Browsing by Author "Blackman JW"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Adaptive Optics Imaging Can Break the Central Caustic Cusp Approach Degeneracy in High-magnification Microlensing Events
    (IOP Publishing on behalf of the American Astronomical Society, 2022-11-01) Terry SK; Bennett DP; Bhattacharya A; Koshimoto N; Beaulieu J-P; Blackman JW; Bond IA; Cole AA; Lu JR; Marquette JB; Ranc C; Rektsini N; Vandorou A
    We report new results for the gravitational microlensing target OGLE-2011-BLG-0950 from adaptive optics images using the Keck Observatory. The original analysis by Choi et al. and reanalysis by Suzuki et al. report degenerate solutions between planetary and stellar binary lens systems. This particular case is the most important type of degeneracy for exoplanet demographics because the distinction between a planetary mass or stellar binary companion has direct consequences for microlensing exoplanet statistics. The 8 and 10 yr baselines allow us to directly measure a relative proper motion of 4.20 ± 0.21 mas yr−1, confirming the detection of the lens star system and ruling out the planetary companion models that predict a ∼4× smaller relative proper motion. The Keck data also rule out the wide stellar binary solution unless one of the components is a stellar remnant. The combination of the lens brightness and close stellar binary light-curve parameters yields primary and secondary star masses of M A = 1.12 − 0.09 + 0.11 and M B = 0.47 − 0.10 + 0.13 M ☉ at a distance of D L = 6.70 − 0.30 + 0.55 kpc and a projected separation of 0.39 − 0.04 + 0.05 au. Assuming that the predicted proper motions are measurably different, the high-resolution imaging method described here can be used to disentangle this degeneracy for events observed by the Roman exoplanet microlensing survey using Roman images taken near the beginning or end of the survey.
  • Thumbnail Image
    Item
    Confirmation of Color-dependent Centroid Shift Measured After 1.8 Years with HST
    (American Astronomical Society, 2023-04-19) Bhattacharya A; Bennett DP; Beaulieu JP; Bond IA; Koshimoto N; Lu JR; Blackman JW; Ranc C; Vandorou A; Terry SK; Marquette JB; Cole AA; Fukui A
    We measured the precise masses of the host and planet in the OGLE-2003-BLG-235 system, when the lens and source were resolving, with 2018 Keck high resolution images. This measurement is in agreement with the observation taken in 2005 with the Hubble Space Telescope (HST). In the 2005 data, the lens and sources were not resolved and the measurement was made using color-dependent centroid shift only. The Nancy Grace Roman Space Telescope will measure masses using data typically taken within 3-4 yr of the peak of the event, which is a much shorter baseline when compared to most of the mass measurements to date. Hence, the color-dependent centroid shift will be one of the primary methods of mass measurements for the Roman telescope. Yet, mass measurements of only two events (OGLE-2003-BLG-235 and OGLE-2005-BLG-071) have been done using the color-dependent centroid shift method so far. The accuracy of the measurements using this method are neither completely known nor well studied. The agreement of the Keck and HST results, as shown in this paper, is very important because this agreement confirms the accuracy of the mass measurements determined at a small lens-source separation using the color-dependent centroid shift method. It also shows that with >100 high resolution images, the Roman telescope will be able to use color-dependent centroid shift at a 3-4 yr time baseline and produce mass measurements. We find that OGLE-2003-BLG-235 is a planetary system that consists of a 2.34 ± 0.43M Jup planet orbiting a 0.56 ± 0.06M ⊙ K-dwarf host star at a distance of 5.26 ± 0.71 kpc from the Sun.
  • Thumbnail Image
    Item
    Unveiling MOA-2007-BLG-192: An M Dwarf Hosting a Likely Super-Earth
    (American Astronomical Society, 2024-07-15) Terry SK; Beaulieu J-P; Bennett DP; Hamdorf E; Bhattacharya A; Chaudhry V; Cole AA; Koshimoto N; Anderson J; Bachelet E; Blackman JW; Bond IA; Lu JR; Marquette JB; Ranc C; Rektsini NE; Sahu K; Vandorou A
    We present an analysis of high-angular-resolution images of the microlensing target MOA-2007-BLG-192 using Keck adaptive optics and the Hubble Space Telescope. The planetary host star is robustly detected as it separates from the background source star in nearly all of the Keck and Hubble data. The amplitude and direction of the lens-source separation allows us to break a degeneracy related to the microlensing parallax and source radius crossing time. Thus, we are able to reduce the number of possible binary-lens solutions by a factor of ∼2, demonstrating the power of high-angular-resolution follow-up imaging for events with sparse light-curve coverage. Following Bennett et al., we apply constraints from the high-resolution imaging on the light-curve modeling to find host star and planet masses of M host = 0.28 ± 0.04 M ☉ and m p = 12.49 − 8.03 + 65.47 M ⊕ at a distance from Earth of D L = 2.16 ± 0.30 kpc. This work illustrates the necessity for the Nancy Grace Roman Galactic Exoplanet Survey to use its own high-resolution imaging to inform light-curve modeling for microlensing planets that the mission discovers.