255 research outputs found
Optical pulsations in HZ Herculis. 5. Pulse-resolved spectrophotometry
Digital spectra of HZ Herculis were obtained with 10 A resolution in the 3,600 - 6,000 A region, synchronously dividing the 1.24-s optical pulsation period into eight 155-ms phase bins. The optical pulses are detected in the data, but their fractional amplitude is only 0.08 percent, a factor of 4 less than typically observed. The separate spectra of each one-eighth of the pulse are identical to within the statistics of the observation. If the X-ray to optical pulse reprocessing mechanism concentrates the optical pulsations into discrete spectral line features, data require the pulses to be distributed among more than four such lines
A Census of Object Types and Redshift Estimates in the SDSS Photometric Catalog from a Trained Decision-Tree Classifier
We have applied ClassX, an oblique decision tree classifier optimized for
astronomical analysis, to the homogeneous multicolor imaging data base of the
Sloan Digital Sky Survey (SDSS), training the software on subsets of SDSS
objects whose nature is precisely known via spectroscopy. We find that the
software, using photometric data only, correctly classifies a very large
fraction of the objects with existing SDSS spectra, both stellar and
extragalactic. ClassX also accurately predicts the redshifts of both normal and
active galaxies in SDSS. To illustrate ClassX applications in SDSS research, we
(a) derive the object content of the SDSS DR2 photometric catalog and (b)
provide a sample catalog of resolved SDSS objects that contains a large number
of candidate AGN galaxies, 27,000, along with 63,000 candidate normal galaxies
at magnitudes substantially fainter than typical magnitudes of SDSS
spectroscopic objects. The surface density of AGN selected by ClassX to i~19 is
in agreement with that quoted by SDSS. When ClassX is applied to the
photometric data fainter than the SDSS spectroscopic limit, the inferred
surface density of AGN rises sharply, as expected. The ability of the
classifier to accurately constrain the redshifts of huge numbers (ultimately ~
10^7) of active galaxies in the photometric data base promises new insights
into fundamental issues of AGN research, such as the evolution of the AGN
luminosity function with cosmic time, the starburst--AGN connection, and
AGN--galactic morphology relationships.Comment: Accepted for publication in The Astronomical Journal, Vol. 130, 2005;
33 pages, 10 figures, 5 tables, AASTeX v5.0. Table 5 will be electronic in
the published journal, but available now at
http://www-int.stsci.edu/~margon/table5.ascii and
http://www-int.stsci.edu/~margon/table5.ascii.g
An Ultraviolet-Excess Optical Candidate for the Luminous Globular Cluster X-ray Source in NGC1851
The intense, bursting X-ray source in the globular cluster NGC 1851 was one
of the first cluster sources discovered, but has remained optically
unidentified for 25 years. We report here on results from Hubble Space
Telescope WFPC2 multicolor images in NGC 1851. Our high spatial resolution
images resolve ~200 objects in the 3'' radius Einstein X-ray error circle, 40
times as many as in previous ground-based work. A color-magnitude diagram of
the cluster clearly reveals a markedly UV-excess object with B~21, (U-B) ~ -0.9
only 2'' from the X-ray position. The UV-excess candidate is 0.12'' distant
from a second, unremarkable star that is 0.5 mag brighter in B; thus
ground-based studies of this field are probably impractical. Three other
UV-excess objects are also present among the ~16,000 objects in the surveyed
region of the cluster, leaving a ~5% probability that a UV-excess object has
fallen in the X-ray error circle by chance. No variability of the candidate is
seen in these data, although a more complete study is required. If this object
is in fact the counterpart of the X-ray source, previous inferences that some
globular cluster X-ray sources are optically subluminous with respect to
low-mass X-ray binaries in the field are now strengthened.Comment: 13 pages including 1 table and 3 figures in AASTeX 4.0; To appear in
The Astrophysical Journal Letters, volume 472 (1996 December 1). Preprint
with full-resolution figures available at
http://www.astro.washington.edu/deutsch/pubs/pubs.htm
Infrared properties of serendipitous X-ray quasars
Near infrared measurements were obtained of 30 quasars originally found serendipitously as X-ray sources in fields of other objects. The observations show that the infrared characteristics of these quasars do not differ significantly from those of quasars selected by other criteria. Because this X-ray selected sample is subject to different selection biases than previous radio and optical surveys, this conclusion is useful in validating previous inferences regarding the infrared colors of 'typical' quasars
Peculiar nature of hard X-ray eclipse in SS433 from INTEGRAL observations
The analysis of INTEGRAL observations (2003-2008) of superaccreting galactic
microquasar SS433 at precessional phases with the maximum disk opening angle is
carried out. The shape and width of the primary X-ray eclipse is found to be
strongly variable suggesting additional absorption in dense stellar wind and
gas outflows from the optical A7I-component. The joint modeling of X-ray
eclipse and precessional X-ray variability by a geometrical model suggests the
binary mass ratio q=m_x/m_v=0.3, allowing an explnation of peculiarities of the
optical variability of SS433, in particular, the substantial precessional
variability at the primary optical eclipse minimum. For the mass function of
the optical star f_v=0.268 M_\odot as derived from Hillwig and Gies (2008)
data, the obtained q yields the masses of the components m_x=5 M_\odot, m_v=15
M_\odot, confirming the black hole nature of the relativistic object in SS433.
The independence of the observed hard X-ray spectrum on the precession phase
suggests that hard X-ray emission is formed in an extended hot corona. The
Monte-Carlo simulations of the broadband X-ray spectrum of SS433 at the maximum
disk opening precessional phases allowed us to determine physical parameters of
the corona (temperature T_{cor}=20 keV, Thomson optical depth \tau=0.2), and to
estimate the jet mass outflow rate \dot M_j=3\times 10^{19} g/s yielding the
kinetic power of the jets \sim 10^{39} erg/s.Comment: 12 pages, 10 figures, Proc. 7th INTEGRAL Workshop, Copenhagen, 8-11
September 200
Infrared Candidates for the Intense Galactic X-ray Source GX 17+2
We present new astrometric solutions and infrared Hubble Space Telescope
observations of GX 17+2 (X1813-140), one of the brightest X-ray sources on the
celestial sphere. Despite 30 years of intensive study, and the existence of a
strong radio counterpart with a sub-arcsecond position, the object remains
optically unidentified. The observed X-ray characteristics strongly suggest
that it is a so-called "Z-source," the rare but important category that
includes Sco X-1 and Cyg X-2. Use of the USNO-A2.0 catalog enables us to
measure the position of optical and infrared objects near the radio source to
sub-arcsecond precision within the International Celestial Reference Frame, for
direct comparison with the radio position, which we also recompute using modern
calibrators. With high confidence we eliminate the V~17.5 star NP Ser, often
listed as the probable optical counterpart of the X-ray source, as a candidate.
Our HST NICMOS observations show two faint objects within our 0.5" radius 90%
confidence error circle. Even the brighter of the two, Star A, is far fainter
than expected (H~19.8), given multiple estimates of the extinction in this
field and our previous understanding of Z sources, but it becomes the best
candidate for the counterpart of GX 17+2. The probability of a chance
coincidence of an unrelated faint object on the radio position is high.
However, if the true counterpart is not Star A, it is fainter still, and our
conclusion that the optical counterpart is surprisingly underluminous is but
strengthened.Comment: 15 pages including 3 figures and 3 tables. Accepted for publication
in The Astrophysical Journa
The optical light curve of GRB 970228 refined
We present the R and V light curves of the optical counterpart of GRB 970228.
A critical analysis of all the available data is made in light of the results
achieved in the recent GRB Symposium held in Huntsville and by considering the
latest information from the HST images on the underlying nebulosity.Comment: 3 pages, 2 .ps figures, Nuclear Physics style file espcrc2.sty
included. To appear in the proceedings of the conference "The Active X-Ray
Sky: Results from BeppoSAX and Rossi-XTE", Rome, Italy, 21-24 October, 1997.
L. Scarsi, H. Bradt, P. Giommi and F. Fiore editors, Nuc. Phys. B Proc. Supp
A Multi-Wavelength Study of the Western Lobe of W50 Powered by the Galactic Microquasar SS 433
W50 remains the only supernova remnant (SNR) confirmed to harbor a
microquasar: the powerful enigmatic source SS 433. Our past study of this
fascinating SNR revealed two X-ray lobes distorting the radio shell as well as
non-thermal X-rays at the site of interaction between the SS 433 eastern jet
and the eastern lobe of W50. In this paper we present the results of a 75 ksec
CHANDRA ACIS-I observation of the peak of W50-west targeted to 1) determine the
nature of the X-ray emission and 2) correlate the X-ray emission with that in
the radio and infrared domains. We have confirmed that at the site of
interaction between the western jet of SS 433 and dense interstellar gas the
X-ray emission is non-thermal in nature. The helical pattern observed in radio
is also seen with CHANDRA. No correlation was found between the infrared and
X-ray emission.Comment: A refereed publication, submitted Sept. 30, 2004, accepted Jan. 12,
2005, to appear in Advances in Space Research. 7 pages, including 4 figures
(3 color) & 1 table (the resolution of most figures has been reduced for
astro-ph submission only). A gzipped postscript or pdf version of the paper
with high-resolution images can be downloaded from:
http://aurora.physics.umanitoba.ca/~moldowan/Astro-Ph
Soil humic substances hinder the propagation of prions
Prions are infectious pathogens causing fatal neurodegenerative disorders, known as transmissible spongiform encephalopathies (TSEs), or prion diseases, which affect different mammalian species. TSEs include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in mule deer, elk, and moose (cervids), and Creutzfeldt-Jakob disease (CJD) in humans. The prominent, if not only, component of prions is a misfolded conformer (PrPSc) of a constitutive sialoglycoprotein, the cellular prion protein (PrPC). A notable feature of prion diseases is horizontal transmission between grazing animals, implying that contaminated soil may serve to propagate the disease. In this respect, it has been reported that grazing animals ingest from tens to hundreds grams of soil per day, either incidentally through the diet, or deliberately in answering salt needs, and that mule deer can develop CWD after grazing in locations that previously housed infected \u202
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