Within the newly formulated composite fermion hierarchy the filling fraction of a spherical quantum Hall system is obtained when it can be expressed as an odd or even denominator fraction. A plot of $\nu\frac{2S}{N-1}$ as a function of $2S$ for a constant number of particles (up to N=10001) exhibits structure of the fractional quantum Hall effect. It is confirmed that $\nu_e +\nu_h=1$ for all particle-hole conjugate systems, except systems with $N_e =N_h$, and $N_e=N_h \pm 1$.

P. Sitko J. J. Quinn D. C. Marinescu

A composite Fermion hierarchy theory is constructed in a way related to the original Haldane picture by applying the composite Fermion (CF) transformation to quasiparticles of Jain states. It is shown that the Jain theory coincides with the Haldane hierarchy theory for principal CF fillings. Within the Fermi liquid approach for few electron systems on the sphere a simple interpretation of many-quasiparticle spectra is given and provides an explanation of failure of CF hierarchy picture when applied to the hierarchical $4/11$ state.

P. Sitko K. -S. Yi J. J. Quinn

The interaction energy of the two-dimensional electron system in the region of fractional quantum Hall effect is considered within the Chern-Simons composite fermion approach. In the limit when Coulomb interaction is very small comparing to the cyclotron energy the RPA results are obtained for the fillings $\nu=1/3, 1/5, 2/3, 2/5, 3/7$ and compared with the exact diagonalization results for small systems (extrapolated for infinite systems). They show very poor agreement suggesting the need for looking for alternative approaches.

P. Sitko

The exclusion statistics of quasiparticles is found at any level of the hierarchy of condensed states of composite fermion excitations (for which experimental indications have recently been found). The hierarchy of condensed states of excitations in boson Jain states is introduced and the statistics of quasiparticles is found. The quantum Hall states of charged $\alpha$-anyons ($\alpha$ -- the exclusion statistics parameter) can be described as incompressible states of $(\alpha+2p)$-anyons ($2p$ -- an even number).

Piotr Sitko

The O VIII phenomenon describes the occurrence of ultra-high ionization absorption lines of the CNO elements (e.g. O VIII, N VII, C VI, and even Ne X) in the optical spectra hot of DO WDs.

K. Werner S. Dreizler J. W. Kruk M. L. Sitko

The debris disks surrounding the pre-main sequence stars HD 31648 and HD 163296 were observed spectroscopically between 3 and 14 microns. Both possess a silicate emission feature at 10 microns which resembles that of the star beta Pictoris and those observed in solar system comets. The structure of the band is consistent with a mixture of olivine and pyroxene material, plus an underlying continuum of unspecified origin. The similarity in both size and structure of the silicate band suggests that the material in these systems had a processing history similar to that in our own solar system prior to the time that the grains were incorporated into comets.

Michael L. Sitko Carol A. Grady David K. Lynch Ray W. Russell Martha S. Hanner

The TW Hydrae Association is the nearest young stellar association. Among its members are HD 98800, HR 4796A, and TW Hydrae itself, the nearest known classical T Tauri star. We have observed these three stars spectroscopically between 3 and 13 microns. In TW Hya the spectrum shows a silicate emission feature that is similar to many other young stars with protostellar disks. The 11.2 micron feature indicative of significant amounts of crystalline olivine is not as strong as in some young stars and solar system comets. In HR 4796A, the thermal emission in the silicate feature is very weak, suggesting little in the way of (small silicate) grains near the star. The silicate band of HD 98800 (observed by us but also reported by Sylvester and Skinner (1996)) is intermediate in strength between TW Hya and HR 4796.

M. L. Sitko D. K. Lynch R. W Russell

The charge of quasiparticles in Pfaffian states of composite fermion excitations (the presence of which is indicated by recent experiments) is found. At the filling fraction of the Pfaffian state $\nu=p/q$ (of the lowest Landau level) the charge is $\pm e/(2q)$. As in the case of the Pfaffian state of electrons the statistics of $N_{qh}$ quasiholes in the Pfaffian state corresponds to the spinor representation of $U(1)\times SO(2N_{qh})$ (the continuous extension of the braid group). Here U(1) is given by the phase factor $e^{i({1/8}+\frac{1}{4m})\pi}$ with $m=1+\alpha$, $\alpha$ -- the exclusion statistics parameter of Jain quasiparticles. The possiblity of Read-Rezayi states of Jain quasiparticles is also discussed.

Piotr Sitko

Mike Lockwood and Mathew Owens discuss how eclipse observations are aiding the development of a climatology of near-Earth space

Mike Lockwood Mat Owens

This paper is based on my April 2018 talk at the Maryland-Penn State dynamics conference, on the occasion of Mike Hochman receiving the Brin Prize.

Mike Boyle