Microlens Parallax Asymmetries Toward the Large Magellanic Cloud
نویسنده
چکیده
If the microlensing events now being detected toward the Large Magellanic Cloud (LMC) are due to lenses in the Milky Way halo, then the events should typically have asymmetries of order 1% due to parallax from the reflex motion of the Earth. By contrast, if the lenses are in the LMC, the parallax effects should be negligible. A ground-based search for such parallax asymmetries would therefore clarify the location of the lenses. A modest effort (2 hours per night on a 1 m telescope) could measure 15 parallax asymmetries over 5 years and so marginally discriminate between the halo and the LMC as the source of the lenses. A dedicated 1 m telescope would approximately double the number of measurements and would therefore clearly distinguish between the alternatives. However, compared to satellite parallaxes, the information extracted from ground-based parallaxes is substantially less useful for understanding the nature of the halo lenses (if that is what they are). The backgrounds of asymmetries due to binary-source and binarylens events are estimated to be approximately 7% and 12% respectively. These complicate the interpretation of detected parallax asymmetries, but not critically. Subject Headings: dark matter – Galaxy: halo – gravitational lensing – Magellanic Clouds 1 Alfred P. Sloan Foundation Fellow
منابع مشابه
4 Resolution of the MACHO - LMC - 5 Puzzle : The Jerk - Parallax Microlens Degeneracy
By extending the constant-acceleration analysis of Smith, Mao, & Paczy´nski to include jerk, I show that microlens parallax measurements are subject to a four-fold discrete degeneracy. The new degeneracy is characterized by a projected velocity˜v j = −(3/4) csc β ec (cos 2 ψ sin 2 β ec + sin 2 ψ) 3/2 v ⊕ , where β ec is the ecliptic latitude, ψ is the phase of the Earth's orbit relative to oppo...
متن کاملar X iv : a st ro - p h / 03 11 54 8 v 1 2 4 N ov 2 00 3 Resolution of the MACHO - LMC - 5 Puzzle : The Jerk - Parallax Microlens Degeneracy
By extending the constant-acceleration analysis of Smith, Mao, & Paczy´nski to include jerk, I show that microlens parallax measurements are subject to a four-fold discrete degeneracy. The new degeneracy is characterized by a projected velocity˜v j = −(3/4) csc β(cos 2 ψ sin 2 β + sin 2 ψ) 3/2 v ⊕ , where β is the ecliptic latitude , ψ is the phase of the Earth's orbit relative to opposition at...
متن کاملMicrolens Parallax Measurements With A Warm Spitzer
Because the Spitzer Space Telescope is in an Earth-trailing orbit, losing about 0.1 AU/yr, it is excellently located to perform microlens parallax observations toward the Magellanic Clouds (LMC/SMC) and the Galactic bulge. These yield the so-called “projected velocity” of the lens, which can distinguish statistically among different populations. A few such measurements toward the LMC/SMC would ...
متن کاملMicrolens Parallaxes with SIRTF
The Space Infrared Telescope Facility (SIRTF) will drift away from the Earth at ∼ 0.1 AU yr. Microlensing events will therefore have different characteristics as seen from the satellite and the Earth. From the difference, it is possible in principle to measure ṽ, the transverse velocity of the lens projected onto the observer plane. Since ṽ has very different values for different populations (d...
متن کاملResolving the Nature of the Lmc Microlensing Event Lmc-5
We present the results from an analysis of Hubble Space Telescope High Resolution Camera data for the Large Magellanic Cloud microlensing event MACHO-LMC-5. By determining the parallax and proper motion of this object we find that the lens is an M dwarf star at a distance of 578 −53pc with a proper motion of 21.39±0.04 mas/yr. Based on the kinematics and location of this star it more likely to ...
متن کامل