8,229 research outputs found
Kinematic study of planetary nebulae in NGC 6822
By measuring precise radial velocities of planetary nebulae (which belong to
the intermediate age population), H II regions, and A-type supergiant stars
(which are members of the young population) in NGC 6822, we aim to determine if
both types of population share the kinematics of the disk of H I found in this
galaxy.
Spectroscopic data for four planetary nebulae were obtained with the high
spectral resolution spectrograph Magellan Inamori Kyocera Echelle (MIKE) on the
Magellan telescope at Las Campanas Observatory. Data for other three PNe and
one H II region were obtained from the SPM Catalog of Extragalactic Planetary
Nebulae which employed the Manchester Echelle Spectrometer attached to the 2.1m
telescope at the Observatorio Astron\'omico Nacional, M\'exico. In the
wavelength calibrated spectra, the heliocentric radial velocities were measured
with a precision better than 5-6 km s. Data for three additional H II
regions and a couple of A-type supergiant stars were collected from the
literature. The heliocentric radial velocities of the different objects were
compared to the velocities of the H i disk at the same position.
From the analysis of radial velocities it is found that H II regions and
A-type supergiants do share the kinematics of the H I disk at the same
position, as expected for these young objects. On the contrary, planetary
nebula velocities differ significantly from that of the H I at the same
position. The kinematics of planetary nebulae is independent from the young
population kinematics and it is closer to the behavior shown by carbon stars,
which are intermediate-age members of the stellar spheroid existing in this
galaxy. Our results are confirming that there are at least two very different
kinematical systems in NGC 6822
A catalog of planetary nebula candidates in the Sculptor spiral galaxy NGC 300
[OIII]5007 on-band off-band images, obtained with the VLT and FORS2
spectrograph in two zones (center and outskirts) of the spiral galaxy NGC300,
are analyzed searching for emission line objects. In particular we search for
planetary nebula (PN) candidates to analyze their distribution and luminosity
properties, to perform follow-up spectroscopy, and to study the planetary
nebula luminosity function, PNLF. In the continuum-subtracted images, a large
number of emission line objects were detected. From this sample we selected as
PN candidates those objects with stellar appearance and no detectable central
star. [OIII]5007 instrumental magnitudes were measured and calibrated by using
spectrophotometric data from the follow-up spectroscopy. We identified more
than a hundred PN candidates and a number of compact HII regions. The PN sample
is the largest one reported for this galaxy so far. For all the objects we
present coordinates, instrumental [OIII]5007 magnitudes and apparent nebular
[OIII]5007 fluxes and magnitudes. The [OIII]5007 observed luminosity function
for PNe (PNLF) was calculated for the whole sample and for the central and
outskirts samples. The three PNLF are similar within uncertainties. We fit the
empirical PNLF to the observed PNLF for all the samples. From our best fit for
the whole sample we derived a maximum value for the apparent magnitudes of
m*(5007)=22.019\pm0.022 and we obtained a tentative estimate of the distance
modulus m(5007)-M(5007)= 26.29 {+0.12} {-0.22} mag, which agrees well with the
recent value derived from Cepheid stars.Comment: 8 pages, 3 figures, one long table. Accepted by A&
Fabrication and Characterization of Multiband Solar Cells Based on Highly Mismatched Alloys
Multiband solar cells are one type of third generation photovoltaic devices in which an increase of the power conversion efficiency is achieved through the absorption of low energy photons while preserving a large band gap that determines the open circuit voltage. The ability to absorb photons from different parts of the solar spectrum originates from the presence of an intermediate energy band located within the band gap of the material. This intermediate band, acting as a stepping stone allows the absorption of low energy photons to transfer electrons from the valence band to the conduction band by a sequential two photons absorption process. It has been demonstrated that highly mismatched alloys offer a potential to be used as a model material system for practical realization of multiband solar cells. Dilute nitride GaAs1-xNx highly mismatched alloy with low mole fraction of N is a prototypical multiband semiconductor with a well-defined intermediate band. Currently, we are using chemical beam epitaxy to synthesize dilute nitride highly mismatched alloys. The materials are characterized by a variety of structural and optical methods to optimize their properties for multiband photovoltaic devices
The UNAM-KIAS Catalog of Isolated Galaxies
A new catalog of isolated galaxies from The Sloan Digital Sky Survey (DR5) is
presented. 1520 isolated galaxies were found in 1.4 steradians of sky. The
selection criteria in this so called UNAM-KIAS catalog was implemented from a
variation on the criteria developed by Karachentseva 1973 including full
redshift information. Through an image processing pipeline that takes advantage
from the high resolution (~ 0.4 ''/pix) and high dynamic range of the SDSS
images, a uniform g band morphological classification for all these galaxies is
presented. We identify 80% (SaSm) spirals (50% later than Sbc types) on one
hand, and a scarce population of early-type E(6.5%) and S0(8%) galaxies
amounting to 14.5% on the other hand. This magnitude-limited catalog is ~ 80%
complete at 16.5, 15.6, 15.0, 14.6 and 14.4 magnitudes in the ugriz bands
respectively. Some representative physical properties including SDSS magnitudes
and color distributions, color-color diagrams, absolute magnitude-color, and
concentration-color diagrams as a function of morphological type are presented.
The UNAM-KIAS Morphological Atlas is also released along with this paper. For
each galaxy of type later than Sa, a mosaic is presented that includes: (1) a
g-band logarithmic image, (2) a g band filtered-enhanced image where a Gaussian
kernel of various sizes was applied and (3) an RGB color image from the SDSS
database. For E/S0/Sa galaxies, in addition to the images in (1), (2) and (3),
plots of r band surface brightness and geometric profiles (ellipticity,
Position Angle PA and A4/B4 coefficients of the Fourier series expansions of
deviations of a pure ellipse) are provided...Comment: 40 pages, 17 figures and 3 table
Hydrazones as Singular Reagents in Asymmetric Organocatalysis
This Minireview summarizes strategies and developments regarding the use of hydrazones as reagents in asymmetric organocatalysis, their distinct roles in nucleophile–electrophile, cycloaddition, and cyclization reactions. The key structural elements governing the reactivity of these reagents in a preferred pathway will be discussed, as well as their different interactions with organocatalysts, leading to diverse activation modes. Along these studies, the synthetic equivalence of N-monoalkyl, N,N-dialkyl, and N-acyl hydrazones with several synthons is also highlighted. Emphasis is also put on the mechanistic studies performed to understand the observed reactivities. Finally, the functional group transformations performed from the available products has also been analyzed, highlighting the synthetic value of these methodologies, which served to access numerous families of valuable multifunctional compounds and nitrogen-containing heterocycles.Ministerio de EconomÃa y Competitividad CTQ2013-48164-C2-1-P, CTQ201348164-C2-2-PEuropean FEDER fundsJunta de AndalucÃa 2012/FQM 107
The UNAM-KIAS Catalog of Isolated Galaxies
A new catalog of isolated galaxies from The Sloan Digital Sky Survey (DR5) is
presented. 1520 isolated galaxies were found in 1.4 steradians of sky. The
selection criteria in this so called UNAM-KIAS catalog was implemented from a
variation on the criteria developed by Karachentseva 1973 including full
redshift information. Through an image processing pipeline that takes advantage
from the high resolution (~ 0.4 ''/pix) and high dynamic range of the SDSS
images, a uniform g band morphological classification for all these galaxies is
presented. We identify 80% (SaSm) spirals (50% later than Sbc types) on one
hand, and a scarce population of early-type E(6.5%) and S0(8%) galaxies
amounting to 14.5% on the other hand. This magnitude-limited catalog is ~ 80%
complete at 16.5, 15.6, 15.0, 14.6 and 14.4 magnitudes in the ugriz bands
respectively. Some representative physical properties including SDSS magnitudes
and color distributions, color-color diagrams, absolute magnitude-color, and
concentration-color diagrams as a function of morphological type are presented.
The UNAM-KIAS Morphological Atlas is also released along with this paper. For
each galaxy of type later than Sa, a mosaic is presented that includes: (1) a
g-band logarithmic image, (2) a g band filtered-enhanced image where a Gaussian
kernel of various sizes was applied and (3) an RGB color image from the SDSS
database. For E/S0/Sa galaxies, in addition to the images in (1), (2) and (3),
plots of r band surface brightness and geometric profiles (ellipticity,
Position Angle PA and A4/B4 coefficients of the Fourier series expansions of
deviations of a pure ellipse) are provided...Comment: 40 pages, 17 figures and 3 table
Phase diagram of silicon from atomistic simulations
In this letter we present a calculation of the temperature-pressure phase
diagram of Si in a range of pressures covering from -5 to 20 GPa and
temperatures up to the melting point. The phase boundaries and triple points
between the diamond, liquid, -Sn and clathrate phases are
reported. We have employed efficient simulation techniques to calculate free
energies and to numerically integrate the Clausius-Clapeyron equation, combined
with a tight binding model capable of an accuracy comparable to that of
first-principles methods. The resulting phase diagram agrees well with the
available experimental data.Comment: 5 pages, 1 figure, accepted in PR
Rejection based multipath reconstruction for background estimation in video sequences with stationary objects
This is the author’s version of a work that was accepted for publication in Computer Vision and Image Understanding. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Computer Vision and Image Understanding, VOL147 (2016) DOI 10.1016/j.cviu.2016.03.012Background estimation in video consists in extracting a foreground-free image from a set of training frames. Moving and stationary objects may affect the background visibility, thus invalidating the assumption of many related literature where background is the temporal dominant data. In this paper, we present a temporal-spatial block-level approach for background estimation in video to cope with moving and stationary objects. First, a Temporal Analysis module obtains a compact representation of the training data by motion filtering and dimensionality reduction. Then, a threshold-free hierarchical clustering determines a set of candidates to represent the background for each spatial location (block). Second, a Spatial Analysis module iteratively reconstructs the background using these candidates. For each spatial location, multiple reconstruction hypotheses (paths) are explored to obtain its neighboring locations by enforcing inter-block similarities and intra-block homogeneity constraints in terms of color discontinuity, color dissimilarity and variability. The experimental results show that the proposed approach outperforms the related state-of-the-art over challenging video sequences in presence of moving and stationary objects.This work was partially supported by the Spanish Government (HAVideo, TEC2014-53176-R) and by the TEC department (Universidad Autónoma de Madrid)
- …