26 research outputs found
The Globular Cluster Populations of Giant Galaxies: Mosaic Imaging of Five Moderate-Luminosity Early-Type Galaxies
This paper presents results from wide-field imaging of the globular cluster
(GC) systems of five intermediate-luminosity (M_V ~-21 to -22) early-type
galaxies. The aim is to accurately quantify the global properties of the GC
systems by measuring them out to large radii. We obtained BVR imaging of four
lenticular galaxies (NGC 5866, NGC 4762, NGC 4754, NGC 3384) and one elliptical
galaxy (NGC 5813) using the KPNO 4m telescope and MOSAIC imager and traced the
GC population to projected galactocentric radii ranging from ~20 kpc to 120
kpc. We combine our imaging with Hubble Space Telescope data to measure the GC
surface density close to the galaxy center. We calculate the total number of
GCs (N_GC) from the integrated radial profile and find N_GC = 340 +/- 80 for
NGC 5866, N_GC = 2900 +/- 400 for NGC 5813, N_GC = 270 +/- 30 for NGC 4762,
N_GC = 115 +/- 15$ for NGC 4754, and N_GC = 120 +/- 30 for NGC 3384. The
measured GC specific frequencies are S_N between 0.6 and 3.6 and T in the range
0.9 to 4.2. These values are consistent with the mean specific frequencies for
the galaxies' morphological types found by our survey and other published data.
Three galaxies (NGC 5866, NGC 5813, NGC 4762) had sufficient numbers of GC
candidates to investigate color bimodality and color gradients in the GC
systems. NGC 5813 shows strong evidence (>3 sigma) for bimodality and a B-R
color gradient resulting from a more centrally concentrated red (metal-rich) GC
subpopulation. We find no evidence for statistically significant color
gradients in the other two galaxies.Comment: 61 pages, 21 figures, 11 tables. Accepted for publication in The
Astronomical Journa
The Infrared Light Curve of SN 2011fe in M101 and the Distance to M101
We present near-infrared light curves of supernova (SN) 2011fe in M101, including 34 epochs in H band starting 14 days before maximum brightness in the B band. The light curve data were obtained with the WIYN High-Resolution Infrared Camera. When the data are calibrated using templates of other Type Ia SNe, we derive an apparent H-band magnitude at the epoch ofB-band maximum of 10.85 ± 0.04. This implies a distance modulus for M101 that ranges from 28.86 to 29.17 mag, depending on which absolute calibration for Type Ia SNe is used
Time-Series Ensemble Photometry and the Search for Variable Stars in the Open Cluster M11
This work presents the first large-scale photometric variability survey of
the intermediate age (~200 Myr) open cluster M11. Thirteen nights of data over
two observing seasons were analyzed (using crowded field and ensemble
photometry techniques) to obtain high relative precision photometry. In this
study we focus on the detection of candidate member variable stars for
follow-up studies. A total of 39 variable stars were detected and can be
categorized as follows: 1 irregular (probably pulsating) variable, 6 delta
Scuti variables, 14 detached eclipsing binary systems, 17 W UMa variables, and
1 unidentified/candidate variable. While previous proper motion studies allow
for cluster membership determination for the brightest stars, we find that
membership determination is significantly hampered below V=15,R=15.5 by the
large population of field stars overlapping the cluster MS. Of the brightest
detected variables that have a high likelihood of cluster membership, we find
five systems where further work could help constrain theoretical stellar
models, including one potential W UMa member of this young cluster.Comment: 38 pages, 13 figures, accepted for December 2005 AJ, high-resolution
version available upon reques
The Unusual Luminosity Function of the Globular Cluster M10
We present the I-band luminosity function of the differentially reddened
globular cluster M10. We combine photometric analysis derived from wide-field
(23' x 23') images that include the outer regions of the cluster and
high-resolution images of the cluster core. After making corrections for
incompleteness and field star contamination, we find that the relative numbers
of stars on the lower giant branch and near the main-sequence turnoff are in
good agreement with theoretical predictions. However, we detect significant (>
6 \sigma) excesses of red giant branch stars above and below the red giant
branch bump using a new statistic (a population ratio) for testing relative
evolutionary timescales of main-sequence and red giant stars. The statistic is
insensitive to assumed cluster chemical composition, age, and main-sequence
mass function. The excess number of red giants cannot be explained by
reasonable systematic errors in our assumed cluster chemical composition, age,
or main-sequence mass function. Moreover, M10 shows excesses when compared to
the cluster M12, which has nearly identical metallicity, age, and
color-magnitude diagram morphology. We discuss possible reasons for this
anomaly, finding that the most likely cause is a mass function slope that shows
significant variations as a function of mass.Comment: 31 pages, 12 figures, accepted for Ap
Evidence That Hydra I is a Tidally Disrupting Milky Way Dwarf Galaxy
The Eastern Banded Structure (EBS) and Hydra I halo overdensities are very nearby (d ~ 10 kpc) objects discovered in Sloan Digital Sky Survey (SDSS) data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field Dark Energy Camera (DECam) imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra I has a thin, well-defined main sequence turnoff of intermediate age (~5â6 Gyr) and metallicity ([Fe/H] = â0.9 dex). We measure statistically significant spreads in both the iron and alpha-element abundances of Ï_[(Fe)/H}= 0.13 ± 0.02 dex and Ï_[É/Fe] = 0.09 ± 0.03 dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra I's intermediate age and [Fe/H]âas well as its low [α/Fe], apparent [Fe/H] spread, and present-day low luminosityâsuggest that its progenitor was a dwarf galaxy, which has subsequently lost more than 99.99% of its stellar mass
The Globular Cluster Population of NGC 7457: Clues to the Evolution of Field S0 Galaxies
In this paper we present the results of a wide-field imaging study of the
globular cluster (GC) system of the field S0 galaxy NGC 7457. To derive the
global properties of the GC system, we obtained deep BVR images with the WIYN
3.5 m telescope and Minimosaic Imager and studied the GC population of NGC 7457
to a projected radius of approximately 30 kpc. Our ground-based data were
combined with archival and published Hubble Space Telescope data to probe the
properties of the GC system close to the galaxy center and reduce contamination
in the GC candidate sample from foreground stars and background galaxies. We
performed surface photometry of NGC 7457 and compared the galaxy's surface
brightness profile with the surface density profile of the GC system. The
profiles have similar shapes in the inner 1 arcminute (3.9 kpc), but the GC
system profile appears to flatten relative to the galaxy light at larger radii.
The GC system of NGC 7457 is noticeably elliptical in our images; we measure an
ellipticity of 0.66 +/- 0.14 for the GC distribution, which is consistent with
our measured ellipticity of the galaxy light. We integrated the radial surface
density profile of the GC system to derive a total number of GCs N_GC = 210 +/-
30. The GC specific frequency normalized by the galaxy luminosity and mass are
S_N = 3.1 +/- 0.7 and T = 4.8 +/- 1.1, respectively. Comparing the derived GC
system properties and other empirical data for NGC 7457 to S0 formation
scenarios suggests that this field S0 galaxy may have formed in an unequal-mass
merger.Comment: 40 pages, 10 figures, accepted for publication in The Astrophysical
Journa