5,940 research outputs found
Mid-infrared observations of young stellar objects in the vicinity of sigma Orionis
We present new mid-infrared observations of objects in the vicinity of the
O-star sigma Orionis, obtained with TIMMI-2 at ESO. By constraining their near-
and mid-infrared spectral energy distributions, we established the nature of
previously known IRAS sources and identified new mid-infrared sources as young
stellar objects with circumstellar disks, likely massive members of the sigma
Ori cluster. For two of these objects we have obtained spectroscopy in the 8-13
micron range in order to investigate the chemistry of the dust grains. TX Ori
exhibits a typical silicate emission feature at 10 micron, with a feature at
about 11.2 micron that we identify as due to crystalline olivine. The IRAS
05358-0238 spectrum is very unusual, with a weak silicate feature and structure
in the range 10-12 micron that may be explained as due to self-absorbed
forsterite. We also provide the first evidence for the presence of
circumstellar disks in the jet sources Haro 5-39/HH 447, V510 Ori/HH 444 and
V603 Ori/HH 445.Comment: 12 pages, 13 figures, accepted for publication by A&
Differential effects of jasmonic acid treatment of Brassica nigra on the attraction of pollinators, parasitoids, and butterflies
Herbivore-induced plant defences influence the behaviour of herbivores as well as that of their natural enemies. Jasmonic acid is one of the key hormones involved in both these direct and indirect induced defences. Jasmonic acid treatment of plants changes the composition of defence chemicals in the plants, induces volatile emission, and increases the production of extrafloral nectar. However, few studies have addressed the potential influence of induced defences on flower nectar chemistry and pollinator behaviour. These have shown that herbivore damage can affect pollination rates and plant fitness. Here, we have investigated the effect of jasmonic acid treatment on floral nectar production and the attraction of pollinators, as well as the effect on the behaviour of an herbivore and its natural enemy. The study system consisted of black mustard plants, Brassica nigra L. (Brassicaceae), pollinators of Brassica nigra (i.e., honeybees and syrphid flies), a specialist herbivore, Pieris rapae L. (Lepidoptera: Pieridae), and a parasitoid wasp that uses Pieris larvae as hosts, Cotesia glomerata L. (Hymenoptera: Braconidae). We show that different trophic levels are differentially affected by jasmonic acid-induced changes. While the herbivore prefers control leaves over jasmonic acid-treated leaves for oviposition, the parasitoid C. glomerata is more attracted to jasmonic acid-treated plants than to control plants. We did not observe differences in pollinator preference, the rates of flower visitation by honeybees and syrphid flies were similar for control and jasmonic acid-treated plants. Plants treated with jasmonic acid secreted less nectar than control plants and the concentrations of glucose and fructose tended to be lower than in nectar from control plants. Jasmonic acid treatment resulted in a lower nectar production than actual feeding damage by P. rapae caterpillars
Optimal dynamic environmental policies of a profit maximizing firm
Marketing;Game Theory;Pollution;environmental economics
Three-micron spectra of AGB stars and supergiants in nearby galaxies
The dependence of stellar molecular bands on the metallicity is studied using
infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and
M-type supergiants in the Large and Small Magellanic Clouds (LMC and SMC) and
in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for
oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB
stars. The equivalent width of acetylene is found to be high even at low
metallicity. The high C2H2 abundance can be explained with a high
carbon-to-oxygen (C/O) ratio for lower metallicity carbon stars. In contrast,
the HCN equivalent width is low: fewer than half of the extra-galactic carbon
stars show the 3.5micron HCN band, and only a few LMC stars show high HCN
equivalent width. HCN abundances are limited by both nitrogen and carbon
elemental abundances. The amount of synthesized nitrogen depends on the initial
mass, and stars with high luminosity (i.e. high initial mass) could have a high
HCN abundance. CH bands are found in both the extra-galactic and Galactic
carbon stars. None of the oxygen-rich LMC stars show SiO bands, except one
possible detection in a low quality spectrum. The limits on the equivalent
widths of the SiO bands are below the expectation of up to 30angstrom for LMC
metallicity. Several possible explanations are discussed. The observations
imply that LMC and SMC carbon stars could reach mass-loss rates as high as
their Galactic counterparts, because there are more carbon atoms available and
more carbonaceous dust can be formed. On the other hand, the lack of SiO
suggests less dust and lower mass-loss rates in low-metallicity oxygen-rich
stars. The effect on the ISM dust enrichment is discussed.Comment: accepted for A&
The low-mass Initial Mass Function in the young cluster NGC 6611
NGC 6611 is the massive young cluster (2-3 Myr) that ionises the Eagle
Nebula. We present very deep photometric observations of the central region of
NGC 6611 obtained with the Hubble Space Telescope and the following filters:
ACS/WFC F775W and F850LP and NIC2 F110W and F160W, loosely equivalent to
ground-based IZJH filters. This survey reaches down to I ~ 26 mag. We construct
the Initial Mass Function (IMF) from ~ 1.5 Msun well into the brown dwarf
regime (down to ~ 0.02 Msun). We have detected 30-35 brown dwarf candidates in
this sample. The low-mass IMF is combined with a higher-mass IMF constructed
from the groundbased catalogue from Oliveira et al. (2005). We compare the
final IMF with those of well studied star forming regions: we find that the IMF
of NGC 6611 more closely resembles that of the low-mass star forming region in
Taurus than that of the more massive Orion Nebula Cluster (ONC). We conclude
that there seems to be no severe environmental effect in the IMF due to the
proximity of the massive stars in NGC 6611.Comment: accepted for publication in MNRAS (main journal); 18 pages, 12
figures and 3 table
Star Formation in the Eagle Nebula and NGC 6611
We present IZJHKL' photometry of the core of the cluster NGC 6611 in the
Eagle Nebula. This photometry is used to constrain the Initial Mass Function
(IMF) and the circumstellar disk frequency of the young stellar objects.
Optical spectroscopy of 258 objects is used to confirm membership and constrain
contamination as well as individual reddening estimates. Our overall aim is to
assess the influence of the ionizing radiation from the massive stars on the
formation and evolution of young low-mass stars and their disks. The disk
frequency determined from the JHKL' colour-colour diagram suggests that the
ionizing radiation from the massive stars has little effect on disk evolution
(Oliveira et al. 2005). The cluster IMF seems indistinguishable from those of
quieter environments; however towards lower masses the tell-tale signs of an
environmental influence are expected to become more noticeable, a question we
are currently addressing with our recently acquired ultra-deep (ACS and NICMOS)
HST images.Comment: in "Triggered Star Formation in a Turbulent ISM", IAU symposium,
poster contribution; a full version of the poster can be found at
http://www.astro.keele.ac.uk/~jacco/papers/IAUS237_Eagle_2006.pd
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