652 research outputs found
Color Effects Associated with the 1999 Microlensing Brightness Peaks in Gravitationally Lensed Quasar Q2237+0305
Photometry of the Q2237+0305gravitational lens in VRI spectral bands with the
1.5-m telescope of the high-altitude Maidanak observatory in 1995-2000 is
presented. Monitoring of Q2237+0305 in July-October 2000, made at nearly daily
basis, did not reveal rapid (night-to-night and intranight) variations of
brightness of the components during this time period. Rather slow changes of
magnitudes of the components were observed, such as 0.08 mag fading of B and C
components and 0.05 mag brightening of D in R band during July 23 - October 7,
2000. By good luck three nights in 1999 were almost at the time of the strong
brightness peak of image C, and approximately in the middle of the ascending
slope of the image A brightness peak. The C component was the most blue one in
the system in 1998 and 1999, having changed its (V-I) color from 0.56 mag to
0.12 mag since August 1997, while its brightness increased almost 1.2 mag
during this time period. The A component behaved similarly between August 1998
and August 2000, having become 0.47 mag brighter in R, and at the same time,
0.15 mag bluer. A correlation between the color variations and variations of
magnitudes of the components is demonstrated to be significant and reaches
0.75, with a regression line slope of 0.33. A color (V-I) vrs color (V-R) plot
shows the components settled in a cluster, stretched along a line with a slope
of 1.31. Both slopes are noticeably smaller than those expected if a standard
galactic interstellar reddening law were responsible for the differences
between the colors of images and their variations over time. We attribute the
brightness and color changes to microlensing of the quasar's structure, which
we conclude is more compact at shorter wavelengths, as predicted by most quasar
models featuring an energizing central source.Comment: 14 pages, 7 figures, LaTeX, submitted to A&
Bosonic Description of Spinning Strings in Dimensions
We write down a general action principle for spinning strings in 2+1
dimensional space-time without introducing Grassmann variables. The action is
written solely in terms of coordinates taking values in the 2+1 Poincare group,
and it has the usual string symmetries, i.e. it is invariant under a)
diffeomorphisms of the world sheet and b) Poincare transformations. The system
can be generalized to an arbitrary number of space-time dimensions, and also to
spinning membranes and p-branes.Comment: Latex, 12 page
Discovery and quantitative spectral analysis of an Ofpe/WN9 (WN11) star in the Sculptor spiral galaxy NGC 300
We have discovered an Ofpe/WN9 (WN11 following Smith et al.) star in the
Sculptor spiral galaxy NGC 300, the first object of this class found outside
the Local Group, during a recent spectroscopic survey of blue supergiant stars
obtained at the ESO VLT. The light curve over a five-month period in late 1999
displays a variability at the 0.1 mag level. The intermediate resolution
spectra (3800-7200 A) show a very close resemblance to the Galactic LBV AG Car
during minimum. We have performed a detailed non-LTE analysis of the stellar
spectrum, and have derived a chemical abundance pattern which includes H, He,
C, N, O, Al, Si and Fe, in addition to the stellar and wind parameters. The
derived stellar properties and the He and N surface enrichments are consistent
with those of other Local Group WN11 stars in the literature, suggesting a
similar quiescent or post-LBV evolutionary status.Comment: 9 pages, 4 figures, 2 tables. Accepted for publication in the
Astrophysical Journal Letter
An Optical Time-Delay for the Lensed BAL Quasar HE2149-2745
We present optical V and i-band light curves of the gravitationally lensed
BAL quasar HE2149-2745. The data, obtained with the 1.5m Danish Telescope
(ESO-La Silla) between October 1998 and December 2000, are the first from a
long-term project aimed at monitoring selected lensed quasars in the Southern
Hemisphere. A time delay of 103+/-12 days is determined from the light curves.
In addition, VLT/FORS1 spectra of HE2149-2745 are deconvolved in order to
obtain the spectrum of the faint lensing galaxy, free of any contamination by
the bright nearby two quasar images. By cross-correlating the spectrum with
galaxy-templates we obtain a tentative redshift estimate of z=0.495+/-0.01.
Adopting this redshift, a Omega=0.3, Lambda=0.7 cosmology, and a chosen
analytical lens model, our time-delay measurement yields a Hubble constant of
H_0=66+/-8 km/s/Mpc with an estimated systematic error of +/-3 km/s/Mpc. Using
non-parametric models yields H_0=65+/-8 km/s/Mpc and confirms that the lens
exhibits a very dense/concentrated mass profile.Comment: 11 pages, accepted for publication in Astronomy & Astrophysic
New rotation periods in the Pleiades: Interpreting activity indicators
We present results of photometric monitoring campaigns of G, K and M dwarfs
in the Pleiades carried out in 1994, 1995 and 1996. We have determined rotation
periods for 18 stars in this cluster. In this paper, we examine the validity of
using observables such as X-ray activity and amplitude of photometric
variations as indicators of angular momentum loss. We report the discovery of
cool, slow rotators with high amplitudes of variation. This contradicts
previous conclusions about the use of amplitudes as an alternate diagnostic of
the saturation of angular momentum loss. We show that the X-ray data can be
used as observational indicators of mass-dependent saturation in the angular
momentum loss proposed on theoretical grounds.Comment: 24 pages, LaTex (AASTeX); includes 8 postscript figures and 4 Latex
tables. To appear in ApJ, Feb. 1, 1998. Postscript version of preprint can be
obtained from http://casa.colorado.edu/~anitak/pubs.htm
Time delays in PG1115+080: new estimates
We report new estimates of the time delays in the quadruple gravitationally
lensed quasar PG1115+080, obtained from the monitoring data in filter R with
the 1.5-m telescope at the Maidanak Mountain (Uzbekistan, Central Asia) in
2004-2006. The time delays are 16.4 days between images C and B, and 12 days
between C and A1+A2, with image C being leading for both pairs. The only known
estimates of the time delays in PG1115 are those based on observations by
Schechter et al. (1997) -- 23.7 and 9.4 days between images C and B, C and
A1+A2, respectively, as calculated by Schechter et al., and 25 and 13.3 days as
revised by Barkana (1997) for the same image components with the use of another
method. The new values of time delays in PG 1115+080 may be expected to provide
larger estimates of the Hubble constant thus decreasing a diversity between the
H_0 estimates taken from gravitationally lensed quasars and with other methods.Comment: 5 pages, 2 figures, Accepted for publication in MNRAS Letter
Pointlike structure for super p-branes
We present an efficient method to understand the p-brane dynamics in a
unified framework. For this purpose, we reformulate the action for super
p-branes in the form appropriate to incorporate the pointlike (parton)
structure of higher dimensional p-branes and intend to interpret the p-brane
dynamics as the collective dynamics of superparticles. In order to examine such
a parton picture of super p-branes, we consider various superparticle
configurations that can be reduced from super p-branes, especially, a
supermembrane, and study the partonic structure of classical p-brane solutions.Comment: 22 pages, corrected typos, to appear in Phys. Rev. D58, 085018 (1998
Towards a tensionless string field theory for the N=(2,0) CFT in d=6
We describe progress in using the field theory of tensionless strings to
arrive at a Lagrangian for the six-dimensional conformal
theory. We construct the free part of the theory and propose an ansatz for the
cubic vertex in light-cone superspace. By requiring closure of the
supersymmetry algebra, we fix the cubic vertex up to two parameters.Comment: 46 pages, 2 figures. V2: references added; minor changes and
improvement
USp(2k) Matrix Model: Nonperturbative Approach to Orientifolds
We discuss theoretical implications of the large k USp(2k) matrix model in
zero dimension. The model appears as the matrix model of type IIB superstrings
on a large orientifold via the matrix twist operation. In the
small volume limit, the model behaves four dimensional and its T dual is
six-dimensional worldvolume theory of type I superstrings in ten spacetime
dimensions. Several theoretical considerations including the analysis on planar
diagrams, the commutativity of the projectors with supersymmetries and the
cancellation of gauge anomalies are given, providing us with the rationales for
the choice of the Lie algebra and the field content. A few classical solutions
are constructed which correspond to Dirichlet p-branes and some fluctuations
are evaluated. The particular scaling limit with matrix T duality
transformation is discussed which derives the F theory compactification on an
elliptic fibered K3.Comment: LaTeX, 29 pages, 3 figures. PostScript problems are fixe
Supersymmetric string model with 30 kappa--symmetries in an extended D=11 superspace and 30/ 32 BPS states
A supersymmetric string model in the D=11 superspace maximally extended by
antisymmetric tensor bosonic coordinates, , is proposed. It
possesses 30 -symmetries and 32 target space supersymmetries. The usual
preserved supersymmetry--symmetry correspondence suggests that it
describes the excitations of a BPS state preserving all but two
supersymmetries. The model can also be formulated in any superspace, n=32 corresponding to D=11. It may also be treated as a
`higher--spin generalization' of the usual Green--Schwarz superstring. Although
the global symmetry of the model is a generalization of the super--Poincar\'e
group, , it may be
formulated in terms of constrained OSp(2n|1) orthosymplectic supertwistors. We
work out this supertwistor realization and its Hamiltonian dynamics.
We also give the supersymmetric p-brane generalization of the model. In
particular, the supersymmetric membrane model describes
excitations of a 30/32 BPS state, as the supersymmetric
string does, while the supersymmetric 3-brane and 5-brane correspond,
respectively, to 28/32 and 24/32 BPS states.Comment: 23 pages, RevTex4. V2: minor corrections in title and terminology,
some references and comments adde
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