413 research outputs found
Revealing the Nature of Algol Disks through Optical and UV Spectroscopy, Synthetic Spectra, and Tomography of TT Hydrae
We have developed a systematic procedure to study the disks in Algol-type
binaries using spectroscopic analysis, synthetic spectra, and tomography. We
analyzed 119 H-alpha spectra of TT Hya, an Algol-type eclipsing interacting
binary, collected from 1985-2001. The new radial velocities enabled us to
derive reliable orbital elements, including a small non-zero eccentricity, and
to improve the accuracy of the absolute dimensions of the system. High
resolution IUE spectra were also analyzed to study the formation of the
ultraviolet lines and continuum. Synthetic spectra of the iron curtain using
our new shellspec program enabled us to derive a characteristic disk
temperature of 7000K. We have demonstrated that the UV emission lines seen
during total primary eclipse cannot originate from the accretion disk, but most
likely arise from a hotter disk-stream interaction region.
The synthetic spectra of the stars, disk, and stream allowed us to derive a
lower limit to the mass transfer rate of 2e-10 solar masses per year. Doppler
tomography of the observed H-alpha profiles revealed a distinct accretion disk.
The difference spectra produced by subtracting the synthetic spectra of the
stars resulted in an image of the disk, which virtually disappeared once the
composite synthetic spectra of the stars and disk were used to calculate the
difference spectra. An intensity enhancement of the resulting tomogram revealed
images of the gas stream and an emission arc. We successfully modeled the gas
stream using shellspec and associated the emission arc with an asymmetry in the
accretion disk.Comment: 46 pages, 15 figures, 6 tables, accepted by Ap
Generalization of Weierstrassian Elliptic Functions to
The Weierstrassian and functions are generalized to
. The and cases have already been used in
gravitational and Yang-Mills instanton solutions which may be interpreted as
explicit realizations of spacetime foam and the monopole condensate,
respectively. The new functions satisfy higher dimensional versions of the
periodicity properties and Legendre's relations obeyed by their familiar
complex counterparts. For , the construction reproduces functions found
earlier by Fueter using quaternionic methods. Integrating over lattice points
along all directions but two, one recovers the original Weierstrassian elliptic
functions.Comment: pp. 9, Late
Spurious Eccentricities of Distorted Binary Components
I discuss the effect of physical distortion on the velocities of close binary
components and how we may use the resulting distortion of velocity curves to
constrain some properties of binary systems, such as inclination and mass
ratio. Precise new velocities for 5 Cet convincingly detect these distortions
with their theoretically predicted phase dependence. We can even use such
distortions of velocity curves to test Lucy's theory of convective gravity
darkening. The observed distortions for TT Hya and 5 Cet require the contact
components of those systems to be gravity darkened, probably somewhat more than
predicted by Lucy's theory but clearly not as much as expected for a radiative
star. These results imply there is no credible evidence for eccentric orbits in
binaries with contact components. I also present some speculative analyses of
the observed properties of a binary encased in a non-rotating common envelope,
if such an object could actually exist, and discuss how the limb darkening of
some recently calculated model atmospheres for giant stars may bias my resuts
for velocity-curve distortions, as well as other results from a wide range of
analyses of binary stars.Comment: 14 pp, 2 tables, 12 fig; under review by Ap
ADAR1 Facilitates HIV-1 Replication in Primary CD4+ T Cells.
Unlike resting CD4+ T cells, activated CD4+T cells are highly susceptible to infection of human immunodeficiency virus 1 (HIV-1). HIV-1 infects T cells and macrophages without activating the nucleic acid sensors and the anti-viral type I interferon response. Adenosine deaminase acting on RNA 1 (ADAR1) is an RNA editing enzyme that displays antiviral activity against several RNA viruses. Mutations in ADAR1 cause the autoimmune disorder Aicardi-Goutieères syndrome (AGS). This disease is characterized by an inappropriate activation of the interferon-stimulated gene response. Here we show that HIV-1 replication, in ADAR1-deficient CD4+T lymphocytes from AGS patients, is blocked at the level of protein translation. Furthermore, viral protein synthesis block is accompanied by an activation of interferon-stimulated genes. RNA silencing of ADAR1 in Jurkat cells also inhibited HIV-1 protein synthesis. Our data support that HIV-1 requires ADAR1 for efficient replication in human CD4+T cells
Detection of gravity modes in the massive binary V380 Cyg from Kepler spacebased photometry and high-resolution spectroscopy
We report the discovery of low-amplitude gravity-mode oscillations in the
massive binary star V380 Cyg, from 180 d of Kepler custom-aperture space
photometry and 5 months of high-resolution high signal-to-noise spectroscopy.
The new data are of unprecedented quality and allowed to improve the orbital
and fundamental parameters for this binary. The orbital solution was subtracted
from the photometric data and led to the detection of periodic intrinsic
variability with frequencies of which some are multiples of the orbital
frequency and others are not. Spectral disentangling allowed the detection of
line-profile variability in the primary. With our discovery of intrinsic
variability interpreted as gravity mode oscillations, V380 Cyg becomes an
important laboratory for future seismic tuning of the near-core physics in
massive B-type stars.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in MNRAS
Letter
Detection of a classical Delta Scuti star in the new eclipsing binary system HIP 7666
HIP 7666 is a variable star newly discovered during the Hipparcos mission and
classified as of unknown type (ESA 1997). During 23 nights between July 2000
and November 2000, over 2300 CCD observations in the V band were obtained from
Hostalets de Pierola and Monegrillo observatories in Spain. These data show
that the new variable is a detached eclipsing binary system with an orbital
period of 2.37229 days. In addition, one of the components undergoes very
short-period oscillations with a main pulsation frequency of 24.46 or 25.47
c/d. HIP 7666 is therefore a new member of the presently very few known
detached eclipsing binary systems with a Delta Scuti type component.Comment: 6 pages, 8 Postscript figure
Pulsations detected in the line profile variations of red giants: Modelling of line moments, line bisector and line shape
Contents: So far, red giant oscillations have been studied from radial
velocity and/or light curve variations, which reveal frequencies of the
oscillation modes. To characterise radial and non-radial oscillations, line
profile variations are a valuable diagnostic. Here we present for the first
time a line profile analysis of pulsating red giants, taking into account the
small line profile variations and the predicted short damping and re-excitation
times. We do so by modelling the time variations in the cross correlation
profiles in terms of oscillation theory.
Aims: The performance of existing diagnostics for mode identification is
investigated for known oscillating giants which have very small line profile
variations. We modify these diagnostics, perform simulations, and characterise
the radial and non-radial modes detected in the cross correlation profiles.
Methods: Moments and line bisectors are computed and analysed for four
giants. The robustness of the discriminant of the moments against small
oscillations with finite lifetimes is investigated. In addition, line profiles
are simulated with short damping and re-excitation times and their line shapes
are compared with the observations.
Results: For three stars, we find evidence for the presence of non-radial
pulsation modes, while for Hydrae perhaps only radial modes are present.
Furthermore the line bisectors are not able to distinguish between different
pulsation modes and are an insufficient diagnostic to discriminate small line
profile variations due to oscillations from exoplanet motion.Comment: 12 pages, 10 figures, accepted by A&
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