John Chi Lin Wang

VARIABLE STARS IN GALACTIC GLOBULAR CLUSTERS

Based on a search of the literature up to 2001 May, the number of known variable stars in Galactic globular clusters is approximately 3000. Of these, more than 2200 have known periods and the majority (approximately 1800) are of the RR Lyrae type. In addition to the RR Lyrae population, there are approximately 100 eclipsing binaries, 120 SX Phoenicis variables, 60 Cepheids (including Population II Cepheids, anomalous Cepheids and RV Tauri), and 120 SR/red variables. The mean period of the fundamental mode RR Lyrae variables is 0.585 days, for the overtone variables it is 0.342 days (0.349 days for the first-overtone pulsators and 0.296 days for the second-overtone pulsators) and approximately 30% are overtone pulsators. These numbers indicate that about 65% of RR Lyrae variables in Galactic globular clusters belong to Oosterhoff type I systems. The mean period of the RR Lyrae variables in the Oosterhoff type I clusters seems to be correlated with metal abundance in the sense that the periods are longer in the more metal poor clusters. Such a correlation does not exist for the Oosterhoff type II clusters. Most of the Cepheids are in clusters with blue horizontal branches.

Effects of internal dust on the narrow-line region Lyman and Balmer decrements

We present detailed calculations on the effects of internal dust on the Balmer and Lyman decrements for a spherically symmetric distribution of low covering factor clouds photoionized by a power law. In the first stage, we assume an open geometry with clouds represented as slabs and consider the effects of Lya resonance and absorption by dust. We consider the important effects of perspective on the emergent fluxes, which in our simplified scheme present either the photoionized face to the observer (f) or the back (b) face. We adopt canonical values for the gas excitation (U f ) and for the ionizing energy distribution (α=-1.4, F ν ∞ν +α )

The ANKH ΔE490Mutation in Calcium Pyrophosphate Dihydrate Crystal Deposition Disease (CPPDD) Affects Tissue Non-specific Alkaline Phosphatase (TNAP) Activities

ANKH (human homolog of progressive ankylosis) regulates inorganic pyrophosphate (PPi) transport. Dominant ANKH mutations were detected in at least five multiplex families with calcium pyrophosphate dihydrate crystal deposition disease (CPPPD). The objective of this study is to assess the functional consequences of one CPPDD-associated ANKH mutation (ΔE490) in chondrogenic ATDC5 cells. Stable ATDC5 transfectants bearing myc-tagged constructs of wild-type ANKH, mutant ANKH (ΔE490) and neo controls were generated. Upon ITS (insulin, transferrin and selenium) induction, expression of chondrocyte markers including alkaline phosphatase activity in the various transfectants was assessed. The ANKH ΔE490- transfectants had low alkaline phosphatase activities throughout ITS treatment due to lower TNAP protein expression and the presence of intracellular low-molecular-weight inhibitors. Our results suggest that the interplay of ANKH and TNAP activities is tightly regulated.

A semi‐analytic model for cyclotron line formation

We present a semi‐analytic, physical motivated model for the formation of the cyclotron fundamental feature, in addition to the higher harmonic features, in static media of moderate depth. The spectra derived from the semi‐analytic model agree well with those obtained from ‘exact’ Monte Carlo simulations. These models are able to produce narrow fundamental and second harmonic features with comparable equivalent widths, which are the main characteristics of the harmonically spaced low energy absorption‐like features observed by the Ginga satellite in the spectra of three classical γ‐ray bursts. We are currently generalizing the semi‐analytic model to dynamic media, in particular, to line formation in a relativistic, radiation driven wind.

Cyclotron resonant scattering in gamma-ray bursts - Further analysis of GB880205

We have extended our previous work by exploring several plane-parallel slab geometries to model the formation of cyclotron line features. We calculated the Compton temperature [ital T][sub [ital C]] as a function of column density [ital N][sub [ital e]] for each of the new geometries. We then fit the resulting spectra to GB880205 exactly as described in Wang [ital et] [ital al]. The results show that the addition of column depth below the photon source plane leads to a modest improvement in [chi][sup 2] which, although not statistically significant, is pleasing because these geometries are more physically realistic.

Line strength variations in gamma‐ray burst GB870303: Possible evidence of neutron star rotation

An exhaustive search of the Ginga data on γ‐ray burst GB870303 reveals two separate time intervals during which statistically significant line features are evident. One (previously unreported) interval shows a single prominent line feature at ≊20 keV; a second, corresponding to the interval reported by Murakami et al., shows two line features at ≊20 and 40 keV. From model fits to the data, we find that both sets of lines are well‐described by cyclotron resonant scattering in a magnetic field B≊1.8×1012 G, and that the differences in the line strengths between the two intervals are significant. The variations are qualitatively similar to those produced by a change in the viewing angle θ relative the magnetic field. We conjecture that the change in θ is due to rotation of the neutron star, and derive limits 45 sec ≲P≲180 sec on the rotation period P.