28 research outputs found
Fast algorithms for matching CCD images to a stellar catalogue
Two new algorithms are described for matching two dimensional coordinate
lists of point sources that are signifcantly faster than previous methods. By
matching rarely occurring triangles (or more complex shapes) in the two lists,
and by ordering searches by decreasing probability of success, it is
demonstrated that very few candidates need be considered to find a successful
match. Moreover, by immediately testing the suitability of a potential match
using an efficient mechanism, the need to process the entire candidate set is
avoided, yielding considerable performance improvements. Triangles are
described by a cosine metric that reduces the density of triangle space,
permitting efficient searches. An alternative shape characterization method
that reduces computational overhead in the construction phase is discussed. The
algorithms are tested on a set of 10 063 wide-field survey images, with
fields-of-view up to 4.8 x 3.6 deg, successfully matching 100% of the images in
a mean elapsed time of 6 ms (2.4 GHz Athlon CPU). The elapsed time of the
searching phase is shown to vary by less than 1 ms for list sizes between 10
and 200 points, demonstrating that fast, robust searches may be completed in
nearly constant time, independent of list size.Comment: Accepted for publication in Publications of the Astronomical Society
of Australi
Learning space attributes: reflections on academic library design and its use
Even though students are not using the print collection, they still choose to go to the library for academic pursuits. The continuing preferences of students for library space can be examined in the light of a hierarchy of needs made up of layers of access and linkages, of uses and activities, of sociability, and of comfort and image. A space which combines attributes from all four levels is an ideal learning space
Long-term photometry and periods for 261 nearby pulsating M giants
We present the results of a 5.5-year CCD photometric campaign that monitored
261 bright, southern, semi-regular variables with relatively precise Hipparcos
parallaxes. The data are supplemented with independent photoelectric
observations of 34 of the brightest stars, including 11 that were not part of
the CCD survey, and a previously unpublished long time-series of VZ Cam.
Pulsation periods and amplitudes are established for 247 of these stars, the
majority of which have not been determined before. All M giants with sufficient
observations for period determination are found to be variable, with 87% of the
sample (at S/N >= 7.5) exhibiting multi-periodic behaviour. The period ratios
of local SRVs are in excellent agreement with those in the Large Magellanic
Cloud. Apparent K-band magnitudes are extracted from multiple NIR catalogues
and analysed to determine the most reliable values. We review the effects of
interstellar and circumstellar extinction and calculate absolute K-band
magnitudes using revised Hipparcos parallaxes.Comment: 18 pages, 15 figures; accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Period-luminosity relations of pulsating M giants in the solar neighbourhood and the Magellanic Clouds
We analyse the results of a 5.5-yr photometric campaign that monitored 247
southern, semi-regular variables with relatively precise Hipparcos parallaxes
to demonstrate an unambiguous detection of Red Giant Branch (RGB) pulsations in
the solar neighbourhood. We show that Sequence A' contains a mixture of AGB and
RGB stars, as indicated by a temperature related shift at the TRGB. Large
Magellanic Cloud (LMC) and Galactic sequences are compared in several ways to
show that the P-L sequence zero-points have a negligible metallicity
dependence. We describe a new method to determine absolute magnitudes from
pulsation periods and calibrate the LMC distance modulus using Hipparcos
parallaxes to find \mu (LMC) = 18.54 +- 0.03 mag. Several sources of systematic
error are discussed to explain discrepancies between the MACHO and OGLE
sequences in the LMC. We derive a relative distance modulus of the Small
Magellanic Cloud (SMC) relative to the LMC of \Delta \mu = 0.41 +- 0.02 mag. A
comparison of other pulsation properties, including period-amplitude and
luminosity-amplitude relations, confirms that RGB pulsation properties are
consistent and universal, indicating that the RGB sequences are suitable as
high-precision distance indicators. The M giants with the shortest periods
bridge the gap between G and K giant solar-like oscillations and M-giant
pulsation, revealing a smooth continuity as we ascend the giant branch.Comment: 12 pages, 17 figures, 1 table. Accepted for publication in MNRA
The Large Magellanic Cloud and the Distance Scale
The Magellanic Clouds, especially the Large Magellanic Cloud, are places
where multiple distance indicators can be compared with each other in a
straight-forward manner at considerable precision. We here review the distances
derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing
Binaries, and show that the results from these distance indicators generally
agree to within their errors, and the distance modulus to the Large Magellanic
Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding
to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing
the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science.
From a presentation at the conference The Fundamental Cosmic Distance Scale:
State of the Art and the Gaia Perspective, Naples, May 201