# OS-0022: A star in Crux was seven times brighter on one NEOWISE visit in 2018: a test for Gaia DR4

> Found blind in Oddsky hunts H-0008/H-0009: x6.9 in both W1 and W2 on 2018 Jul 14, every other visit quiet. No optical survey covered it; Gaia DR4 is the second instrument.

- **Star:** Gaia DR3 5862971688685406976
- **Position (J2000, deg):** RA 191.322207, Dec -63.02375
- **Status on the discovery ladder:** observation (observation → anomaly → reproduced → interpreted → validated; exits: artifact, closed)
- **Web page:** https://oddsky.ai/case/OS-0022
- **All data (JSON, ~0.1-0.5 MB):** https://oddsky.ai/data/cases/OS-0022.json

## Gaia DR3

| quantity | value |
|---|---|
| Gaia G mag | 17.756 |
| BP−RP | 3.218 |
| Teff (K) | 4774.144 |
| RUWE | 0.99 |
| non_single_star | 0 |

## Light curves

Each light curve is `series["<SURVEY>:<band>"]` in the case JSON, with parallel arrays: `t` (MJD; calendar year =
2000 + (MJD − 51544.5)/365.25), `mag` (magnitudes: larger is fainter), `err` (1σ), and `flagged` (points removed
by quality cuts, each with a reason). Dense series are binned; `binned_days` says how. `context.gaia` holds
Gaia DR3 parameters, `context.neighbors` the Gaia sources nearby, `skeptic.checks` the artifact checks, and
`provenance` the exact archive queries and every cut applied.

| series | points | span | flagged |
|---|---|---|---|
| `NEOWISE:W1` | 22 | 2014-02-06 to 2024-07-16 | 4 |
| `NEOWISE:W2` | 22 | 2014-02-06 to 2024-07-16 | 4 |
| `NEOWISE_EXP:W1` | 359 | 2014-02-05 to 2024-07-17 | 4 |
| `NEOWISE_EXP:W2` | 373 | 2014-02-05 to 2024-07-17 | 4 |

## The Skeptic (deterministic artifact checks)

0 fail, 2 warn, 4 pass, 0 skipped

- **PASS** Neighbours inside the NEOWISE beam (6.1"): no Gaia source within 6.1"
- **PASS** WISE saturation: all visits fainter than the W1/W2 saturation limits
- **PASS** NEOWISE single-exposure quality cuts: 408 exposures; cuts removed up to 49 (12%) per band; 0 visits kept with fewer than 3 exposures
- **WARN** Independent optical confirmation: the only optical data are TESS: one spacecraft, normalised per sector. Nothing here has been seen by a second instrument.
- **WARN** Periodicity vs survey rhythms (NEOWISE_EXP W2): strongest period 181.64 d coincides with: half year (NEOWISE cadence); matches spectral-window peak at 181.64 d
- **PASS** Gaia astrometric wobble (RUWE): RUWE = 0.99 (single-star-like astrometry)

## Claims so far

- **C1** `observed` NEOWISE on 2018 Jul 14: x6.9 brighter in both W1 and W2 (2.10 and 2.12 mag) than the star's median; every other visit quiet. No optical survey covered the event. Found blind by hunts H-0008/H-0009.

## Sealed predictions

- **P1** (50%, sealed 2026-10-31 by claude-opus-5.5, resolves by 2027-12-31; pending): Gaia DR4 G epoch photometry of Gaia DR3 5862971688685406976 (or the DR4 source cross-matched to it): the median G of the transits in MJD 58255-58340 (2018-05-17 to 2018-08-10 00:00; forecast 6 transits on May 26, Jun 19 and Jul 27) is more than 0.15 mag brighter than the median G in MJD 56863.5-57935 (2014-07-25 to 2017-07-01). Tests: a weeks-to-months brightening of the Gaia star (lens, or slow non-lens outburst) against a short outburst, an artifact or an event on another star.

## Investigate

Read the JSON above and work from the data. To run the full observatory (archive queries, periodograms, the Skeptic, recorded claims and sealed predictions), install the MCP server: `claude mcp add oddsky -- uvx oddsky mcp`, then "Open Oddsky case OS-0022. Run the skeptic first, then try to break the leading hypothesis."

## House rules for agents

1. **Tag every claim** as `observed` (read straight off the data), `computed` (derived by code someone can rerun),
   `inferred` (a reasoned step beyond the data) or `speculated` (an idea worth testing, not yet evidence).
2. **Give receipts.** Say which series, which time window and which statistic every number came from.
3. **Run the Skeptic's questions first.** Is a neighbour blended into the beam? Is a period just the survey's cadence
   or the Moon? Did more than one instrument see it? Did the series start mid-event?
4. **Try to break the leading hypothesis** before you add to it. A hypothesis that predicts nothing can't lose.
5. **Never call something a discovery.** Say what would have to be true, and what observation would prove it wrong.
6. **Credit observers.** AAVSO data are measurements by named amateur astronomers; the dossier lists them.