2,674 research outputs found
Towards precision distances and 3D dust maps using broadband Period--Magnitude relations of RR Lyrae stars
We determine the period-magnitude relations of RR Lyrae stars in 13
photometric bandpasses from 0.4 to 12 {\mu}m using timeseries observations of
134 stars. The Bayesian formalism, extended from our previous work to include
the effects of line-of-sight dust extinction, allows for the simultaneous
inference of the posterior distribution of the mean absolute magnitude, slope
of the period-magnitude power-law, and intrinsic scatter about a perfect
power-law for each bandpass. In addition, the distance modulus and
line-of-sight dust extinction to each RR Lyrae star in the calibration sample
is determined, yielding a sample median fractional distance error of 0.66%. The
intrinsic scatter in all bands appears to be larger than the photometric
errors, except in WISE W1 (3.4 {\mu}m) and W2 (4.6 {\mu}m) where the
photometric error ( mag) is to be comparable or larger
than the intrinsic scatter. Additional observations at these wavelengths could
improve the inferred distances to these sources further. As an application of
the methodology, we infer the distance to the RRc-type star RZCep at low
Galactic latitude () to be mag
( pc) with colour excess mag. This
distance, equivalent to a parallax of microarcsec, is consistent
with the published HST parallax measurement but with an uncertainty that is 13
times smaller than the HST measurement. If our measurements (and methodology)
hold up to scrutiny, the distances to these stars have been determined to an
accuracy comparable to those expected with Gaia. As RR Lyrae are one of the
primary components of the cosmic distance ladder, the achievement of sub-1%
distance errors within a formalism that accounts for dust extinction may be
considered a strong buttressing of the path to eventual 1% uncertainties in
Hubble's constant.Comment: 21 pages, 29 figures, 2 tables, abstract abridged for arXiv. Comments
solicited on referee report (received June 9, 2014) linked:
https://gist.github.com/profjsb/c6c4e2f3a20ea02f1762 . Public archive of code
used to generate results and figures:
https://github.com/ckleinastro/period_luminosity_relation_fittin
Present and Future Prospects for GRB Standard Candles
Following our previous work, we conclude that a GRB standard candle
constructed from the Ghirlanda et al. power-law relation between the
geometry-corrected energy (E_gamma) and the peak of the rest-frame prompt burst
spectrum (E_p) is not yet cosmographically useful, despite holding some
potential advantages over SNe Ia. This is due largely to the small sample of
\~20 GRBs with the required measured redshifts, jet-breaks, and peak energies,
and to the strong sensitivity of the goodness-of-fit of the power-law to input
assumptions. The most important such finding concerns the sensitivity to the
generally unknown density (and density profile), of the circumburst medium.
Although the E_p-E_gamma relation is a highly significant correlation over many
cosmologies, until the sample expands to include many low-z events, it will be
most sensitive to Omega_M but essentially insensitive to Omega_Lambda and w,
with some hope of constraining dw/dt with high-z GRB data alone. The relation
clearly represents a significant improvement in the search for an empirical GRB
standard candle, but is further hindered by an unknown physical basis for the
relation, the lack of a low-z training set to calibrate the relation in a
cosmology-independent way, and several major potential systematic uncertainties
and selection effects. Until these concerns are addressed, a larger sample is
acquired, and attempts are made to marginalize or perform Monte Carlo
simulations over the unknown density distribution, we urge caution concerning
claims of the utility of GRBs for cosmography and especially the attempts to
combine GRBs with SNe Ia.Comment: 5 pages, 2 figures, "Proceedings, Gamma-Ray Bursts in the Afterglow
Era: 4th Workshop, Rome, Italy, Oct 18-22, 2004". Accepted to Il Nuovo
Cimento. For more details, see astro-ph/0408413 (ApJ accepted), and other
work from the cosmicbooms.net Team at http://www.cosmicbooms.net
The Genetic Basis of Mutation Rate Variation in Yeast.
Mutations are the root source of genetic variation and underlie the process of evolution. Although the rates at which mutations occur vary considerably between species, little is known about differences within species, or the genetic and molecular basis of these differences. Here, we leveraged the power of the yeast Saccharomyces cerevisiae as a model system to uncover natural genetic variants that underlie variation in mutation rate. We developed a high-throughput fluctuation assay and used it to quantify mutation rates in seven natural yeast isolates and in 1040 segregant progeny from a cross between BY, a laboratory strain, and RM, a wine strain. We observed that mutation rate varies among yeast strains and is heritable (H 2 = 0.49). We performed linkage mapping in the segregants and identified four quantitative trait loci underlying mutation rate variation in the cross. We fine-mapped two quantitative trait loci to the underlying causal genes, RAD5 and MKT1, that contribute to mutation rate variation. These genes also underlie sensitivity to the DNA-damaging agents 4NQO and MMS, suggesting a connection between spontaneous mutation rate and mutagen sensitivity
Toward an Understanding of the Progenitors of Gamma-Ray Bursts
The various possibilities for the progenitors of gamma-ray bursts (GRBs)
manifest in differing observable properties. Through deep spectroscopic and
high-resolution imaging observations of some GRB hosts, I demonstrate that
well-localized long-duration GRBs are connected with otherwise normal
star-forming galaxies at moderate redshifts of order unity. I test various
progenitor scenarios by examining the offset distribution of GRBs about their
apparent hosts, making extensive use of ground-based optical data from Keck and
Palomar and space-based imaging from the Hubble Space Telescope. The offset
distribution appears to be inconsistent with the coalescing neutron star binary
hypothesis but statistically consistent with a population of progenitors that
closely traces the ultra-violet light of galaxies. This is naturally explained
by bursts which originate from the collapse of massive stars. This claim is
further supported by the unambiguous detections of emission ''bumps'' which can
be explained as supernovae that occur at approximately the same time as the
associated GRB; if true, GRB 980326 and GRB 011121 provide strong observational
evidence connecting cosmological GRBs to high-redshift supernovae and implicate
massive stars as the progenitors of some long-duration GRBs. Interestingly,
most alternative models of these bumps require wind-stratified circumburst
media; this too, implicates massive stars. In addition to this work, I also
constructed the Jacobs Camera (JCAM), a dual-beam optical camera for the
Palomar 200-inch Telescope designed to follow-up rapid GRB localizations
(abridged).Comment: Ph.D. thesis, Caltech. 196 pages including low-resolution figures.
Abstract to be published in PASP, February 2003. Defended April 1, 2002. A
high-resolution PDF version may be found at
http://www-cfa.harvard.edu/~jbloom/thesis.htm
The Banking Crisis and Cultural Resources: The Role of the RTC and FDIC When Liquidating Historic Properties
Long-Term Consequences of Secondary School Vouchers: Evidence from Administrative Records in Colombia
Colombia's PACES program provided over 125,000 poor children with vouchers that covered half the cost of private secondary school. The vouchers were renewable annually conditional on adequate academic progress. Since many vouchers were assigned by lottery, program effects can reliably be assessed by comparing lottery winners and losers. Estimates using administrative records suggest the PACES program increased secondary school completion rates by 15-20 percent. Correcting for the greater percentage of lottery winners taking college admissions tests, the program increased test scores by two-tenths of a standard deviation in the distribution of potential test scores. Boys, who have lower scores than girls in this population, show larger test score gains, especially in math.
The Corrected Log N-Log Fluence Distribution of Cosmological Gamma-Ray Bursts
Recent analysis of relativistically expanding shells of cosmological
gamma-ray bursts has shown that if the bursts are cosmological, then most
likely total energy (E_0) is standard and not peak luminosity (L_0). Assuming a
flat Friedmann cosmology (q_o = 1/2, Lambda = 0) and constant rate density
(rho_0) of bursting sources, we fit a standard candle energy to a uniformly
selected log N-log S in the BATSE 3B catalog correcting for fluence efficiency
and averaging over 48 observed spectral shapes. We find the data consistent
with E_0 = 7.3^{+0.7}_{-1.0} X 10^{51} ergs and discuss implications of this
energy for cosmological models of gamma-ray bursts.Comment: A five page LateX file that uses the Revtex conference proceedings
macro aipbook.sty, and includes three postscript figures using psfig. To Be
published in the Proceedings of the Third Hunstville Symposium on Gamma-Ray
Bursts, eds. C. Kouveliotou, M.S. Briggs and G.J. Fishman (New York:AIP).
Postscript version availible at http://nis-www.lanl.gov/~jsbloom/LOG_S.p
Book Review: Meeting of Minds: Intellectual and Religious Interaction in East Asian Traditions of Thought
Meeting of Minds: Intellectual and Religious Interaction in East Asian Traditions of Thought, a volume of eleven essays written in honor of Wing-tsit Chan and William Theodore de Bary, proposes to explore how Confucian and Neo-Confucian traditions have responded to and have influenced other traditions (Buddhist, Taoist, folk, Japanese nativist, and so on) in China and Japan. The essays are arranged first geographically (seven articles on China precede four on Japan) and then roughly chronologically. All essays, save one, describe Sung or post-Sung developments. A few sentences per essay must suffice in this review. [excerpt
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