First Microlens Mass Measurement: PLANET Photometry of EROS BLG-2000-5

By J. An, M. Albrow, J. Beaulieu, J. Caldwell, D. DePoy, M. Dominik, B. Gaudi, A. Gould, J. Greenhill, K. Hill and 10 more. 2001

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We analyze PLANET photometric observations of the caustic-crossing binary lens microlensing event, EROS BLG-2000-5, and find that modeling the observed light curve requires incorporation of the microlens parallax and the binary orbital motion. The projected Einstein radius (E = 3.61 ± 0.11 AU) is derived from the measurement of the microlens parallax, and we are also able to infer the angular Einstein radius (θE = 1.38 ± 0.12 mas) from the finite source effect on the light curve, combined with an estimate of the angular size of the source given by the source position in a color-magnitude diagram. The lens mass, M = 0.612 ± 0.057 M☉, is found by combining these two quantities. This is the first time that parallax effects are detected for a caustic-crossing event and also the first time that the lens mass degeneracy has been completely broken through photometric monitoring alone. The combination of E and θE also allows us to conclude that the lens lies in the near side of the disk, within 2.6 kpc of the Sun, while the radial velocity measurement indicates that the source is a Galactic bulge giant.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

FREQUENCY OF SOLAR-LIKE SYSTEMS AND OF ICE AND GAS GIANTS BEYOND THE SNOW LINE FROM HIGH-MAGNIFICATION MICROLENSING EVENTS IN 2005–2008 (2010, background): “The EROS team issued only a few alerts, but one of these led to the first mass measurement of an unseen object (An et al. 2002), and the first spatially resolved high-resolution spectrum of another star (Castro et al. 2001).”
OGLE-2003-BLG-262: Finite-Source Effects from a Point-Mass Lens (2003, background): “…passing close to or over the face of the source star, the great majority of the actualθE measurements made over the ensuing decade used binary-lens events in which the source passed over the binary caustic (Albrow et al. 1999a, 2000a, 2001; Afonso et al. 2000; Alcock et al. 2000; An et al. 2002).”
The OGLE view of microlensing towards the Magellanic Clouds – IV. OGLE-III SMC data and final conclusions on MACHOs (2011, methodology): “We adopted the geocentric formalism to describe the 3 http://ogle.astrouw.edu.pl/ogle3/ews/2005/smc-001.html parallax effects (An et al. 2002, Gould 2004), where we assume the reference system to be located at the Earth at the time t0,par = 2454476.23, which we choose close to the peak of the event.”
A Jovian-Mass Planet in Microlensing Event OGLE-2005-BLG-071 (2005, background): “An et al. 2002), we constrain the host mass to be 0.08 M, !”
MOA-2009-BLG-387Lb: a massive planet orbiting an M dwarf (2011, methodology): “(8) To introduce parallax effects, we use the geocentric formalism (An et al. 2002; Gould 2004) which ensures that the three standard microlensing parameters (t0, tE, u0) are nearly the same as for the no-parallax fit.”
Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition (2006, background): “These systems remain the predominant outlet for the direct measurement of individual stellar masses, either through the detection of orbital motion or microlensing techniques (An et al. 2002).”