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Title:
On Planetary Companions to the MACHO 98-BLG-35 Microlens Star
Authors:
Rhie, S. H.; Bennett, D. P.; Becker, A. C.; Peterson, B. A.; Fragile, P. C.; Johnson, B. R.; Quinn, J. L.; Crouch, A.; Gray, J.; King, L.; Messenger, B.; Thomson, S.; Bond, I. A.; Abe, F.; Carter, B. S.; Dodd, R. J.; Hearnshaw, J. B.; Honda, M.; Jugaku, J.; Kabe, S.; Kilmartin, P. M.; Koribalski, B. S.; Masuda, K.; Matsubara, Y.; Muraki, Y.; Nakamura, T.; Nankivell, G. R.; Noda, S.; Rattenbury, N. J.; Reid, M.; Rumsey, N. J.; Saito, To.; Sato, H.; Sato, S.; Sekiguchi, M.; Sullivan, D. J.; Sumi, T.; Watase, Y.; Yanagisawa, T.; Yock, P. C. M.; Yoshizawa, M.
Affiliation:
AA(Department of Physics, University of Notre Dame, Notre Dame, IN 46556), AB(Department of Physics, University of Notre Dame, Notre Dame, IN 46556.; Center for Particle Astrophysics, University of California, Berkeley, CA 94720), AC(Center for Particle Astrophysics, University of California, Berkeley, CA 94720.; Departments of Astronomy and Physics, University of Washington, Seattle, WA 98195), AD(Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, ACT 2611, Australia), AE(Department of Physics, University of Notre Dame, Notre Dame, IN 46556), AF(Tate Laboratory of Physics, University of Minnesota, Minneapolis, MN 55455), AG(Department of Physics, University of Notre Dame, Notre Dame, IN 46556), AH(Department of Mathematics and Statistics, Monash University, Clayton, Victoria 3168, Australia), AI(Department of Mathematics and Statistics, Monash University, Clayton, Victoria 3168, Australia), AJ(Department of Physics, University of Notre Dame, Notre Dame, IN 46556), AK(Department of Mathematics and Statistics, Monash University, Clayton, Victoria 3168, Australia), AL(Department of Mathematics and Statistics, Monash University, Clayton, Victoria 3168, Australia), AM(Faculty of Science, University of Auckland, Auckland, New Zealand.; Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand), AN(STE Laboratory, Nagoya University, Nagoya 464, Japan), AO(Carter National Observatory, PO Box 2909, Wellington, New Zealand), AP(Faculty of Science, University of Auckland, Auckland, New Zealand.; Carter National Observatory, PO Box 2909, Wellington, New Zealand.; School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand), AQ(Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand), AR(Institute for Cosmic Ray Research, University of Tokyo, Tokyo 188, Japan), AS(Research Institute of Civilization, 2-29-3 Sakuragaoka, Tama-shi 206, Japan), AT(KEK Laboratory, Tsukuba 305, Japan), AU(Faculty of Science, University of Auckland, Auckland, New Zealand.; Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand), AV(Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 2121, Australia), AW(STE Laboratory, Nagoya University, Nagoya 464, Japan), AX(STE Laboratory, Nagoya University, Nagoya 464, Japan), AY(STE Laboratory, Nagoya University, Nagoya 464, Japan), AZ(Department of Physics, Kyoto University, Kyoto 606, Japan), BA(Carter National Observatory, PO Box 2909, Wellington, New Zealand), BB(STE Laboratory, Nagoya University, Nagoya 464, Japan), BC(Faculty of Science, University of Auckland, Auckland, New Zealand), BD(School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand.; Carter National Observatory, PO Box 2909, Wellington, New Zealand), BE(Carter National Observatory, PO Box 2909, Wellington, New Zealand), BF(Tokyo Metropolitan College of Aeronautics, 8-52-1 Minami-senjyu, Tokyo 116, Japan), BG(Department of Physics, Kyoto University, Kyoto 606, Japan), BH(Department of Physics, Nagoya University, Nagoya 464, Japan), BI(Institute for Cosmic Ray Research, University of Tokyo, Tokyo 188, Japan), BJ(School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand), BK(STE Laboratory, Nagoya University, Nagoya 464, Japan), BL(KEK Laboratory, Tsukuba 305, Japan), BM(STE Laboratory, Nagoya University, Nagoya 464, Japan), BN(Faculty of Science, University of Auckland, Auckland, New Zealand), BO(National Astronomical Observatory, Mitaka, Tokyo 181, Japan)
Publication:
The Astrophysical Journal, Volume 533, Issue 1, pp. 378-391. (ApJ Homepage)
Publication Date:
04/2000
Origin:
UCP
ApJ Keywords:
COSMOLOGY: GRAVITATIONAL LENSING, STARS: PLANETARY SYSTEMS, STARS: LOW-MASS, BROWN DWARFS
DOI:
10.1086/308634
Bibliographic Code:
2000ApJ...533..378R

Abstract

We present observations of the microlensing event MACHO 98-BLG-35, which reached a peak magnification factor of almost 80. These observations by the Microlensing Planet Search (MPS) and MOA collaborations place strong constraints on the possible planetary system of the lens star and show intriguing evidence for a low-mass planet with a mass fraction 4×10-5<=ɛ<=2×10-4. A giant planet with ɛ=10-3 is excluded from 95% of the region between 0.4 and 2.5 RE from the lens star, where RE is the Einstein ring radius of the lens. This exclusion region is more extensive than the generic ``lensing zone,'' which is 0.6-1.6 RE. For smaller mass planets, we can exclude 57% of the ``lensing zone'' for ɛ=10-4 and 14% of the lensing zone for ɛ=10-5. The mass fraction ɛ=10-5 corresponds to an Earth-mass planet for a lensing star of mass ~0.3 Msolar. A number of similar events will provide statistically significant constraints on the prevalence of Earth-mass planets. In order to put our limits in more familiar terms, we have compared our results to those expected for a solar system clone, averaging over possible lens system distances and orientations. We find that such a system is ruled out at the 90% confidence level. A copy of the solar system with Jupiter replaced by a second Saturn-mass planet can be ruled out at 70% confidence. Our low-mass planetary signal (few Earth masses to Neptune mass) is significant at the 4.5 σ confidence level. If this planetary interpretation is correct, the MACHO 98-BLG-35 lens system constitutes the first detection of a low-mass planet orbiting an ordinary star without gas giant planets.20
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