583 research outputs found
Asymptotic Giant Branch Variables in the Galaxy and the Local Group
AGB variables, particularly the large amplitude Mira type, are a vital step
on the distance scale ladder. They will prove particularly important in the era
of space telescopes and extremely large ground-based telescopes with adaptive
optics, which will be optimized for infrared observing. Our current
understanding of the distances to these stars is reviewed with particular
emphasis on improvements that came from Hipparcos as well as on recent work on
Local Group galaxies. In addition to providing the essential calibration for
extragalactic distances Gaia may also provide unprecedented insight into the
poorly understood mass-loss process itself.Comment: Accepted for publication in Astrophysics and Space Science. From a
presentation at the conference "The Fundamental Cosmic Distance Scale: State
of the Art and Gaia Perspective, Naples May 2011. 8 Pages, 9 Figure
Resolved Stellar Populations at the Distance of Virgo
Top of the wish list of any astronomer who wants to understand galaxy
formation and evolution is to resolve the stellar populations of a sample of
giant elliptical galaxies: to take spectra of the stars and make
Colour-Magnitude Diagrams going down to the oldest main sequence turn-offs. It
is only by measuring the relative numbers of stars on Main Sequence Turnoffs at
ages ranging back to the time of the earliest star formation in the Universe
that we can obtain unambiguous star formation histories. Understanding star
formation histories of individual galaxies underpins all our theories of galaxy
formation and evolution. To date we only have detailed star formation histories
for the nearest-by objects in the Local Group, namely galaxies within 700kpc of
our own. This means predominantly small diffuse dwarf galaxies in a poor group
environment. To sample the full range of galaxy types and to consider galaxies
in a high density environment (where much mass in the Universe resides) we need
to be able to resolve stars at the distance of the Virgo (~17Mpc) or Fornax
(~18Mpc) clusters. This ambitious goal requires an Extremely Large Telescope
(ELT), with a diameter of 50-150m, operating in the optical/near-IR at its
diffraction limit.Comment: proceedings IAU 232 "Extremely Large Telescopes", eds Whitelock,
Leibundgut and Dennefel
The APM Survey for Cool Carbon Stars in the Galactic Halo - II The Search for Dwarf Carbon Stars
We present proper motion measurements for carbon stars found during the APM
Survey for Cool Carbon Stars in the Galactic Halo (Totten & Irwin, 1998).
Measurements are obtained using a combination of POSSI, POSSII and UKST survey
plates supplemented where necessary by CCD frames taken at the Isaac Newton
Telescope. We find no significant proper motion for any of the new APM
colour-selected carbon stars and so conclude that there are no dwarf carbon
stars present within this sample. We also present proper motion measurements
for three previously known dwarf carbon stars and demonstrate that these
measurements agree favourably with those previously quoted in the literature,
verifying our method of determining proper motions. Results from a
complimentary program of JHK photometry obtained at the South African
Astronomical Observatory are also presented. Dwarf carbon stars are believed to
have anomalous near-infrared colours, and this feature is used for further
investigation of the nature of the APM carbon stars. Our results support the
use of JHK photomtery as a dwarf/giant discriminator and also reinforce the
conclusion that none of the new APM-selected carbon stars are dwarfs. Finally,
proper motion measurements combined with extant JHK photometry are presented
for a sample of previously known Halo carbon stars, suggesting that one of
these stars, CLS29, is likely to be a previously unrecognised dwarf carbon
star.Comment: 13 pages, 5 figures, accepted for publication in MNRAS, Also
available at http://www.astro.keele.ac.uk/~ejt/publications.htm
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