29,986 research outputs found
Current Topics in D0 B Physics
An overview of selected topics in DO B-Physics is presented, covering
relevant detector characteristics, and with emphasis on the most recent results
in the Bs, FCNC and rare decay programs.Comment: 4 pages, 3 figures, for the D0 Collaboration, 10th International
Conference on B-Physics at Hadron Machines - BEAUTY 2005 - June 20 to 24,
2005 in Assisi, Ital
Film holder for curved vacuum platen
Vacuum apparatus for holding photographic film of various widths against cylindrically curved patens is discussed. Construction details and method of operation are explained. Illustration of equipment is provided
New freshwater sponges from Amazonian waters
Four species of freshwater sponges have their first register of occurrence for Amazonian waters upon specimens collected from Culuene and Sete de Setembro Rivers (Xingú basin), Tapirapés River (Araguaia basin) and Cuieiras River. Trochospongilla pennsylvanica (POTTS 1882) and Trochospongilla variabilis BONETTO & EZCURRA DE DRAGO (1973) occurred as minute specimens inside large sponges of the genus Metania GRAY (1867) or of the genus Drulia GRAY (1867). T. pennsylvanica has its first register of occurrence for the Neotropical region. Spongilla spoliata n. sp. resembles Spongilla inarmata ANNADALE (1918) and Spongilla aspinosa POTTS (1880) but is readily separated from these two species on account of the characteristic spines on its microscleres. Radiospongilla amazonensis n. sp. differs from its congeners by the particular characteristics of its megascleres and gemmoscleres
An estimate of the time variation of the O/H radial gradient from planetary nebulae
Radial abundance gradients are a common feature of spiral galaxies, and in
the case of the Galaxy both the magnitude of the gradients and their variations
are among the most important constraints of chemical evolution models.
Planetary nebulae (PN) are particularly interesting objects to study the
gradients and their variations. Owing to their bright emission spectra, they
can be observed even at large galactocentric distances, and the derived
abundances are relatively accurate, with uncertainties of about 0.1 to 0.2 dex,
particularly for the elements that are not synthesized in their progenitor
stars. On the other hand, as the offspring of intermediate mass stars, with
main sequence masses in the interval of 1 to 8 solar masses, they are
representative of objects with a reasonable age span. In this paper, we present
an estimate of the time variation of the O/H radial gradient in a sample
containing over 200 nebulae with accurate abundances. Our results are
consistent with a flattening of the O/H gradient roughly from -0.11 dex/kpc to
-0.06 dex/kpc during the last 9 Gyr, or from -0.08 dex/kpc to -0.06 dex/kpc
during the last 5 Gyr.Comment: 9 pages, 7 encapsulated postscript figures, LaTeX, uses Astronomy and
Astrophysics macro aa.cls, graphicx package, to be published in Astronomy and
Astrophysics (2002), Also available at: http://www.astro.iag.usp.br/~macie
Stellar Populations and the Star Formation Histories of LSB Galaxies: I. Optical and H-alpha Imaging
This paper presents optical and H-alpha imaging for a large sample of LSB
galaxies selected from the PSS-II catalogs (Schombert et. al 1992). As noted in
previous work, LSB galaxies span a range of luminosities (-10 > M_V > -20) and
sizes (0.3 kpc < R_V25 < 10 kpc), although they are consistent in their
irregular morphology. Their H-alpha luminosities (L(H-alpha) range from 10^36
to 10^41 ergs s^-1 (corresponding to a range in star formation, using canonical
prescriptions, from 10^-5 to 1 M_solar yr^-1). Although their optical colors
are at the extreme blue edge for galaxies, they are similar to the colors of
dwarf galaxies (van Zee 2001) and gas-rich irregulars (Hunter & Elmegreen
2006). However, their star formation rates per unit stellar mass are a factor
of ten less than other galaxies of the same baryonic mass, indicating that they
are not simply quiescent versions of more active star forming galaxies. This
paper presents the data, reduction techniques and new philosophy of data
storage and presentation. Later papers in this series will explore the stellar
population and star formation history of LSB galaxies using this dataset.Comment: 33 pages, 17 figures, 2 tables, accepted for Advances in
Astronomy/Hindaw
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