890 research outputs found
Radio-continuum detections of Galactic Planetary Nebulae I. MASH PNe detected in large-scale radio surveys
We present an updated and newly compiled radio-continuum data-base for MASH
PNe detected in the extant large scale "blind" radio-continuum surveys (NVSS,
SUMSS/MGPS-2 and PMN) and, for a small number of MASH PNe, observed and
detected in targeted radio-continuum observations. We found radio counterparts
for approximately 250 MASH PNe. In comparison with the percentage of previously
known Galactic PNe detected in the NVSS and MGPS-2 radio-continuum surveys and
according to their position on the flux density-angular diameter and the radio
brightness temperature evolutionary diagrams we conclude, unsurprisingly, that
the MASH sample presents the radio-faint end of the known Galactic PNe
population. Also, we present radio-continuum spectral properties of a small
sub-sample of MASH PNe located in the strip between declinations -30arcdeg and
-40arcdeg, that are detected in both the NVSS and MGPS-2 radio surveys.Comment: 13 figures and 7 tables, accepted for publication in MNRA
Geobase Information System Impacts on Space Image Formats
As Geobase Information Systems increase in number, size and complexity, the format compatability of satellite remote sensing data becomes increasingly more important. Because of the vast and continually increasing quantity of data available from remote sensing systems the utility of these data is increasingly dependent on the degree to which their formats facilitate, or hinder, their incorporation into Geobase Information Systems. To merge satellite data into a geobase system requires that they both have a compatible geographic referencing system. Greater acceptance of satellite data by the user community will be facilitated if the data are in a form which most readily corresponds to existing geobase data structures. The conference addressed a number of specific topics and made recommendations
Remote sensing applications to hydrologic modeling in the southern Sierra Nevada and portions of the San Joaquin Valley, volume 1
The author has identified the following significant results. Characteristics of LANDSAT MSS imagery present problems in using satellite radiation measurements to estimate the shortwave albedo of an alpine snow cover. Every 15 minute USGS quadrangle contains over 100,000 pixels which poses a computation problem if each pixel is to be evaluated individually. The sampling interval may be sufficiently great to mask some effects of terrain and vegetation on reflectance. Three frames of LANDSAT imagery are needed for complete coverage of the study area, yet less than one third of the area coverage from each frame covers an area of interest. Because of distortions inherent in the imagery, information regarding spacecraft altitude, attitude, and position must be statistically derived with respect to ground control points in the image whose geodetic locations are known. An inspection of shade points indicates that up to one third of the most heavily snow covered areas may saturate in bands 4 through 6. LANDSAT's 9 day repeat cycle is not optimum for snow cover reflectance modeling because the most pronounced changes in albedo occur most nearly following a new snowfall. Such a snowfall, occurring between overpasses, is inadequately represented by extrapolation from the previous overpasses
The binary fraction of planetary nebula central stars I. A high-precision, I-band excess search
In an attempt to determine how many planetary nebulae derive from binary
interactions, we have started a project to measure their unbiased binary
fraction. This number, when compared to the binary fraction of the presumed
parent population can give a first handle on the origin of planetary nebulae.
By detecting 27 bona fide central stars in the I band we have found that 30% of
our sample have an I band excess between one and a few sigmas, possibly
denoting companions brighter than M3-4V and with separations smaller than
approximately 1000 AU. By accounting for the undetectable companions, we
determine a de-biased binary fraction of 67-78% for all companions at all
separations. We compare this number to a main sequence binary fraction of
(50+/-4)% determined for spectral types F6V-G2V, appropriate if the progenitors
of today's PN central star population is indeed the F6V-G2V stars. The error on
our estimate could be between 10 and 30%. We conclude that the central star
binary fraction may be larger than expected from the putative parent
population. Using the more sensitive J band of a subset of 11 central stars,
the binary fraction is 54% for companions brighter than approximately M5-6V and
with separations smaller than about 900 AU. De-biassing this number we obtain a
binary fraction of 100-107%. The two numbers should be the same and the
discrepancy is likely due to small number statistics.
We also present an accurately vetted compilation of observed main sequence
star magnitudes, colours and masses, which can serve as a reference for future
studies. We also present synthetic colours of hot stars as a function of
temperature (20-170kK) and gravity (log g= 6-8) for Solar and PG1159
compositions.Comment: 22 pages, 6 figures, 12 tables, accepted by MNRA
The planetary nebula Abell 48 and its [WN4] central star
We have conducted a multi-wavelength study of the planetary nebula Abell 48
and give a revised classification of its nucleus as a hydrogen-deficient star
of type [WN4]. The surrounding nebula has a morphology typical of PNe and
importantly, is not enriched in nitrogen, and thus not the 'peeled atmosphere'
of a massive star. Indeed, no WN4 star is known to be surrounded by such a
compact nebula. The ionized mass of the nebula is also a powerful discriminant
between the low-mass PN and high-mass WR ejecta interpretations. The ionized
mass would be impossibly high if a distance corresponding to a Pop I star was
adopted, but at a distance of 2 kpc, the mass is quite typical of moderately
evolved PNe. At this distance, the ionizing star then has a luminosity of ~5000
Lsolar, again rather typical for a PN central star. We give a brief discussion
of the implications of this discovery for the late-stage evolution of
intermediate-mass stars.Comment: EUROWD12 Proceeding
Remote sensing applications to hydrologic modeling
An energy balance snowmelt model for rugged terrain was devised and coupled to a flow model. A literature review of remote sensing applications to hydrologic modeling was included along with a software development outline
Confirmation of G6.31+0.54 as a part of a Galactic supernova remnant
A combination of archival multi-frequency radio observations with narrow-band
HAlpha optical imagery and new confirmatory optical spectroscopy have shown
that candidate supernova remnant G6.31+0.54 can now be confirmed as part of a
Galactic supernova remnant (SNR). It has non-thermal emission, an optical
emission line spectrum displaying shock excitation and standard SNR line
ratios, fine filamentary structures in HAlpha typical of optical remnants and
closely overlapping radio and optical footprints. An X-ray ROSAT source 1RXS
J175752.1-231105 was also found that matches the radio and optical emission
though a definite association is not proven. Nevertheless, taken together, all
these observed properties point to a clear SNR identification for this source.
We provide a rough estimate for the kinematic distance to G6.31+0.54 of
~4.5kpc. The detected optical filaments are some ~10arcminutes in extent (or
about 13 pc at the assumed distance). However, as only a partial arcuate
structure of the SNR can be seen (and not a full shell) the full angular extent
of the SNR is unclear. Hence the physical extent of the observed partial shell
is also difficult to estimate. If we assume an approximately circular shell
then a conservative fit to the optical arc shaped filaments gives an angular
diameter of ~20 arcminutes corresponding to a physical diameter of ~26 pc that
shows this to be an evolved remnant.Comment: Accepted for publishing in MNRAS 8 pages, 8 figure
Testing the binary hypothesis for the formation and shaping of planetary nebulae
There is no quantitative theory to explain why a high 80% of all planetary
nebulae are non-spherical. The Binary Hypothesis states that a companion to the
progenitor of a central star of planetary nebula is required to shape the
nebula and even for a planetary nebula to be formed at all. A way to test this
hypothesis is to estimate the binary fraction of central stars of planetary
nebulae and to compare it with that of the main sequence population.
Preliminary results from photometric variability and the infrared excess
techniques indicate that the binary fraction of central stars of planetary
nebulae is higher than that of the main sequence, implying that PNe could
preferentially form via a binary channel. This article briefly reviews these
results and current studies aiming to refine the binary fraction.Comment: EUROWD12 Proceeding
Planetary nebulae : getting closer to an unbiased binary fraction
Why 80% of planetary nebulae are not spherical is not yet understood. The
Binary Hypothesis states that a companion to the progenitor of the central star
of a planetary nebula is required to shape the nebula and even for a planetary
nebula to be formed at all. A way to test this hypothesis is to estimate the
binary fraction of central stars of planetary nebula and to compare it with the
main sequence population. Preliminary results from photometric variability and
infrared excess techniques indicate that the binary fraction of central stars
of planetary nebulae is higher than that of the putative main sequence
progenitor population, implying that PNe could be preferentially formed via a
binary channel. This article briefly reviews these results and future studies
aiming to refine the binary fraction.Comment: SF2A 2012 proceeding
A catalogue of integrated H\alpha\ fluxes for ~1100 Galactic planetary nebulae
We present new determinations of the integrated H\alpha\ flux for ~1100
Galactic planetary nebulae measured from the Southern H-Alpha Sky Survey Atlas
(SHASSA) and its northern counterpart, the Virginia Tech Spectral-Line Survey
(VTSS). This catalogue is the largest homogeneous database of its kind,
tripling the number of currently available measurements.Comment: 2 pages, 2 figures, presented at the IAU Symposium "Planetary
Nebulae: an Eye to the Future" No. 283, 201
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