The Formation Rate of Blue Stragglers in 47 Tucanae

We investigate the effects of changes in the blue straggler formation rate in globular clusters on the blue straggler distribution in the color-magnitude diagram. We find that the blue straggler distribution is highly sensitive to the past formation rate. Comparing our models to new UBV observations of a region close to the core of 47 Tucanae suggests that this cluster may have stopped forming blue straggler formation several Gyr ago. This cessation of formation can be associated with an epoch of primordial binary burning which has been invoked in other clusters to infer the imminence of core collapse.Comment: 17 pages, 9 figures, submitted to the Astrophysical Journa

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

Implications for the Formation of Blue Straggler Stars from HST Ultraviolet Observations of NGC 188

We present results of a Hubble Space Telescope far-ultraviolet (FUV) survey searching for white dwarf (WD) companions to blue straggler stars (BSSs) in open cluster NGC 188. The majority of NGC 188 BSSs (15 of 21) are single-lined binaries with properties suggestive of mass-transfer formation via Roche lobe overflow, specifically through an asymptotic giant branch star transferring mass to a main sequence secondary, yielding a BSS binary with a WD companion. In NGC 188, a BSS formed by this mechanism within the past 400 Myr will have a WD companion hot and luminous enough to be directly detected as a FUV photometric excess with HST. Comparing expected BSS FUV emission to observed photometry reveals four BSSs with WD companions above 12,000 K (younger than 250 Myr) and three WD companions with temperatures between 11,000-12,000 K. These BSS+WD binaries all formed through recent mass transfer. The location of the young BSSs in an optical color-magnitude diagram (CMD) indicates that distance from the zero-age main sequence does not necessarily correlate with BSS age. There is no clear CMD separation between mass transfer-formed BSSs and those likely formed through other mechanisms, such as collisions. The seven detected WD companions place a lower limit on the mass-transfer formation frequency of 33%. We consider other possible formation mechanisms by comparing properties of the BSS population to theoretical predictions. We conclude that 14 BSS binaries likely formed from mass transfer, resulting in an inferred mass-transfer formation frequency of approximately 67%.Comment: 13 pages, 6 figures, accepted to the Astrophysical Journa

Detection of white dwarf companions to blue stragglers in the open cluster NGC 188: direct evidence for recent mass transfer

Several possible formation pathways for blue straggler stars have been developed recently, but no one pathway has yet been observationally confirmed for a specific blue straggler. Here we report the first findings from a Hubble Space Telescope ACS/SBC far-UV photometric program to search for white dwarf companions to blue straggler stars. We find three hot and young white dwarf companions to blue straggler stars in the 7-Gyr open cluster NGC 188, indicating that mass transfer in these systems ended less than 300 Myr ago. These companions are direct and secure observational evidence that these blue straggler stars were formed through mass transfer in binary stars. Their existence in a well-studied cluster environment allows for observational constraints of both the current binary system and the progenitor binary system, mapping the entire mass transfer history.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical Journal Letter

The Spatial Structure of Young Stellar Clusters. III. Physical Properties and Evolutionary States

We analyze the physical properties of stellar clusters that are detected in massive star-forming regions in the MYStIX project--a comparative, multiwavelength study of young stellar clusters within 3.6 kpc that contain at least one O-type star. Tabulated properties of subclusters in these regions include physical sizes and shapes, intrinsic numbers of stars, absorptions by the molecular clouds, and median subcluster ages. Physical signs of dynamical evolution are present in the relations of these properties, including statistically significant correlations between subcluster size, central density, and age, which are likely the result of cluster expansion after gas removal. We argue that many of the subclusters identified in Paper I are gravitationally bound because their radii are significantly less than what would be expected from freely expanding clumps of stars with a typical initial stellar velocity dispersion of ~3 km/s for star-forming regions. We explore a model for cluster formation in which structurally simpler clusters are built up hierarchically through the mergers of subclusters--subcluster mergers are indicated by an inverse relation between the numbers of stars in a subcluster and their central densities (also seen as a density vs. radius relation that is less steep than would be expected from pure expansion). We discuss implications of these effects for the dynamical relaxation of young stellar clusters.Comment: Accepted for publication in The Astrophysical Journal ; 48 pages, 13 figures, and 6 table

Lecture Hall Sequences, \u3cem\u3eq\u3c/em\u3e-Series, and Asymmetric Partition Identities

We use generalized lecture hall partitions to discover a new pair of q-series identities. These identities are unusual in that they involve partitions into parts from asymmetric residue classes, much like the little Göllnitz partition theorems. We derive a two-parameter generalization of our identities that, surprisingly, gives new analytic counterparts of the little Göllnitz theorems. Finally, we show that the little Göllnitz theorems also involve “lecture hall sequences,” that is, sequences constrained by the ratio of consecutive parts

Follow-up analysis of federal process of care data reported from three acute care hospitals in rural Appalachia

BACKGROUND: This investigation evaluated standardized process of care data collected on selected hospitals serving a remote rural section of westernmost North Carolina. METHODS: Centers for Medicare and Medicaid Services data were analyzed retrospectively for multiple clinical parameters at Fannin Regional Hospital, Murphy Medical Center, and Union General Hospital. Data were analyzed by paired t-test for individual comparisons among the three study hospitals to compare the three facilities with each other, as well as with state and national average for each parameter. RESULTS: Centers for Medicare and Medicaid Services "Hospital Compare" data from 2011 showed Fannin Regional Hospital to have significantly higher composite scores on standardized clinical process of care measures relative to the national average, compared with Murphy Medical Center (P = 0.01) and Union General Hospital (P = 0.01). This difference was noted to persist when Fannin Regional Hospital was compared with Union General Hospital using common state reference data (P = 0.02). When compared with national averages, mean process of care scores reported from Murphy Medical Center and Union General Hospital were both lower but not significantly different (-3.44 versus -6.07, respectively, P = 0.54). CONCLUSION: The range of process of care scores submitted by acute care hospitals in western North Carolina is considerable. Centers for Medicare and Medicaid Services "Hospital Compare" information suggests that process of care measurements at Fannin Regional Hospital are significantly higher than at either Murphy Medical Center or Union General Hospital, relative to state and national benchmarks. Further investigation is needed to determine what impact these differences in process of care may have on hospital volume and/or market share in this region. Additional research is planned to identify process of care trends in this demographic and geographically rural area

Intrauterine pregnancy following low-dose gonadotropin ovulation induction and direct intraperitoneal insemination for severe cervical stenosis

BACKGROUND: We present a case of primary infertility related to extreme cervical stenosis, a subset of cervical factor infertility which accounts for approximately 5% of all clinical infertility referrals. CASE PRESENTATION: A 37 year-old nulligravida was successfully treated with ovulation induction via recombinant follicle stimulating hormone (FSH) and direct intraperitoneal insemination (IPI). Anticipating controlled ovarian hyperstimulation with in vitro fertilization/embryo transfer (IVF), the patient underwent hysteroscopy and cervical recanalization, but safe intrauterine access was not possible due to severe proximal cervical stricture. Hysterosalpingogram established bilateral tubal patency and confirmed an irregular cervical contour. Since the cervical canal could not be traversed, neither standard intrauterine insemination nor transcervical embryo transfer could be offered. Prepared spermatozoa were therefore placed intraperitoneally at both tubal fimbria under real-time transvaginal sonographic guidance using a 17 gage single-lumen IVF needle. Supplementary progesterone was administered as 200 mg/d lozenge (troche) plus 200 mg/d rectal suppository, maintained from the day following IPI to the 8(th )gestational week. A singleton intrauterine pregnancy was achieved after the second ovulation induction attempt. CONCLUSIONS: In this report, we outline the relevance of cervical factor infertility to reproductive medicine practice. Additionally, our andrology evaluation, ovulation induction approach, spermatozoa preparation, and insemination technique in such cases are described