Browsing by Author "Cole AA"

Now showing 1 - 6 of 6
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    A Candidate High-velocity Exoplanet System in the Galactic Bulge
    (American Astronomical Society, Washington, 2025-03) Terry SK; Beaulieu J-P; Bennett DP; Bhattacharya A; Hulberg J; Huston MJ; Koshimoto N; Blackman JW; Bond IA; Cole AA; Lu JR; Ranc C; Rektsini NE; Vandorou A
    We present an analysis of adaptive optics images from the Keck I telescope of the microlensing event MOA-2011-BLG-262. The original discovery paper by Bennett et al. reports two possibilities for the lens system: a nearby gas giant lens with an exomoon companion or a very low-mass star with a planetary companion in the Galactic bulge. The ∼10 yr baseline between the microlensing event and the Keck follow-up observations allows us to detect the faint candidate lens host (star) at K = 22.3 mag and confirm the distant lens system interpretation. The combination of the host star brightness and light curve parameters yields host star and planet masses of Mhost = 0.19 ± 0.03 M⊙ and mp = 28.92 ± 4.75 M⊕ at a distance of DL = 7.49 ± 0.91 kpc. We perform a multiepoch cross reference to Gaia Data Release 3 and measure a transverse velocity for the candidate lens system of vL = 541.31 ± 65.75 km s−1. We conclude this event consists of the highest-velocity exoplanet system detected to date, and also the lowest-mass microlensing host star with a confirmed mass measurement. The high-velocity nature of the lens system can be definitively confirmed with an additional epoch of high-resolution imaging at any time now. The methods outlined in this work demonstrate that the Roman Galactic Exoplanet Survey will be able to securely measure low-mass host stars in the bulge.
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    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.
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    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.
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    OGLE-2014-BLG-1760: A Jupiter-Sun Analogue Residing in the Galactic Bulge
    (IOP Publishing on behalf of The American Astronomical Society, 2025-09-01) Rektsini NE; Ranc C; Koshimoto N; Beaulieu J-P; Bennett DP; Cole AA; Terry SK; Bhattacharya A; Bachelet É; Bond IA; Udalski A; Blackman JW; Vandorou A; Plunkett TJ; Marquette J-B
    We present the analysis of OGLE-2014-BLG-1760, a planetary system in the galactic bulge. We combine Keck Adaptive Optics follow-up observations in K-band with re-reduced light-curve data to confirm the source and lens star identifications and stellar types. The re-reduced Microlensing Observations in Astrophysics data set had an important impact on the light-curve model. We find the Einstein ring crossing time of the event to be ∼2.5 days shorter than previous fits, which increases the planetary mass-ratio and decreases the source angular size by a factor of 0.25. Our OSIRIS images obtained 6 yr after the peak of the event show a source-lens separation of 54.20 ± 0.23 mas, which leads to a relative proper motion of μrel = 9.14 ± 0.05 mas yr−1 and is larger than the previous light-curve-only models. Our analysis shows that the event consists of a Jupiter-mass planet of Mp = 0.931 ± 0.117 MJup orbiting a K-dwarf star of M* = 0.803 ± 0.097 M⊙ with a K-magnitude of KL = 18.30 ± 0.05, located in the galactic bulge or bar. We also attempt to constrain the source properties using the source angular size θ* and K-magnitude. Our results favor the scenario of the source being a younger star in the galactic disk, behind the galactic bulge, but future multicolor observations are needed to constrain the source and thus the lens properties.
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    OGLE-2016-BLG-1195Lb: A Sub-Neptune Beyond the Snow Line of an M-dwarf Confirmed by Keck Adaptive Optics
    (IOP Publishing, 2025-05-20) Vandorou A; Dang L; Bennett DP; Koshimoto N; Terry SK; Udalski A; Beaulieu J-P; Alard C; Bhattacharya A; Blackman JW; Bond IA; Bouchoutrouch-Ku T; Cole AA; Cowan NB; Marquette J-B; Ranc C; Rektsini NE; Cetre S; Lyke J; Marin E; Wizinowich P
    We present the analysis of high-resolution follow-up observations of OGLE-2016-BLG-1195 using Laser Guide Star Adaptive Optics with Keck, seven years after the event’s peak. We resolve the lens, measuring its flux and the relative source-lens proper motion, thus finding the system to be a Mp = 10.08 ± 1.18M planet orbiting an M-dwarf, ML = 0.62 ± 0.05Me, beyond the snow line, with a projected separation of r = 2.24 ± 0.21 au at DL = 7.45 ± 0.55 kpc. Our results are consistent with the discovery paper, which reports values with 1σ uncertainties based on a single mass–distance constraint from finite source effects. However, both the discovery paper and our follow-up results disagree with the analysis of a different group that also present the planetary signal detection. The latter utilizes Spitzer photometry to measure a parallax signal claiming the system is an Earth-mass planet orbiting an ultracool dwarf. Their parallax signal though is improbable since it suggests a lens star in the disk moving perpendicular to or counter to the Galactic disk rotation. Moreover, microlensing parallaxes can be impacted by systematic errors in the photometry. Therefore, we reanalyze the Spitzer photometry using a pixel level decorrelation model to detrend detector systematics. We find that we cannot confidently recover the same detrended light curve that is likely dominated by systematic errors in the photometric data. The results of this paper act as a cautionary tale that a careful understanding of detector systematics and how they influence astrophysical constraints is crucial.
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    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.