23 research outputs found
The Giant Branches of Open and Globular Clusters in the Infrared as Metallicity Indicators: A Comparison with Theory
We apply the giant branch slope-[Fe/H] relation derived by Kuchinski et al.
[AJ, 109, 1131 (1995)] to a sample of open clusters. We find that the slope of
the giant branch in K vs. (J-K) color-magnitude diagrams correlates with [Fe/H]
for open clusters as it does for metal-rich globular clusters but that the open
cluster data are systematically shifted to less negative values of giant branch
slope, at constant [Fe/H]. We use isochrone models to examine the theoretical
basis for this relationship and find that for a given value of [Fe/H], the
slope of the relationship remains constant with decreasing population age but
the relation shifts to less negative values of giant branch slope with
decreasing age. Both of these theoretical predictions agree with the trends
found in the data. Finally, we derive new coefficients for the giant branch
slope-[Fe/H] relation for specific members of 3 populations, metal-rich
globular clusters, bulge stars and open clusters.Comment: 16 pages including 3 figures (AASTEX), AJ Accepted, also available at
http://www.astronomy.ohio-state.edu/~martini/pubs.htm
Implications of New JHK Photometry and a Deep Infrared Luminosity Function for the Galactic Bulge
We present deep near-IR photometry for Galactic bulge stars in Baade's
Window, and another minor axis field at . We combine our data with previously published photometry
and construct a luminosity function over the range ,
deeper than any previously published. The slope of this luminosity function and
the magnitude of the tip of the first ascent giant branch are consistent with
theoretical values derived from isochrones with appropriate age and
metallicity.
We use the relationship between [Fe/H] and the giant branch slope derived
from near-IR observations of metal rich globular clusters by Kuchinski {\it et
al.} [AJ, 109, 1131 (1995)] to calculate the mean metallicity for several bulge
fields along the minor axis. For Baade's Window we derive , consistent with the recent estimate of
McWilliam \& Rich [ApJS, 91, 749 (1994)], but somewhat lower than previous
estimates based on CO and TiO absorption bands and the colors of M giants
by Frogel {\it et al.} [ApJ, 353, 494 (1990)]. Between and
we find a gradient in of dex/degree or dex/kpc for kpc, consistent with
other independent derivations. We derive a helium abundance for Baade's Window
with the and methods and find that implying
.
Next, we find that the bolometric corrections for bulge K giants () are in excellent agreement with empirical derivations based on observations
of globular cluster and local field stars. However, for the redder M giants weComment: Accepted by the Astronomical Journal. 43 pages, uuencoded compressed
PostScript, no figures or tables. A complete (text, figs and tables) preprint
is also available at
ftp://bessel.mps.ohio-state.edu/pub/terndrup/bwphot.tar.Z (compressed tar
file with PostScript
The Metallicity and Reddening of Stars in the Inner Galactic Bulge
We present a preliminary analysis of K, J-K color magnitude diagrams (CMDs)
for 7 different positions on or close to the minor axis of the Milky Way at
Galactic latitudes between +0.1^\circ and -2.8^\circ. From the slopes of the
(linear) giant branches in these CMDs we derive a dependence of on
latitude for b between -0.8^\circ and -2.8^\circ of -0.085 \pm 0.033
dex/degree. When combined with the data from Tiede et al. we find for
-0.8^\circ \leq b \leq -10.3^\circ the slope in is -0.064 \pm 0.012
dex/degree. An extrapolation to the Galactic Center predicts [Fe/H] = +0.034
\pm 0.053 dex. We also derive average values for the extinction in the K band
(A_K) of between 2.15 and 0.27 for the inner bulge fields corresponding to
average values of E(J-K) of between 3.46 and 0.44. There is a well defined
linear relation between the average extinction for a field and the star-to-star
scatter in the extinction for the stars within each field. This result suggests
that the typical apparent angular scale size for an absorbing cloud is small
compared with the field size (90\arcsec on a side). Finally, from an
examination of the luminosity function of bright giants in each field we
conclude that the young component of the stellar population observed near the
Galactic center declines in density much more quickly than the overall bulge
population and is undetectable beyond 1^\circ from the Galactic center.Comment: accepted for publication in Astron. Jour. Compressed file contains
the text, 9 figures, and 6 tables prepared with AAS Latex macros v. 4.
Distances to Populous Clusters in the LMC via the K-Band Luminosity of the Red Clump
We present results from a study of the distances and distribution of a sample
of intermediate-age clusters in the Large Magellanic Cloud. Using deep
near-infrared photometry obtained with ISPI on the CTIO 4m, we have measured
the apparent K-band magnitude of the core helium burning red clump stars in 17
LMC clusters. We combine cluster ages and metallicities with the work of
Grocholski & Sarajedini to predict each cluster's absolute K-band red clump
magnitude, and thereby calculate absolute cluster distances. An analysis of
these data shows that the cluster distribution is in good agreement with the
thick, inclined disk geometry of the LMC, as defined by its field stars. We
also find that the old globular clusters follow the same distribution,
suggesting that the LMC's disk formed at about the same time as the globular
clusters, ~ 13 Gyr ago. Finally, we have used our cluster distances in
conjunction with the disk geometry to calculate the distance to the LMC center,
for which we find (m-M)o = 18.40 +/- 0.04_{ran} +/- 0.08_{sys}, or Do = 47.9
+/- 0.9 +/- 1.8 kpc.Comment: 31 pages including 5 figures and 7 tables. Accepted for publication
in the August 2007 issue of A
The Clustering of Extragalactic Extremely Red Objects
We have measured the angular and spatial clustering of 671 K5
Extremely Red Objects (EROs) from a 0.98 square degree sub-region of the NOAO
Deep Wide-Field Survey (NDWFS). Our study covers nearly 5 times the area and
has twice the sample size of any previous ERO clustering study. The wide field
of view and BwRIK passbands of the NDWFS allow us to place improved constraints
on the clustering of z=1 EROs. We find the angular clustering of EROs is
slightly weaker than in previous measurements, and w(1')=0.25+/-0.05 for
K<18.40 EROs. We find no significant correlation of ERO spatial clustering with
redshift, apparent color or absolute magnitude, although given the
uncertainties, such correlations remain plausible. We find the spatial
clustering of K5 EROs is well approximated by a power-law, with
r_0=9.7+/-1.1 Mpc/h in comoving coordinates. This is comparable to the
clustering of 4L* early-type galaxies at z<1, and is consistent with the
brightest EROs being the progenitors of the most massive ellipticals. There is
evidence of the angular clustering of EROs decreasing with increasing apparent
magnitude, when NDWFS measurements of ERO clustering are combined with those
from the literature. Unless the redshift distribution of K>20 EROs is very
broad, the spatial clustering of EROs decreases from r_0=9.7+/-1.1 Mpc/h for
K20 EROs.Comment: Accepted for publication in the ApJ. 29 pages with 10 figures. The
NOAO Deep Wide-Field Survey Bootes data release is available online at
http://www.noao.edu/noao/noaodeep
The Stellar Populations in the Outer Regions of M33. I. Metallicity Distribution Function
We present deep CCD photometry in the VI passbands using the WIYN 3.5m
telescope of a field located approximately 20' southeast of the center of M33;
this field includes the region studied by Mould & Kristian in their 1986 paper.
The color-magnitude diagram (CMD) extends to I~25 and shows a prominent red
giant branch (RGB), along with significant numbers of asymptotic giant branch
and young main sequence stars. The red clump of core helium burning stars is
also discernable near the limit of our CMD. The I-band apparent magnitude of
the red giant branch tip implies a distance modulus of (m-M)_I = 24.77 +/-
0.06, which combined with an adopted reddening of E(V-I)=0.06 +/- 0.02 yields
an absolute modulus of (m-M)_0 = 24.69 +/- 0.07 (867 +/- 28 kpc) for M33. Over
the range of deprojected radii covered by our field (~8.5 to ~12.5 kpc), we
find a significant age gradient with an upper limit of ~1 Gyr (~0.25 Gyr/kpc).
Comparison of the RGB photometry to empirical giant branch sequences for
Galactic globulars allows us to use the dereddened color of these stars to
construct a metallicity distribution function (MDF). The primary peak in the
MDF is at a metallicity of [Fe/H] ~ -1.0 with a tail to lower abundances. The
peak does show radial variation with a slope of d[Fe/H]/dR_{deproj} = -0.06 +/-
0.01 dex/kpc. This gradient is consistent with the variation seen in the inner
disk regions of M33. As such, we conclude that the vast majority of stars in
this field belong to the disk of M33, not the halo as previously thought.Comment: 34 pages, 13 figures, accepted to The Astronomical Journal, July
2004, high resolution version available at
ftp://www.astro.ufl.edu/pub/ata/sarajedini_m33.pd
From Stars to Super-planets: the Low-Mass IMF in the Young Cluster IC348
We investigate the low-mass population of the young cluster IC348 down to the
deuterium-burning limit, a fiducial boundary between brown dwarf and planetary
mass objects, using a new and innovative method for the spectral classification
of late-type objects. Using photometric indices, constructed from HST/NICMOS
narrow-band imaging, that measure the strength of the 1.9 micron water band, we
determine the spectral type and reddening for every M-type star in the field,
thereby separating cluster members from the interloper population. Due to the
efficiency of our spectral classification technique, our study is complete from
approx 0.7 Msun to 0.015 Msun. The mass function derived for the cluster in
this interval, dN/dlogM \propto M^{0.5}, is similar to that obtained for the
Pleiades, but appears significantly more abundant in brown dwarfs than the mass
function for companions to nearby sun-like stars. This provides compelling
observational evidence for different formation and evolutionary histories for
substellar objects formed in isolation vs. as companions. Because our
determination of the IMF is complete to very low masses, we can place
interesting constraints on the role of physical processes such as fragmentation
in the star and planet formation process and the fraction of dark matter in the
Galactic halo that resides in substellar objects.Comment: 37 pages, 16 figs, 6 tables (Table 4 is a separate LaTeX file)
Accepted for publication in Astrophysical Journal (Oct 1, 2000 issue
The Frequency of Barred Spiral Galaxies in the Near-IR
We have determined the fraction of barred galaxies in the H-band for a
statistically well-defined sample of 186 spirals drawn from the Ohio State
University Bright Spiral Galaxy survey. We find 56% of our sample to be
strongly barred at H, while another 16% is weakly barred. Only 27% of our
sample is unbarred in the near-infrared. The RC3 and the Carnegie Atlas of
Galaxies both classify only about 30% of our sample as strongly barred. Thus
strong bars are nearly twice as prevalent in the near-infrared as in the
optical. The frequency of genuine optically hidden bars is significant, but
lower than many claims in the literature: 40% of the galaxies in our sample
that are classified as unbarred in the RC3 show evidence for a bar in the
H-band, while for the Carnegie Atlas this fraction is 66%. Our data reveal no
significant trend in bar fraction as a function of morphology in either the
optical or H-band. Optical surveys of high redshift galaxies may be strongly
biased against finding bars, as bars are increasingly difficult to detect at
bluer rest wavelengths.Comment: LaTeX with AASTeX style file, 23 pages with 6 figures. Accepted for
publication in The Astronomical Journal (Feb. 2000