Thermonuclear burst physics with RXTE

Recently we have made measurements of thermonuclear burst energetics and recurrence times which are unprecedented in their precision, largely thanks to the sensitivity of the Rossi X-ray Timing Explorer. In the "Clocked Burster", GS 1826-24, hydrogen burns during the burst via the rapid-proton (rp) process, which has received particular attention in recent years through theoretical and modelling studies. The burst energies and the measured variation of alpha (the ratio of persistent to burst flux) with accretion rate strongly suggests solar metallicity in the neutron star atmosphere, although this is not consistent with the corresponding variation of the recurrence time. Possible explanations include extra heating between the bursts, or a change in the fraction of the neutron star over which accretion takes place. I also present results from 4U 1746-37, which exhibits regular burst trains which are interrupted by "out of phase" bursts.Comment: 4 pages, 2 figures, AIP conference proceedings format. To appear in the proceedings of the "X-ray Timing 2003: Rossi and Beyond" meeting held in Cambridge, MA, November, 200

Implications of kHz QPOs for the spin frequencies and magnetic fields of neutron stars: new results from Circinus X-1

Detection of paired kilohertz quasi-periodic oscillations (kHz QPOs) in the X-ray emission of a compact object is compelling evidence that the object is an accreting neutron star. In many neutron stars, the stellar spin rate is equal or roughly equal to Delta-nu, the frequency separation of the QPO pair, or to 2Delta-nu. Hence, if the mechanism that produces the kilohertz QPOs is similar in all stars, measurement of Delta-nu can provide an estimate of the star's spin rate. The involvement of the stellar spin in producing Delta-nu indicates that the magnetic fields of these stars are dynamically important. We focus here on the implications of the paired kHz QPOs recently discovered in the low-mass X-ray binary (LMXB) system Cir X-1 (Boutloukos et al. 2006). The kHz QPOs discovered in Cir X-1 are generally similar to those seen in other stars, establishing that the compact object in the Cir X-1 system is a neutron star. However, the frequency nu-u of its upper kHz QPO is up to a factor of three smaller than is typical, and Delta-nu varies by about a factor 2 (167 Hz, the largest variation so far observed). Periodic oscillations have not yet been detected from Cir X-1, so its spin rate has not yet been measured directly. The low values of nu-u and the large variation of Delta-nu challenge current models of the generation of kHz QPOs. Improving our understanding of Cir X-1 will improve our knowledge of the spin rates and magnetic fields of all neutron stars.Comment: 3 pages, 3 figures, a table with all known accreting millisecond X-ray pulsars up to October 2007. To appear in "40 Years of Pulsars, Millisecond Pulsars, Magnetars and More" conference proceeding

Planning and Implementing Student-Led IEPs for Students With EBD

Students with emotional and behavioral disorders (EBD) have difficulties in transitioning to postschool environments. Research has documented that postsecondary outcomes for students with EBD in the areas of education, employment, and community participation continue to be limited and, therefore, in need of improvement. Some of the outcomes relate to how transition programs integrate effective practices to support students with EBD. In this article, we describe a student-led Individualized Education Program (IEP) practice and provide step-by-step directions that can be used for planning and conducting student-led IEPs

Practical Strategies for Improving Postsecondary Outcomes for Students with EBD

Transition from high school to adulthood is a difficult period of life for all youth, especially those with disabilities. Research indicates students with emotional and behavioral disorders (EBD) experience difficulties in transitioning to a postschool environment. Their postschool outcomes in the areas of education, employment, and community participation continue to concern researchers, practitioners, and families and, therefore, demand improvement. Identification and implementation of transition-related evidence-based practices is essential for teachers who work with students with EBD to increase the likelihood of positive adult outcomes for these students. Discussed in this article are transition-related recommendations and practical strategies that may be used by teachers and other education professionals preparing students with EBD for life after school

Polar kicks and the spin period - eccentricity relation in double neutron stars

We present results of a population synthesis study aimed at examining the role of spin-kick alignment in producing a correlation between the spin period of the first-born neutron star and the orbital eccentricity of observed double neutron star binaries in the Galactic disk. We find spin-kick alignment to be compatible with the observed correlation, but not to alleviate the requirements for low kick velocities suggested in previous population synthesis studies. Our results furthermore suggest low- and high-eccentricity systems may form through two distinct formation channels distinguished by the presence or absence of a stable mass transfer phase before the formation of the second neutron star. The presence of highly eccentric systems in the observed sample of double neutron stars may furthermore support the notion that neutron stars accrete matter when moving through the envelope of a giant companion.Comment: To appear in the proceedings of "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007, McGill University, Montreal, Canad