41 research outputs found
Low-mass pre--main-sequence stars in the Magellanic Clouds
[Abridged] The stellar Initial Mass Function (IMF) suggests that sub-solar
stars form in very large numbers. Most attractive places for catching low-mass
star formation in the act are young stellar clusters and associations, still
(half-)embedded in star-forming regions. The low-mass stars in such regions are
still in their pre--main-sequence (PMS) evolutionary phase. The peculiar nature
of these objects and the contamination of their samples by the evolved
populations of the Galactic disk impose demanding observational techniques for
the detection of complete numbers of PMS stars in the Milky Way. The Magellanic
Clouds, the companion galaxies to our own, demonstrate an exceptional star
formation activity. The low extinction and stellar field contamination in
star-forming regions of these galaxies imply a more efficient detection of
low-mass PMS stars than in the Milky Way, but their distance from us make the
application of special detection techniques unfeasible. Nonetheless, imaging
with the Hubble Space Telescope yield the discovery of solar and sub-solar PMS
stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of
such objects are identified as the low-mass stellar content of their
star-forming regions, changing completely our picture of young stellar systems
outside the Milky Way, and extending the extragalactic stellar IMF below the
persisting threshold of a few solar masses. This review presents the recent
developments in the investigation of PMS stars in the Magellanic Clouds, with
special focus on the limitations by single-epoch photometry that can only be
circumvented by the detailed study of the observable behavior of these stars in
the color-magnitude diagram. The achieved characterization of the low-mass PMS
stars in the Magellanic Clouds allowed thus a more comprehensive understanding
of the star formation process in our neighboring galaxies.Comment: Review paper, 26 pages (in LaTeX style for Springer journals), 4
figures. Accepted for publication in Space Science Review
Phytoplankton in a temperate-zone salt marsh: Net production and exchanges with coastal waters
Phytoplankton production and associated variables were measured in Flax Pond, a 52 ha salt marsh on the north shore of Long Island, New York, from July 1972 to October 1973. Measurements made up to five times per day, once per week, yielded a mean annual net primary production, determined by the 14 C technique, of 20.5 mg C/m 3 /h; daily means were as high as 60.0 mg C/m 3 /h. However, when productivity was calculated for the entire marsh ecosystem, the shallow water in the salt marsh produced only 11.7 g C/m 2 of marsh/year. There was a net flux of phytoplankton from the coastal waters into the marsh; during the summer up to 0.2 g chlorophy 11/m 2 of marsh was carried in with the tides daily and remained in the marsh. Analysis of the productivity data, as well as variables associated with productivity (pH, standing crop, nutrients, extinction coefficient), indicated that the aquatic portion of the marsh behaved more as a net consumer rather than a net producer of phytoplankton.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46630/1/227_2004_Article_BF00391561.pd