249 research outputs found
Observations of red-giant variable stars by Aboriginal Australians
Aboriginal Australians carefully observe the properties and positions of
stars, including both overt and subtle changes in their brightness, for
subsistence and social application. These observations are encoded in oral
tradition. I examine two Aboriginal oral traditions from South Australia that
describe the periodic changing brightness in three pulsating, red-giant
variable stars: Betelgeuse (Alpha Orionis), Aldebaran (Alpha Tauri), and
Antares (Alpha Scorpii). The Australian Aboriginal accounts stand as the only
known descriptions of pulsating variable stars in any Indigenous oral tradition
in the world. Researchers examining these oral traditions over the last
century, including anthropologists and astronomers, missed the description of
these stars as being variable in nature as the ethnographic record contained
several misidentifications of stars and celestial objects. Arguably,
ethnographers working on Indigenous Knowledge Systems should have academic
training in both the natural and social sciences.Comment: The Australian Journal of Anthropology (2018
Identification of the Red Supergiant Progenitor of Supernova 2005cs: Do the Progenitors of Type II-P Supernovae Have Low Mass?
The stars that end their lives as supernovae (SNe) have been directly
observed in only a handful of cases, due mainly to the extreme difficulty in
identifying them in images obtained prior to the SN explosions. Here we report
the identification of the progenitor for the recent Type II-plateau
(core-collapse) SN 2005cs in pre-explosion archival images of the Whirlpool
Galaxy (M51) obtained with the Hubble Space Telescope (HST) Advanced Camera for
Surveys (ACS). From high-quality ground-based images of the SN from the
Canada-France-Hawaii Telescope, we precisely determine the position of the SN
and are able to isolate the SN progenitor to within 0".04 in the HST/ACS
optical images. We further pinpoint the SN location to within 0".005 from
HST/ACS ultraviolet images of the SN, confirming our progenitor identification.
From photometry of the SN progenitor obtained with the pre-SN ACS images, and
also limits to its brightness in pre-SN HST/NICMOS images, we infer that the
progenitor is a red supergiant star of spectral type K0--M3, with initial mass
7--9 Msun. We also discuss the implications of the SN 2005cs progenitor
identification and its mass estimate. There is an emerging trend that the most
common Type II-plateau SNe originate from low-mass supergiants 8--15 Msun.Comment: Submitted to ApJ. A high resolution version can be found at
http://astron.berkeley.edu/~weidong/sn05cs.p
DDO 216-A1: A Central Globular Cluster in a Low-luminosity Transition-type Galaxy
United States. National Aeronautics and Space Administration (HST GO-13768)United States. National Aeronautics and Space Administration (AST-1517226)United States. National Aeronautics and Space Administration (HST-AR-12836)United States. National Aeronautics and Space Administration (HST-AR-13888)United States. National Aeronautics and Space Administration (HST-AR-13896
Stellar Metallicities and Kinematics in a Gas-Rich Dwarf Galaxy: First Calcium Triplet Spectroscopy of RGB Stars in WLM
We present the first determination of the radial velocities and metallicities
of 78 red giant stars in the isolated dwarf irregular galaxy WLM. Observations
of the calcium II triplet in these stars were made with FORS2 at the VLT-UT2 in
two separated fields of view in WLM, and the [Fe/H] values were conformed to
the Carretta & Gratton (1997) metallicity scale. The mean metallicity is
= -1.27 +/- 0.04 dex, with a standard deviation of 0.37. We find that
the stars in the inner field are more metal rich by [Fe/H] =0.30 +/- 0.06 dex.
These results are in agreement with previous photometric studies that found a
radial population gradient, as well as the expectation of higher metallicities
in the central star forming regions. Age estimates using Victoria-Regina
stellar models show that the youngest stars in the sample (< 6 Gyr) are more
metal rich by [Fe/H] = 0.32 +/- 0.08 dex. These stars also show a lower
velocity dispersion at all elliptical radii compared to the metal-poor stars.
Kinematics for the whole red giant sample suggest a velocity gradient
approximately half that of the gas rotation curve, with the stellar component
occupying a thicker disk decoupled from the HI rotation plane. Taken together,
the kinematics, metallicities, and ages in our sample suggest a young
metal-rich, and kinematically cold stellar population in the central gas-rich
regions of WLM, surrounded by a separate dynamically hot halo of older, metal
poor stars.Comment: 10 pages, 12 figures, 5 tables. Accepted for publication in the Ap
Star formation at the edge of the Local Group: a rising star formation history in the isolated galaxy WLM
We present the star formation history (SFH) of the isolated (D~970 kpc) Local
Group dwarf galaxy WLM measured from color-magnitude diagrams constructed from
deep Hubble Space Telescope imaging. Our observations include a central (0.5
) and outer field (0.7 ) that reach below the oldest main sequence
turnoff. WLM has no early dominant episode of star formation: 20% of its
stellar mass formed by ~12.5 Gyr ago (z~5). It also has an SFR that rises to
the present with 50% of the stellar mass within the most recent 5 Gyr (z<0.7).
There is evidence of a strong age gradient: the mean age of the outer field is
5 Gyr older than the inner field despite being only 0.4 kpc apart. Some models
suggest such steep gradients are associated with strong stellar feedback and
dark matter core creation. The SFHs of real isolated dwarf galaxies and those
from the the Feedback In Realistic Environment suite are in good agreement for
, but in worse agreement at lower
masses (). These differences may be
explainable by systematics in the models (e.g., reionization model) and/or
observations (HST field placement). We suggest that a coordinated effort to get
deep CMDs between HST/JWST (crowded central fields) and WFIRST (wide-area halo
coverage) is the optimal path for measuring global SFHs of isolated dwarf
galaxies.Comment: 13 pages, 13 Figures, 4 Tables. Re-submitted to MNRAS after
addressing the referee's comment
The increasing importance of sustainability for building ownership
Purpose — This study seeks to investigate the degree to which energy efficiency is incorporated into office building refurbishment and capital expenditure with the emphasis placed on a cost-benefit analysis from the owner’s perspective. Design/methodology/approach – In order to develop a research framework, a thorough literature review was conducted of three disciplines being construction technology, building refurbishment and property management. The study identifies differences between varying levels of capital expenditure to ensure an existing building is more energy efficient, with the emphasis placed on the cost of implementation and the potential for tenants to acknowledge the increased energy efficiency via higher rents. Findings – Office buildings have been identified as a contributor to global warming during the construction phase, however during the building lifecycle there is a greater contribution to CO2 omissions. Whilst various building designs and construction techniques have evolved to improve energy efficiency, the focus has largely been placed on new buildings where it is easier to incorporate change and innovative approaches. However, the proportion of new buildings constructed each year is relatively small in comparison to existing building stock, which requires regular capital expenditure to maintain and attract new tenants within a competitive marketplace. Practical implications – The increasing importance of energy efficiency affects the office market in a variety of different ways. Originality/value – This paper identifies important links between the environment and the built environment, and the implications for office building owners
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