842 research outputs found
Catalogue of candidate emission-line objects in the Small Magellanic Cloud
H\alpha and [O III] narrow band, wide field (7 * 7 degree), CCD images of the
Small Magellanic Cloud were compared and a catalogue of candidate planetary
nebulae and H\alpha emission-line stars was compiled. The catalogue contains
131 planetary nebulae candidates, 23 of which are already known to be or are
probable planetary nebulae or very low excitation objects. Also, 218
emission-line candidates have been identified with 113 already known. Our
catalogue therefore provides a useful supplement to those of Meyssonnier &
Azzopardi (1993) and Sanduleak, MacConnell & Davis Phillip (1978). Further
observations are required to confirm the identity of the unknown objects.Comment: 8 pages, accepted by MNRA
Wavelength dependence of angular diameters of M giants: an observational perspective
We discuss the wavelength dependence of angular diameters of M giants from an
observational perspective. Observers cannot directly measure an optical-depth
radius for a star, despite this being a common theoretical definition. Instead,
they can use an interferometer to measure the square of the fringe visibility.
We present new plots of the wavelength-dependent centre-to-limb variation (CLV)
of intensity of the stellar disk as well as visibility for Mira and non-Mira M
giant models. We use the terms ``CLV spectra'' and ``visibility spectra'' for
these plots. We discuss a model-predicted extreme limb-darkening effect (also
called the narrow-bright-core effect) in very strong TiO bands which can lead
to a misinterpretation of the size of a star in these bands. We find no
evidence as yet that this effect occurs in real stars. Our CLV spectra can
explain the similarity in visibilities of R Dor (M8IIIe) that have been
observed recently despite the use of two different passbands. We compare
several observations with models and find the models generally under-estimate
the observed variation in visibility with wavelength. We present CLV and
visibility spectra for a model that is applicable to the M supergiant alpha
Ori.Comment: 16 pages with figures. Accepted by MNRA
Hipparcos red stars in the HpV_{T2} and VI_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibrated
instantaneous (epoch) Cousins color indices using newly derived
photometry. Three new sets of ground-based Cousins data have
been obtained for more than 170 carbon and red M giants. These datasets in
combination with the published sources of photometry served to obtain the
calibration curves linking Hipparcos/Tycho with the Cousins
index. In total, 321 carbon stars and 4464 M- and S-type stars have new
indices. The standard error of the mean is about 0.1 mag or better down
to although it deteriorates rapidly at fainter magnitudes. These
indices can be used to verify the published Hipparcos color
indices. Thus, we have identified a handful of new cases where, instead of the
real target, a random field star has been observed. A considerable fraction of
the DMSA/C and DMSA/V solutions for red stars appear not to be warranted. Most
likely such spurious solutions may originate from usage of a heavily biased
color in the astrometric processing.Comment: 10 figures, 1 electronic table, accepted in A&
The Optical Emission from Gamma-ray Quasars
We present photometric observations of six radio-loud quasars that were
detected by the COMPTEL gamma-ray telescope. The data encompasses seven
wavebands in the optical and near-infrared. After correction for Galactic
extinction, we find a wide range in optical slopes. Two sources are as blue as
optically-selected quasars, and are likely to be dominated by the accretion
disc emission, while three others show colours consistent with a red
synchrotron component. We discuss the properties of the COMPTEL sample of
quasars, as well as the implications our observations have for multi-wavelength
modelling of gamma-ray quasars.Comment: 12 pages, 3 figures, accepted for publication in P.A.S.A; minor typos
correcte
The origin of HE0107-5240 and the production of O and Na in extremely metal-poor stars
We elaborate the binary scenario for the origin of HE0107-5240, the most
metal-poor star yet observed ([Fe/H] = -5.3), using current knowledge of the
evolution of extremely metal-poor stars. From the observed C/N value, we
estimate the binary separation and period. Nucleosynthesis in a helium
convective zone into which hydrogen has been injected allows us to discuss the
origin of surface O and Na as well as the abundance distribution of s-process
elements. We can explain the observed abundances of 12C, 13C, N, O, and Na and
predict future observations to validate the Pop III nature of HE0107-5240.Comment: 4 pages, 3 figures, proceedings of the conference, "Nuclei in the
Cosmos VIII", Nuclear Physics A in pres
Detection of lithium in nearby young late-M dwarfs
Late M-type dwarfs in the solar neighborhood include a mixture of very
low-mass stars and brown dwarfs which is difficult to disentangle due to the
lack of constraints on their age such as trigonometric parallax, lithium
detection and space velocity.
We search for young brown dwarf candidates among a sample of 28 nearby late-M
dwarfs with spectral types between M5.0 and M9.0, and we also search for debris
disks around three of them.
Based on theoretical models, we used the color , the -band absolute
magnitude and the detection of the Li I 6708 doublet line as a strong
constraint to estimate masses and ages of our targets. For the search of debris
disks, we observed three targets at submillimeter wavelength of 850 m.
We report here the first clear detections of lithium absorption in four
targets and a marginal detection in one target. Our mass estimates indicate
that two of them are young brown dwarfs, two are young brown dwarf candidates
and one is a young very low-mass star. The closest young field brown dwarf in
our sample at only 15 pc is an excellent benchmark for further studying
physical properties of brown dwarfs in the range 100150 Myr. We did not
detect any debris disks around three late-M dwarfs, and we estimated upper
limits to the dust mass of debris disks around them.Comment: 10 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
New limb-darkening coefficients and synthetic photometry for model-atmosphere grids at Galactic, LMC, and SMC abundances
New grids of Atlas9 models have been calculated using revised convection
parameters and updated opacity-distribution functions, for chemical
compositions intended to be representative of solar, [M/H] = +0.3, +0.5, Large
Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC) abundances. The grids
cover T(eff) = 3.5-50kK, from log(g) = 5.0 to the effective Eddington limit.
Limb-darkening coefficients and synthetic photometry are presented in the
UBVRIJHKLM, uvby, ugriz, WFCAM, Hipparcos/Tycho, and Kepler passbands for these
models, and for Castelli's comparable `new-ODF' grids. Flux distributions are
given for the new models. The sensitivity of limb-darkening coefficients to the
adopted physics is illustrated
Accretion properties of T Tauri stars in sigma Ori
Accretion disks around young stars evolve in time with time scales of few
million years. We present here a study of the accretion properties of a sample
of 35 stars in the ~3 million year old star-forming region sigma Ori. Of these,
31 are objects with evidence of disks, based on their IR excess emission. We
use near-IR hydrogen recombination lines (Pa_gamma) to measure their mass
accretion rate. We find that the accretion rates are significantly lower in
sigma Ori than in younger regions, such as rho-Oph, consistently with viscous
disk evolution. The He I 1.083 micron line is detected (either in absorption or
in emission) in 72% of the stars with disks, providing evidence of
accretion-powered activity also in very low accretors, where other accretion
indicators dissapear.Comment: Astronomy and Astrophysics, accepte
Surfing, self-medicating and safety: buying non-prescription and complementary medicines via the internet
© 2003 BMJ Publishing Group & Institute for Healthcare ImprovementObjective: To examine whether the sale of medicines via the internet supports their safe and appropriate use. Design: e-Pharmacy websites were identified using key words and a metasearch engine and the quality of information published on these websites was surveyed using the DISCERN tool. A case scenario and internet pharmacy practice standards were also used to evaluate the quality of care delivered. Setting and participants: Between July and September 2001 104 websites were surveyed and 27 sent either Sudafed (pseudoephedrine HCl), St John’s wort products, or both to a residential address in Melbourne, Australia. Main outcome measures: Quality of health information (DISCERN ratings), information exchanged between e-pharmacy staff and consumers, and product and delivery costs. Results: Of 104 e-pharmacies from at least 13 different countries, 63 websites provided some health information but overall the quality of the information was poor. Only three website operators provided adequate advice to consumers to avoid a potential drug interaction. The costs for a daily dose of pseudoephedrine HCl (240 mg) ranged from A3.04, and delivery costs from A62.70. Conclusion: Consumers who self-select medicines from websites have insufficient access to information and advice at the point of ordering and on delivery to make informed decisions about their safe and appropriate use.T L Bessell, J N Anderson, C A Silagy, L N Sansom and J E Hille
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