The properties of Low Surface Brightness galaxies

A description is given of the samples of Low Surface Brightness galaxies (LSBs) used for comparison with models of their chemical and spectro-photometric evolution (Boissier et al., this Volume). These samples show the large variation and scatter in observed global properties of LSBs, some of which cannot be modeled without adding starbursts or truncations to their star formation history.Comment: To appear in the Proceedings of the Euroconference on The Evolution of Galaxies: III. From simple approaches to self-consistent models (Kluwer). 4 page

Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development?

International audienceThe use of shelterwoods to favour the development of natural or underplanted seedlings is common in temperate forests but rare in the pine forests of the Mediterranean area. Our aim was to assess the use of shelterwoods in Aleppo pine (Pinus halepensis) woodlands in southern France to promote the survival and growth of two co-occurring oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex. Twelve Aleppo pine stands were selected and differentially thinned to create a light shelterwood (G = 32 m2/ha, irradiance 13%), a medium shelterwood (G = 19 m2/ha, irradiance 33%) and a dense shelterwood (G = 10 m2/ha, irradiance 52%). A total of 1248 sowing points, half composed of Q. pubescens and half of Q. ilex, were then set up in these three conditions. Seedling survival and growth were monitored for three years and plant stress was assessed by measuring predawn leaf potential and photosynthetic performance through the Fv ∕Fm ratio. Soil moisture was also recorded at two depths during two growing seasons. Survival was high for both species in all three conditions due to three consecutive wet years. The lowest survival was recorded for Q. pubescens in the dense shelterwoods. Growth in diameter and height increased from the dense to the light shelterwoods. Shrubs developed more strongly in the light shelterwood, and increasing shrub cover enhanced height growth. Photosynthetic performance was lowest for Q. pubescens in dense shelterwoods and highest in light shelterwoods, whereas the reverse was true for Q. ilex. The lowest predawn potentials were recorded in the dense shelterwoods even though higher soil water content values were measured in this treatment during the summer drought. We show that light shelterwoods were more beneficial to growth than denser ones, indicating control by light availability during the three years of the study. However, as lower soil moisture and faster understorey development were also recorded in this condition, more extended observation is needed to determine whether this benefit persists in subsequent years

High Angular Resolution Mid-infrared Imaging of Young Stars in Orion BN/KL

We present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3-0.5" resolution from 4.7 to 22 microns. The young stellar objects designated infrared source-n and radio source-I are believed to dominate the BN/KL region. We have detected extended emission from a probable accretion disk around source-n but infer a stellar luminosity on the order of only 2000 Lsun. Although source-I is believed to be more luminous, we do not detect an infrared counterpart even at the longest wavelengths. However, we resolve the closeby infrared source, IRc2, into an arc of knots ~1000 AU long at all wavelengths. Although the physical relation of source-I to IRc2 remains ambiguous, we suggest these sources mark a high density core (10^7-10^8 pc^-3 over 1000 AU) within the larger BN/KL star forming cluster. The high density may be a consequence of the core being young and heavily embedded. We suggest the energetics of the BN/KL region may be dominated by this cluster core rather than one or two individual sources.Comment: 13 pages including 3 color figures. Accepted to The Astrophysical Journal Letters pending slight reduction in length. High resolution figures (jpeg) may be found at http://cfa-www.harvard.edu/~lincoln/keck.bnkl.midir.ppr