111 research outputs found
The Tidal Tails of 47 Tucanae
The Galactic globular cluster 47 Tucanae (47 Tuc) shows a rare increase in
its velocity dispersion profile at large radii, indicative of energetic, yet
bound, stars at large radii dominating the velocity dispersion and,
potentially, of ongoing evaporation. Escaping stars will form tidal tails, as
seen with several Galactic globular clusters, however, the tidal tails of 47
Tuc are yet to be uncovered. We model these tails of 47 Tuc using the most
accurate input data available, with the specific aim of determining their
locations, as well as the densities of the epicyclic overdensities within the
tails. The overdensities from our models show an increase of 3-4% above the
Galactic background and, therefore, should be easily detectable using matched
filtering techniques. We find that the most influential parameter with regard
to both the locations and densities of the epicyclic overdensities is the
Heliocentric distance to the cluster. Hence, uncovering these tidal features
observationally will contribute greatly to the ongoing problem of determining
the distance to 47 Tuc, tightly constraining the distance of the cluster
independent of other methods. Using our streakline method for determining the
locations of the tidal tails and their overdensities, we show how, in
principle, the shape and extent of the tidal tails of any Galactic globular
cluster can be determined without resorting to computationally expensive N-body
simulations.Comment: Original paper has 10 pages, 10 figures and 2 tables. Please note
that this now includes an erratum. Erratum has 6 pages, 8 figures and 2
tables. Ignore the exclamation marks in Section 2 of the erratum, these are
an artifact of the LaTeX class file used to produce the manuscrip
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
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