1,186 research outputs found
HST/FOS Eclipse Observations of the Nova-like Cataclysmic Variable UX Ursae Majoris
[abridged abstract]
We present and analyze Hubble Space Telescope observations of the eclipsing
nova-like cataclysmic variable UX UMa obtained with the Faint Object
Spectrograph. Two eclipses each were observed with the G160L grating (covering
the ultraviolet waveband) in August of 1994 and with the PRISM (covering the
near-ultraviolet to near-infrared) in November of the same year. The system was
50% brighter in November than in August, which, if due to a change in the
accretion rate, indicates a fairly substantial increase in Mdot_acc by >~ 50%.
Model disk spectra constructed as ensembles of stellar atmospheres provide
poor descriptions of the observed post-eclipse spectra, despite the fact that
UX UMa's light should be dominated by the disk at this time. Suitably scaled
single temperature model stellar atmospheres with T_eff = 12,500-14,500 K
actually provide a better match to both the ultraviolet and optical
post-eclipse spectra. Evidently, great care must be taken in attempts to derive
accretion rates from comparisons of disk models to observations.
One way to reconcile disk models with the observed post-eclipse spectra is to
postulate the presence of a significant amount of optically thin material in
the system. Such an optically thin component might be associated with the
transition region (``chromosphere'') between the disk photosphere and the fast
wind from the system, whose presence has been suggested by Knigge & Drew
(1997).Comment: 35 pages, including 12 figures; to appear in the ApJ (Vol. 499
Phase resolved spectroscopy and Kepler photometry of the ultracompact AM CVn binary SDSS J190817.07+394036.4
{\it Kepler} satellite photometry and phase-resolved spectroscopy of the
ultracompact AM CVn type binary SDSS J190817.07+394036.4 are presented. The
average spectra reveal a variety of weak metal lines of different species,
including silicon, sulphur and magnesium as well as many lines of nitrogen,
beside the strong absorption lines of neutral helium. The phase-folded spectra
and the Doppler tomograms reveal an S-wave in emission in the core of the He I
4471 \AA\,absorption line at a period of \,sec
identifying this as the orbital period of the system. The Si II, Mg II and the
core of some He I lines show an S-wave in absorption with a phase offset of
compared to the S-wave in emission. The N II, Si III and some
helium lines do not show any phase variability at all. The spectroscopic
orbital period is in excellent agreement with a period at \,sec detected in the three year {\it Kepler} lightcurve. A
Fourier analysis of the Q6 to Q17 short cadence data obtained by {\it Kepler}
revealed a large number of frequencies above the noise level where the majority
shows a large variability in frequency and amplitude. In an O-C analysis we
measured a xs\,s for some of
the strongest variations and set a limit for the orbital period to be
s\,s. The shape of the phase folded
lightcurve on the orbital period indicates the motion of the bright spot.
Models of the system were constructed to see whether the phases of the radial
velocity curves and the lightcurve variation can be combined to a coherent
picture. However, from the measured phases neither the absorption nor the
emission can be explained to originate in the bright spot.Comment: Accepted for publication in MNRAS, 15 pages, 14 figures, 5 table
GJ 900: A new hierarchical system with low-mass components
Speckle interferometric observations made with the 6 m telescope of the
Special Astrophysical Observatory of the Russian Academy of Sciences in 2000
revealed the triple nature of the nearby ( mas)
low-mass young ( Myr) star GJ 900. The configuration of the triple
system allowed it to be dynamically unstable. Differential photometry performed
from 2000 through 2004 yielded - and -band absolute magnitudes and
spectral types for the components to be =6.660.08,
=9.150.11, =10.080.26, =4.840.08,
=6.760.20, =7.390.31, K5--K7,
M3--M4, M5--M6. The ``mass--luminosity''
relation is used to estimate the individual masses of the components:
,
,
. From the observations of the
components relative motion in the period 2000--2006, we conclude that GJ 900 is
a hierarchical triple star with the possible orbital periods
P80 yrs and P20 yrs. An analysis of the 2MASS
images of the region around GJ 900 leads us to suggest that the system can
include other very-low-mass components.Comment: 7 pages, 5 figure
Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim
Multicolor (BVRI) light curves of the eclipsing classical nova V Per are
presented, and a total of twelve new eclipse timings are measured for the
system. When combined with previous eclipse timings from the literature, these
timings yield a revised ephemeris for the times of mid-eclipse given by HJD =
2,447,442.8260(1) + 0.107123474(3) E. The eclipse profiles are analyzed with a
parameter-fitting model that assumes four sources of luminosity: a white dwarf
primary star, a main-sequence secondary star, a flared accretion disk with a
rim, and a bright spot at the intersection of the mass-transfer stream and the
disk periphery. A matrix of model solutions are computed, covering an extensive
range of plausible parameter values. The solution matrix is then explored to
determine the optimum values for the fitting parameters and their associated
errors. For models that treat the accretion disk as a flat structure without a
rim, optimum fits require that the disk have a flat temperature profile.
Although models with a truncated inner disk (R_in >> R_wd) result in a steeper
temperature profile, steady-state models with a temperature profile
characterized by T(r) \propto r^{-3/4} are found only for models with a
significant disk rim. A comparison of the observed brightness and color at
mid-eclipse with the photometric properties of the best-fitting model suggests
that V Per lies at a distance of ~ 1 kpc.Comment: Accepted for publication in The Astrophysical Journal. Thirty-nine
pages, including 9 figures. V2 - updated to include additional references and
related discussion to previous work overlooked in the original version, and
to correct a typo in the ephemeris given in the abstract. V3 - Minor typos
corrected. The paper is scheduled for the 20 June 2006 issue of the ApJ. V4 -
An error in equation (9) has been corrected. The results presented in the
paper were not affected, as all computations were made using the correct
formulation of this equatio
An International Ultraviolet Explorer Archival Study of Dwarf Novae in Outburst
We present a synthetic spectral analysis of nearly the entire far ultraviolet
International Ultraviolet Explorer (IUE) archive of spectra of dwarf novae in
or near outburst. The study includes 46 systems of all dwarf nova subtypes both
above and below the period gap. The spectra were uniformly analyzed using
synthetic spectral codes for optically thick accretion disks and stellar
photospheres along with the best-available distance measurements or estimates.
We present newly estimated accretion rates and discuss the implications of our
study for disk accretion physics and CV evolution.Comment: Accepted for publication in the ApJ, Part
Diagnostic value of a heart-type fatty acid-binding protein (H-FABP) bedside test in suspected acute coronary syndrome in primary care
AbstractBackgroundTo determine the diagnostic accuracy of a rapid heart-type fatty acid-binding protein (H-FABP) test in patients suspected of acute coronary syndrome (ACS) in primary care.MethodsGeneral practitioners included 298 patients suspected of ACS. In all patients, whether referred to hospital or not, ECG and cardiac biomarker testing was performed. ACS was determined in accordance with international guidelines. Multivariate analysis was used to determine the value of H-FABP in addition to clinical findings.ResultsMean patient age was 66years (SD 14), 52% was female and 66 patients (22%) were diagnosed with ACS. The H-FABP bedside test was performed within 24h (median 3.1, IQR 1.5 to 7.1) after symptom onset. The positive predictive value (PPV) of H-FABP was 65% (95% confidence interval (CI) 50–78). The negative predictive value (NPV) was 85% (95% CI 80–88). Sensitivity was 39% (29–51%) and specificity 94% (90–96%). Within 6h after symptom onset, the PPV was 72% (55–84) and the NPV was 83% (77–88), sensitivity 43% (31–57%) and specificity 94% (89–97%). Adding the H-FABP test to a diagnostic model for ACS led to an increase in the area under the receiver operating curve from 0.66 (95% CI 0.58–0.73) to 0.75 (95% CI 0.68–0.82).ConclusionThe H-FABP rapid test provides modest additional diagnostic certainty in primary care. It cannot be used to safely exclude rule out ACS. The test can only be used safely in patients otherwise NOT referred to hospital by the GP, as an extra precaution not to miss ACS (‘rule in’)
Stellar Iron Abundances: non-LTE Effects
We report new statistical equilibrium calculations for Fe I and Fe II in the
atmosphere of Late-Type stars. We used atomic models for Fe I and Fe II having
respectively 256 and 190 levels, as well as 2117 and 3443 radiative
transitions. Photoionization cross-sections are from the Iron Project. These
atomic models were used to investigate non-LTE effects in iron abundances of
Late-Type stars with different atmospheric parameters.
We found that most Fe I lines in metal-poor stars are formed in conditions
far from LTE. We derived metallicity corrections of about 0.3 dex with respect
to LTE values, for the case of stars with [Fe/H] ~ -3.0. Fe II is found not to
be affected by significant non-LTE effects. The main non-LTE effect invoked in
the case of Fe I is overionization by ultraviolet radiation, thus classical
ionization equilibrium is far to be satisfied. An important consequence is that
surface gravities derived by LTE analysis are in error and should be corrected
before final abundances corrections.
This apparently solves the observed discrepancy between spectroscopic surface
gravities derived by LTE analyses and those derived from Hipparcos parallaxes.
A table of non-LTE [Fe/H] and log g values for a sample of metal-poor late-type
stars is given.Comment: 22 pages, 9 figures, 1 table, ApJ style, accepte
Searching for Planets in the Hyades II: Some Implications of Stellar Magnetic Activity
The Hyades constitute a homogeneous sample of stars ideal for investigating
the dependence of planet formation on the mass of the central star. Due to
their youth, Hyades members are much more chromospherically active than stars
traditionally surveyed for planets using high precision radial velocity (RV)
techniques. Therefore, we have conducted a detailed investigation of whether
magnetic activity of our Hyades target stars will interfere with our ability to
make precise RV searches for substellar companions. We measure chromospheric
activity (which we take as a proxy for magnetic activity) by computing the
equivalent of the R'HK activity index from the Ca II K line. is not
constant in the Hyades: we confirm that it decreases with increasing
temperature in the F stars, and also find it decreases for stars cooler than
mid-K. We examine correlations between simultaneously measured R'HK and RV
using both a classical statistical test and a Bayesian odds ratio test. We find
that there is a significant correlation between R'HK and the RV in only 5 of
the 82 stars in this sample. Thus, simple Rprime HK-RV correlations will
generally not be effective in correcting the measured RV values for the effects
of magnetic activity in the Hyades. We argue that this implies long timescale
activity variations (of order a few years; i.e., magnetic cycles or growth and
decay of plage regions) will not significantly hinder our search for planets in
the Hyades if the stars are closely monitored for chromospheric activity. The
trends in the RV scatter (sigma'_v) with , vsini, and P_rot for our stars
is generally consistent with those found in field stars in the Lick planet
search data, with the notable exception of a shallower dependence of sigma'_v
on for F stars.Comment: 15 pages, 7 figures, 3 tables; To appear in the July 2002 issue of
The Astronomical Journa
Some Like it Hot: The X-Ray Emission of The Giant Star YY Mensae
(Abridged abstract) We present an analysis of the X-ray emission of the
rapidly rotating giant star YY Mensae observed by Chandra HETGS and XMM-Newton.
Although no obvious flare was detected, the X-ray luminosity changed by a
factor of two between the XMM-Newton and Chandra observations taken 4 months
apart. The coronal abundances and the emission measure distribution have been
derived from three different methods using optically thin collisional
ionization equilibrium models. The abundances show an inverse first ionization
potential (FIP) effect. We further find a high N abundance which we interpret
as a signature of material processed in the CNO cycle. The corona is dominated
by a very high temperature (20-40 MK) plasma, which places YY Men among the
magnetically active stars with the hottest coronae. Lower temperature plasma
also coexists, albeit with much lower emission measure. Line broadening is
reported, which we interpret as Doppler thermal broadening, although rotational
broadening due to X-ray emitting material high above the surface could be
present as well. We use two different formalisms to discuss the shape of the
emission measure distribution. The first one infers the properties of coronal
loops, whereas the second formalism uses flares as a statistical ensemble. We
find that most of the loops in the corona of YY Men have their maximum
temperature equal to or slightly larger than about 30 MK. We also find that
small flares could contribute significantly to the coronal heating in YY Men.
Although there is no evidence of flare variability in the X-ray light curves,
we argue that YY Men's distance and X-ray brightness does not allow us to
detect flares with peak luminosities Lx <= 10^{31} erg/s with current
detectors.Comment: Accepted paper to appear in Astrophysical Journal, issue Nov 10, 2004
(v615). This a revised version. Small typos are corrected. Figure 7 and its
caption and some related text in Sct 7.2 are changed, without incidence for
the conclusion
Two canine CD1a proteins are differentially expressed in skin
Lipid antigens are presented to T cells by the CD1 family of proteins. In this study, we characterize the complete dog (Canis familiaris) CD1 locus, which is located on chromosome 38. The canine locus contains eight CD1A genes (canCD1A), of which five are pseudogenes, one canCD1B, one canCD1C, one canCD1D, and one canCD1E gene. In vivo expression of canine CD1 proteins was shown for canCD1a6, canCD1a8, and canCD1b, using a panel of anti-CD1 monoclonal antibodies (mAbs). CanCD1a6 and canCD1a8 are recognized by two distinct mAbs. Furthermore, we show differential transcription of the three canCD1A genes in canine tissues. In canine skin, the transcription level of canCD1A8 was higher than that of canCD1A6, and no transcription of canCD1A2 was detected. Based on protein modeling and protein sequence alignment, we predict that both canine CD1a proteins can bind different glycolipids in their groove. Besides differences in ectodomain structure, we observed the unique presence of three types of cytoplasmic tails encoded by canCD1A genes. cDNA sequencing and expressed sequence tag sequences confirmed the existence of a short, human CD1a-like cytoplasmic tail of four amino acids, of an intermediate length form of 15 amino acids, and of a long form of 31 amino acids
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