Combined Analysis of the Binary Lens Caustic‐crossing Event MACHO 98‐SMC‐1

Afonso, C.; Alard, C.; Albert, J.; Andersen, J.; Ansari, R.; Aubourg, É.; Bareyre, P.; Bauer, F. F.; Beaulieu, J. P.; Bouquet, A.; Char, S.; Charlot, X.; Couchot, F.; Coutures, C.; Derue, F.; Ferlet, R.; Glicenstein, J. F.; Goldman, B.; Gould, Andrew; Graff, D.; Gros, M.; Haïssinski, J.; Hamilton, J. C.; Hardin, D.; Kat, J. de; Kim, A.; Lasserre, T.; Lesquoy, É.; Loup, C.; Magneville, C.; Marquette, J. B.; Maurice, É.; Milsztajn, A.; Moniez, M.; Palanque-Delabrouille, N.; Perdereau, O.; Prévôt, L.; Regnault, Nicolas; Rich, J.; Spiro, M.; Vidal‐Madjar, A.; Vigroux, L.; Zylberajch, S.; Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Cook, K. H.; Drake, A. J.; Freeman, K. C.; Griest, K.; King, Lindsay J.; Lehner, M. J.; Marshall, Stuart; Minniti, D.; Peterson, Bruce A.; Pratt, M. R.; Quinn, Peter J.; Rodgers, A. W.; Stetson, P. B.; Stubbs, C. W.; Sutherland, William J.; Tomaney, A.; Vandehei, T.; Rhie, Sun Hong; Bennett, D. P.; Fragile, P. Chris; Johnson, B. R.; Quinn, J.; Udalski, A.; Kubiak, M.; Szymański, M. K.; Pietrzyński, G.; Woźniak, P. R.; Zebrun, K.; Albrow, M. D.; Caldwell, J.; Depoy, D. L.; Dominik, M.; Gaudi, B. Scott; Greenhill, J.; Hill, K.; Kane, Stephen R.; Martín, Roland; Menzies, John; Naber, R. M.; Pogge, Richard W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.

doi:10.1086/308561

Cited by 103 publications

(125 citation statements)

References 9 publications

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“…1997(Alcock et h E al. , 2000Albrow et al 1999Albrow et al , 2000aAlbrow et al , 2000bAfonso et al 2000), all by using the source as an "" angular ruler ÏÏ (Gould 1994a ;Nemiro † & Wickramasinghe 1994 ;Witt & Mao 1994). Similarly, has been determined for only r8 E about a half-dozen events (Alcock et al 1995 ;Bennett et al 1997 ;Mao 1999).…”

Section: Geometrymentioning

confidence: 99%

A Natural Formalism for Microlensing

Gould¹

2000

ApJ

245

252

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If the standard microlensing geometry is inverted so that the Einstein ring is projected onto the observer plane rather than the source plane, then the relations between the observables and the under-(h E , r8 E ) lying physical quantities become immediately obvious. Here and are the angular and (M, n rel ) h E r8 E projected Einstein radii, M is the mass of the lens, and is the lens-source relative parallax. I recast n rel the basic formalism of microlensing in light of this more natural geometry and in terms of observables. I then Ðnd that the relations between observable and physical quantities assume an exceptionally simple form. In an appendix, I propose a set of notational conventions.

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Section: Geometrymentioning

confidence: 99%

A Natural Formalism for Microlensing

Gould¹

2000

ApJ

245

252

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“…Gravitational microlensing surveys (Liebes 1964;Paczyń ski 1986;Alcock et al 1993;Aubourg et al 1993; Udalski et al 1993;Bond et al 2001) have the potential to detect completely dark stellar remnants, but for most microlensing events, the mass can only be estimated very crudely based on the observed Einstein ring diameter crossing timet t. For an individual microlensing event, the mass can only be estimated so crudely that a 7 M black hole cannot be distinguished from a 0.5 M star. However, for some microlensing events, it is possible to measure other parameters besidest t that allow tighter constraints on the lens mass (Refsdal 1966;Gould 1992;Nemiroff & Wickramasinghe 1994;Alcock et al 1995Alcock et al , 1997cAlcock et al , 2001aBennett et al 1996;Han & Gould 1997;Afonso et al 2000). For longtimescale microlensing events, which are often due to massive lenses, it is frequently possible to measure the microlensing parallax effect (Refsdal 1966;Gould 1992;Alcock et al 1995), which is an observable deviation in the microlensing light curve due to the orbital motion of the Earth.…”

Section: Introductionmentioning

confidence: 99%

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Bennett

Becker

Quinn

et al. 2002

ApJ

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135

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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 six 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 distances and masses of the lens objects based on a standard model of the Galactic velocity distribution. This analysis indicates that the most likely masses of five of the six lenses are greater than 1 M , 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=M ¼ 6 þ10 À3 and M=M ¼ 6 þ7 À3 , respectively. The observed upper limits on the absolute brightness of main-sequence stars for these lenses are less than 1 L , 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 six events may lie in the foreground Galactic disk or in the Sagittarius (Sgr) dwarf galaxy behind the bulge, but we find that bulge sources are likely to dominate our microlensing parallax event sample. Future Hubble Space Telescope 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 the Space Interferometry Mission or the Keck or VLT interferometers, as explained by Delplancke, Gó rski, & Richichi, will allow direct measurements of the lens masses for stellar remnant lenses as well.

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“…Microlensing experiments like MACHO (Alcock et al (1997); Alcock et al (2000)), EROS (Afonso et al (2000); Lasserre et al (2000)) and OGLE (Udalski et al (1998)), found that the events detected towards the galactic bulge and the LMC were consistent with the lensing objects being small (in size) stars, with a mass of ∼ 0.6M , a very good match to a WD star. These faint objects could account for about 20 % to 30 % of the dark matter in the galactic halo, in this case the prime candidates are faint Halo WDs.…”

Section: Renewed Interest In Low-luminosity Starsmentioning

confidence: 95%

“…The search, in this case, was motivated by the results of the microlensing experiments (MACHO (Alcock et al (1997); Alcock et al (2000)), EROS (Afonso et al (2000); Lasserre et al (2000)) and OGLE (Udalski et al (1998)), that suggested that up to 30% of the Halo baryonic dark matter could be in the form of WDs. So far, the observed density of matter in halo WDs has only an upper limit of ρ halo w d < 4 × 10 −5 M pc −3 (Harris et al (2006)).…”

Section: Cool White Dwarfsmentioning

confidence: 99%

Do Low Luminosity Stars Matter?

Ruíz

2009

Proc. IAU

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Abstract. Historically, low luminosity stars have attracted very little attention, in part because they are difficult to see except with large telescopes, however, by neglecting to study them we are leaving out the vast majority of stars in the Universe. Low mass stars evolve very slowly, it takes them trillions of years to burn their hydrogen, after which, they just turn into a He white dwarf, without ever going through the red giant phase. This lack of observable evolution partly explains the lack of interest in them. The search for the "missing mass" in the galactic plane turned things around and during the 60s and 70s the search for large M/L objects placed M-dwarfs and cool WDs among objects of astrophysical interest. New fields of astronomical research, like BDs and exoplanets appeared as spin-offs from efforts to find the "missing mass". The search for halo white dwarfs, believed to be responsible for the observed microlensing events, is pursued by several groups. The progress in these last few years has been tremendous, here I present highlights some of the great successes in the field and point to some of the still unsolved issues.

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Combined Analysis of the Binary Lens Caustic‐crossing Event MACHO 98‐SMC‐1

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Cited by 103 publications

References 9 publications

A Natural Formalism for Microlensing

A Natural Formalism for Microlensing

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Do Low Luminosity Stars Matter?

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