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Astron. Astrophys. 338, 56-61 (1998)

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Detecting luminous gravitational microlenses using spectroscopy

S. Mao 1, J. Reetz 2 and D.J. Lennon 2

1 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85740 Garching, Germany
2 Universitäts-Sternwarte, Scheinerstrasse 1, D-81679 Munich, Germany

Received 15 April 1998 / Accepted 9 June 1998


We propose a new method to detect the gravitational lenses in the ongoing microlensing experiments using medium and high resolution spectroscopy ([FORMULA]). Since the radial velocity of the lens and lensed source typically differs by [FORMULA], the spectral lines from the lens and source will be shifted relative to each other by [FORMULA]Å in the optical. We simulate realistic composite spectra assuming different spectral types for the lens and source and study the lens detectability as a function of the signal-to-noise ratio, spectral resolution and lens-to-source light ratio. We show that it is possible to measure the difference in radial velocity from an unequivocal signature in the difference of cross- and auto-correlation functions calculated from two spectra obtained at different magnifications. If the lens is brighter than 10% ([FORMULA]) of the unmagnified source we find that a spectral resolution of [FORMULA] and a signal-to-noise of 50 (at magnification maximum) are sufficient to determine the relative radial velocity of the lens. At [FORMULA], the spectral resolution of high resolution spectrographs of 8-10m class telescopes, the lens could even be detected at a brightness of [FORMULA] ([FORMULA]) of the source. Radial velocities higher than [FORMULA] can be measured with an accuracy of a few [FORMULA]. Practical difficulties and observation strategies are also discussed.

Key words: gravitational lensing – stars: kinematics – techniques: spectroscopic – methods: data analysis

Send offprint requests to: S. Mao
Correspondence to: smao@mpa-garching.mpg.de

© European Southern Observatory (ESO) 1998

Online publication: September 8, 1998