Galactic substructure traced by RR Lyraes in SDSS Stripe 82

Using a sample of 407 RR Lyrae stars extracted from SDSS Stripe 82, we study the degree of substructure in the Galactic halo. We identify overdensities associated with the known substructures of the Hercules-Aquila Cloud and the Sagittarius Stream, and find a further previously-unknown substructure, the Pisces Overdensity, at ~100 kpc from the Sun. Together, the three substructures account for ~80% of our RR Lyrae sample. We also study the density distribution of RR Lyraes in the halo and find that the profile is best fit by a broken power law with an inner slope of -2.4 and a break radius of ~25 kpc, consistent with previous studies. We conclude that the halo is predominantly made up of the debris from in-falling satellites, with little or no underlying smooth component.Comment: 4 pages, 2 figures, to appear in the proceedings of "Assembling the Puzzle of the Milky Way", Le Grand Bornand (Apr. 17-22, 2011), C. Reyle, A. Robin, M. Schultheis (eds.

A discrete chemo-dynamical model of the dwarf spheroidal galaxy Sculptor: mass profile, velocity anisotropy and internal rotation

We present a new discrete chemo-dynamical axisymmetric modeling technique, which we apply to the dwarf spheroidal galaxy Sculptor. The major improvement over previous Jeans models is that realistic chemical distributions are included directly in the dynamical modelling of the discrete data. This avoids loss of information due to spatial binning and eliminates the need for hard cuts to remove contaminants and to separate stars based on their chemical properties. Using a combined likelihood in position, metallicity and kinematics, we find that our models naturally separate Sculptor stars into a metal-rich and a metal-poor population. Allowing for non-spherical symmetry, our approach provides a central slope of the dark matter density of $\gamma = 0.5 \pm 0.3$. The metal-rich population is nearly isotropic (with $\beta_r^{red} = 0.0\pm0.1$) while the metal-poor population is tangentially anisotropic (with $\beta_r^{blue} = -0.2\pm0.1$) around the half light radius of $0.26$ kpc. A weak internal rotation of the metal-rich population is revealed with $v_{max}/\sigma_0 = 0.15 \pm 0.15$. We run tests using mock data to show that a discrete dataset with $\sim 6000$ stars is required to distinguish between a core ($\gamma = 0$) and cusp ($\gamma = 1$), and to constrain the possible internal rotation to better than $1\,\sigma$ confidence with our model. We conclude that our discrete chemo-dynamical modelling technique provides a flexible and powerful tool to robustly constrain the internal dynamics of multiple populations, and the total mass distribution in a stellar system.Comment: Accepted by MNRA

Studying Gender in Conference Talks -- data from the 223rd meeting of the American Astronomical Society

We present a study on the gender balance, in speakers and attendees, at the recent major astronomical conference, the American Astronomical Society meeting 223, in Washington, DC. We conducted an informal survey, yielding over 300 responses by volunteers at the meeting. Each response included gender data about a single talk given at the meeting, recording the gender of the speaker and all question-askers. In total, 225 individual AAS talks were sampled. We analyze basic statistical properties of this sample. We find that the gender ratio of the speakers closely matched the gender ratio of the conference attendees. The audience asked an average of 2.8 questions per talk. Talks given by women had a slightly higher number of questions asked (3.2$\pm$0.2) than talks given by men (2.6$\pm$0.1). The most significant result from this study is that while the gender ratio of speakers very closely mirrors that of conference attendees, women are under-represented in the question-asker category. We interpret this to be an age-effect, as senior scientists may be more likely to ask questions, and are more commonly men. A strong dependence on the gender of session chairs is found, whereby women ask disproportionately fewer questions in sessions chaired by men. While our results point to laudable progress in gender-balanced speaker selection, we believe future surveys of this kind would help ensure that collaboration at such meetings is as inclusive as possible.Comment: 4 pages, 5 figures. Comments welcome

The Mass of the Large Magellanic Cloud from the Three-Dimensional Kinematics of its Globular Clusters

We estimate the mass of the Large Magellanic Cloud (LMC) using the kinematics of 30 LMC globular clusters (GCs). We combine proper motions (PMs) measured with HST, Gaia, or a combination of the two, from a recent study by Bennet et al. (2022) with literature line-of-sight velocities (LOSVs) to give 3 components of motion. With these, we derive a 3D velocity dispersion anisotropy $\beta = -0.72 ^{+0.62} _{-1.07}$, consistent with the GCs forming a flattened system with significant azimuthal motion. We then apply a tracer mass estimator and measure an enclosed mass $M (<13.2 \mathrm{kpc})= 2.66^{+0.42} _{-0.36} \times 10^{10} \mathrm{M}_\odot$. This is broadly consistent with results from previous studies of the LOSVs of GCs and other luminous tracers. Assuming a cosmologically-constrained NFW distribution for the dark matter, this implies a virial mass $M_\mathrm{virial} = 1.80^{+1.05} _{-0.54} \times 10^{11} \mathrm{M}_\odot$. Despite being an extrapolation by almost an order of magnitude in radius, this result is consistent with published estimates from other methods that are directly sensitive to the LMC's total mass. Our results support the conclusion that the LMC is approximately 17$^{+10}_{-6}$% of the Milky Way's mass, making it a significant contributor to the Local Group (LG) potential.Comment: 17 pages, 19 figures, 1 table, accepted for publication in Ap

HRD on the Margins: Exploring Resistance to HRD in Adult Education

This paper examines the debates and critiques surrounding HRD and confronts myths about HRD philosophy and practice. We argue that the HRD field is marginalized in adult education and reflect on both the problems this situation creates and the possibilities of ever bridging these two fields