J/MNRAS/498/L6 Gaia DR2 predictions of microlensing events (McGill+, 2020)
Predictions of Gaia's prize microlensing events are flawed.
McGill P., Everall A., Boubert D., Smith L.C.
<Mon. Not. R. Astron. Soc., 498, L6-L10 (2020)>
=2020MNRAS.498L...6M 2020MNRAS.498L...6M (SIMBAD/NED BibCode)
ADC_Keywords: Gravitational lensing ; Optical
Keywords: gravitational lensing: micro
Abstract:
Precision astrometry from the second Gaia data release has allowed
astronomers to predict 5787 microlensing events, with 528 of these
having maximums within the extended Gaia mission (J2014.5-J2026.5).
Future analysis of the Gaia time-series astrometry of these events
will, in some cases, lead to precise gravitational mass measurements
of the lens. We find that 61 per cent of events predicted during the
extended Gaia mission with sources brighter than G=18 are likely to be
spurious, with the background source in these cases commonly being
either a duplicate detection or a binary companion of the lens. We
present quality cuts to identify these spurious events and a revised
list of microlensing event candidates. Our findings imply that half of
the predictable astrometric microlensing events during the Gaia
mission have yet to be identified.
Description:
We analyse the predicted microlensing events found by searches solely
using Gaia DR2, giving us a total sample of 5787 distinct events
caused by 4436 lenses. Although many of these studies predict some of
the same events, there are key differences. Mustill et al.
(2018A&A...617A.135M 2018A&A...617A.135M, Cat. J/A+A/617/A135) searched for photometric
events caused by lenses within 100pc over the next 20yr. Kluter et al.
(2018A&A...615L..11K 2018A&A...615L..11K) presented two ongoing astrometric events that at
the time required immediate follow-up. Bramich (2018A&A...618A..44B 2018A&A...618A..44B,
Cat. J/A+A/618/A44) presented a catalogue of photometric and
astrometric events with maximums during the extended Gaia mission
(J2014.5-J2026.5). Kluter et al. (2018A&A...620A.175K 2018A&A...620A.175K, hereafter
K18b), presented a catalogue of predicted photometric and astrometric
events with maximums between J2014.5 and J2065. Bramich & Nielsen
(2018AcA....68..183B 2018AcA....68..183B, Cat. J/AcA/68/183) presented a catalogue of
photometric and astrometric events with maximums between the end of
the extended Gaia mission and the end of the century
(J2026.5-J2100.0). Finally, McGill et al. (2019MNRAS.483.4210M 2019MNRAS.483.4210M)
presented two photometric events that required immediate follow-up in
J2019.0. Each of these studies used different event detectability
criteria, lens and source selection criteria, and lens mass estimates,
which resulted in different sets of events. In most cases, where two
different studies found the same event, the predictions were
consistent.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 151 6534 List of the microlensing events predicted using
Gaia DR2
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/618/A44 : Predicted microlensing events from Gaia DR2 (Bramich, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR2L Gaia DR2 source identifier of the lens
21- 39 I19 --- GaiaDR2S Gaia DR2 source identifier of the source
41- 56 A16 --- 2MASSL 2MASS source designation of the lens
58- 73 A16 --- 2MASSS 2MASS source designation of the source
75- 82 F8.3 yr Tminsep Time of closest approach of the lens and
source (in julian years) as calculated by the
study which found the event
84- 88 A5 --- vconf Indicates whether the source and lens have
been identified in legacy imaging data (1)
90- 92 I3 --- Nobs Number of times the source was observed by
Gaia according to Boubert et al.
2020MNRAS.497.1826B 2020MNRAS.497.1826B)
94- 97 A4 --- Ref Reference of the study that found the event
(2)
99- 104 F6.3 mag GmagL Gaia DR2 G-band magnitude of the lens
106- 111 F6.3 mag GmagS Gaia DR2 G-band magnitude of the source
113- 119 F7.3 --- sigmaAL Error in the along scan direction of the
source (3)
121- 126 F6.3 mag BP-RPL ? Gaia DR2 BP-RP colour of the lens
128- 133 F6.3 mag BP-RPS ? Gaia DR2 BP-RP colour of the source
135- 136 I2 --- MatchOAL Gaia DR2 number of astrometric matched
observations for the lens
138- 139 I2 --- MatchOAS Gaia DR2 number of astrometric matched
observations for the source
141- 149 F9.3 --- Psi Astrometric quality indicator Ψ (4)
151 I1 --- Solved Number of parameters of the source
astrometric solution from Gaia DR2
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Note (1): Flag as follows:
True = the event has been visually confirmed
False = the event has been confirmed to be spurious via visual inspection
- = either inspection of the imaging data was inconclusive, or the
event was not looked at
Note (2): Reference as follows:
K18b = Kluter et al. (2018A&A...620A.175K 2018A&A...620A.175K)
B18a = Bramich (2018A&A...618A..44B 2018A&A...618A..44B, Cat. J/A+A/618/A44)
Mc19 = Mcgill et al. (2019MNRAS.483.4210M 2019MNRAS.483.4210M)
K18a = Kluter et al. (2018A&A...615L..11K 2018A&A...615L..11K)
Note (3): We estimated the typical centroiding uncertainty from the harmonic
mean of the equatorial positional uncertainties:
σAL=sqrt[ν/(1/σ2α+1/σ2δ)],
where ν is the ASTROMETRICNGOODOBSAL from Gaia DR2
Note (4): We define the quantity
Ψ=ASTROMETRICSIGMA5DMAX/((1.2mas)xγ(G)), where the
γ(G)=max[1,100.2(G-18)] function is flat for G=<18 and then
transitions to exponential growth
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 14-Aug-2023