Predicted microlensing events from analysis of Gaia Data Release 2

Astrometric microlensing can be used to make precise measurements of the masses of lens stars that are independent of their assumed internal physics. Such direct mass measurements, obtained purely by observing the gravitational effects of the stars on external objects, are crucial for validating theoretical stellar models. Specifically, astrometric microlensing provides a channel to direct mass measurements of single stars for which so few measurements exist. To use the astrometric solutions and photometric measurements of ~1.7 billion stars from Gaia Data Release 2 to predict microlensing events during the nominal Gaia mission and beyond. This will enable astronomers to observe the entirety of each event with appropriate observing resources. The data will allow precise lens mass measurements for white dwarfs and low-mass main sequence stars helping to constrain stellar evolutionary models. I search for source-lens pairs in GDR2 that could lead to events between 25/07/2014 and 25/07/2026. I estimate lens masses using GDR2 photometry and parallaxes, and appropriate model isochrones. Combined with source and lens parallax measurements from GDR2, this allows the Einstein radius to be computed for each pair. By considering the paths on the sky, I calculate the microlensing signals that are to be expected. I present a list of 76 predicted microlensing events. 9 and 5 astrometric events will be caused by LAWD37 and Stein2051B. 9 events will exhibit detectable photometric and astrometric signatures. Of the remaining events, ten will exhibit astrometric signals with amplitudes above 0.5 mas, while the rest are low-amplitude astrometric events with amplitudes between 0.131 and 0.5 mas. 5 and 2 events will reach their peaks during 2018 and 2019. 5 of the photometric events have the potential to evolve into high-magnification events, which may also probe for planetary companions to the lenses.Comment: Accepted A&

One to Hear Me An Exegetical Analysis of Job 31:1-7,35-37 which Explores the Presence of God in the Context of Human Suffering

This study will provide the reader with an exegetical analysis of Job 31: 1-7 and 35-37which explores the presence of God in the context of human suffering. Passages found elsewhere in Job will be connected to chapter 31 to elucidate the book\u27s storyline and major themes. Lastly, a discussion of Job\u27s theological relevance will consider the book\u27s significance in the wider framework of the Old and New Testaments

A New Algorithm For Difference Image Analysis

In the context of difference image analysis (DIA), we present a new method for determining the convolution kernel matching a pair of images of the same field. Unlike the standard DIA technique which involves modelling the kernel as a linear combination of basis functions, we consider the kernel as a discrete pixel array and solve for the kernel pixel values directly using linear least-squares. The removal of basis functions from the kernel model is advantageous for a number of compelling reasons. Firstly, it removes the need for the user to specify such functions, which makes for a much simpler user application and avoids the risk of an inappropriate choice. Secondly, basis functions are constructed around the origin of the kernel coordinate system, which requires that the two images are perfectly aligned for an optimal result. The pixel kernel model is sufficiently flexible to correct for image misalignments, and in the case of a simple translation between images, image resampling becomes unnecessary. Our new algorithm can be extended to spatially varying kernels by solving for individual pixel kernels in a grid of image sub-regions and interpolating the solutions to obtain the kernel at any one pixel.Comment: MNRAS Letters Accepte

The unusually large population of Blazhko variables in the globular cluster NGC 5024 (M53)

We report the discovery of amplitude and phase modulations typical of the Blazhko effect in 22 RRc and 9 RRab type RR Lyrae stars in NGC 5024 (M53). This brings the confirmed Blazhko variables in this cluster to 23 RRc and 11 RRab, that represent 66% and 37% of the total population of RRc and RRab stars in the cluster respectively, making NGC 5024 the globular cluster with the largest presently known population of Blazhko RRc stars. We place a lower limit on the overall incidence rate of the Blazhko effect among the RR Lyrae population in this cluster of 52%. New data have allowed us to refine the pulsation periods. The limitations imposed by the time span and sampling of our data prevents reliable estimations of the modulation periods. The amplitudes of the modulations range between 0.02 and 0.39 mag. The RRab and RRc are neatly separated in the CMD, and the RRc Blazhko variables are on averge redder than their stable couterparts; these two facts may support the hypothesis that the HB evolution in this cluster is towards the red and that the Blazhko modulations in the RRc stars are connected with the pulsation mode switch.Comment: ACCEPTED IN MNRAS 14 pages, 9 figures and 6 table

RR Lyrae mode switching in globular cluster M 68 (NGC 4590)

D.M.B. acknowledges NPRP grant # X-019-1-006 from the Qatar National Research Fund (a member of Qatar Foundation). A.A.F. acknowledges the support of DGAPA-UNAM through project IN106615-17.We build on our detailed analysis of time-series observations of the globular cluster M 68 to investigate the irregular pulsational behaviour of four of the RR Lyrae stars in this cluster. M 68 is one of only two globular clusters in which mode switching of RR Lyrae stars has previously been reported. We discuss one additional case, as well as a case of irregular behaviour, and we briefly revisit the two previously reported cases with a homogeneous analysis. We find that in 2013, V45 was pulsating in the first-overtone mode alone, despite being previously reported as a double-mode (fundamental and first overtone) pulsator in 1994, and that the amplitude of the fundamental mode in V7 is increasing with time. We also suggest that V21 might not have switched pulsation modes as previously reported, although the first overtone seems to be becoming less dominant. Finally, our analysis of available archival data confirms that V33 lost a pulsation mode between 1950 and 1986.Publisher PDFPeer reviewe

Structure and star formation in disk galaxies. II. Optical Imaging

Peer reviewe