J/ApJ/897/180 Multiband photometry of microlensing event Kojima-1 (Zang+, 2020) ================================================================================ Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event. Zang W., Dong S., Gould A., Calchi Novati S., Chen P., Yang H., Li S.-S., Mao S., Alton K.B., Brimacombe J., Carey S., Christie G.W., Delplancke-Strobele F., Feliz D.L., Gaudi B.S., Green J., Hu S., Jayasinghe T., Koff R.A., Kurtenkov A., Merand A., Minev M., Mutel R., Natusch T., Roth T., Shvartzvald Y., Sun F., Vanmunster T., Zhu W. =2020ApJ...897..180Z ================================================================================ ADC_Keywords: Gravitational lensing; Photometry, UBVRIJKLMNH Keywords: Gravitational microlensing ; Satellite microlensing parallax ; Stellar masses ; Stellar distance Abstract: We report the lens mass and distance measurements of the nearby microlensing event TCPJ05074264+2447555 (Kojima-1). We measure the microlens parallax vector {pi}_E_ 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 {pi}_E_ determination with the angular Einstein radius {theta}_E_ measured by VLTI-GRAVITY observations, we find that the lens is a star with mass M_L_=0.495{+/-}0.063M{odot} at a distance DL=429{+/-}21pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is {mu}_rel,hel_=26.55{+/-}0.36mas/yr, so with currently available adaptive-optics 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. Description: We use ground-based follow-up data to derive basic single-lens parameters and constrain microlens parallax. To minimize the impact on microlens parallax measurements from possible systematic errors, we choose the ground-based data that were carefully selected and used by Dong+, 2019ApJ...871...70D, including the data from All-Sky Automatic Survey for Supernovae (ASAS-SN), 0.6m telescopes at Post Observatory (RP), 0.5m Iowa Robotic Telescope (Iowa) at the Winer Observatory (Arizona, USA), 0.4m telescope at Auckland Observatory (AO), and the 1.3m SMARTS telescope at Cerro Tololo Inter-American Observatory (CTIO). For Spitzer, observations start on 2017 December 19 (HJD'=8107.2, HJD'=HJD-2450000). The observations ended on 2018 January 23 (HJD'=8143.7). In total, 21 data points were taken, all using the 3.6{mu}m channel (L-band) of the IRAC camera. Objects: ----------------------------------------------------------- RA (2000) DE Designation(s) ----------------------------------------------------------- 05 07 42.72 +24 47 56.4 Kojima-1 = TCP J05074264+2447555 ----------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file fig1.dat 51 5482 The light curves and data points of Kojima-1 -------------------------------------------------------------------------------- See also: I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018) I/345 : Gaia DR2 (Gaia Collaboration, 2018) II/366 : ASAS-SN catalog of variable stars (Jayasinghe+, 2018-2020) J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014) J/ApJ/814/92 : Spitzer IRAC events observed in crowded fields (Calchi+, 2015) J/MNRAS/458/3012 : OGLE-III Parallax microlensing events (Wyrzykowski+, 2016) J/AJ/154/210 : 2015 high-cadence Spitzer microlensing events (Zhu+, 2017) J/ApJ/891/3 : Follow-up LCs of 2 Spitzer microlensing events (Zang+, 2020) Byte-by-byte Description of file: fig1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 A12 --- Obs Observatory identifier (1) 14- 22 A9 --- Band Passband 24- 37 F14.6 d JD [2457832/2458157] Julian Date (2) 39- 45 F7.3 mag mag [9.53/153] Observed magnitude in Band (3) 47- 51 F5.3 mag e_mag [0.002/0.3] Uncertainty in mag -------------------------------------------------------------------------------- Note (1): Observatories as follows: A0 = Auckland Observatory; AT0 = Antelope Hill Observatory CBABO = Center for Backyard Astronomy Belgium Observatory CTIO = Cerro Tololo Inter-American Observatory CTO-NM-43cm = Coral Towers Observatory; 43cm instrument CTO-NM-51cm = Coral Towers Observatory; 51cm instrument CTO-NM-Savannah = Coral Towers Observatory; Savannah instrument DBO = Desert Bloom Observatory IW = Iowa Robotic Telescope PTF = Peking University 40cm Telescope RP = Post Observatory Rozhen-2m = Bulgarian National Astronomical Observatory; 2m instrument Rozhen-50cm = Bulgarian National Astronomical Observatory; 50cm instrument WH = Weihai Observatory of Shandong University ASAS-SN = All-Sky Automatic Survey for Supernovae Spitzer = Spitzer Note (2): Note that the Spitzer dates are Heliocentric Julian Dates. Note (3): The Spitzer data is in relative flux density units. All passbands with "Rel" indicate a relative magnitude. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Coralie Fix [CDS], 30-Sep-2021