1,133 research outputs found
Hoktiwe (for L. Rain Prud’homme-Cranford)
This is a cento composed using extracted sentences from both the 1932 and 2019 published dictionaries of Ishakkoy, also known as Atakapan, a dormant Indigenous language from Louisiana and Texas. The corpus of texts in the language is small, however the published materials have hundreds of example sentences. These were extracted and used to make new compositions, presenting a model for corpus expansion and creative composition in an Indigenous language
An analysis of ultraviolet spectra of Extreme Helium Stars and new clues to their origins
Abundances of about 18 elements including the heavy elements Y and Zr are
determined from Hubble Space Telescope Space Telescope Imaging Spectrograph
ultraviolet spectra of seven extreme helium stars (EHes): LSE 78, BD+10 2179,
V1920 Cyg, HD 124448, PV Tel, LS IV -1 2, and FQ Aqr. New optical spectra of
the three stars -- BD+10 2179, V1920 Cyg, and HD 124448 were analysed. The
abundance analyses is done using LTE line formation and LTE model atmospheres
especially constructed for these EHe stars. The stellar parameters derived from
an EHe's UV spectrum are in satisfactory agreement with those derived from its
optical spectrum. Adopted abundances for the seven EHes are from a combination
of the UV and optical analyses. Published results for an additional ten EHes
provide abundances obtained in a nearly uniform manner for a total of 17 EHes,
the largest sample on record. The initial metallicity of an EHe is indicated by
the abundance of elements from Al to Ni; Fe is adopted to be the representative
of initial metallicity. Iron abundances range from approximately solar to about
one-hundredth of solar. Clues to EHe evolution are contained within the H, He,
C, N, O, Y, and Zr abundances. Two novel results are (i) the O abundance for
some stars is close to the predicted initial abundance yet the N abundance
indicates almost complete conversion of initial C, N, and O to N by the
CNO-cycles; (ii) three of the seven stars with UV spectra show a strong
enhancement of Y and Zr attributable to an s-process. The observed compositions
are discussed in light of expectations from accretion of a He white dwarf by a
CO white dwarf.Comment: 126 pages, 15 figures, 20 Tables, accepted for publication in the Ap
Extreme helium stars: non-LTE matters Helium and hydrogen spectra of the unique objects V652 Her and HD144941
Quantitative analyses of low-mass hydrogen-deficient (super-)giant stars -
so-called extreme helium stars - to date face two major difficulties. First,
theory fails to reproduce the observed helium lines in their entirety, wings
and line cores. Second, a general mismatch exists for effective temperatures
derived from ionization equilibria and from spectral energy distributions.
Here, we demonstrate how the issue can be resolved using state-of-the-art
non-LTE line-formation for these chemically peculiar objects. Two unique
high-gravity B-type objects are discussed in detail, the pulsating variable
V652 Her and the metal-poor star HD144941. In the first case atmospheric
parameters from published LTE analyses are largely recovered, in the other a
systematic offset is found. Hydrogen abundances are systematically smaller than
previously reported, by up to a factor ~2. Extreme helium stars turn out to be
important testbeds for non-LTE model atoms for helium. Improved non-LTE
computations show that analyses assuming LTE or based on older non-LTE model
atoms can predict equivalent widths, for the HeI 10830A transition in
particular, in error by up to a factor ~3.Comment: 4 pages, 5 figures; accepted for publication in A&
Multi-wavelength photometric variation of PG1605+072
In a large coordinated attempt to further our understanding of the -mode
pulsating sdB star PG1605+072, the Multi-Site Spectroscopic Telescope (MSST)
collaboration has obtained simultaneous time-resolved spectroscopic and
photometric observations. The photometry was extended by additional WET data
which increased the time base. This contribution outlines the analysis of the
MSST photometric light curve, including the four-colour BUSCA data from which
chromatic amplitudes have been derived, as well as supplementary FUV spectra
and light curves from two different epochs. These results have the potential to
complement the interpretation of the published spectroscopic information.Comment: 6 pages, to be published in "Interpretation of asteroseismic data",
proceedings of the HELAS NA5 Workshop, eds. W. Dziembowski, M. Breger and M.
Thompson, Communications in Asteroseismology, 15
The MultiSite Spectroscopic Telescope campaign: 2m spectroscopy of the V361 Hya variable PG1605+072
We present results and analysis for the 2m spectroscopic part of the
MultiSite Spectroscopic Telescope (MSST) campaign undertaken in May/June 2002.
The goal of the project was to observe the pulsating subdwarf B star PG1605+072
simultaneously in velocity and photometry and to resolve as many of the >50
known modes as possible, which will allow a detailed asteroseismological
analysis. We have obtained over 150 hours of spectroscopy, leading to an
unprecedented noise level of only 207m/s. We report here the detection of 20
frequencies in velocity, with two more likely just below our detection
threshold. In particular, we detect 6 linear combinations, making PG1605+072
only the second star known to show such frequencies in velocity. We investigate
the phases of these combinations and their parent modes and find relationships
between them that cannot be easily understood based on current theory. These
observations, when combined with our simultaneous photometry, should allow
asteroseismology of this most complicated of sdB pulsators.Comment: 9 pages, 5 figures, accepted for publication in A&A; Figure 1 at
lower resolution than accepted versio
Abundances of neutron-capture elements in the Hot Extreme-Helium Stars V1920 Cygni and HD 124448
Analysis of HST STIS ultraviolet spectra of two hot extreme helium stars
(EHes): V1920 Cyg and HD 124448 provide the first measurements of abundances of
neutron-capture elements for EHes. Although the two stars have similar
abundances for elements up through the iron-group, they differ strikingly in
their abundances of heavier elements: V1920 Cyg is enriched by a factor of 30
in light neutron-capture elements (Y/Fe, Zr/Fe) relative to HD 124448. These
differences in abundances of neutron-capture elements among EHes mirrors that
exhibited by the RCrB stars, and is evidence supporting the view that there is
an evolutionary connection between these two groups of hydrogen-deficient
stars. Also, the abundances of Y and Zr in V1920 Cyg provide evidence that at
least one EHe star went through a s-process synthesis episode in its earlier
evolution.Comment: 4 pages (embedded figure and table), accepted for publication in ApJ
Letter
Mycobacterium tuberculosis MycP1 Protease Plays a Dual Role in Regulation of ESX-1 Secretion and Virulence
SummaryMycobacterium tuberculosis uses the ESX-1 secretion system to deliver virulence proteins during infection of host cells. Here we report a mechanism of posttranscriptional control of ESX-1 mediated by MycP1, a M. tuberculosis serine protease. We show that MycP1 is required for ESX-1 secretion but that, unexpectedly, genetic inactivation of MycP1 protease activity increases secretion of ESX-1 substrates. We demonstrate that EspB, an ESX-1 substrate required for secretion, is a target of MycP1 in vitro and in vivo. During macrophage infection, an inactive MycP1 protease mutant causes hyperactivation of ESX-1-stimulated innate signaling pathways. MycP1 is required for growth in mice during acute infection, while loss of its protease activity leads to attenuated virulence during chronic infection. As the key ESX-1 substrates ESAT-6 and CFP-10 are highly immunogenic, fine-tuning of their secretion by MycP1 may balance virulence and immune detection and be essential for successful maintenance of long-term M. tuberculosis infection
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