The POINT-AGAPE Microlensing Survey: First Constraint on MACHOs towards M31

To reveal the galactic dark matter in the form of MACHOs ("Massive Astrophysical Compact Halo Objects"), the POINT-AGAPE collaboration is carrying out a search for gravitational microlensing towards M31. A clear microlensing signal is detected. The high-threshold analysis of 3-year data leads to 7 bright and short microlensing candidates. The preliminary estimation of the detection efficiency implies that less than 25% (60%) of standard halos can be composed of objects with masses between 10^{-4} and 10^{-1} (10^{-1} and 1) solar mass at the 95% C.L. This result is compatible with previous microlensing results towards the Magellanic Clouds and gives the first constraints on MACHOs for a distant spiral galaxy.Comment: 4 pages, 2 figures, to appear in the proceedings of the XXXIXth Rencontres de Moriond "Exploring the Universe", La Thuile, Italy, March 28-April 4, 200

Microlensing Parallax for Observers in Heliocentric Motion

Motivated by the ongoing Spitzer observational campaign, and the forecoming K2 one, we revisit, working in an heliocentric reference frame, the geometrical foundation for the analysis of the microlensing parallax, as measured with the simultaneous observation of the same microlensing event from two observers with relative distance of order AU. For the case of observers at rest we discuss the well known fourfold microlensing parallax degeneracy and determine an equation for the degenerate directions of the lens trajectory. For the case of observers in motion, we write down an extension of the Gould (1994) relationship between the microlensing parallax and the observable quantities and, at the same time, we highlight the functional dependence of these same quantities from the timescale of the underlying microlensing event. Furthermore, through a series of examples, we show the importance of taking into account the motion of the observers to correctly recover the parameters of the underlying microlensing event. In particular we discuss the cases of the amplitude of the microlensing parallax and that of the difference of the timescales between the observed microlensing events, key to understand the breaking of the microlensing parallax degeneracy. Finally, we consider the case of the simultaneous observation of the same microlensing event from ground and two satellites, a case relevant for the expected joint K2 and Spitzer observational programs in 2016.Comment: Accepted for publication in Ap

Pixel lensing: Microlensing towards M31

Pixel lensing is gravitational microlensing of unresolved stars. The main target explored up to now has been the nearby galaxy of Andromeda, M31. The scientific issues of interest are the search for dark matter in form of compact halo objects, the study of the characteristics of the luminous lens and source populations and the possibility of detecting extra-solar (and extra-galactic) planets. In the present work we intend to give an updated overview of the observational status in this field.Comment: Invited article for the GRG special issue on gravitational lensing (Ph. Jetzer, Y. Mellier and V. Perlick Eds.

Newtonian Limit of Induced Gravity

We discuss the weak-field limit of induced gravity and show that results directly depend on the coupling and self-interaction potential of the scalar field. A static spherically symmetric exact solution is found and its conformal properties are studied. As an application, it is shown that the light deflection angle and the microlensing quantities can be parametrized by the coupling of the theory.Comment: 15 pages, LATEX, to appear in Grav & Cos

MiNDSTEp differential photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756: microlensing and a new time delay

Aims. We present V and R photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756. The data were taken by the MiNDSTEp collaboration with the 1.54 m Danish telescope at the ESO La Silla observatory from 2008 to 2012. Methods. Differential photometry has been carried out using the image subtraction method as implemented in the HOTPAnTS package, additionally using GALFIT for quasar photometry. Results. The quasar WFI 2033-4723 showed brightness variations of order 0.5 mag in V and R during the campaign. The two lensed components of quasar HE 0047-1756 varied by 0.2–0.3 mag within five years. We provide, for the first time, an estimate of the time delay of component B with respect to A of Δt = (7.6 ± 1.8) days for this object. We also find evidence for a secular evolution of the magnitude difference between components A and B in both filters, which we explain as due to a long-duration microlensing event. Finally we find that both quasars WFI 2033-4723 and HE 0047-1756 become bluer when brighter, which is consistent with previous studies

High-precision photometry by telescope defocussing – VIII. WASP-22, WASP-41, WASP-42 and WASP-55

We present 13 high-precision and four additional light curves of four bright southern-hemisphere transiting planetary systems: WASP-22, WASP-41, WASP-42 and WASP-55. In the cases of WASP-42 and WASP-55, these are the first follow-up observations since their discovery papers. We present refined measurements of the physical properties and orbital ephemerides of all four systems. No indications of transit timing variations were seen. All four planets have radii inflated above those expected from theoretical models of gas-giant planets; WASP-55 b is the most discrepant with a mass of 0.63 MJup and a radius of 1.34 RJup. WASP-41 shows brightness anomalies during transit due to the planet occulting spots on the stellar surface. Two anomalies observed 3.1 d apart are very likely due to the same spot. We measure its change in position and determine a rotation period for the host star of 18.6 ± 1.5 d, in good agreement with a published measurement from spot-induced brightness modulation, and a sky-projected orbital obliquity of λ = 6 ± 11°. We conclude with a compilation of obliquity measurements from spot-tracking analyses and a discussion of this technique in the study of the orbital configurations of hot Jupiters