The star that glowed before it dimmed

In 2018 this Sun-like star started glowing in the infrared. Three years later it began to fade. Something hot came first.

A Sun-like star whose infrared suddenly brightened in 2017-18 with ~1,000 K dust, followed about 3 years later by ragged optical dips of up to 2 mag. The dips are more strongly coloured than interstellar dust, so small grains are blocking the light. The infrared excess faded as the optical recovered, and by 2025-26 the star is back to its pre-event brightness and flat to 0.005 mag; the best explanation is a one-off cloud of debris, plausibly from a planetary collision.

Claims

C1 [observed] Before late 2017 the infrared was boringly photospheric: 8 NEOWISE visits from 2014-05 to 2017-11 have W1 = 11.654 (median, scatter ~0.01 mag) and W1-W2 between -0.05 and -0.09, i.e. no detectable warm dust.
C2 [computed] The infrared brightened abruptly between consecutive NEOWISE visits on 2017-11-15 (MJD 58072) and 2018-04-19 (MJD 58227): W1 by 0.34 mag and W2 by 0.78 mag, and W1-W2 jumped from -0.09 to +0.35. Over 2018-04 to 2020-04 the median excess vs. 2014-17 was -0.41 mag in W1 (20 sigma) and -0.80 mag in W2 (39 sigma).
C3 [inferred] The excess alone (total minus the 2014-17 photosphere) is +45% of the stellar flux in W1 and +110% in W2, giving an excess W1-W2 of about 0.9 mag (Vega); a single blackbody with that 3.4/4.6 micron ratio has T ~ 1000 K (range ~850-1050 K across visits). Hot dust, far hotter than a cold debris belt. (Hand arithmetic on tool outputs; no tool computes excess temperature.)
C4 [computed] The infrared excess faded over 2020-2023: W1-W2 = +0.32 (2020-04), +0.22 (2020-11), +0.17 (2021-11), +0.16 (2022-04), -0.01 (2022-11), -0.09 (2023-11); W1 tracks the colour (r = -0.98). The last three visits (2023-04 to 2024-04) match the 2014-17 level to within 0.01 mag in W1 and W2. NEOWISE ends in 2024, so there is no infrared after 2024-04.
C5 [computed] When AAVSO coverage begins (2021-08-26) the star is already deep in an event: the first 60 days have median V = 14.67 vs. V = 13.52 implied by the Gaia DR3 2014-17 mean (+1.15 mag). Within the event, dips reach up to 1.8 mag below a 300-day running baseline on timescales of days to weeks (faintest V 15.05, faintest B 16.51), with 18 excursions, all between 2021-08 and 2022-06.
C6 [inferred] TESS sectors 8 (2019-02) and 34-35 (2021-01 to 2021-03) contain no excursion deeper than 0.05 mag and only ~1-2% day-to-day wiggles, so the deep, fast dips were not happening then, even though the infrared excess had been present since 2018-04. The infrared therefore led the dipping by at least ~2.9 years. Caveat: TESS is normalised per sector, so a smooth constant dimming during a sector would be invisible.
C7 [computed] The dimming is strongly chromatic and steeper than interstellar reddening: from 2000+ near-simultaneous pairs, dB/dV = 1.55 (ISM 1.32), dI/dV = 0.45 (ISM 0.59), dB/dI = 2.86 (ISM 2.24), with r = 0.90-0.98.
C8 [inferred] A colour slope steeper than ISM dust means the occulter is not grey: it is dominated by small (sub-micron) grains, not large grains or an opaque solid body. Caveat: these are a single observer's magnitudes and the crossband slopes could absorb uncorrected colour terms at the ~10% level.
C9 [computed] Recovery: the V seasonal median went from 13.587 (2022-09 to 2023-07) to 13.506 (2024-06 to 2025-07) to 13.489 (2025-08 to 2026-06), reaching ~13.47-13.48 by mid-2023. The optical recovery (2022-23) coincides with the disappearance of the infrared excess (2022-11 to 2023-11).
C10 [computed] Since early 2025 the star has been flat: same-season medians Feb-Jun 2025 vs Feb-Jun 2026 differ by -0.0045 mag in V (1.5 sigma), 0.000 in B and -0.0035 in I. No excursion beyond the 4 sigma (0.14 mag) threshold after 2022-06. The current season (Oct 2026, V = 13.489, n = 16) matches the first half of 2026 (13.486). V is now equal to the Gaia-implied 13.52 within the ~0.03-0.05 mag uncertainty of a G-to-V transformation.
C11 [computed] A step occurs at MJD ~60721.7 (2025-02-16), across a 10-day gap: I brightens by 0.120 mag (15.7 sigma), R by 0.047, B by 0.021 and V by 0.013. The brightening grows toward the red, the opposite of dust clearing.
C12 [inferred] The 2025-02 step is almost certainly a calibration change by the single observer (comparison stars, aperture or filter) rather than the star. It also makes the apparent 2024/25 to 2025/26 brightening in I (-0.08) and R (-0.05) unreliable; only B and V, which barely moved, should be used to judge late recovery.
C13 [observed] Apparent 2026-06 brightening is not astrophysical: on MJD 61196.98, V is 0.37 mag and I 0.45 mag bright while B and R, taken within ~5 minutes, are normal. On 61197.98, V, B and R are 0.3-0.5 mag bright and I is only 0.12 mag bright. Real brightness changes would show up in all four filters together. These are end-of-season, low-altitude frames.
C14 [inferred] The 3.85 arcsec neighbour (G = 16.91, BP-RP = 1.84, 3.8% of the target G flux) cannot produce the optical dips (losing it entirely would dim the blend by 0.04 mag). It sits inside the WISE beam: assuming G-W1 ~ 2.6 for its colour, it is ~9% of the W1 flux, so to fake the IR excess it would have to brighten ~5x in W1 and ~12x in W2 for four years, then fade exactly as the target recovers. Possible in principle (e.g. an eruptive red star), but contrived.
C15 [observed] All optical evidence for the event in this case comes from one AAVSO observer (HMB). No TESS sector overlaps the deep dips (sectors 34-35 end 2021-03, sector 61 starts 2023-01), and ASAS-SN is unavailable. So the Skeptic's 'independent confirmation: pass' refers to the dataset, not to the event itself.
C16 [computed] TESS shows a 4.13 d periodicity (LS power 0.17, side peaks at 4.03 and 4.22 d that look like sector-gap aliases) not matching any spacecraft or Earth rhythm. AAVSO V shows no periodicity in 2-400 d beyond the trend (top peak 323 d, power 0.08, close to the yearly observing window).
C17 [inferred] Timing tension for any single-cloud picture: blackbody grains at 1000 K around a roughly solar-luminosity star (Teff 5760 K, abs G 4.6) sit at r ~ (278/1000)^2 ~ 0.08 au, where the orbital period is ~8 days. Dust that close should cross the line of sight within weeks of appearing, not ~3 years later. So either the emitters are superheated small grains much farther out, or the hot emitter and the later occulter are not the same material (e.g. a hot body or cloud on an eccentric orbit, or dust spreading along an orbit).
C18 [computed] The new irexcess tool reproduces C3, which was hand arithmetic: over the 2014-17 photosphere, the 2018-20 excess is +44% in W1 and +108% in W2, with a W1/W2 colour temperature of 998 K.

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