807 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
Spitzer Observations of Large Amplitude Variables in the LMC and IC 1613
The 3.6 and 4.5 micron characteristics of AGB variables in the LMC and IC1613
are discussed. For C-rich Mira variables there is a very clear
period-luminosity-colour relation, where the [3.6]-[4.5] colour is associated
with the amount of circumstellar material and correlated with the pulsation
amplitude. The [4.5] period-luminosity relation for dusty stars is
approximately one mag brighter than for their naked counterparts with
comparable periods.Comment: 5 pages, 4 figures, to appear in Proceedings of "Wide-Field
Variability Surveys: A 21st Century Perspective
Asymptotic Giant Branch Stars in the Leo I Dwarf Spheroidal Galaxy
Twenty six Asymptotic Giant Branch (AGB) variables are identified in the
Local Group galaxy Leo I. These include 7 Mira and 5 semi-regular variables for
which periods, amplitudes and mean magnitudes are determined. The large range
of periods for the Miras, 158<P<523 days, suggests an AGB spanning a
significant age range. The youngest must be around 1.6 Gyr while the oldest
could be 10 Gyr or more. Two of these old Miras are found in the outer regions
of Leo I (over 490 arcsec from the centre) where stars on the extended AGB are
rare. They could provide an interesting test of third dredge-up and mass loss
in old stars with low metallicity and are worth further detailed investigation.
At least two stars, one a Mira, the other an irregular variable, are undergoing
obscuration events due to dust ejection.
An application of the Mira period-luminosity relation to these stars yields a
distance modulus for Leo I of (m-M)=21.80 \pm 0.11 mag (internal), \pm 0.12
(total) (on a scale that puts the LMC at 18.39 mag) in good agreement with
other determinations.Comment: 10 pages, 8 figures, accepted for publication in MNRAS
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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