67,038 research outputs found
Empirical Uncertainty Estimators for Astrometry from Digital Databases
In order to understand the positional uncertainties of arbitrary objects in
several of the current major databases containing astrometric information, a
sample of extragalactic radio sources with precise positions in the
International Celestial Reference Frame (ICRF) is compared with the available
positions of their optical counterparts. The discrepancies between the radio
and various optical positions are used to derive empirical uncertainty
estimators for the USNO-A2.0, USNO-A1.0, Guide Star Selection System (GSSS)
images, and the first and second Digitized Sky Surveys (DSS-I and DSS-II). In
addition, an estimate of the uncertainty when the USNO-A2.0 catalog is
transferred to different image data is provided. These optical astrometric
frame uncertainties can in some cases be the dominant error term when
cross-identifying sources at different wavelengths.Comment: 12 pages including 2 figures and 1 table. Accepted for publication in
The Astronomical Journal, October 1999. Values in Table 1 for DSS I corrected
99-07-1
Infrared composition of the Large Magellanic Cloud
The evolution of galaxies and the history of star formation in the Universe
are among the most important topics in today's astrophysics. Especially, the
role of small, irregular galaxies in the star-formation history of the Universe
is not yet clear. Using the data from the AKARI IRC survey of the Large
Magellanic Cloud at 3.2, 7, 11, 15, and 24 {\mu}m wavelengths, i.e., at the
mid- and near-infrared, we have constructed a multiwavelength catalog
containing data from a cross-correlation with a number of other databases at
different wavelengths. We present the separation of different classes of stars
in the LMC in color-color, and color-magnitude, diagrams, and analyze their
contribution to the total LMC flux, related to point sources at different
infrared wavelengths
NaviCell: a web-based environment for navigation, curation and maintenance of large molecular interaction maps
Molecular biology knowledge can be systematically represented in a
computer-readable form as a comprehensive map of molecular interactions. There
exist a number of maps of molecular interactions containing detailed
description of various cell mechanisms. It is difficult to explore these large
maps, to comment their content and to maintain them. Though there exist several
tools addressing these problems individually, the scientific community still
lacks an environment that combines these three capabilities together. NaviCell
is a web-based environment for exploiting large maps of molecular interactions,
created in CellDesigner, allowing their easy exploration, curation and
maintenance. NaviCell combines three features: (1) efficient map browsing based
on Google Maps engine; (2) semantic zooming for viewing different levels of
details or of abstraction of the map and (3) integrated web-based blog for
collecting the community feedback. NaviCell can be easily used by experts in
the field of molecular biology for studying molecular entities of their
interest in the context of signaling pathways and cross-talks between pathways
within a global signaling network. NaviCell allows both exploration of detailed
molecular mechanisms represented on the map and a more abstract view of the map
up to a top-level modular representation. NaviCell facilitates curation,
maintenance and updating the comprehensive maps of molecular interactions in an
interactive fashion due to an imbedded blogging system. NaviCell provides an
easy way to explore large-scale maps of molecular interactions, thanks to the
Google Maps and WordPress interfaces, already familiar to many users. Semantic
zooming used for navigating geographical maps is adopted for molecular maps in
NaviCell, making any level of visualization meaningful to the user. In
addition, NaviCell provides a framework for community-based map curation.Comment: 20 pages, 5 figures, submitte
Improved and Quality-assessed Emission and Absorption Line measurements in Sloan Digital Sky Survey galaxies
We present a new database of absorption and emission-line measurements based
on the entire spectral atlas from the Sloan Digital Sky Survey (SDSS) 7th data
release of galaxies within a redshift of 0.2. Our work makes use of the
publicly available penalized pixel-fitting(pPXF) and gas and absorption line
fitting (gandalf) IDL codes, aiming to improve the existing measurements for
stellar kinematics, the strength of various absorption-line features, and the
flux and width of the emissions from different species of ionised gas. Our fit
to the stellar continuum uses both standard stellar population models and
empirical templates obtained by combining a large number of stellar spectra in
order to fit a subsample of high-quality SDSS spectra for quiescent galaxies.
Furthermore, our fit to the nebular spectrum includes an exhaustive list of
both recombination and forbidden lines. Foreground Galactic extinction is
implicitly treated in our models, whereas reddening in the SDSS galaxies is
included in the form of a simple dust screen component affecting the entire
spectrum that is accompanied by a second reddening component affecting only the
ionised gas emission. In order to check for systematic departures, we provide a
quality assessment for our fit to the SDSS spectra in our sample. This quality
assessment also allows the identification of objects with either problematic
data or peculiar features. For example, based on the quality assessment,
approximately 1% of the SDSS spectra classified as "galaxies" by the SDSS
pipeline do in fact require additional broad lines to be matched, even though
they do not show a strong continuum from an active nucleus, as do the SDSS
objects classified as "quasars". Finally, we provide new spectral templates for
galaxies of different Hubble types, obtained by combining the results of our
spectral fit for a subsample of 452 morphologically selected objects.Comment: Accepted for publication in ApJS. 23 pages, 14 figures, 4 tables. A
version with high-resolution figures is available at
http://gem.yonsei.ac.kr/~ksoh/ossy/arXiv/Oh_11_OSSY.pd
Using Virtual Environments as a Visual Interface for Accessing Cultural Database Contents
Cultural institutions have to deal with an enormous amount of data, which are stored in cultural databases usually designed for and managed by professionals. Difficulties in accessing such databases usually preclude or limit their use for the general public. Moreover, in the historic, artistic and cultural areas, an important part of the information associated to an object is related to its original historical and spatial context, an evidence that is often not disclosed, or is difficult to explain, to the non experts. For this reason, it is important to try to re-contextualize - where possible - the elements of cultural collections in the places where these objects were in the past. To this end, in this work we propose the integration of databases and Virtual Reality technologies to develop novel visual interfaces to improve the accessibility, for the non experts, to the contents of cultural databases. Virtual Reality is used to re-create the contextual environment of the objects in the database, which can be explored to gain new insights on specific elements and to improve the awareness of relationships between them. The use of two different types of Virtual Environments has been investigated in the development of the proposed visual interfaces. Results of their evaluation by a user panel, in order to assess the accessibility and effectiveness of both interfaces in relation to each other and with a classic text-based interface, are also presente
Cool carbon stars in the halo and in dwarf galaxies: Halpha, colours, and variabiity
The population of cool carbon (C) stars located far from the galactic plane
is probably made of debris of small galaxies such as the Sagittarius dwarf
spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the
Galaxy. We aim to know this population better through spectroscopy, 2MASS
photometric colours, and variability data. When possible, we compared the halo
results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and
the solar neighbourhood. We first present a few new discoveries of C stars in
the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty
percent show Halpha in emission. The narrow location in the JHK diagram of the
halo C stars is found to differ from that of similar C stars in the above
galaxies. The light curves of the Catalina and LINEAR variability databases
were exploited to derive the pulsation periods of 66 halo C stars. A few
supplementary periods were obtained with the TAROT telescopes. We confirm that
the period distribution of the halo strongly resembles that of Fornax, and we
found that is it very different from the C stars in the solar neighbourhood.
There is a larger proportion of short period Mira/SRa variables in the halo
than in Sgr, but the survey for C stars in this dwarf galaxy is not complete,
and the study of their variability needs to be continued to investigate the
link between Sgr and the cool halo C stars.Comment: 11 pages, 10 figures + one appendix of 26 pages; accepted for
publication in Astronomy and Astrophysic
The ALADIN Interactive Sky Atlas
The Aladin interactive sky atlas, developed at CDS, is a service providing
simultaneous access to digitized images of the sky, astronomical catalogues,
and databases.
The driving motivation is to facilitate direct, visual comparison of
observational data at any wavelength with images of the optical sky, and with
reference catalogues.
The set of available sky images consists of the STScI Digitized Sky Surveys,
completed with high resolution images of crowded regions scanned at the MAMA
facility in Paris.
A Java WWW interface to the system is available at:
http://aladin.u-strasbg.fr/Comment: 8 pages, 3 Postscript figures; to be published in A&
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