Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and Related Systems

We present an analysis of over 2200 V images taken on 14 nights at the Mt. Laguna 1 m telescope of the open cluster M67. Our observations overlap but extend beyond the field analyzed by Gilliland et al. (1991), and complement data recently published by van den Berg et al. (2002) and Stassun et al. (2002). We show variability in the light curves of all 4 of the known W UMa variables on timescales ranging from a day to decades (for AH Cnc). We have modeled the light curve of AH Cnc, and the total eclipses allow us to determine q = 0.16 +0.03/-0.02 and i = 86 +4/-8 degrees. The position of this system near the turnoff of M67 makes it useful for constraining the turnoff mass for the cluster. We have also detected two unusual features in the light curve of AH Cnc that may be caused by prominences. We have also monitored cluster blue stragglers for variability, and we present evidence hinting at low level variations in the stragglers S752, S968, and S1263, and we place limits on the variability of a number of other cluster blue stragglers. Finally, we provide photometry of the sub-subgiant branch star S1063 showing variability on timescales similar to the orbital period, while the ``red straggler'' S1040 shows evidence of an unexplained drop in brightness at phases corresponding to the passage of the white dwarf in front of the giant.Comment: 44 pages, 16 figures, AASTeX, accepted for A

Adaptive Lévy processes and area-restricted search in human foraging

A considerable amount of research has claimed that animals’ foraging behaviors display movement lengths with power-law distributed tails, characteristic of Lévy flights and Lévy walks. Though these claims have recently come into question, the proposal that many animals forage using Lévy processes nonetheless remains. A Lévy process does not consider when or where resources are encountered, and samples movement lengths independently of past experience. However, Lévy processes too have come into question based on the observation that in patchy resource environments resource-sensitive foraging strategies, like area-restricted search, perform better than Lévy flights yet can still generate heavy-tailed distributions of movement lengths. To investigate these questions further, we tracked humans as they searched for hidden resources in an open-field virtual environment, with either patchy or dispersed resource distributions. Supporting previous research, for both conditions logarithmic binning methods were consistent with Lévy flights and rank-frequency methods–comparing alternative distributions using maximum likelihood methods–showed the strongest support for bounded power-law distributions (truncated Lévy flights). However, goodness-of-fit tests found that even bounded power-law distributions only accurately characterized movement behavior for 4 (out of 32) participants. Moreover, paths in the patchy environment (but not the dispersed environment) showed a transition to intensive search following resource encounters, characteristic of area-restricted search. Transferring paths between environments revealed that paths generated in the patchy environment were adapted to that environment. Our results suggest that though power-law distributions do not accurately reflect human search, Lévy processes may still describe movement in dispersed environments, but not in patchy environments–where search was area-restricted. Furthermore, our results indicate that search strategies cannot be inferred without knowing how organisms respond to resources–as both patched and dispersed conditions led to similar Lévy-like movement distributions

Dynamical Formation of Close Binaries in Globular Clusters II: Cataclysmic Variables

We answer the long-standing question of which production mechanism is responsible for the cataclysmic variables (CVs) in globular clusters. Arguments have been given that range from mostly primordial presence to a significant contribution of later dynamical formation in close stellar encounters. We conclude, based on a thorough analysis of a homogeneous {\it Chandra} data set, that the majority of CVs in globulars has a dynamical origin.Comment: submitted to ApJL; comments welcom

ROTSE All Sky Surveys for Variable Stars I: Test Fields

The ROTSE-I experiment has generated CCD photometry for the entire Northern sky in two epochs nightly since March 1998. These sky patrol data are a powerful resource for studies of astrophysical transients. As a demonstration project, we present first results of a search for periodic variable stars derived from ROTSE-I observations. Variable identification, period determination, and type classification are conducted via automatic algorithms. In a set of nine ROTSE-I sky patrol fields covering about 2000 square degrees we identify 1781 periodic variable stars with mean magnitudes between m_v=10.0 and m_v=15.5. About 90% of these objects are newly identified as variable. Examples of many familiar types are presented. All classifications for this study have been manually confirmed. The selection criteria for this analysis have been conservatively defined, and are known to be biased against some variable classes. This preliminary study includes only 5.6% of the total ROTSE-I sky coverage, suggesting that the full ROTSE-I variable catalog will include more than 32,000 periodic variable stars.Comment: Accepted for publication in AJ 4/00. LaTeX manuscript. (28 pages, 11 postscript figures and 1 gif

Blue Stragglers in Galactic Open Clusters and the Integrated Spectral Energy Distributions

Synthetic integrated spectral properties of the old Galactic open clusters are studies in this work, where twenty-seven Galactic open clusters of ages >= 1Gyr are selected as the working sample. Based on the photometric observations of these open clusters, synthetic integrated spectrum has been made for the stellar population of each cluster. The effects of blue straggler stars (BSSs) on the conventional simple stellar population (SSP) model are analyzed on an individual cluster base. It is shown that the BSSs, whose holding positions in the color-magnitude diagrams (CMDs) cannot be predicted by the current single-star evolution theory, present significant modifications to the integrated properties of theoretical SSP model. The synthesized integrated spectral energy distributions (ISEDs) of our sample clusters are dramatically different from the SSPs based on isochrone only. The BSSs corrected ISEDs of stellar populations show systematic enhancements towards shorter wavelength in the spectra. When measured with wide-band colors in unresolvable conditions, the age of a stellar population can be seriously under-estimated by the conventional SSP model. Therefore, considering the common existence of BSS component in real stellar populations, a considerable amount of alternations on the conventional ISEDs should be expected when applying the technique of evolutionary population synthesis (EPS) to more complicated stellar systems.Comment: 45 pages, 21 figures Accepted for publication in ApJ (Feburary 1, 2005 issue

The contested and contingent outcomes of Thatcherism in the UK

The death of Margaret Thatcher in April 2013 sparked a range of discussions and debates about the significance of her period in office and the political project to which she gave her name: Thatcherism. This article argues that Thatcherism is best understood as a symbolically important part of the emergence of first-phase neoliberalism. It engages with contemporary debates about Thatcherism among Marxist commentators and suggests that several apparently divergent positions can help us now reach a more useful analysis of Thatcherism’s short- and long-term outcomes for British political economy. The outcomes identified include: an initial crisis in the neoliberal project in the UK; the transformation of the party political system to be reflective of the politics of neoliberalism, rather than its contestation; long-term attempts at the inculcation of the neoliberal individual; de-industrialisation and financial sector dependence; and a fractured and partially unconscious working class. In all long-term outcomes, the contribution of Thatcherism is best understood as partial and largely negative, in that it cleared the way for a longer-term and more constructive attempt to embed neoliberal political economy. The paper concludes by suggesting that this analysis can inform current debates on the left of British politics about how to oppose and challenge the imposition of neoliberal discipline today

Simulation for the oblique impact of a lattice system

The oblique collision between an elastic disk and an elastic wall is numerically studied. We investigate the dependency of the tangential coefficient of restitution on the incident angle of impact. From the results of simulation, our model reproduces experimental results and can be explained by a phenomenological theory of the oblique impact.Comment: 30 pages, 9 figures, submitted to J. Phys. Soc. Japa

High-Precision Scanning Water Vapor Radiometers for Cosmic Microwave Background Site Characterization and Comparison

The compelling science case for the observation of B-mode polarization in the cosmic microwave background (CMB) is driving the CMB community to expand the observed sky fraction, either by extending survey sizes or by deploying receivers to potential new northern sites. For ground-based CMB instruments, poorly-mixed atmospheric water vapor constitutes the primary source of short-term sky noise. This results in short-timescale brightness fluctuations, which must be rejected by some form of modulation. To maximize the sensitivity of ground-based CMB observations, it is useful to understand the effects of atmospheric water vapor over timescales and angular scales relevant for CMB polarization measurements. To this end, we have undertaken a campaign to perform a coordinated characterization of current and potential future observing sites using scanning 183 GHz water vapor radiometers (WVRs). So far, we have deployed two identical WVR units; one at the South Pole, Antarctica, and the other at Summit Station, Greenland. The former site has a long heritage of ground-based CMB observations and is the current location of the Bicep/Keck Array telescopes as well as the South Pole Telescope. The latter site, though less well characterized, is under consideration as a northern-hemisphere location for future CMB receivers. Data collection from this campaign began in January 2016 at South Pole and July 2016 at Summit Station. Data analysis is ongoing to reduce the data to a single spatial and temporal statistic that can be used for one-to-one site comparison.Comment: Published in Proc. SPIE. Presented at SPIE Astronomical Telescopes and Instrumentation Conference 10708: Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI, June 2018. 10 pages, 11 figure

Availability of Previously Unprocessed ALSEP Raw Instrument Data, Derivative Data, and Metadata Products

In year 2010, 440 original data archival tapes for the Apollo Lunar Science Experiment Package (ALSEP) experiments were found at the Washington National Records Center. These tapes hold raw instrument data received from the Moon for all the ALSEP instruments for the period of April through June 1975. We have recently completed extraction of binary files from these tapes, and we have delivered them to the NASA Space Science Data Cordinated Archive (NSSDCA). We are currently processing the raw data into higher order data products in file formats more readily usable by contemporary researchers. These data products will fill a number of gaps in the current ALSEP data collection at NSSDCA. In addition, we have estabilished a digital, searcheable archive of ALSEP document and metadata as part of the web portal of the Lunar and Planetary Institute. It currently holds approx. 700 documents totaling approx. 40,000 page

The Multiple Origin of Blue Straggler Stars: Theory vs. Observations

In this chapter we review the various suggested channels for the formation and evolution of blue straggler stars (BSSs) in different environments and their observational predictions. These include mass transfer during binary stellar evolution - case A/B/C and D (wind Roche-lobe overflow) mass transfer, stellar collisions during single and binary encounters in dense stellar cluster, and coupled dynamical and stellar evolution of triple systems. We also explore the importance of the BSS and binary dynamics in stellar clusters. We review the various observed properties of BSSs in different environments (halo and bulge BSSs, BSSs in globular clusters and BSSs in old open clusters), and compare the current observations with the theoretical predictions for BSS formation. We try to constrain the likely progenitors and processes that play a role in the formation of BSSs and their evolution. We find that multiple channels of BSS formation are likely to take part in producing the observed BSSs, and we point out the strengths and weaknesses of each the formation channel in respect to the observational constraints. Finally we point out directions to further explore the origin of BSS, and highlight eclipsing binary BSSs as important observational tool.Comment: Chapter 11, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe