1,814 research outputs found
New low-mass members of the Octans stellar association and an updated 30-40 Myr lithium age
The Octans association is one of several young stellar moving groups recently
discovered in the Solar neighbourhood, and hence a valuable laboratory for
studies of stellar, circumstellar disc and planetary evolution. However, a lack
of low-mass members or any members with trigonometric parallaxes means the age,
distance and space motion of the group are poorly constrained. To better
determine its membership and age, we present the first spectroscopic survey for
new K and M-type Octans members, resulting in the discovery of 29 UV-bright
K5-M4 stars with kinematics, photometry and distances consistent with existing
members. Nine new members possess strong Li I absorption, which allow us to
estimate a lithium age of 30-40 Myr, similar to that of the Tucana-Horologium
association and bracketed by the firm lithium depletion boundary ages of the
Beta Pictoris (20 Myr) and Argus/IC 2391 (50 Myr) associations. Several stars
also show hints in our medium-resolution spectra of fast rotation or
spectroscopic binarity. More so than other nearby associations, Octans is much
larger than its age and internal velocity dispersion imply. It may be the
dispersing remnant of a sparse, extended structure which includes some younger
members of the foreground Octans-Near association recently proposed by
Zuckerman and collaborators.Comment: Accepted for publication in MNRAS (16 pages, 5 tables
The effects of climate change and variation in New Zealand: An assessment using the CLIMPACTS system
Along with a need to better understand the climate and biophysical systems of New Zealand, the need to develop an improved capacity for evaluating possible changes in climate and their effects on the New Zealand environment has been recognised. Since the middle of 1993 the CLIMPACTS programme, has been focused on the development of such a capacity, in the first instance for the agricultural sector. the goals of this present assessment are:
1. To present current knowledge on likely scenarios of climate change and associated uncertainties in New Zealand;
2. To present current knowledge, based on quantitative analyses using a consistent set of scenarios, on the likely effects of climate change on a range of agricultural and horticultural crops of economic importance;
3. To demonstrate, by way of this report and the associated technical report, the capacity that has been developed for ongoing assessments of this kind in New Zealand. This report has been prepared for both the science and policy communities in New Zealand. There are two main components:
1. The detailed findings of the assessment, presented in a series of chapters;
2. An annex, which contains technical details on models used in the assessment
New members of the TW Hydrae Association and two accreting M-dwarfs in Scorpius-Centaurus
We report the serendipitous discovery of several young mid-M stars found
during a search for new members of the 30-40 Myr-old Octans Association. Only
one of the stars may be considered a possible Octans(-Near) member. However,
two stars have proper motions, kinematic distances, radial velocities,
photometry and Li I 6708AA measurements consistent with membership in the 8-10
Myr-old TW Hydrae Association. Another may be an outlying member of TW Hydrae
but has a velocity similar to that predicted by membership in Octans. We also
identify two new lithium-rich members of the neighbouring Scorpius-Centaurus OB
Association (Sco-Cen). Both exhibit large 12 and 22 micron excesses and strong,
variable H-alpha emission which we attribute to accretion from circumstellar
discs. Such stars are thought to be incredibly rare at the ~16 Myr median age
of Sco-Cen and they join only one other confirmed M-type and three higher-mass
accretors outside of Upper Scorpius. The serendipitous discovery of two
accreting stars hosting large quantities of circumstellar material may be
indicative of a sizeable age spread in Sco-Cen, or further evidence that disc
dispersal and planet formation time-scales are longer around lower-mass stars.
To aid future studies of Sco-Cen we also provide a newly-compiled catalogue of
305 early-type Hipparcos members with spectroscopic radial velocities sourced
from the literature.Comment: 12 pages. Accepted for publication in MNRA
Development of 2 underseat energy absorbers for application to crashworthy passenger seats for general aviation aircraft
This report presents the methodology and results of a program conducted to develop two underseat energy absorber (E/A) concepts for application to nonadjustable crashworthy passenger seats for general aviation aircraft. One concept utilizes an inflated air bag, and the other, a convoluted sheet metal bellows. Prototypes of both were designed, built, and tested. Both concepts demonstrated the necessary features of an energy absorber (load-limiter); however, the air bag concept is particularly encouraging because of its light weight. Several seat frame concepts also were investigated as a means of resisting longitudinal and lateral loads and of guiding the primary vertical stroke of the underseat energy absorber. Further development of a seat system design using the underseat energy absorbers is recommended because they provide greatly enhanced crash survivability as compared with existing general aviation aircraft seats
Luminosity Distributions within Rich Clusters - III: A comparative study of seven Abell/ACO clusters
We recover the luminosity distributions over a wide range of absolute
magnitude (-24.5 < M_{R} < -16.5) for a sample of seven rich southern galaxy
clusters. We find a large variation in the ratio of dwarf to giant galaxies,
DGR: 0.8\le \le 3.1. This variation is shown to be inconsistent with a
ubiquitous cluster luminosity function. The DGR shows a smaller variation from
cluster to cluster in the inner regions (r \ls 0.56 Mpc). Outside these regions
we find the DGR to be strongly anti-correlated with the mean local projected
galaxy density with the DGR increasing towards lower densities. In addition the
DGR in the outer regions shows some correlation with Bautz-Morgan type. Radial
analysis of the clusters indicate that the dwarf galaxies are less centrally
clustered than the giants and form a significant halo around clusters. We
conclude that measurements of the total cluster luminosity distribution based
on the inner core alone are likely to be severe underestimates of the dwarf
component, the integrated cluster luminosity and the contribution of galaxy
masses to the cluster's total mass. Further work is required to quantify this.
The observational evidence that the unrelaxed, lower density outer regions of
clusters are dwarf-rich, adds credence to the recent evidence and conjecture
that the field is a predominantly dwarf rich environment and that the dwarf
galaxies are under-represented in measures of the local field luminosity
function.Comment: 31 pages including 11 figures. Also available from
http://star-www.st-and.ac.uk/~spd3/bib.htm
First detection of a low-mass stellar halo around the young open cluster Eta Chamaeleontis
We have identified several lithium-rich low-mass (0.08<M<0.3 Msun) stars
within 5.5 deg of the young open cluster Eta Chamaeleontis, nearly four times
the radius of previous search efforts. Of these stars we propose 4 new probable
cluster members, and 3 possible members requiring further investigation. These
findings are consistent with a dynamical origin for the current configuration
of the cluster, without the need to invoke an abnormal Initial Mass Function
deficient in low-mass objects. Candidates were selected on the basis of DENIS
and 2MASS photometry, NOMAD astrometry and extensive follow-up spectroscopy.Comment: 5 Pages. 5 Figures and 1 Table. Accepted for publication in MNRAS
Letters. Higher resolution figures available at
http://www.mso.anu.edu.au/~murphysj/
National Application of Sustainability Indicators for Australian Fisheries Part 2: Ecosystem based frameworks for aquaculture, multi-fishery and international applications FRDC Report – Project 2000/145
Objectives: 1. Develop initial ESD reporting framework for the Aquaculture Sector 2. Initiate development of an ESD Framework for Cross Fishery and Marine Planning issues 3. Further refine and promote the international adoption of the concepts developed by the ESD national framework for wild capture fisherie
Spatially Resolved Spectroscopy of Starburst and Post-Starburst Galaxies in The Rich z~0.55 Cluster CL0016+16
We have used the Low Resolution Imaging Spectrograph (LRIS) on the W.M. Keck
I telescope to obtain spatially resolved spectroscopy of a small sample of six
post-starburst and three dusty-starburst galaxies in the rich cluster CL0016+16
at z=0.55. We use this to measure radial profiles of the Hdelta and OII3727
lines which are diagnostic probes of the mechanisms that give rise to the
abrupt changes in star-formation rates in these galaxies. In the post-starburst
sample we are unable to detect any radial gradients in the Hdelta line
equivalent width - although one galaxy exhibits a gradient from one side of the
galaxy to the other. The absence of Hdelta gradients in these galaxies is
consistent with their production via interaction with the intra-cluster medium,
however, our limited spatial sampling prevents us from drawing robust
conclusions. All members of the sample have early type morphologies, typical of
post-starburst galaxies in general, but lack the high incidence of tidal tails
and disturbances seen in local field samples. This argues against a merger
origin and adds weight to a scenario where truncation by the intra-cluster
medium is at work. The post-starburst spectral signature is consistent over the
radial extent probed with no evidence of OII3727 emission and strong Hdelta
absorption at all radii i.e. the post-starburst classification is not an
aperture effect. In contrast the dusty-starburst sample shows a tendency for a
central concentration of OII3727 emission. This is most straightforwardly
interpreted as the consequence of a central starburst. However, other
possibilities exist such as a non-uniform dust distribution (which is expected
in such galaxies) and/or a non-uniform starburst age distribution. The sample
exhibit late type and irregular morphologies.Comment: accepted for publication in PAS
Luminosity Distributions within Rich Clusters - II: Demonstration and Verification via Simulation
We present detailed simulations of long exposure CCD images. The simulations
are used to explore the validity of the statistical method for reconstructing
the luminosity distribution of galaxies within a rich cluster i.e. by the
subtraction of field number-counts from those of a sight-line through the
cluster. In particular we use the simulations to establish the reliability of
our observational data presented in Paper 3. Based on our intended CCD
field-of-view (6.5 by 6.5 arcmins) and a 1-sigma detection limit of 26 mags per
sq arcsecond, we conclude that the luminosity distribution can be robustly
determined over a wide range of absolute magnitude (-23 < M_{R} < -16)
provided:
(a) the cluster has an Abell richness 1.5 or greater,
(b) the cluster's redshift lies in the range 0.1 < z < 0.3,
(c) the seeing is better than FWHM 1.25'' and
(d) the photometric zero points are accurate to within Delta m = \pm 0.12.
If these conditions are not met then the recovered luminosity distribution is
unreliable and potentially grossly miss-leading. Finally although the method
clearly has limitations, within these limitations the technique represents an
extremely promising probe of galaxy evolution and environmental dependencies.Comment: 24 pages, 8 figures accepted for publication in MNRAS also available
from http://star-www.st-and.ac.uk/~spd3/bib.htm
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