7,174 research outputs found
An imaging and spectroscopic study of the planetary nebulae in NGC 5128 (Centaurus A): Planetary nebulae catalogues
Imaging and spectroscopic observations of planetary nebulae (PNe) in the
nearest large elliptical galaxy NGC 5128 (Centaurus A), were obtained to find
more PNe and measure their radial velocities. NTT imaging was obtained in 15
fields in NGC 5128 over an area of about 1 square degree with EMMI using [O
III] and off-band filters. Newly detected sources, combined with literature
PNe, were used as input for VLT FLAMES multi-fibre spectroscopy in MEDUSA mode.
Spectra of the 4600-5100A region were analysed and velocities measured based on
emission lines of [O III]4959,5007A and often H-beta. The chief results are
catalogues of 1118 PN candidates and 1267 spectroscopically confirmed PNe in
NGC 5128. The catalogue of PN candidates contains 1060 PNe discovered with EMMI
imaging and 58 from literature surveys. The spectroscopic PN catalogue has
FLAMES radial velocity and emission line measurements for 1135 PNe, of which
486 are new. Another 132 PN radial velocities are available from the
literature. For 629 PNe observed with FLAMES, H-beta was measured in addition
to [O III]. Nine targets show double-lined or more complex profiles, and their
possible origin is discussed. FLAMES spectra of 48 globular clusters were also
targetted: 11 had emission lines detected (two with multiple components), but
only 3 are PNe likely to belong to the host globular. The total of 1267
confirmed PNe in NGC 5128 with radial velocity measurements (1135 with small
velocity errors) is the largest collection of individual kinematic probes in an
early-type galaxy. This PN dataset, as well as the catalogue of PN candidates,
are valuable resources for detailed investigation of the stellar population of
NGC 5128. [Abridged]Comment: 19 pages, 11 figures. Accepted for publication in Astronomy and
Astrophysics. Tables 7 - 11 available in electronic form at CDS. Replaced
with a few typos fixe
Electromagnetic properties of ice coated surfaces
The electromagnetic scattering from ice coated structures is examined. The influence of ice is shown from a measurement standpoint and related to a simple analytical model. A hardware system for the realistic measurement of ice coated structures is also being developed to use in an existing NASA Lewis icing tunnel. Presently, initial measurements have been performed with a simulated tunnel to aid in the development
Searching for central stars of planetary nebulae in Gaia DR2
Context: Accurate distance measurements are fundamental to the study of
Planetary Nebulae (PNe) but have long been elusive. The most accurate and
model-independent distance measurements for galactic PNe come from the
trigonometric parallaxes of their central stars, which were only available for
a few tens of objects prior to the Gaia mission.
Aims: Accurate identification of PN central stars in the Gaia source
catalogues is a critical prerequisite for leveraging the unprecedented scope
and precision of the trigonometric parallaxes measured by Gaia. Our aim is to
build a complete sample of PN central star detections with minimal
contamination.
Methods: We develop and apply an automated technique based on the likelihood
ratio method to match candidate central stars in Gaia Data Release 2 (DR2) to
known PNe in the Hong Kong/AAO/Strasbourg H (HASH) PN catalogue, taking
into account the BP--RP colours of the \emph{Gaia} sources as well as their
positional offsets from the nebula centres. These parameter distributions for
both true central stars and background sources are inferred directly from the
data.
Results: We present a catalogue of over 1000 Gaia sources that our method has
automatically identified as likely PN central stars. We demonstrate how the
best matches enable us to trace nebula and central star evolution and to
validate existing statistical distance scales, and discuss the prospects for
further refinement of the matching based on additional data. We also compare
the accuracy of our catalogue to that of previous works.Comment: 15 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Performance of Photon-Pair Quantum Key Distribution Systems
We analyze the quantitative improvement in performance provided by a novel
quantum key distribution (QKD) system that employs a correlated photon source
(CPS) and a photon-number resolving detector (PNR). Our calculations suggest
that given current technology, the CPR implementation offers an improvement of
several orders of magnitude in secure bit rate over previously described
implementations
Invisible sunspots and rate of solar magnetic flux emergence
Aims.
We study the visibility of sunspots and its influence on observed values of sunspot region parameters.
Methods.
We use Virtual Observatory tools provided by AstroGrid to analyse a sample of 6862 sunspot regions. By studying the distributions of locations where sunspots were first and last observed on the solar disk, we derive the visibility function of sunspots, the rate of magnetic flux emergence and the ratio between the durations of growth and decay phases of solar active regions.
Results.
We demonstrate that the visibility of small sunspots has a strong centre-to-limb variation, far larger than would be expected from geometrical (projection) effects. This results in a large number of young spots being invisible: 44% of new regions emerging in the west of the Sun go undetected. For sunspot regions that are detected, large differences exist between actual locations and times of flux emergence, and the apparent ones derived from sunspot data. The duration of the growth phase of solar regions has been, up to now, underestimated
Electromagnetic properties of material coated surfaces
The electromagnetic properties of material coated conducting surfaces were investigated. The coating geometries consist of uniform layers over a planar surface, irregularly shaped formations near edges and randomly positioned, electrically small, irregularly shaped formations over a surface. Techniques to measure the scattered field and constitutive parameters from these geometries were studied. The significance of the scattered field from these geometries warrants further study
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