339 research outputs found
Effects of winter on genetic structure of a natural population of Drosophila melanogaster
International audienc
Are imprinting and inbreeding two related phenomena?
International audienc
Évolution de la fertilité et de la viabilité de populations expérimentales de drosophila melanogaster dérivées d'un seul couple
International audienc
Atomic data for neutron-capture elements II. Photoionization and recombination properties of low-charge krypton ions
We present multi-configuration Breit-Pauli distorted-wave photoionization
(PI) cross sections and radiative recombination (RR) and dielectronic
recombination (DR) rate coefficients for the first six krypton ions. These were
calculated with the AUTOSTRUCTURE code, using semi-relativistic radial
wavefunctions in intermediate coupling. Kr has been detected in several
planetary nebulae (PNe) and H II regions, and is a useful tracer of
neutron-capture nucleosynthesis. PI, RR, and DR data are required to accurately
correct for unobserved Kr ions in ionized nebulae, and hence to determine
elemental Kr abundances. PI cross sections have been determined for ground
configuration states of Kr^0--Kr^5+ up to 100 Rydbergs. Our Kr^+ PI
calculations were significantly improved through comparison with experimental
measurements. RR and DR rate coefficients were determined from the direct and
resonant PI cross sections at temperatures (10^1--10^7)z^2 K, where z is the
charge. We account for Delta n=0 DR core excitations, and find that DR is the
dominant recombination mechanism for all but Kr^+ at photoionized plasma
temperatures. Internal uncertainties are estimated by comparing results
computed with three different configuration-interaction expansions for each
ion, and by testing the sensitivity to variations in the orbital radial scaling
parameters. The PI cross sections are generally uncertain by 30-50% near the
ground state thresholds. Near 10^4 K, the RR rate coefficients are typically
uncertain by <10%, while those of DR exhibit uncertainties of factors of 2 to
3, due to the unknown energies of near-threshold autoionizing resonances. With
the charge transfer rate coefficients presented in the third paper of this
series, these data enable robust Kr abundance determinations in photoionized
nebulae for the first time.Comment: 19 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysic
Insertion polymorphism of retrotransposable elements in populations of the insular, endemic species Drosophila madeirensis
The insertion site numbers of the retrotransposable elements (TE) 412, gypsy and bilbo were determined in individuals of five distinct natural populations of the endemic species Drosophila madeirensis from the island of Madeira. The TE distributions were compared to those of the paleartic, widespread and phylogenetically closely related species, D. subobscura. In situ hybridization and Southern blots showed that in D. madeirensis the number of insertion sites ranged between 10 and 15, three and six, and 35 and 42 for elements 412, gypsy and bilbo, respectively. The corresponding values for D. subobscura were similar. Two of these elements, 412 and gypsy, had very few insertions in the heterochromatin, unlike bilbo, which displayed a high heterochromatic insertion number. The Southern band polymorphism was very high, leading to within-population variation of 97.2%, whatever the population and the TE concerned. Using the polymorphic TE insertion sites as markers to analyse population structure by AMOVA, adapted for RAPD (Randomly Amplified Polymorphic DNA) data, we found small but significant genetic differences between the populations on Madeira. This slight differentiation, coupled with similar copy numbers for each TE between populations, suggests that the D. madeirensis species consists of a single, only slightly subdivided population. These data also show that insular populations and endemic species of Drosophila can have as many copies of TEs as more widespread species.info:eu-repo/semantics/publishedVersio
Atomic data for neutron-capture elements I. Photoionization and recombination properties of low-charge selenium ions
We present multi-configuration Breit-Pauli AUTOSTRUCTURE calculations of
distorted-wave photoionization (PI) cross sections, and total and partial
final-state resolved radiative recombination (RR) and dielectronic
recombination (DR) rate coefficients for the first six ions of the trans-iron
element Se. These calculations were motivated by the recent detection of Se
emission lines in a large number of planetary nebulae. Se is a potentially
useful tracer of neutron-capture nucleosynthesis, but accurate determinations
of its abundance in photoionized nebulae have been hindered by the lack of
atomic data governing its ionization balance. Our calculations were carried out
in intermediate coupling with semi-relativistic radial wavefunctions. PI and
recombination data were determined for levels within the ground configuration
of each ion, and experimental PI cross-section measurements were used to
benchmark our results. For DR, we allowed dn=0 core excitations, which are
important at photoionized plasma temperatures. DR is the dominant recombination
process for each of these Se ions at temperatures representative of
photoionized nebulae (~10^4 K). To estimate the uncertainties of these data, we
compared results from three different configuration-interaction expansions for
each ion, and tested the sensitivity of the results to the radial scaling
factors in the structure calculations. We find that the internal uncertainties
are typically 30-50% for the direct PI cross sections and ~10% for the computed
RR rate coefficients, while those for low-temperature DR can be considerably
larger (from 15-30% up to two orders of magnitude) due to the unknown energies
of near-threshold autoionization resonances. The results are suitable for
incorporation into photoionization codes used to numerically simulate
astrophysical nebulae, and will enable robust determinations of nebular Se
abundances.Comment: 17 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Lanthanides and other spectral oddities in a Centauri
Context: There is considerable interest in the helium variable a Cen as a
bridge between helium-weak and helium-strong CP stars. Aims: We investigate Ce
III and other possible lanthanides in the spectrum the of hottest chemically
peculiar (CP) star in which these elements have been found. A {Kr II line
appears within a broad absorption which we suggest may be due to a high-level
transition in C II. Methods: Wavelengths and equivalent widths are measured on
high-resolution UVES spectra, analyzed, and their phase-variations
investigated. Results: New, robust identifications of Ce III and Kr II are
demonstrated. Nd III is likely present. A broad absorption near 4619[A] is
present at all phases of a Cen, and in some other early B stars. Conclusions:
The presence of lanthanides in a Cen strengthens the view that this star is a
significant link between the cooler CP stars and the hotter helium-peculiar
stars. Broad absorptions in a Cen are not well explained.Comment: Research Note accepted by Astronomy and Astrophysics; 4 pages, 4
Figs. 2 Table
- …