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

Batista, V.; Dong, S.; Gould, A.; Beaulieu, J. P.; Cassan, A.; Christie, G. W.; Han, C.; Udalski, A.; Allen, W.; DePoy, D. L.; Gal-Yam, A.; Gaudi, B. S.; Johnson, B.; Kaspi, S.; Lee, C. U.; Maoz, D.; McCormick, J.; McGreer, I.; Monard, B.; Natusch, T.; Ofek, E.; Park, B.-G.; Pogge, R. W.; Polishook, D.; Shporer, A.; Albrow, M. D.; Bennett, D. P.; Brillant, S.; Bode, M.; Bramich, D. M.; Burgdorf, M.; Caldwell, J. A. R.; Calitz, H.; Cole, A.; Cook, K. H.; Coutures, Ch.; Dieters, S.; Dominik, M.; Prester, D. D.; Donatowicz, J.; Fouqué, P.; Greenhill, J.; Hoffman, M.; Horne, K.; Jørgensen, U. G.; Kains, N.; Kane, S.; Kubas, D.; Marquette, J. B.; Martin, R.; Meintjes, P.; Menzies, J.; Pollard, K. R.; Sahu, K. C.; Snodgrass, Colin; Steele, I.; Tsapras, Y.; Wambsganss, J.; Williams, A.; Zub, M.; Wyrzykowski, Ł.; Kubiak, M.; Szymański, M. K.; Pietrzyński, G.; Soszyński, I.; Szewczyk, O.; Ulaczyk, K.; Abe, F.; Bond, I. A.; Fukui, A.; Furusawa, K.; Hearnshaw, J. B.; Holderness, S.; Itow, Y.; Kamiya, K.; Kilmartin, P. M.; Korpela, A.; Lin, W.; Ling, C. H.; Masuda, K.; Matsubara, Y.; Miyake, N.; Muraki, Y.; Nagaya, M.; Ohnishi, K.; Okumura, T.; Perrott, Y. C.; Rattenbury, N.; Saito, T.; Sako, T.; Skuljan, L.; Sullivan, D.; Sumi, T.; Sweatman, W. L.; Tristram, P. J. and Yock, P. C. M. (2009). Mass measurement of a single unseen star and planetary detection efficiency for OGLE 2007-BLG-050. Astronomy & Astrophysics, 508(1) pp. 467–478.



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 θE = 0.48 ± 0.01 mas and the parallax πE = 0.12 ± 0.03, leading to an estimate of the lens mass M = 0.50 ± 0.14 Mʘ and its distance to the observer DL=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, mp), where r is the projected planet-star separation and mp 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 ΔΧ2 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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