We present the Fe, Ca, Ti, Ni, Ba, Na, and O abundances for a sample of 53 red giant branch stars in the globular cluster (GC) NGC 5024 (M53). The abundances were measured from high signal-to-noise medium resolution spectra collected with the Hydra multi-object spectrograph on the Wisconsin–Indiana–Yale–NOAO 3.5 m telescope. M53 is of interest because previous studies based on the morphology of the cluster’s horizontal branch suggested that it might be composed primarily of first generation (FG) stars and differ from the majority of other GCs with multiple populations, which have been found to be dominated by the second generation (SG) stars. Our sample has an average [Fe/H] = −2.07 with a standard deviation of 0.07 dex. This value is consistent with previously published results. The alpha-element abundances in our sample are also consistent with the trends seen in Milky Way halo stars at similar metallicities, with enhanced [Ca/Fe] and [Ti/Fe] relative to solar. We find that the Na–O anti-correlation in M53 is not as extended as other GCs with similar masses and metallicities. The ratio of SG to the total number of stars in our sample is approximately 0.27 and the SG generation is more centrally concentrated. These findings further support that M53 might be a mostly FG cluster and could give further insight into how GCs formed the light element abundance patterns we observe in them today.

We present an analysis of the internal bulk rotation in the metal-poor globular cluster (GC) NGC 5024 (M53) using radial velocities (RVs) of individual cluster members. We use RV measurements from a previous abundance study of M53 done using the Hydra multi-object spectrograph on the WIYN 3.5 m telescope. The Hydra sample greatly increases the number of RVs available in the central regions of the cluster where the internal rotation is the strongest. The sample of cluster members is further increased through two previous kinematic studies of M53. The combined total sample contains 245 cluster members. With our sample, we are able to create a velocity dispersion profile of the cluster and derive a central velocity dispersion s =  -4.0 0.3 km s ; 0 1 we find that M53 inner regions are characterized by a peak amplitude of rotation equal to  -1.4 0.1 km s 1 corresponding to a relatively high value of the ratio of the rotation speed to central velocity dispersion ( s =  V 0.35 0.04 rot 0). Our data also reveal a radial variation in the orientation of the projected rotation axis suggesting complex internal kinematics.

NGC 5053 provides a rich environment to test our understanding of the complex evolution of globular clusters (GCs). Recent studies have found that this cluster has interesting morphological features beyond the typical spherical distribution of GCs, suggesting that external tidal effects have played an important role in its evolution and current properties. Additionally, simulations have shown that NGC 5053 could be a likely candidate to belong to the Sagittarius dwarf galaxy (Sgr dSph) stream. Using the Wisconsin-Indiana-Yale-NOAO-Hydra multi-object spectrograph, we have collected high quality (signal-to-noise ratio ∼ 75-90), medium-resolution spectra for red giant branch stars in NGC 5053. Using these spectra we have measured the Fe, Ca, Ti, Ni, Ba, Na, and O abundances in the cluster. We measure an average cluster [Fe/H] abundance of −2.45 with a standard deviation of 0.04 dex, making NGC 5053 one of the most metal-poor GCs in the Milky Way (MW). The [Ca/Fe], [Ti/Fe], and [Ba/Fe] we measure are consistent with the abundances of MW halo stars at a similar metallicity, with alphaenhanced ratios and slightly depleted [Ba/Fe]. The Na and O abundances show the Na-O anti-correlation found in most GCs. From our abundance analysis it appears that NGC 5053 is at least chemically similar to other GCs found in the MW. This does not, however, rule out NGC 5053 being associated with the Sgr dSph stream.

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Time-resolved spectra throughout the orbit of EF Eri during its low accretion state were obtained with the Solar Blind Channel on the Advanced Camera for Surveys onboard the Hubble Space Telescope. The overall spectral distribution exhibits peaks at 1500 and 1700Å, while the UV light curves display a quasisinusoidal modulation over the binary orbit. Models of white dwarfs with a hot spot and cyclotron emission were attempted to fit the spectral variations throughout the orbit. A non-magnetic white dwarf with a temperature of ∼10,000K and a hot spot with central temperature of 15,000K generally matches the broad absorptions at 1400 and 1600Å with those expected for the quasimolecular H features H 2 and H + 2 . However, the flux in the core of the Lyα absorption does not go to zero, implying an additional component, and the flux variations throughout the orbit are not well matched at long wavelengths. Alternatively, a 9500K white dwarf with a 100 MG cyclotron component can fit the lowest (phase 0.0) fluxes, but the highest fluxes (phase 0.5) require an additional source of magnetic field or temperature. The 100 MG field required for the UV fit is much higher than that which fits the optical/IR wavelengths, which would support previous suggestions of a complex field structure in polars.