Chandra and Hubble Study of a New Transient X-ray Source in M31

We present X-ray and optical observations of a new transient X-ray source in M31 first detected 23-May-2004 at R.A.=00:43:09.940 +/- 0.65'', Dec.=41:23:32.49 +/- 0.66''. The X-ray lightcurve shows two peaks separated by several months, reminiscent of many Galactic X-ray novae. The location and X-ray spectrum of the source suggest it is a low mass X-ray binary (LMXB). Follow-up HST ACS observations of the location both during and after the outburst provide a high-confidence detection of variability for one star within the X-ray position error ellipse. This star has $\Delta$B ~ 1 mag, and there is only a ~1% chance of finding such a variable in the error ellipse. We consider this star a good candidate for the optical counterpart of the X-ray source. The luminosity of this candidate provides a prediction for the orbital period of the system of 2.3$^{+3.7}_{-1.2}$ days.Comment: 17 pages, 3 figures, 4 tables, accepted for publication in Ap

Millisecond Pulsar Ages: Implications of Binary Evolution and a Maximum Spin Limit

In the absence of constraints from the binary companion or supernova remnant, the standard method for estimating pulsar ages is to infer an age from the rate of spin-down. While the generic spin-down age may give realistic estimates for normal pulsars, it can fail for pulsars with very short periods. Details of the spin-up process during the low mass X-ray binary phase pose additional constraints on the period (P) and spin-down rates (Pdot) that may consequently affect the age estimate. Here, we propose a new recipe to estimate millisecond pulsar (MSP) ages that parametrically incorporates constraints arising from binary evolution and limiting physics. We show that the standard method can be improved by this approach to achieve age estimates closer to the true age whilst the standard spin-down age may over- or under-estimate the age of the pulsar by more than a factor of ~10 in the millisecond regime. We use this approach to analyze the population on a broader scale. For instance, in order to understand the dominant energy loss mechanism after the onset of radio emission, we test for a range of plausible braking indices. We find that a braking index of n=3 is consistent with the observed MSP population. We demonstrate the existence and quantify the potential contributions of two main sources of age corruption: the previously known "age bias" due to secular acceleration and "age contamination" driven by sub-Eddington progenitor accretion rates. We explicitly show that descendants of LMXBs that have accreted at very low rates will exhibit ages that appear older than the age of the Galaxy. We further elaborate on this technique, the implications and potential solutions it offers regarding MSP evolution, the underlying age distribution and the post-accretion energy loss mechanism.Comment: Replaced with version published by ApJ. Tables reformatted and minor changes to the text. Full resolution color figures and movies available at http://www.kiziltan.org/research.html#age

The application of parameter sensitivity analysis methods to inverse simulation models

Knowledge of the sensitivity of inverse solutions to variation of parameters of a model can be very useful in making engineering design decisions. This paper describes how parameter sensitivity analysis can be carried out for inverse simulations generated through approximate transfer function inversion methods and also by the use of feedback principles. Emphasis is placed on the use of sensitivity models and the paper includes examples and a case study involving a model of an underwater vehicle. It is shown that the use of sensitivity models can provide physical understanding of inverse simulation solutions that is not directly available using parameter sensitivity analysis methods that involve parameter perturbations and response differencing

Optical Constraints on an X-ray Transient Source in M31

We have detected a transient X-ray source in the M31 bulge through a continuing monitoring campaign with the Chandra ACIS-I camera. The source was detected at R.A.=00:42:33.428 +/- 0.11'', Dec.=+41:17:03.37 +/- 0.11'' in only a single observation taken 2004 May 23. Fortuitous optical HST/ACS imaging of the transient location prior to the X-ray outburst, along with follow-up HST/ACS imaging during and after the outburst, reveals no transient optical source brighter than B (equivalent) = 25.5. The location of the source and its X-ray properties suggest it is a low mass X-ray binary (LMXB). Assuming the transient is similar to many Galactic X-ray novae, the X-ray luminosity of (3.9 +/- 0.5) X 10$^{37}$ erg s$^{-1}$ and the upper-limit on the optical luminosity provide a prediction of <1.6 days for the orbital period of the binary system.Comment: 15 pages, 3 figures, accepted for publication in Ap

A Soft X-ray Transient in the M31 Bulge

We have examined a probable soft X-ray transient source in the M31 bulge at R.A.=0:42:41.814 +/- 0.08", Dec. = 41:16:35.86 +/- 0.07". On the three occasions we observed the source, its spectrum was soft (kT_{in} ~1 keV). The brightest detection of the source was 2004 July 17 with a 0.3-7 keV luminosity of ~5 X 10^{37} erg/s. The only previous detection of the source was in 1979 by the Einstein observatory. The multiple detections over 25 years suggest the duty cycle of the source is in the range 0.02-0.06. Coordinated HST/ACS imaging before, during, and after the outburst revealed no variable optical source within the position errors of the X-ray source. The optical data place a firm upper limit on the brightness of the counterpart of the X-ray outburst of B>24.7, suggesting the binary has a period <5.2 days. The X-ray spectrum and lack of bright stars at the source location indicate the source was a soft transient event occurring in a low-mass X-ray binary, making this source a good black hole candidate in M31.Comment: 18 pages, 4 tables, 3 figures, accepted for publication in Ap

Hydrodynamics of the stream-disk impact in interacting binaries

We use hydrodynamic simulations to provide quantitative estimates of the effects of the impact of the accretion stream on disks in interacting binaries. For low accretion rates, efficient radiative cooling of the hotspot region can occur, and the primary consequence of the stream impact is stream overflow toward smaller disk radii. The stream is well described by a ballistic trajectory, but larger masses of gas are swept up and overflow at smaller, but still highly supersonic, velocities. If cooling is inefficient, overflow still occurs, but there is no coherent stream inward of the disk rim. Qualitatively, the resulting structure appears as a bulge extending downstream along the disk rim. We calculate the mass fraction and velocity of the overflowing component as a function of the important system parameters, and discuss the implications of the results for X-ray observations and doppler tomography of cataclysmic variables, low-mass X-ray binaries and supersoft X-ray sources.Comment: 16 pages, including 8 figures. 1 color figure as a jpeg. ApJ, in pres

Chapter 3 Wetland Design and Development

The history of efforts to design and develop wetland sites is extensive and rich, especially in the United States. This chapter provides an annotated view of the current state of wetland design and recommends an approach to future efforts using “Hydrogeomorphic Methodology.” Experience over the past century indicates that the most important part of wetland design and development is upfront work to: (1) determine what type of wetland historically occurred in, and is appropriate for a site; (2) understand and attempt to emulate the key ecological processes that created and sustained specific wetland types; (3) compare historical landscapes and wetland attributes with contemporary landscape and site conditions to understand remediating needs; and (4) determine management objectives and capabilities. The foundation for hydrogeomorphic assessments is analysis of historical and current information about geology and geomorphology, soils, topography and elevation, hydrological regimes, plant and animal communities, and physical anthropogenic features. The availability of this information is discussed and the sequence of actions used to prepare hydrogeomorphic matrices of potential historical vegetation communities and maps is provided as in application of information. Specific considerations for designing wetland infrastructure and restoring wetland vegetation are reviewed. An example of a wetland restoration project for the Duck Creek Conservation Area, Missouri is provided to demonstrate use of the hydrogeomorphic approach. We believe that future wetland design and development strategies should include the following actions: (1) wetland conservation must seek to achieve incremental gains at landscape-level scales; (2) the foundation of wetland design is determining the appropriate wetland type for the site being considered; (3) wetland designs should seek to restore and emulate historical form and process as completely as possible and to make systems as self-sustainable as possible; and (4) future design and development of wetlands must anticipate change related to climate, land uses, encroachments, and water availability and rights

Chapter 3 Wetland Design and Development

The history of efforts to design and develop wetland sites is extensive and rich, especially in the United States. This chapter provides an annotated view of the current state of wetland design and recommends an approach to future efforts using “Hydrogeomorphic Methodology.” Experience over the past century indicates that the most important part of wetland design and development is upfront work to: (1) determine what type of wetland historically occurred in, and is appropriate for a site; (2) understand and attempt to emulate the key ecological processes that created and sustained specific wetland types; (3) compare historical landscapes and wetland attributes with contemporary landscape and site conditions to understand remediating needs; and (4) determine management objectives and capabilities. The foundation for hydrogeomorphic assessments is analysis of historical and current information about geology and geomorphology, soils, topography and elevation, hydrological regimes, plant and animal communities, and physical anthropogenic features. The availability of this information is discussed and the sequence of actions used to prepare hydrogeomorphic matrices of potential historical vegetation communities and maps is provided as in application of information. Specific considerations for designing wetland infrastructure and restoring wetland vegetation are reviewed. An example of a wetland restoration project for the Duck Creek Conservation Area, Missouri is provided to demonstrate use of the hydrogeomorphic approach. We believe that future wetland design and development strategies should include the following actions: (1) wetland conservation must seek to achieve incremental gains at landscape-level scales; (2) the foundation of wetland design is determining the appropriate wetland type for the site being considered; (3) wetland designs should seek to restore and emulate historical form and process as completely as possible and to make systems as self-sustainable as possible; and (4) future design and development of wetlands must anticipate change related to climate, land uses, encroachments, and water availability and rights

Circulating asymmetric dimethylarginine and cognitive decline : A 4‐year follow‐up study of the 1936 Aberdeen Birth Cohort

ACKNOWLEDGEMENTS The authors gratefully acknowledge all participants of the ABC36 study. They acknowledge their colleagues, Prof Lawrence Whalley, Prof Ian Deary and the late Prof John Starr who developed the study. F.T. acknowledges support by the Rural and Environment Science and Analytical Services Division of the Scottish government (RESAS). Funding Information NHS Grampian R&D Endowments. Grant Number: 11/08 Scottish government Rural and Environment Science and Analytical Services DivisionPeer reviewedPublisher PD