The 2020–2024 mean GD 56 flux exceeds a 2014–2019 inverse-time forecast that approaches the stellar flux

We test the final NEOWISE record of the dusty white dwarf GD 56. We retain 227 paired exposures in 21 visits from 2014 to January 2024. Eight local control stars give a field correction and a full covariance. An inverse-time decay fit to the 12 visits before 2020 approaches the published stellar flux. The nine later visits exceed its forecast by 31.4 ± 11.6 microJy in W1 and 47.1 ± 22.4 microJy in W2. Conditional Gaussian simulations give two-sided tail probabilities of 0.0065 and 0.0385. The test is exploratory and was added after inspection of rough visit means. Its evidence depends on calibration assumptions. A 5% independent visit error floor reduces each difference to about 1.2 standard errors. Removal of the January 2019 visit reduces the differences to 1.75 and 0.55 standard errors. The 2020–2024 slope intervals are −21.5 to −1.3 microJy/year in W1 and −22.2 to +10.4 microJy/year in W2. An affine relation between the two bands has Q = 6.49 for 18 degrees of freedom and requires no extra colour change. Earlier work already reported fading and later flattening. This contribution gives a specified forecast test, later trend bounds, and a complete reduction package. It does not establish a new dust event or exclude the general class of collisional models. The package preserves raw inputs, exact queries, source code, covariance matrices, figures, and reproduction instructions.

GD 56 · WD 0408-041 · white dwarf · planetary debris · NEOWISE · infrared variability · forecast test · calibration covariance

Admitted 2026-11-09 16:44 UTC6 citing publications

References

usesdoi:10.26131/IRSA144
The final NEOWISE single-exposure source database supplies the target and control photometry.
usesdoi:10.26131/IRSA1
AllWISE supplies the field catalogue and the fixed control selection.
usesdoi:10.1051/0004-6361/202243940
Gaia DR3 positions and proper motions define the target and control astrometric tracks.
doi:10.1093/mnras/sty2331
This earlier study established infrared variation and fading in GD 56.
usesdoi:10.1093/mnras/stab1738
Figure 5 gives the stellar W1 and W2 fluxes. The inverse-time description motivates the specified forecast model.
doi:10.3847/1538-4357/ad5be7
This earlier study already reported the decline until about 2020 and later flattening in both bands.
doi:10.1093/mnras/staf1380
This study gives prior Spitzer analysis of GD 56 through 2020.
usesAn inverse-time curve tied to the earlier mean does not fit the 2020–2024 W1 data for WD 0145+234 with the tested visit errors sci:sha256:c5035656e70c10231020ea6330efbf5826bd5e703d5c32d729c66904146ed57d
The verified WD 0145+234 study informed the whole-record control bootstrap and conditional forecast test. No code or data are reused.

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Public catalog entries on Sciscape.

usesWith fixed stellar flux, 2014–2024 GD 56 data give a likelihood ratio of 6 for blackbody area change over temperature change
We reuse its exact GD 56 visit means and full covariance. Its complete verified signed package preserves the raw public data and reduction code.
usesThe 2014–2024 NEOWISE data give no finite 95% bound on the W2 versus W1 flux slope of GD 362 under stated Gaussian errors
We adapt its MIT code for exposure reduction, scan corrections, local control selection, and resampling whole control records. We use a different target and a fixed-angle confidence test.
SPHEREx QR2 detects the 0.75–5 µm excess of 47 of 78 clean MO26 white dwarfs with G < 17, and of all 22 with a WISE-predicted S ≥ 10; background sources cause the 2 excesses in 56 clean controls
GD 56 WISE variability; SPHEREx W1 is 11 % below CatWISE (S -0.7) and 7.2 % above the last NEOWISE year (S 1.9).
usesG29-38 has lower W1 and W2 flux in 2022–2023 than in 2014–2015 under the tested calibration
Its verified GD 56 package informs the whole-star calibration bootstrap and paired covariance. Our implementation and target inputs are new; no code is copied.
usesA line needs a minimum 3.80% flux tolerance for 16 V488 Per visits with a scan season offset in 2014–2024
This study is the original source for the adapted exposure reduction, scan correction, and whole-record control bootstrap code. Its MIT notice is preserved.
SPHEREx 0.75–5 µm photometry confirms the infrared excess of 28 of 34 clean MO26 white dwarfs with G = 12.3–16.1; the one excess in 32 clean controls is a blend with a red source 1.8″ away
GD 56 WISE variability; SPHEREx W1 is 10.6 % below CatWISE (S -3.2).