342 research outputs found
IUE observations of the 1982-84 eclipse of Epsilon Aurigae
The major characteristics in the ultraviolet of the 1982-84 eclipse of Eps Aur as observed with IUE by various workers are summarized. This star can be observed over the entire IUE wavelength range, from 1200 to 3200 A, in low dispersion, allowing eclipse light curves to be obtained in broadband regions, but due to its steep spectral gradient and the sensitivities of IUE cameras, high resolution exposures adequately cover only the regions from 1700-1900 and 2400-3200 A. In many ways, the UV data confirms or expands upon interpretations of the stem made from observations in other wavelength regions, but in other respects the system remains as enigmatic as before
Ambipolar Drift Heating in Turbulent Molecular Clouds
Although thermal pressure is unimportant dynamically in most molecular gas,
the temperature is an important diagnostic of dynamical processes and physical
conditions. This is the first of two papers on thermal equilibrium in molecular
clouds. We present calculations of frictional heating by ion-neutral (or
ambipolar) drift in three-dimensional simulations of turbulent, magnetized
molecular clouds.
We show that ambipolar drift heating is a strong function of position in a
turbulent cloud, and its average value can be significantly larger than the
average cosmic ray heating rate. The volume averaged heating rate per unit
volume due to ambipolar drift, H_AD ~ |JxB|^2 ~ B^4/L_B^2, is found to depend
on the rms Alfvenic Mach number, M_A, and on the average field strength, as
H_AD ~ M_A^2^4. This implies that the typical scale of variation of the
magnetic field, L_B, is inversely proportional to M_A, which we also
demonstrate.Comment: 37 pages, 9 figures include
Effet des prétraitemetns auxiniques sur la croissance des plants de gombo au Gabon
Le gombo est une plante maraîchère à usage alimentaire et médicinal au Gabon. La présente étude a été réalisée en vue d'induire la croissance de ce légume et d'accroitre la production. Des graines de gombo ont été prétraitées pendant 24 h dans 6 solutions d'auxine de concentrations entre 1 et 10-5M. Elles ont ensuite été mises en culture sous serre pendant 30 j. Les paramètres morphologiques de croissance suivants ont été évalués : la germination des graines, la croissance primaire et secondaire des tiges, ainsi que la surface foliaire des plants. Les résultats ont montré que les concentrations élevées d'auxine supérieures à 10-2M ont inhibé tous les paramètres morphométriques étudiés. Les doses auxiniques inférieures ou égales à 10-2M ont, par contre, stimulé la croissance de cette plante, proportionnellement à la concentration auxinique. Les traitements auxiniques de concentrations 10-2M peuvent donc être envisagés dans l'amélioration de la croissance des plants de gombo au Gabon.Okra is a nutritional and medicinal plant, widely cultivated in Gabon. The present study is undertaken in order to improve biomass' production. Hence, okra's seeds were pretreated by immersion in 6 auxin solutions during 24 h and cultivated under greenhouse conditions. Growth parameters, estimated 30 days after sowing, were: seed germination, longitudinal and diametric growths of the stem and leaf area. Results show that high concentrations of auxin (>10-2M) reduced the morphometric parameters of okra. But lowest concentrations (10-2M to 10-5M) increase all parameters measured proportionally to the level of the compound. Therefore, the use of auxin, at the lowest concentrations, of about 10-2M, may be envisioned in order to improve okra production in Gabon.Keywords : Auxin, okra, pretreatments, morphometric parameters, improvement, growth, Gabo
FUSE Detection of Galactic OVI Emission in the Halo above the Perseus Arm
Background observations obtained with the Far Ultraviolet Spectroscopic
Explorer (FUSE) toward l=95.4, b=36.1 show OVI 1032,1038 in emission. This
sight line probes a region of stronger-than-average soft X-ray emission in the
direction of high-velocity cloud Complex C above a part of the disk where
Halpha filaments rise into the halo. The OVI intensities, 1600+/-300
ph/s/cm^2/sr (1032A) and 800+/-300 ph/s/cm^2/sr (1038A), are the lowest
detected in emission in the Milky Way to date. A second sight line nearby
(l=99.3, b=43.3) also shows OVI 1032 emission, but with too low a
signal-to-noise ratio to obtain reliable measurements. The measured
intensities, velocities, and FWHMs of the OVI doublet and the CII* line at
1037A are consistent with a model in which the observed emission is produced in
the Galactic halo by hot gas ejected by supernovae in the Perseus arm. An
association of the observed gas with Complex C appears unlikely.Comment: accepted for publication in ApJL, 11 pages including 3 figure
The FUSE survey of OVI absorption in and near the Galaxy
We present FUSE observations of OVI absorption in a sample of 100
extragalactic targets and 2 distant halo stars. We describe the details of the
calibration, alignment in velocity, continuum fitting, and manner in which
contaminants were removed (Galactic H2, absorption intrinsic to the background
target and intergalactic Ly-beta lines). We searched for OVI absorption in the
velocity range -1200 to 1200 km/s. With a few exceptions, we only find OVI
between -400 and 400 km/s; the exceptions may be intergalactic OVI. We discuss
the separation of the observed OVI absorption into components associated with
the Galactic halo and components at high-velocity, which are probably located
in the neighborhood of the Galaxy. We describe the measurements of equivalent
width and column density, and we analyze the different contributions to the
errors. We conclude that low-velocity Galactic OVI absorption occurs along all
sightlines - the few non-detections only occur in noisy spectra. We further
show that high-velocity OVI is very common, having equivalent width >65 mAA in
50% of the sightlines and >30 mAA in 70% of the high-quality sightlines. The
high-velocity OVI absorption has velocities relative to the LSR of
+/-(100--330) km/s; there is no correlation between velocity and absorption
strength. We present 50 km/s wide OVI channel maps. These show evidence for the
imprint of Galactic rotation. They also highlight two known HI high-velocity
clouds (complex~C and the Magellanic Stream). The channel maps further show
that OVI at velocities <-200 km/s occurs along all sightlines in the region
l=20-150, b200 km/s occurs along all sightlines
in the region l=180-300, b>20 (abbreviated).Comment: 85 pages, 127 figures, 13 color figures, 3 tables, AASTeX preprint
format. All figures are in PNG format due to space concerns. Bound copies of
manuscript and two accompanying articles are available upon request.
submitted to ApJ
A Far-Ultraviolet Spectroscopic Survey of Luminous Cool Stars
FUSE ultraviolet spectra of 8 giant and supergiant stars reveal that high
temperature (3 X 10^5 K) atmospheres are common in luminous cool stars and
extend across the color-magnitude diagram from Alpha Car (F0 II) to the cool
giant Alpha Tau (K5 III). Emission present in these spectra includes
chromospheric H-Lyman Beta, Fe II, C I, and transition region lines of C III, O
VI, Si III, Si IV. Emission lines of Fe XVIII and Fe XIX signaling temperatures
of ~10^7 K and coronal material are found in the most active stars, Beta Cet
and 31 Com. A short-term flux variation, perhaps a flare, was detected in Beta
Cet during our observation. Stellar surface fluxes of the emission of C III and
O VI are correlated and decrease rapidly towards the cooler stars, reminiscent
of the decay of magnetically-heated atmospheres. Profiles of the C III (977A)
lines suggest that mass outflow is underway at T~80,000 K, and the winds are
warm. Indications of outflow at higher temperatures (3 X 10^5K) are revealed by
O VI asymmetries and the line widths themselves. High temperature species are
absent in the M-supergiant Alpha Ori. Narrow fluorescent lines of Fe II appear
in the spectra of many giants and supergiants, apparently pumped by H Lyman
Alpha, and formed in extended atmospheres. Instrumental characteristics that
affect cool star spectra are discussed.Comment: Accept for publication in The Astrophysical Journal; 22 pages of
text, 23 figures and 8 table
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