping ~10,000 deg^2 of sky to recalibrate LINEAR photometry, and
achieve errors of 0.03 mag for sources not limited by photon statistics, with
errors of 0.2 mag at r~18. With its 200 observations per object on average,
LINEAR data provide time domain information for the brightest 4 magnitudes of
SDSS survey. At the same time, LINEAR extends the deepest similar wide-area
variability survey, the Northern Sky Variability Survey, by 3 mag. We briefly
discuss the properties of about 7,000 visually confirmed periodic variables,
dominated by roughly equal fractions of RR Lyrae stars and eclipsing binary
stars, and analyze their distribution in optical and infra-red color-color
diagrams. The LINEAR dataset is publicly available from the SkyDOT website
(http://skydot.lanl.gov).
09/2011;
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[show abstract]
[hide abstract]
ABSTRACT: Time-resolved databases with large spatial coverage are quickly becoming a
standard tool for all types of astronomical studies. We report preliminary
results from our search for stellar flares in the 2MASS calibration fields. A
sample of 4343 M dwarfs, spatially matched between the SDSS and the 2MASS
calibration fields, each with hundreds to thousands of epochs in near infrared
bandpasses, is analyzed using a modified Welch-Stetson index to characterize
the variability. A Monte Carlo model was used to assess the noise of the
variability index. We find significnat residuals above the noise with power-law
slopes of -3.37 and -4.05 for our JH and HKs distributions respectively. This
is evidence for flares being observed from M dwarfs in infrared photometry.
01/2011;
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Hakeem M. Oluseyi, Andrew C. Becker,
Christopher C. Culliton,
Muhammad Furqan,
Keri L. Hoadley,
Paul Regencia,
Akeem J. Wells,
Lynne Jones,
Simon Krughoff,
Branimir Sesar,
Suzanne Jacoby
[show abstract]
[hide abstract]
ABSTRACT: The Large Synoptic Survey Telescope (LSST) is an anticipated to undertake a 10–year, 3π steradian survey that promises to observe millions of new periodic variable stars. We report on a study to determine the efficiency of the LSST to recover the light curve properties of RR Lyrae stars. An LSST light curve simulation tool was used to sample input idealized light curves or RR Lyrae stars observed in SDSS Stripe 82 data, returning each as it would have been observed by LSST, including realistic photometric scatter, limiting magnitudes, and telescope downtime. Our results show that the LSST will be capable of mapping the spatial distributions and chemical compositions of halo stellar overdensities using RR Lyrae discovered across 3π steradians and out to nearly 1.5 Mpc. LSST will thus enable the mapping of halo merger streams, the discovery of new dwarf galaxies, and the mapping galactic halos throughout the Local Group galaxies.
Proceedings of the International Astronomical Union 11/2010; 6:300 - 304.
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Branimir Sesar,
Željko Ivezić,
Skyler H. Grammer,
Dylan P. Morgan, Andrew C. Becker,
Mario Jurić,
Nathan De Lee,
James Annis,
Timothy C. Beers,
Xiaohui Fan,
Robert H. Lupton,
James E. Gunn,
Gillian R. Knapp,
Linhua Jiang,
Sebastian Jester,
David E. Johnston,
and Hubert Lampeitl
[show abstract]
[hide abstract]
ABSTRACT: We present an improved analysis of halo substructure traced by RR Lyrae stars in the Sloan Digital Sky Survey (SDSS) stripe 82 region. With the addition of SDSS-II data, a revised selection method based on new ugriz light curve templates results in a sample of 483 RR Lyrae stars that is essentially free of contamination. The main result from our first study persists: the spatial distribution of halo stars at galactocentric distances 5-100 kpc is highly inhomogeneous. At least 20% of halo stars within 30 kpc from the Galactic center can be statistically associated with substructure. We present strong direct evidence, based on both RR Lyrae stars and main-sequence stars, that the halo stellar number density profile significantly steepens beyond a Galactocentric distance of ~30 kpc, and a larger fraction of the stars are associated with substructure. By using a novel method that simultaneously combines data for RR Lyrae and main-sequence stars, and using photometric metallicity estimates for main-sequence stars derived from deep co-added u-band data, we measure the metallicity of the Sagittarius dSph tidal stream (trailing arm) toward R.A. ~2h-3h and decl. ~ 0° to be 0.3 dex higher ([Fe/H] = –1.2) than that of surrounding halo field stars. Together with a similar result for another major halo substructure, the Monoceros stream, these results support theoretical predictions that an early forming, smooth inner halo, is metal-poor compared to high surface brightness material that have been accreted onto a later-forming outer halo. The mean metallicity of stars in the outer halo that are not associated with detectable clumps may still be more metal-poor than the bulk of inner-halo stars, as has been argued from other data sets.
The Astrophysical Journal 12/2009; 708(1):717. · 6.02 Impact Factor
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LSST Science Collaboration,
Paul A. Abell,
Julius Allison,
Scott F. Anderson,
John R. Andrew,
J. Roger P. Angel,
Lee Armus,
David Arnett,
S. J. Asztalos,
Tim S. Axelrod, [......],
Oliver Wiecha,
Benjamin F. Williams,
Beth Willman,
David Wittman,
Sidney C. Wolff,
W. Michael Wood-Vasey,
Przemek Wozniak,
Patrick Young,
Andrew Zentner,
Hu Zhan
[show abstract]
[hide abstract]
ABSTRACT: A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.
12/2009;
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Richard Kessler, Andrew C. Becker,
David Cinabro,
Jake Vanderplas,
Joshua A. Frieman,
John Marriner,
Tamara M. Davis,
Benjamin Dilday,
Jon Holtzman,
Saurabh W. Jha, [......],
Adam G. Riess,
Roger Romani,
Donald P. Schneider,
Jesper Sollerman,
Naohiro Takanashi,
Kouichi Tokita,
Kurt van der Heyden,
J. C. Wheeler,
Naoki Yasuda,
and Donald York
[show abstract]
[hide abstract]
ABSTRACT: We present measurements of the Hubble diagram for 103 Type Ia supernovae (SNe) with redshifts 0.04 < z < 0.42, discovered during the first season (Fall 2005) of the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. These data fill in the redshift "desert" between low- and high-redshift SN Ia surveys. Within the framework of the MLCS2K2 light-curve fitting method, we use the SDSS-II SN sample to infer the mean reddening parameter for host galaxies, RV = 2.18 ± 0.14stat ± 0.48syst, and find that the intrinsic distribution of host-galaxy extinction is well fitted by an exponential function, P(AV ) = exp(–AV /τV), with τV = 0.334 ± 0.088 mag. We combine the SDSS-II measurements with new distance estimates for published SN data from the ESSENCE survey, the Supernova Legacy Survey (SNLS), the Hubble Space Telescope (HST), and a compilation of Nearby SN Ia measurements. A new feature in our analysis is the use of detailed Monte Carlo simulations of all surveys to account for selection biases, including those from spectroscopic targeting. Combining the SN Hubble diagram with measurements of baryon acoustic oscillations from the SDSS Luminous Red Galaxy sample and with cosmic microwave background temperature anisotropy measurements from the Wilkinson Microwave Anisotropy Probe, we estimate the cosmological parameters w and ΩM, assuming a spatially flat cosmological model (FwCDM) with constant dark energy equation of state parameter, w. We also consider constraints upon ΩM and ΩΛ for a cosmological constant model (ΛCDM) with w = –1 and non-zero spatial curvature. For the FwCDM model and the combined sample of 288 SNe Ia, we find w = –0.76 ± 0.07(stat) ± 0.11(syst), ΩM = 0.307 ± 0.019(stat) ± 0.023(syst) using MLCS2K2 and w = –0.96 ± 0.06(stat) ± 0.12(syst), ΩM = 0.265 ± 0.016(stat) ± 0.025(syst) using the SALT-II fitter. We trace the discrepancy between these results to a difference in the rest-frame UV model combined with a different luminosity correction from color variations; these differences mostly affect the distance estimates for the SNLS and HST SNe. We present detailed discussions of systematic errors for both light-curve methods and find that they both show data-model discrepancies in rest-frame U band. For the SALT-II approach, we also see strong evidence for redshift-dependence of the color-luminosity parameter (β). Restricting the analysis to the 136 SNe Ia in the Nearby+SDSS-II samples, we find much better agreement between the two analysis methods but with larger uncertainties: w = –0.92 ± 0.13(stat)+0.10 –0.33(syst) for MLCS2K2 and w = –0.92 ± 0.11(stat)+0.07 –0.15 (syst) for SALT-II.
The Astrophysical Journal Supplement Series 10/2009; 185(1):32. · 13.46 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present a flare rate analysis of 50,130 M dwarf light curves in Sloan Digital Sky Survey Stripe 82. We identified 271 flares using a customized variability index to search ∼2.5 million photometric observations for flux increases in the u and g bands. Every image of a flaring observation was examined by eye and with a point-spread function-matching and image subtraction tool to guard against false positives. Flaring is found to be strongly correlated with the appearance of Hα in emission in the quiet spectrum. Of the 99 flare stars that have spectra, we classify eight as relatively inactive. The flaring fraction is found to increase strongly in stars with redder colors during quiescence, which can be attributed to the increasing flare visibility and increasing active fraction for redder stars. The flaring fraction is strongly correlated with |Z| distance such that most stars that flare are within 300 pc of the Galactic plane. We derive flare u-band luminosities and find that the most luminous flares occur on the earlier-type m dwarfs. Our best estimate of the lower limit on the flaring rate (averaged over Stripe 82) for flares with Δu 0.7 mag on stars with u < 22 is 1.3 flares hr −1 deg −2 but can vary significantly with the line of sight.
The Astronomical Journal. 09/2009; 138:633-648.
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Nathan A. Kaib, Andrew C. Becker,
R. Lynne Jones,
Andrew W. Puckett,
Dmitry Bizyaev,
Benjamin Dilday,
Joshua A. Frieman,
Daniel J. Oravetz,
Kaike Pan,
Thomas Quinn,
Donald P. Schneider,
and Shannon Watters
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a minor planet (2006 SQ372) on an orbit with a perihelion of 24 AU and a semimajor axis of 796 AU. Dynamical simulations show that this is a transient orbit and is unstable on a timescale of ~200 Myr. Falling near the upper semimajor axis range of the scattered disk and the lower semimajor axis range of the Oort Cloud, previous membership in either class is possible. By modeling the production of similar orbits from the Oort Cloud as well as from the scattered disk, we find that the Oort Cloud produces 16 times as many objects on SQ372-like orbits as the scattered disk. Given this result, we believe this to be the most distant long-period comet (LPC) ever discovered. Furthermore, our simulation results also indicate that 2000 OO67 has had a similar dynamical history. Unaffected by the "Jupiter-Saturn Barrier," these two objects are most likely LPCs from the inner Oort Cloud.
The Astrophysical Journal 03/2009; 695(1):268. · 6.02 Impact Factor
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Lucianne M. Walkowicz, Andrew C. Becker,
Scott F. Anderson,
Joshua S. Bloom,
Leonid Georgiev,
Josh Grindlay,
Knox Long,
Anjum Mukadam,
Andrej Prsa,
Joshua Pepper,
Arne Rau,
Branimir Sesar,
Nicole Silvestri,
Nathan Smith,
Keivan Stassun,
Paula Szkody
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ABSTRACT: The next decade of survey astronomy has the potential to transform our knowledge of variable stars. Stellar variability underpins our knowledge of the cosmological distance ladder, and provides direct tests of stellar formation and evolution theory. Variable stars can also be used to probe the fundamental physics of gravity and degenerate material in ways that are otherwise impossible in the laboratory. The computational and engineering advances of the past decade have made large-scale, time-domain surveys an immediate reality. Some surveys proposed for the next decade promise to gather more data than in the prior cumulative history of astronomy. The actual implementation of these surveys will have broad implications for the types of science that will be enabled. We examine the design considerations for an optimal time-domain photometric survey dedicated to variable star science, including: observing cadence, wavelength coverage, photometric and astrometric accuracy, single-epoch and cumulative depth, overall sky coverage, and data access by the broader astronomical community. The best surveys must combine aspects from each of these considerations to fully realize the potential for the next decade of time-domain science.
03/2009;
