234 research outputs found
The Initial Mass Function: Now and Then
We examine whether existing data in clusters, both old and young, and in the
field of the Galactic disk and halo is consistent with a universal slope for
the initial mass function (IMF). The most reasonable statement that can be made
at the current time is that there is no strong evidence to support a claim of
any real variations in this slope. If the IMF slope is universal then this in
itself is remarkable implying that variations in metallicity, gas density or
other environmental factors in the star formation process play no part in
determining the slope of the mass function.Comment: 10 pages, postscript. To appear in "Proceedings 7th Annual
Astrophysics Conference in Maryland-STAR FORMATION NEAR AND FAR
The Double Cluster G185 in M31
We have identified a small globular cluster in M31 located approximately 4
arcseconds northwest of the M31 globular cluster G185. While several multiple
globular clusters have been observed in the Magellanic Clouds none have been
found in the Galaxy or in M31. We estimate the probability of such a chance
line-of-sight alignment occuring near the nucleus of M31 to be 0.09 +/- 0.03
and find no obvious indication of any tidal deformation in either cluster, as
would be expected if the clusters were interacting.
Two-dimensional modelling suggests G185 has a King (1966) [AJ, 71, 64]
concentration of c = 1.11 +/- 0.08 while the companion has c = 0.67 +/- 0.17
and is physically smaller than G185. Both objects have integrated dereddened
colors similar to those of Galactic globular clusters.Comment: 22 pages, ~1Mb postscript file
http://www.astro.ubc.ca/~holland/bib.html/
ftp://nukta.astro.ubc.ca/pub/holland/G185_preprint.ps.
Deep HST V- and I-Band Observations of Two Globular Clusters in the Halo of M31
We present deep (V ~= 27) V- and I-band stellar photometry of G302 and G312,
two globular star clusters in the halo of M31. These data were obtained using
the Hubble Space Telescope's Wide Field/Planetary Camera 2. We find iron
abundances of [Fe/H] = -1.85 +/- 0.12 for G302 and [Fe/H] = -0.56 +/- 0.03 for
G312, consistent with spectroscopic measurements. The color-magnitude diagrams
for each cluster show no evidence for an intermediate-aged population of stars,
or a second parameter effect in the morphology of the horizontal branch. G302
shows no evidence for a color gradient but the inner regions of G312 are bluer
than the outer regions. G312 shows no evidence of ellipticity or an extended
halo of unbound stars. G302 has a projected ellipticity of 0.195 +/- 0.012 with
the projected major axis oriented towards the center of M31. G302 also shows
evidence of an extended asymmetric stellar halo extending to at least twice the
fitted Michie-King tidal radius. The amount of mass beyond the tidal radius of
G302 is consistent with the stellar escape rates which have been predicted by
N-body simulations of globular clusters in the Galactic tidal field.Comment: 29 pages, 21 Postscript figures, uses aaspp4.sty, to be published in
the October 1997 A
Globular Clusters in NGC 1275
We present the results of a deep photometric study of the outer halo of NGC
1275, the highly active cD galaxy at the center of the Perseus cluster. We find
a modest excess of faint () starlike objects in its halo, indicating
a population of old-halo globular clusters. However, the total estimated
cluster population corresponds to a specific frequency of ,
no larger than that of normal giant ellipticals and three times lower than that
of other central cD galaxies such as M87. We discuss several ideas for the
origin of this galaxy. Our results reinforce the view that high (ie:
highly efficient globular cluster formation) is not associated with cooling
flows, or with recent starburst or merger phenomena.Comment: 25 pages, latex, postscript figures, tarred, Unix compressed,
postscript version of paper and figures available at
http://www.physics.mcmaster.ca/Grads/DKaisler/office.htm
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