26 research outputs found
The s process in asymptotic giant branch stars of low metallicity and the composition of carbon-enhanced metal-poor stars
We present models for the slow neutron-capture process (s process) in
asymptotic giant branch (AGB) stars of metallicity [Fe/H]=-2.3 and masses 0.9
Msun to 6 Msun. We encountered different regimes of neutron-capture
nucleosynthesis increasing in importance as the stellar mass decreases: the
22Ne(alpha,n)25Mg reaction activated during the thermal pulses, the
13C(alpha,n)16O reaction activated in radiative conditions during the
interpulse periods, and the 13C(alpha,n)16O reaction activated during the
thermal pulses, also as a result of mild proton ingestion episodes. The models
where the 13C burns radiatively (masses ~ 2 Msun) produce an overall good match
to carbon-enhanced metal-poor (CEMP) stars showing s-process enhancements
(CEMP-s), except they produce too much Na and F. On the other hand, none of our
models can provide a match to the composition of CEMP stars also showing
rapid-process enhancements (CEMP-s/r). The models fail to reproduce the
observed Eu abundances, and they also fail to reproduce the correlation between
the Eu and Ba abundances. They also cannot match the ratio of heavy to light
s-process elements observed in many CEMP-s/r stars, which can be more than ten
times higher than in the solar system. To explain the composition of CEMP-s/r
stars we need to invoke the existence of a different "s/r" neutron-capture
process either with features in-between the s and the r processes, or generated
by superpositions of different neutron-capture processes in the same
astrophysical site or in sites linked to each other - for example, in multiple
stellar systems.Comment: 51 pages, 10 figures, 6 tables. Accepted for publication on The
Astrophysical Journa
An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers
Solar chromospheric observations of sunspot umbrae offer an exceptional view of magneto-hydrodynamic wave phenomena. In recent years, a wealth of wave signatures related to propagating magneto-acoustic modes have been presented, which demonstrate complex spatial and temporal structuring of the wave components. Theoretical modelling has demonstrated how these ubiquitous waves are consistent with an m=0 slow magneto-acoustic mode, which are excited by trapped sub-photospheric acoustic (p-mode) waves. However, the spectrum of umbral waves is broad, suggesting that the observed signatures represent the superposition of numerous frequencies and/or modes. We apply Fourier filtering, in both spatial and temporal domains, to extract chromospheric umbral wave characteristics consistent with an m=1 slow magneto-acoustic mode. This identification has not been described before. Angular frequencies of 0.037 +/- 0.007 rad/s (2.1 +/- 0.4 deg/s), corresponding to a period approximately 170 s for the m=1 mode are uncovered for spatial wavenumbers in the range of 0.45<k<0.90 arcsec^-1 (5000-9000 km). Theoretical dispersion relations are solved, with corresponding eigenfunctions computed, which allows the density perturbations to be investigated and compared with our observations. Such magnetohydrodynamic modelling confirms our interpretation that the identified wave signatures are the first direct observations of an m=1 slow magneto-acoustic mode in the chromospheric umbra of a sunspot
Neutron spectroscopy of 26Mg states : Constraining the stellar neutron source 22Ne(α,n)25Mg
This work reports on accurate, high-resolution measurements of the 25Mg(n,γ)26Mg and 25Mg(n,tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved 25Mg(n,γ)26Mg parametrization. The relevant resonances for n+25Mg were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in 26Mg. With this information experimental upper limits of the reaction rates for 22Ne(α,n)25Mg and 22Ne(α,γ)26Mg were established, potentially leading to a significantly higher (α,n)/(α,γ) ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M⊙
Neutron spectroscopy of ²⁶Mg states: Constraining the stellar neutron source ²²Ne(α,n)²⁵Mg
This work reports on accurate, high-resolution measurements of the 25Mg(n,γ)26Mg and 25Mg(n,tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved 25Mg(n,γ)26Mg parametrization. The relevant resonances for n+25Mg were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in 26Mg. With this information experimental upper limits of the reaction rates for 22Ne(α,n)25Mg and 22Ne(α,γ)26Mg were established, potentially leading to a significantly higher (α,n)/(α,γ)
ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M⊙
LOSS OF PIGH EXPRESSION FREQUENTLY RESULTS IN A GPI-NEGATIVE SUBCLONE LACKING CD52 MEMBRANE EXPRESSION, CONFERRING ALEMTUZUMAB RESISTANCE TO B CELL ACUTE LYMPHOBLASTIC LEUKEMIA
Immunobiology of allogeneic stem cell transplantation and immunotherapy of hematological disease
Loss of the GPI-anchor in B-lymphoblastic leukemia by epigenetic downregulation of PIGH expression
Dermatology-oncolog
Decreased Cell Wall Galactosaminogalactan in Aspergillus nidulans Mediates Dysregulated Inflammation in the Chronic Granulomatous Disease Host
Author Disclosure Statement No competing financial interests exist.Peer reviewedPostprin