202 research outputs found
Origin and age of The Hillocks and implications for post‐glacial landscape development in the upper Lake Wakatipu catchment, New Zealand
Future demand: How could or should our transport system evolve in order to support mobility in the future?
New Zealand’s land transport programme has a current expenditure target for the next ten years of 10bn to change the shape of the road network and improve its quality and capacity. Yet such investment plans are in the face of a country, like several others, that has experienced a decade-long interruption to a long-run trend of growth in car travel.The NZ Ministry of Transport in 2014 undertook a major piece of strategic work to address the following focal question. How could or should our transport system evolve in order to support mobility in the future? The work involved a number of elements but centred upon a scenario planning exercise. This involved a wide cross-section of expertise and stakeholders in the identification of key drivers of change and critical uncertainties for the future for a time horizon of 2042. Two key unknowns were explored: (i) what will society want to do in future? (uncertainty about whether people will be more inclined to connect physically or virtually); and what will society be able to afford to do? (uncertainty about the affordability of energy relative to other costs of living). Four plausible and divergent scenarios were developed for future transport and society in New Zealand. Alongside the narratives for these different worlds, a simple structural model was developed to estimate quantification of levels of car travel in 2042 for the different scenarios. This revealed that from 2014 to 2042, total car travel could range from a growth of 35% to a decline of 53%.The subsequent examination of the focal question above led to a series of insights and recommended responses for policymakers and other decision makers to consider. Three important principles emerged from the work:(1)It is access not mobility per se that is key to a thriving New Zealand. There are uncertainties over what make-up of access will be desirable and affordable in future.(2)There is a need to ensure a resilient provision of access options that provides for adaptability of behaviour over time. This means a combined and coordinated effort to evolve and improve roading and proximity and digital communications.(3)The transport system’s nature and scale partly determine the demand placed upon it. Therefore when evolving the transport system one should have in mind providing for demand believed to be appropriate (and feasible) rather than providing for the demand that it may be tempting to predict
Assessing debris flows using LIDAR differencing: 18 May 2005 Matata event, New Zealand
The town of Matata in the Eastern Bay of Plenty (New Zealand) experienced an extreme rainfall event on the 18 May 2005. This event triggered widespread landslips and large debris flows in the Awatarariki and Waitepuru catchments behind Matata. The Light Detection and Ranging technology (LIDAR) data sets flown prior to and following this event have been differenced and used in conjunction with a detailed field study to identify the distribution of debris and major sediment pathways which, from the Awatarariki catchment, transported at least 350,000 ± 50,000 m3 of debris. Debris flows were initially confined to stream valleys and controlled by the density and hydraulic thrust of the currents, before emerging onto the Awatarariki debris fan where a complex system of unconfined sediment pathways developed. Here, large boulders, clasts, logs and entire homes were deposited as the flows decelerated. Downstream from the debris fan, the pre-existing coastal foredune topography played a significant role in deflecting the more dilute currents that in filled lagoonal swale systems in both directions. The differenced LIDAR data have revealed several sectors characterised by significant variation in clast size, thickness and volume of debris as well as areas where post-debris flow cleanup and grading operations have resulted in man-made levees, sediment dumps, scoured channels and substantial graded areas. The application of differenced LIDAR data to a debris flow event demonstrates the techniques potential as a precise and powerful tool for hazard mapping and assessment
Abundances in intermediate-mass AGB stars undergoing third dredge-up and hot-bottom burning
High dispersion near-infrared spectra have been taken of seven
highly-evolved, variable, intermediate-mass (4-6 Msun) AGB stars in the LMC and
SMC in order to look for C, N and O variations that are expected to arise from
third dredge-up and hot-bottom burning. The pulsation of the objects has been
modelled, yielding stellar masses, and spectral synthesis calculations have
been performed in order to derive abundances from the observed spectra. For two
stars, abundances of C, N, O, Na, Al, Ti, Sc and Fe were derived and compared
with the abundances predicted by detailed AGB models. Both stars show very
large N enhancements and C deficiencies. These results provide the first
observational confirmation of the long-predicted production of primary nitrogen
by the combination of third dredge-up and hot-bottom burning in
intermediate-mass AGB stars. It was not possible to derive abundances for the
remaining five stars: three were too cool to model, while another two had
strong shocks in their atmospheres which caused strong emission to fill the
line cores and made abundance determination impossible. The latter occurrence
allows us to predict the pulsation phase interval during which observations
should be made if successful abundance analysis is to be possible.Comment: Accepted for publication in MNRA
Abundance analysis for long period variables. Velocity effects studied with O-rich dynamic model atmospheres
(abbreviated) Measuring the surface abundances of AGB stars is an important
tool for studying the effects of nucleosynthesis and mixing in the interior of
low- to intermediate mass stars during their final evolutionary phases. The
atmospheres of AGB stars can be strongly affected by stellar pulsation and the
development of a stellar wind, though, and the abundance determination of these
objects should therefore be based on dynamic model atmospheres. We investigate
the effects of stellar pulsation and mass loss on the appearance of selected
spectral features (line profiles, line intensities) and on the derived
elemental abundances by performing a systematic comparison of hydrostatic and
dynamic model atmospheres. High-resolution synthetic spectra in the near
infrared range were calculated based on two dynamic model atmospheres (at
various phases during the pulsation cycle) as well as a grid of hydrostatic
COMARCS models. Equivalent widths of a selection of atomic and molecular lines
were derived in both cases and compared with each other. In the case of the
dynamic models, the equivalent widths of all investigated features vary over
the pulsation cycle. A consistent reproduction of the derived variations with a
set of hydrostatic models is not possible, but several individual phases and
spectral features can be reproduced well with the help of specific hydrostatic
atmospheric models. In addition, we show that the variations in equivalent
width that we found on the basis of the adopted dynamic model atmospheres agree
qualitatively with observational results for the Mira R Cas over its light
cycle. The findings of our modelling form a starting point to deal with the
problem of abundance determination in strongly dynamic AGB stars (i.e.,
long-period variables).Comment: 13 pages, 22 figures, accepted for publication in A&
Prospects of Stellar Abundance Studies from Near-IR Spectra Observed with the E-ELT
In 2006 ESO Council authorized a Phase B study of a European AO-telescope
with a 42 m segmented primary with a 5-mirror design, the E-ELT. Several
reports and working groups have already presented science cases for an E-ELT,
specifically exploiting the new capabilities of such a large telescope. One of
the aims of the design has been to find a balance in the performances between
an E-ELT and the James Webb Space Telescope, JWST. Apart from the larger
photon-collecting area, the strengths of the former is the higher attainable
spatial and spectral resolutions. The E-ELT AO system will have an optimal
performance in the near-IR, which makes it specially advantageous.
High-resolution spectroscopy in the near-infrared has, however, not been
discussed much. This paper aims at filling that gap, by specifically discussing
spectroscopy of stellar (mainly red giant), photospheric abundances. Based on
studies in the literature of stellar abundances, at the needed medium to high
spectral resolutions in the near-infrared (0.8-2.4 microns), I will try to
extrapolate published results to the performance of the E-ELT and explore what
could be done at the E-ELT in this field. A discussion on what instrument
characteristics that would be needed for stellar abundance analyses in the
near-IR will be given.Comment: Accepted for publication in Astronomische Nachrichten, A
Low-temperature gas opacity - AESOPUS: a versatile and quick computational tool
We introduce a new tool - AESOPUS: Accurate Equation of State and OPacity
Utility Software - for computing the equation of state and the Rosseland mean
(RM) opacities of matter in the ideal gas phase. Results are given as a
function of one pair of state variables, (i.e. temperature T in the range 3.2
<= log(T) <= 4.5, and parameter R= rho/(T/10^6 K)^3 in the range -8 <= log(R)
<= 1), and arbitrary chemical mixture. The chemistry is presently solved for
about 800 species, consisting of almost 300 atomic and 500 molecular species.
The gas opacities account for many continuum and discrete sources, including
atomic opacities, molecular absorption bands, and collision-induced absorption.
Several tests made on AESOPUS have proved that the new opacity tool is accurate
in the results,flexible in the management of the input prescriptions, and agile
in terms of computational time requirement. We set up a web-interface
(http://stev.oapd.inaf.it/aesopus) which enables the user to compute and
shortly retrieve RM opacity tables according to his/her specific needs,
allowing a full degree of freedom in specifying the chemical composition of the
gas. Useful applications may regard RM opacities of gas mixtures with i)
scaled-solar abundances of metals, choosing among various solar mixture
compilations available in the literature; ii) varying CNO abundances, suitable
for evolutionary models of red and asymptotic giant branch stars and massive
stars in the Wolf-Rayet stages; iii) various degrees of enhancement in
alpha-elements, and C-N, Na-O and Mg-Al abundance anti-correlations, necessary
to properly describe the properties of stars in early-type galaxies and
Galactic globular clusters; iv) zero-metal abundances appropriate for studies
of gas opacity in primordial conditions.Comment: 32 pages, 34 postscript figures, A&A in press; new section 4.1.2
showing first tests with stellar models, sections 2.2, 2.2.2 and 5 expanded;
interactive web-page at http://stev.oapd.inaf.it/aesopu
The evolutionary state of Miras with changing pulsation periods
Context: Miras are long-period variables thought to be in the asymptotic
giant branch (AGB) phase of evolution. In about one percent of known Miras, the
pulsation period is changing. It has been speculated that this changing period
is the consequence of a recent thermal pulse in these stars. Aims: We aim to
clarify the evolutionary state of these stars, and to determine in particular
whether or not they are in the thermally-pulsing (TP-)AGB phase. Methods: One
important piece of information that has been neglected so far when determining
the evolutionary state is the presence of the radio-active s-process element
technetium (Tc). We obtained high-resolution, high signal-to-noise-ratio
optical spectra of a dozen prominent Mira variables with changing pulsation
period to search for this indicator of TPs and dredge-up. We also use the
spectra to measure lithium (Li) abundances. Furthermore, we establish the
evolutionary states of our sample stars by means of their present-day periods
and luminosities. Results: Among the twelve sample stars observed in this
programme, five were found to show absorption lines of Tc. BH Cru is found to
be a carbon-star, its period increase in the past decades possibly having
stopped by now. We report a possible switch in the pulsation mode of T UMi from
Mira-like to semi-regular variability in the past two years. R Nor, on the
other hand, is probably a fairly massive AGB star, which could be true for all
meandering Miras. Finally, we assign RU Vul to the metal-poor thick disk with
properties very similar to the short-period, metal-poor Miras. Conclusions: We
conclude that there is no clear correlation between period change class and Tc
presence. The stars that are most likely to have experienced a recent TP are BH
Cru and R Hya, although their rates of period change are quite different.Comment: 11 pages, 7 figures, 2 tables; accepted for publication in A&
The puzzling dredge-up pattern in NGC 1978
Low-mass stars are element factories that efficiently release their products
in the final stages of their evolution by means of stellar winds. Since they
are large in number, they contribute significantly to the cosmic matter cycle.
To assess this contribution quantitatively, it is crucial to obtain a detailed
picture of the stellar interior, particularly with regard to nucleosynthesis
and mixing mechanisms. We seek to benchmark stellar evolutionary models of
low-mass stars. In particular, we measure the surface abundance of ^{12}C in
thermally pulsing AGB stars with well-known mass and metallicity, which can be
used to infer information about the onset and efficiency of the third
dredge-up. We recorded high-resolution near-infrared spectra of AGB stars in
the LMC cluster NGC 1978. The sample comprised both oxygen-rich and carbon-rich
stars, and is well-constrained in terms of the stellar mass, metallicity, and
age. We derived the C/O and ^{12}C/^{13}C ratio from the target spectra by a
comparison to synthetic spectra. Then, we compared the outcomes of stellar
evolutionary models with our measurements. The M stars in NGC 1978 show values
of C/O and ^{12}C/^{13}C that can best be explained with moderate extra-mixing
on the RGB coupled to a moderate oxygen enhancement in the chemical
composition. These oxygen-rich stars do not seem to have undergone third
dredge-up episodes (yet). The C stars show carbon-to-oxygen and carbon isotopic
ratios consistent with the occurrence of the third dredge-up. We did not find S
stars in this cluster. None of the theoretical schemes that we considered was
able to reproduce the observations appropriately. Instead, we discuss some
non-standard scenarios to explain the puzzling abundance pattern in NGC 1978.Comment: 16 pages, 9 figures, 4 tables, accepted for publication in A&A,
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