673 research outputs found
A search for L dwarf binary systems
We present analysis of HST Planetary Camera images of twenty L dwarfs
identified in the course of the Two Micron All-Sky Survey. Four of the targets
have faint, red companions at separations between 0.07 and 0.29 arcseconds (1.6
to 7.6 AU). In three cases, the bolometric magnitudes of the components differ
by less than 0.3 magnitudes. Since the cooling rate for brown dwarfs is a
strong function of mass, similarity in luminosities implies comparable masses.
The faint component in the 2M0850 system, however, is over 1.3 magnitudes
fainter than the primary in the I-band, and ~0.8 magnitudes fainter in M(bol).
Indeed, 2M0850B is ~0.8 magnitudes fainter in I than the lowest luminosity L
dwarf currently known, while the absolute magnitude we deduce at J is almost
identical with M_J for Gl 229B. Theoretical models indicate a mass ratio of
\~0.75. The mean separation of the L dwarf binaries in the current sample is
smaller by a factor of two than amongst M dwarfs. We discuss the implications
of these results for the temperature scale in the L/T transition region and for
the binary frequency amongst L dwarfs.Comment: 38 pages, 11 figures; accepted for A
H_2 Emission From Disks Around Herbig Ae and T Tauri Stars
We present the initial results of a deep ISO-SWS survey
for the low J pure rotational emission lines of H2
toward a number of Herbig Ae and T Tauri stars.
The objects are selected to be as isolated as possible
from molecular clouds, with a spectral energy distribution
characteristic of a circumstellar disk. For most
of them the presence of a disk has been established
directly by millimeter interferometry. The S (1) line is
detected in most sources with a peak flux of 0.3-1 Jy.
The S(0) line is definitely seen in 2 objects: GG Tau
and HD 163296. The observations suggest the presence
of "warm" gas at T_(kin) ≈ 100 K with a mass of a
few % of the total gas+ dust mass, derived assuming
a gas-to-dust ratio of 100:1. The S(1) peak flux does
not show a strong correlation with spectral type of
the central star or continuum flux at 1.3 millimeter.
Possible origins for the warm gas seen in H_2 are discussed,
and comparisons with model calculations are
made
Quasiperiodic spin-orbit motion and spin tunes in storage rings
We present an in-depth analysis of the concept of spin precession frequency
for integrable orbital motion in storage rings. Spin motion on the periodic
closed orbit of a storage ring can be analyzed in terms of the Floquet theorem
for equations of motion with periodic parameters and a spin precession
frequency emerges in a Floquet exponent as an additional frequency of the
system. To define a spin precession frequency on nonperiodic synchro-betatron
orbits we exploit the important concept of quasiperiodicity. This allows a
generalization of the Floquet theorem so that a spin precession frequency can
be defined in this case too. This frequency appears in a Floquet-like exponent
as an additional frequency in the system in analogy with the case of motion on
the closed orbit. These circumstances lead naturally to the definition of the
uniform precession rate and a definition of spin tune. A spin tune is a uniform
precession rate obtained when certain conditions are fulfilled. Having defined
spin tune we define spin-orbit resonance on synchro--betatron orbits and
examine its consequences. We give conditions for the existence of uniform
precession rates and spin tunes (e.g. where small divisors are controlled by
applying a Diophantine condition) and illustrate the various aspects of our
description with several examples. The formalism also suggests the use of
spectral analysis to ``measure'' spin tune during computer simulations of spin
motion on synchro-betatron orbits.Comment: 62 pages, 1 figure. A slight extension of the published versio
Covariant and Heavy Quark Symmetric Quark Models
There exist relativistic quark models (potential or MIT-bag) which satisfy
the heavy quark symmetry (HQS) relations among meson decay constants and form
factors. Covariant construction of the momentum eigenstates, developed here,
can correct for spurious center-of-mass motion contributions.Proton form factor
and M1 transitions in quarkonia are calculated. Explicit expression for the
Isgur-Wise function is found and model determined deviations from HQS are
studied. All results depend on the model parameters only. No additional ad hoc
assumptions are needed.Comment: 34 pages (2 figures not included but avaliable upon request), LATEX,
(to be published in Phys.Rev.D
The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. IV. Lupus Observed with MIPS
We present maps of 7.78 square degrees of the Lupus molecular cloud complex
at 24, 70, and m. They were made with the Spitzer Space Telescope's
Multiband Imaging Photometer for Spitzer (MIPS) instrument as part of the
Spitzer Legacy Program, ``From Molecular Cores to Planet-Forming Disks'' (c2d).
The maps cover three separate regions in Lupus, denoted I, III, and IV. We
discuss the c2d pipeline and how our data processing differs from it. We
compare source counts in the three regions with two other data sets and
predicted star counts from the Wainscoat model. This comparison shows the
contribution from background galaxies in Lupus I. We also create two color
magnitude diagrams using the 2MASS and MIPS data. From these results, we can
identify background galaxies and distinguish them from probable young stellar
objects. The sources in our catalogs are classified based on their spectral
energy distribution (SED) from 2MASS and Spitzer wavelengths to create a sample
of young stellar object candidates. From 2MASS data, we create extinction maps
for each region and note a strong corresponence between the extinction and the
m emission. The masses we derived in each Lupus cloud from our
extinction maps are compared to masses estimated from CO and CO
and found to be similar to our extinction masses in some regions, but
significantly different in others. Finally, based on our color-magnitude
diagrams, we selected 12 of our reddest candidate young stellar objects for
individual discussion. Five of the 12 appear to be newly-discovered YSOs.Comment: 15 pages, 17 figures, uses emulateapj.cls. Accepted for publication
in ApJ. A version with high-quality figures can be found at
http://peggysue.as.utexas.edu/SIRTF
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First measurement of neutrino oscillation parameters using neutrinos and antineutrinos by NOvA.
The NOvA experiment has seen a 4.4σ signal of ν[over ¯]_{e} appearance in a 2 GeV ν[over ¯]_{μ} beam at a distance of 810 km. Using 12.33×10^{20} protons on target delivered to the Fermilab NuMI neutrino beamline, the experiment recorded 27 ν[over ¯]_{μ}→ν[over ¯]_{e} candidates with a background of 10.3 and 102 ν[over ¯]_{μ}→ν[over ¯]_{μ} candidates. This new antineutrino data are combined with neutrino data to measure the parameters |Δm_{32}^{2}|=2.48_{-0.06}^{+0.11}×10^{-3} eV^{2}/c^{4} and sin^{2}θ_{23} in the ranges from (0.53-0.60) and (0.45-0.48) in the normal neutrino mass hierarchy. The data exclude most values near δ_{CP}=π/2 for the inverted mass hierarchy by more than 3σ and favor the normal neutrino mass hierarchy by 1.9σ and θ_{23} values in the upper octant by 1.6σ
GASPS observations of Herbig Ae/Be stars with PACS/Herschel. The atomic and molecular content of their protoplanetary discs
We observed a sample of 20 representative Herbig Ae/Be stars and five A-type
debris discs with PACS onboard of Herschel. The observations were done in
spectroscopic mode, and cover far-IR lines of [OI], [CII], CO, CH+, H2O and OH.
We have a [OI]63 micron detection rate of 100% for the Herbig Ae/Be and 0% for
the debris discs. [OI]145 micron is only detected in 25%, CO J=18-17 in 45%
(and less for higher J transitions) of the Herbig Ae/Be stars and for [CII] 157
micron, we often found spatially variable background contamination. We show the
first detection of water in a Herbig Ae disc, HD 163296, which has a settled
disc. Hydroxyl is detected as well in this disc. CH+, first seen in HD 100546,
is now detected for the second time in a Herbig Ae star, HD 97048. We report
fluxes for each line and use the observations as line diagnostics of the gas
properties. Furthermore, we look for correlations between the strength of the
emission lines and stellar or disc parameters, such as stellar luminosity, UV
and X-ray flux, accretion rate, PAH band strength, and flaring. We find that
the stellar UV flux is the dominant excitation mechanism of [OI]63 micron, with
the highest line fluxes found in those objects with a large amount of flaring
and greatest PAH strength. Neither the amount of accretion nor the X-ray
luminosity has an influence on the line strength. We find correlations between
the line flux of [OI]63 micron and [OI]145 micron, CO J = 18-17 and [OI]6300
\AA, and between the continuum flux at 63 micron and at 1.3 mm, while we find
weak correlations between the line flux of [OI]63 micron and the PAH
luminosity, the line flux of CO J = 3-2, the continuum flux at 63 micron, the
stellar effective temperature and the Brgamma luminosity. (Abbreviated version)Comment: 20 pages, 29 figures, accepted by Astronomy and Astrophysic
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Observation of seasonal variation of atmospheric multiple-muon events in the NOvA Near Detector
Using two years of data from the NOvA Near Detector at Fermilab, we report a seasonal variation of cosmic ray induced multiple-muon (Nμ≥2) event rates which has an opposite phase to the seasonal variation in the atmospheric temperature. The strength of the seasonal multiple-muon variation is shown to increase as a function of the muon multiplicity. However, no significant dependence of the strength of the seasonal variation of the multiple-muon variation is seen as a function of the muon zenith angle, or the spatial or angular separation between the correlated muons
Interferon β-1a in relapsing multiple sclerosis: four-year extension of the European IFNβ-1a Dose-C omparison Study
Background: Multiple sclerosis (MS) is a chronic disease requiring long-term monitoring of treatment. Objective: To assess the four-year clinical efficacy of intramuscular (IM) IFNb-1a in patients with relapsing MS from the European IFNb-1a Dose-C omparison Study. Methods: Patients who completed 36 months of treatment (Part 1) of the European IFNb-1a Dose-C omparison Study were given the option to continue double-blind treatment with IFNb-1a 30 mcg or 60 mcg IM once weekly (Part 2). Analyses of 48-month data were performed on sustained disability progression, relapses, and neutralizing antibody (NA b) formation. Results: O f 608/802 subjects who completed 36 months of treatment, 493 subjects continued treatment and 446 completed 48 months of treatment and follow-up. IFNb-1a 30 mcg and 60 mcg IM once weekly were equally effective for up to 48 months. There were no significant differences between doses over 48 months on any of the clinical endpoints, including rate of disability progression, cumulative percentage of patients who progressed (48 and 43, respectively), and annual relapse rates; relapses tended to decrease over 48 months. The incidence of patients who were positive for NAbs at any time during the study was low in both treatment groups. Conclusion: C ompared with 60-mcg IM IFNb-1a once weekly, a dose of 30 mcg IM IFNb-1a once weekly maintains the same clinical efficacy over four years
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