5 research outputs found
A new determination of the orbit and masses of the Be binary system delta Scorpii
The binary star delta Sco (HD143275) underwent remarkable brightening in the
visible in 2000, and continues to be irregularly variable. The system was
observed with the Sydney University Stellar Interferometer (SUSI) in 1999,
2000, 2001, 2006 and 2007. The 1999 observations were consistent with
predictions based on the previously published orbital elements. The subsequent
observations can only be explained by assuming that an optically bright
emission region with an angular size of > 2 +/- 1 mas formed around the primary
in 2000. By 2006/2007 the size of this region grew to an estimated > 4 mas.
We have determined a consistent set of orbital elements by simultaneously
fitting all the published interferometric and spectroscopic data as well as the
SUSI data reported here. The resulting elements and the brightness ratio for
the system measured prior to the outburst in 2000 have been used to estimate
the masses of the components. We find Ma = 15 +/- 7 Msun and Mb = 8.0 +/- 3.6
Msun. The dynamical parallax is estimated to be 7.03 +/- 0.15 mas, which is in
good agreement with the revised HIPPARCOS parallax.Comment: 8 pages, 4 figs. Accepted for publication in MNRA
The Arabidopsis Cell Division Cycle
Plant cells have evolved a complex circuitry to regulate cell division. In many aspects, the plant cell cycle follows a basic strategy similar to other eukaryotes. However, several key issues are unique to plant cells. In this chapter, both the conserved and unique cellular and molecular properties of the plant cell cycle are reviewed. In addition to division of individual cells, the specific characteristic of plant organogenesis and development make that cell proliferation control is of primary importance during development. Therefore, special attention should be given to consider plant cell division control in a developmental context. Proper organogenesis depends on the formation of different cell types. In plants, many of the processes leading to cell differentiation rely on the occurrence of a different cycle, termed the endoreplication cycle, whereby cells undergo repeated full genome duplication events in the absence of mitosis and increase their ploidy. Recent findings are focusing on the relevance of changes in chromatin organization for a correct cell cycle progression and, conversely, in the relevance of a correct functioning of chromatin remodelling complexes to prevent alterations in both the cell cycle and the endocycle