TCP J05074264+2447555 / Kojima-1L - Nearby microlensing planet toward the galactic anti-centre

Nucita et al. (2017) "TCP J05074264+2447555 as a bright microlensing event due to a binary system with very low mass ratio component: hint for a new planetary system?"
http://www.astronomerstelegram.org/?read=10934

Best fit model is for a binary with mass ratio 5×10^-5, which suggests the secondary is a planet with a few times the mass of the Earth.

Lazarus wrote:

Nucita et al. (2017) "TCP J05074264+2447555 as a bright microlensing event due to a binary system with very low mass ratio component: hint for a new planetary system?"
http://www.astronomerstelegram.org/?read=10934

Best fit model is for a binary with mass ratio 5×10^-5, which suggests the secondary is a planet with a few times the mass of the Earth.

Follow-up, now with the added designation Kojima-1 for the event, which is somewhat more manageable...

Fukui et al. "Kojima-1Lb is a Mildly Cold Neptune around the Brightest Microlensing Host Star"
https://arxiv.org/abs/1909.11802

Lens is a K/M boundary star at ~500 pc with a Neptune at 1 AU.

Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event
https://arxiv.org/abs/1912.00038

Quote :

We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555. We measure the microlens parallax vector πE using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this πE determination with the angular Einstein radius θE measured by VLTI GRAVITY observations, we find that the lens is a star with mass ML=0.495±0.063 M⊙ at a distance DL=429±21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is μrel,hel=26.55±0.36 masyr−1, so with currently available adaptive-optics (AO) instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.

Since this system is apparently getting much more attention than other microlensing systems, I've split it into its own thread.