5,758 research outputs found
Age and Dust Degeneracy for Starburst Galaxies Solved?
A spectral evolution model of galaxies that includes both stellar and dust
effects is newly built. xApplying the model to 22 nearby starburst galaxies, we
have shown that far infrared luminosity of galaxies helps to break the
age-dustiness degeneracy. We have derived a unique solution of age and the
dustiness for each starburst galaxy. The resulting starburst ages and optical
depths are in the range and , respectively. The result is robust and is almost independent of model
assumptions such as dust distributions, extinction curves, and burst strengths.
With the rapidly growing sensitivity of submillimeter detectors, it should
become possible in the near future to determine the age and of
star-forming galaxies at redshifts and beyond. Accurate estimates
of for Lyman-break galaxies and high-z galaxies might require a
substantial revision of the previously claimed picture of star formation
history over the Hubble time.Comment: Latex (aas2pp4) 15 pages, 1 table, 6 figures. Accepted for Ap
Field-Induced Effects of Anisotropic Magnetic Interactions in SrCu2(BO3)2
We observed a field-induced staggered magnetization in the 2D frustrated
dimer-singlet spin system SrCu2(BO3)2 by 11B NMR, from which the magnitudes of
the intradimer Dzyaloshinsky-Moriya interaction and the staggered g-tensor were
determined. These anisotropic interactions cause singlet-triplet mixing and
eliminate a quantum phase transition at the expected critical field Hc for gap
closing. They also provide a quantitative account for some puzzling phenomena
such as the onset of a uniform magnetization below the and the persistence of
the excitation gap above Hc. The gap was accurately determined from the
activation energy of the nuclear relaxation rate.Comment: 8 pages, 5 figures, published versio
The Ages of Dwarf Ellipticals
We present narrow band photometry of 91 dwarf ellipticals in the Coma and
Fornax clusters taken through the Stromgren (uvby) filter system. Dividing the
sample by dwarf morphology into nucleated (dEN) and non-nucleated (dE) dwarfs
reveals two distinct populations of early-type systems based on integrated
colors. The class of dEN galaxies are redder in their continuum colors as
compared to bright cluster ellipticals and dE type dwarfs, and their position
in multi-color diagrams can only be explained by an older mean age for their
underlying stellar populations. By comparison with the narrow band photometry
of the M87 globular cluster system (Jordan et al. 2002), we find that dENs are
a higher metallicity continuation of the old, metal-poor color sequence of
galactic globulars and the blue population of M87 globulars. Bright ellipticals
and dE dwarfs, on the other hand, follow the color sequence of the metal-rich,
red population of M87 globulars. A comparison to SED models, convolved to a
simple metallicity model, finds that dENs and blue globulars are 3 to 4 Gyrs
older than cluster ellipticals and 5 Gyrs older than dE type galaxies. The
implication is that globulars and dEN galaxies are primordial and have
metallicities set by external constraints such as the enrichment of their
formation clouds. Bright ellipticals and dE galaxies have metallicities and
ages that suggest an extended phase of initial star formation to produce a
younger mean age, even if their formation epoch is similar to that of dENs and
blue globulars, and an internally driven chemical evolutionary history.Comment: 13 pages AAS LaTeX, 6 figures, accepted for publication in A
Results from the EPL monkey-pod flight experiments conducted aboard the NASA/Ames CV-990, May 1976
The participation of the Environmental Physiology Laboratory (EPL) in the general purpose laboratory concept verification test 3 is documented. The EPL Monkey-Pod Experiment was designed to incorporate a 10-12 kg, pig tailed monkey, Macaca nemestrina, into the pod and measure the physiological responses of the animal continously. Four major elements comprise the EPL Monkey-Pod Experiment System: (1) a fiberglass pod containing the instrumented monkey plus feeder and watering devices, (2) an inner console containing the SKYLAB mass spectrometer with its associated valving and electronic controls, sensing, control and monitoring units for lower body negative pressure, feeder activity, waterer activity, temperatures, and gas metabolism calibration, (3) an umbilical complex comprising gas flow lines and electrical cabling between the inner and outer console and (4) an outer console in principle representing the experiment support to be provided from general space craft sources
Results from the EPL monkey-pod experiment conducted as part of the 1974 NASA-Ames CVT/GPL 3
For abstract, see vol. 2
Captain Cook and the Pacific Islands
ill. ; 28 cmIncludes bibliographical referencesPacific Islands Studies Conference (3rd : 1978 : University of Hawaii)Editors' Introduction / Jane N. Hurd and Michiko Kodama -- Opening Remarks / Carl J. Daeufer -- Hawaii Foundation for History and the Humanities / William J. Bonk -- The Role of the Bishop Museum in the Pacific / Edward C. Creutz -- Introductory Remarks / Jane N. Hurd -- The Yorkshire Haunts of Captain Cook / John Charles -- Some Historical Materials that Relate to the Pre-Captain Cook Pacific in Continental European Institutions / Richard Mayer -- Some British Sources of Information on Voyages to Hawaii, 1786-1820 / Bruce Palmer -- The Scientific Significance of Cook's Third Voyage / Charles H. Lamoureux -- The Consequences of Cook's Hawaiian Contacts on the Local Population / Peter N. D. Pirie -- Agricultural Pattern and Nutritional Status of People in the South Pacific Countries / Yeuh-Heng Yang -- Captain Cook and Pacific Islanders: "All Imaginable Humanity"? / Timothy J. Macnaught -- Mental Health in the Pacific / Kenneth O. Sanborn -- Interests and Dependencies: The Pacific After Cook / Craig Severence -- Summation and Closing Remarks / James McCutcheon
Results from the EPL monkey-pod experiment conducted as part of the 1974 NASA/Ames shuttle CVT-2
The participation of the Environmental Physiology Laboratory (EPL) in the general purpose laboratory concept verification test 3 is documented. The EPL Monkey-Pod Experiment was designed to incorporate a 10-12 kg, pig tailed monkey, Macaca nemestrina, into the pod and measure the physiological responses of the animal continuously. Four major elements comprise the EPL Monkey-Pod Experiment System: (1) a fiberglass pod containing the instrumented monkey plus feeder and watering devices, (2) an inner console containing the SKYLAB mass spectrometer with its associated valving and electronic controls, sensing, control and monitoring units for lower body negative pressure, feeder activity, waterer activity, temperatures, and gas metabolism calibration, (3) an umbilical complex comprising gas flow lines and electrical cabling between the inner and outer console and (4) an outer console in principle representing the experiment support to be provided from general spacecraft sources
A Robust Age Indicator for Old Stellar Populations
We derive new spectral H_gamma index definitions which are robust age
indicators for old and relatively old stellar populations and thus have great
potential for solving the age-metallicity degeneracy of galaxy spectra. To
study H_gamma as a function of age, metallicity and resolution, we used a new
spectral synthesis model which predicts SEDs of single-age, single-metallicity
stellar populations at resolution FWHM=1.8A (which can be smoothed to different
resolutions), allowing direct measurements of the equivalent widths of
particular absorption features. We find that the H_gamma strong age
disentangling power strongly depends strongly on the adopted resolution and
galaxy velocity dispersion. We propose a system of indices which are completely
insensitive to metallicity and stable against resolution, allowing the study of
galaxies up to ~300 km/s. Observational spectra of very high S/N and relatively
high dispersion, are required to gain this unprecedented age discriminating
power. Once such spectra are obtained, accurate and reliable estimates for the
luminosity-weighted average stellar ages of these galaxies will become possible
for the first time, without assessing their metallicities. We measured this
index for two globular clusters, a number of low-luminosity elliptical galaxies
and a standard S0 galaxy. We find a large spread in the average stellar ages of
a sample of low-luminosity ellipticals. In particular these indices yield 4 Gyr
for M32, in agreement with the age provided by an extraordinary fit to the full
spectrum of this galaxy that we achieve here.Comment: 22 pages, 4 figures. ApJ, in press. Models and details can be found
at http://www.ioa.s.u-tokyo.ac.jp/~vazdekis
Young red supergiants and the near infrared light appearance of disk galaxies
Disk galaxies often show prominent nonaxisymmetric features at near-infrared
wavelengths. Such features may indicate variations in the surface density of
stellar mass, contributions from young red supergiants in star forming regions,
or substantial dust obscuration. To distinguish among these possibilities, we
have searched for spatial variations in the 2.3 micron photometric CO index
within the disks of three nearby galaxies (NGC 278, NGC 2649, & NGC 5713). This
index measures the strength of the absorption bands of molecular CO in stellar
atmospheres, and is strong in cool, low surface-gravity stars, reaching the
largest values for red supergiants. We observe significant spatial CO index
variations in two galaxies (NGC 278 & NGC 5713), indicating that the dominant
stellar population in the near-infrared is not everywhere the same. Central CO
index peaks are present in two galaxies; these could be due to either
metallicity gradients or recent star formation activity. In addition,
significant azimuthal CO index variations are seen in NGC 278. Because strong
azimuthal metallicity gradients are physically implausible in disk galaxies,
these features are most naturally explained by the presence of a young stellar
population. The fraction of 2 micron light due to young stellar populations in
star forming regions can be calculated from our data. Overall, young stellar
populations can contribute ~3% of a (normal) galaxy's near infrared flux.
Locally, this fraction may rise to ~33%. Thus, young stars do not dominate the
total near infrared flux, but can be locally dominant in star forming regions,
and can bias estimates of spiral arm amplitude or other nonaxisymmetric
structures in galaxies' mass distributions.Comment: 28 pages including 3 postscript figures. A fourth figure is in jpeg
format. Uses AASTeX. Accepted for publication in The Astronomical Journa
Mechanistic studies on DNA damage by minor groove binding copper–phenanthroline conjugates
Copper–phenanthroline complexes oxidatively damage and cleave nucleic acids. Copper bis-phenanthroline and copper complexes of mono- and bis-phenanthroline conjugates are used as research tools for studying nucleic acid structure and binding interactions. The mechanism of DNA oxidation and cleavage by these complexes was examined using two copper–phenanthroline conjugates of the sequence-specific binding molecule, distamycin. The complexes contained either one or two phenanthroline units that were bonded to the DNA-binding domain through a linker via the 3-position of the copper ligand. A duplex containing independently generated 2-deoxyribonolactone facilitated kinetic analysis of DNA cleavage. Oxidation rate constants were highly dependent upon the ligand environment but rate constants describing elimination of the alkali-labile 2-deoxyribonolactone intermediate were not. Rate constants describing DNA cleavage induced by each molecule were 11–54 times larger than the respective oxidation rate constants. The experiments indicate that DNA cleavage resulting from β-elimination of 2-deoxyribonolactone by copper–phenanthroline complexes is a general mechanism utilized by this family of molecules. In addition, the experiments confirm that DNA damage mediated by mono- and bis-phenanthroline copper complexes proceeds through distinct species, albeit with similar outcomes
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