1,523 research outputs found
Photoassociative Frequency Shift in a Quantum Degenerate Gas
We observe a light-induced frequency shift in single-photon photoassociative
spectra of magnetically trapped, quantum degenerate 7Li. The shift is a
manifestation of the coupling between the threshold continuum scattering states
and discrete bound levels in the excited-state molecular potential induced by
the photoassociation laser. The frequency shift is observed to be linear in the
laser intensity with a measured proportionality constant that is in good
agreement with theoretical predictions. The frequency shift has important
implications for a scheme to alter the interactions between atoms in a
Bose-Einstein condensate using photoassociation resonances.Comment: 3 figure
A catalogue of integrated H-alpha fluxes for 1,258 Galactic planetary nebulae
We present a catalogue of new integrated H-alpha fluxes for 1258 Galactic
planetary nebulae (PNe), with the majority, totalling 1234, measured from the
Southern H-Alpha Sky Survey Atlas (SHASSA) and/or the Virginia Tech
Spectral-line Survey (VTSS). Aperture photometry on the continuum-subtracted
digital images was performed to extract H-alpha + [NII] fluxes in the case of
SHASSA, and H-alpha fluxes from VTSS. The [NII] contribution was then
deconvolved from the SHASSA flux using spectrophotometric data taken from the
literature or derived by us. Comparison with previous work shows that the flux
scale presented here has no significant zero-point error. Our catalogue is the
largest compilation of homogeneously derived PN fluxes in any waveband yet
measured, and will be an important legacy and fresh benchmark for the
community. Amongst its many applications, it can be used to determine
statistical distances for these PNe, determine new absolute magnitudes for
delineating the faint end of the PN luminosity function, provide baseline data
for photoionization and hydrodynamical modelling, and allow better estimates of
Zanstra temperatures for PN central stars with accurate optical photometry. We
also provide total H-alpha fluxes for another 75 objects which were formerly
classified as PNe, as well as independent reddening determinations for ~270
PNe, derived from a comparison of our H-alpha data with the best literature
H-beta fluxes. In an appendix, we list corrected H-alpha fluxes for 49 PNe
taken from the literature, including 24 PNe not detected on SHASSA or VTSS,
re-calibrated to a common zero-point.Comment: 49 pages, 7 figures, 10 tables, to appear in MNRAS. This version
includes full-length tables 1 and
The H\alpha\ surface brightness - radius relation: a robust statistical distance indicator for planetary nebulae
Measuring the distances to Galactic planetary nebulae (PNe) has been an
intractable problem for many decades. We have now established a robust optical
statistical distance indicator, the H surface brightness- radius or S-r
relation, which addresses this problem. We developed this relation from a
critically evaluated sample of primary calibrating PNe. The robust nature of
the method results from our revised calibrating distances with significantly
reduced systematic uncertainties, and the recent availability of high-quality
data, including updated nebular diameters and integrated H fluxes. The
S-r technique is simple in its application, requiring only an angular size, an
integrated H\alpha\ flux, and the reddening to the PN. From these quantities,
an intrinsic radius is calculated, which when combined with the angular size,
yields the distance directly. Furthermore, we have found that optically thick
PNe tend to populate the upper bound of the trend, while optically-thin PNe
fall along the lower boundary in the S-r plane. This enables sub-trends to be
developed which offer even better precision in the determination of distances,
as good as 18 per cent in the case of optically-thin, high-excitation PNe. This
is significantly better than any previous statistical indicator. We use this
technique to create a catalogue of statistical distances for over 1100 Galactic
PNe, the largest such compilation in the literature to date. Finally, in an
appendix, we investigate both a set of transitional PNe and a range of PN
mimics in the S-r plane, to demonstrate its use as a diagnostic tool.
Interestingly, stellar ejecta around massive stars plot on a tight locus in S-r
space with the potential to act as a separate distance indicator for these
objects.Comment: 49 pages, 17 tables, 8 figures. Published in MNRAS; supplementary
tables are included at end of this manuscrip
Planetary nebulae and their mimics: the MASH-MEN Project
The total number of true, likely and possible planetary nebulae (PN) now
known in the Milky Way is about 3000, approximately twice the number known a
decade ago. The new discoveries are a legacy of the recent availability of
wide-field, narrowband imaging surveys, primarily in the light of H-alpha. The
two most important are the AAO/UKST SuperCOSMOS H-alpha survey - SHS and the
Isaac Newton photometric H-alpha survey - IPHAS, which are responsible for most
of the new discoveries. A serious problem with previous PN catalogues is that
several different kinds of astrophysical objects are able to mimic PN in some
of their observed properties leading to significant contamination. These
objects include H II regions and Stromgren zones around young O/B stars,
reflection nebulae, Wolf-Rayet ejecta, supernova remnants, Herbig-Haro objects,
young stellar objects, B[e] stars, symbiotic stars and outflows, late-type
stars, cataclysmic variables, low redshift emission-line galaxies, and even
image/detector flaws. PN catalogues such as the Macquarie/AAO/Strasbourg
H-alpha Planetary Nebula catalogue (MASH) have been carefully vetted to remove
these mimics using the wealth of new wide-field multi-wavelength data and our
100% follow-up spectroscopy to produce a compilation of new PN discoveries of
high purity. During this process significant numbers of PN mimics have been
identified. The aim of this project is to compile these MASH rejects into a
catalogue of Miscellaneous Emission Nebulae (MEN) and to highlight the most
unusual and interesting examples. A new global analysis of these MEN objects is
underway before publishing the MEN catalogue online categorizing objects by
type together with their spectra and multi-wavelength images.Comment: 2 pages, IAU 283: An Eye To The Future proceeding
Photoionization models of the Eskimo nebula: evidence for a binary central star?
The ionizing star of the planetary nebula NGC 2392 is too cool to explain the
high excitation of the nebular shell, and an additional ionizing source is
necessary. We use photoionization modeling to estimate the temperature and
luminosity of the putative companion. Our results show it is likely to be a
very hot (Teff ~ 250kK), dense white dwarf. If the stars form a close binary,
they may merge within a Hubble time, possibly producing a Type Ia supernova.Comment: 2 pages, 1 figure, presented at the IAU Symposium 282 "From
Interacting Binaries to Exoplanets: Essential Modeling Tools", Tatransk\'a
Lomnica, Slovakia, 201
Binary Central Stars of Planetary Nebulae Discovered Through Photometric Variability. III. The Central Star of Abell 65
A growing number of close binary stars are being discovered among central stars of planetary nebulae. Recent and ongoing surveys are finding new systems and contributing to our knowledge of the evolution of close binary systems. The push to find more systems was largely based on early discoveries which suggested that 10%–15% of all central stars are close binaries. One goal of this series of papers is confirmation and classification of these systems as close binaries and determination of binary system parameters. Here we provide time-resolved multi-wavelength photometry of the central star of Abell 65 as well as further analysis of the nebula and discussion of possible binary–nebula connections. Our results for Abell 65 confirm recent work showing that it has a close, cool binary companion, though several of our model parameters disagree with the recently published values. With our longer time baseline of photometric observations from 1989 to 2009 we also provide a more precise orbital period of 1.0037577 days
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
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