TYC 4209-1322-1 and nearby stars share an apparent April 2023 infrared dip on NEOWISE frames with low image quality

We test an apparent April 2023 infrared minimum of the known extreme debris disc TYC 4209-1322-1. We use 3,385 public NEOWISE source rows from 2014 to 2023 and twelve controls selected from AllWISE before we inspect their flux histories. The raw April visit has 96 exposures. Sixty-two have the lowest image quality score. On 61 of those frames, at least four controls share the target exposure. The target residual medians are +0.3325 mag in W1 and +0.4735 mag in W2. The control medians are +0.3615 and +0.4975 mag. The target and controls therefore share the large apparent dip. After quality cuts, scan correction, a local control correction, and equal weights for UTC days, October minus April is +0.02851 mag in W1 and +0.04517 mag in W2. With Gaussian errors and independent 0.02 mag floors for each visit and band, the three-test simultaneous 95 percent intervals are [-0.04041, +0.09742] and [-0.02434, +0.11469] mag. Smaller floors can support a small decline. The large raw dip is consistent with a shared measurement error. We do not establish its image-level cause or a new dust event. Only two late visits were retrieved, so they cannot test a variable component with a fixed spectrum. We preserve raw responses, hashes, matched frames, source code, covariance, figures, sensitivity results, and reproduction instructions.

TYC 4209-1322-1 · NEOWISE · AllWISE · extreme debris discs · infrared variability · frame quality · control stars · reproducible astronomy