10,030 research outputs found
Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies: II. Surface Photometry and the Properties of the Underlying Stellar Population
We present the results from an analysis of surface photometry of B, R, and
Halpha images of a total of 114 nearby galaxies drawn from the Palomar/Las
Campanas Imaging Atlas of Blue Compact Dwarf galaxies. Surface brightness and
color profiles for the complete sample have been obtained. We determine the
exponential and Sersic profiles that best fit the surface brightness
distribution of the underlying stellar population detected in these galaxies.
We also compute the (B-R) color and total absolute magnitude of the underlying
stellar population and compared them to the integrated properties of the
galaxies in the sample. Our analysis shows that the (B-R) color of the
underlying population is systematically redder than the integrated color,
except in those galaxies where the integrated colors are strongly contaminated
by line and nebular-continuum emission. We also find that galaxies with
relatively red underlying stellar populations (typically (B-R)>~1mag) show
structural properties compatible with those of dwarf elliptical galaxies (i.e.
a smooth light distribution, fainter extrapolated central surface brightness
and larger scale lengths than BCD galaxies with blue underlying stellar
populations). At least ~15% of the galaxies in the sample are compatible with
being dwarf elliptical (dE) galaxies experiencing a burst of star formation.
For the remaining BCD galaxies in the sample we do not find any correlation
between the recent star formation activity and their structural differences
with respect to other types of dwarf galaxies.Comment: 35 pages, 6 figures, accepted for publication in ApJS. Postscript
files of panels f1a-f1o of figure 1 are available online at
http://www.ociw.edu/~agpaz/astro-ph/apjs2004
Gaussian Decoherence and Gaussian Echo from Spin Environments
We examine an exactly solvable model of decoherence -- a spin-system
interacting with a collection of environment spins. We show that in this simple
model (introduced some time ago to illustrate environment--induced
superselection) generic assumptions about the coupling strengths lead to a
universal (Gaussian) suppression of coherence between pointer states. We
explore the regime of validity of this result and discuss its relation to
spectral features of the environment. We also consider its relevance to the
experiments on the so-called Loschmidt echo (which measures, in effect, the
fidelity between the initial and time-reversed or "echo" signal). In
particular, we show that for partial reversals (e.g., when of only a part of
the total Hamiltonian changes sign) fidelity will exhibit a Gaussian dependence
on the time of reversal. In such cases echo may become independent of the
details of the reversal procedure or the specifics of the coupling to the
environment. This puzzling behavior was observed in several NMR experiments.
Natural candidates for such two environments (one of which is easily reversed,
while the other is ``irreversible'') are suggested for the experiment involving
ferrocene.Comment: Improved text and figures, to appear in the special issue of Acta
Physica Polonica B celebrating the 100th anniversary of Smoluchowski's
equation and his paper explaining Brownian motion (in
http://th-www.if.uj.edu.pl/acta/vol38/pdf/v38p1685.pdf
The Curious Case of NGC6908
The object NGC6908 was once thought to be simply a surface-brightness
enhancement in the eastern spiral arm of the nearby spiral galaxy NGC6907.
Based on an examination of near-infrared imaging, the object is shown in fact
to be a lenticular S0(6/7) galaxy hidden in the optical glare of the disk and
spiral structure of the larger galaxy. New radial velocities of NGC6908
(3,060+/-16 (emission); 3,113+/-73 km/s (absorption)) have been obtained at the
Baade 6.5m and the duPont 2.5m telescopes at Las Campanas, Chile placing
NGC6908 at the same expansion-velocity distance as NGC6907 (3,190+/-5 km/s),
eliminating the possibility of a purely chance line-of-sight coincidence. The
once-enigmatic asymmetries in the disk and outer spiral structure of NGC6907
are now explained as being due to an advanced merger event. Newly discovered
tails and debris in the outer reaches of this galaxy further support the merger
scenario for this system. This pair of galaxies is a rather striking example of
two objects discovered over 100 years ago, whose true nature was lost until
modern detectors operating at infrared wavelengths gave us a new
(high-contrast) look. Other examples of embedded merger remnants may also
reveal themselves in the growing samples of near-infrared imaging of nearby
galaxies; and a pilot study does reveal several other promising candidates for
follow-up observations.Comment: 17 pages, 8 figures, accepted for publication in A
Fractional Newton-Raphson Method Accelerated with Aitken's Method
The Newton-Raphson (N-R) method is characterized by the fact that generating
a divergent sequence can lead to the creation of a fractal, on the other hand
the order of the fractional derivatives seems to be closely related to the
fractal dimension, based on the above, a method was developed that makes use of
the N-R method and the fractional derivative of Riemann-Liouville (R-L) that
has been named as the Fractional Newton-Raphson (F N-R) method.
In the following work we present a way to obtain the convergence of the F N-R
method, which seems to be at least linearly convergent for the case where the
order of the derivative is different from one, a simplified way to
construct the fractional derivative and fractional integral operators of R-L is
presented, an introduction to the Aitken's method is made and it is explained
why it has the capacity to accelerate the convergence of iterative methods to
finally present the results that were obtained when implementing the Aitken's
method in F N-R method.Comment: Newton-Raphson Method, Fractional Calculus, Fractional Derivative of
Riemann-Liouville, Method of Aitken. arXiv admin note: substantial text
overlap with arXiv:1710.0763
Mapping the star formation history of Mrk86: I. Data and models
We have obtained optical (BVR, [OIII]5007 and Halpha), near infrared (JHK)
imaging and long-slit optical spectroscopy for the Blue Compact Dwarf galaxy
Mrk86 (NGC2537). In this paper, the first of two, we present optical-near-
infrared colors and emission-line fluxes for the currently star-forming
regions, intemediate aged starburst and underlying stellar population. We also
describe the evolutionary synthesis models used in Paper II. The R and Halpha
luminosity distributions of the galaxy star-forming regions show maxima at
M_R=-9.5 and L_Halpha=10^37.3 erg s^-1. The underlying stellar population shows
an exponential surface brigthness profile with central value, mu_E,0=21.5 mag
arcsec^-2, and scale, alpha=0.88 kpc, both measured in the R-band image. In the
galaxy outer regions, dominated by this component, no significant color
gradients are observed. Finally, a set of evolutionary synthesis models have
been developed, covering a wide range in metallicity and burst strength.Comment: 21 pages, 14 figures, 2 landscape tables, accepted for publication in
Astronomy & Astrophysics Supplement Series, for higher resolution images see
ftp://cutrex.fis.ucm.es/pub/OUT/gil/PAPERS/aa00_I.ps.g
Decoherence and the Loschmidt echo
Environment--induced decoherence causes entropy increase. It can be
quantified using, e.g., the purity . When the
Hamiltonian of a quantum system is perturbed, its sensitivity to such
perturbation can be measured by the Loschmidt echo . It is given by
the average squared overlap between the perturbed and unperturbed state. We
describe the relation between the temporal behavior of and . In this way we show that the decay of the Loschmidt echo can be analyzed
using tools developed in the study of decoherence. In particular, for systems
with a classically chaotic Hamiltonian the decay of and
has a regime where it is dominated by the classical Lyapunov exponent
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