421 research outputs found
Proliferative kidney disease (PKD) of rainbow trout: temperature- and time-related changes of Tetracapsuloides bryosalmonae DNA in the kidney
Proliferative kidney disease (PKD) of salmonids, caused by Tetracapsuloides bryosalmonae, can lead to high mortalities at elevated water temperature. We evaluated the hypothesis that this mortality is caused by increasing parasite intensity. T. bryosalmonae-infected rainbow trout (Oncorhynchus mykiss) were reared at different water temperatures and changes in parasite concentrations in the kidney were compared to cumulative mortalities. Results of parasite quantification by a newly developed real-time PCR agreed with the number of parasites detected by immunohistochemistry, except for very low or very high parasite loads because of heterogenous distribution of the parasites in the kidney. Two experiments were performed, where fish were exposed to temperatures of 12, 14, 16, 18 or 19°C after an initial exposure to an infectious environment at 12-16°C resulting in 100% prevalence of infected fish after 5 to 14 days of exposure. While mortalities differed significantly between all investigated water temperatures, significant differences in final parasite loads were only found between fish kept at 12°C and all other groups. Differences in parasite load between fish kept at 14°C to 19°C were not significant. These findings provide evidence that there is no direct link between parasite intensity and fish mortalit
Individual tracking reveals long-distance flight-path control in a nocturnally migrating moth
Each year, trillions of insects make long-range seasonal migrations. These movements are relatively well understood at a population level, but how individual insects achieve them remains elusive. Behavioral responses to conditions en route are little studied, primarily owing to the challenges of tracking individual insects. Using a light aircraft and individual radio tracking, we show that nocturnally migrating death's-head hawkmoths maintain control of their flight trajectories over long distances. The moths did not just fly with favorable tailwinds; during a given night, they also adjusted for head and crosswinds to precisely hold course. This behavior indicates that the moths use a sophisticated internal compass to maintain seasonally beneficial migratory trajectories independent of wind conditions, illuminating how insects traverse long distances to take advantage of seasonal resources
The night-sky at the Calar Alto Observatory
We present a characterization of the main properties of the night-sky at the
Calar Alto observatory for the time period between 2004 and 2007. We use
optical spectrophotometric data, photometric calibrated images taken in
moonless observing periods, together with the observing conditions regularly
monitored at the observatory, such as atmospheric extinction and seeing. We
derive, for the first time, the typical moonless night-sky optical spectrum for
the observatory. The spectrum shows a strong contamination by different
pollution lines, in particular from Mercury lines, which contribution to the
sky-brightness in the different bands is of the order of ~0.09 mag, ~0.16 mag
and ~0.10 mag in B, V and R respectively. The zenith-corrected values of the
moonless night-sky surface brightness are 22.39, 22.86, 22.01, 21.36 and 19.25
mag arcsec^-2 in U, B, V, R and I, which indicates that Calar Alto is a
particularly dark site for optical observations up to the I-band. The fraction
of astronomical useful nights at the observatory is ~70%, with a ~30% of
photometric nights. The typical extinction at the observatory is k_V~0.15 mag
in the Winter season, with little dispersion. In summer the extinction has a
wider range of values, although it does not reach the extreme peaks observed at
other sites. The median seeing for the last two years (2005-6) was ~0.90",
being smaller in the Summer (~0.87") than in the Winter (~0.96"). We conclude
in general that after 26 years of operations Calar Alto is still a good
astronomical site, being a natural candidate for future large aperture optical
telescopes.Comment: 16 pages, 5 figures, accepted for publishing in the Publications of
Astronomical Society of the Pacific (PASP
Envelope Ejection: an Alternative Process for some Early Case B Binaries
We discuss the evolution of binaries with moderately high masses (about 10 -
30 solar masses), and with periods of about 3 - 300d, corresponding mostly to
early Case B. These are usually thought to evolve either by reasonably
conservative Roche-lobe overflow, if the initial mass ratio is fairly mild, or
else by highly non-conservative common-envelope evolution, with spiral-in to
short periods (hours, typically), if the initial mass ratio is rather extreme.
We discuss here a handful of binaries from part of this period range (about 50
- 250d), which appear to have followed a different path: we argue that they
must have lost a large proportion of initial mass (about 70 - 80%), but without
shortening their periods at all. We suggest that their behaviour may be due to
the fact that stars of such masses, when evolved also to rather large radii,
are not far from the Humphreys-Davidson limit where single stars lose their
envelopes spontaneously in P Cygni winds, and so have envelopes which are only
lightly bound to the core. These envelopes therefore may be relatively easily
dissipated by the perturbing effect of a companion. In addition, some or all of
the stars considered here may have been close to the Cepheid instability strip
when they filled their Roche lobes. One or other, or both, of high luminosity
and Cepheid instability, in combination with an appropriately close binary
companion, may be implicated
On the photometric variability of blue supergiants in NGC 300 and its impact on the Flux-weighted Gravity-Luminosity Relationship
We present a study of the photometric variability of spectroscopically
confirmed supergiants in NGC 300, comprising 28 epochs extending over a period
of five months. We find 15 clearly photometrically variable blue supergiants in
a sample of nearly 70 such stars, showing maximum light amplitudes ranging from
0.08 to 0.23 magnitudes in the V band, and one variable red supergiant. We show
their light curves, and determine semi-periods for two A2 Ia stars. Assuming
that the observed changes correspond to similar variations in the bolometric
luminosity, we test for the influence of this variability on the Flux-weighted
Gravity--Luminosity Relationship and find a negligible effect, showing that the
calibration of this relationship, which has the potential to measure
extragalactic distances at the Cepheid accuracy level, is not affected by the
stellar photometric variability in any significant way.Comment: 9 pages, 3 figures, 3 tables. Accepted for publication in the
Astrophysical Journa
Velocity Dispersion of Dissolving OB Associations Affected by External Pressure of Formation Environment
This paper presents a possible way to understand dissolution of OB
associations (or groups). Assuming rapid escape of parental cloud gas from
associations, we show that the shadow of the formation environment for
associations can be partially imprinted on the velocity dispersion at their
dissolution. This conclusion is not surprising as long as associations are
formed in a multiphase interstellar medium, because the external pressure
should suppress expansion caused by the internal motion of the parental clouds.
Our model predicts a few km s as the internal velocity dispersion.
Observationally, the internal velocity dispersion is km s which
is smaller than our prediction. This suggests that the dissipation of internal
energy happens before the formation of OB associations.Comment: 6 pages. AJ accepte
Calibrating the projection factor for Galactic Cepheids
The projection factor (p), which converts the radial velocity to pulsational
velocity, is an important parameter in the Baade-Wesselink (BW) type analysis
and distance scale work. The p-factor is either adopted as a constant or
linearly depending on the logarithmic of pulsating periods. The aim of this
work is to calibrate the p-factor if a Cepheid has both the BW distance and an
independent distance measurement, and examine the p-factor for delta Cephei --
the prototype of classical Cepheids. We calibrated the p-factor for several
Galactic Cepheids that have both the latest BW distances and independent
distances either from Hipparcos parallaxes or main-sequence fitting distances
to Cepheid-hosted stellar clusters. Based on 25 Cepheids, the calibrated
p-factor relation is consistent with latest p-factor relation in literature.
The calibrated p-factor relation also indicates that this relation may not be
linear and may exhibit an intrinsic scatter. We also examined the discrepancy
of empirical p-factors for delta Cephei, and found that the reasons for this
discrepancy include the disagreement of angular diameters, the treatment of
radial velocity data, and the phase interval adopted during the fitting
procedure. Finally, we investigated the impact of the input p-factor in two BW
methodologies for delta Cephei, and found that different p-factors can be
adopted in these BW methodologies and yet result in the same angular diameters.Comment: 6 pages, 6 figures and 2 tables. A&A accepte
The MACHO Project LMC Variable Star Inventory. VI. The Second-overtone Mode of Cepheid Pulsation From First/Second Overtone (FO/SO) Beat Cepheids
MACHO Project photometry of 45 LMC FO/SO beat Cepheids which pulsate in the
first and second overtone (FO and SOo, respectively) has been analysed to
determine the lightcurve characteristics for the SO mode of Cepheid pulsation.
We predict that singly-periodic SO Cepheids will have nearly sinusoidal
lightcurves; that we will only be able to discern SO Cepheids from fundamental
(F) and (FO) Cepheids for P <= 1.4 days; and that the SO distribution will
overlap the short-period edge of the LMC FO Cepheid period-luminosity relation
(when both are plotted as a function of photometric period).
We also report the discovery of one SO Cepheid candidate,
MACHO*05:03:39.670:04:32, with a photometric period of 0.775961 +/- 0.000019
days and an instrumental amplitude of 0.047 +/- 0.009 mag in V.Comment: 23 pages, 7 Encapsulated PostScript figures. Accepted for publication
in the Astrophysical Journa
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