Method · photometry

ASAS-SN image-subtraction reconciliation: fade slopes, catalogue comparison, camera tie-in and depression check

Independent check on whether the post-2015 fade stopped in 2018, and an explanation of why the public ASAS-SN catalogue disagrees with the published image-subtraction rate.

PhotometryVersion 1.0Licence MIT1 runUsed on 1 mystery

Questions it answers

Did the slow fade continue, stop or reverse after 2018?

Code Python

Download module (.py)asassn_isub_reduce.pyView source

Runs and results 1 run

Run	Mystery	Measured	Result	Against	Date
RUN0DEEBS2Q3XBJ	Tabby's	Least-squares slope of nightly medians (mmag/yr), night and season bootstrap	{'cat_minus_isub': '-2.68 ± 0.88', 'g_2018.5_2026.85': '+0.19 ± 0.16 (±0.36 season)', 'catalogue_V_same_nights': '+3.10 ± 1.49', 'isub_V_2015.7_2018.2_same_nights': '+5.78 ± 1.23'}	AAVSO_V_2015.7_2018.2 +8.5 ± 2.6 · AAVSO_V_2018.5_2026.8 -0.04 ± 0.32 · Simon_et_al_2015_2017 +6.3 ± 1.4

Applied to

Tabby's star (KIC 8462852)

4 datasetsAAVSO International Database export for KIC 8462852, 1 July 2018 to 29 October 2026 (77,195 observations, with comparison stars), AAVSO International Database export for KIC 8462852, October 2015 to June 2018 (66,875 observations, with comparison stars), ASAS-SN V-band light curve of KIC 8462852 (source AP14246098, camera bd), 2015-2018, ASAS-SN v1 image-subtraction light curve of KIC 8462852, 2015-2026 (V and g)

References

ASAS-SN 2015-2017: fade of 6.3 +/- 1.4 mmag per year, more extreme than 99.4 per cent of 1,078 comparison stars; ASAS V 2006-2017 shows brightening 2006-07, dimming 2009-13 (15.8 +/- 1.5 mmag/yr) and brightening around 2014, so a straight line is a poor description. The modern-era reference for the fade's non-monotonic history.