J/AJ/154/210 2015 high-cadence Spitzer microlensing events (Zhu+, 2017)
Toward a Galactic distribution of planets.
I. Methodology and planet sensitivities of the 2015 high-cadence Spitzer
microlens sample.
Zhu W., Udalski A., Novati S.C., Chung S.-J., Jung Y.K., Ryu Y.-H.,
Shin I.-G., Gould A., Lee C.-U., Albrow M.D., Yee J.C., Han C.,
Hwang K.-H., Cha S.-M., Kim D.-J., Kim H.-W., Kim S.-L., Kim Y.-H., Lee Y.,
Park B.-G., Pogge R.W., (the KMTNet Collaboration), Poleski R., Mroz P.,
Pietrukowicz P., Skowron J., Szymanski M.K., KozLowski S., Ulaczyk K.,
Pawlak M., (the OGLE Collaboration), Beichman C., Bryden G., Carey S.,
Fausnaugh M., Gaudi B.S., Henderson C.B., Shvartzvald Y., Wibking B.
<Astron. J., 154, 210 (2017)>
=2017AJ....154..210Z 2017AJ....154..210Z (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Gravitational lensing ; Exoplanets ; Ephemerides ;
Photometry, RI
Keywords: gravitational lensing: micro - methods: statistical -
planetary systems -
planets and satellites: dynamical evolution and stability
Abstract:
We analyze an ensemble of microlensing events from the 2015 Spitzer
microlensing campaign, all of which were densely monitored by
ground-based high-cadence survey teams. The simultaneous observations
from Spitzer and the ground yield measurements of the microlensing
parallax vector πE, from which compact constraints on the
microlens properties are derived, including ~<25% uncertainties on the
lens mass and distance. With the current sample, we demonstrate that
the majority of microlenses are indeed in the mass range of M dwarfs.
The planet sensitivities of all 41 events in the sample are calculated,
from which we provide constraints on the planet distribution function.
In particular, assuming a planet distribution function that is uniform
in log q, where q is the planet-to-star mass ratio, we find a 95%
upper limit on the fraction of stars that host typical microlensing
planets of 49%, which is consistent with previous studies. Based on
this planet-free sample, we develop the methodology to statistically
study the Galactic distribution of planets using microlensing parallax
measurements. Under the assumption that the planet distributions are
the same in the bulge as in the disk, we predict that ∼1/3 of all
planet detections from the microlensing campaigns with Spitzer should
be in the bulge. This prediction will be tested with a much larger
sample, and deviations from it can be used to constrain the abundance
of planets in the bulge relative to the disk.
Description:
Following the Yee et al. (2015ApJ...810..155Y 2015ApJ...810..155Y) protocol, the 2015 Spitzer
microlensing campaign observed 170 microlensing events that were first
found in the ground-based microlensing surveys, namely, the Optical
Gravitational Lensing Experiment (OGLE; Udalski 2003AcA....53..291U 2003AcA....53..291U;
Udalski et al. 2015AcA....65....1U 2015AcA....65....1U) and the Microlensing Observations in
Astrophysics (MOA; Bond et al. 2001MNRAS.327..868B 2001MNRAS.327..868B; Sako et al.
2008ExA....22...51S 2008ExA....22...51S). In this work, we present analysis of 50 of them that
fall within the footprints of OGLE and the prime fields of the newly
established KMTNet (Korean Microlensing Telescope Network; Kim et al.
2016JKAS...49...37K 2016JKAS...49...37K).
All events in our sample were found by the OGLE collaboration in real
time through its Early Warning System (Udalski et al. 1994, Cat. II/213;
Udalski 2003AcA....53..291U 2003AcA....53..291U), based on observations with the 1.4 deg2
camera on its 1.3 m Warsaw Telescope at the Las Campanas Observatory
in Chile (Udalski 2003AcA....53..291U 2003AcA....53..291U; Udalski et al. 2015AcA....65....1U 2015AcA....65....1U).
These events received OGLE-IV observations with cadences varying from
3 to 30 per day.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 104 50 Summary of the 50 events in our sample
table2.dat 119 171 Best-fit parameters and associated uncertainties
for the 50 events
--------------------------------------------------------------------------------
See also:
II/213 : OGLE Galactic Bulge periodic variables (Udalski+ 1996)
J/AcA/50/1 : OGLE microlensing events in Galactic Bulge (Udalski+, 2000)
J/A+A/466/157 : Bulge Microlensing Events (Soto+, 2007)
J/ApJ/778/150 : Microlensing events toward the Bulge from MOA-II
(Sumi+, 2013)
J/ApJS/216/12 : OGLE-III Galactic bulge microlensing events
(Wyrzykowski+, 2015)
J/MNRAS/458/3012 : OGLE-III Parallax microlensing events (Wyrzykowski+, 2016)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- OGLE [11/1533] OGLE identifier
(OGLE-2015-BLG-NNNN)
6- 15 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
17- 26 F10.6 deg DEdeg Declination in decimal degrees (J2000)
28- 36 F9.6 deg GLON [] Galactic longitude
38- 46 F9.6 deg GLAT Galactic latitude
48- 63 A16 --- Obs.Date1 Subjective selection date (YYYY-MM-DDThh:mm)
(1)
65- 74 A10 "date" Obs.Date2 Objective selection date (1)
76- 81 A6 --- Field OGLE-IV field identifier (BLGNNN)
83- 84 I2 d-1 o_Field [3/30] Cadence of Field; per day
86- 92 F7.2 d HJD1 [7183.32/7213.65] Heliocentric Julian Date of
Spitzer observation start (HJD-2450000.0)
94-100 F7.2 d HJD2 [7198.41/7223.07] Heliocentric Julian Date of
Spitzer observation end (HJD-2450000.0)
102-104 I3 --- SNum [17/131] Number of Spitzer observations
--------------------------------------------------------------------------------
Note (1): As detailed in Yee et al. (2015ApJ...810..155Y 2015ApJ...810..155Y), the Spitzer program
is designed to maximize the sum of the products ΣiSiPi, where Si
is the planet sensitivity of event i and Pi is the probability to measure
the microlens parallax of this event. As a consequence, the Spitzer team
started selecting targets beginning in early 2015 May, although Spitzer did
not start taking data until JD'=JD-2450000=7180.2 (2015 June 6.7). To enforce
our blindness to the existence of planets in any events, we select events if
(1) they meet certain objective criteria at the time of one of the uploads of
targets to Spitzer, in which case they are considered as "objectively chosen",
or (2) they do not meet objective criteria but are nevertheless selected on
the basis that the Spitzer team believes that by selecting them the quantity
ΣiSiPi can be maximized. Events selected in the latter case are
known as "subjectively chosen".
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- OGLE [11/1533] OGLE identifier (OGLE-2015-BLG-NNNN)
6- 8 A3 --- Sol Solution type (see Equation 9)
10- 13 F4.1 --- Delchi2 [0/80.8] Difference between given solution and
best solution (1)
15- 22 F8.3 d t0 [7125.53/7236.56] Heliocentric Julian Date of
peak time (HJD-2450000.0)
24- 28 F5.3 d e_t0 [0.003/0.5] Uncertainty in t0
30- 36 F7.4 --- u0 [-0.9943/0.9941] Impact parameter
38- 43 F6.4 --- e_u0 [0.0003/0.12] Uncertainty in u0
45- 50 F6.2 d tE [4.39/116] Einstein timescale
52- 56 F5.2 d e_tE [0.06/18] Uncertainty in tE
58- 64 F7.4 mas piEN [-1.77/3.2] North component of microlensing
parallax πE,N
66- 71 F6.4 mas e_piEN [0.0017/0.4] Uncertainty in piEN
73- 79 F7.4 mas piEE [-1.5/0.34] East component of microlensing
parallax πE,E
81- 86 F6.4 mas e_piEE [0.0017/0.4] Uncertainty in piEE
88- 93 F6.3 mag Imag [15.132/20.407] Total baseline OGLE-IV I band
magnitude (2)
95-100 F6.3 --- Blend [-0.15/0.956]? Blending fraction in I band (3)
102-106 F5.3 --- e_Blend [0.003/0.3]? Uncertainty in Blend
108-113 F6.3 mag I-3.6 [0.83/10.5] The (I-3.6µm) color
115-119 F5.3 mag e_I-3.6 [0.011/0.6] Uncertainty in I-3.6
--------------------------------------------------------------------------------
Note (1): For each event, we only include solutions that have
Δχ2<100 from the lowest value.
Note (2): The uncertainty of Ibase is ∼1 mmag, primarily arising from
OGLE-IV's data recording format. In addition, the calibration precision of
OGLE-IV I band to the standard system, ∼10 mmag, is not included here, on the
base that it does not affect the determination of microlensing parameters.
Note (3): We assume no blending for events OGLE-2015-BLG-(0011, 0029, 0081,
0772, 0798, 1096, 1188, 1289, 1297, 1341, 1470), because free blending would
lead to severely negative blending.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 06-Aug-2018