J/A+A/674/A25 Gaia DR3. spurious signals (Holl+, 2023)
Gaia Data Release 3.
Gaia scan-angle dependent signals and spurious periods,
Holl B., Fabricius C., Portell J., Lindegren L., Panuzzo P., Bernet M.,
Castaneda J., Jevardat de Fombelle G., Audard M., Ducourant C.,
Harrison D.L., Evans D.W., Busso G., Sozzetti A., Gosset E., Arenou F.,
De Angeli F., Riello M., Eyer L., Rimoldini L., Gavras P., Mowlavi N.,
Nienartowicz K., Lecoeur-Taibi I., Garcia-Lario P., Pourbaix D.
<Astron. Astrophys. 674, A25 (2023)>
=2023A&A...674A..25H 2023A&A...674A..25H (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Stars, variable ; Photometry ; Optical ;
Radial velocities
Mission_Name: Gaia
Keywords: methods: data analyses - techniques: photometric -
methods: numerical - techniques: radial velocities - astrometry
Abstract:
Gaia DR3 time series data may contain spurious signals related to the
time-dependent scan angle.
We aim to explain the origin of scan-angle dependent signals and how
they can lead to spurious periods, provide statistics to identify them
in the data, and suggest how to deal with them in Gaia DR3 data and in
future releases.
Using real Gaia (DR3) data, alongside numerical and analytical models,
we visualise and explain the features observed in the data.
We demonstrated with Gaia (DR3) data that source structure
(multiplicity or extendedness) or pollution from close-by bright
objects can cause biases in the image parameter determination from
which photometric, astrometric and (indirectly) radial velocity time
series are derived. These biases are a function of the time-dependent
scan direction of the instrument and thus can introduce scan-angle
dependent signals, which due to the scanning law induced sampling of
Gaia can result in specific spurious periodic signals. Numerical
simulations in which period search is performed on Gaia time series
with a scan-angle dependent signal qualitatively reproduce the general
structure observed in the spurious period distribution of photometry
and astrometry, as well as the associated spatial distributions on the
sky. A variety of statistics allows for the deeper understanding and
identification of affected sources.
The origin of the scan-angle dependent signals and subsequent spurious
periods is well-understood and is in majority caused by
fixed-orientation optical pairs with separation <0.5" (amongst which
binaries with P≫5y) and (cores of) distant galaxies. Though the
majority of sources with affected derived parameters have been
filtered out from the Gaia archive nsstwobody_orbit and several
vari-tables, there remain Gaia DR3 data that should be treated with
care (note that no sources were filtered from gaia_source). Finally,
the various statistics discussed in the paper can not only be used to
identify and filter affected sources, but alternatively reveal new
information about them not available through other means, especially
in terms of binarity on sub-arcsecond scale.
Description:
As part of this paper the table varispurioussignals
is published in the Gaia DR3 archive for all 11754237 sources with
published photometric time series, i.e., sources in gaia_source with
hasepochphotometry=true. Of these, 10509536 sources are variables
(Eyer et al., 2022, arXiv:2206.06416) and 1257319 are part of the Gaia
Andromeda Photometric Survey (GAPS) (Evans et al., 2022,
arXiv:2206.05591) which one can identify in gaia_source by their
photvariableflag=VARIABLE and inandromedasurvey=true flags,
respectively. Note that 12618 sources overlap between the two.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
vspursig.sam 455 1000 Spurious signals (varivarispursign)
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See also:
I/355 : Gaia DR3 Part 1: Main sources
I/356 : Gaia DR3 Part 2: Extra-galactic
I/357 : Gaia DR3 Part 3: Non-single stars
I/358 : Gaia DR3 Part 4: Variability
I/359 : Gaia DR3 Part 5: Solar System
I/360 : Gaia DR3 Part 6: Performance verification
Byte-by-byte Description of file: vspursig.sam
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- Source Source Identifier (source_id)
21- 35 F15.11 deg RAdeg Right ascension (ICRS) at Ep=2016.0
(ra)
37- 51 F15.11 deg DEdeg Declination (ICRS) at Ep=2016.0 (dec)
53- 65 A13 --- VarFlag Photometric variability flag
(photvariableflag)
67 I1 --- And [0/1] Flag indicating that the source
is present in the Gaia Andromeda
Photometric Survey (GAPS)
(inandromedasurvey)
69- 71 I3 --- NobsAll Number of observations in common for
G, BP and RP bands, used in
computation of the Spearman
correlation excess factor fields
(numobscommonallbands)
73- 75 I3 --- NobsgFoV Number of selected observations of
G FoV transits, used in the
frequency fields (numobsg_fov)
77- 87 F11.8 d-1 GLSFreqgFoV Frequency identified by Generalised
Least Squares period search on
G FoV timeseries (glsfreqg_fov)
89- 96 F8.6 --- GLSFreqAmplgFoV Normalised amplitude of the
frequency identified by Generalised
Least Squares period search on
G FoV timeseries
(glsfreqamplgfov)
98-106 F9.6 --- GLSFreqSDEgFoV Signal Detection Efficiency (SDE) of
the frequency identified by
Generalised Least Squares period
search on G FoV timeseries
(glsfreqsdegfov)
108-122 E15.8 --- GLSFreqFAPgFoV False Alarm Probability (FAP) of the
frequency identified by Generalised
Least Squares period search on
G FoV timeseries (double)
(glsfreqfapgfov)
124-134 F11.8 d-1 NHMFundFreqgFoV ? Fundamental frequency identified
by non-linear harmonic modelling on
G FoV timeseries, initialised by
the Generalised Least Squares
frequency (nhmfundfreqgfov)
136-144 F9.6 d-1 e_NHMFundFreqgFoV ? Uncertainty of the fundamental
frequency identified by non-linear
harmonic modelling on G FoV
timeseries
(nhmfundfreqerrorg_fov)
146-154 F9.6 --- spearmanCorrExfgFoV ? G-band FoV photometry Spearman
correlation with corrected flux
excess factor
(spearmancorrexfgfov)
156-158 I3 --- Nobs-EPSLgFoV Number of G-band FoV photometry
observations excluding EPSL, used
for the IPD correlation and scan
angle modelling in the G band
(numobsexclepslg_fov)
160-168 F9.6 --- spearmanCorrIPDgFoV ? G-band FoV photometry Spearman
correlation with IPD model
(spearmancorripdgfov)
170-182 E13.6 mag SAMoffsetgFoV ? Magnitude offset of the scan angle
model fit to G-band FoV photometry
(scananglemodeloffsetg_fov)
184-195 E12.6 mag SAMamplgFoV ? Amplitude of the scan angle model
fit to G-band FoV photometry
(scananglemodelamplg_fov)
197-208 E12.6 --- SAMamplSignigFoV ? Significance of the amplitude of
the scan angle model fit to G-band
FoV photometry
(scananglemodelamplsiggfov)
210-221 E12.6 deg SAMphasegFoV ? Phase of the scan angle model fit
to G-band FoV photometry
(scananglemodelphaseg_fov)
223-234 E12.6 --- SAMredchi2gFoV ? Reduced Chi2 of the scan angle
model fit to G-band FoV photometry
(scananglemodelredchi2gfov)
236-248 E13.6 --- SAMf2gFoV ? F2 goodness-of-fit of the scan
angle model fit to G-band FoV
photometry
(scananglemodelf2g_fov)
250-258 F9.6 --- spearmanCorrExfBP ? BP-band photometry Spearman
correlation with corrected flux
excess factor
(spearmancorrexf_bp)
260-262 I3 --- Nobs-epslBP Number of BP-band photometry
observations excluding EPSL, used
for the IPD correlation and scan
angle modelling in the BP band
(numobsexclepslbp)
264-272 F9.6 --- spearmanCorrIPDBP ? BP-band Spearman correlation with
IPD model (spearmancorripd_bp)
274-286 E13.6 mag SAMoffsetBP ? Magnitude offset of the scan angle
model fit to BP-band photometry
(scananglemodeloffsetbp)
288-299 E12.6 mag SAMamplBP ? Amplitude of the scan angle model
fit to BP-band photometry
(scananglemodelamplbp)
301-312 E12.6 --- SAMamplSigniBP ? Significance of the amplitude of
the scan angle model fit to BP-band
photometry
(scananglemodelamplsig_bp)
314-325 E12.6 deg SAMphaseBP ? Phase of the scan angle model fit
to BP-band photometry
(scananglemodelphasebp)
327-338 E12.6 --- SAMredchi2BP ? Reduced Chi2 of the scan angle
model fit to BP-band photometry
(scananglemodelredchi2_bp)
340-352 E13.6 --- SAMf2BP ? F2 goodness-of-fit of the scan
angle model fit to BP-band
photometry (scananglemodelf2bp)
354-362 F9.6 --- spearmanCorrExfRP ? RP-band photometry Spearman
correlation with corrected flux
excess factor
(spearmancorrexf_rp)
364-366 I3 --- Nobs-epslRP Number of RP-band photometry
observations excluding EPSL, used
for the IPD correlation and scan
angle modelling in the RP band
(numobsexclepslrp)
368-376 F9.6 --- spearmanCorrIPDRP ? RP-band Spearman correlation with
IPD model (spearmancorripd_rp)
378-389 E12.6 mag SAMoffsetRP ? Magnitude offset of the scan angle
model fit to RP-band photometry
(scananglemodeloffsetrp)
391-402 E12.6 mag SAMamplRP ? Amplitude of the scan angle model
fit to RP-band photometry
(scananglemodelamplrp)
404-415 E12.6 --- SAMamplSigniRP ? Significance of the amplitude of
the scan angle model fit to RP-band
photometry
(scananglemodelamplsig_rp)
417-428 E12.6 deg SAMphaseRP ? Phase of the scan angle model fit
to RP-band photometry
(scananglemodelphaserp)
430-441 E12.6 --- SAMredchi2RP ? Reduced Chi2 of the scan angle
model fit to RP-band photometry
(scananglemodelredchi2_rp)
443-455 E13.6 --- SAMf2RP ? F2 goodness-of-fit of the scan
angle model fit to RP-band
photometry (scananglemodelf2rp)
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Acknowledgements:
Berry Holl, Berry.Holl(at)unige.ch
(End) Francois-Xavier Pineau, Patricia Vannier [CDS] 21-Mar-2023