Kinematic fingerprint of core-collapsed globular clusters

Dynamical evolution drives globular clusters toward core collapse, which strongly shapes their internal properties. Diagnostics of core collapse have so far been based on photometry only, namely on the study of the concentration of the density profiles. Here we present a new method to robustly identify core-collapsed clusters based on the study of their stellar kinematics. We introduce the \textit{kinematic concentration} parameter, $c_k$, the ratio between the global and local degree of energy equipartition reached by a cluster, and show through extensive direct $N$-body simulations that clusters approaching core collapse and in the post-core collapse phase are strictly characterized by $c_k>1$. The kinematic concentration provides a suitable diagnostic to identify core-collapsed clusters, independent from any other previous methods based on photometry. We also explore the effects of incomplete radial and stellar mass coverage on the calculation of $c_k$ and find that our method can be applied to state-of-art kinematic datasets.Comment: Accepted for publication in MNRAS Lette

Models of Individual Blue Stragglers

This chapter describes the current state of models of individual blue stragglers. Stellar collisions, binary mergers (or coalescence), and partial or ongoing mass transfer have all been studied in some detail. The products of stellar collisions retain memory of their parent stars and are not fully mixed. Very high initial rotation rates must be reduced by an unknown process to allow the stars to collapse to the main sequence. The more massive collision products have shorter lifetimes than normal stars of the same mass, while products between low mass stars are long-lived and look very much like normal stars of their mass. Mass transfer can result in a merger, or can produce another binary system with a blue straggler and the remnant of the original primary. The products of binary mass transfer cover a larger portion of the colour-magnitude diagram than collision products for two reasons: there are more possible configurations which produce blue stragglers, and there are differing contributions to the blended light of the system. The effects of rotation may be substantial in both collision and merger products, and could result in significant mixing unless angular momentum is lost shortly after the formation event. Surface abundances may provide ways to distinguish between the formation mechanisms, but care must be taking to model the various mixing mechanisms properly before drawing strong conclusions. Avenues for future work are outlined.Comment: Chapter 12, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe

Globular Cluster Scale Sizes in Giant Galaxies: Orbital Anisotropy and Tidally Under-filling Clusters in M87, NGC 1399, and NGC 5128

We investigate the shallow increase in globular cluster half-light radii with projected galactocentric distance $R_{gc}$ observed in the giant galaxies M87, NGC 1399, and NGC 5128. To model the trend in each galaxy, we explore the effects of orbital anisotropy and tidally under-filling clusters. While a strong degeneracy exists between the two parameters, we use kinematic studies to help constrain the distance $R_\beta$ beyond which cluster orbits become anisotropic, as well as the distance $R_{f\alpha}$ beyond which clusters are tidally under-filling. For M87 we find $R_\beta > 27$ kpc and $20 < R_{f\alpha} 13$ kpc and $10 < R_{f\alpha} < 30$ kpc. The connection of $R_{f\alpha}$ with each galaxy's mass profile indicates the relationship between size and $R_{gc}$ may be imposed at formation, with only inner clusters being tidally affected. The best fitted models suggest the dynamical histories of brightest cluster galaxies yield similar present-day distributions of cluster properties. For NGC 5128, the central giant in a small galaxy group, we find $R_\beta > 5$ kpc and $R_{f\alpha} > 30$ kpc. While we cannot rule out a dependence on $R_{gc}$, NGC 5128 is well fitted by a tidally filling cluster population with an isotropic distribution of orbits, suggesting it may have formed via an initial fast accretion phase. Perturbations from the surrounding environment may also affect a galaxy's orbital anisotropy profile, as outer clusters in M87 and NGC 1399 have primarily radial orbits while outer NGC 5128 clusters remain isotropic.Comment: 16 pages, 7 figures, 4 tables, Accepted for publication in MNRA

Assessment of wind speeds based on damage observations from the Angus (Ontario) Tornado of 17 June 2014

A tornado occurred in Angus, Ontario, during the late afternoon hours of 17 June 2014. The authors conducted a damage investigation on the morning following the storm. The damage indicators support the classification of the tornado as an EF-2 on the Enhanced Fujita Scale, including the observation of several complete roof failures of recently-constructed, wood-frame houses. Most of the damage to residential homes was contained along two streets, with the tornado appearing to have gone down the backyards between the two. In total, 101 houses were observed to have sustained some level of damage. The evidence suggests that the quality of construction likely affected the performance of failed roofs. A detailed fragility analysis was conducted to assess wind speeds associated with these failures of the roof-to-wall connections. An overturned and lofted box truck provided the opportunity to correlate this failure with adjacent, repetitive failures of roof sheathing, shingles, and garage doors. </jats:p

Modelling Collision Products of Triple-Star Mergers

In dense stellar clusters, binary-single and binary-binary encounters can ultimately lead to collisions involving two or more stars. A comprehensive survey of multi-star collisions would need to explore an enormous amount of parameter space, but here we focus on a number of representative cases involving low-mass main-sequence stars. Using both Smoothed Particle Hydrodynamics (SPH) calculations and a much faster fluid sorting software package (MMAS), we study scenarios in which a newly formed product from an initial collision collides with a third parent star. By varying the order in which the parent stars collide, as well as the orbital parameters of the collision trajectories, we investigate how factors such as shock heating affect the chemical composition and structure profiles of the collision product. Our simulations and models indicate that the distribution of most chemical elements within the final product is not significantly affected by the order in which the stars collide, the direction of approach of the third parent star, or the periastron separations of the collisions. We find that the sizes of the products, and hence their collisional cross sections for subsequent encounters, are sensitive to the order and geometry of the collisions. For the cases that we consider, the radius of the product formed in the first (single-single star) collision ranges anywhere from roughly 2 to 30 times the sum of the radii of its parent stars. The final product formed in our triple-star collisions can easily be as large or larger than a typical red giant. We therefore expect the collisional cross section of a newly formed product to be greatly enhanced over that of a thermally relaxed star of the same mass.Comment: 20 pages, submitted to MNRA

Intraovarian insertion of autologous platelet growth factors as cell-free concentrate: Fertility recovery and first unassisted conception with term delivery at age over 40

Background: The use of autologous platelet-rich plasma as an ovarian treatment has not been standardized and remains controversial. Case Presentation: A 41½-year old woman with diminished ovarian reserve (serum anti- Müllerian hormone = 0.163 mg/mL) and a history of 10 unsuccessful in vitro fertilization cycles presented for reproductive endocrinology consult. She and her partner declined donor oocyte in vitro fertilization. They were both in good general health and laboratory tests were unremarkable, except for mild thrombocytosis (platelets = 386K; normal range 150-379K) discovered in the female. The patient underwent intraovarian injection of fresh platelet-derived growth factor concentrate administered as an enriched cell-free substrate. Serum anti- Müllerian hormone increased by 115% within 6 wks of treatment. Spontaneous ovulation occurred the month after injection and subsequently the serum human chorionic gonadotropin was noted at 804 mIU/mL. Following an uneventful obstetrical course, a male infant was delivered at term without complication. Conclusion: This is the first description of intraovarian injection of enriched platelet-derived growth factors followed by unassisted pregnancy and live birth. As a refinement of conventional ovarian platelet-rich plasma therapy, this procedure may be particularly valuable for refractory cases where prognosis for pregnancy appears especially bleak. A putative role for thrombocytosis is also viewed in parallel with mechanisms of action as advanced earlier. With continued experience in ovarian application of autologous platelet growth factors, additional research will evaluate laboratory protocol/sample preparation, injection technique, and patient selection. Key words: Ovarian rejuvenation, Platelet-rich plasma, Cytokines, Infertility, IVF