3,390 research outputs found
Indications of a Large Fraction of Spectroscopic Binaries Among Nuclei of Planetary Nebulae
Previous work indicates that about 10% of planetary-nebula nuclei (PNNi) are
photometrically variable short-period binaries with periods of hours to a few
days. These systems have most likely descended from common-envelope (CE)
interactions in initially much wider binaries. Population-synthesis studies
suggest that these very close pairs could be the short-period tail of a much
larger post-CE binary population with periods of up to a few months. We have
initiated a radial-velocity (RV) survey of PNNi with the WIYN 3.5-m telescope
and Hydra spectrograph, which is aimed at discovering these intermediate-period
binaries. We present initial results showing that 10 out of 11 well-observed
PNNi have variable RVs, suggesting that a significant binary population may be
present. However, further observations are required because we have as yet been
unable to fit our sparse measurements with definite orbital periods, and
because some of the RV variability might be due to variations in the stellar
winds of some of our PNNi.Comment: 11 pages, 1 table, no figures. Accepted by the Astrophysical Journal
Letter
The 5Ă—5 -- Russia's cyber statecraft
17 USC 105 interim-entered record; under review.The article of record as published may be found at https://www.atlanticcouncil.org/content-series/the-5x5/the-5x5-russias-cyber-statecraft
The pulsating DA white dwarf star EC 14012-1446: results from four epochs of time-resolved photometry
The pulsating DA white dwarfs are the coolest degenerate stars that undergo
self-driven oscillations. Understanding their interior structure will help to
understand the previous evolution of the star. To this end, we report the
analysis of more than 200 h of time-resolved CCD photometry of the pulsating DA
white dwarf star EC 14012-1446 acquired during four observing epochs in three
different years, including a coordinated three-site campaign. A total of 19
independent frequencies in the star's light variations together with 148
combination signals up to fifth order could be detected. We are unable to
obtain the period spacing of the normal modes and therefore a mass estimate of
the star, but we infer a fairly short rotation period of 0.61 +/- 0.03 d,
assuming the rotationally split modes are l=1. The pulsation modes of the star
undergo amplitude and frequency variations, in the sense that modes with higher
radial overtone show more pronounced variability and that amplitude changes are
always accompanied by frequency variations. Most of the second-order
combination frequencies detected have amplitudes that are a function of their
parent mode amplitudes, but we found a few cases of possible resonantly excited
modes. We point out the complications in the analysis and interpretation of
data sets of pulsating white dwarfs that are affected by combination
frequencies of the form f_A+f_B-f_C intruding into the frequency range of the
independent modes.Comment: 14 pages, 6 figures, 6 tables. MNRAS, in pres
Hairy Tongue
Hairy tongue (lingua villosa) is a commonly observed condition of defective desquamation of the filiform papillae that results from a variety of precipitating factors. [1] The condition is most frequently referred to as black hairy tongue (lingua villosa nigra); however, hairy tongue may also appear brown, white, green, pink, or any of a variety of hues depending on the specific etiology and secondary factors (eg, use of colored mouthwashes, breath mints, candies). [2, 3] See the images below
Osteosclerotic myeloma with peripheral neuropathy
A case of solitary osteosclerotic myeloma with peripheral neuropathy and unusual radiological features is presented. The association of myeloma and clinical peripheral neuropathy is unusual, but occurs more commonly with osteosclerotic lesions. The radiological appearance of a lytic focus involving contiguous vertebrae with a surrounding rim of sclerosis is extremely uncommon, but the diagnosis of myeloma should, in future, be suspected in these circumstances. The literature is briefly reviewed.S. Afr. Med. J., 48, 1246 (1974)
The effects of moderately fast shellular rotation on adiabatic oscillations
We investigate adiabatic oscillations for delta Scuti star models, taking
into account a moderate rotation velocity ~100 \km/s. The resulting oscillation
frequencies include corrections for rotation up to second order in the rotation
rate including those of near degeneracy. Effects of either a uniform rotation
or a rotation profile assuming local angular momentum conservation of the form
Omega=Omega(r) on oscillation frequencies are compared. As expected, important
differences (around 3 microHz) are obtained in the and mixed mode regions.
For higher frequency p modes, differences range between 1 microHz and 3
microHz. Such differences are likely to be detectable with future space
missions such as COROT, where precisions in frequency around 0.5 microHz will
be reachable.Comment: A&A, in press (18 pag, 14 fig
Asteroseismology of the Beta Cephei star Nu Eridani -- IV. The 2003-4 multisite photometric campaign and the combined 2002-4 data
The second multisite photometric campaign devoted to Nu Eri is reported. For
Nu Eri, analysis of the new data adds four independent frequencies to the nine
derived previously from the 2002-3 data, three in the range from 7.20 to 7.93
c/d, and a low one, equal to 0.614 c/d. Combining the new and the old data
results in two further independent frequencies, equal to 6.7322 and 6.2236 c/d.
Altogether, the oscillation spectrum is shown to consist of 12 high frequencies
and two low ones. The latter have u amplitudes about twice as large as the v
and y amplitudes, a signature of high radial-order g modes. Thus, the
suggestion that Nu Eri is both a Beta Cephei and an SPB star, put forward on
the basis of the first campaign's data, is confirmed.
Nine of the 12 high frequencies form three triplets, of which two are new.
The triplets represent rotationally split l=1 modes, although in case of the
smallest-amplitude one this may be questioned. Mean separations and asymmetries
of the triplets are derived with accuracy sufficient for meaningful comparison
with models.
The first comparison star, Mu Eri, is shown to be an SPB variable with an
oscillation spectrum consisting of six frequencies, three of which are
equidistant in period. The star is also found to be an eclipsing variable. The
eclipse is a transit, probably total, the secondary is fainter than the primary
by several magnitudes, and the system is widely detached.
The second comparison star, Xi Eri, is confirmed to be a Delta Scuti
variable. To the frequency of 10.8742 c/d seen already in the first campaign's
data, another one, equal to 17.2524 c/d, is added.Comment: 13 pages, 8 figures, MNRAS, in pres
Searching for solar-like oscillations in the delta Scuti star rho Puppis
Despite the shallow convective envelopes of delta Scuti pulsators, solar-like
oscillations are theoretically predicted to be excited in those stars as well.
To search for such stochastic oscillations we organised a spectroscopic
multi-site campaign for the bright, metal-rich delta Sct star rho Puppis. We
obtained a total of 2763 high-resolution spectra using four telescopes. We
discuss the reduction and analysis with the iodine cell technique, developed
for searching for low-amplitude radial velocity variations, in the presence of
high-amplitude variability. Furthermore, we have determined the angular
diameter of rho Puppis to be 1.68 \pm 0.03 mas, translating into a radius of
3.52 \pm 0.07Rsun. Using this value, the frequency of maximum power of possible
solar-like oscillations, is expected at ~43 \pm 2 c/d (498 \pm 23 muHz). The
dominant delta Scuti-type pulsation mode of rho Puppis is known to be the
radial fundamental mode which allows us to determine the mean density of the
star, and therefore an expected large frequency separation of 2.73 c/d (31.6
muHz). We conclude that 1) the radial velocity amplitudes of the delta Scuti
pulsations are different for different spectral lines; 2) we can exclude
solar-like oscillations to be present in rho Puppis with an amplitude per
radial mode larger than 0.5 m/s.Comment: 14 pages, 12 figure, accepted for MNRA
Particle decay branching ratios for states of astrophysical importance in 19Ne
We have measured proton and alpha-particle branching ratios of excited states
in 19Ne formed using the 19F(3He,t) reaction at a beam energy of 25 MeV. These
ratios have a large impact on the astrophysical reaction rates of
15O(alpha,gamma), 18F(p,gamma) and 18F(p,alpha), which are of interest in
understanding energy generation in x-ray bursts and in interpreting anticipated
gamma-ray observations of novae. We detect decay protons and alpha-particles
using a silicon detector array in coincidence with tritons measured in the
focal plane detector of our Enge split-pole spectrograph. The silicon array
consists of five strip detectors of the type used in the Louvain-Edinburgh
Detector Array, subtending angles from 130 degrees to 165 degrees with
approximately 14% lab efficiency. The correlation angular distributions give
additional confidence in some prior spin-parity assignments that were based on
gamma branchings. We measure Gamma_p/Gamma=0.387+-0.016 for the 665 keV proton
resonance, which agrees well with the direct measurement of Bardayan et al.Comment: 5 pages, 2 figures, 3 tables. Prepared using RevTex 4 and BibTex.
Further minor revisions, incl. fig. 1 font size increase, 1 table removal,
and minor changes to the tex
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