Short-duration lensing events: I. wide-orbit planets? free-floating low-mass objects? or high-velocity stars?

Abstract

Short duration lensing events tend to be generated by low-mass lenses or by lenses with high transverse velocities. Furthermore, for any given lens mass and speed, events of short duration are preferentially caused by nearby lenses (mesolenses) that can be studied in detail, or else by lenses so close to the source star that finite-source-size effects may be detected, yielding information about both the Einstein ring radius and the surface of the lensed star. Planets causing short-duration events may be in orbits with any orientation, and may have semimajor axes smaller than an AU, or they may reach the outer limits of their planetary systems, in the region corresponding to the Solar System's Oort Cloud. They can have masses larger than Jupiter's or smaller than Pluto's. Lensing therefore has a unique potential to expand our understanding of planetary systems. A particular advantage of lensing is that it can provide precision measurements of system parameters, including the masses of and projected separation between star and planet. We demonstrate how the parameters can be extracted and show that a great deal can be learned. For example, it is remarkable that the gravitational mass of nearby free-floating planet-mass lenses can be measured by complementing observations of a photometric event with deep images that detect the planet itself. A fraction of short events may be caused by high-velocity stars located within a kpc. Many high-velocity lenses are likely to be neutron stars that received large natal kicks. Other high-speed stars may be members of the halo population. Still others may be hypervelocity stars that have been ejected from the Galactic Center, or runaway stars escaped from close binaries, possibly including the progenitor binaries of Type Ia supernovae.

17 pages; 2 figures; submitted to ApJ 3 July 2009

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Cited by in corpus (11)

• Close encounters involving free-floating planets in star clusters
• The dynamical fate of planetary systems in young star clusters
• Kepler-1649b: An Exo-Venus in the Solar Neighborhood
• Short-duration lensing events: II. Expectations and Protocols
• Microlensing by a wide-separation planet: detectability and boundness
• On the detection of free-floating planets through microlensing towards the Magellanic Clouds
• Modelling the Inner Debris Disc of HR 8799
• Kepler K2 Campaign 9: I. Candidate short-duration events from the first space-based survey for planetary microlensing
• History of Globulettes in the Milky Way
• Mass-velocity dispersion relation by using the \textit{Gaia} data and its effect on interpreting short-duration and degenerate microlensing events
• Gravitational Microlensing Rates in Milky Way Globular Clusters