Spitzer Space Telescope Observations of Low Mass X-ray Binaries

We present preliminary results from our archival Spitzer Space Telescope program aimed at characterizing the mid-IR properties of compact objects, both isolated and in binary systems, i.e. white dwarfs, X-ray binaries, cataclysmic variables, and magnetars. Most of these sources are too faint at mid-IR wavelengths to be observable from the ground, so this study provides the very first comprehensive look at the mid-IR emission of these objects. Here we present our results for the low mass X-ray binaries. We considered all of the systems listed in the most recent catalog of Liu et al. (2007) that have known optical counterparts. The particular goals of our projects encompass: to establish the mid-IR spectral energy distribution, to search for the signatures of jets, circumbinary disks, low mass or planetary companions and debris disks, and to study the local environment of these sources.Comment: 6 pages, updated and expanded version of article to appear in Proceedings of "A Population Explosion: The Nature and Evolution of X-ray Binaries in Diverse Environments", 28 Oct - 2 Nov, St. Pete Beach, FL; eds. R.M. Bandyopadhyay, S. Wachter, D. Gelino, C.R. Gelino; AIP Conference Proceedings Serie

Borrowing Constraints and the Tenure Choice of Young Households

In this paper we analyze the factors that affect the tenure choice of young adults, highlighting the impact of mortgage lender imposed borrowing constraints. The data set is a panel of youth age 20-33 for the years 1985-90. Our methods differ from most prior studies in many ways including consideration of possible sample selection bias, a richer model of the stochastic error structure, better measurement of which households are bound by borrowing constraints, and a fuller consideration of the endogeneity of wealth and income. Once all changes are implemented, we find ownership tendencies to be quite sensitive to economic variables. Specifically, potential earnings, the relative cost of owning a home, and especially borrowing constraints affect the tendency to own a home. In our sample of youth, 37% of households are constrained even after choosing their loan-to-value ratio to minimize the impact of the separate wealth and income requirements. The constraints reduce the probability of ownership of these households by 10 to 20 percentage points (a third to a half) depending on the particular characteristics of the household.

Green investment strategies: a positive force in cities

Deterioration of urban neighborhoods is known to induce out migration, but how well do public investments to reverse decline actually work? To evaluate Philadelphia’s greening investment, researchers measured property buyers’ willingness to pay more—and found that greening works.Community development

The COLD-SAT Experiment for Cryogenic Fluid Management Technology

Future national space transportation missions will depend on the use of cryogenic fluid management technology development needs for these missions. In-space testing will be conducted in order to show low gravity cryogenic fluid management concepts and to acquire a technical data base. Liquid H2 is the preferred test fluid due to its propellant use. The design of COLD-SAT (Cryogenic On-orbit Liquid Depot Storage, Acquisition, and Transfer Satellite), an Expendable Launch Vehicle (ELV) launched orbital spacecraft that will perform subcritical liquid H2 storage and transfer experiments under low gravity conditions is studied. An Atlas launch vehicle will place COLD-SAT into a circular orbit, and the 3-axis controlled spacecraft bus will provide electric power, experiment control, and data management, attitude control, and propulsive accelerations for the experiments. Low levels of acceleration will provide data on the effects that low gravity might have on the heat and mass transfer processes used. The experiment module will contain 3 liquid H2 tanks; fluid transfer, pressurization and venting equipment; and instrumentation

Expected Home Ownership and Real Wealth Accumulation of Youth

This paper describes the real wealth accumulation of American youth and relates this behavior to variations in real constant-quality house prices in their localities of residence. We argue that increases in the real constant-quality house price have two offsetting effects on wealth. First, the greater the local constant-quality price of housing, the greater the wealth needed to meet the lender imposed down payment constraint if housing demand is price inelastic. However, increased real constant-quality house price reduces the likelihood of home ownership and thus the desire the accumulate wealth needed for a down payment. Using a panel data set for youth age 20-33 for the years 1985 through 1990 we find that the combined direct and indirect impact of variations in real constant-quality house price on wealth is modest for changes near the average real house price, but youths' wealth declines substantially in areas with high real house price.

X-Ray Binaries and the Dynamical States of Globular Clusters

We summarize and discuss recent work (Fregeau 2007) that presents the confluence of three results suggesting that most Galactic globular clusters are still in the process of core contraction, and have not yet reached the thermal equilibrium phase driven by binary scattering interactions: that 1) the three clusters that appear to be overabundant in X-ray binaries per unit encounter frequency are observationally classified as "core-collapsed," 2) recent numerical simulations of cluster evolution with primordial binaries show that structural parameters of clusters in the binary-burning phase agree only with "core-collapsed" clusters, and 3) a cluster in the binary-burning phase for the last few Gyr should have about 5 times more dynamically formed X-ray sources than if it were in the core contraction phase for the same time.Comment: Conference proceedings from "A Population Explosion: The Nature and Evolution of X-ray Binaries in Diverse Environments," 28 Oct - 2 Nov, St. Petersburg Beach, FL. 4 page

INTEGRAL and New Classes of High-Mass X-ray Binaries

The gamma-ray observatory INTEGRAL, launched in October 2002, produces a wealth of discoveries and new results on compact high energy Galactic objects, nuclear gamma-ray line emission, diffuse line and continuum emission, cosmic background radiation, AGN and high energy transients. Two important serendipitous discoveries made by the INTEGRAL mission are new classes of X-ray binaries, namely the highly-obscured high-mass X-ray binaries, and the super-giant fast transients. In this paper I will review the current status of these discoveries.Comment: 3 pages, 1 figure, submitted; Proceedings "The nature and evolution of X-ray binaries in diverse environments", St Petersburg/FL, USA, 28 Oct - 02 Nov 200

Multiwavelength Studies of X-ray Binaries

Simultaneous multiwavelength studies of X-ray binaries have been remarkably successful and resulted in improved physical constraints, a new understanding of the dependence of mass accretion rate on X-ray state, as well as insights on the time-dependent relationship between disk structure and mass-transfer rate. I will give some examples of the tremendous gains we have obtained in our understanding of XRBs by using multiwavelength observations. I will end with an appeal that while Spitzer cryogens are still available a special effort be put forth to obtaining coordinated observations including the mid-infrared: Whereas the optical and near-IR originate as superpositions of the secondary star and of accretion processes, the mid-IR crucially detects jet synchrotron emission from NSs that is virtually immeasurable at other wavelengths. A further benefit of Spitzer observations is that mid-infrared wavelengths can easily penetrate regions that are heavily obscured. Many X-ray binaries lie in the Galactic plane and as such are often heavily obscured in the optical by interstellar extinction. The infrared component of the SED, vital to the study of jets and dust, can be provided {\it only} by Spitzer; in the X-rays we currently have an unprecedented six satellites available and in the optical and radio dozens of ground-based facilities to complement the Spitzer observations.Comment: 5 pages including figures, in conference proceedings A Population Explosion: The Nature and Evolution of X-ray Binaries in Diverse Environments, eds. Bandyopadhyay, Wachter, Gelino, & Gelin

Probing Clumpy Stellar Winds in SFXTs

Quantitative constraints on the wind clumping of massive stars can be obtained from the study of the hard X-ray variability of SFXTs. In these systems, a large fraction of the hard X-ray emission is emitted in the form of flares with typical duration of 3 ksec, frequency of 7 days and luminosity of $10^{36}$ ergs/s. Such flares are most probably emitted by the interaction of a compact object orbiting at $\sim10$ R$_*$ with wind clumps ($10^{22-23}$ g). The density ratio between the clumps and the inter-clump medium is $10^{2-4}$ . The parameters of the clumps and of the inter-clump medium are in good agreement with macro-clumping scenario and line-driven instability simulations.Comment: 3 pages, A Population Explosion: The Nature and Evolution of X-ray Binaries in Diverse Environment