Direct detection of a microlens in the Milky Way

Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Drake, A. J.; Freeman, K. C.; Geha, Marla; Griest, K.; Keller, Stefan; Lehner, M. J.; Marshall, S.; Minniti, D.; Nelson, C A; Peterson, Bruce A.; Popowski, Piotr; Pratt, M. R.; Quinn, Peter J.; Stubbs, C. W.; Sutherland, William J.; Tomaney, A.; Vandehei, T.; Welch, D. L.

doi:10.1038/414617a

Cited by 136 publications

(187 citation statements)

References 11 publications

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“…In particular, MACHO-LMC 1, 5, 9, 14 and 21 are strong candidates based only on MACHO photometry while Bennett et al (2005) argued that MACHO-LMC-4, 13 and 15 are strong candidates because of high precision followup photometry. We might note, however, that of these candidates, MACHO-LMC-14 is most likely due to LMC self-lensing and MACHO-LMC-5 is due to lensing by a normal red-dwarf star in the disk of the Milky Way (Alcock et al 2001d;Gould 2004).…”

Section: Discussion Of the Resultsmentioning

confidence: 99%

Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Tisserand

Guillou

Afonso

et al. 2007

A&A

920

908

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Aims. The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called "machos") could be a major component of the dark matter halo of the Milky Way galaxy. To this end, EROS-2 monitored over 6.7 years 33 × 10 6 stars in the Magellanic clouds for microlensing events caused by such objects. Methods. In this work, we use only a subsample of 7 × 10 6 bright stars spread over 84 deg 2 of the LMC and 9 deg 2 of the SMC. The strategy of using only bright stars helps to discriminate against background events due to variable stars and allows a simple determination of the effects of source confusion (blending). The use of a large solid angle makes the survey relatively insensitive to effects that could make the optical depth strongly direction dependent. Results. Using this sample of bright stars, only one candidate event was found, whereas ∼39 events would have been expected if the Halo were entirely populated by objects of mass M ∼ 0.4 M . Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud (LMC) due to such lenses is τ < 0.36 × 10 −7 (95% CL), corresponding to a fraction of the halo mass of less than 8%. This optical depth is considerably less than that measured by the MACHO collaboration in the central region of the LMC. More generally, machos in the mass range 0.6 × 10 −7 M < M < 15 M are ruled out as the primary occupants of the Milky Way Halo.

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Section: Discussion Of the Resultsmentioning

confidence: 99%

Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Tisserand

Guillou

Afonso

et al. 2007

A&A

920

908

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“…The fundamental parameters of a star are its mass, M, radius, R, and luminosity, L. A direct measurement of mass can be done for the components in detached eclipsing binary systems with an accuracy of about 1−2 per cent (Andersen 1991) or for single stars in the rare case of a microlensing event (Alcock et al 2001). The radius of single stars can be measured to about 1 per cent with interferometric methods or to about the same precision for eclipsing binary stars.…”

Section: Fundamental Parameters Of Starsmentioning

confidence: 99%

Accurate fundamental parameters of CoRoT asteroseismic targets

Bruntt

2009

A&A

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Context. The CoRoT satellite has provided high-quality light curves of several solar-like stars. Analysis of these light curves provides oscillation frequencies that make it possible to probe the interior of the stars. However, additional constraints on the fundamental parameters of the stars are important for the theoretical modelling to be successful. Aims. We estimate the fundamental parameters (mass, radius, and luminosity) of the first four solar-like targets to be observed in the asteroseismic field. In addition, we determine their effective temperature, metallicity, and detailed abundance patterns.Methods. To constrain the stellar mass, radius and age we used the shotgun software, which compares the location of the stars in the Hertzsprung-Russell diagram with theoretical evolution models. This method takes the uncertainties of the observed parameters into account, including the large separation determined from the solar-like oscillations. We determined the effective temperatures and abundance patterns in the stars from the analysis of high-resolution spectra obtained with the HARPS, NARVAL, ELODIE and FEROS spectrographs. Results. We determined the mass, radius, and luminosity of the four CoRoT targets to within 5−10%, 2−4% and 5−13%, respectively. The quality of the stellar spectra determines how well we can constrain the effective temperature. For the two best spectra we get 1-σ uncertainties below 60 K and 100−150 K for the other two. The uncertainty on the surface gravity is less than 0.08 dex for three stars, while it is 0.15 dex for HD 181906. The reason for the larger uncertainty is that the spectrum has two components with a luminosity ratio of L p /L s = 0.50 ± 0.15. While Hipparcos astrometric data strongly suggest it is a binary star, we find evidence that the fainter star may be a background star, since it is less luminous but hotter.

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“…However, reliable mass estimates for isolated stars have been determined with microlensing only twice. Alcock et al (2001) and Gould et al (2009) each measured both θ E and π E respectively for MACHO LMC-5 and OGLE 2007-BLG-224. For MACHO LMC-5, good measurements of π rel and μ rel were obtained with the original photometric data and additional high resolution photometry of the lens (HST observations).…”

Section: Mass and Distance Estimates Of The Lens Starmentioning

confidence: 99%

“…The microlens parallax π E has been measured for more than twenty single lenses (Alcock et al 1995 [the first parallax measurement], Poindexter et al 2005, and references therein), while the angular Einstein radius θ E has been measured for only few cases of single lenses (Alcock et al 1997(Alcock et al , 2001Smith et al 2003b;Yoo et al 2004a;Jiang et al 2004;Cassan et al 2006;Gould et al 2009). However, reliable mass estimates for isolated stars have been determined with microlensing only twice.…”

Section: Mass and Distance Estimates Of The Lens Starmentioning

confidence: 99%

Mass measurement of a single unseen star and planetary detection efficiency for OGLE 2007-BLG-050

Batista¹,

Dong²,

Gould³

et al. 2009

A&A

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Aims. We analyze OGLE-2007-BLG-050, a high magnification microlensing event (A ∼ 432) whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects. We compute planet detection efficiencies for this event in order to determine its sensitivity to the presence of planets around the lens star. Methods. Both finite-source and parallax effects permit a measurement of the angular Einstein radius θ E = 0.48 ± 0.01 mas and the parallax π E = 0.12 ± 0.03, leading to an estimate of the lens mass M = 0.50 ± 0.14 M and its distance to the observer D L = 5.5 ± 0.4 kpc. This is only the second determination of a reasonably precise (<30%) mass estimate for an isolated unseen object, using any method. This allows us to calculate the planetary detection efficiency in physical units (r ⊥ , m p ), where r ⊥ is the projected planet-star separation and m p is the planet mass. Results. When computing planet detection efficiency, we did not find any planetary signature, i.e. none of the planetary configurations provides a Δχ 2 improvement higher than 60, and our detection efficiency results reveal significant sensitivity to Neptune-mass planets, and to a lesser extent Earth-mass planets in some configurations. Indeed, Jupiter and Neptune-mass planets are excluded with a high confidence for a large projected separation range between the planet and the lens star, respectively [0.6-10] and [1.4-4] AU, and Earth-mass planets are excluded with a 10% confidence in the lensing zone, i.e. [1.8-3.1] AU.

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Direct detection of a microlens in the Milky Way

Cited by 136 publications

References 11 publications

Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Accurate fundamental parameters of CoRoT asteroseismic targets

Mass measurement of a single unseen star and planetary detection efficiency for OGLE 2007-BLG-050

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