7,645 research outputs found
FUSE, STIS, and Keck spectroscopic analysis of the UV-bright star vZ 1128 in M3 (NGC 5272)
We present a spectral analysis of the UV-bright star vZ 1128 in M3 based on
observations with the Far Ultraviolet Spectroscopic Explorer (FUSE), the Space
Telescope Imaging Spectrograph (STIS), and the Keck HIRES echelle spectrograph.
By fitting the H I, He I, and He II lines in the Keck spectrum with non-LTE
H-He models, we obtain Teff = 36,600 K, log g = 3.95, and log N(He)/N(H) =
-0.84. The star's FUSE and STIS spectra show photospheric absorption from C, N,
O, Al, Si, P, S, Fe, and Ni. No stellar features from elements beyond the iron
peak are observed. Both components of the N V 1240 doublet exhibit P~Cygni
profiles, indicating a weak stellar wind, but no other wind features are seen.
The star's photospheric abundances appear to have changed little since it left
the red giant branch (RGB). Its C, N, O, Al, Si, Fe, and Ni abundances are
consistent with published values for the red-giant stars in M3, and the
relative abundances of C, N, and O follow the trends seen on the cluster RGB.
In particular, its low C abundance suggests that the star left the asymptotic
giant branch before the onset of third dredge-up.Comment: 15 pages, 10 figures, to be published in MNRA
Post-Newtonian corrections to the motion of spinning bodies in NRGR
In this paper we include spin and multipole moment effects in the formalism
used to describe the motion of extended objects recently introduced in
hep-th/0409156. A suitable description for spinning bodies is developed and
spin-orbit, spin-spin and quadrupole-spin Hamiltonians are found at leading
order. The existence of tidal, as well as self induced finite size effects is
shown, and the contribution to the Hamiltonian is calculated in the latter. It
is shown that tidal deformations start formally at O(v^6) and O(v^10) for
maximally rotating general and compact objects respectively, whereas self
induced effects can show up at leading order. Agreement is found for the cases
where the results are known.Comment: 18 pages, 9 figures. Typos corrected, to appear in Physical Review
On the Significance of Absorption Features in HST/COS Data
We present empirical scaling relations for the significance of absorption
features detected in medium resolution, far-UV spectra obtained with the Cosmic
Origins Spectrograph (COS). These relations properly account for both the
extended wings of the COS line spread function and the non-Poissonian noise
properties of the data, which we characterize for the first time, and predict
limiting equivalent widths that deviate from the empirical behavior by \leq 5%
when the wavelength and Doppler parameter are in the ranges \lambda = 1150-1750
A and b > 10 km/s. We have tested a number of coaddition algorithms and find
the noise properties of individual exposures to be closer to the Poissonian
ideal than coadded data in all cases. For unresolved absorption lines, limiting
equivalent widths for coadded data are 6% larger than limiting equivalent
widths derived from individual exposures with the same signal-to-noise. This
ratio scales with b-value for resolved absorption lines, with coadded data
having a limiting equivalent width that is 25% larger than individual exposures
when b \approx 150 km/s.Comment: 25 pages, 3 tables, 7 figures, accepted for publication in PAS
Scattering of Spinning Test Particles by Plane Gravitational and Electromagnetic Waves
The Mathisson-Papapetrou-Dixon (MPD) equations for the motion of electrically
neutral massive spinning particles are analysed, in the pole-dipole
approximation, in an Einstein-Maxwell plane-wave background spacetime. By
exploiting the high symmetry of such spacetimes these equations are reduced to
a system of tractable ordinary differential equations. Classes of exact
solutions are given, corresponding to particular initial conditions for the
directions of the particle spin relative to the direction of the propagating
background fields. For Einstein-Maxwell pulses a scattering cross section is
defined that reduces in certain limits to those associated with the scattering
of scalar and Dirac particles based on classical and quantum field theoretic
techniques. The relative simplicity of the MPD approach and its use of
macroscopic spin distributions suggests that it may have advantages in those
astrophysical situations that involve strong classical gravitational and
electromagnetic environments.Comment: Submitted to Classical and Quantum Gravity. 12 page
Twisting the N=2 String
The most general homogeneous monodromy conditions in string theory
are classified in terms of the conjugacy classes of the global symmetry group
. For classes which generate a discrete subgroup \G,
the corresponding target space backgrounds {\bf C}^{1,1}/\G include half
spaces, complex orbifolds and tori. We propose a generalization of the
intercept formula to matrix-valued twists, but find massless physical states
only for (untwisted) and (\`a la Mathur
and Mukhi), as well as for being a parabolic element of . In
particular, the sixteen -twisted sectors of the string are
investigated, and the corresponding ground states are identified via
bosonization and BRST cohomology. We find enough room for an extended multiplet
of `spacetime' supersymmetry, with the number of supersymmetries being
dependent on global `spacetime' topology. However, world-sheet locality for the
chiral vertex operators does not permit interactions among all massless
`spacetime' fermions.Comment: 42 pages, LaTeX, no figures, 120 kb, ITP-UH-24/93, DESY 93-191
(abstract and introduction clarified, minor corrections added
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