J/MNRAS/513/420 NGTS Variability Study (Briegal+, 2022)
Periodic stellar variability from almost a million NGTS light curves.
Briegal J.T., Gillen E., Queloz D., Hodgkin S., Acton J.S., Anderson D.R.,
Armstrong D.J., Battley M.P., Bayliss D., Burleigh M.R., Bryant E.M.,
Casewell S.L., Costes J.C., Eigmuller P., Gill S., Goad M.R., Gunther M.N.,
Henderson B.A., Jackman J.A.G., Jenkins J.S., Kreutzer L.T., Lendl M.,
Smith G.D., Tilbrook R.H., Watson C.A., West R.G., Wheatley P.J.
<Mon. Not. R. Astron. Soc. 513, 420-438 (2022)>
=2022MNRAS.513..420B 2022MNRAS.513..420B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Photometry
Keywords: methods: data-analysis - techniques: photometric - stars: activity -
Hertzprung-Russell and colour-magnitude diagrams - stars: rotation -
stars: variables: general
Abstract:
We analyse 829481 stars from the Next Generation Transit Survey
(NGTS) to extract variability periods. We utilise a generalisation of
the autocorrelation function(the G-ACF), which applies to irregularly
sampled time series data. We extract variability periods for
16,880stars from late-A through to mid-M spectral types and periods
between 0.1 and 130 days with no assumed variability model. We find
variable signals associated with a number of astrophysical phenomena,
including stellar rotation, pulsations and multiple-star systems. The
extracted variability periods are compared with stellar parameters
taken from Gaia DR2, which allows us to identify distinct regions of
variability in the Hertzsprung-Russell Diagram. We explore a sample of
rotational main-sequence objects in period-colour space, in which we
observe a dearth of rotation periods between 15 and 25 days. This
'bi-modality' was previously only seen in space-based data. We
demonstrate that stars in sub-samples above and below the period gap
appear to arise from a stellar population not significantly
contaminated by excess multiple systems. We also observe a small
population of long-period variable M-dwarfs, which highlight a
departure from the predictions made by rotational evolution models
fitted to solar-type main-sequence objects. The NGTSdata spans a
period and spectral type range that links previous rotation studies
such as those using data from Kepler, K2 and MEarth.
Description:
In this study, we extract robust variability periods for 16880
stars out of 829481 stars observed with the NGTS, based in Paranal,
Chile. This is the largest ground-based systematic photometric
variability study conducted to date with such precise and high-cadence
photometry and highlights both the advantages of such studies as well
as the challenges. Using precise ground-based photometry, plus a
generalization of the autocorrelation function to irregularly sampled
data, we are able to detect variability amplitudes down to levels of
0.3 per cent. The contamination of signals by systematics
demonstrates that using ground-based photometry requires further
thought than using much cleaner space-based data in order to avoid
false positives arising through aliases. The most common source of
aliases arose from Moon contaminated signals as well as aliasing from
the 1-d periodic sampling intrinsic to ground-based observations. We
demonstrate we are able to overcome these limitations and produce
robust variability signals across our sample.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ngtsrot.dat 164 16880 Rotation periods and catalogue identifiers for
16880 stars observed with NGTS
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/322 : UCAC4 Catalogue (Zacharias+, 2012)
IV/38 : TESS Input Catalog - v8.0 (TIC-8) (Stassun+, 2019)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
Byte-by-byte Description of file: ngtsrot.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- NGTS NGTS source designation (NGNNNN-NNNN-NNNN)
20- 28 F9.5 deg RAdeg NGTS source right ascension (J2000)
30- 38 F9.5 deg DEdeg NGTS source declination (J2000)
40- 47 F8.5 mag Imag NGTS I-band magnitude
49- 57 F9.5 d Per Extracted variability period
59- 65 F7.5 --- Ampl 5-95 percentile relative flux
67- 85 I19 --- GAIADR1 Cross-matched Gaia DR1 identifier
87-105 I19 --- GAIADR2 Cross-matched Gaia DR2 identifier
107-116 I10 --- TIC ? Cross-matched Tess Input Catalogue (v8)
identifier
118-133 A16 --- 2MASS Cross-matched 2MASS identifier
135-153 A19 --- WISE Cross-matched WISE identifier
155-164 A10 --- UCAC4 Cross-matched UCAC4 identifier
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Acknowledgements:
Joshua Briegal, jtb34(at)cam.ac.uk
(End) Patricia Vannier [CDS] 21-Feb-2022