398 research outputs found
The Luminosity and Mass Functions of Low-Mass Stars in the Galactic Disk: I. The Calibration Region
We present measurements of the luminosity and mass functions of low-mass
stars constructed from a catalog of matched Sloan Digital Sky Survey (SDSS) and
2 Micron All Sky Survey (2MASS) detections. This photometric catalog contains
more than 25,000 matched SDSS and 2MASS point sources spanning ~30 square
degrees on the sky. We have obtained follow-up spectroscopy, complete to J=16,
of more than 500 low mass dwarf candidates within a 1 square degree sub-sample,
and thousands of additional dwarf candidates in the remaining 29 square
degrees. This spectroscopic sample verifies that the photometric sample is
complete, uncontaminated, and unbiased at the 99% level globally, and at the
95% level in each color range. We use this sample to derive the luminosity and
mass functions of low-mass stars over nearly a decade in mass (0.7 M_sun > M_*
> 0.1 M_sun). We find that the logarithmically binned mass function is best fit
with an M_c=0.29 log-normal distribution, with a 90% confidence interval of
M_c=0.20--0.50. These 90% confidence intervals correspond to linearly binned
mass functions peaking between 0.27 M_sun and 0.12 M_sun, where the best fit MF
turns over at 0.17 M_sun. A power law fit to the entire mass range sampled
here, however, returns a best fit of alpha=1.1 (where the Salpeter slope is
alpha = 2.35). These results agree well with most previous investigations,
though differences in the analytic formalisms adopted to describe those mass
functions can give the false impression of disagreement. Given the richness of
modern-day astronomical datasets, we are entering the regime whereby stronger
conclusions can be drawn by comparing the actual datapoints measured in
different mass functions, rather than the results of analytic analyses that
impose structure on the data a priori. (abridged)Comment: Accepted for publication in the Astronomical Journal. 21 pages,
emulateapj format, 12 figures. Figures 1, 4, 11 and 12 degraded for astroph;
full resolution version available for download at
http://www.cfa.harvard.edu/~kcovey
The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release
We present the fifth edition of the Sloan Digital Sky Survey (SDSS) Quasar
Catalog, which is based upon the SDSS Seventh Data Release. The catalog, which
contains 105,783 spectroscopically confirmed quasars, represents the conclusion
of the SDSS-I and SDSS-II quasar survey. The catalog consists of the SDSS
objects that have luminosities larger than M_i = -22.0 (in a cosmology with H_0
= 70 km/s/Mpc Omega_M = 0.3, and Omega_Lambda = 0.7) have at least one emission
line with FWHM larger than 1000 km/s or have interesting/complex absorption
features, are fainter than i > 15.0 and have highly reliable redshifts. The
catalog covers an area of 9380 deg^2. The quasar redshifts range from 0.065 to
5.46, with a median value of 1.49; the catalog includes 1248 quasars at
redshifts greater than four, of which 56 are at redshifts greater than five.
The catalog contains 9210 quasars with i < 18; slightly over half of the
entries have i< 19. For each object the catalog presents positions accurate to
better than 0.1" rms per coordinate, five-band (ugriz) CCD-based photometry
with typical accuracy of 0.03 mag, and information on the morphology and
selection method. The catalog also contains radio, near-infrared, and X-ray
emission properties of the quasars, when available, from other large-area
surveys. The calibrated digital spectra cover the wavelength region 3800-9200
Ang. at a spectral resolution R = 2000 the spectra can be retrieved from the
SDSS public database using the information provided in the catalog. Over 96% of
the objects in the catalog were discovered by the SDSS. We also include a
supplemental list of an additional 207 quasars with SDSS spectra whose archive
photometric information is incomplete.Comment: Accepted, to appear in AJ, 7 figures, electronic version of Table 2
is available, see
http://www.sdss.org/dr7/products/value_added/qsocat_dr7.htm
Infrared Photometry of Late-M, L, and T Dwarfs
We present ZJHKL'M' photometry of a sample of 58 late-M, L, and T dwarfs,
most of which are identified from the Sloan Digital Sky Survey and the Two
Micron All-Sky Survey. Near-infrared spectra and spectral classifications for
most of this sample are presented in a companion paper by Geballe et al. We
derive the luminosities of 18 dwarfs in the sample and the results imply that
the effective temperature range for the L dwarfs in our sample is approximately
2200-1300 K and for the T dwarfs 1300-800 K. We obtained new photometric data
at the United Kingdom Infrared Telescope for: 42 dwarfs at Z, 34 dwarfs at JHK,
21 dwarfs at L', as well as M' data for two L dwarfs and two T dwarfs. The M'
data provide the first accurate photometry for L and T dwarfs in this bandpass
- for a T2 and a T5 dwarf, we find K-M'=1.2 and 1.6, respectively. These colors
are much bluer than predicted by models suggesting that CO may be more abundant
in these objects than expected, as has been found for the T6 dwarf Gl 229B. We
also find that K-L' increases monotonically through most of the M, L, and T
subclasses, but it is almost constant between types L6 and T5. The degeneracy
is probably due to the onset of methane absorption at the blue edge of the L'
bandpass. The JHK colors of L dwarfs show significant scatter, suggesting that
the fluxes in these bandpasses are sensitive to variations in photospheric dust
properties. The H-K colors of the later T dwarfs also show some scatter which
we suggest is due to variations in pressure-induced molecular hydrogen opacity,
which is sensitive to gravity and metallicity.Comment: 33 pages incl. 6 figures, accepted by ApJ August 200
LSST Science Book, Version 2.0
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.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
Study of and decays and determination of the CKM angle
We report a study of the suppressed and favored
decays, where the neutral meson is detected
through its decays to the and CP-even and
final states. The measurement is carried out using a proton-proton
collision data sample collected by the LHCb experiment, corresponding to an
integrated luminosity of 3.0~fb. We observe the first significant
signals in the CP-even final states of the meson for both the suppressed
and favored modes, as well as
in the doubly Cabibbo-suppressed final state of the decay. Evidence for the ADS suppressed decay , with , is also presented. From the observed
yields in the , and their
charge conjugate decay modes, we measure the value of the weak phase to be
. This is one of the most precise
single-measurement determinations of to date.Comment: 22 pages, 9 figures; All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-020.htm
Observation of resonances consistent with pentaquark states in decays
Observations of exotic structures in the channel, that we refer to
as pentaquark-charmonium states, in decays are
presented. The data sample corresponds to an integrated luminosity of 3/fb
acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude
analysis is performed on the three-body final-state that reproduces the
two-body mass and angular distributions. To obtain a satisfactory fit of the
structures seen in the mass spectrum, it is necessary to include two
Breit-Wigner amplitudes that each describe a resonant state. The significance
of each of these resonances is more than 9 standard deviations. One has a mass
of MeV and a width of MeV, while the second
is narrower, with a mass of MeV and a width of MeV. The preferred assignments are of opposite parity, with one
state having spin 3/2 and the other 5/2.Comment: 48 pages, 18 figures including the supplementary material, v2 after
referee's comments, now 19 figure
Study of boson production in association with beauty and charm
The associated production of a boson with a jet originating from either a
light parton or heavy-flavor quark is studied in the forward region using
proton-proton collisions. The analysis uses data corresponding to integrated
luminosities of 1.0 and collected with the LHCb detector
at center-of-mass energies of 7 and 8 TeV, respectively. The bosons are
reconstructed using the decay and muons with a transverse
momentum, , larger than 20 GeV in the pseudorapidity range
GeV
and . The sum of the muon and jet momenta must satisfy
GeV. The fraction of jet events that originate from beauty
and charm quarks is measured, along with the charge asymmetries of the
and production cross-sections. The ratio of the jet to
jet production cross-sections is also measured using the
decay. All results are in agreement with Standard Model predictions
Measurements of long-range near-side angular correlations in TeV proton-lead collisions in the forward region
Two-particle angular correlations are studied in proton-lead collisions at a
nucleon-nucleon centre-of-mass energy of TeV, collected
with the LHCb detector at the LHC. The analysis is based on data recorded in
two beam configurations, in which either the direction of the proton or that of
the lead ion is analysed. The correlations are measured in the laboratory
system as a function of relative pseudorapidity, , and relative
azimuthal angle, , for events in different classes of event
activity and for different bins of particle transverse momentum. In
high-activity events a long-range correlation on the near side, , is observed in the pseudorapidity range . This
measurement of long-range correlations on the near side in proton-lead
collisions extends previous observations into the forward region up to
. The correlation increases with growing event activity and is found
to be more pronounced in the direction of the lead beam. However, the
correlation in the direction of the lead and proton beams are found to be
compatible when comparing events with similar absolute activity in the
direction analysed.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-040.htm
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