2,659 research outputs found
UBVRIJKL light curves of classical Cepheids
Photoelectric observations and light curves of UBVRIJKL system for classical Cepheid variable stars - tables and graph
Communications of the Lunar and Planetary Laboratory, volume 4, part 3 - Ubvrijkl photometry of the bright stars
Multicolor photometric analysis of bright stars - table
Relativistic jet models for the BL Lacertae object Mrk 421 during three epochs of observation
Coordinated observation of the nearby BL Lacertae object Mrk 421 obtained during May 1980, January 1984, and March 1984 are described. These observations give a time-frozen picture of the continuous spectrum of Mrk 421 at X-ray, ultraviolet, optical, and radio wavelengths. The observed spectra have been fitted to an inhomogeneous relativistic jet model. In general, the models reproduce the data well. Many of the observed differences during the three epochs can be attributed to variations in the opening angle of the jet and in the angle that the jet makes to the line of sight. The jet models obtained here are compared with the homogeneous, spherically symmetric, synchrotron self-Compton models for this source. The models are also compared with the relativistic jet models obtained for other active galactic nuclei
Measurement of the mass of the τ lepton
A data-driven energy scan in the immediate vicinity of the τ pair production threshold has been performed using the Beijing Spectrometer at the Beijing Electron-Positron Collider. Approximately 5 pb^(-1) of data, distributed over 12 scan points, have been collected. A previous mass value for the τ lepton, obtained using only the eμ final state, has been published. In this paper, the final BES result on the mass measurement is presented. The analysis is based on the combined data from the ee, eμ, eh, μμ, μh, and hh final states, where h denotes a charged π or K. A maximum likelihood fit to the τ pair production cross section data yields the value m_τ=1776.96_(-0.21)-0.17^(+0.18+0.25) MeV
Diffraction-limited near-IR imaging at Keck reveals asymmetric, time-variable nebula around carbon star CIT 6
We present multi-epoch, diffraction-limited images of the nebula around the
carbon star CIT 6 at 2.2 microns and 3.1 microns from aperture masking on the
Keck-I telescope. The near-IR nebula is resolved into two main components, an
elongated, bright feature showing time-variable asymmetry and a fainter
component about 60 milliarcseconds away with a cooler color temperature. These
images were precisely registered (~35 milliarcseconds) with respect to recent
visible images from the Hubble Space Telescope (Trammell et al. 2000), which
showed a bipolar structure in scattered light. The dominant near-IR feature is
associated with the northern lobe of this scattering nebula, and the
multi-wavelength dataset can be understood in terms of a bipolar dust shell
around CIT 6. Variability of the near-IR morphology is qualitatively consistent
with previously observed changes in red polarization, caused by varying
illumination geometry due to non-uniform dust production. The blue emission
morphology and polarization properties can not be explained by the above model
alone, but require the presence of a wide binary companion in the vicinity of
the southern polar lobe. The physical mechanisms responsible for the breaking
of spherical symmetry around extreme carbon stars, such as CIT 6 and IRC+10216,
remain uncertain.Comment: 18 pages, 5 figures (one in color), to appear in the Astrophysical
Journa
First analysis of anisotropic flow with Lee--Yang zeroes
We report on the first analysis of directed and elliptic flow with the new
method of Lee--Yang zeroes. Experimental data are presented for Ru+Ru reactions
at 1.69 AGeV measured with the FOPI detector at SIS/GSI. The results obtained
with several methods, based on the event-plane reconstruction, on Lee--Yang
zeroes, and on multi-particle cumulants (up to 5th order) applied for the first
time at SIS energies, are compared. They show conclusive evidence that
azimuthal correlations between nucleons and composite particles at this energy
are largely dominated by anisotropic flow.Comment: 5 pages, 3 figures, submitted to Phys. Rev. C Rapid Co
Isospin dependence of relative yields of and mesons at 1.528 AGeV
Results on and meson production in Ru +
Ru and Zr + Zr collisions at a beam kinetic
energy of 1.528 GeV, measured with the FOPI detector at GSI-Darmstadt, are
investigated as a possible probe of isospin effects in high density nuclear
matter. The measured double ratio ()/() is
compared to the predictions of a thermal model and a Relativistic Mean Field
transport model using two different collision scenarios and under different
assumptions on the stiffness of the symmetry energy. We find a good agreement
with the thermal model prediction and the assumption of a soft symmetry energy
for infinite nuclear matter while more realistic transport simulations of the
collisions show a similar agreement with the data but also exhibit a reduced
sensitivity to the symmetry term.Comment: 5 pages, 3 figures. accepted for publication in Phys. Rev.
The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies
We report on a large HST imaging survey of BL Lac objects, at spatial
resolution ~10 times better than previous ground-based surveys. We focus on
data reduction and analysis, describing the procedures used to model the host
galaxy surface brightness radial profiles. A total of 69 host galaxies were
resolved out of 110 objects observed, including almost all sources at z < 0.5.
We classify them morphologically by fitting with either an exponential disk or
a de~Vaucouleurs profile; when one fit is preferred over the other, in 58 of 69
cases, it is invariably the elliptical morphology. This is a very strong result
given the large number of BL Lac objects, the unprecedented spatial resolution,
and the homogeneity of the data set. With the present reclassification of the
host galaxy of 1418+546 as an elliptical, there remain no undisputed examples
of a disk galaxy hosting a BL Lac nucleus. This implies that, at 99%
confidence, fewer than 7% of BL Lacs can be in disk galaxies. The apparent
magnitude of the host galaxies varies with distance as expected if the absolute
magnitudes are approximately the same, with a spread of +-1 mag, out to
redshift z < 0.5. At larger redshifts, only 6 of 23 BL Lacs are resolved so the
present data do not constrain possible luminosity evolution of the host
galaxies. The collective Hubble diagram for BL Lac host galaxies and radio
galaxies strongly supports their unification.Comment: Accepted for publication on ApJS. 43 pages. 10 figures. Figure 1 can
also be downloaded from http://icarus.stsci.edu/~scarpa/tmp/hst_figure1.ta
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