43 research outputs found
A Survey for Planetary Nebulae in M31 Globular Clusters
We report the results of an [O III] 5007 spectroscopic survey for planetary
nebulae (PNe) located within the star clusters of M31. By examining R ~ 5000
spectra taken with the WIYN+Hydra spectrograph, we identify 3 PN candidates in
a sample of 274 likely globular clusters, 2 candidates in objects which may be
globular clusters, and 5 candidates in a set of 85 younger systems. The
possible PNe are all faint, between ~2.5 and ~6.8 mag down the PN luminosity
function, and, partly as a consequence of our selection criteria, have high
excitation, with [O III] 5007 to H-beta ratios ranging from 2 to ~12. We
discuss the individual candidates, their likelihood of cluster membership, and
the possibility that they were formed via binary interactions within the
clusters. Our data are consistent with the suggestion that PN formation within
globular clusters correlates with binary encounter frequency, though, due to
the small numbers and large uncertainties in the candidate list, this study
does not provide sufficient evidence to confirm the hypothesis.Comment: Accepted for publication in the Astrophysical Journal. 54 pages,
including 9 figures and 4 table
Investigation of Excited State Charge Redistribution of the Reduced Anionic Flavin in DNA Photolyase and Simple Solvents by Stark Spectroscopy
Diffuse light and galaxy interactions in the core of nearby clusters
The kinematics of the diffuse light in the densest regions of the nearby
clusters can be unmasked using the planetary nebulae (PNs) as probes of the
stellar motions. The position-velocity diagrams around the brightest cluster
galaxies (BCGs) identify the relative contributions from the outer halos and
the intracluster light (ICL), defined as the light radiated by the stars
floating in the cluster potential. The kinematics of the ICL can then be used
to asses the dynamical status of the nearby cluster cores and to infer their
formation histories. The cores of the Virgo and Coma are observed to be far
from equilibrium, with mergers currently on-going, while the ICL properties in
the Fornax and Hydra clusters show the presence of sub-components being
accreted in their cores, but superposed to an otherwise relaxed population of
stars. Finally the comparison of the observed ICL properties with those
predicted from Lambda-CDM simulations indicates a qualitative agreement and
provides insights on the ICL formation. Both observations and simulations
indicate that BCG halos and ICL are physically distinct components, with the
``hotter" ICL dominating at large radial distances from the BCGs halos as the
latter become progressively fainter.Comment: 14 pages, 5 figures. Invited review to appear in the proceedings of
"Galaxies and their masks" eds. Block, D.L., Freeman, K.C. and Puerari, I.,
2010, Springer (New York
The Planetary Nebula System of M33
We report the results of a photometric and spectroscopic survey for planetary
nebulae (PNe) in the Local Group spiral galaxy M33. We use our sample of 152
PNe to derive an [O III] planetary nebula luminosity function (PNLF) distance
of (m-M)_0 = 24.86^+0.07-0.11 (0.94^+0.03-0.05 Mpc). Although this value is ~
15% larger than the galaxy's Cepheid distance, the discrepancy likely arises
from differing assumptions about the system's internal extinction. Our
photometry (which extends >3 mag down the PNLF), also reveals that the
faint-end of M33's PN luminosity function is non-monotonic, with an inflection
point ~2 mag below the PNLF cutoff. We argue that this feature is due to the
galaxy's large population of high core-mass planetaries, and that its amplitude
may eventually be useful as a diagnostic for studies of stellar populations.
Fiber-coupled spectroscopy of 140 of the PN candidates confirms that M33's PN
population rotates along with the old disk, with a small asymmetric drift of \~
10km/s. Remarkably, the population's line-of-sight velocity dispersion varies
little over ~4 optical disk scale lengths, with sigma_{rad}~20km/s. We show
that this is due to a combination of factors, including a decline in the radial
component of the velocity ellipsoid at small galactocentric radii, and a
gradient in the ratio of the vertical to radial velocity dispersion. We use our
data to show that the mass scale length of M33's disk is ~2.3 times larger than
that of the system's IR luminosity and that the disk's V-band mass-to-light
ratio changes from M/L_V ~0.3 in the galaxy's inner regions to M/L_V ~2.0 at ~9
kpc. Models in which the dark matter is distributed in the plane of the galaxy
are excluded by our data. (abridged)Comment: 45 pages, including 12 figures (some with reduced resolution);
accepted for publication in the Astrophysical Journa
Origins Space Telescope: Baseline mission concept
The Origins Space Telescope will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did galaxies evolve from the earliest galactic systems to those found in the Universe today? How do habitable planets form? How common are life-bearing worlds? To answer these alluring questions, Origins will operate at mid-and far-infrared (IR) wavelengths and offer powerful spectroscopic instruments and sensitivity three orders of magnitude better than that of the Herschel Space Observatory, the largest telescope flown in space to date. We describe the baseline concept for Origins recommended to the 2020 US Decadal Survey in Astronomy and Astrophysics. The baseline design includes a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. A mid-infrared instrument (Mid-Infrared Spectrometer and Camera Transit spectrometer) will measure the spectra of transiting exoplanets in the 2.8 to 20 μm wavelength range and offer unprecedented spectrophotometric precision, enabling definitive exoplanet biosignature detections. The far-IR imager polarimeter will be able to survey thousands of square degrees with broadband imaging at 50 and 250 μm. The Origins Survey Spectrometer will cover wavelengths from 25 to 588 μm, making wide-area and deep spectroscopic surveys with spectral resolving power R ∼ 300, and pointed observations at R ∼ 40,000 and 300,000 with selectable instrument modes. Origins was designed to minimize complexity. The architecture is similar to that of the Spitzer Space Telescope and requires very few deployments after launch, while the cryothermal system design leverages James Webb Space Telescope technology and experience. A combination of current-state-of-the-art cryocoolers and next-generation detector technology will enable Origins\u27 natural background-limited sensitivity
Comment letters to the National Commission on Commission on Fraudulent Financial Reporting, 1987 (Treadway Commission) Vol. 1
https://egrove.olemiss.edu/aicpa_sop/1661/thumbnail.jp
External Churning and Internal Flexibility: Evidence on the Functional Flexibility and Core-Periphery Hypotheses
Origins Space Telescope: baseline mission concept
The Origins Space Telescope will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did galaxies evolve from the earliest galactic systems to those found in the Universe today? How do habitable planets form? How common are life-bearing worlds? To answer these alluring questions, Origins will operate at mid- and far-infrared (IR) wavelengths and offer powerful spectroscopic instruments and sensitivity three orders of magnitude better than that of the Herschel Space Observatory, the largest telescope flown in space to date. We describe the baseline concept for Origins recommended to the 2020 US Decadal Survey in Astronomy and Astrophysics. The baseline design includes a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. A mid-infrared instrument (Mid-Infrared Spectrometer and Camera Transit spectrometer) will measure the spectra of transiting exoplanets in the 2.8 to 20 μm wavelength range and offer unprecedented spectrophotometric precision, enabling definitive exoplanet biosignature detections. The far-IR imager polarimeter will be able to survey thousands of square degrees with broadband imaging at 50 and 250 μm. The Origins Survey Spectrometer will cover wavelengths from 25 to 588 μm, making wide-area and deep spectroscopic surveys with spectral resolving power R ∼ 300, and pointed observations at R ∼ 40,000 and 300,000 with selectable instrument modes. Origins was designed to minimize complexity. The architecture is similar to that of the Spitzer Space Telescope and requires very few deployments after launch, while the cryothermal system design leverages James Webb Space Telescope technology and experience. A combination of current-state-of-the-art cryocoolers and next-generation detector technology will enable Origins’ natural background-limited sensitivity
Relevance of meiotic recombination in public health: lessons from the monodelphis domestica
Errors in meiotic recombination and its sequelae are one of the fundamental causes of newborn morbidity and mortality and results in a significant burden on public health. Current dogma regarding mechanisms of human meiosis states that recombination must occur in order for chromosomes to segregate properly. Recently, investigators have reported a positive correlation between reduced or absent recombination on chromosome 21 and a reduced genome-wide recombination rate. Although recombination rates vary among individuals, successful disjunction is not inextricably tied to recombination rate, and successful meiotic disjunction can occur in the absence of recombination. In addition to individual variation, recombination rates vary between genders and among different species. To better explore relationships between nondisjunction, disjunction and recombination, studies of an animal model with inherently lower genome-wide rates of recombination are useful. This project assesses the role of meiotic recombination in disjunction and nondisjunction based on studies of humans and Monodelphis domestica. Understanding the mechanisms that influence correct chromosomal segregation during meiosis could lead to methods of prophylaxis that could reduce the occurrence of such errors, and subsequently reduce newborn morbidity and mortality