9 research outputs found
H-delta in the Integrated Light of Galaxies: What Are We Actually Measuring?
We present a cautionary study exploring the reliability of the H-delta line
in the integrated spectra of galaxies for determining galaxy ages. Our database
consists of the observed integrated spectra of ~120 early-type galaxies, of 7
metal-rich globular clusters in M31 and the Galactic globular cluster 47 Tuc,
and of the open cluster M67. We have measured H-delta using index definitions
designed to assess contamination from the CN molecule in and around H-delta by
choosing combinations of bandpasses that both avoid and include a region of CN
molecular lines redward of H-delta. We find systematic differences in the ages
derived from H-delta measurements among the various definitions when extracting
ages from H-delta in old stellar populations with enhanced CN bands due to
non-solar abundance ratios. We propose that neighboring CN lines have a strong
effect on pseudocontinuum and central bandpass levels. For stellar populations
which have non-solar abundance ratios in C and/or N, population synthesis
models that do not account for abundance ratio variations cannot reproduce
accurately the CN 4216 \AA band, which leads to a corresponding inaccuracy in
reproducing the various H-delta indices. Hence, caution must be used when
extracting galaxy ages from the H-delta line in old stellar populations with
significant non-solar abundance ratios.Comment: 8 figures, 2 table
UBVRI Light Curves of 44 Type Ia Supernovae
We present UBVRI photometry of 44 type-Ia supernovae (SN Ia) observed from
1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence
Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The
data set comprises 2190 observations and is the largest homogeneously observed
and reduced sample of SN Ia to date, nearly doubling the number of
well-observed, nearby SN Ia with published multicolor CCD light curves. The
large sample of U-band photometry is a unique addition, with important
connections to SN Ia observed at high redshift. The decline rate of SN Ia
U-band light curves correlates well with the decline rate in other bands, as
does the U-B color at maximum light. However, the U-band peak magnitudes show
an increased dispersion relative to other bands even after accounting for
extinction and decline rate, amounting to an additional ~40% intrinsic scatter
compared to B-band.Comment: 84 authors, 71 pages, 51 tables, 10 figures. Accepted for publication
in the Astronomical Journal. Version with high-res figures and electronic
data at http://astron.berkeley.edu/~saurabh/cfa2snIa
CfA3: 185 Type Ia Supernova Light Curves from the CfA
We present multi-band photometry of 185 type-Ia supernovae (SN Ia), with over
11500 observations. These were acquired between 2001 and 2008 at the F. L.
Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics (CfA).
This sample contains the largest number of homogeneously-observed and reduced
nearby SN Ia (z < 0.08) published to date. It more than doubles the nearby
sample, bringing SN Ia cosmology to the point where systematic uncertainties
dominate. Our natural system photometry has a precision of 0.02 mag or better
in BVRIr'i' and roughly 0.04 mag in U for points brighter than 17.5 mag. We
also estimate a systematic uncertainty of 0.03 mag in our SN Ia standard system
BVRIr'i' photometry and 0.07 mag for U. Comparisons of our standard system
photometry with published SN Ia light curves and comparison stars, where
available for the same SN, reveal agreement at the level of a few hundredths
mag in most cases. We find that 1991bg-like SN Ia are sufficiently distinct
from other SN Ia in their color and light-curve-shape/luminosity relation that
they should be treated separately in light-curve/distance fitter training
samples. The CfA3 sample will contribute to the development of better
light-curve/distance fitters, particularly in the few dozen cases where
near-infrared photometry has been obtained and, together, can help disentangle
host-galaxy reddening from intrinsic supernova color, reducing the systematic
uncertainty in SN Ia distances due to dust.Comment: Accepted to the Astrophysical Journal. Minor changes from last
version. Light curves, comparison star photometry, and passband tables are
available at http://www.cfa.harvard.edu/supernova/CfA3
Emotions and Affect in Writing Center Administration: A Roundtable on the Emotional Dimensions of Administrative Work
This synchronous roundtable examines the ways that emotions and affect appear in writing center administration. Roundtable participants are contributors to a forthcoming edited collection focusing on emotions and affect in writing center work and will be speaking to their experiences with emotions and affect as administrators across a number of contexts