393 research outputs found
Supercongruences of Atkin and Swinnerton-Dyer type for Legendre polynomials
AbstractIn this paper we prove some generalisations of congruences of Atkin and Swinnerton-Dyer type. This is done in the form of congruences for numbers Pn(A√Δ), where Pn(t) are the orthogonal polynomials of Legendre. The proofs are based on complex multiplication of elliptic functions
Absolute properties of BG Ind - a bright F3 system just leaving the Main Sequence
We present photometric and spectroscopic analysis of the bright detached
eclipsing binary BG Ind. The masses of the components are found to be 1.428 +-
0.008 and 1.293 +- 0.008 Msun and the radii to be 2.290+-0.017 and 1.680+-0.038
Rsun for primary and secondary stars, respectively. Spectra- and
isochrone-fitting coupled with color indices calibration yield
[Fe/H]=-0.2+-0.1. At an age of 2.65+-0.20 Gyr BG Ind is well advanced in the
main-sequence evolutionary phase - in fact, its primary is at TAMS or just
beyond it. Together with three similar systems (BK Peg, BW Aqr and GX Gem) it
offers an interesting opportunity to test the theoretical description of
overshooting in the critical mass range 1.2-1.5 Msun.Comment: 8 pages, 5 figures, corrected bugs in author lis
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
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
Photometric Analysis of Recently Discovered Eclipsing Binary GSC 00008-00901
Photometric analysis of light curves of newly discovered eclipsing
binary GSC 0008-00901 is presented. The orbital period is improved to
0.28948(11) days. Photometric parameters are determined, as well. The analysis
yielded to conclusion that system is an over-contact binary of W UMa type with
components not in thermal contact. The light curves from 2005 show the presence
of a spot on the surface of one of the components, while light curves from 2006
are not affected by maculation.Comment: Accepted for publication in Astrophysics & Space Scienc
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
Asiago eclipsing binaries program. II. V505 Per
The orbit and fundamental physical parameters of the double-lined eclipsing
binary V505 Per are derived by means of Echelle high resolution, high S/N
spectroscopy and B, V photometry. Effective temperatures, gravities, rotational
velocities and metallicities are obtained from atmospheric chi^2 analysis. An
E(B-V)<=0.01 mag reddening is derived from interstellar NaI and KI lines. The
distance to the system computed from orbital parameters (60.6 +/- 1 pc) is
identical to the newly re-reduced Hipparcos parallax (61.5 +/- 1.9 pc). The
masses of the two components (M(1) = 1.2693 +/- 0.0011 and M(2) = 1.2514 +/-
0.0012 Msun) place them in the transition region between convective and
radiative stellar cores of the HR diagram, with the more massive of the two
showing already the effect of evolution within the Main Sequence band (T(1) =
6512 +/- 21 K, T(2) = 6462 +/- 12 K, R(1) = 1.287 +/- 0.014, R(2) = 1.266 +/-
0.013 Rsun). This makes this system of particular relevance to theoretical
stellar models, as a test on the overshooting. We compare the firm
observational results for V505 Per component stars with the predictions of
various libraries of theoretical stellar models (BaSTI, Padova, Granada,
Yonsei-Yale, Victoria-Regina) as well as BaSTI models computed specifically for
the masses and chemical abundances of V505 Per. We found that the overshooting
at the masses of V505 Per component stars is already pretty low, but not null,
and described by efficiencies lambda(OV)=0.093 and 0.087 for the 1.27 and 1.25
Msun components, respectively. According to the computed BaSTI models, the age
of the system is about 0.9 Gyr and the element diffusion during this time has
reduced the surface metallicity from the initial [M/H]=-0.03 to the current
[M/H]=-0.13, in excellent agreement with observed [M/H]=-0.12 +/- 0.03.Comment: accepted in press by A&
The stellar mass ratio of GK Persei
We study the absorption lines present in the spectra of the long-period
cataclysmic variable GK Per during its quiescent state, which are associated
with the secondary star. By comparing quiescent data with outburst spectra we
infer that the donor star appears identical during the two states and the inner
face of the secondary star is not noticeably irradiated by flux from the
accreting regions. We obtain new values for the radial velocity semi-amplitude
of the secondary star, Kk = 120.5 +- 0.7 km/s, a projected rotational velocity,
Vksin i = 61.5 +- 11.8 km/s and consequently a measurement of the stellar mass
ratio of GK Per, q = Mk/Mwd = 0.55 +- 0.21. The inferred white dwarf radial
velocities are greater than those measured traditionally using the wings of
Doppler-broadened emission lines suspected to originate in an accretion disk,
highlighting the unsuitability of emission lines for mass determinations in
cataclysmic variables. We determine mass limits for both components in the
binary, Mk >= 0.48 +- 0.32 Msolar and Mwd >= 0.87 +- 0.24 Msolar.Comment: 8 pages, 8 figures, accepted by MNRA
The EVIL-MC Model for Ellipsoidal Variations of Planet-Hosting Stars and Applications to the HAT-P-7 System
We present a new model for Ellipsoidal Variations Induced by a Low-Mass
Companion, the EVIL-MC model. We employ several approximations appropriate for
planetary systems to substantially increase the computational efficiency of our
model relative to more general ellipsoidal variation models and improve upon
the accuracy of simpler models. This new approach gives us a unique ability to
rapidly and accurately determine planetary system parameters. We use the
EVIL-MC model to analyze Kepler Quarter 0-2 (Q0-2) observations of the HAT-P-7
system, an F-type star orbited by a nearly Jupiter-mass companion. Our analysis
corroborates previous estimates of the planet-star mass ratio q = (1.10 +/-
0.06) x 10^(-3), and we have revised the planet's dayside brightness
temperature to 2680 +10/-20 K. We also find a large difference between the day-
and nightside planetary flux, with little nightside emission. Preliminary
dynamical+radiative modeling of the atmosphere indicates this result is
qualitatively consistent with high altitude absorption of stellar heating.
Similar analyses of Kepler and CoRoT photometry of other planets using EVIL-MC
will play a key role in providing constraints on the properties of many
extrasolar systems, especially given the limited resources for follow-up and
characterization of these systems. However, as we highlight, there are
important degeneracies between the contributions from ellipsoidal variations
and planetary emission and reflection. Consequently, for many of the hottest
and brightest Kepler and CoRoT planets, accurate estimates of the planetary
emission and reflection, diagnostic of atmospheric heat budgets, will require
accurate modeling of the photometric contribution from the stellar ellipsoidal
variation.Comment: Accepted to ApJ; minor revisions to original submission; An IDL
version of the EVIL-MC model is publicly available at
http://www.lpl.arizona.edu/~bjackson/idl_code/index.htm
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