Joint Motions of the Knee, Hip, and Trunk during a Single-Leg Step-Down Test and Running

The purpose of this study was to examine the relationship between kinematic variables at the knee, hip, and trunk during a single-leg step-down test (SDT) and running. Twenty-five healthy subjects (12 male, 13 female) participated in the study; mean ± SD age, 32.8 ± 5.9 years; height, 173.9 ± 8.7 cm; body mass, 70.84 ± 11.3 kg; run volume, 59.5 ± 30.4 km/wk; cadence, 173.1 ± 11.5 steps/min). Dominant leg peak knee flexion was identified during the run (PKF-RUN) and used to find frontal plane knee and hip, and sagittal plane trunk angles. The same treadmill-matched knee flexion angle for the run was used to find the knee flexion angle identified during the SDT (TMKF-SDT). Knee, hip, and trunk angles were also identified at the point of the SDT where the heel made contact with the ground (HEEL-SDT). Two separate two-tailed paired samples t-tests were used to analyze the difference between the means of each test condition and Pearson Product Correlation coefficients were computed for each condition. Statistics revealed significant differences in frontal plane knee and hip angles between PKF-RUN (6.18 degrees ± 8.90) and TMKF-SDT (8.13 degrees ± 8.88), t(24) = -2.21, p = 0.037 for frontal plane knee adduction, and; PKF-RUN (11.14 degrees ± 3.22) and TMKF-SDT (6.48 degrees ± 4.53), t(24) = 6.17, p \u3c 0.0001 for frontal plane hip adduction. There were significant differences between mean PKF-RUN (6.18 degrees ± 8.90) and HEEL-SDT (16.65 degrees ± 12.60), t(24) = -6.79, p \u3c 0.0001 frontal plane knee adduction, and; PKF-RUN (11.14 degrees ± 3.22) and HEEL-SDT (17.84 degrees ± 5.63), t(24) = -6.45, p \u3c 0.0001 for frontal plane hip adduction. No significant differences were found between mean PKF-RUN (6.44 degrees ± 3.67) and TMKF-SDT (6.33 degrees ± 6.46), t(24) = 0.104, p = 0.918 sagittal plane trunk flexion. There were significant differences between mean PKF-RUN (6.44 degrees ± 3.67) and HEEL-SDT (10.32 degrees ± 10.04), t(24) = -2.19, p = 0.039 sagittal plane trunk flexion. Correlations between PKF-RUN and TMKF-SDT were strong in the knee (r = 0.88, p \u3c 0.0001, R2 = 0.768) and moderate in the hip (r = 0.57, p = 0.003, R2 = 0.325). Correlations between PKF-RUN and HEEL-SDT were strong in the knee (r = 0.80, p \u3c 0.0001, R2 = 0.634) and fair in the hip (r = 0.42, p = 0.038, R2 = 0.175). For the trunk, correlations between PKF-RUN and TMKF-SDT were moderate (r = 0.53, p = 0.006, R2 = 0.285) and correlations between PKF-RUN and HEEL-SDT were fair-to-moderate (r = 0.49, p = 0.014, R2 = 0.237). The SDT and running may not be directly relatable to one another in the knee and hip. The trunk is also not relatable to running at the bottom of the SDT. Clinicians should use caution when utilizing the SDT

Simulating CCD images of elliptical galaxies

We introduce a procedure developed by the ``Teramo Stellar Populations Tools'' group (Teramo-SPoT), specifically optimized to obtain realistic simulations of CCD images of elliptical galaxies. Particular attention is devoted to include the Surface Brightness Fluctuation (SBF) signal observed in ellipticals and to simulate the Globular Cluster (GC) system in the galaxy, and the distribution of background galaxies present in real CCD frames. In addition to the physical properties of the simulated objects - galaxy distance and brightness profile, luminosity function of GC and background galaxies, etc. - the tool presented allows the user to set some of the main instrumental properties - FoV, zero point magnitude, exposure time, etc.Comment: Presented at From Stars to Galaxies: Building the Pieces to Build up the Universe (StarGal 2006), Venice, Italy, 16-20 Oct 200

On the Metallicity-Color Relations and Bimodal Color Distributions in Extragalactic Globular Cluster Systems

We perform a series of numerical experiments to study how the nonlinear metallicity--color relations predicted by different stellar population models affect the color distributions observed in extragalactic globular cluster systems. % We present simulations in the $UBVRIJHK$ bandpasses based on five different sets of simple stellar population (SSP) models. The presence of photometric scatter in the colors is included as well. % We find that unimodal metallicity distributions frequently ``project'' into bimodal color distributions. The likelihood of this effect depends on both the mean and dispersion of the metallicity distribution, as well as of course on the SSP model used for the transformation. % Adopting the Teramo-SPoT SSP models for reference, we find that optical--to--near-IR colors should be favored with respect to other colors to avoid the bias effect in globular cluster color distributions discussed by \citet{yoon06}. In particular, colors such as \vh\ or \vk are more robust against nonlinearity of the metallicity--color relation, and an observed bimodal distribution in such colors is more likely to indicate a true underlying bimodal metallicity distribution. Similar conclusions come from the simulations based on different SSP models, although we also identify exceptions to this result.Comment: ApJ accepte

The luminosity function of the Large Magellanic Cloud globular cluster NGC 1866

We present {\it Hubble Space Telescope} {\it V,I} photometry of the central region of the LMC cluster NGC 1866, reaching magnitudes as faint as V=27 mag. We find evidence that the cluster luminosity function shows a strong dependence on the distance from the cluster center, with a clear deficiency of low luminosity stars in the inner region. We discuss a {\it global} cluster luminosity function as obtained from stars in all the investigated region, which appears in impressive agreement with the prediction from a Salpeter mass distribution. We also revisit the use of NGC 1866 as a probe for determining the efficiency of core overshooting, and conclude that a definitive answer to this question is not possible from this cluster.Comment: AJ accepted, 16 pages, 19 figures, uses aastex.cl

New optical and near-infrared Surface Brightness Fluctuations models. A primary distance indicator ranging from Globular Clusters to distant galaxies?

We present new theoretical models for Surface Brightness Fluctuations (SBF) both for optical and near-infrared bands in standard ground-based and Hubble Space Telescope filter systems. Simple Stellar Population simulations are adopted. Models cover the age and metallicity ranges from $t=5$ to $15~Gyr$ and from $Z=0.0001$ to 0.04 respectively. Effects due to the variation of the Initial Mass Function and the stellar color-temperature relations are explored. Particular attention is devoted to very bright stars in the color-magnitude diagram and to investigate the effects of mass loss along the Red Giant Branch (RGB) and the Asymptotic Giant Branch (AGB). It is found that $U$ and $B$ bands SBF amplitudes are powerful diagnostics for the morphology of the Horizontal Branch and the Post-AGB stars population. We point out that a careful treatment of mass loss process along the RGB and AGB is fundamental in determining reliable SBF evaluations. The SBF measurements are used to give robust constraints on the evolution of AGB stars, suggesting that mass loss activity on AGB stars should be twice more efficient than on the RGB stars. Our models are able to reproduce the absolute SBF magnitudes of the Galactic Globular Clusters and of galaxies, and their integrated colors. New calibrations of absolute SBF magnitude in $V$, $R$, $I$, and $K$ photometric filters are provided, which appear reliable enough to directly gauge distances bypassing other distance indicators. The SBF technique is also used as stellar population tracer to derive age and metallicity of a selected sample of galaxies of known distances. Finally, {\it SBF color} versus {\it integrated color} diagrams are proposed as particularly useful in removing the well known {\it age-metallicity degeneracy} affecting our knowledge of remote stellar systems.Comment: AJ accepted, 46 pages, 21 figures, 10 tables, uses aastex.cl

Blue Straggler Stars: The Spectacular Population in M80

Using HST-WFPC2 observations in two ultraviolet (UV) filters (F225W and F336W) of the central region of the high density Galactic Globular cluster (GGC) M80 we have identified 305 Blue Straggler Stars (BSS) which represents the largest and most concentrated population of BSS ever observed in a GGC. We also identify the largest, clean sample of evolved BSS yet found. The high stellar density alone cannot explain the BSS, and we suggest that in M80 we are witnessing a transient dynamical state, during which stellar interactions are delaying the core-collapse process leading to an exceptionally large population of collisional-BSS.Comment: 15 pages, 5 figures, Astrophysical Journal Letters, in pres

CCD Photometry of Galactic Globular Clusters. IV. The NGC 1851 RR Lyraes

The variable star population of the galactic globular cluster NGC 1851 (C0512-400) has been studied by CCD photometry, from observations made in the B, V, and I bands during 1993-4. Light curves are presented for 29 variables, seven of which are new discoveries. The behavior of the RR lyraes in the period-temperature diagram appears normal when compared to clusters which bracket the NGC 1851 metallicity. Reddening and metallicity are re-evaluated, with no compelling evidence to change from accepted values. Photometry for stars within an annulus with radii 80 and 260 arcsec agrees to better than 0.02 mag in all colors with extensive earlier photometry, to at least V = 18.5. Instability strip boundary positions for several clusters shows a trend for the red boundary to move to redder colors as the metallicity increases.Comment: 29 pages, 9 figures, accepted by A.

The distance to the LMC cluster NGC 1866 and the surrounding field

We use the Main Sequence stars in the LMC cluster NGC 1866 and of Red Clump stars in the local field to obtain two independent estimates of the LMC distance. We apply an empirical Main Sequence-fitting technique based on a large sample of subdwarfs with accurate {\sl Hipparcos} parallaxes in order to estimate the cluster distance modulus, and the multicolor Red Clump method to derive distance and reddening of the LMC field. We find that the Main Sequence-fitting and the Red Clump distance moduli are in significant disagreement; NGC 1866 distance is equal to $\rm (m-M)_{0,NGC 1866}=18.33\pm$0.08 (consistent with a previous estimate using the same data and theoretical Main Sequence isochrones), while the field stars provide $\rm (m-M)_{0,field}=18.53\pm$0.07. This difference reflects the more general dichotomy in the LMC distance estimates found in the literature. Various possible causes for this disagreement are explored, with particular attention paid to the still uncertain metallicity of the cluster and the star formation history of the field stars.Comment: 5 pages, incl. 1 figure, uses emulateapj.sty, ApJ accepte

Discovery of another peculiar radial distribution of Blue Stragglers in Globular Clusters: The case of 47 Tuc

We have used high resolution WFPC2-HST and wide field ground-based observations to construct a catalog of blue straggler stars (BSS) in the globular cluster 47 Tuc spanning the entire radial extent of the cluster. The BSS distribution is highly peaked in the cluster center, rapidly decreases at intermediate radii, and finally rises again at larger radii. The observed distribution closely resembles that discovered in M3 by Ferraro et al (1993,1997). To date, complete BSS surveys covering the full radial extent (HST in the center and wide field CCD ground based observations of the exterior) have been performed for only these two clusters. Both show a bimodal radial distribution, despite their different dynamical properties. BSS surveys covering the full spatial extent of more globular clusters are clearly required to determine how common bimodality is and what its consequence is for theories of BSS formation and cluster dynamics.Comment: 21 pages, 6 figures, accepted for pubblication in Ap

A Chandra X-ray Study of the Globular Cluster M80

We report our analysis of a Chandra X-ray observation of the rich globular cluster M80, in which we detect some 19 sources to a limiting 0.5-2.5 keV X-ray luminosity of 7*10^30 ergs/s within the half-mass radius. X-ray spectra indicate that two of these sources are quiescent low-mass X-ray binaries (qLMXBs) containing neutron stars. We identify five sources as probable cataclysmic variables (CVs), one of which seems to be heavily absorbed, implying high inclination. The brightest CV may be the X-ray counterpart of Nova 1860 T Sco. The concentration of the X-ray sources within the cluster core implies an average mass of 1.2+/-0.2 Msun, consistent with the binary nature of these systems and very similar to the radial distribution of the blue stragglers in this cluster. The X-ray and blue straggler source populations in M80 are compared to those in the similar globular cluster 47 Tuc.Comment: Submitted to ApJ. 15 pages, 6 figure