[en] The CTIO 4 m CCD prime-focus camera was used to obtain B and V photometry to V of about 24 mag of stars in the globular cluster NGC 7099. The color-magnitude diagram exhibits very well defined narrow cluster sequences with no blue straggler candidates and no indication of a binary star sequence lying above and to the right of the main sequence. A subdwarf-based distance modulus to the cluster of 14.65 is derived. It is found that the best fit to model isochrones is for models with enhanced oxygen abundance and an age near 17 Gyr. 38 references

[en] UBV observations of three X-ray sources in Omega Cen (sources A, D, and E of Hertz and Grindlay, 1983), obtained with a CCD detector on the 4-m telescope at CTIO in February and August 1985, are reported. The results are presented in images, graphs, and tables and characterized in detail. No optical cataclysmic variable candidates are found down to V = 24.5 mag, corresponding to M(V) = 10.6 in the cluster. It is inferred that these low-luminosity sources, located outside the globular cluster, may be superposed unrelated objects rather than close mass-exchange binaries. 35 references

[en] A differential comparison of precise CCD photometry in the globular clusters NGC 288, NGC 362, and NGC 1261 shows that differences exist in the positions of the main-sequence turnoff in these clusters that are most naturally explained if NGC 288 is some 3 billion yr older than NGC 362 and about 1 to 2 billion yr older than NGC 1261. This implies that the formation time for the Galactic halo is significantly longer than a freefall time. Consideration of the inferred ages and horizontal-branch morphologies of the clusters Pal 12, NGC 288, NGC 362, and NGC 1261, all with similar metal abundances, suggests that age may be the parameter that, after overall metal abundance, most determines horizontal-branch morphology. 56 refs

[en] The main-sequence LFs are derived for three fields at different radial distances from the center of the globular cluster M30. It is found that the LFs become flatter with decreasing radius. The observed radial dependence of the slope of the LF is compared with the predictions of mass segregation from the multi-mass component King (1966) models computed by Pryor et al. (1986). The models are shown to be consistent within the errors with an equipartition model with a global mass function slope of x = 0.9, confirming the validity of the mass segregation corrections of Pryor et al. 24 refs

[en] Spectrophotometric observations of a previously uncataloged 17th magnitude hot DA white dwarf are reported. Simple models can reproduce the visible spectrum if the star has log g = 8.0 + or - 0.5 and T(eff) = 22,500 + or - 2000 K. The implied distance is about 200 pc. It is plausible that photospheric emission from this star is responsible for the observed X-ray source. Identification of this object with the X-ray source would imply a photosphere free of traces of helium inferred in other X-ray-emitting DAs, and would support previous suggestions that current DA model atmospheres are in need of revision at X-ray wavelengths. 31 references

[en] Fast magnetization dynamics in the micro- and nanometer regime are an interesting field of research. On these length scales magnetic structures can be designed to contain a single vortex or a single domain wall. Both size and speed of these patterns are of great interest in todays research for prospective non-volatile data storage devices. Especially the possibility to move domain-walls by spin-polarized current gained a lot of interest. Magnetic configurations can be imaged by soft X-ray magnetic microscopy with a spatial resolution down to 15 nm. By a stroboscopic pump and probe measurement scheme a temporal resolution below 100 ps is achieved. This provides the opportunity to directly image changes in magnetic domains and domain-wall motion. We image oscillations of a single domain wall in a confining potential in time steps of 200 ps by time resolved X-ray microscopy at the full-field soft X-ray transmission microscope at the Advanced Light Source in Berkeley (beamline 6.1.2). Domain walls are prepared in permalloy nanostructures with a restoring potential. The oscillation of a 180^o domain wall is triggered by nanosecond current pulses. The spin-polarized current and the accompanying Oersted field can contribute to the motion of the wall. By analysis of the distinct domain-wall dynamics the dominant contribution is determined. In our geometry the motion of the wall is determined by the Oersted field although the spin-polarized current directly flows through the ferromagnetic structure. An analytical model of a rigid particle precisely describes the domain-wall motion. Oscillations are studied for different pulse length and amplitudes. From the observed oscillations we extract the driving force, the confining potential, and the domain-wall mass. Nonharmonic terms determine the motion of the wall. The influence of the nonharmonic potential is studied by looking at various phase spaces of the domain-wall motion.

[en] A color-difference technique for estimating the relative ages of globular clusters with similar chemical compositions on the basis of their CM diagrams is described and demonstrated. The theoretical basis and implementation of the procedure are explained, and results for groups of globular clusters with m/H = about -2, -1.6, and -1.3, and for two special cases (Palomar 12 and NGC 5139) are presented in extensive tables and graphs and discussed in detail. It is found that the more metal-deficient globular clusters are nearly coeval (differences less than 0.5 Gyr), whereas the most metal-rich globular clusters exhibit significant age differences (about 2 Gyr). This result is shown to contradict Galactic evolution models postulating halo collapse in less than a few times 100 Myr. 77 refs

[en] Spectra in the region of the Ca II infrared triplet (about 8300-8900 A) have been obtained for a number of low-mass X-ray binaries (LMXB) and a small sample of other cataclysmic variables. The secondary (mass-losing) star is detected strongly in only a small number of systems, indicating that the accretion disks normally contribute the majority of the flux even at these wavelengths. Emission lines of Ca II and/or H are present in some of these binaries. New photometry is presented for many of these systems. 44 refs

[en] Broadband B, V photometry was obtained for 1154 stars in the field of Pal 12. The Pal 12 main sequence is shown to contain an excess fringe of stars along its red edge which are probably binaries. The color-magnitude diagram of Pal 12 is found to be anomalous, with the principal sequences not lying near or between those of the typical Galactic globular clusters 46 Tucanae and M5. This result can be explained by Pal 12 being younger than the other two clusters by 25-30 percent. 71 refs

[en] Spectra from five nights near maximum light are presented for SN 1989B in NGC 3627. SN 1989B appears to be a typical Type Ia supernova with an envelope expansion velocity of about 10,600 km/s near maximum light. The presence of diffuse interstellar bands and Na I absorption attributable to the interstellar medium (ISM) of NGC 3627 indicates significant obscuration of the supernova. If relations between the strengths of these features and E(B - V) derived for the Galaxy can be applied to the ISM of NGC 3627, the indicated E(B - V) is about 0.8 for SN 1989B. 11 refs