Alien Registration- Lambert, David G. (Robbinston, Washington County)

https://digitalmaine.com/alien_docs/1413/thumbnail.jp

Rubidium and lead abundances in giant stars of the globular clusters M 13 and NGC 6752

We present measurements of the neutron-capture elements Rb and Pb in five giant stars of the globular cluster NGC 6752 and Pb measurements in four giants of the globular cluster M 13. The abundances were derived by comparing synthetic spectra with high resolution, high signal-to-noise ratio spectra obtained using HDS on the Subaru telescope and MIKE on the Magellan telescope. The program stars span the range of the O-Al abundance variation. In NGC 6752, the mean abundances are [Rb/Fe] = -0.17 +/- 0.06 (sigma = 0.14), [Rb/Zr] = -0.12 +/- 0.06 (sigma = 0.13), and [Pb/Fe] = -0.17 +/- 0.04 (sigma = 0.08). In M 13 the mean abundance is [Pb/Fe] = -0.28 +/- 0.03 (sigma = 0.06). Within the measurement uncertainties, we find no evidence for a star-to-star variation for either Rb or Pb within these clusters. None of the abundance ratios [Rb/Fe], [Rb/Zr], or [Pb/Fe] are correlated with the Al abundance. NGC 6752 may have slightly lower abundances of [Rb/Fe] and [Rb/Zr] compared to the small sample of field stars at the same metallicity. For M 13 and NGC 6752 the Pb abundances are in accord with predictions from a Galactic chemical evolution model. If metal-poor intermediate-mass asymptotic giant branch stars did produce the globular cluster abundance anomalies, then such stars do not synthesize significant quantities of Rb or Pb. Alternatively, if such stars do synthesize large amounts of Rb or Pb, then they are not responsible for the abundance anomalies seen in globular clusters.Comment: Accepted for publication in Ap

The Interstellar Rubidium Isotope Ratio toward Rho Ophiuchi A

The isotope ratio, 85Rb/87Rb, places constraints on models of the nucleosynthesis of heavy elements, but there is no precise determination of the ratio for material beyond the Solar System. We report the first measurement of the interstellar Rb isotope ratio. Our measurement of the Rb I line at 7800 A for the diffuse gas toward rho Oph A yields a value of 1.21 +/- 0.30 (1-sigma) that differs significantly from the meteoritic value of 2.59. The Rb/K elemental abundance ratio for the cloud also is lower than that seen in meteorites. Comparison of the 85Rb/K and 87Rb/K ratios with meteoritic values indicates that the interstellar 85Rb abundance in this direction is lower than the Solar System abundance. We attribute the lower abundance to a reduced contribution from the r-process. Interstellar abundances for Kr, Cd, and Sn are consistent with much less r-process synthesis for the solar neighborhood compared to the amount inferred for the Solar System.Comment: 12 pages with 2 figures and 1 table; will appear in ApJ Letter

High-Resolution Measurements of Intersystem Bands of Carbon Monoxide toward X Persei

In an echelle spectrum of X Per acquired with the Space Telescope Imaging Spectrograph we have identified individual rotational lines of 11 triplet-singlet (intersystem) absorption bands of ^12CO. Four bands provide first detections for interstellar clouds. From a comparison with the zeta Oph sight line we find that X Per is obscured by a higher 12CO column density of 1.4 x 10^16 cm-2. Together with the high spectral resolution of 1.3 km s-1, this allows (i) an improved measurement of previously published f-values for seven bands, and (ii) an extraction of the first astrophysical oscillator strengths for d-X (8-0), (9-0), and (10-0), as well as for e-X (12-0). The ^13CO d-X (12-0) band, previously suspected to exist toward zeta Oph, is now readily resolved and modeled. Our derived intersystem f-values for ^12CO include a few mild (leq 34%) disagreements with recent predictions from a perturbation analysis calculated for the interstellar excitation temperature. Overall, the comparison confirms the superiority of employing multiple singlet levels in the calculations of mixing coefficients over previous single-level predictions.Comment: 11 pages (incl. 1 figure). Accepted by ApJ Letter

Rubidium and lead abundances in giant stars of the globular clusters M4 and M5

We present measurements of the neutron-capture elements Rb and Pb for bright giants in the globular clusters M4 and M5. The clusters are of similar metallicity ([Fe/H] = -1.2) but M4 is decidedly s-process enriched relative to M5: [Ba/Fe] = +0.6 for M4 but 0.0 for M5. The Rb and Pb abundances were derived by comparing synthetic spectra with high-resolution, high signal-to-noise ratio spectra obtained with MIKE on the Magellan telescope. Abundances of Y, Zr, La, and Eu were also obtained. In M4, the mean abundances from 12 giants are [Rb/Fe] = 0.39 +/- 0.02 (sigma = 0.07), [Rb/Zr] = 0.17 +/- 0.03 (sigma = 0.08), and [Pb/Fe] = 0.30 +/- 0.02 (sigma = 0.07). In M5, the mean abundances from two giants are [Rb/Fe] = 0.00 +/- 0.05 (sigma = 0.06), [Rb/Zr] = 0.08 +/- 0.08 (sigma = 0.11), and [Pb/Fe] = -0.35 +/- 0.02 (sigma = 0.04). Within the measurement uncertainties, the abundance ratios [Rb/Fe], [Pb/Fe] and [Rb/X] for X = Y, Zr, La are constant from star-to-star in each cluster and none of these ratios are correlated with O or Na abundances. While M4 has a higher Rb abundance than M5, the ratios [Rb/X] are similar in both clusters indicating that the nature of the s-products are very similar for each cluster but the gas from which M4's stars formed had a higher concentration of these products.Comment: Accepted for publication in Ap

Precision of the determination of focal depth from the spectral ratio of Love/Rayleigh surface waves

The precision with which the focal depth may be determined using Love/Rayleigh-wave spectral ratios depends on the accuracy of the models for Earth structure and for source mechanism used in the focal depth calculations. Estimates of the precision of the focal depth determination are obtained using the partial derivatives of Love/Rayleigh spectral ratios with respect to the parameters: focal depth, shear velocity, dip angle, and slip angle. We find that errors caused by imprecise knowledge of any of these parameters can be important in practice

Finding cool subdwarfs using a V-J reduced proper-motion diagram: Stellar parameters for 91 candidates

We present the results of a search for cool subdwarfs for which our candidates were drawn from a V-J reduced proper-motion diagram constructed by Salim & Gould (2002). Kinematic (U, V, and W) and self-consistent stellar parameters (Teff, log g, [Fe/H], and V_t) are derived for 91 candidate subdwarfs based on high resolution spectra. The observed stars span 3900K < Teff < 6200K and -2.63 < [Fe/H] < 0.25 including only 3 giants (log g < 4.0). Of the sample, 77 stars have MgH lines present in their spectra. With more than 56% of our candidate subdwarfs having [Fe/H] < -1.5, we show that the V-J reduced proper-motion diagram readily identifies metal-poor stars.Comment: PASP (in press

Intersecting D5-brane models with massive vector-like leptons

We construct eight-stack intersecting D5-brane models, with an orbifold transverse space, that yield the (non-supersymmetric) standard model up to vector-like leptons. The matter includes right-chiral neutrinos and the models have the renormalisable Yukawa couplings to tachyonic Higgs doublets needed to generate mass terms for {\it all} matter, including the vector-like leptons. The models are constrained by the requirement that twisted tadpoles cancel, that the gauge boson coupled to the weak hypercharge $U(1)_Y$ does not get a string-scale mass via a generalised Green-Schwarz mechanism, and that there are no surviving, unwanted gauged U(1) symmetries coupled to matter. Gauge coupling constant ratios close to those measured are easily obtained for reasonable values of the parameters, consistently with having the string scale close to the electroweak scale, as required to avoid the hierarchy problem. Unwanted (colour-triplet, charged-singlet, and neutral-singlet) scalar tachyons can be removed by a suitable choice of the parameters.Comment: 15 pages, LaTeX fil