521 research outputs found
Asteroseismological Observations of the Central Star of the Planetary Nebula NGC 1501
We report on a global CCD time-series photometric campaign to decode the
pulsations of the nucleus of the planetary nebula NGC1501. The star is hot and
hydrogen-deficient, similar to the pre-white-dwarf PG 1159 stars. NGC1501 shows
pulsational brightness variations of a few percent with periods ranging from 19
to 87 minutes. The variations are very complex, suggesting a pulsation spectrum
that requires a long unbroken time series to resolve. Our CCD photometry of the
star covers a two-week period in 1991 November, and used a global network of
observatories. We obtained nearly continuous coverage over an interval of one
week in the middle of the run. We have identified 10 pulsation periods, ranging
from 5235 s down to 1154 s. We find strong evidence that the modes are indeed
nonradial g-modes. The ratios of the frequencies of the largest-amplitude modes
agree with those expected for modes that are trapped by a density discontinuity
in the outer layers. We offer a model for the pulsation spectrum that includes
a common period spacing of 22.3 s and a rotation period of 1.17 days; the
period spacing allows us to assign a seismological mass of 0.55+/-0.03 Msun.Comment: 12 pages, AASTEX, 7 tables, 6 EPS figures, to appear in AJ, 12/96
Corrected version repairs table formatting and adds missing Table
Gravitational Microlensing Evidence for a Planet Orbiting a Binary Star System
The study of extra-solar planetary systems has emerged as a new discipline of
observational astronomy in the past few years with the discovery of a number of
extra-solar planets. The properties of most of these extra-solar planets were
not anticipated by theoretical work on the formation of planetary systems. Here
we report observations and light curve modeling of gravitational microlensing
event MACHO-97-BLG-41, which indicates that the lens system consists of a
planet orbiting a binary star system. According to this model, the mass ratio
of the binary star system is 3.8:1 and the stars are most likely to be a late K
dwarf and an M dwarf with a separation of about 1.8 AU. A planet of about 3
Jupiter masses orbits this system at a distance of about 7 AU. If our
interpretation of this light curve is correct, it represents the first
discovery of a planet orbiting a binary star system and the first detection of
a Jovian planet via the gravitational microlensing technique. It suggests that
giant planets may be common in short period binary star systems.Comment: 11 pages, with 1 color and 2 b/w Figures included (published version
Pattern of Disease after Murine Hepatitis Virus Strain 3 Infection Correlates with Macrophage Activation and Not Viral Replication
Murine hepatitis virus strain (MHV-3) produces a strain-dependent pattern of disease which has been used as a model for fulminant viral hepatitis. This study was undertaken to examine whether there was a correlation between macrophage activation and susceptibility or resistance to MHV-3 infection. Peritoneal macrophages were isolated from resistant A/J and susceptible BALB/cJ mice and, following stimulation with MHV-3 or lipopolysaccharide (LPS), analyzed for transcription of mRNA and production of interleukin-1 (IL-1), tumor necrosis factor alpha (TNF-alpha), transforming growth factor beta (TGF-beta), mouse fibrinogen-like protein (musfiblp), tissue factor (TF), leukotriene B4, and prostaglandin E2 (PGE2). Macrophages from BALB/cJ mice produced greater amounts of IL-1, TNF-alpha, TGF-beta, leukotriene B4, and musfiblp following MHV-3 infection than macrophages from resistant A/J mice, whereas in response to LPS, equivalent amounts of IL-1, TNF-alpha, TGF-beta, and TF were produced by macrophages from both strains of mice. Levels of mRNA of IL-1, TNF-alpha, and musfiblp were greater and more persistent in BALB/cJ than in A/J macrophages, whereas the levels and kinetics of IL-1, TNF-alpha, and TF mRNA following LPS stimulation were identical in macrophages from both strains of mice. Levels of production of PGE2 by MHV-3-stimulated macrophages from resistant and susceptible mice were equivalent; however, the time course for induction of PGE2, differed, but the total quantity of PGE2 produced was insufficient to inhibit induction of musfiblp, a procoagulant known to correlate with development of fulminant hepatic necrosis in susceptible mice. These results demonstrate marked differences in production of inflammatory mediators to MHV-3 infection in macrophages from resistant A/J and susceptible BALB/cJ mice, which may explain the marked hepatic necrosis and fibrin deposition and account for the lethality of MHV-3 in susceptible mice
Typical equilibrium state of an embedded quantum system
We consider an arbitrary quantum system coupled non perturbatively to a large
arbitrary and fully quantum environment. In [G. Ithier and F. Benaych-Georges,
Phys. Rev. A 96, 012108 (2017)] the typicality of the dynamics of such an
embedded quantum system was established for several classes of random
interactions. In other words, the time evolution of its quantum state does not
depend on the microscopic details of the interaction. Focusing at the long time
regime, we use this property to calculate analytically a new partition function
characterizing the stationary state and involving the overlaps between
eigenvectors of a bare and a dressed Hamiltonian. This partition function
provides a new thermodynamical ensemble which includes the microcanonical and
canonical ensembles as particular cases. We check our predictions with
numerical simulations.Comment: 1 figure, 5 pages. This article supersedes the part on the
equilibrium state in arXiv:1510.0435
Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058-5234
We present the analysis of a total of 177h of high-quality optical
time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC
20058-5234. The bulk of the observations (135h) were obtained during a WET
campaign (XCOV15) in July 1997 that featured coordinated observing from 4
southern observatory sites over an 8-day period. The remaining data (42h) were
obtained in June 2004 at Mt John Observatory in NZ over a one-week observing
period. This work significantly extends the discovery observations of this
low-amplitude (few percent) pulsator by increasing the number of detected
frequencies from 8 to 18, and employs a simulation procedure to confirm the
reality of these frequencies to a high level of significance (1 in 1000). The
nature of the observed pulsation spectrum precludes identification of unique
pulsation mode properties using any clearly discernable trends. However, we
have used a global modelling procedure employing genetic algorithm techniques
to identify the n, l values of 8 pulsation modes, and thereby obtain
asteroseismic measurements of several model parameters, including the stellar
mass (0.55 M_sun) and T_eff (~28200 K). These values are consistent with those
derived from published spectral fitting: T_eff ~ 28400 K and log g ~ 7.86. We
also present persuasive evidence from apparent rotational mode splitting for
two of the modes that indicates this compact object is a relatively rapid
rotator with a period of 2h. In direct analogy with the corresponding
properties of the hydrogen (DAV) atmosphere pulsators, the stable low-amplitude
pulsation behaviour of EC 20058 is entirely consistent with its inferred
effective temperature, which indicates it is close to the blue edge of the DBV
instability strip. (abridged)Comment: 19 pages, 8 figures, 5 tables, MNRAS accepte
The detailed optical light curve of GRB 030329
(Abridged) We present densely sampled BVRI light curves of the optical
transient associated with the gamma-ray burst GRB 030329, the result of a
coordinated observing campaign conducted at five observatories. Augmented with
published observations of this GRB, the compiled optical dataset contains 2687
photometric measurements, obtained between 78 minutes and 79 days after the
burst. We show that the underlying supernova 2003dh evolved faster than, and
was probably somewhat fainter than the type Ic SN 1998bw, associated with GRB
980425. We find that our data can be described by a broken power-law decay
perturbed by a complex variable component. The early- and late-time decay
slopes are determined to be ~1.1 and ~2, respectively. Assuming this single
power-law model, we constrain the break to lie between ~3 and ~8 days after the
burst. This simple, singly-broken power-law model, derived only from the
analysis of our optical observations, may also account for available multi-band
data, provided that the break happened ~8 days after the burst. The more
complex double-jet model of Berger et al. provides a comparable fit to the
optical, X-ray, mm and radio observations of this event. We detect a
significant change in optical colors during the first day. Our color analysis
is consistent with a cooling break frequency sweeping through the optical band
during the first day. The light curves of GRB 030329 reveal a rich array of
variations, superposed over the mean power-law decay. We find that the early
variations are asymmetric, with a steep rise followed by a relatively slower
(by a factor of about two) decline. The variations maintain a similar time
scale during the first four days, and then get significantly longer.Comment: 14 pages, 12 figures, accepted for publication in ApJ with minor
changes. See the GRB030329 Data Treasury at
http://wise-obs.tau.ac.il/GRB030329
Normal modes and discovery of high-order cross-frequencies in the DBV white dwarf GD 358
We present a detailed mode identification performed on the 1994 Whole Earth Telescope (WET) run on GD 358. The results are compared with that obtained for the same star from the 1990 WET data. The two temporal spectra show very few qualitative differences, although amplitude changes are seen in most modes, including the disappearance of the mode identified as k=14 in the 1990 data. The excellent coverage and signal-to-noise ratio obtained during the 1994 run lead to the secure identification of combination frequencies up to fourth order, i.e. peaks that are sums or differences of up to four parent frequencies, including a virtually complete set of second-order frequencies, as expected from harmonic distortion. We show how the third-order frequencies are expected to affect the triplet structure of the normal modes by back-interacting with them. Finally, a search for â=2 modes was unsuccessful, not verifying the suspicion that such modes had been uncovered in the 1990 data set
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