We have used the infrared Barnes-Evans surface brightness technique to derive the radii and distances of 34 Galactic Cepheid variables. Radius and distance results obtained from both versions of the technique are in excellent agreement. The radii of 28 variables are used to determine the period-radius relation. This relation is found to have a smaller dispersion than in previous studies, and is identical to the period-radius relation found by Laney & Stobie from a completely independent method, a fact which provides persuasive evidence that the Cepheid period-radius relation is now determined at a very high confidence level. We use the accurate infrared distances to determine period-luminosity relations in the V , I , J , H and K passbands from the Galactic sample of Cepheids. We derive improved slopes of these relations from updated LMC Cepheid samples and adopt these slopes to obtain accurate absolute calibrations of the PL relation. By comparing these relations to the ones defined by the LMC Cepheids, we derive strikingly consistent and precise values for the LMC distance modulus in each of the passbands which yield a mean value of µ • (LMC) = 18.46 ± 0.02.By analyzing the observed dispersions of the PL relations defined by the LMC and Galactic samples of Cepheids, we disentangle the contributions due to uncertainties in the reddenings, in distance measurement and due to metallicity effects, and we estimate the intrinsic dispersion of the PL relation with the Wesenheit function. Assuming that the Galactic Cepheid distances are typically accurate to ±3% (as shown in a previous Paper), and an intrinsic spread in [Fe/H] of ∼ 0.4 dex among the Cepheids of our sample as obtained by Fry & Carney, the observed dispersion of the Galactic Cepheid PL relation suggests a metallicity dependence of ∆µ/∆[Fe/H] ≈ 0.2, about half the value suggested -3by Sasselov et al. from EROS data. When we apply this correction, the LMC distance modulus is increased to 18.52 ± 0.06 with most of this uncertainty being due to the adopted metallicity correction.Our results show that the infrared Barnes-Evans technique is very insensitive to both Cepheid metallicity and adopted reddening, and therefore a very powerful tool to derive accurate distances to nearby galaxies by a direct application of the technique to their Cepheid variables, rather than by comparing PL relations of different galaxies, which introduces much more sensitivity to metallicity and absorption corrections which are usually difficult to determine.

We present new integrated light spectroscopy of globular clusters in NGC 5128, a nearby giant elliptical galaxy less than 4 Mpc away, in order to measure radial velocities and derive ages, metallicities, and alpha-element abundance ratios. Using the Gemini South 8-meter telescope with the instrument GMOS, we obtained spectroscopy in the range of ∼ 3400 − 5700Å for 72 globular clusters with signal-to-noise greater than 30Å −1 and we have also discovered 35 new globular clusters within NGC 5128 from our radial velocity measurements. We measured and compared the Lick indices from Hδ A through Fe5406 with the single stellar population models of Thomas et al. (2003) and Thomas et al. (2004) in order to derive age, metallicity and [α/Fe] values. We also measure Lick indices for 41 Milky Way globular clusters from Puzia et al. (2002) and Schiavon et al. (2005) with the same methodology for direct comparison. Our results show that 68% of the NGC 5128 GCs have old ages (> 8 Gyr), 14% have intermediate ages (5 − 8 Gyr), and 18% have young ages (< 5 Gyr). However, when we look at the metallicity of the globular clusters as a function of age, we find 92% of metalpoor GCs and 56% of metal-rich GCs in NGC 5128 have ages > 8 Gyr, indicating that the majority of both metallicity subpopulations of globular clusters formed early, with a significant population of young and metal-rich globular clusters forming later. Our metallicity distribution function generated directly from spectroscopic Lick indices is clearly bimodal, as is the color distribution of the same set of globular clusters. Thus the metallicity bimodality is real and not an artifact of the color to metallicity conversion. However, the metallicity distribution function obtained from comparison with the single stellar population models is consistent with a unimodal, bimodal, or multimodal shape. The [α/Fe] values are supersolar with a mean value of 0.14 ± 0.04, indicating a fast formation timescale. However, the GCs in NGC 5128 are not as [α/Fe] enhanced as the Milky Way GCs also examined in this study. Our measured indices also indicate that the globular clusters in NGC 5128 may have a slight overabundance in nitrogen and a wider range of calcium strength compared to the Milky Way globular clusters. Our results support a rapid, early formation of the globular cluster system in NGC 5128, with subsequent major accretion and/or GC and star forming events in more recent times.

New radial velocity measurements for previously known and newly confirmed globular clusters in the nearby massive galaxy NGC 5128 are presented. We have obtained spectroscopy from LDSS-2/Magellan, VIMOS/VLT, and Hydra/CTIO from which we have measured the radial velocities of 218 known, and identified 155 new, globular clusters. The current sample of confirmed globular clusters in NGC 5128 is now 605 with 564 of these having radial velocity measurements, the second largest kinematic database for any galaxy. We have performed a new kinematic analysis of the globular cluster system that extends out to 45 ′ in galactocentric radius. We have examined the systemic velocity, projected rotation amplitude and axis, and the projected velocity dispersion of the globular clusters as functions of galactocentric distance and metallicity. Our results indicate that the metalpoor globular clusters have a very mild rotation signature of 26 ± 15 km s −1 . The metal-rich globular clusters are rotating with a higher, though still small signature of 43 ± 15 km s −1 around the isophotal major axis of NGC 5128 within 15 ′ . Their velocity dispersions are consistent within the uncertainties and the profiles appear flat or declining within 20 ′ . We note the small sample of metal-rich globular clusters with ages less than 5 Gyr in the literature appear to have different kinematic properties than the old, metal-rich globular cluster subpopulation. The mass and mass-to-light ratios have also been estimated using the globular clusters as tracer particles for NGC 5128. Out to a distance of 20 ′ , we have obtained a mass of (5.9 ± 2.0) × 10 11 M ⊙ and a mass-to-light ratio in the B-band of 16 M ⊙ /L B⊙ . Combined with previous work on the ages and metallicities of its globular clusters, as well as properties of its stellar halo, our findings suggest NGC 5128 formed via hierarchical merging over other methods of formation, such as major merging at late times.

We have obtained the radii and distances of 16 galactic Cepheids supposed to be members in open clusters or associations using the new optical and near-infrared calibrations of the surface brightness (Barnes-Evans) method given by Fouqué & Gieren (1997). We find excellent agreement of the radii and distances produced by both infrared techniques which use the V, V-K (K on the Carter system) and K, J-K magnitude-color combinations, respectively, and typical random errors as small as ∼2 percent. We discuss in detail possible systematic errors in our infrared solutions and conclude that the typical total uncertainty of the infrared distance and radius of a Cepheid is about 3 percent in both infrared solutions, provided that the data are of excellent quality and that the amplitude of the color curve used in the solution is larger than ∼0.3 mag. The optical V, V-R distance and radius of a given Cepheid can deviate by as much as ∼30 percent from the infrared value, due to large systematic and random errors caused by microturbulence and gravity variations which affect the optical V-R color, but not the V-K and J-K colors, as shown by Laney & Stobie (1995). We find excellent agreement of our infrared radii with the infrared radii derived by Laney & Stobie (1995) for these variables from an application of the maximum likelihood technique, which further increases our confidence that the total errors in our infrared solutions are not larger than ∼3 percent. In an Appendix we discuss the relative advantages and disadvantages of our infrared surface brightness technique and the maximum likelihood technique. We compare the adopted infrared distances of the Cepheid variables to the ZAMS-fitting distances of their supposed host clusters and associations and find an unweighted mean value of the distance ratio of 1.02 ± 0.04. A detailed discussion of the individual Cepheids shows that the uncertainty of the ZAMS-fitting distances varies considerably from cluster to cluster. We find clear evidence that four Cepheids are not cluster members (SZ Tau, T Mon, U Car and SV Vul) while we confirm cluster membership for V Cen and BB Sgr for which the former evidence for cluster membership was only weak. After rejection of non-members, we find a weighted mean distance ratio of 0.969 ± 0.014, with a standard deviation of 0.05, which demonstrates that both distance indicators are accurate to better than 5%, including systematic errors, and that there is excellent agreement between both distance scales.

Abstract. We present new near-IR light curves for six Cepheids in the young blue LMC cluster NGC 1866 as well as high precision radial velocity curves for ten Cepheids in NGC 1866 and two in NGC 2031. For the six Cepheids in NGC 1866 with new J and K light curves we determine distances and absolute magnitudes by applying the near-IR surface brightness method. We find that the formal error estimates on the derived distances are underestimated by about a factor of two. We find excellent agreement between the absolute magnitudes for the low metallicity LMC Cepheids with the Period-Luminosity (P-L) relation determined by the near-IR surface brightness (ISB) method for Galactic Cepheids suggesting that the slope of the P-L relations for low metallicity and solar metallicity samples could be very similar in contrast to other recent findings. Still there appears to be significant disagreement between the observed slopes of the OGLE based apparent P-L relations in the LMC and the slopes derived from ISB analysis of Galactic Cepheids, and by inference for Magellanic Cloud Cepheids, indicating a possible intrinsic problem with the ISB method itself. Resolving this problem could reaffirm the P-L relation as the prime distance indicator applicable as well to metallicities significantly different from the LMC value.