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[en] We review briefly the fundamental equations of a semimicroscopic core-particle coupling method that makes no reference to an intrinsic system of coordinates. We then demonstrate how an intrinsic system can be introduced in the strong coupling limit so as to yield a completely equivalent formulation. It is emphasized that the conventional core-particle coupling calculation introduces a further approximation that avoids what has hitherto been the most time-consuming feature of the full theory, and that this approximation can be introduced either in the intrinsic system, the usual case, or in the laboratory system, our preference. A new algorithm is described for the full theory that largely removes the difference in complexity between the two types of calculation. Comparison of the full and approximate theories for some representative cases provides a basis for the assessment of the accuracy of the traditional approach. We find that for well-deformed nuclei, e.g., 157Gd and 157Tb, the core-coupling method and the full theory give similar results. copyright 1997 The American Physical Society
[en] Put forward more than three decades ago as an alternative to conventional shell-model calculations, the Kerman-Klein method has proved feasible previously only when applied to unrealistically small configuration spaces or when phenomenological simplifications have been superposed. Starting from a spherical shell-model Hamiltonian, we describe a fully microscopic calculation, free of the above limitations, of the properties of the ground-state band of a typical deformed rare-earth nucleus, 158Gd. copyright 1997 The American Physical Society
[en] We reexamine the long-standing problem of the microscopic derivation of a particle-core coupling model. We base our research on the Klein-Kerman approach, as amended by Doenau and Frauendorf. We describe the formalism to calculate energy spectra and transition strengths in some detail. We apply our formalism to the rotational nuclei 155,157Gd, where recent experimental data requires an explanation. We find no clear evidence of a need for Coriolis attenuation, though such an effect may be masked by the use of a quadrupole-quadrupole coupling strength as a fitting parameter
[en] The most consistently useful simple model for the study of odd deformed nuclei, the particle-rotor model (strong-coupling limit of the core-particle coupling model) has nevertheless been beset by a long-standing problem: It is necessary in many cases to introduce an ad hoc parameter that reduces the size of the Coriolis interaction coupling the collective and single-particle motions. Of the numerous suggestions put forward for the origin of this supplementary interaction, none of those actually tested by calculations has been accepted as the solution of the problem. In this paper we seek a solution for the difficulty within the framework of a general formalism that starts from the spherical shell model and is capable of treating an arbitrary linear combination of multipole and pairing forces. With the restriction of the interaction to the familiar sum of a quadrupole multipole force and a monopole pairing force, we have previously studied a semimicroscopic version of the formalism whose framework is nevertheless more comprehensive than any previously applied to the problem. We obtained solutions for low-lying bands of several strongly deformed odd rare-earth nuclei and found good agreement with experiment, except for an exaggerated staggering of levels for K=(1)/(2) bands, which can be understood as a manifestation of the Coriolis attenuation problem. We argue that within the formalism utilized, the only way to improve the physics is to add interactions to the model Hamiltonian. We verify that by adding a magnetic dipole interaction of essentially fixed strength, we can fit the K=(1)/(2) bands without destroying the agreement with other bands. In addition we show that our solution also fits 163Er, a classic test case of Coriolis attenuation that we had not previously studied. copyright 1997 The American Physical Society
[en] In a previous paper a semimicroscopic core-particle coupling method that includes the conventional strong coupling core-particle model as a limiting case was applied to spectra and electromagnetic properties of several well-deformed odd nuclei. This work coupled a large single particle space to the ground-state bands of the neighboring even cores. In this paper, we generalize the theory to include excited bands of the cores, such as β and γ bands, and thereby show that the resulting theory can account for the location and structure of all bands up to about 1.5 MeV. copyright 1996 The American Physical Society
[en] In two previous papers, the Kerman-Klein-Doenau-Frauendorf model was used to study rotational bands of odd deformed nuclei. Here we describe backbending for odd nuclei using the same model. The backbending in the neighboring even nuclei is described by a phenomenological two-band model, and this core is then coupled to a large single-particle space, as in our previous work. The results obtained for energies and M1 transition rates are compared with experimental data for 165Lu and for energies alone to the experimental data for 179W. For the case of 165Lu comparison is also made with previous theoretical work. copyright 1996 The American Physical Society
[en] We present statistical characteristics of 1578 δ Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodríguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of δ Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodríguez's work. All the δ Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing δ Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.
[en] We conducted a search for occultations of bright stars by Kuiper Belt Objects (KBOs) to estimate the density of subkilometer KBOs in the sky. We report here the first results of this occultation survey of the outer solar system conducted in 2007 June and 2008 June/July at the MMT Observatory using Megacam, the large MMT optical imager. We used Megacam in a novel shutterless continuous-readout mode to achieve high-precision photometry at 200 Hz, which with point-spread function convolution results in an effective sampling of ∼30 Hz. We present an analysis of 220 star hours of data at a signal-to-noise ratio of 25 or greater, taken from images of fields within 3 deg. of the ecliptic plane. The survey efficiency is greater than 10% for occultations by KBOs of diameter d ≥ 0.7 km, and we report no detections in our data set. We set a new 95% confidence level upper limit for the surface density Σ N(d) of KBOs larger than 1 km: Σ N(d ≥ 1 km) ≤ 2.0 x 108 deg-2, and for KBOs larger than 0.7 km Σ N(d ≥ 0.7 km) ≤ 4.8 x 108 deg-2.
[en] P/2011 S1 (Gibbs) is an outer solar system comet or active Centaur with a similar orbit to that of the famous 29P/Schwassmann-Wachmann 1. P/2011 S1 (Gibbs) has been observed by the Pan-STARRS 1 (PS1) sky survey from 2010 to 2012. The resulting data allow us to perform multi-color studies of the nucleus and coma of the comet. Analysis of PS1 images reveals that P/2011 S1 (Gibbs) has a small nucleus <4 km radius, with colors g P1 – r P1 = 0.5 ± 0.02, r P1 – i P1 = 0.12 ± 0.02, and i P1 – z P1 = 0.46 ± 0.03. The comet remained active from 2010 to 2012, with a model-dependent mass-loss rate of ∼100 kg s–1. The mass-loss rate per unit surface area of P/2011 S1 (Gibbs) is as high as that of 29P/Schwassmann-Wachmann 1, making it one of the most active Centaurs. The mass-loss rate also varies with time from ∼40 kg s–1 to 150 kg s–1. Due to its rather circular orbit, we propose that P/2011 S1 (Gibbs) has 29P/Schwassmann-Wachmann 1-like outbursts that control the outgassing rate. The results indicate that it may have a similar surface composition to that of 29P/Schwassmann-Wachmann 1. Our numerical simulations show that the future orbital evolution of P/2011 S1 (Gibbs) is more similar to that of the main population of Centaurs than to that of 29P/Schwassmann-Wachmann 1. The results also demonstrate that P/2011 S1 (Gibbs) is dynamically unstable and can only remain near its current orbit for roughly a thousand years.
[en] We present a pre-survey study of using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) high sampling rate video mode guide star images to search for trans-Neptunian objects (TNOs). Guide stars are primarily used by Pan-STARRS to compensate for image motion and hence improve the point-spread function. With suitable selection of the guide stars within the Pan-STARRS 7 deg2 field of view, the light curves of these guide stars can also be used to search for occultations by TNOs. The best target stars for this purpose are stars with high signal-to-noise ratio (S/N) and small angular size. In order to do this, we compiled a catalog using the S/N calculated from stars with mV < 13 mag in the Tycho2 catalog, then cross matched these stars with the Two Micron All Sky Survey catalog, and estimated their angular sizes from (V - K) color. We also outlined a new detection method based on matched filter that is optimized to search for diffraction patterns in the light curves due to occultation by sub-kilometer TNOs. A detection threshold is set to compromise between real detections and false positives. Depending on the theoretical size distribution model used, we expect to find up to a hundred events during the three-year lifetime of the Pan-STARRS-1 project. The high sampling (30 Hz) of the project facilitates detections of small objects (as small as 400 m), which are numerous according to power-law size distribution, and thus allows us to verify various models and further constrain our understanding of the structure in the outer reach of the solar system. We have tested the detection algorithm and the pipeline on a set of engineering data (taken at 10 Hz instead of 30 Hz). No events were found within the engineering data, which is consistent with the small size of the data set and the theoretical models. Meanwhile, with a total of ∼22 star-hours video mode data (|β| < 100), we are able to set an upper limit of N(>0.5 km) ∼ 2.47 x 1010 deg-2 at 95% confidence limit.