-
D P Bennett, S H Rhie,
S Nikolaev,
B S Gaudi,
A Udalski,
A Gould,
G W Christie,
D Maoz,
S Dong,
J Mccormick,
M K Szymaski,
P J Tristram,
B Macintosh,
K H Cook,
M Kubiak,
G Pietrzyski,
I Soszyski,
O Szewczyk,
K Ulaczyk,
L Wyrzykowski
N.J. RattenburyThe MOA Collaboration) M. Albrow J.-P. Beaulieu D.M. Bramich M.J. Burgdorf J. Greenhill. 07/2010; 1629(35).
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D. P. Bennett, S. H. Rhie,
S. Nikolaev,
B. S. Gaudi,
A. Udalski,
A. Gould,
G. W. Christie,
D. Maoz,
S. Dong,
J McCormick, [......],
S. Dieters,
P. Fouque,
J. Greenhill,
K. Horne,
C. Snodgrass,
I. Steele,
Y. Tsapras,
B. Chaboyer,
A. Crocker,
S. Frank
[show abstract]
[hide abstract]
ABSTRACT: We present a new analysis of the Jupiter+Saturn analog system, OGLE-2006-BLG-109Lb,c, which was the first double planet system discovered with the gravitational microlensing method. This is the only multi-planet system discovered by any method with measured masses for the star and both planets. In addition to the signatures of two planets, this event also exhibits a microlensing parallax signature and finite source effects that provide a direct measure of the masses of the star and planets, and the expected brightness of the host star is confirmed by Keck AO imaging, yielding masses of M_* = 0.51(+0.05-0.04) M_sun, M_b = 231+-19 M_earth, M_c = 86+-7 M_earth. The Saturn-analog planet in this system had a planetary light curve deviation that lasted for 11 days, and as a result, the effects of the orbital motion are visible in the microlensing light curve. We find that four of the six orbital parameters are tightly constrained and that a fifth parameter, the orbital acceleration, is weakly constrained. No orbital information is available for the Jupiter-analog planet, but its presence helps to constrain the orbital motion of the Saturn-analog planet. Assuming co-planar orbits, we find an orbital eccentricity of eccentricity = 0.15 (+0.17-0.10) and an orbital inclination of i = 64 (+4-7) deg. The 95% confidence level lower limit on the inclination of i > 49 deg. implies that this planetary system can be detected and studied via radial velocity measurements using a telescope of >30m aperture. Comment: 48 pages including 10 figures, to be published in ApJ
The Astrophysical Journal 11/2009; · 6.02 Impact Factor
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C. Alcock,
R. A. Allsman,
D. Alves,
T. S. Axelrod,
A. C. Becker,
D. P. Bennett,
K. H. Cook,
A. J. Drake,
K. C. Freeman,
K. Griest, [......],
B. A. Peterson,
M. R. Pratt,
P. J. Quinn, S. H. Rhie,
A. W. Rodgers,
P. B. Stetson,
C. W. Stubbs,
W. Sutherland,
A. Tomaney,
and T. Vandehei
[show abstract]
[hide abstract]
ABSTRACT: We present photometric observations and analysis of the second microlensing event detected toward the Small Magellanic Cloud (SMC), MACHO Alert 98-SMC-1. This event was detected early enough to allow intensive observation of the light curve. These observations revealed 98-SMC-1 to be the first caustic crossing binary microlensing event toward the Magellanic Clouds to be discovered in progress. Frequent coverage of the evolving light curve allowed an accurate prediction for the date of the source crossing out of the lens caustic structure. The caustic crossing temporal width, along with the angular size of the source star, measures the proper motion of the lens with respect to the source and thus allows an estimate of the location of the lens. Lenses located in the Galactic halo would have a velocity projected to the SMC of ~1500 kms-1, while an SMC lens would typically have ~60 kms-1. The event light curve allows us to obtain a unique fit to the parameters of the binary lens and to estimate the proper motion of the lensing system. We have performed a joint fit to the MACHO/GMAN data presented here, including recent EROS data of this event from Afonso and collaborators. These joint data are sufficient to constrain the time t* for the lens to move an angle equal to the source angular radius: t*=0.116±0.010 days. We estimate a radius for the lensed source of R*=1.1 ± 0.1 R☉ from its unblended color and magnitude. This yields a projected velocity of = 76 ± 10 kms-1. Only 0.12% of halo lenses would be expected to have a value at least as small as this, while 38% of SMC lenses would be expected to have as large as this. This implies that the lensing system is more likely to reside in the SMC than in the Galactic halo. Similar observations of future Magellanic Cloud microlensing events will help to determine the contribution of MACHOS to the Galaxy's dark halo.
The Astrophysical Journal 01/2009; 518(1):44. · 6.02 Impact Factor
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N. J. Rattenbury,
F Abe,
D. P. Bennett,
I. A. Bond,
J. J. Calitz,
A. Claret,
K. H. Cook,
Y. Furuta,
A. Gal-Yam,
J. F. Glicenstein, [......],
L. Philpott, S. H. Rhie,
T Sako,
D. J. Sullivan,
T Sumi,
D. M. Terndrup,
P. J. Tristram,
J. Wood,
T Yanagisawa,
P. C. M. Yock
[show abstract]
[hide abstract]
ABSTRACT: We report a measurement of the shape of the source star in microlensing event MOA 2002-BLG-33. The lens for this event was a close binary whose centre-of-mass passed almost directly in front of the source star. At this time, the source star was closely bounded on all sides by a caustic of the lens. This allowed the oblateness of the source star to be constrained. We found that a/b = 1.02^{+0.04}_{-0.02} where a and b are its semi-major and semi-minor axes respectively. The angular resolution of this measurement is approximately 0.04 microarcsec. We also report HST images of the event that confirm a previous identification of the source star as an F8-G2 turn-off main-sequence star.
07/2005;
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F Abe,
D. P. Bennett,
I. A. Bond,
J. J. Calitz,
A. Claret,
K. H. Cook,
Y. Furuta,
A. Gal-Yam,
J. F. Glicenstein,
J. B. Hearnshaw, [......],
L. Philpott,
N. J. Rattenbury, S. H. Rhie,
T Sako,
D. J. Sullivan,
T Sumi,
D. M. Terndrup,
P. J. Tristram,
T Yanagisawa,
P. C. M. Yock
[show abstract]
[hide abstract]
ABSTRACT: We report a measurement of limb darkening of a solar-like star in the very high magnification microlensing event MOA 2002-BLG-33. A 15 hour deviation from the light curve profile expected for a single lens was monitored intensively in V and I passbands by five telescopes spanning the globe. Our modelling of the light curve showed the lens to be a close binary system whose centre-of-mass passed almost directly in front of the source star. The source star was identified as an F8-G2 main sequence turn-off star. The measured stellar profiles agree with current stellar atmosphere theory to within ~4% in two passbands. The effective angular resolution of the measurements is <1 micro-arcsec. These are the first limb darkening measurements obtained by microlensing for a Solar-like star. Comment: Accepted for publication in A&A Letters. 5 pages, 2 embedded colour ps figures plus 1 jpg figure. Version with all figures embedded available from: http://www.roe.ac.uk/~iab/moa33paper/
10/2003;
-
[show abstract]
[hide abstract]
ABSTRACT: We present an re-analysis of the longest timescale gravitational microlensing event discovered to date: MACHO-99-BLG-22/OGLE-1999-BUL-32, which was discovered by both the MACHO and OGLE microlensing alert systems. Our analysis of this microlensing parallax event includes a likelihood analysis of the lens position based upon a standard model of the Galactic velocity distribution, and this implies that the lens could be a black hole of ~100 M_solar at a distance of a few hundred parsecs in the Galactic disk or a massive stellar remnant (black hole or neutron star) in the Galactic bulge. Our new analysis includes data from the MACHO, GMAN, and MPS collaborations in addition to the OGLE data used in a previous analysis by Mao et al (2002). The crucial feature that distinguishes our analysis from that of Mao et al is an accurate constraint on the direction of lens motion and an analysis of the implications of this direction.
07/2002;
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D. P. Bennett,
A. C. Becker,
J. L. Quinn,
A. B. Tomaney,
C. Alcock,
R. A. Allsman,
D. R. Alves,
T. S. Axelrod,
J. J. Calitz,
K. H. Cook, [......],
C. A. Nelson,
B. A. Peterson,
P. Popowski,
M. R. Pratt,
P J Quinn, S. H. Rhie,
C. W. Stubbs,
W. Sutherland,
T. Vandehei,
D. Welch
[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the longest timescale microlensing events discovered by the MACHO Collaboration during a 7 year survey of the Galactic bulge. We find 6 events that exhibit very strong microlensing parallax signals due, in part, to accurate photometric data from the GMAN and MPS collaborations. The microlensing parallax fit parameters are used in a likelihood analysis, which is able to estimate the distance and masses of the lens objects based upon a standard model of the Galactic velocity distribution. This analysis indicates that the most likely masses of 5 of the 6 lenses are > 1 Msun, which suggests that a substantial fraction of the Galactic lenses may be massive stellar remnants. This could explain the observed excess of long timescale microlensing events. The lenses for events MACHO-96-BLG-5 and MACHO-98-BLG-6 are the most massive, with mass estimates of M/Msun = 6 +10/-3 and M/Msun = 6 +7/-3, respectively. The observed upper limits on the absolute brightness of main sequence stars for these lenses are < 1 Lsun, so both lenses are black hole candidates. The black hole interpretation is also favored by a likelihood analysis with a Bayesian prior using a conventional model for the lens mass function. We consider the possibility that the source stars for some of these 6 events may lie in the foreground or background of the Galactic bulge, but we find that this is unlikely. Future HST observations of these events can either confirm the black hole lens hypothesis or detect the lens stars and provide a direct measurement of their masses. Future observations of similar events by SIM or the Keck or VLTI interferometers will allow direct measurements of the lens masses for stellar remnant lenses as well. Comment: 47 pages, with 26 included postscript figures. Includes a new likelihood analysis with a mass function prior
The Astrophysical Journal 09/2001; 579(2):679. · 6.02 Impact Factor
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D. P. Bennett,
M. Clampin,
K. H. Cook,
A. Drake,
A. Gould,
K. Horne,
S. Horner,
D. Jewitt,
G. Langston,
T. Lauer,
A. Lumsdaine,
D. Minniti,
S. Peale, S. H. Rhie,
M. Shao,
R. Stevenson,
D. Tenerelli,
D. Tytler,
N. Woolf
[show abstract]
[hide abstract]
ABSTRACT: GEST is a comprehensive extra-solar planet search mission sensitive to
planets with masses as low as that of Mars. GEST will monitor the
Galactic bulge for 8 months per year for three years to detect planets
via gravitational microlensing and transits. GEST's microlensing survey
will detect low-mass planets at separations of > 0.6 AU via high
signal-to-noise variations of gravitational microlensing light curves.
These planetary signals do not require follow-up observations to confirm
the planetary interpretation, and they yield direct measurements of the
star:planet mass ratio. GEST will be able to detect 100 Earth-mass
planets at 1 AU (assuming 1 such planet per star) and will detect its
first Earth-mass planets within a few months of launch. The GEST
microlensing survey is the only proposed planet search program sensitive
to old, free-floating planets. GEST's transit survey will search ~
108 Galactic bulge stars for giant planets at separations of
< 30 AU, and it is anticipated that more than 50,000 new giant
planets will be discovered. When the Galactic bulge is not visible, GEST
will survey ~ 1200 square degrees for Kuiper Belt Objects (KBOs) and
operate a Participating Scienctist Program (PSP) with observational
programs selected via competitive proposals. The KBO survey should
discover 100,000 new KBOs.
11/2000; 32:1417.
-
K. H. Cook,
D. P. Bennett,
M. Clampin,
A. J. Drake,
A. Gould,
K. Horne,
S. D. Horner,
D. C. Jewitt,
G. I. Langston,
T. R. Lauer,
A. Lumsdaine,
D. Minniti,
S. J. Peale, S. H. Rhie,
M. Shao,
R. L. Stevenson,
D. Tenerelli,
D. Tytler,
N. J. Woolf
[show abstract]
[hide abstract]
ABSTRACT: A secondary science goal of the proposed Galactic Exoplanet Survey
Telescope (GEST) is to discover ~ 100,000 new Kuiper Belt Objects
(KBOs). Using a fraction of each season when GEST's primary target, the
Galactic bulge, is not visible, GEST will survey ~ 1200 square degrees
of sky near the ecliptic plane down to a limiting red magnitude of R ~
26.5. GEST's KBO survey will be repeated at specific weekly, monthly,
and yearly intervals to permit orbit determination. GEST will also do a
deep KBO survey which aims to detect KBOs as faint as 29th magnitude in
a single 1 square degree field. The number of KBOs that GEST will
discover excedes the number of known KBOs by a factor of ~ 300 and the
number of KBOs expected from other proposed telescopes by a factor of
10. This will enable the measurement of the number of KBOs in the more
distant mean motion resonances, the measurement of the radial extent of
the Kuiper Belt, and the measurement of the relative abundances of the
classical, resonant and scattered KBO populations.
09/2000; 32:1031.
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C. Afonso,
C. Alard,
J. N. Albert,
J. Andersen,
R. Ansari,
É. Aubourg,
P. Bareyre,
F. Bauer,
J. P. Beaulieu,
A. Bouquet, [......],
R. Martin,
J. Menzies,
R. M. Naber,
R. W. Pogge,
K. R. Pollard,
P. D. Sackett,
K. C. Sahu,
P. Vermaak,
R. Watson,
A. Williams
[show abstract]
[hide abstract]
ABSTRACT: We fit the data for the binary lens microlensing event MACHO 98-SMC-1 from five different microlensing collaborations and find two distinct solutions characterized by binary separation d and mass ratio q: (d,q) = (0.54,0.50) and (d,q) = (3.65,0.36), where d is in units of the Einstein radius. However, the relative proper motion of the lens is very similar in the two solutions, 1.30 km s-1 kpc-1 and 1.48 km s-1 kpc-1, thus confirming that the lens is in the Small Magellanic Cloud. The close binary can be either rotating or approximately static but the wide binary must be rotating at close to its maximum allowed rate to be consistent with all the data. We measure limb-darkening coefficients for five bands ranging from I to V. As expected, these progressively decrease with rising wavelength. This is the first measurement of limb darkening for a metal-poor A star.
The Astrophysical Journal 01/2000; 532(1):340. · 6.02 Impact Factor
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D. P. Bennett,
C. Alcock,
R. A. Allsman,
D. Alves,
T. S. Axelrod,
D. Becker,
K. H. Cook,
A. Crouch,
A. D. Drake,
P. C. Fragile, [......],
J. L. Quinn,
P. J. Quinn, S. H. Rhie,
P. Stetson,
C. W. Stubbs,
W. Sutherland,
S. Thomson,
A. B. Tomaney,
T. Vandehei,
D. Welch
[show abstract]
[hide abstract]
ABSTRACT: We present the analysis of microlensing parallax events discovered by
the MACHO/GMAN and Microlensing Planet Search (MPS) Collaborations. We
find two events towards the Galactic bulge which are likely to be caused
by black hole lenses: MACHO-96-BLG-5 and MACHO-98-BLG-6. The
microlensing parallax constraint on the lens masses and the observed
upper limit on the lens brightness imply that these lenses are likely to
be black holes. If so, they would be the first isolated black holes in
the stellar mass range yet discovered. Our microlensing parallax
analysis of Large Magellanic Could (LMC) microlensing events yields a
single event, MACHO-LMC-22 which appears to have a significant parallax
signal. The microlensing parallax analysis indicates that the lens does
not reside in the Milky Way's thin disk or in the vicinity of the LMC.
The parallax analysis suggests that the lens star must reside in the
Milky Way's thick disk or dark halo. This lends support to recent
suggestions that old, blue white dwarfs seen in the Hubble Deep Fields
might be responsible for the excess microlensing signal seen toward the
LMC. This work was funded by the NSF, the NASA Origins Program and the
DOE (through LLNL).
11/1999; 31:1422.
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J. L. Quinn,
C. Alcock,
R. A. Allsman,
D. Alves,
T. S. Axelrod,
D. Becker,
D. P. Bennett,
K. H. Cook,
A. D. Drake,
K. C. Freeman, [......],
C. A. Nelson,
B. A. Peterson,
P. Popowski,
P. J. Quinn, S. H. Rhie,
C. W. Stubbs,
W. Sutherland,
A. B. Tomaney,
T. Vandehei,
D. Welch
[show abstract]
[hide abstract]
ABSTRACT: Microlensing event MACHO-96-BLG-5 is the longest microlensing event
observed to date, and it has a strong microlensing parallax signal which
allows an estimate of the distance and mass of the lens. The mass
estimate indicates that the that the lens is probably a black hole
stellar remnants, and if so, it would be the first isolated black hole
stellar remnant yet discovered. However, the lens mass estimate has a
systematic uncertainty due to the fact that the source star of
MACHO-96-BLG-5 is significantly blended with stars unresolved from
ground based images. Here, we present the analysis of HST WFPC2 images
of MACHO-96-BLG-5 which allows a probable identification of the lensed
source star and removes this systematic uncertainty in the lens mass
estimate. Since the blending of stellar images is common in microlensing
data, the technique presented here will be useful for removing similar
ambiguities from similar microlensing events. This work was funded by
the NSF through the Center for Particle Astrophysics and by the DOE
(through LLNL).
11/1999; 31:1423.
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D. P. Bennett, S. H. Rhie,
A. C. Becker,
N. Butler,
J. Dann,
S. Kaspi,
E. M. Leibowitz,
Y. Lipkin,
D. Maoz,
H. Mendelson,
B. A. Peterson,
J. Quinn,
O. Shemmer,
S. Thomson,
S. E. Turner
Nature 11/1999; 402(6757):57-59. · 36.28 Impact Factor
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D. P. Bennett, S. H. Rhie,
A. C. Becker,
N. Butler,
J. Dann,
S. Kaspi,
E. M. Leibowitz,
Y. Lipkin,
D. Maoz,
H. Mendelson,
B. A. Peterson,
J. Quinn,
O. Shemmer,
S. Thomson,
S. E. Turner
[show abstract]
[hide abstract]
ABSTRACT: The study of extra-solar planetary systems has emerged as a new discipline of observational astronomy in the past few years with the discovery of a number of extra-solar planets. The properties of most of these extra-solar planets were not anticipated by theoretical work on the formation of planetary systems. Here we report observations and light curve modeling of gravitational microlensing event MACHO-97-BLG-41, which indicates that the lens system consists of a planet orbiting a binary star system. According to this model, the mass ratio of the binary star system is 3.8:1 and the stars are most likely to be a late K dwarf and an M dwarf with a separation of about 1.8 AU. A planet of about 3 Jupiter masses orbits this system at a distance of about 7 AU. If our interpretation of this light curve is correct, it represents the first discovery of a planet orbiting a binary star system and the first detection of a Jovian planet via the gravitational microlensing technique. It suggests that giant planets may be common in short period binary star systems. Comment: 11 pages, with 1 color and 2 b/w Figures included (published version)
08/1999;
-
[show abstract]
[hide abstract]
ABSTRACT: We fit the data for the binary-lens microlensing event MACHO 98-SMC-1 from 5 different microlensing collaborations and find two distinct solutions characterized by binary separation d and mass ratio q: (d,q)=(0.54,0.50) and (d,q)=(3.65,0.36), where d is in units of the Einstein radius. However, the relative proper motion of the lens is very similar in the two solutions, 1.30 km/s/kpc and 1.48 km/s/kpc, thus confirming that the lens is in the Small Magellanic Cloud. The close binary can be either rotating or approximately static but the wide binary must be rotating at close its maximum allowed rate to be consistent with all the data. We measure limb-darkening coefficients for five bands ranging from I to V. As expected, these progressively decrease with rising wavelength. This is the first measurement of limb darkening for a metal-poor A star. Comment: 29 pages + 9 figures + 2 tables, submitted to ApJ
07/1999;
-
S. H. Rhie,
D. P. Bennett,
A. C. Becker,
B. A. Peterson,
P. C. Fragile,
B. R. Johnson,
J. L. Quinn,
A. Crouch,
J Gray,
L King, [......],
To. Saito,
H Sato,
S Sato,
M Sekiguchi,
D. J. Sullivan,
T Sumi,
Y. Watase,
T Yanagisawa,
P. C. M. Yock,
M Yoshizawa
[show abstract]
[hide abstract]
ABSTRACT: We present observations of microlensing event MACHO-98-BLG-35 which reached a peak magnification factor of almost 80. These observations by the Microlensing Planet Search (MPS) and the 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 $4\times 10^{-5} \leq \epsilon \leq 2\times 10^{-4}$. A giant planet with $\epsilon = 10^{-3}$ is excluded from 95% of the region between 0.4 and 2.5 $R_E$ from the lens star, where $R_E$ is the Einstein ring radius of the lens. This exclusion region is more extensive than the generic "lensing zone" which is $0.6 - 1.6 R_E$. For smaller mass planets, we can exclude 57% of the "lensing zone" for $\epsilon = 10^{-4}$ and 14% of the lensing zone for $\epsilon = 10^{-5}$. The mass fraction $\epsilon = 10^{-5}$ corresponds to an Earth mass planet for a lensing star of mass $\sim 0.3 \msun$. 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 $4.5\sigma$ 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. Comment: ApJ, April 1, 2000; 27 pages including 8 color postscript figures
05/1999;
-
[show abstract]
[hide abstract]
ABSTRACT: We present the observations of the binary lensing event MACHO-98-SMC-1 conducted at the Mt.~Stromlo 74" telescope by the Microlensing Planet Search (MPS) collaboration. The MPS data constrain the first caustic crossing to have occurred after 1998 June 5.55 UT and thus directly rule out one of the two fits presented by the PLANET collaboration (model II). This substantially reduces the uncertainty in the the relative proper motion estimations of the lens object. We perform joint binary microlensing fits of the MPS data together with the publicly available data from the EROS, MACHO/GMAN and OGLE collaborations. We also study the binary lens fit parameters previously published by the PLANET and MACHO/GMAN collaborations by using them as initial values for $\chi^2$ minimization. Fits based on the PLANET model I appear to be in conflict with the GMAN-CTIO data. From our best fit, we find that the lens system has a proper motion of $\mu = 1.3\pm 0.2 \kmsk$ with respect to the source, which implies that the lens system is most likely to be located in the Small Magellanic Cloud strengthening the conclusion of previous reports. Comment: 20 pages, 4 color figures
12/1998;
-
S. H. Rhie,
D. P. Bennett,
P. C. Fragile,
L. J. King,
J. Quinn,
A. C. Becker,
B. R. Johnson,
B. A. Peterson,
F. Abe,
K. Masuda, [......],
B. Watase,
B. S. Koribalski,
T. Nakamura,
H. Sato,
N. J. Rattenbury,
P. C. M. Yock,
M. Reid,
D. J. Sullivan,
T. Saito,
M. Yoshizawa
[show abstract]
[hide abstract]
ABSTRACT: The Microlensing Planet Search (MPS) project monitors microlensing
events discovered in progress in search of microlensing planets orbiting
faint stars toward the Galactic Bulge. We report on observations by the
MPS and MOA Collaborations of high magnification microlensing event
MACHO-98-BLG-35 which has a low amplitude deviation which is consistent
with the expected deviation caused by a planet with a mass of 2 x 10(-5)
of the mass of the primary lens. We indicate how, for future events,
additional observations might provide data sufficient to claim discovery
of a low mass planet, and we also discuss the future explansion of the
MPS Project.
11/1998; 30:1415.
-
A. C. Becker,
C. Alcock,
R. A. Allsman,
D. R. Alves,
T. S. Axelrod,
D. P. Bennett,
K. H. Cook,
A. J. Drake,
K. C. Freeman,
K. Griest, [......],
G. Wyper,
A. Heller,
S. Kaspi,
O. Kovo,
D. Maoz,
A. Retter, S. H. Rhie,
P. Stetson,
A. Walker,
MACHO Collaboration
[show abstract]
[hide abstract]
ABSTRACT: We present the lightcurves of 22 gravitational microlensing events from
the first six years of the MACHO Project gravitational microlensing
survey which are likely examples of lensing by binary systems. These
events were selected from a total sample of ~ 300 events which were
either detected by the MACHO Alert System or discovered through
retrospective analyses of the MACHO database. Many of these events
appear to have undergone a caustic or cusp crossing, and 2 of the events
are well fit with lensing by binary systems with large mass ratios,
indicating secondary companions of approximately planetary mass. The
event rate is roughly consistent with predictions based upon our
knowledge of the properties of binary stars. The utility of binary
lensing in helping to solve the Galactic dark matter problem is
demonstrated with analyses of 3 binary microlensing events seen towards
the Magellanic Clouds. Source star resolution during caustic crossings
in 2 of these events allows us to estimate the location of the lensing
systems, assuming each source is a single star and not a short period
binary. * MACHO LMC-9 appears to be a binary lensing event with a
caustic crossing partially resolved in 2 observations. The resulting
lens proper motion appears too small for a single source and LMC disk
lens. However, it is considerably less likely to be a single source star
and Galactic halo lens. We estimate the a priori probability of a short
period binary source with a detectable binary character to be ~ 10 %. If
the source is also a binary, then we currently have no constraints on
the lens location. * The most recent of these events, MACHO 98-SMC-1,
was detected in real-time. Follow-up observations by the MACHO/GMAN,
PLANET, MPS, EROS and OGLE microlensing collaborations lead to the
robust conclusion that the lens likely resides in the SMC.
11/1998; 30:1415.
-
The MACHO Collaboration: D. P. Bennett,
C. Alcock,
R. A. Allsman,
D. Alves,
T. S. Axelrod,
A. Becker,
K. H. Cook,
K. C. Freeman,
K. Griest,
M. J. Lehner, [......],
D. Minniti,
B. A. Peterson,
M. R. Pratt,
P J Quinn, S. H. Rhie,
A. W. Rodgers,
C. W. Stubbs,
W. Sutherland,
T. Vandehei,
D. Welch
[show abstract]
[hide abstract]
ABSTRACT: We present the lightcurves of two microlensing events from the MACHO Project data that are likely to be due to lenses with masses similar to Jupiter's mass. Although the MACHO Project survey data are not sufficient to definitively establish the identification of planetary mass lenses in these cases, observations by microlensing follow-up networks such as GMAN and PLANET should be able to definitively determine the planetary nature of similar events which may occur in the near future.
01/1997;
