The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda I

Images have been obtained with the Hubble Space Telescope WFPC2 camera of Andromeda I, a dwarf spheroidal (dSph) galaxy that lies in the outer halo of M31. The resulting color-magnitude diagrams reveal for the first time the morphology of the horizontal branch in this system. We find that, in a similar fashion to many of the galactic dSph companions, the horizontal branch (HB) of And~I is predominantly red. Combined with the metal abundance of this dSph, this red HB morphology indicates that And I can be classified as a ``second parameter'' system in the outer halo of M31. This result then supports the hypothesis that the outer halo of M31 formed in the same extended chaotic manner as is postulated for the outer halo of the Galaxy.Comment: 26 pages using aas2pp4.sty, including 2 tables and 7 figures, to be published in AJ. Figure 1 is in gif form. To include in main ps file, use xv to create a ps file called Da_Costa.fig1.ps and uncomment appropriate lines in .tex fil

The Next Generation Virgo cluster Survey. V. modelling the dynamics of M87 with the Made-to-Measure method

We study the dynamics of the giant elliptical galaxy M87 from the central to the outermost regions with the made-to-measure (M2M) method. We use a new catalogue of 922 globular cluster line-of- sight velocities extending to a projected radius of 180 kpc (equivalent to 25 M87 effective radii), and SAURON integral field unit data within the central 2.4 kpc. 263 globular clusters, mainly located beyond 40 kpc, are newly observed by the Next Generation Virgo Survey (NGVS). For the M2M modelling, the gravitational potential is taken as a combination of a luminous matter potential with a constant stellar mass-to-light ratio and a dark matter potential modelled as a logarithmic potential. Our best dynamical model returns a stellar mass-to-light ratio in the I band of M/LI = 6.0(+ -0.3) M_sun/L_sun with a dark matter potential scale velocity of 591(+ -50) km/s and scale radius of 42(+ -10) kpc. We determine the total mass of M87 within 180 kpc to be (1.5 + - 0.2) 10^13 M_sun. The mass within 40 kpc is smaller than previous estimates determined using globular cluster kinematics that did not extend beyond 45 kpc. With our new globular cluster velocities at much larger radii, we see that globular clusters around 40 kpc show an anomalously large velocity dispersion which affected previous results. The mass we derived is in good agreement with that inferred from ROSAT X-ray observation out to 180 kpc. Within 30 kpc our mass is also consistent with that inferred from Chandra and XMM-Newton X-ray observations, while within 120 kpc it is about 20% smaller. The model velocity dispersion anisotropy beta parameter for the globular clusters in M87 is small, varying from -0.2 at the centre to 0.2 at 40 kpc, and gradually decreasing to zero at 120 kpc.Comment: 20 pages, 16 figures, Accepted by Ap

Adolescent substance use: a prospective longitudinal model of substance use onset among South African adolescents

Substance use onset among Colored adolescents between eighth and ninth grades in an urban area of Cape Town, South Africa was examined using latent transition analysis. Longitudinal self-report data regarding substance use (N = 1118, 50.9% female) were collected in 2004 and 2005. Results indicated that the pattern of onset was similar across genders; adolescents first tried either alcohol or cigarettes, followed by both, then dagga (cannabis), and then inhalants. The prevalence of lifetime cigarette use was slightly greater for females; dagga (cannabis) and inhalant use were greater for males. The similarity of developmental onset in the current sample to previous international work supports the promise of adapting prevention programs across contexts. The study’s limitations are noted.Web of Scienc

Student Readiness of Colleges: A Qualitative Study

Using the framework of belonging, this qualitative study explores how one upper midwestern college engages in student-readiness and explores the disconnects that create barriers to student-readiness. The study investigates ‘student readiness’ broadly through the literature and more specifically by narrowing efforts to a detailed examination of one college by conducting interviews, observations, and collecting artifacts. The results of the study revealed that the college addressed student readiness differently depending on perspectives of staff/faculty, administration, and students. Three themes emerged after coding and examination of the data: supports, community and disconnect

The Next Generation Virgo Cluster Survey. VI. The Kinematics of Ultra-compact Dwarfs and Globular Clusters in M87

The origin of ultra-compact dwarfs (UCDs)--objects larger and more massive than typical globular clusters (GCs), but more compact than typical dwarf galaxies--has been hotly debated in the 15 years since their discovery. Even whether UCDs should be considered galactic in origin, or simply the most extreme GCs, is not yet settled. We present the dynamical properties of 97 spectroscopically confirmed UCDs (rh >~10 pc) and 911 GCs associated with central cD galaxy of the Virgo cluster, M87. Our UCDs, of which 89% have M_star > ~2X10^6 M_sun and 92% are as blue as the classic blue GCs, nearly triple the sample of previous confirmed Virgo UCDs, providing by far the best opportunity for studying the global dynamics of a UCD system. We found that (1) UCDs have a surface number density profile that is shallower than that of the blue GCs in the inner ~ 70 kpc and as steep as that of the red GCs at larger radii; (2) UCDs exhibit a significantly stronger rotation than the GCs, and the blue GCs seem to have a velocity field that is more consistent with that of the surrounding dwarf ellipticals than with that of UCDs; (3) UCDs have a radially increasing orbital anisotropy profile, and are tangentially-biased at radii < ~ 40 kpc and radially-biased further out. In contrast, the blue GCs become more tangentially-biased at larger radii beyond ~ 40 kpc; (4) GCs with M_star > 2X10^6 M_sun have rotational properties indistinguishable from the less massive ones, suggesting that it is the size, instead of mass, that differentiates UCDs from GCs as kinematically distinct populations. We conclude that most UCDs in M87 are not consistent with being merely the most luminous and extended examples of otherwise normal GCs. The radially-biased orbital structure of UCDs at large radii is in general agreement with the "tidally threshed dwarf galaxy" scenario.Comment: 27 pages, 21 figures. To appear in The Astrophysical Journa

Understanding leisure-related program effects by using process data in the HealthWise South Africa Project

As the push for evidence-based programming gathers momentum, many human services programs and interventions are under increased scrutiny to justify their effectiveness across different conditions and populations. Government agencies and the public want to be assured that their resources are being put to good use on programs that are effective and efficient. Thus, programs are increasingly based on theory and evaluated through randomized control trials using longitudinal data. Despite this progress, hypothesized outcomes are often not detected and/or their effect sizes are small. Moreover, findings may go against intuition or “gut feelings” on the part of project staff. Given the need to understand how program implementation issues relate to outcomes, this study focuses on whether process measures that focus on program implementation and fidelity can shed light on associated outcomes. In particular, we linked the process evaluation of the HealthWise motivation lesson with outcomes across four waves of data collection. We hypothesized that HealthWise would increase learners’ intrinsic and identified forms of motivation, and decrease amotivation and extrinsic motivation. We did not hypothesize a direction of effects on introjected motivation due to its conceptual ambiguity. Data came from youth in four intervention schools (n = 902, 41.1%) and five control schools (n = 1291, 58.9%) who were participating in a multi-cohort, longitudinal study. The schools were in a township near Cape Town, South Africa. For each cohort, baseline data are collected on learners as they begin grade 8. We currently have four waves of data collected on the first cohort, which is the focus of this paper. The mean age of the sample at wave 3 was 15.0 years (SD = .86) and 51% of students were female. Results suggested that there was evidence of an overall program effect of the curriculum on amotivation regardless of fidelity of implementation. Compared to the control schools, all treatment school learners reported lower levels of amotivation in wave 4 compared to wave 3, as hypothesized. Using process evaluation data to monitor implementation fi147 delity, however, we also conclude that the school with better trained teachers who also reported higher levels of program fidelity had better outcomes than the other schools. We discuss the implications of linking process data with outcome data and the associated methodological challenges in linking these data.Web of Scienc