2,677 research outputs found
The Ages and Abundances of the M87 Globular Clusters
A subset of 150 globular clusters in M87 has been selected on the basis of
S/N ratio for abundance and age determinations from the sample of Paper I.
Indices measuring the strength of the strongest spectral features were
determined for the M87 GCs and from new data for twelve galactic GCs. Combining
the new and existing data for the galactic GCs and comparing the colors
and the line indices gives qualitative indications for the ages and abundances
of the GCs. Quantitative results are obtained by applying the Worthey (1994)
models for the integrated light of stellar systems of a single age, calibrated
by observations of galactic GCs, to deduce abundances and ages for the objects
in our sample.
We find that the M87 GCs span a wide range in metallicity, from very metal
poor to somewhat above solar metallicity. The mean [Fe/H] of -0.95 dex is
higher than that of the galactic GC system, and there is a metal rich tail that
reaches to higher [Fe/H] than one finds among the galactic GCs. The mean
metallicity of the M87 GC system is about a factor of four lower than that of
the M87 stellar halo at a fixed projected radius . The metallicity inferred
from the X-ray studies is similar to that of the M87 stellar halo, not to that
of GCs. We infer the relative abundances of Na, Mg, and Fe in the M87 GCs from
the strength of their spectral features. The behavior of these elements between
the metal rich and metal poor M87 GCs is similar to that shown by the galactic
GCs and by halo stars in the Galaxy. The pattern of chemical evolution in these
disparate old stellar systems is indistinguishable. We obtain a median age for
the M87 GC system of 13 Gyr, similar to that of the galactic GCs, with a small
dispersion about this value.Comment: 56 pages with included postscript figures; added derived M87 GC
metallicities to Table 2, a statistical analysis of possible bimodality, an
appendix on the metallicity calibration of U-R and the Washington system, and
other smaller changes. Accepted for publication in ApJ. (See paper for
complete version of the Abstract.
The Surface Brightness Fluctuations and Globular Cluster Populations of M87 and its Companions
Using the surface brightness fluctuations in HST WFPC-2 images, we determine
that M87, NGC 4486B, and NGC 4478 are all at a distance of ~16 Mpc, while NGC
4476 lies in the background at ~21 Mpc. We also examine the globular clusters
of M87 using archived HST fields. We detect the bimodal color distribution, and
find that the amplitude of the red peak relative to the blue peak is greatest
near the center. This feature is in good agreement with the merger model of
elliptical galaxy formation, where some of the clusters originated in
progenitor galaxies while other formed during mergers.Comment: 5 pages, 2 figure
A note on the sources for the 1945 constitutional debates in Indonesia
A close examination of the papers held in the archive of Mr A.K. Pringgodigdo in the Nationaal Archief in The Hague indicates that Muhammad Yamin, presumably for the purpose of his own self-aggrandisement, changed important sections of the original text in his 1959-60 edition of the 1945 constitutional debates in Indonesia. Furthermore, the New Order’s efforts to reduce the legacy and legitimacy of Soekarno led Nugroho Notosusanto, in particular, to use Yamin’s work in an effort to diminish Sukarno’s role in the development of the state ideology of Pancasila
Globular Cluster Abundances from High-Resolution Integrated Light Spectra, I: 47 Tuc
We describe the detailed chemical abundance analysis of a high-resolution
(R~35,000), integrated-light (IL), spectrum of the core of the Galactic
globular cluster 47 Tuc, obtained using the du Pont echelle at Las Campanas. We
develop an abundance analysis strategy that can be applied to spatial
unresolved extra- galactic clusters. We have computed abundances for Na, Mg,
Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Ba, La, Nd and Eu. For an
analysis with the known color-magnitude diagram (cmd) for 47 Tuc we obtain a
mean [Fe/H] value of -0.75 +/-0.026+/-0.045 dex (random and systematic error),
in good agreement with the mean of 5 recent high resolution abundance studies,
at -0.70 dex. Typical random errors on our mean [X/Fe] ratios are 0.07-0.10
dex, similar to studies of individual stars in 47 Tuc, although Na and Al
appear enhanced, perhaps due to proton burning in the most luminous cluster
stars. Our IL abundance analysis with an unknown cmd employed theoretical
Teramo isochrones; however, we apply zero-point abundance corrections to
account for the factor of 3 underprediction of stars at the AGB bump
luminosity. While line diagnostics alone provide only mild constraints on the
cluster age (ruling-out ages younger than ~2 Gyr), when theoretical IL B-V
colors are combined with metallicity derived from the Fe I lines, the age is
constrained to 10--15 Gyr and we obtain [Fe/H]=-0.70 +/-0.021 +/-0.052 dex. We
find that Fe I line diagnostics may also be used to constrain the horizontal
branch morphology of an unresolved cluster. Lastly, our spectrum synthesis of
5.4 million TiO lines indicates that the 7300-7600A TiO window should be useful
for estimating the effect of M giants on the IL abundances, and important for
clusters more metal-rich than 47 Tuc.Comment: 40 pages text & references, 4 tables, 19 figures (72 pages total).
Changes include addition of B-V color to help constrain GC age. To appear in
Ap
Discovery of the Pre-Main Sequence Population of the Stellar Association LH 95 in the Large Magellanic Cloud with Hubble Space Telescope ACS Observations
We report the discovery of an extraordinary number of pre-main sequence (PMS)
stars in the vicinity of the stellar association LH 95 in the Large Magellanic
Cloud (LMC). Using the {\em Advanced Camera for Surveys} on-board the {\em
Hubble} Space Telescope in wide-field mode we obtained deep high-resolution
imaging of the main body of the association and of a nearby representative LMC
background field. These observations allowed us to construct the
color-magnitude diagram (CMD) of the association in unprecedented detail, and
to decontaminate the CMD for the average LMC stellar population. The most
significant result is the direct detection of a substantial population of PMS
stars and their clustering properties with respect to the distribution of the
higher mass members of the association. Although LH 95 represents a rather
modest star forming region, our photometry, with a detection limit \lsim 28
mag, reveals in its vicinity more than 2,500 PMS stars with masses down to
M{\solar}. Our observations offer, thus, a new perspective of a
typical LMC association: The stellar content of LH 95 is found to extend from
bright OB stars to faint red PMS stars, suggesting a fully populated Initial
Mass Function (IMF) from the massive blue giants down to the sub-solar mass
regime.Comment: Accepted for Publication in ApJ Letters - 4 Pages ApJ paper format -
3 figures in low-resolution/grayscal
The Globular Cluster System in the Inner Region of M87
1057 globular cluster candidates have been identified in a WFPC2 image of the
inner region of M87. The Globular Cluster Luminosity Function (GCLF) can be
well fit by a Gaussian profile with a mean value of m_V^0=23.67 +/- 0.07 mag
and sigma=1.39 +/- 0.06 mag (compared to m_V^0=23.74 mag and sigma=1.44 mag
from an earlier study using the same data by Whitmore it et al. 1995). The GCLF
in five radial bins is found to be statistically the same at all points,
showing no clear evidence of dynamical destruction processes based on the
luminosity function (LF), in contradiction to the claim by Gnedin (1997).
Similarly, there is no obvious correlation between the half light radius of the
clusters and the galactocentric distance. The core radius of the globular
cluster density distribution is R_c=56'', considerably larger than the core of
the stellar component (R_c=6.8''). The mean color of the cluster candidates is
V-I=1.09 mag which corresponds to an average metallicity of Fe/H = -0.74 dex.
The color distribution is bimodal everywhere, with a blue peak at V-I=0.95 mag
and a red peak at V-I=1.20 mag. The red population is only 0.1 magnitude bluer
than the underlying galaxy, indicating that these clusters formed late in the
metal enrichment history of the galaxy and were possibly created in a burst of
star/cluster formation 3-6 Gyr after the blue population. We also find that
both the red and the blue cluster distributions have a more elliptical shape
(Hubble type E3.5) than the nearly spherical galaxy. The average half light
radius of the clusters is ~2.5 pc which is comparable to the 3 pc average
effective radius of the Milky Way clusters, though the red candidates are ~20%
smaller than the blue ones.Comment: 40 pages, 17 figures, 4 tables, latex, accepted for publication in
the Ap
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