6,109 research outputs found
Pre-discovery observations of disrupting asteroid P/2010 A2
No full textSolar system object P/2010 A2 is the first-noticed example of the aftermath of a recently disrupted asteroid, probably resulting from a collision. Nearly a year elapsed between its inferred initiation in early 2009 and its eventual detection in early 2010. Here, we use new observations to assess the factors underlying the visibility, especially to understand the delayed discovery. We present pre-discovery observations from the LINEAR telescope and set limits to the early-time brightness from SOHO and STEREO satellite coronagraphic images. Consideration of the circumstances of discovery of P/2010 A2 suggests that similar objects must be common, and that future all-sky surveys will reveal them in large numbers.United States. National Aeronautics and Space Administration (NNH06ZDA001N)United States. National Aeronautics and Space Administration (06-NEOO06-0001)United States. Air Force (Contract FA8721-05-C-0002
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Book Review: Planetary Crusts: Their Composition, Origin and Evolution, Stuart Ross Taylor, Scott M. McLennan
No full textBook Review: Planetary Crusts: Their Composition, Origin and Evolution, Stuart Ross Taylor, Scott M. McLennan. Cambridge University Press (2009).The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202
Where is the party? Explaining positions on same-sex marriage in Europe among would-be members of parliament
No full textThe rapid adoption of marriage equality legislation for non-heterosexual individuals in Europe is attributed to many factors, including dramatic shifts in public opinion, the work of transnational activists and changing international norms. Usually, these factors must be filtered through the halls of parliaments where most policy change happens. Given the importance of parliamentarians’ attitudes, it is surprising that we know so little about how attitudes towards same-sex marriage are distributed across political candidates in Europe and what factors shape them. This article fills that gap by using an underutilised dataset on the political preferences of candidates for parliamentary office. We find that beyond attachment to party families, a candidate’s religiosity and practice has a greater effect on a would-be Member of Parliament’s attitudes towards same-sex marriage. The findings suggest that the success of parliamentary action on lesbian, gay, bisexual and transgender rights depends not on the partisan composition of the legislature, but rather on the representation of secular candidates.</p
REVEALING THE NATURE OF EXTREME CORONAL-LINE EMITTER SDSS J095209.56+214313.3
No full textExtreme coronal-line emitter (ECLE) SDSS J095209.56+214313.3, known by its strong, fading, high-ionization lines, has been a long-standing candidate for a tidal disruption event; however, a supernova (SN) origin has not yet been ruled out. Here we add several new pieces of information to the puzzle of the nature of the transient that powered its variable coronal lines: (1) an optical light curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that serendipitously catches the optical flare, and (2) late-time observations of the host galaxy with the Swift Ultraviolet and Optical Telescope (UVOT) and X-ray telescope (XRT) and the ground-based Mercator telescope. The well-sampled, ~10 yr long, unfiltered LINEAR light curve constrains the onset of the flare to a precision of ±5 days and enables us to place a lower limit on the peak optical magnitude. Difference imaging allows us to estimate the location of the flare in proximity of the host galaxy core. Comparison of the GALEX data (early 2006) with the recently acquired Swift UVOT (2015 June) and Mercator observations (2015 April) demonstrates a decrease in the UV flux over a ~10 yr period, confirming that the flare was UV-bright. The long-lived UV-bright emission, detected 1.8 rest-frame years after the start of the flare, strongly disfavors an SN origin. These new data allow us to conclude that the flare was indeed powered by the tidal disruption of a star by a supermassive black hole and that tidal disruption events are in fact capable of powering the enigmatic class of ECLEs
EXPLORING THE VARIABLE SKY WITH LINEAR. I. PHOTOMETRIC RECALIBRATION WITH THE SLOAN DIGITAL SKY SURVEY
No full textWe describe photometric recalibration of data obtained by the asteroid survey LINEAR. Although LINEAR was designed for astrometric discovery of moving objects, the data set described here contains over 5 billion photometric measurements for about 25 million objects, mostly stars. We use Sloan Digital Sky Survey (SDSS) data from the overlapping ~10,000 deg[superscript 2] of sky to recalibrate LINEAR photometry and achieve errors of 0.03 mag for sources not limited by photon statistics with errors of 0.2 mag at r ~ 18. With its 200 observations per object on average, LINEAR data provide time domain information for the brightest four magnitudes of the SDSS survey. At the same time, LINEAR extends the deepest similar wide-area variability survey, the Northern Sky Variability Survey, by 3 mag. We briefly discuss the properties of about 7000 visually confirmed periodic variables, dominated by roughly equal fractions of RR Lyrae stars and eclipsing binary stars, and analyze their distribution in optical and infrared color-color diagrams. The LINEAR data set is publicly available from the SkyDOT Web site
James Harrington's prescription for Healing and Settling
No full text10 James Harrington's prescription for healing and settling Jonathan Scott James Harrington's The Commonwealth of Oceana (1656) has been intermittently ..
CHARACTERIZING THE OPTICAL VARIABILITY OF BRIGHT BLAZARS: VARIABILITY-BASED SELECTION OF FERMI ACTIVE GALACTIC NUCLEI
No full textWe investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ~30% of γ-ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ, and driving amplitudes on short timescales [^ over σ]. Imposing cuts on minimum τ and [^ over σ] allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several-arcminute error ellipses of γ-ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E ≥ 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8'. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other γ-ray blazars and is likely to be the γ-ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ~3 years in the rest frame of the jet, in contrast with the ~320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics
Virus removal by ultrafiltration: understanding long-term performance change by application of Bayesian analysis
No full textAbstract not availableGuido Carvajal, Amos Branch, Scott A. Sisson, David J. Roser, Ben van den Akker, Paul Monis, Petra Reeve, Alexandra Keegan, Rudi Regel, Stuart J. Kha
Systemic infection exacerbates cerebrovascular dysfunction in Alzheimer’s disease
No full textWe studied the effects of systemic infection on brain cytokine level and cerebral vascular function in Alzheimer’s disease (AD) and vascular dementia (VaD), in superior temporal cortex (BA22) from AD (n = 75), VaD (n = 22) and age-matched controls (n = 46), stratified according to the presence or absence of terminal systemic infection. Brain cytokine levels were measured using Mesoscale Discovery Multiplex Assays and markers of cerebrovascular function were assessed by ELISA. Multiple brain cytokines were elevated in AD and VaD: interleukin (IL)-15 and IL-17A were maximally elevated in end-stage Alzheimer’s disease (Braak tangle stage V-VI) whereas IL-2, IL-5, IL12p40 and IL-16 were highest in intermediate Braak tangle stage III-IV disease. Several cytokines (IL-1β, IL-6, TNF-α, IL-8 and IL-15) were further raised in AD with systemic infection. Cerebral hypoperfusion, indicated by decreased myelin-associated glycoprotein:proteolipid protein-1 (MAG:PLP1) and increased vascular endothelial growth factor-A (VEGF), and blood-brain barrier leakiness, indicated by raised levels of fibrinogen, were exacerbated in AD and VaD, and also in non-dementia controls, with systemic infection. Aβ42 level did not vary with infection or in association with brain cytokine levels. In controls, cortical perfusion declined with increasing interferon-γ (IFN-γ), IL-2, IL-4, IL-6, IL-10, IL-12p70, IL-13 and tumour necrosis factor-α (TNF-α) but these relationships were lost with progression of AD, and with infection (even in BS 0-II brains). Cortical platelet-derived growth factor receptor-β (PDGFRβ), a pericyte marker, was reduced, and endothelin-1 (EDN1) level was increased in AD; these were related to Aβ level and disease progression and only modestly affected by systemic infection. Our findings indicate that systemic infection alters brain cytokine levels and exacerbates cerebral hypoperfusion and BBB leakiness associated with AD and VaD, independently of the level of insoluble Aβ. Our findings highlight systemic infection as an important contributor to dementia, requiring early identification and treatment in the elderly population
Exploring the variable sky with Linear. II. Halo structure and substructure traced by RR Lyrae stars to 30 kpc
No full textWe present a sample of ~5000 RR Lyrae stars selected from the recalibrated LINEAR data set and detected at heliocentric distances between 5 kpc and 30 kpc over ~8000 deg[superscript 2] of sky. The coordinates and light curve properties, such as period and Oosterhoff type, are made publicly available. We analyze in detail the light curve properties and Galactic distribution of the subset of ~4000 type ab RR Lyrae (RRab) stars, including a search for new halo substructures and the number density distribution as a function of Oosterhoff type. We find evidence for the Oosterhoff dichotomy among field RR Lyrae stars, with the ratio of the type II and I subsamples of about 1:4, but with a weaker separation than for globular cluster stars. The wide sky coverage and depth of this sample allow unique constraints for the number density distribution of halo RRab stars as a function of galactocentric distance: it can be described as an oblate ellipsoid with an axis ratio q = 0.63 and with either a single or a double power law with a power-law index in the range –2 to –3. Consistent with previous studies, we find that the Oosterhoff type II subsample has a steeper number density profile than the Oosterhoff type I subsample. Using the group-finding algorithm EnLink, we detected seven candidate halo groups, only one of which is statistically spurious. Three of these groups are near globular clusters (M53/NGC 5053, M3, M13), and one is near a known halo substructure (Virgo Stellar Stream); the remaining three groups do not seem to be near any known halo substructures or globular clusters and seem to have a higher ratio of Oosterhoff type II to Oosterhoff type I RRab stars than what is found in the halo. The extended morphology and the position (outside the tidal radius) of some of the groups near globular clusters are suggestive of tidal streams possibly originating from globular clusters. Spectroscopic follow-up of detected halo groups is encouraged.United States. Air Force (Contract FA8721-05-C-0002
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