100 research outputs found
STRONGLY SINGULAR INTEGRALS ON STRATIFIED GROUPS
We consider a class of spectral multipliers on stratified Lie groups which generalise the class of Hoermander multipliers and include multipliers with an oscillatory factor. Oscillating multipliers have been examined extensively in the euclidean setting where sharp, endpoint L^p estimates are well known. In the Lie group setting, corresponding L^p bounds for oscillating spectral multipliers have been established by several authors but only in the open range of exponents. In this paper we establish the endpoint L^p(G) bound when G is a stratified Lie group. More importantly we begin to address whether these estimates are sharp
From refined estimates for spherical harmonics to a sharp multiplier theorem on the Grushin sphere
We prove a sharp multiplier theorem of MihlinâHörmander type for the Grushin operator on the unit sphere in R 3 , and a corresponding boundedness result for the associated BochnerâRiesz means. The proof hinges on precise pointwise bounds for spherical harmonics
On the maximal operator of a general Ornstein--Uhlenbeck semigroup
If Q is a real, symmetric and positive definite nxn matrix, and
B a real nxn matrix whose eigenvalues have negative real parts,
we consider the Ornstein--Uhlenbeck semigroup on R^n with covariance Q
and drift matrix B. Our main result is that the associated maximal operator
is of weak type (1,1) with respect to the invariant measure.
The proof has a geometric gist and hinges on the
``forbidden zones method'' previously introduced by the third author.
For large values of the time parameter,
we also prove a refinement of this result, in the spirit of a conjecture due to Talagrand
Palomar 13: a velocity dispersion inflated by binaries ?
Recently, combining radial velocities from Keck/HIRES echelle spectra with
published proper motion membership probabilities, Cote et al (2002) observed a
sample of 21 stars, probable members of Palomar 13, a globular cluster in the
Galactic halo. Their projected velocity dispersion sigma_p = 2.2 +/-0.4 km/s
gives a mass-to-light ratio M/L_V = 40 +24/-17, about one order of magnitude
larger than the usual estimate for globular clusters. We present here radial
velocities measured from three different CCD frames of commissioning
observations obtained with the new ESO/VLT instrument FLAMES (Fibre Large Array
Multi Element Spectrograph). From these data, now publicly available, we
measure the homogeneous radial velocities of eight probable members of this
globular cluster. A new projected velocity dispersion sigma_p = 0.6-0.9 +/-0.3
km/s implies Palomar 13 mass-to-light ratio M/L_V = 3-7, similar to the usual
value for globular clusters. We discuss briefly the two most obvious reasons
for the previous unusual mass-to-light ratio finding: binaries, now clearly
detected, and more homogeneous data from the multi-fibre FLAMES spectrograph.Comment: 9 pages, 2 Postscript figure
Uncertainty inequalities on groups and homogeneous spaces via isoperimetric inequalities
We prove a family of uncertainty inequalities on fairly general groups
and homogeneous spaces, both in the smooth and in the discrete setting. The
crucial point is the proof of the endpoint, which is derived from a
general weak isoperimetric inequality.Comment: 17 page
Constraining Cosmic Evolution of Type Ia Supernovae
We present the first large-scale effort of creating composite spectra of
high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift
counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88
high-redshift SNe Ia with excellent light-curve information. In addition, we
have obtained 397 spectra of low-redshift SNe through a multiple-decade effort
at Lick and Keck Observatories, and we have used 45 UV spectra obtained by
HST/IUE. The low-redshift spectra act as a control sample when comparing to the
ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra
appear very similar. The addition of galaxy light to the Lick composite spectra
allows a nearly perfect match of the overall spectral-energy distribution with
the ESSENCE composite spectra, indicating that the high-redshift SNe are more
contaminated with host-galaxy light than their low-redshift counterparts. This
is caused by observing objects at all redshifts with the same slit width, which
corresponds to different projected distances. After correcting for the
galaxy-light contamination, subtle differences in the spectra remain. We have
estimated the systematic errors when using current spectral templates for
K-corrections to be ~0.02 mag. The variance in the composite spectra give an
estimate of the intrinsic variance in low-redshift maximum-light SN spectra of
~3% in the optical and growing toward the UV. The difference between the
maximum light low and high-redshift spectra constrain SN evolution between our
samples to be < 10% in the rest-frame optical.Comment: 22 pages, 22 figures, submitted to ApJ. Composite spectra can be
downloaded from http://astro.berkeley.edu/~rfoley/composite
A compact dust shell in the symbiotic system HM Sge
We present high spatial resolution observations of the mid-infrared core of
the dusty symbiotic system HM Sge. The MIDI interferometer was used with the
VLT UTs and ATs providing baselines oriented from PA=42° to 105°. The
MIDI visibilities are compared with the ones predicted in the frame of various
spherical dust shells published in the literature involving single or double
dusty shells. The mid-IR environment is unresolved by a 8m telescope and the
MIDI spectrum exhibits a level similar to the ISO spectra recorded 10 yr ago.
The estimated Gaussian HWHM of the shell of 12AU in the 8-9m range, and
18AU in the 11-12m range, are much smaller than the angular separation
between the Mira and the White Dwarf of 60AU. The discrepancies between the
HWHM at different angle orientations suggest an increasing level of asymmetry
from 13 to 8m. The observations are well fitted by the densest and
smallest model published in the literature based on the ISO data, although such
a model does not account for the variations of near-IR photometry due to the
Mira pulsation cycle suggesting a much smaller optical thickness. These
observations also discard the two shells models, developed to take into account
the effect of the WD illumination onto the dusty wind of the Mira. These
observations show that a high rate of dust formation is occurring in the
vicinity of the Mira which seems to be not highly perturbed by the hot
companion
Palomar 13's Last Stand
We present a proper motion and CCD photometric study of stars in the distant
halo globular cluster Palomar 13. The absolute proper motion of Pal 13 with
respect to the background galaxies, derived from moderate scale photographic
plates separated by a 40-year baseline, is milliarc-seconds per year. The
resultant total space velocity (315 km s) implies that Pal 13 is in the
inner part of its orbit near perigalacticon. Orbital integration reveals the
cluster to possess an inclined, very eccentric, retrograde orbit. These data
confirm that Pal 13 is a paradigm "young halo" globular cluster.
The derived proper motions for cluster stars are used to produce membership
probabilities and a cleaned CCD UBV catalogue for Pal 13. With this data set we
have made small revisions to Pal 13's distance, metallicity, position and light
profile. The membership of four previously reported RR Lyrae variables and a
proportionally large group of blue straggler stars are confirmed. As expected,
the blue stragglers are centrally concentrated.
The small size of this cluster, combined with the shape of its light profile,
which shows a clear departure from a classical King function beyond the tidal
radius, suggests that Pal 13 is in the final throes of destruction. This could
explain the large blue straggler specific frequency, as destructive processes
would preferentially strip less massive stars.Comment: 54 pages, 9 figures, 7 tables, accapted for publication in February
2001 A
Generalized uncertainty inequalities
In this paper, Heisenberg-Pauli-Weyl-type uncertainty inequalities are
obtained for a pair of positive-self adjoint operators on a Hilbert space,
whose spectral projectors satisfy a ``balance condition'' involving certain
operator norms. This result is then applied to obtain uncertainty inequalities
on Riemannian manifolds, Riemannian symmetric spaces of non-compact type,
homogeneous graphs and unimodular Lie groups with sublaplacians.Comment: 19 page
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