128 research outputs found
Mahnruf an die Diener der evangelischen Kirche / Neu hrsg. von Pfarrer Oehler
Mahnruf an die Diener der evangelischen Kirche / Neu hrsg. von Pfarrer Oehlerhttps://scholar.csl.edu/ebooks/1035/thumbnail.jp
Broad and Luminous [OIII] and [NII] in Globular Cluster ULXs
We consider an accretion-disc origin for the broad and luminous
forbidden-line emission observed in ultraluminous X-ray (ULX) sources
CXOJ033831.8-352604 and XMMU 122939.7+075333 in globular clusters hosted by
elliptical galaxies NGC 1399 and NGC 4472, respectively. We will refer to the
latter by the globular cluster name RZ2109. The first has strong [OIII] and
[NII], the second only [OIII]. Both H and H are very weak or
undetected in both objects. We assume that the large line widths are due to
Keplerian rotation around a compact object and derive expressions for maximum
line luminosities. These idealized models require central masses
and \gtrsim30000\Msun for CXOJ033831.8-352604 and RZ2109, respectively. An
independent, bootstrap argument for the total disc mass yields, for both
systems, M_{\mathrm{disc}}\gtrsim10^{-4}\Msun for a purely metallic disc (and
two orders of magnitude larger for solar metallicities). If Roche-lobe overflow
is implicated, viscous time-scales are yr. Standard disc theory
then offers another limit on the central masses. Lobe radii for a \sim1\Msun
donor are cm. We therefore rule out Roche-lobe overflow of a
white dwarf in both systems. Red giants could fill the necessary lobes. Whether
they are too metal-poor to produce the strong forbidden lines without strong
hydrogen emission is unclear.Comment: Accepted to MNRAS Letters, 5 pages, 6 figure
On the influence of the magnetic field of the GSI experimental storage ring on the time-modulation of the EC-decay rates of the H-like mother ions
We investigate the influence of the magnetic field of the
Experimental storage ring (ESR) at GSI on the periodic time-dependence of the
orbital K-shell electron capture decay ) rates of the H--like heavy ions.
We approximate the magnetic field of the ESR by a uniform magnetic field.
Unlike the assertion by Lambiase et al., arXiv: 0811.2302 [nucl-th], we show
that a motion of the H-like heavy ion in a uniform magnetic field cannot be the
origin of the periodic time-dependence of the EC-decay rates of the H-like
heavy ions.Comment: 3 pages, 1 figur
Automated NanoSIMS Measurements of Spinel Stardust from the Murray Meteorite
We report new O isotopic data on 41 presolar oxide grains, 38 MgAl2O4
(spinel) and 3 Al2O3 from the CM2 meteorite Murray, identified with a recently
developed automated measurement system for the NanoSIMS. We have also obtained
Mg-Al isotopic results on 29 of the same grains (26 spinel and 3 Al2O3). The
majority of the grains have O isotopic compositions typical of most presolar
oxides, fall well into the four previously defined groups, and are most likely
condensates from either red giant branch or asymptotic giant branch stars. We
have also discovered several grains with more unusual O and Mg compositions
suggesting formation in extreme astrophysical environments, such as novae and
supernovae. One of these grains has massive enrichments in 17O, 25Mg, and 26Mg,
which are isotopic signatures indicative of condensation from nova ejecta. Two
grains of supernova origin were also discovered: one has a large 18O/16O ratio
typical of Group 4 presolar oxides; another grain is substantially enriched in
16O, and also contains radiogenic 44Ca from the decay of 44Ti, a likely
condensate from material originating in the O-rich inner zones of a Type II
supernova. In addition, several Group 2 presolar spinel grains also have large
25Mg and 26Mg isotopic anomalies that are difficult to explain by standard
nucleosynthesis in low-mass stars. Auger elemental spectral analyses were
performed on the grains and qualitatively suggest that presolar spinel may not
have higher-than- stoichiometric Al/Mg ratios, in contrast to SIMS results
obtained here and reported previously.Comment: 58 pages, 10 figures, 1 table, published in Ap
Elemental Abundances in the Ejecta of Old Classical Novae from Late-Epoch Spitzer Spectra
We present Spitzer Space Telescope mid-infrared IRS spectra, supplemented by
ground-based optical observations, of the classical novae V1974 Cyg, V382 Vel,
and V1494 Aql more than 11, 8, and 4 years after outburst respectively. The
spectra are dominated by forbidden emission from neon and oxygen, though in
some cases, there are weak signatures of magnesium, sulfur, and argon. We
investigate the geometry and distribution of the late time ejecta by
examination of the emission line profiles. Using nebular analysis in the low
density regime, we estimate lower limits on the abundances in these novae. In
V1974 Cyg and V382 Vel, our observations confirm the abundance estimates
presented by other authors and support the claims that these eruptions occurred
on ONe white dwarfs. We report the first detection of neon emission in V1494
Aql and show that the system most likely contains a CO white dwarf.Comment: 22 pages, 12 figure
The frequency of occurrence of novae hosting an ONe white dwarf
In this paper, we revisit the problem of the determination of the frequency
of occurrence of galactic nova outbursts which involve an oxygen-neon (ONe)
white dwarf. The improvement with respect to previous work on the subject
derives from the fact that we use the results that our evolutionary
calculations provide for the final mass and for the chemical profiles of
intermediate-to-massive primary components of close binary systems. In
particular, the final evolutionary stages, such as the carbon burning phase,
have been carefully followed for the whole range of masses of interest. The
chemical profiles obtained with our evolutionary code are of interest in
determining the chemical composition of the ejecta after being processed
through the thermonuclear runaway, although such other factors as the
efficiency of the mixing between the accreted material and that of the
underlying white dwarf must also be considered. In our calculations of the
frequency of occurrence of nova outbursts involving an ONe white dwarf, we also
take into account the observational selection effects introduced by the
different recurrence times of the outbursts and by the spatial distribution of
novae. In spite of the very different evolutionary sequences, we find that
approximately 1/3 of the novae observed in outburst should involve an
oxygen-neon white dwarf, in agreement with previous theoretical estimates.Comment: 9 pages, 6 figures, accepted for publication in A&
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