J/AJ/164/102 OGLE, KMTNet & Spitzer EWS2017-BLG-1038 light curve (Malpas+, 2022)
OGLE-2017-BLG-1038; A Possible Brown-dwarf Binary Revealed by Spitzer
Microlensing Parallax.
Malpas A., Albrow M.D., Yee J.C., Gould A., Udalski A., Martin A.H.,
Beichman C.A., Bryden G., Novati S.C., Carey S., Henderson C.B., Gaudi B.S.,
Shvartzvald Y., Zhu W., Cha S.-M., Chung S.-J., Han C., Hwang K.-H.,
Jung Y.K., Kim D.-J., Kim H.-W., Kim S.-L., Lee C.-U., Lee D.-J., Lee Y.,
Park B.-G., Pogge R.W., Ryu Y.-H., Shin I.-G., Zang W., Iwanek P.,
Kozlowski S., Mroz P., Pietrukowicz P., Poleski R., Rybicki K.A.,
Skowron J., Soszynski I., Szymanski M.K., Ulaczyk K., Spitzer team,
KMTNet Collaboration, OGLE Collaboration
<Astron. J., 164, 102 (2022)>
=2022AJ....164..102M 2022AJ....164..102M
ADC_Keywords: Gravitational lensing; Stars, brown dwarf;
Stars, double and multiple; Photometry, VRI
Keywords: Binary lens microlensing ; Gravitational microlensing ;
Satellite microlensing parallax ; Brown dwarfs ; Gaussian
Processes regression
Abstract:
We report the analysis of microlensing event OGLE-2017-BLG-1038,
observed by the Optical Gravitational Lensing Experiment, Korean
Microlensing Telescope Network, and Spitzer telescopes. The event is
caused by a giant source star in the Galactic Bulge passing over a
large resonant binary-lens caustic. The availability of space-based
data allows the full set of physical parameters to be calculated.
However, there exists an eightfold degeneracy in the parallax
measurement. The four best solutions correspond to very-low-mass
binaries near (M1=170-50+40MJ and M2=110-30+20MJ), or
well below (M1=22.5-0.4+0.7MJ and M2=13.3-0.3+0.4MJ)
the boundary between stars and brown dwarfs. A conventional analysis,
with scaled uncertainties for Spitzer data, implies a very-low-mass
brown-dwarf binary lens at a distance of 2kpc. Compensating for
systematic Spitzer errors using a Gaussian process model suggests that
a higher mass M-dwarf binary at 6kpc is equally likely. A Bayesian
comparison based on a galactic model favors the larger-mass solutions.
We demonstrate how this degeneracy can be resolved within the next
10years through infrared adaptive-optics imaging with a 40m class
telescope.
Description:
OGLE-2017-BLG-1038 was first identified as a microlensing event
candidate by the Optical Gravitational Lensing Experiment early
warning system (OGLE), on 2017 June 3, from their ongoing survey
(mostly in the I band) using the 1.3m Warsaw telescope in the Las
Campanas Observatory in Chile.
The Korean Microlensing Telescope Network (KMTNet) also discovered
this event as KMT-2017-BLG-0363 and observed it in the V and I bands.
OGLE-2017-BLG-1038 was observed in two overlapping KMTNet search
fields (BLG03 and BLG43), from each of the three KMTNet telescopes:
the Cerro Tololo Inter-American Observatory (KMT-C), the South African
Astronomical Observatory (KMT-S), and the Siding Springs Observatory
(KMT-A). This resulted in a cadence of ∼15minutes between successive
observations.
The end of the event was also observed by the Spitzer Space Telescope
Infrared Array Camera (IRAC) instrument at an approximately 1day
cadence. While both the KMTNet and OGLE observations were made as part
of regular survey operations, the Spitzer observations were scheduled
for this event specifically as part of a program to enable
space-parallax measurements for microlensing events. This event was
selected for Spitzer observations on 2017 June 13 (HJD=7918.11) and
met the objective criteria on 2017 June 19 (HJD'=7923.95).
Objects:
----------------------------------------------------------------
RA (2000) DE Designation(s)
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17 58 36.55 -27 18 58.3 EWS 2017-BLG-1038 = EWS 2017-BLG-1038
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig1.dat 39 5780 Magnification curves resulting from the fitted
static binary-lens model
fig6.dat 26 38 Spitzer magnification curve
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
J/A+A/327/1039 : Structure and evolution of low-mass stars (Chabrier+ 1997)
J/AcA/50/421 : OGLE-II DIA BUL_SC1 field (Wozniak, 2000)
J/ApJ/640/1051 : 25pc sample of Sun-like stars (Grether+, 2006)
J/A+A/533/A134 : Abundances of microlensed stars in the Bulge (Bensby+, 2011)
J/ApJS/216/7 : Planets Around Low-Mass Stars (PALMS). IV. (Bowler+, 2015)
J/ApJ/814/92 : Spitzer IRAC events observed in crowded fields (Calchi+, 2015)
J/AJ/154/210 : 2015 high-cadence Spitzer microlensing events (Zhu+, 2017)
J/AJ/159/256 : Light curve of OGLE-2018-BLG-0677 (Herrera-Martin+, 2020)
J/AJ/160/74 : Optical and IR photometry of OGLE-2017-BLG-0406 (Hirao+, 2020)
J/AJ/159/262 : OGLE/KMTnet VI photometry of OGLE-2019-BLG-0551 (Mroz+, 2020)
Byte-by-byte Description of file: fig1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- ObsID Observatory identifier; OGLE or KMTNet
9- 17 F9.4 d HJD [7885/7970] Heliocentric Julian Date HJD-2450000
19- 28 F10.3 --- Flux [33333/275753] Observed flux
30- 39 F10.5 --- e_Flux [197/2964] Uncertainty in Flux
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Byte-by-byte Description of file: fig6.dat
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Bytes Format Units Label Explanations
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1- 9 F9.4 d HJD [7931/7969] Heliocentric Julian Date HJD-2450000
11- 17 F7.4 --- Flux [56.1/90.6] Observed flux
19- 26 F8.6 --- e_Flux [0.1/0.3] Uncertainty in Flux
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 18-Nov-2022