499 research outputs found
Automated optical identification of a large complete northern hemisphere sample of flat spectrum radio sources with S_6cm > 200 mJy
This paper describes the automated optical APM identification of radio
sources from the Jodrell Bank - VLA Astrometric Survey (JVAS), as used for the
search for distant radio-loud quasars. The sample has been used to investigate
possible relations between optical and radio properties of flat spectrum radio
sources. From the 915 sources in the sample, 756 have an optical APM
identification at a red (e) and/or blue (o) plate,resulting in an
identification fraction of 83% with a completeness and reliability of 98% and
99% respectively. About 20% are optically identified with extended APM objects
on the red plates, e.g. galaxies. However the distinction between galaxies and
quasars can not be done properly near the magnitude limit of the POSS-I plates.
The identification fraction appears to decrease from >90% for sources with a 5
GHz flux density of >1 Jy, to <80% for sources at 0.2 Jy. The identification
fraction, in particular that for unresolved quasars, is found to be lower for
sources with steeper radio spectra. In agreement with previous studies, we find
that the quasars at low radio flux density levels also tend to have fainter
optical magnitudes, although there is a large spread. In addition, objects with
a steep radio-to-optical spectral index are found to be mainly highly polarised
quasars, supporting the idea that in these objects the polarised synchrotron
component is more prominent. It is shown that the large spread in
radio-to-optical spectral index is possibly caused by source to source
variations in the Doppler boosting of the synchrotron component [Abridged].Comment: LaTex, 17 pages, 5 gif figures, 4 tables. Accepted for publication in
MNRAS. High resolution figures can be found at http://www.roe.ac.uk/~ignas
The Biological Standard of Living in the two Germanies.
Physical stature is used as a proxy for the biological standard of living in the two Germanies before and after unification in an analysis of a cross-sectional sample (1998) of adult heights, as well as among military recruits of the 1990s. West Germans tended to be taller than East Germans throughout the period under consideration. Contrary to official proclamations of a classless society, there were substantial social differences in physical stature in East-Germany. Social differences in height were greater in the East among females, and less among males than in the West. The difficulties experienced by the East-German population after 1961 is evident in the increase in social inequality of physical stature thereafter, as well as in the increasing gap relative to the height of the West-German population. After unification, however, there is a tendency for East-German males, but not of females, to catch up with their West-German counterparts
The near-infrared detection of PSR B0540-69 and its nebula
The ~1700 year old PSR B0540-69 in the LMC is considered the twin of the Crab
pulsar because of its similar spin parameters, magnetic field, and energetics.
Its optical spectrum is fit by a power-law, ascribed to synchrotron radiation,
like for the young Crab and Vela pulsars. nIR observations, never performed for
PSR B0540-69, are crucial to determine whether the optical power-law spectrum
extends to longer wavelengths or a new break occurs, like it happens for both
the Crab and Vela pulsars in the mIR, hinting at an even more complex particle
energy and density distribution in the pulsar magnetosphere. We observed PSR
B0540-69 in the J, H, and Ks bands with the VLT to detect it, for the first
time, in the nIR and characterise its optical-to-nIR spectrum. To disentangle
the pulsar emission from that of its pulsar wind nebula (PWN), we obtained
high-spatial resolution adaptive optics images with NACO. We could clearly
identify PSR B0540-69 in our J, H, and Ks-band images and measure its flux
(J=20.14, H=19.33, Ks=18.55, with an overall error of +/- 0.1 magnitudes in
each band). The joint fit to the available optical and nIR photometry with a
power-law spectrum gives a spectral index alpha=0.70 +/-0.04. The comparison
between our NACO images and HST optical ones does not reveal any apparent
difference in the PWN morphology as a function of wavelength. The PWN
optical-to-nIR spectrum is also fit by a single power-law, with spectral index
alpha=0.56+/- 0.03, slightly flatter than the pulsar's. Using NACO at the VLT,
we obtained the first detection of PSR B0540-69 and its PWN in the nIR. Due to
the small angular scale of the PWN (~4") only the spatial resolution of the
JWST will make it possible to extend the study of the pulsar and PWN spectrum
towards the mid-IR.Comment: 11 pages, 10 figures, Accepted for publication on Astronomy and
Astrophysic
ABSOLUTE PROPER MOTIONS OUTSIDE the PLANE (APOP) - A STEP TOWARD the GSC2.4
Zhaoxiang Qi, et al, ABSOLUTE PROPER MOTIONS OUTSIDE THE PLANE (APOP)âA STEP TOWARD THE GSC2.4, The Astronomical Journal, 150:137 (12pp), October 2015, doi:10.1088/0004-6256/150/4/137. © 2015. The American Astronomical Society. All rights reserved.We present a new catalog of absolute proper motions and updated positions derived from the same Space Telescope Science Institute digitized Schmidt survey plates utilized for the construction of Guide Star Catalog II. As special attention was devoted to the absolutization process and the removal of position, magnitude, and color dependent systematic errors through the use of both stars and galaxies, this release is solely based on plate data outside the galactic plane, i.e., ?b? â„ 27°. The resulting global zero point error is less than 0.6 mas yr-1, and the precision is better than 4.0 mas yr-1 for objects brighter than RF = 18.5, rising to 9.0 mas yr-1 for objects with magnitudes in the range 18.5 < RF < 20.0. The catalog covers 22,525 square degrees and lists 100,774,153 objects to the limiting magnitude of RF ⌠20.8. Alignment with the International Celestial Reference System was made using 1288 objects common to the second realization of the International Celestial Reference Frame (ICRF2) at radio wavelengths. As a result, the coordinate axes realized by our astrometric data are believed to be aligned with the extragalactic radio frame to within ±0.2 mas at the reference epoch J2000.0. This makes our compilation one of the deepest and densest ICRF-registered astrometric catalogs outside the galactic plane. Although the Gaia mission is poised to set the new standard in catalog astronomy and will in many ways supersede this catalog, the methods and procedures reported here will prove useful to remove astrometric magnitude- and color-dependent systematic errors from the next generation of ground-based surveys reaching significantly deeper than the Gaia catalog.Peer reviewe
Photometry of Variable Stars from Dome A, Antarctica
Dome A on the Antarctic plateau is likely one of the best observing sites on
Earth thanks to the excellent atmospheric conditions present at the site during
the long polar winter night. We present high-cadence time-series aperture
photometry of 10,000 stars with i<14.5 mag located in a 23 square-degree region
centered on the south celestial pole. The photometry was obtained with one of
the CSTAR telescopes during 128 days of the 2008 Antarctic winter.
We used this photometric data set to derive site statistics for Dome A and to
search for variable stars. Thanks to the nearly-uninterrupted synoptic
coverage, we find 6 times as many variables as previous surveys with similar
magnitude limits. We detected 157 variable stars, of which 55% are
unclassified, 27% are likely binaries and 17% are likely pulsating stars. The
latter category includes delta Scuti, gamma Doradus and RR Lyrae variables. One
variable may be a transiting exoplanet.Comment: Accepted for publication in the Astronomical Journal. PDF version
with high-resolution figures available at
http://faculty.physics.tamu.edu/lmacri/papers/wang11.pd
HST and VLT observations of the neutron star 1E 1207.4-5209
1E 1207.4-5209, the peculiar Central Compact object in the G296.5+10.0
supernova remnant, has been proposed to be an "anti-magnetar" - a young neutron
star born with a weak dipole field. Accretion, possibly of supernova fallback
material, has also been invoked to explain a large surface temperature
anisotropy as well as the generation of peculiar cyclotron absorption features
superimposed to its thermal spectrum. Interestingly enough, a faint
optical/infrared source was proposed as a possible counterpart to 1E
1207.4-5209, but later questioned, based on coarse positional coincidence.
Considering the large offset of 1E 1207.4-5209 with respect to the center of
its host supernova remnant, the source should move at ~70 mas/yr. Thus, we
tested the association by measuring the proper motion of the proposed optical
counterpart. Using HST observations spanning 3.75 years, we computed a 3 sigma
upper limit of 7 mas/yr. Absolute astrometry on the same HST data set also
places the optical source significantly off the 99% confidence Chandra
position. This allows us to safely rule out the association. Using the HST data
set, coupled to ground-based observations collected at the ESO/VLT, we set the
deepest limits ever obtained to the optical/infrared emission from 1E
1207.4-5209. By combining such limits to the constraints derived from X-ray
timing, we rule out accretion as the source of the thermal anisotropy of the
neutron star.Comment: 8 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
Cosmological Distance Measurement of 12 Nearby Supernovae IIP with ROTSE-IIIB
We present cosmological analysis of 12 nearby () Type IIP supernovae
(SNe IIP) observed with the ROTSE-IIIb telescope. To achieve precise
photometry, we present a new image differencing technique that is implemented
for the first time on the ROTSE SN photometry pipeline. With this method, we
find up to a 20\% increase in the detection efficiency and significant
reduction in residual RMS scatter of the SN lightcurves when compared to the
previous pipeline performance. We use the published optical spectra and
broadband photometry of well studied SNe IIP to establish temporal models for
ejecta velocity and photospheric temperature evolution for our SNe IIP
population. This study yields measurements that are competitive to other
methods even when the data are limited to a single epoch during the
photospheric phase of SNe IIP. Using the fully reduced ROTSE photometry and
optical spectra, we apply these models to the respective photometric epochs for
each SN in the ROTSE IIP sample. This facilitates the use of the Expanding
Photosphere Method (EPM) to obtain distance estimates to their respective host
galaxies. We then perform cosmological parameter fitting using these EPM
distances from which we measure the Hubble constant to be
, which is consistent with the
standard model values derived using other independent techniques.Comment: 19 pages, 13 figure
Forward Global Photometric Calibration of the Dark Energy Survey
Many scientific goals for the Dark Energy Survey (DES) require calibration of
optical/NIR broadband photometry that is stable in time and uniform
over the celestial sky to one percent or better. It is also necessary to limit
to similar accuracy systematic uncertainty in the calibrated broadband
magnitudes due to uncertainty in the spectrum of the source. Here we present a
"Forward Global Calibration Method (FGCM)" for photometric calibration of the
DES, and we present results of its application to the first three years of the
survey (Y3A1). The FGCM combines data taken with auxiliary instrumentation at
the observatory with data from the broad-band survey imaging itself and models
of the instrument and atmosphere to estimate the spatial- and time-dependence
of the passbands of individual DES survey exposures. "Standard" passbands are
chosen that are typical of the passbands encountered during the survey. The
passband of any individual observation is combined with an estimate of the
source spectral shape to yield a magnitude in the standard
system. This "chromatic correction" to the standard system is necessary to
achieve sub-percent calibrations. The FGCM achieves reproducible and stable
photometric calibration of standard magnitudes of stellar
sources over the multi-year Y3A1 data sample with residual random calibration
errors of per exposure. The accuracy of the
calibration is uniform across the DES footprint to
within . The systematic uncertainties of magnitudes in
the standard system due to the spectra of sources are less than
for main sequence stars with .Comment: 25 pages, submitted to A
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