157 research outputs found
The Orbital Period of Scorpius X-1
The orbital period of Sco X-1 was first identified by Gottlieb et al. (1975).
While this has been confirmed on multiple occasions, this work, based on nearly
a century of photographic data, has remained the reference in defining the
system ephemeris ever since. It was, however, called into question when
Vanderlinde et al. (2003) claimed to find the one-year alias of the historical
period in RXTE/ASM data and suggested that this was the true period rather than
that of Gottlieb et al. (1975). We examine data from the All Sky Automated
Survey (ASAS) spanning 2001-2009. We confirm that the period of Gottlieb et al.
(1975) is in fact the correct one, at least in the optical, with the one-year
alias strongly rejected by these data. We also provide a modern time of minimum
light based on the ASAS data.Comment: 3 pages, 2 figures, accepted for publication in the Astrophysical
Journa
Radio sources in the Chandra Galactic Bulge Survey
We discuss radio sources in the Chandra Galactic Bulge Survey region. By cross-matching the X-ray sources in this field with the NRAO VLA Sky Survey archival data, we find 12 candidate matches. We present a classification scheme for radio/X-ray matches in surveys taken in or near the Galactic plane, taking into account other multiwavelength data. We show that none of the matches found here is likely to be due to coronal activity from normal stars because the radio to X-ray flux ratios are systematically too high. We show that one of the source could be a radio pulsar, and that one could be a planetary nebula, but that the bulk of the sources are likely to be background active galactic nuclei (AGN), with many confirmed through a variety of approaches. Several of the AGN are bright enough in the near-infrared (and presumably in the optical) to use as probes of the interstellar medium in the inner Galaxy
Links Between Optical and X-ray Light in Scorpius X-1
We observed the low-mass X-ray binary Sco X-1 for 12 nights simultaneously
using the Rossi X-Ray Timing Explorer and the Otto Struve Telescope at McDonald
Observatory at 1 second time resolution. This is among the most comprehensive
simultaneous X-Ray/optical data sets of Sco X-1. Evidence of reprocessing was
observed in the form of nine positive, near-zero lag peaks in the cross
correlation function, eight of which were relatively small and took the shape
of piecewise exponential functions. These peaks were initially identified by
eye, after which a computational identification scheme was developed to confirm
their significance. Based on their short lags (less than 4 seconds), as well as
their occurrence on the flaring branch and soft apex, the small cross
correlation features are likely to be caused by reprocessing off the outer
disc, although the companion could still make a contribution to their tails.
The Z track was parameterized using a rank number scheme so that the system's
location on the track could be numerically defined. Plotting the results
against the optical reveals an increasing step function when moving from the
horizontal to the normal to the flaring branch, with differential optical
levels at ~0.47, ~0.57, and ~1.1 respectively. An additional correlation
between Z track location and the optical was found on the upper flaring branch.
An optical intensity histogram reveals a transition region between the normal
and flaring branches with only intermediate fluxes.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Societ
Variability of Optical Counterparts in the Chandra Galactic Bulge Survey
We present optical lightcurves of variable stars consistent with the
positions of X-ray sources identified with the Chandra X-ray Observatory for
the Chandra Galactic Bulge Survey. Using data from the Mosaic-II instrument on
the Blanco 4m Telescope at CTIO, we gathered time-resolved photometric data on
timescales from hr to 8 days over the of the X-ray survey
containing sources from the initial GBS catalog. Among the lightcurve
morphologies we identify are flickering in interacting binaries, eclipsing
sources, dwarf nova outbursts, ellipsoidal variations, long period variables,
spotted stars, and flare stars. of X-ray sources have at least one
potential optical counterpart. of these candidate counterparts are
detectably variable; a much greater fraction than expected for randomly
selected field stars, which suggests that most of these variables are real
counterparts. We discuss individual sources of interest, provide variability
information on candidate counterparts, and discuss the characteristics of the
variable population.Comment: Accepted for publication in the Astrophysical Journal Supplement
High C/O Chemistry and Weak Thermal Inversion in the Extremely Irradiated Atmosphere of Exoplanet WASP-12b
The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior as opposed to the silicate-dominated composition as found on Earth; the solar C/O is 0.54. Theory, shows that high C/O leads to a diversity of carbon-rich planets that can have very different interiors and atmospheres from those in the solar system. Here we report the detection of C/O greater than or equal to 1 in a planetary atmosphere. The transiting hot Jupiter WASP-12b has a dayside atmosphere depleted in water vapour and enhanced in methane by over two orders of magnitude compared to a solar-abundance chemical equilibrium model at the expected temperatures. The observed concentrations of the prominent molecules CO, CH4, and H2O are consistent with theoretical expectations for an atmosphere with the observed C/O = 1. The C/O ratios are not known for giant planets in the solar system, although they are expected to equal the solar value. If high C/O ratios are common, then extrasolar planets are likely very different in interior composition, and formed very differently, from expectations based on solar composition, potentially explaining the large diversity in observed radii. We also find that the extremely irradiated atmosphere (greater than 2500 K) of WASP-12b lacks a prominent thermal inversion, or a stratosphere, and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres
Calcium-sensing receptor antagonists abrogate airway hyperresponsiveness and inflammation in allergic asthma
Airway hyperresponsiveness and inflammation are fundamental hallmarks of allergic asthma that are accompanied by increases in certain polycations, such as eosinophil cationic protein. Levels of these cations in body fluids correlate with asthma severity. We show that polycations and elevated extracellular calcium activate the human recombinant and native calcium-sensing receptor (CaSR), leading to intracellular calcium mobilization, cyclic adenosine monophosphate breakdown, and p38 mitogen-activated protein kinase phosphorylation in airway smooth muscle (ASM) cells. These effects can be prevented by CaSR antagonists, termed calcilytics. Moreover, asthmatic patients and allergen-sensitized mice expressed more CaSR in ASMs than did their healthy counterparts. Indeed, polycations induced hyperreactivity in mouse bronchi, and this effect was prevented by calcilytics and absent in mice with CaSR ablation from ASM. Calcilytics also reduced airway hyperresponsiveness and inflammation in allergen-sensitized mice in vivo. These data show that a functional CaSR is up-regulated in asthmatic ASM and targeted by locally produced polycations to induce hyperresponsiveness and inflammation. Thus, calcilytics may represent effective asthma therapeutics
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