10,457 research outputs found
Newly discovered halos and outer features around southern planetary nebulae
We have used the SuperCOSMOS H-alpha Survey to look for faint outer
structures such as halos, ansae and jets around known planetary nebulae across
4000 square degrees of the southern Milky Way. Our search will contribute to a
more accurate census of these features in the Galactic PN population. Candidate
common-envelope PNe have also been identified on the basis of their
microstructures. We also intend to determine more reliable distances for these
PNe, which should allow a much better statistical basis for the post-AGB total
mass budget. Our survey offers fresh scope to address this important issue.Comment: 2 pages, 1 figure. To be published in Planetary Nebulae: an Eye to
the Future, Proceedings of IAU Symposium 283, held in Puerto de la Cruz,
Tenerife, Spain, July 25-29 201
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
Household Expenditure and the Income Tax Rebates of 2001
Under the Economic Growth and Tax Relief Reconciliation Act of 2001, most U.S. taxpayers received a tax rebate between July and September, 2001. The week in which the rebate was mailed was based on the second-to-last digit of the taxpayer's Social Security number, a digit that is effectively randomly assigned. Using special questions about the rebates added to the Consumer Expenditure Survey, we exploit this historically unique experiment to measure the change in consumption expenditures caused by receipt of the rebate and to test the Permanent Income Hypothesis and related models. We find that households spent about 20-40 percent of their rebates on non-durable goods during the three-month period in which their rebates were received, and roughly another third of their rebates during the subsequent three-month period. The implied effects on aggregate consumption demand are significant. The estimated responses are largest for households with relatively low liquid wealth and low income, consistent with liquidity constraints.
The H surface brightness radius plane as a diagnostic tool for photoionized nebulae
The H surface brightness radius () relation is a robust
distance indicator for planetary nebulae (PNe), further enhanced by different
populations of PNe having distinct loci in space. Other types of
photoionized nebulae also plot in quite distinct regions in the plane,
allowing its use as a diagnostic tool. In particular, the nova shells and
massive star ejecta (MSE) plot on relatively tight loci illustrating their
evolutionary sequences. For the MSE, there is potential to develop a distance
indicator for these objects, based on their trend in space. As
high-resolution, narrowband surveys of the nearest galaxies become more
commonplace, the plane is a potentially useful diagnostic tool to help
identify the various ionized nebulae in these systems.Comment: 4 pages, 2 figures. To appear in the proceedings of the 11th Pacific
Rim Conference on Stellar Astrophysics: Physics and Chemistry of the Late
Stages of Stellar Evolution, held in Hong Kong, Dec 201
New light on Galactic post-asymptotic giant branch stars. I. First distance catalogue
We have commenced a detailed analysis of the known sample of Galactic
post-asymptotic giant branch (PAGB) objects compiled in the Toru\'n catalogue
of Szczerba et al., and present, for the first time, homogeneously derived
distance determinations for the 209 likely and 87 possible catalogued PAGB
stars from that compilation. Knowing distances are essential in determining
meaningful physical characteristics for these sources and this has been
difficult to determine for most objects previously. The distances were
determined by modelling their spectral energy distributions (SED) with multiple
black-body curves, and integrating under the overall fit to determine the total
distance-dependent flux. This method works because the luminosity of these
central stars is very nearly constant from the tip of the AGB phase to the
beginning of the white-dwarf cooling track. This then enables us to use a
standard-candle luminosity to estimate the SED distances. For Galactic thin
disk PAGB objects, we use three luminosity bins based on typical observational
characteristics, ranging between 3500 and 12000 L_sun. We further adopt a
default luminosity of 1700 L_sun for all halo PAGB objects. We have also
applied the above technique to a further sample of 69 related nebulae not in
the current edition of the Toru\'n catalogue. In a follow-up paper we will
estimate distances to the subset of RV Tauri variables using empirical
period-luminosity relations, and to the R\,CrB stars, allowing a population
comparison of these objects with the other subclasses of PAGB stars for the
first time.Comment: 24 pages, 8 tables, 4 figures. Submitted to MNRAS. Appendix B
containing full list of SED figures excluded in this versio
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