Bibcode
DOI
Rosenberg, A.; Saviane, I.; Piotto, G.; Aparicio, A.; Zaggia, S. R.
Bibliographical reference
Astronomical Journal, vol. 115, p. 648
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2
1998
Journal
Citations
56
Refereed citations
48
Description
Deep V and I CCD images of the loosely populated Galactic globular
cluster Pal 1 and the surrounding field have been obtained with the
Isaac Newton Telescope. A color-magnitude diagram (CMD) down to V(lim)
24 and a luminosity function down to V(lim) = 23.25 have been
constructed. Adopting a reddening E(V - I) = 0.20 +/- 0.04 and comparing
the CMD of Pal 1 with that of 47 Tucanae, we obtain a distance modulus
(m - M)0 = 15.25 +/- 0.25, indicating that Pal 1 is located 3.7 +/- 0.4
kpc above the Galactic disk and 17.3 +/- 1.6 kpc from the Galactic
center. Comparison with 47 Tuc and M71 shows that Pal 1 must be
significantly younger. The best-fitting isochrones, as listed by
Bertelli et al. (1994), yield an age between 6.3 and 8 Gyr, which would
make Pal 1 the youngest Galactic globular cluster identified thus far,
casting some doubt on the real nature of this object. The luminosity
function shows some evidence of mass segregation, consistent with the
very short relaxation time. The global mass function can be fitted with
a power law of slope x = -1.4 +/- 0.7. This mass function is anomalously
flat, suggesting either a strong dynamical evolution or an initial mass
function significantly different from most other halo globular clusters.
A discussion of the possible nature of Pal 1 is presented.