17,039 research outputs found
A Search for Optical Variability of Type 2 Quasars in SDSS Stripe 82
Hundreds of Type 2 quasars have been identified in Sloan Digital Sky Survey
(SDSS) data, and there is substantial evidence that they are generally galaxies
with highly obscured central engines, in accord with unified models for active
galactic nuclei (AGNs). A straightforward expectation of unified models is that
highly obscured Type 2 AGNs should show little or no optical variability on
timescales of days to years. As a test of this prediction, we have carried out
a search for variability in Type 2 quasars in SDSS Stripe 82 using
difference-imaging photometry. Starting with the Type 2 AGN catalogs of
Zakamska et al. (2003) and Reyes et al. (2008), we find evidence of significant
g-band variability in 17 out of 173 objects for which light curves could be
measured from the Stripe 82 data. To determine the nature of this variability,
we obtained new Keck spectropolarimetry observations for seven of these
variable AGNs. The Keck data show that these objects have low continuum
polarizations (p<~1% in most cases) and all seven have broad H-alpha and/or
MgII emission lines in their total (unpolarized) spectra, indicating that they
should actually be classified as Type 1 AGNs. We conclude that the primary
reason variability is found in the SDSS-selected Type 2 AGN samples is that
these samples contain a small fraction of Type 1 AGNs as contaminants, and it
is not necessary to invoke more exotic possible explanations such as a
population of "naked" or unobscured Type 2 quasars. Aside from misclassified
Type 1 objects, the Type 2 quasars do not generally show detectable optical
variability over the duration of the Stripe 82 survey.Comment: 14 pages, 8 figures. Accepted for publication in A
The casting and powder-metallurgy forming of precipitation-hardenable stainless steels
Casting and powder metallurgy techniques for shaping precipitation hardened stainless steel
The String Deviation Equation
The relative motion of many particles can be described by the geodesic
deviation equation. This can be derived from the second covariant variation of
the point particle's action. It is shown that the second covariant variation of
the string action leads to a string deviation equation.Comment: 18 pages, some small changes, no tables or diagrams, LaTex2
Supernova Environments in Hubble Space Telescope Images
The locations of supernovae in the local stellar and gaseous environment in galaxies contain important clues to their progenitor stars. Access to this information, however, has been hampered by the limited resolution achieved by ground-based observations. High spatial resolution Hubble Space Telescope (HST) images of galaxy fields in which supernovae had been observed can improve the situation considerably. We have examined the immediate environments of a few dozen supernovae using archival post-refurbishment HST images. Although our analysis is limited due to signal-to-noise ratio and filter bandpass considerations, the images allow us for the first time to resolve individual stars in, and to derive detailed color-magnitude diagrams for, several environments. We are able to place more rigorous constraints on the masses of these supernovae. A search was made for late-time emission from supernovae in the archival images, and for the progenitor stars in presupernova images of the host galaxies. In particular, we highlight the results for the Type II SN 1979C in M100. In addition, we have identified the progenitor of the Type IIn SN 1997bs in NGC 3627. We also add to the statistical inferences that can be made from studying the association of SNe with recent star-forming regions
Market Reaction to the Adoption of IFRS in Europe
This study examines the European stock market reaction to sixteen events associated with the adoption of International Financial Reporting Standards (IFRS) in Europe. European IFRS adoption represented a major milestone towards financial reporting convergence yet spurred controversy reaching the highest levels of government. We find a more positive reaction for firms with lower quality pre-adoption information, which is more pronounced in banks, and with higher pre-adoption information asymmetry, consistent with investors expecting net information quality benefits from IFRS adoption. We also find that the reaction is less positive for firms domiciled in code law countries, consistent with investors' concerns over enforcement of IFRS in those countries. Finally, we find a positive reaction to IFRS adoption events for firms with high quality pre-adoption information, consistent with investors expecting net convergence benefits from IFRS adoption. Overall, the findings suggest that investors in European firms perceived net benefits associated with IFRS adoption.IFRS, IAS 39, Convergence, Europe, Event Study
ALMA Observations of Circumnuclear Disks in Early Type Galaxies: 12CO(2-1) and Continuum Properties
We present results from an Atacama Large Millimeter/submillimeter Array
(ALMA) Cycle 2 program to map CO(2-1) emission in nearby early-type galaxies
(ETGs) that host circumnuclear gas disks. We obtained resolution
Band 6 observations of seven ETGs selected on the basis of dust disks in Hubble
Space Telescope images. We detect CO emission in five at high signal-to-noise
ratio with the remaining two only faintly detected. All CO emission is
coincident with the dust and is in dynamically cold rotation. Four ETGs show
evidence of rapid central rotation; these are prime candidates for
higher-resolution ALMA observations to measure the black hole masses. In this
paper we focus on the molecular gas and continuum properties. Total gas masses
and H column densities for our five CO-bright galaxies are on average
and cm over the kpc-scale
disks, and analysis suggests that these disks are stabilized against
gravitational fragmentation. The continuum emission of all seven galaxies is
dominated by a central, unresolved source, and in five we also detect a
spatially extended component. The 230 GHz nuclear continua are modeled as
power laws ranging from to within the
observed frequency band. The extended continuum profiles of the two
radio-bright (and CO-faint) galaxies are roughly aligned with their radio jet
and suggests resolved synchrotron jets. The extended continua of the CO-bright
disks are coincident with optically thick dust absorption and have spectral
slopes that are consistent with thermal dust emission.Comment: 20 pages, 10 figures; accepted for publication in Ap
The Voluntary Adjustment of Railroad Obligations
Automatic memory management techniques eliminate many programming errors that are both hard to find and to correct. However, these techniques are not yet used in embedded systems with hard realtime applications. The reason is that current methods for automatic memory management have a number of drawbacks. The two major ones are: (1) not being able to always guarantee short real-time deadlines and (2) using large amounts of extra memory. Memory is usually a scarce resource in embedded applications. In this paper we present a new technique, Real-Time Reference Counting (RTRC) that overcomes the current problems and makes automatic memory management attractive also for hard real-time applications. The main contribution of RTRC is that often all memory can be used to store live objects. This should be compared to a memory overhead of about 500% for garbage collectors based on copying techniques and about 50% for garbage collectors based on mark-and-sweep techniques
Fair Value Hierarchy Measures: Post-Implementation Evidence on IFRS 7
Using a balance sheet valuation model, this study examines if information on the fair value hierarchy of on-balance sheet financial assets and financial liabilities are incorporated in the market’s valuation of companies’ equities in Singapore. The results of the study show significant associations between as-reported Level 1 and Level 2 fair value measures of financial assets and market values. However, the results are not significant for Level 3 fair value measures of financial assets and each of the three levels of fair value measures of financial liabilities. The results also show that returns are more positively associated with as-reported gains and losses from Level 1 and Level 2 fair value measures than those from Level 3 fair value measures. Overall, the evidence suggests that information on the fair value hierarchy of IFRS 7 Financial Instruments: Disclosures are used by market participants in their pricing decisions. The market however appears to place greater weights on fair value changes taken to the income statement than those taken to OCI, notwithstanding the level of the fair value measure. While the fixation with income statement measures remains a puzzle, the results are consistent with prior studies that show that investors largely ignore OCI in their pricing of shares
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