224 research outputs found
Spectroscopy of Stellar-Like Objects Contained in the Second Byurakan Survey. I
The results of spectroscopic observations of 363 star-like objects from the
Second Byurakan Survey (SBS) are reported. This SBS's subsample has proven to
be a rich source of newly identified quasars, Seyfert type galaxies, degenerate
stars and hot subdwarfs. In the subsample here studied, we identified 35 new
QSOs, 142 White Dwarfs (WDs) the majority of which, 114 are of DA type, 55
subdwarfs (29 of which are sdB-type stars), 10 HBB, 16 NHB, 54 G-type and 25
F-type stars, two objects with composite spectra, four Cataclismic Variables
(CV), two peculiar emission line stars, 17 objects with continuous spectra, as
well as one planetary nebula. Among the 35 QSOs we have found two Broad
Absorption Line (BAL) QSOs, namely SBS 1423+500 and SBS 1435+500A. Magnitudes,
redshifts, and slit spectra for all QSOs, also some typical spectra of the
peculiar stars are presented. We estimate the minimum surface density of bright
QSOs in redshift range 0.3<z<2.2 to be 0.05 per sq. deg. for B<17.0 and 0.10
per sq. deg. for B<17.5.Comment: 22 pages, 3 tables, 4 figures, PASP in pres
Structure and evolution of strange attractors in non-elastic triangular billiards
We study pinball billiard dynamics in an equilateral triangular table. In
such dynamics, collisions with the walls are non-elastic: the outgoing angle
with the normal vector to the boundary is a uniform factor
smaller than the incoming angle. This leads to contraction in phase space for
the discrete-time dynamics between consecutive collisions, and hence to
attractors of zero Lebesgue measure, which are almost always fractal strange
attractors with chaotic dynamics, due to the presence of an expansion
mechanism. We study the structure of these strange attractors and their
evolution as the contraction parameter is varied. For in
the interval (0, 1/3), we prove rigorously that the attractor has the structure
of a Cantor set times an interval, whereas for larger values of the
billiard dynamics gives rise to nonaccessible regions in phase space. For
close to 1, the attractor splits into three transitive components,
the basins of attraction of which have fractal basin boundaries.Comment: 12 pages, 10 figures; submitted for publication. One video file
available at http://sistemas.fciencias.unam.mx/~dsanders
Bifurcations of periodic and chaotic attractors in pinball billiards with focusing boundaries
We study the dynamics of billiard models with a modified collision rule: the
outgoing angle from a collision is a uniform contraction, by a factor lambda,
of the incident angle. These pinball billiards interpolate between a
one-dimensional map when lambda=0 and the classical Hamiltonian case of elastic
collisions when lambda=1. For all lambda<1, the dynamics is dissipative, and
thus gives rise to attractors, which may be periodic or chaotic. Motivated by
recent rigorous results of Markarian, Pujals and Sambarino, we numerically
investigate and characterise the bifurcations of the resulting attractors as
the contraction parameter is varied. Some billiards exhibit only periodic
attractors, some only chaotic attractors, and others have coexistence of the
two types.Comment: 30 pages, 17 figures. v2: Minor changes after referee comments.
Version with some higher-quality figures available at
http://sistemas.fciencias.unam.mx/~dsanders/publications.htm
Exponential speed of mixing for skew-products with singularities
Let be the
endomorphism given by where is a positive real number. We prove that is
topologically mixing and if then is mixing with respect to Lebesgue
measure. Furthermore we prove that the speed of mixing is exponential.Comment: 23 pages, 3 figure
The Diverse Infrared Properties of a Complete Sample of Star-Forming Dwarf Galaxies
We present mid-infrared Spitzer Space Telescope observations of a complete
sample of star-forming dwarf galaxies selected from the KPNO International
Spectroscopic Survey. The galaxies span a wide range in mid-infrared
properties. Contrary to expectations, some of the galaxies emit strongly at 8
micron indicating the presence of hot dust and/or PAHs. The ratio of this
mid-infrared dust emission to the stellar emission is compared with the
galaxies' luminosity, star-formation rate, metallicity, and optical reddening.
We find that the strength of the 8.0 micron dust emission to the stellar
emission ratio is more strongly correlated with the star-formation rate than it
is with the metallicity or the optical reddening in these systems. Nonetheless,
there is a correlation between the 8.0 micron luminosity and metallicity. The
slope of this luminosity-metallicity correlation is shallower than
corresponding ones in the B-band and 3.6 micron. The precise nature of the 8.0
micron emission seen in these galaxies (i.e., PAH versus hot dust or some
combination of the two) will require future study, including deep mid-IR
spectroscopy.Comment: 14 pages, accepted Ap
Spectral Observations of Faint Markarian Galaxies of the Second Byurakan Survey. II
We continue the program of spectroscopic observations of objects from the
Second Byurakan Survey (SBS). This survey contains more than 1300 galaxies and
1700 star-like objects with m(pg)<19.5. Our work is aimed towards the
construction of a complete sample of faint Markarian galaxies. Here, we present
spectroscopic data for 43 galaxies. Amongst them six new Seyfert galaxies are
found, namely two Sy 1 type (SBS 1343+544 and SBS 1433+500), one Sy 2 type (SBS
1620+545) and three likely Sy 2 type galaxies (SBS 1205+556, SBS 1344+527, SBS
1436+597). SBS 1343+544 falls into the luminosity gap between low-redshift QSOs
and high luminosity Sefert galaxies. In the sample studied here, another 36
emission-line galaxies were spectroscopically confirmed. Thus far, 102 SBS
galaxies brighter than m(pg)=17.5 have been observed with the Cananea 2.1m GHO
telescope. The apparent magnitude and redshift distributions, the spectral
classification, the relative intensities of emission lines, and other
parameters, as well as slit spectra for all 43 observed galaxies are presented.Comment: 7 pages, 7 figures, 2 tables, Latex, aaspp4.sty and aj_pt.sty,
Submitted to Astronomical Journa
Dust Properties and Star-Formation Rates in Star-Forming Dwarf Galaxies
We have used the Spitzer Space Telescope to study the dust properties of a
sample of star-forming dwarf galaxies. The differences in the mid-infrared
spectral energy distributions for these galaxies which, in general, are low
metallicity systems, indicate differences in the physical properties, heating,
and/or distribution of the dust. Specifically, these galaxies have more hot
dust and/or very small grains and less PAH emission than either spiral or
higher luminosity starburst galaxies. As has been shown in previous studies,
there is a gradual decrease in PAH emission as a function of metallicity.
Because much of the energy from star formation in galaxies is re-radiated in
the mid-infrared, star-formation rate indicators based on both line and
continuum measurements in this wavelength range are coming into more common
usage. We show that the variations in the interstellar medium properties of
galaxies in our sample, as measured in the mid-infrared, result in over an
order of magnitude spread in the computed star-formation rates.Comment: 25 pages, 11 figures, 4 tables, ApJ accepte
The Radio Quiescence of Active Galaxies with High Accretion Rates
We present 6 cm Very Large Array observations of the Greene & Ho (2004)
sample of 19 low-mass active galaxies with high accretion rates. This is one of
the only studies of a uniform sample of narrow-line Seyfert 1 (NLS1) galaxies
with such high sensitivity and resolution. Although we detect only one source,
the entire sample is very radio-quiet down to strong limits. GH10 was found to
have a radio power of 8.5 x 10^21 W/Hz, and a ratio R = f(6 cm)/f(4400 A) of
2.8. The 3 sigma upper limits for the remaining nondetections correspond to
radio powers from 3 x 10^20 to 8 x 10^21 W/Hz and 0.47 < R <9.9. Stacking all
nondetections yields an even stronger upper limit of R < 0.27. An assessment of
existing observations in the literature confirms our finding that NLS1s are
consistently radio-quiet, with a radio-loud fraction of 0%-6%, which is
significantly lower than the 10%-20% observed in the general quasar population.
By analogy with stellar-mass black holes, we argue that AGNs undergo a state
transition at L_bol/L_Edd~0.01. Below this value a radiatively inefficient
accretion flow effectively drives an outflow, which disappears when the flow
turns into an optically thick, geometrically thin disk, or a radiation
pressure-dominated slim disk at still higher L_bol/L_Edd.Comment: To appear in ApJ; 8 pages, 3 figures; uses emulateapj5.st
Chaos and stability in a two-parameter family of convex billiard tables
We study, by numerical simulations and semi-rigorous arguments, a
two-parameter family of convex, two-dimensional billiard tables, generalizing
the one-parameter class of oval billiards of Benettin--Strelcyn [Phys. Rev. A
17, 773 (1978)]. We observe interesting dynamical phenomena when the billiard
tables are continuously deformed from the integrable circular billiard to
different versions of completely-chaotic stadia. In particular, we conjecture
that a new class of ergodic billiard tables is obtained in certain regions of
the two-dimensional parameter space, when the billiards are close to skewed
stadia. We provide heuristic arguments supporting this conjecture, and give
numerical confirmation using the powerful method of Lyapunov-weighted dynamics.Comment: 19 pages, 13 figures. Submitted for publication. Supplementary video
available at http://sistemas.fciencias.unam.mx/~dsanders
The Second Byurakan Survey Galaxies. I. The Optical Database
A database for the entire catalog of the Second Byurakan Survey (SBS)
galaxies is presented. It contains new measurements of their optical parameters
and additional information taken from the literature and other databases. The
measurements were made using Ipg(near-infrared), Fpg(red) and Jpg(blue) band
images from photographic sky survey plates obtained by the Palomar Schmidt
telescope and extracted from the STScI Digital Sky Survey (DSS). The database
provides accurate coordinates, morphological type, spectral and activity
classes, apparent magnitudes and diameters, axial ratios, and position angles,
as well as number counts of neighboring objects in a circle of radius 50 kpc.
The total number of individual SBS objects in the database is now 1676. The 188
Markarian galaxies which were re-discovered by SBS are not included in this
database. We also include redshifts that are now available for 1576 SBS
objects, as well as 2MASS infrared magnitudes for 1117 SBS galaxies.Comment: 13 pages, 1 figure, 1 tabl
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