Bibcode
DOI
Aparicio, Antonio; Carrera, Ricardo; Martínez-Delgado, David
Referencia bibliográfica
The Astronomical Journal, Volume 122, Issue 5, pp. 2524-2537.
Fecha de publicación:
11
2001
Número de citas
114
Número de citas referidas
101
Descripción
The photometric and morphological properties, as well as the star
formation history, of the Draco dwarf spheroidal galaxy are analyzed on
the basis of wide-field CCD photometry of the resolved stars covering
about 1 deg2. Draco is at a distance of d=80+/-7 kpc and has
a metallicity, [Fe/H], of -1.8+/-0.2. No metallicity gradient is
detected. The star surface density distribution can be fitted by a
single exponential law of scale length α=5.0′+/-0.1′.
The central surface magnitude is
μ''V''=24.4+/-0.5, and the core
radius is rc=7.5′+/-0.3′ (equivalent to
rc=175+/-7 pc). Within errors, the same scale lengths are
found for the density profiles along the semimajor and semiminor axes
(rescaled to semimajor-axis units, using the ellipticity of the galaxy)
of Draco. There are hence no evidences of a tidal tail associated with
Draco. The tidal radius of the galaxy is found to be
rt~=42' (~=1 kpc). The possibility that the large
mass-to-light relation in Draco could be accounted for by a convenient
spatial orientation is tested. An upper limit to Draco's size along the
line of sight is ~14 kpc. This is too small to account for the velocity
dispersion of Draco if it were due to projection effects only, and it
implies that other mechanisms (e.g., dark matter) are required. The
stellar population of Draco is mainly old. Although some
intermediate-age population is present in Draco, most of the star
formation (up to 90%) took place before ~10 Gyr ago. No significant star
formation activity is detected in the last ~2 Gyr. Two methods (partial
model and subgiant) have been used to investigate the star formation
history of Draco, both producing results in good qualitative agreement.
No difference is found between the scale lengths of the distributions of
old (>~9 Gyr) and young (~2-3 Gyr) stars, indicating either that both
populations were formed under the same kinematic conditions, or that any
initial difference was afterward erased.