# OS-0005: Breathing in, breathing out

> A giant star swelling and shrinking every 14 months, brightening a thousandfold. Strange to the eye, ordinary to astrophysics.

- **Star:** R Cyg (TYC 3564-982-1, TIC 27082559, ASASSN-V J193649.33+501200.0, WISEA J193649.35+501159.5, WISE J193649.33+501159.4, AKARI-IRC-V1 J1936493+501159, Gaia DR3 2135109439204739200, AAVSO 1934+49, AG+50 1398, BD+49  3064, CCDM J19368+5013A, CSS 1150, DO 37531, GC 27152, GCRV 12027, GEN# +1.00185456, GSC 03564-00982, HD 185456, IDS 19341+4959 A, IRAS 19354+5005, IRC +50301, PPM  37581, RAFGL 2422, S1* 616, SAO  31822, SKY# 36602, V* R Cyg, [LFO93] 1935+50, [LMW2001] 686, 2MASS J19364937+5011597, WDS J19368+5012A, ASAS J193650+5012.0, WEB 16927, Gaia DR2 2135109439204739200, KIC 11868592)
- **Position (J2000, deg):** RA 294.20565827354, Dec 50.19992431583001
- **Status on the discovery ladder:** observation (observation → anomaly → reproduced → interpreted → validated; exits: artifact, closed)
- **Web page:** https://oddsky.ai/case/OS-0005
- **All data (JSON, ~0.1-0.5 MB):** https://oddsky.ai/data/cases/OS-0005.json
- **Case directory in git:** https://github.com/oddsky-org/oddsky/tree/main/cases/OS-0005

## Gaia DR3

| quantity | value |
|---|---|
| Gaia G mag | 9.24 |
| BP−RP | 6.018 |
| distance (pc) | 597.095 |
| absolute G | 0.36 |
| RUWE | 1.42 |
| 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 |
|---|---|---|---|
| `AAVSO:B` | 327 | 1996-09-16 to 2026-10-25 | 4 |
| `AAVSO:CR` | 4 | 2009-10-29 to 2021-05-26 | 4 |
| `AAVSO:CV` | 61 | 2012-09-13 to 2024-11-17 | 4 |
| `AAVSO:I` | 212 | 2004-07-12 to 2024-10-21 | 4 |
| `AAVSO:R` | 336 | 1996-09-16 to 2026-04-05 | 4 |
| `AAVSO:SG` | 1 | 2026-07-29 to 2026-07-29 | 4 |
| `AAVSO:TG` | 418 | 2006-06-29 to 2026-10-16 | 4 |
| `AAVSO:V` | 1583 | 1964-07-21 to 2026-10-25 | 4 |
| `AAVSO:Vis.` | 2827 | 1852-08-29 to 2026-10-23 | 4 |
| `TESS:TESS` | 221 | 2019-07-18 to 2024-01-30 | 4 |

## The Skeptic (deterministic artifact checks)

4 fail, 5 warn, 5 pass, 1 skipped

- **PASS** Neighbours inside the TESS beam (42.0"): 9 Gaia source(s) within 42.0"; brightest contributes 0.2% of the target's G flux at 14.6"
- **PASS** Neighbours inside the AAVSO beam (5.0"): 2 Gaia source(s) within 5.0"; brightest contributes 0.0% of the target's G flux at 4.6"
- **PASS** TESS aperture contamination (CROWDSAP): worst sector: 0.99 of aperture flux is from the target
- **PASS** Independent optical confirmation: optical data from 27 independent source(s): AAVSO observer MVD (740), AAVSO observer SGEA (496), AAVSO observer TRE (436), AAVSO observer MEV (385), AAVSO observer JENJ (132), AAVSO observer LCLA (118), AAVSO observer AAM (107), AAVSO observer KNAA (69), AAVSO observer SRIC (64), AAVSO observer AMIF (53), AAVSO observer MJOE (50), AAVSO observer DFEA (50), AAVSO observer TYGA (47), AAVSO observer GTZ (43), AAVSO observer LOT (42), AAVSO observer GSEB (42), AAVSO observer FGP (39), AAVSO observer WN (37), AAVSO observer TUB (37), AAVSO observer PJEE (35), AAVSO observer BCP (35), AAVSO observer AAUA (34), AAVSO observer LMJ (27), AAVSO observer FGIA (26), AAVSO observer FRL (20), AAVSO observer MZK (20), TESS (146120)
- **WARN** Does AAVSO start at the star's normal brightness?: first 60 days of V: median 7.25; Gaia DR3 (2014-17 mean) implies V = 13.88; difference -6.64 mag. The series begins mid-event: its own median is not the star's normal state.
- **SKIP** Multi-band consistency of the main event: no significant V-band event
- **WARN** Periodicity vs survey rhythms (AAVSO V): strongest period 433.98 d coincides with: matches spectral-window peak at 429.07 d
- **PASS** Periodicity vs survey rhythms (TESS TESS): strongest period 7.50 d is not a known survey/Earth rhythm (not yet evidence it is real)
- **FAIL** TESS dips vs spacecraft events (S40): 2 dip(s); 2 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge
- **FAIL** TESS dips vs spacecraft events (S41): 1 dip(s); 1 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge
- **WARN** TESS dips vs spacecraft events (S54): 3 dip(s); 1 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge
- **FAIL** TESS dips vs spacecraft events (S55): 1 dip(s); 1 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge
- **WARN** TESS dips vs spacecraft events (S56): 6 dip(s); 4 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge
- **FAIL** TESS dips vs spacecraft events (S74): 1 dip(s); 1 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge
- **WARN** Gaia astrometric wobble (RUWE): RUWE = 1.42 1.4: likely an unresolved companion, or a photocentre shifted by variability

## 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-0005. 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.