1,294 research outputs found
The morphology of the Magellanic Clouds revealed by stars of different age: results from the DENIS survey
The spatial distribution of sources populating different regions of the
colour-magnitude diagram (I-J, I) extracted from the DENIS catalogue towards
the Magellanic Clouds (DCMC -- Cioni et al. 2000) reveal significantly
different morphologies. Each region is associated to a different age group. The
Large Magellanic Cloud (LMC) shows an extended circular shape with a prominent,
off center bar, a nucleus and irregular spiral arms. The Small Magellanic Cloud
shows a perturbated structure with a prominent central concentration of stars.
Old and young populations are offset from one another.Comment: 4 pages and 7 figures, accepted for publication in A&A Journal
Letter
Oxygen- and carbon-rich variable red giant populations in the Magellanic Clouds from EROS, OGLE, MACHO, and 2MASS photometry
The carbon-to-oxygen (C/O) ratio of asymptotic giant branch (AGB) stars
constitutes an important index of evolutionary and environment/metallicity
factor. We develop a method for mass C/O classification of AGBs in photometric
surveys without using periods. For this purpose we rely on the slopes in the
tracks of individual stars in the colour-magnitude diagram. We demonstrate that
our method enables the separation of C-rich and O-rich AGB stars with little
confusion. For the Magellanic Clouds we demonstrate that this method works for
several photometric surveys and filter combinations. As we rely on no period
identification, our results are relatively insensitive to the phase coverage,
aliasing, and time-sampling problems that plague period analyses. For a
subsample of our stars, we verify our C/O classification against published C/O
catalogues. With our method we are able to produce C/O maps of the entire
Magellanic Clouds. Our purely photometric method for classification of C- and
O-rich AGBs constitutes a method of choice for large, near-infrared photometric
surveys. Because our method depends on the slope of colour-magnitude variation
but not on magnitude zero point, it remains applicable to objects with unknown
distances.Comment: 14 pages, 16 figures, 1 table, accepted for publication in Astronomy
& Astrophysic
Three aspects of red giant studies in the Magellanic Clouds
There are three important aspects concerning the study of the red giant and
in particular of the asymptotic giant branch (AGB) stars in the Magellanic
Clouds. These are: the surface distribution, the luminosity function and the
variability. The spatial distribution of AGB stars is an efficient tool to
study the structure of the galaxies and their metalicity by analysing the ratio
between carbon- and oxygen-rich AGB stars. The shape of the luminosity function
carries informations about the star formation rate in the Clouds and it can be
mathematically related to their history. Most AGB stars vary their magnitude in
a few to several hundred years time; the one epoch DENIS magnitudes for both
Large and Small Magellanic Cloud AGB stars outline the same relations as a
function of period.Comment: 8 pages, 6 figures, invited talk, to be published in: Mass-Losing
Pulsating Stars and their Circumstellar Matter, Y. Nakada & M. Honma (eds)
Kluwer ASSL serie
The Tip of the Red Giant Branch and Distance of the Magellanic Clouds: results from the DENIS survey
We present a precise determination of the apparent magnitude of the tip of
the red giant branch (TRGB) in the I (0.8 micron), J (1.25 micron), and K_S
(2.15 micron) bands from the luminosity function of a sample of data extracted
from the DENIS catalogue towards the Magellanic Clouds (Cioni et al. 2000).
From the J and Ks magnitudes we derive bolometric magnitudes m_bol. We
present a new algorithm for the determination of the TRGB magnitude, which we
describe in detail and test extensively using Monte-Carlo simulations. We note
that any method that searches for a peak in the first derivative (used by most
authors) or the second derivative (used by us) of the observed luminosity
function does not yield an unbiased estimate for the actual magnitude of the
TRGB discontinuity. We stress the importance of correcting for this bias, which
is not generally done. We combine the results of our algorithm with theoretical
predictions to derive the distance modulus of the Magellanic Clouds. We obtain
m-M = 18.55 (0.04 formal, 0.08 systematic) for the Large Magellanic Cloud
(LMC), and m-M = 18.99 (0.03 formal, 0.08 systematic) for the Small Magellanic
Cloud (SMC). These are among the most accurate determinations of these
quantities currently available, which is a direct consequence of the large size
of our sample and the insensitivity of near infrared observations to dust
extinction.Comment: 16 pages, 8 figures, revised version, accepted for publication in A&
Feeding behaviour of larval European sea bass (Dicentrarchus labrax L.) in relation to temperature and prey density
The feeding behaviour of larval European sea bass (Dicentrarchus labrax, L.) was analysed in relation to temperature and prey
density under controlled laboratory conditions with the aim to assess the ability of larval fish to change the feeding tactic as a
response to environmental changes. Larvae were acclimated for 20 days at three different temperatures (19, 22 and 26°C), and
their feeding behaviour was then video-recorded in experimental trials, at two prey densities, consisting of swarms of 400/l
and 1440/l Artemia nauplii. Results showed that there was a significant effect of the interaction between temperature and prey
density on the proportion of swimming activity that was reduced at the high temperature-high prey density combination. This
suggested a switching in the larval feeding behaviour from an active to an ambush tactic, when the temperature reached 26°C
and the prey density was 1440 /l Artemia nauplii. These results are consistent with the current literature on fish larval behaviour
in showing that the foraging tactic can be modulated by the interaction of different abiotic and biotic factors characterising the
rearing environment
Efficacy of an Aqueous Extract of Stellaria media (L.) Cyr. against Eimeria legionensis Infection (Apicomplexa: Eimeridae) in Red-legged Partridges (Alectoris rufa)
Aims: Coccidiosis is one of the most frequent causes of morbidity and mortality in farmed redlegged partridges (Alectoris rufa). The aim of this study was to evaluate the effects of the plant Stellaria media (Caryophyllaceae) on coccidia-infected red-legged partridges.
Methodology: Of 9 replicates of redlegged partridges, each composed by 6 coccidia-infected birds (Eimeria legionensis), 3 replicates (S group) received an aqueous extract (12 ml/l) of S. media with drinking water for 3 consecutive days, while 3 further replicates (D group) received 20% sodium sulfaquinoxaline (2 g/l) with drinking water for 3 consecutive days. The remaining 3 replicates did not receive any treatment (C group). The day before the beginning of the treatment (day 0), the last day of the treatment (day 3) and 7 days after the end of the treatment (day 10), individual fresh faecal samples were collected from all examined birds and analysed for presence and number of coccidian oocysts/gram of faeces (OPG). Data were statistically elaborated with the Analysis of Variance (ANOVA) and the Test of Student-Newman-Keuls for multiple comparisons. The percentage of reduction of the mean OPG number was also assessed. In addition, all birds were clinically observed in order to evaluate the appearance of diarrhoea and of other signs of clinical coccidiosis.
Results: Seven days after the end of the treatment, birds of the C group showed diarrhoea and significant (P<0.05) higher OPG numbers respect to those of S and D groups, while no significant differences resulted between S and D groups. Moreover, percentages of OPG reduction of 98.61% and 99.60% and of 99.23% and 78.46% were found at day 3 and day 10 for group S and group D, respectively, while an increased mean OPG number was observed in the untreated group (C).
Conclusion: After oral administration to the examined red-legged partridges S. media was able not only to prevent the clinical form of coccidiosis, but also to give a significant reduction of E. legionensis OPG number in faecal samples of birds treated with this plant. This reduction resulted comparable to that observed in animals treated with the commercial drug
Magellanic Cloud Structure from Near-IR Surveys I: The Viewing Angles of the LMC
We present a detailed study of the viewing angles of the LMC disk plane. We
find that our viewing direction differs considerably from the commonly accepted
values, which has important implications for the structure of the LMC. The
discussion is based on an analysis of spatial variations in the apparent
magnitude of features in the near-IR color-magnitude diagrams extracted from
the DENIS and 2MASS surveys. Sinusoidal brightness variations with a
peak-to-peak amplitude of approximately 0.25 mag are detected as function of
position angle, for both AGB and RGB stars. This is naturally interpreted as
the result of distance variations, due to one side of the LMC plane being
closer to us than the opposite side. The best fitting geometric model of an
inclined plane yields an inclination angle i = 34.7 +/- 6.2 degrees and
line-of-nodes position angle Theta = 122.5 +/- 8.3 degrees. There is tentative
evidence that the LMC disk plane may be warped. Traditional methods to estimate
the position angle of the line of nodes have used either the major axis
position angle Theta_maj of the spatial distribution of tracers on the sky, or
the position angle Theta_max of the line of maximum gradient in the velocity
field, given that for a circular disk Theta_maj = Theta_max = Theta. The
present study does not rely on the assumption of circular symmetry, and is
considerably more accurate than previous studies of its kind. We find that the
actual position angle of the line of nodes differs considerably from both
Theta_maj and Theta_max, for which measurements have fallen in the range
140-190 degrees. This indicates that the intrinsic shape of the LMC disk is not
circular, but elliptical, as discussed further in Paper II. [Abridged]Comment: Astronomical Journal, in press. 44 pages, LaTeX, with 8 PostScript
figures. Contains minor revisions with respect to previously posted version.
Check out http://www.stsci.edu/~marel/lmc.html for a large scale (23x21
degree) stellar number-density image of the LMC constructed from RGB and AGB
stars in the 2MASS and DENIS surveys. The paper is available with higher
resolution figures from http://www.stsci.edu/~marel/abstracts/abs_R31.htm
Weeds for weed control: Asteraceae essential oils as natural herbicides.
The aim of this study was to test the botanical family of
Asteraceae as a source of natural herbicides. Twenty
Asteraceae species were collected during flowering time
and evaluated in terms of the yield and quality of essential
oils (germination inhibition and growth of weeds).
Half the species showed a sufficient yield of essential oil
(from about 0.1% to 1.43%) when testing these phytochemicals
in vitro as germination inhibitors of two typical
weeds, Amaranthus retroflexus and Setaria viridis.
Despite the higher tolerance of S. viridis, the concentration
of 100 lg L
1 of essential oils of the two Artemisia
species and Xanthium strumarium could totally inhibit
germination. In addition, at 10 lg L
1, the same essential
oils showed full inhibition of A. retroflexus seeds. A
comparison of their effectiveness at suboptimal doses
led to a further selection of the most promising sources
of essential oils. After their chemical characterisation,
the essential oils were tested as post-emergence herbicides
on seedlings of the above-cited weeds. After spraying
the weeds at different concentrations (10, 100 and
1000 mg L
1) during two different phenological stages
of weed seedlings (cotyledons and the third true leaf),
the essential oils of Artemisia annua and X. strumarium
showed the best performance. The essential oils of
X. strumarium were then tested again on both weeds to
monitor the dynamics of plant injury. A reduction in
plant fresh weight (about 20%–30% after 10 days) and
chlorophyll content (destroyed, after the same amount
of time) was found, thus confirming the total and rapid
effectiveness of these essential oils. In summary, A. annua
and X. strumarium have elicited considerable agronomic
interest and appear to be suitable as a source of
essential oils to act as natural herbicides
Imaging of the Stellar Population of IC10 with Laser Guide Star Adaptive Optics and the Hubble Space Telescope
We present adaptive optics (AO) images of the central starburst region of the
dwarf irregular galaxy IC10. The Keck 2 telescope laser guide star was used to
achieve near diffraction-limited performance at H and K' (Strehls of 18% and
32%, respectively). The images are centered on the putative Wolf-Rayet (W-R)
object [MAC92]24. We combine our AO images with F814W data from HST. By
comparing the K' vs. [F814W]-K' color-magnitude diagram (CMD) with theoretical
isochrones, we find that the stellar population is best represented by at least
two bursts of star formation, one ~ 10 Myr ago and one much older (150-500
Myr). Young, blue stars are concentrated in the vicinity of [MAC92]24. This
population represents an OB association with a half-light radius of about 3 pc.
We resolve the W-R object [MAC92]24 into at least six blue stars. Four of these
components have near-IR colors and luminosities that make them robust WN star
candidates. By matching the location of C-stars in the CMD with those in the
SMC we derive a distance modulus for IC10 of about 24.5 mag. and a foreground
reddening of E(B-V) = 0.95. We find a more precise distance by locating the tip
of the giant branch in the F814W, H, and K' luminosity functions. We find a
weighted mean distance modulus of 24.48 +/- 0.08. The systematic error in this
measurement, due to a possible difference in the properties of the RGB
populations in IC10 and the SMC, is +/- 0.16 mag.Comment: 13 pages, 13 figures, ApJ in pres
- …