For studies examining risk factors of sexually transmitted infections (STIs), confounding can stem from characteristics of partners of study subjects, and persist after adjustment for the subjects’ individual-level characteristics. Two conditions that can result in confounding by the subjects’ partners are: (C1) partner choice is assortative by the risk factor examined and, (C2) sexual activity is associated with the risk factor. The objective of this paper is to illustrate the potential impact of the assortativity bias in studies examining STI risk factors, using smoking and human papillomavirus (HPV) as an example. We developed an HPV transmission-dynamic mathematical model in which we nested a cross-sectional study assessing the smoking–HPV association. In our base case, we assumed (1) no effect of smoking on HPV, and (2) conditions C1–C2 hold for smoking (based on empirical data). The assortativity bias caused an overestimation of the odds ratio (OR) in the simulated study after perfect adjustment for the subjects’ individual-level characteristics (adjusted OR 1·51 instead of 1·00). The bias was amplified by a lower basic reproductive number (R0), greater mixing assortativity and stronger association of smoking with sexual activity. Adjustment for characteristics of partners is needed to mitigate assortativity bias.

In this brief review I sum up some recent progress in the area of stellar dynamics, focusing on the dynamics of self-bound stellar associations in isolation and in (approximate) equilibrium. The basics of stellar dynamics are first outlined and the importance of stellar evolution is stressed. Subsequently I argue that the evolution of multi-mass clusters in the point-mass approximation still holds clues to the dynamics of galaxy nuclei. I take a more personal standpoint when discussing the role of stellar evolution on the dynamics over relaxation time scales and draw from several recent models to underscore that a major step forward has been made in the coupling of stellar evolution and dynamics. I then briefly visit the issue of multiple stars and highlight some as yet unsolved problems.

The motion of a black hole about the centre of gravity of its host galaxy induces a strong response from the surrounding stellar population. We consider the case of a harmonic potential and show that half of the stars on circular orbits in that potential shift to an orbit of lower energy, while the other half receive a positive boost. The black hole itself remains on an orbit of fixed amplitude and merely acts as a catalyst for the evolution of the stellar energy distribution function f(E). We then consider orbits in the logarithmic potential and identify the response of stars near resonant energies. The kinematic signature of black hole motion imprints the stellar line-of-sight mean velocity to a magnitude ≃ 13% the local root mean-square velocity dispersion σ. The high velocity dispersion at the 5:2 resonance hints to an observable effect at a distance ≃ 3 times the hole's influence radius.

Given that numerous amphibians are suffering population declines, it is becoming increasingly important to examine the relationship between disease and environmental disturbance. Indeed, while many studies relate anthropogenic activity to changes in the parasitism of snails and fishes, little is known of the impact on the parasites of amphibians, particularly from agriculture. For 2 years, the parasite communities of metamorphic northern leopard frogs from 7 agricultural wetlands were compared with those from 2 reference wetlands to study differences in parasite community diversity and abundance of various species under pristine conditions and 3 categories of disturbance: only agricultural landscape, only pesticides, and agricultural landscape with pesticides. Agricultural (and urban) area was negatively related to species richness, and associated with the near absence of adult parasites and species that infect birds or mammals. We suggest that agriculture and urbanization may hinder parasite transmission to frogs by limiting access of other vertebrate hosts of their parasites to wetlands. The only parasite found at all localities was an unidentified echinostome infecting the kidneys. This parasite dominated communities in localities surrounded by the most agricultural land, suggesting generalist parasites may persist in disrupted habitats. Community composition was associated with dissolved organic carbon and conductivity, but few links were found with pesticides. Pollution effects may be masked by a strong impact of land use on parasite transmission.

The discovery of $\sim$500 planetary nebulae (PNe) in the bulge region allows us to probe the bulge out to $\sim8$ kpc. This opens up the possibility to track bulge-disc interactions to unprecedented details. We present an exploration of bulge dynamics with Nbody models of a triaxial bulge embedded in an exponential disc (Peyaud 2005).

A major goal of contemporary astrophysics is understanding theorigin of the most massive galaxies in the universe, particularly nearbyellipticals and spirals. Theoretical models ofgalaxy formation have existed for many decades, although observationalevidence at both low and high redshifts is only beginning to put constraints on different ideas. We briefly describe theseobservations and how they are revealing the methods by which galaxies form by contrastingand comparing fiducial rapid collapse and hierarchical formation modelpredictions. The available data show that cluster ellipticals must haverapidly formed at z > 2, and that up to50% of all massive galaxies at z ~ 2.5 are involved in major mergers.While the former is consistent with the monolithic collapse picture, weargue that hierarchical formation is the only model that can reproduce all the available observations.

New GSC-II proper motions of RR Lyrae and Blue Horizontal Branch (BHB) stars near the North Galactic Pole are used to show that the Galactic Halo 5 kpc above the Plane has a significantly retrograde galactic rotation.

We summarize results from the first year of the Lenses Structure andDynamics Survey (LSD). Using the Echelle Imager and Spectrograph atthe Keck-II Telescope, we have measured spatially resolved velocitydispersion profiles of a sample of distant (up to z=1) early-typegalaxies that are gravitational lenses. By combining lensing anddynamical analyses we can set firm limits on the dark matter densityprofile, the controversial inner slope of the dark matter halo, themass-to-light ratio of the luminous component, the total massdistribution, and on the velocity ellipsoid by breaking the massanisotropy-relation. The implications of these measurements in termson the epoch and mechanism of formation of E/S0 galaxies and of thevalue of the Hubble constant are briefly discussed.

We use the method of statistical parallaxes to construct the rotationcurve of the Milky Way spanning the Galactocentric distance intervalfrom 2 to 14 kpc based on observational data for young disk populationsand refine the distance scales of the objects belonging to young diskpopulations (classical Cepheids, young open clusters, blue supergiants,HII regions, and HI).

We obtain ages and metallicities of four open clusters fromcharacteristics of SB2 eclipsing binary members of these clusters.In addition, we present similar estimates obtained with a modificationof the color-magnitude diagram method for six open and globular clusters.

A sample of nearly 400 stars, selected from the Tycho-2 catalog, has beenobserved towards the North Galactic Pole with the high resolution echellespectrograph Elodie. Combining those data with a local sample from the Hipparcos catalog, adetailed study of the disk components is done. A dynamical analysis is alsoperformed, enabling us to put new constraints on the local mass density.

A capture scenario of the origin of ω Centauri is studied numerically. We show that the most serious problem of this scenario - how to move a progenitor of ω Cen from a typical dwarf orbit to the current position of ω Cen - can be solve for a nucleated dwarf galaxy with Hernquistdensity profile.

Recent progress on the structure and dynamics of bulges is reviewed.Those aspects that link galaxy bulges either to oblate spheroids akin toelliptical galaxies or to rapidly-rotating, flattened systems more nearlyresembling the products of disk internal transformations, are highlighted. Theanalysis of surface brightness profiles derived from HST data is reviewed toshow that unresolved nuclear components detected by HST have biased thedetermination of surface brightness profiles obtained from the ground; r1/4 profiles are virtually nonexistent in galaxybulges. Predictions from accretion N-body models on the shape of surfacebrightness profiles are discussed. The position of bulges on the FundamentalPlane (FP) of elliptical galaxies is examined to infer clues on bulgepopulation ages and bulge dynamical structure. Kinematic diagnostics on theinternal dynamics of bulges are examined. Finally, a new approach to thekinematic analysis of galaxies, based on the use of synthetic spectra of singlestellar population models instead of the standard stellar templates, ispresented.

We use a Fourier analysis method to study the spiral structure of the discgalaxies in the Frei et al. (1996) sample. We show that m=1components are more often associated with asymmetries between the twoarms of an m=2 spiral than with global lopsidedness of the disc. Thepower in the m=2 components is correlated with the arm class. Themajority of galaxies with arm class 9 or 12 show clear signs ofmodulation in their spiral arms, suggesting the action of anamplification mechanism like the Swing amplification. Finally we report new detections of underlying large-scale bisymmetric components in flocculent spiral galaxies.

A simple model for the evolution of an isothermal disk has been developed.It combines both the chemical evolution (through the Age-MetallicityRelation) and dynamical evolution (through the age-dispersion relation). Applying this model to a sample of Red Clump Stars from the Tycho-2 catalog,observed with the high resolution echelle spectrograph Elodie at theObservatoire de Haute Provence, we derive the underlying Star FormationHistory and compare it with local determinations using chromosphericactivity survey by Rocha-Pinto et al. (2000b).

We have compiled a new catalogue of open clusters in the Galaxy which updates the previous catalogues of Lyngå (1987) and of Mermilliod (1995) (included in the WEBDA database). New objects and new data, in particular, data on kinematics (proper motions, radial velocities) that were not present in the old catalogues, have been included. Virtually all the clusters (1622) presently known were included, which represents an increment of about 450 objects relative to the Lyngå (1987) catalogue. The catalogue is presented in a single table containing all the important data (positions, reddenings, distances, ages, kinematics) which makes it easy to use. The catalogue includes mean absolute proper motions for hundreds of open clusters (Dias et al. 2001, 2002a) obtained using the Tycho2 proper motions. Unpublished mean radial velocities of several dozens of clusters are also presented in this work. The catalogue is being constantly updated and the latest version can be accessed on-line at http://www.astro.iag.usp.br/~wilton/ were more data such as membership probabilities for individual stars can also be accessed.

As the first step in our study of the spiralstructure of disk galaxies in the Frei sample, we determine the valuesof their deprojection angles. We introduce two methods based on the analysis of the spiral structure. Thesetwo methods behave as well as the rest of the methods used normally in the literature.

The kinematical parameters of the local field RR Lyrae populationand the zero-point of the log $P-\langle M_K\rangle$ relation for thesevariables are inferred by applying the statistical parallax(maximum-likeli-hood) technique to a sample of 182 RR Lyraes withknown periods, radial-velocities, metallicities, K-bandphotometry, and absolute proper motions on the ICRS system.Hipparcos, Tycho-2, SPM, UCAC, NPM1, and the Four-Million StarCatalog (Volchkov et al. 1992) were used asthe sources of proper motions; the proper motions of the last twocatalogs are reduced to the Hipparcos (ICRS) system (Dambis &Rastorguev 2001). The K-band magnitudes were adopted fromthe list of Fernley et al. (1998) andsupplemented by the data of the 2MASS Second Incremental DataRelease. The parameters of the velocity distribution are found tobe: ($U_0 = -10 \pm 10$, $V_0 = -51 \pm 8$, $W_0 = -14 \pm5)$ km s-1; ($\sigma_U = 62 \pm 10$, $\sigma_V = 45 \pm 8$,$\sigma_W = 28 \pm 6$) km s-1: and ($U_0 = -23 \pm 13$, $V_0 = -213 \pm 12$, $W_0 = -5 \pm 8$) km s-1; ($\sigma_U = 157 \pm 12$, $\sigma_V = 98 \pm 8$, $\sigma_W = 91 \pm 7$) km s-1 for the thick-disk (41 stars) andhalo (141 stars) objects, respectively. The zero-point of theinfrared PL relation of Jones et al. (1992)(based on the results obtained using the Baade-Wesselink method)is confirmed: we find $\langle M_K\rangle= -2.33 \cdot \log P_{\rm F}-0.82 \pm0.12$ compared to $\langle M_K\rangle= -2.33 \cdot \log P_{\rm F}-0.88$ asinferred by Jones et al. (1992). A conversion ofthe resulting log $P-\langle M_K\rangle $ relation to V-band luminositiesyields the metallicity-luminosity relation $\langle M_V\rangle= +1.04 + 0.14\cdot [$Fe/H$] \pm 0.11$. Our results imply a solar Galactocentric distance of $R_0 = 7.6 \pm 0.4$ kpc and an LMC distance modulus of $DM_{\rm LMC} = 18.18 \pm 0.12$ (cluster RR Lyraes) or $DM_{\rm LMC} = 18.11 \pm 0.12$ (field RR Lyraes), thereby favoringthe so-called short distance scale.

We present the first determination of fundamental parameters (positions, reddenings, distances, ages and kinematics) for a sample of 22 open clusters in the solar vicinity. A systematic search for unknown open clusters using the astrometric and photometric data included in the Tycho2 catalogue has resulted in the identification of several candidates. In this work, we introduce 11 of the most promising open cluster candidates. The reality of the stellar aggregates is supported by the analysis of proper motions, colour-magnitude diagrams, stellar density distributions, and by the visual inspection of the Digitised Sky Survey (DSS) plates. The proper motion data included in the Tycho2 catalogue has also allowed us to identify members in 11 open clusters for which no information, besides their positions and estimates of their apparent diameters, was previously available. Reddenings, distances and ages were determined for most objects using colour-magnitude diagrams for cluster members, built using the photometry included in Tycho2, complemented by spectral types found in the literature. We find that the majority of the aggregates are nearby (closer than ~500 pc) open clusters.