The Extreme Microlensing Event OGLE-2007-BLG-224: Terrestrial Parallax Observation of a Thick-Disk Brown Dwarf

Parallax is the most fundamental technique to measure distances to astronomical objects. Although terrestrial parallax was pioneered over 2000 years ago by Hipparchus (ca. 140 BCE) to measure the distance to the Moon, the baseline of the Earth is so small that terrestrial parallax can generally only be applied to objects in the Solar System. However, there exists a class of extreme gravitational microlensing events in which the effects of terrestrial parallax can be readily detected and so permit the measurement of the distance, mass, and transverse velocity of the lens. Here we report observations of the first such extreme microlensing event OGLE-2007-BLG-224, from which we infer that the lens is a brown dwarf of mass M=0.056 +- 0.004 Msun, with a distance of 525 +- 40 pc and a transverse velocity of 113 +- 21 km/s. The velocity places the lens in the thick disk, making this the lowest-mass thick-disk brown dwarf detected so far. Follow-up observations may allow one to observe the light from the brown dwarf itself, thus serving as an important constraint for evolutionary models of these objects and potentially opening a new window on sub-stellar objects. The low a priori probability of detecting a thick-disk brown dwarf in this event, when combined with additional evidence from other observations, suggests that old substellar objects may be more common than previously assumed.Comment: ApJ Letters, in press, 15 pages including 2 figure

Vranologion, sive, Systema variorvm avthorvm, qvi de sphæra, ac sideribvs, eorvmqve motibvs græcè commentati sunt. ... Omnia vel græcè ac latinè nunc primùm edita, vel antè non edita. Cura & studio Dionysii Petavii ... Acesserunt Variarum dissertationum libri octo, ad authores illos intelligendos imprimis vtiles, eodem authore.

The Greek texts except two have Latin translations in parallel columns.Title vignette.S. Andreæ Computus. Interprete Dionysio Petauio.--Fragmentum Græcum de Paschate.--Notæ Dionysij Petauij ad Geminum, Ptolemæum, & Hipparchum.--Fragmentum Aetij De significationibus stellarum. Interprete Cornario.--Index rerum memorabilium.--Subiecti sunt Variarum dissertationum libri VIII, authore Dionysio Petauio. 1. Astronomy, Greek. 2. Chronology. I. Achilles Tatius. II. Aetius of Florida. III. Andreas, Saint, archbishop of Crete. IV. Argyros, Isaac, ca. 1312-ca. 1373. v. Gaza, Theodorus, 1398-1478. VI. Geminus VII. Herwart von Hohenburg, Johann Georg, 1553-1622. X. Ptolemaeus, Claudius. XI. Cornarius, Janus, 1500-1558, tr. XII. Hildericus von Varel, Edo, 1533-1599, tr. XIII. Leoniceno, Nicola, 1428-1524, tr. XIV. Perrelle, Jean, fl. 1535, tr.Gemini Isagoge. Interprete Edone Hilderico.--Ptolemæus De apparentiis inerrantium. Interprete Dionysio Petauio.--Ptolemæi Inerrantium significationes. Latinè per Nicolaum Leonicū.--Calendarium vetus romanum cum ortu occasúque stellarum ex Ouidio, Columella, Plinio. A Dionysio Petauio coniectum.--Calendarium romanum ab Ioanne Georgio Hervuart editum.--Achillis Tatij Isagoge ad Arati Phænomena. Interprete Dionysio Petauio.--Eiusdem Tatij Fragmenta Græca.--Hipparchi Bithyni ad Arati, & Eudoxi Phænomena libri tres. Interprete Dionysio Petauio.--Achillis Tatij ad Arati Phænomena, qui liber falsò Eratostheni tribuitur. Interprete Dionysio Petauio.--Arati genus, & vita. Interprete Dionysio Petauio.--Theodorus Gaza De mensibus. Interprete Ioanne Perrello.--S. Maximi Computus. Interprete Dionysio Petauio.--Isaaci Argyri Computus. Interprete Dionysio Petauio.--Eiusdem Computus alter. Interprete Dionysio Petauio.--Mode of access: Internet

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COSMAS Indicopleustes. Excerpta de TaprobaneEPIPHANIUS (S.), Cypri episcopus. PhysiologusGEORGIUS Chœroboscus. ExcerptaGEORGIUS Gemistus Pletho. Descriptio orbis terrarum, e StraboneHERMES Trismegistus. Iatromathematica, seu canon de decubitu infirmorumHERODIANUS. De inclinatis, encliticis et syncliticis particulisHERODIANUS. Excerpta et fragmentaHIPPARCHUS. De XII zodiaci signisPETOSIRIS. Organum de vita et mortePETOSIRIS. Excerpta de rebus medico-astrologicisPROTAGORAS. Excerpta ex iatromathematicis Mercurii et Petosiridis, etc. astrologicaPYTHAGORAS. Prognostica supputatioPYTHAGORAS. Excerpta ex iatromathematicis Mercurii et Petosiridis, etc. astrologicaTHEODOSIUS, Alexandrinus grammaticus. Excerpta grammatica et metricaNumérisation effectuée à partir d'un document de substitution.(1) Cycli lunaris et solaris, selenodromium, etc. astronomica ; — (6 v°) Petosiridis organum de vita et morte ; — (9 v°) Hipparchi opusculum de XII. zodiaci signis ; — (12 v°) Anonymi methodus futura divinandi : Ἐὰν τίς σε τούτου... ; — (15) Brontologium ; — (16) Pythagoræ prognostica supputatio ; — (16 v°) Protagoræ [Pythagoræ] excerpta ex iatromathematicis Mercurii et Petosiridis, etc. astrologica ; — (24) Georgii Gemisti Plethonis excerpta ex Strabone ; — (40) Theodosii et Herodiani, vel Heliodori [Georgii Chœrobosci], excerpta grammatica et metrica ; — (90) S. Epiphanii Cypri physiologus ; — (114 v°) [Cosmæ Indicopleustæ] excerpta de TaprobaneHurault.-Reg. 2733