# OS-0006: The star that won't stay quiet

> Every few weeks, for a century of amateur records, it leaps fiftyfold in brightness in a day. Something is feeding on its neighbour.

- **Star:** SS Cyg (TIC 190696047, UCAC4 668-104538, WISE J214242.91+433510.2, LAMOST J214242.80+433509.8, WISEA J214242.90+433510.3, Gaia DR3 1972957892448494592, SRGA J214243.4+433509, 3XMM J214242.9+433510, [KRL2007b] 389, PLX 5240, SBC9 1326, 1H 2140+433, 2E  4511, 2RE J2142+433, 3A 2140+433, AAVSO 2138+43, ALS 11959, BD+42  4189a, CSI+42  4189  1, EM* CDS 1268, GCRV 13641, GEN# +1.00206697, HD 206697, INTEGRAL1 121, KPD 2140+4321, LS III +43   24, RE J2142+433, RE J214241+433511, SBC7   872, SV* HV    84, TYC 3196-723-1, UBV M  50941, UCAC2  46852538, USNO 568, V* SS Cyg, [BM83] X2140+433, [FS2003] 1134, [KW97] 59-12, PLX 5240.00, 1E 2140.7+4321)
- **Position (J2000, deg):** RA 325.67834770733, Dec 43.58607440069
- **Status on the discovery ladder:** observation (observation → anomaly → reproduced → interpreted → validated; exits: artifact, closed)
- **Web page:** https://oddsky.ai/case/OS-0006
- **All data (JSON, ~0.1-0.5 MB):** https://oddsky.ai/data/cases/OS-0006.json
- **Case directory in git:** https://github.com/oddsky-org/oddsky/tree/main/cases/OS-0006

## Gaia DR3

| quantity | value |
|---|---|
| Gaia G mag | 11.671 |
| BP−RP | 1.177 |
| Teff (K) | 5582.823 |
| distance (pc) | 112.942 |
| absolute G | 6.407 |
| RUWE | 2.327 |
| 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` | 2166 | 1966-09-07 to 2026-10-25 | 4 |
| `AAVSO:CR` | 269 | 1959-08-29 to 2024-12-30 | 4 |
| `AAVSO:CV` | 1489 | 2005-07-11 to 2026-10-24 | 4 |
| `AAVSO:I` | 2794 | 2002-10-08 to 2026-10-25 | 4 |
| `AAVSO:R` | 2082 | 1993-08-22 to 2026-10-25 | 4 |
| `AAVSO:SG` | 4 | 2024-11-16 to 2025-08-07 | 4 |
| `AAVSO:SI` | 4 | 2024-11-16 to 2025-08-07 | 4 |
| `AAVSO:SR` | 4 | 2024-11-16 to 2025-08-07 | 4 |
| `AAVSO:TB` | 356 | 2010-07-20 to 2026-08-15 | 4 |
| `AAVSO:TG` | 986 | 2006-06-29 to 2026-10-26 | 4 |
| `AAVSO:TR` | 423 | 2010-10-05 to 2026-08-15 | 4 |
| `AAVSO:V` | 2051 | 1966-09-07 to 2026-10-24 | 4 |
| `AAVSO:Vis.` | 2186 | 1889-11-06 to 2026-10-24 | 4 |
| `NEOWISE:W1` | 20 | 2014-06-13 to 2024-06-11 | 4 |
| `NEOWISE:W2` | 21 | 2014-06-13 to 2024-06-11 | 4 |
| `TESS:TESS` | 123 | 2019-08-15 to 2024-09-30 | 4 |

## The Skeptic (deterministic artifact checks)

1 fail, 6 warn, 8 pass, 0 skipped

- **PASS** Neighbours inside the NEOWISE beam (6.1"): 1 Gaia source(s) within 6.1"; brightest contributes 1.0% of the target's G flux at 5.3"
- **PASS** Neighbours inside the TESS beam (42.0"): 18 Gaia source(s) within 42.0"; brightest contributes 1.5% of the target's G flux at 12.7"
- **PASS** Neighbours inside the AAVSO beam (5.0"): no Gaia source within 5.0"
- **WARN** TESS aperture contamination (CROWDSAP): worst sector: 0.84 of aperture flux is from the target
- **WARN** WISE saturation: 1 of 42 visits are at or brighter than saturation (W1<8, W2<7)
- **PASS** NEOWISE single-exposure quality cuts: 396 exposures; cuts removed up to 85 (21%) per band; 0 visits kept with fewer than 3 exposures
- **PASS** Independent optical confirmation: optical data from 216 independent source(s): AAVSO observer SHPI (76939), AAVSO observer JM (46811), AAVSO observer ATE (40918), AAVSO observer GFB (31550), AAVSO observer PVA (30229), AAVSO observer LMN (28682), AAVSO observer LMA (26924), AAVSO observer MXL (17524), AAVSO observer CCHD (16685), AAVSO observer JSJA (15231), AAVSO observer BJAK (14525), AAVSO observer HBB (12678), AAVSO observer KTU (11620), AAVSO observer JJI (11435), AAVSO observer TPV (11217), AAVSO observer TRT (9894), AAVSO observer TFUA (8789), AAVSO observer HUZ (8251), AAVSO observer JPG (6880), AAVSO observer KPK (6683), AAVSO observer TRE (5812), AAVSO observer OFA (5503), AAVSO observer FJQ (5287), AAVSO observer SDB (5255), AAVSO observer MMAO (5208), AAVSO observer RBCA (5187), AAVSO observer CTX (4694), AAVSO observer RFDA (4527), AAVSO observer SGRA (3992), AAVSO observer MZK (3760), AAVSO observer KMI (3423), AAVSO observer BXS (2943), AAVSO observer OAR (2929), AAVSO observer SGOR (2843), AAVSO observer PSD (2771), AAVSO observer VMT (2730), AAVSO observer BETB (2035), AAVSO observer BDG (1942), AAVSO observer SJAR (1899), AAVSO observer CMP (1889), AAVSO observer PJEE (1884), AAVSO observer BKL (1735), AAVSO observer GBL (1555), AAVSO observer TDY (1536), AAVSO observer DUBF (1486), AAVSO observer DROJ (1481), AAVSO observer LMJ (1424), AAVSO observer WGR (1411), AAVSO observer DGSA (1388), AAVSO observer GKA (1279), AAVSO observer BPAK (1225), AAVSO observer RJWA (1223), AAVSO observer HKEB (1145), AAVSO observer SIAK (1095), AAVSO observer KMP (1083), AAVSO observer DJED (1029), AAVSO observer SGEA (1006), AAVSO observer RHM (995), AAVSO observer SRIC (990), AAVSO observer DFS (936), AAVSO observer HDE (936), AAVSO observer SKA (861), AAVSO observer PJT (840), AAVSO observer WDAE (778), AAVSO observer WTHB (665), AAVSO observer WIV (638), AAVSO observer PJMB (619), AAVSO observer YIGA (558), AAVSO observer CMM (528), AAVSO observer PHA (527), AAVSO observer GLAA (525), AAVSO observer VJA (518), AAVSO observer DIL (507), AAVSO observer RIV (505), AAVSO observer PRV (491), AAVSO observer OYE (488), AAVSO observer MRV (481), AAVSO observer NOT (471), AAVSO observer BJAA (462), AAVSO observer DERA (459), AAVSO observer VRG (454), AAVSO observer BDQ (447), AAVSO observer ODEA (439), AAVSO observer LBG (424), AAVSO observer KADB (417), AAVSO observer BLEB (410), AAVSO observer WKL (405), AAVSO observer MJOD (403), AAVSO observer VYP (392), AAVSO observer PXR (388), AAVSO observer MEV (382), AAVSO observer KVTA (361), AAVSO observer SHRA (354), AAVSO observer DMAC (347), AAVSO observer FSRA (346), AAVSO observer KWKA (343), AAVSO observer GSEB (337), AAVSO observer PEDB (336), AAVSO observer SGCA (323), AAVSO observer SLQ (307), AAVSO observer ROE (299), AAVSO observer NMR (290), AAVSO observer NKEA (269), AAVSO observer FGP (245), AAVSO observer MMIW (236), AAVSO observer QLEA (226), AAVSO observer SDM (218), AAVSO observer PIV (208), AAVSO observer PAH (200), AAVSO observer ZRE (193), AAVSO observer DMN (193), AAVSO observer RCCA (189), AAVSO observer OJJ (186), AAVSO observer BCP (182), AAVSO observer FDAD (181), AAVSO observer GCHB (179), AAVSO observer PDM (176), AAVSO observer BOA (169), AAVSO observer HWAC (160), AAVSO observer SDN (157), AAVSO observer SHS (157), AAVSO observer VBPA (145), AAVSO observer BJFB (134), AAVSO observer BYZ (132), AAVSO observer CMAF (128), AAVSO observer LPAC (125), AAVSO observer AUMA (122), AAVSO observer PEJ (120), AAVSO observer FGI (116), AAVSO observer BJOK (113), AAVSO observer FRGA (111), AAVSO observer KPRB (109), AAVSO observer WME (107), AAVSO observer RMU (106), AAVSO observer PMAV (106), AAVSO observer BRIA (105), AAVSO observer FRL (104), AAVSO observer UJHA (104), AAVSO observer GTOA (104), AAVSO observer PTFA (102), AAVSO observer FMDC (100), AAVSO observer KMD (95), AAVSO observer RES (95), AAVSO observer PMAK (86), AAVSO observer DPOA (86), AAVSO observer MLHA (85), AAVSO observer CGRE (85), AAVSO observer CKU (84), AAVSO observer KMWA (82), AAVSO observer SANGA (81), AAVSO observer OCN (75), AAVSO observer FMG (74), AAVSO observer KSQ (74), AAVSO observer AAM (73), AAVSO observer CMD (72), AAVSO observer MGW (71), AAVSO observer BHOB (70), AAVSO observer VPAD (69), AAVSO observer HJW (67), AAVSO observer TIA (64), AAVSO observer BAAE (64), AAVSO observer HJA (64), AAVSO observer FDA (61), AAVSO observer MJOE (58), AAVSO observer BANP (58), AAVSO observer SJMJ (56), AAVSO observer GRL (56), AAVSO observer AMN (55), AAVSO observer WMOB (54), AAVSO observer DFEA (53), AAVSO observer PBC (51), AAVSO observer SNOB (51), AAVSO observer CPE (50), AAVSO observer LWHA (50), AAVSO observer ASAL (49), AAVSO observer KPI (48), AAVSO observer DPP (47), AAVSO observer RAEA (47), AAVSO observer BVS (46), AAVSO observer FERA (43), AAVSO observer SSTC (42), AAVSO observer CRI (41), AAVSO observer JGRC (39), AAVSO observer PYG (36), AAVSO observer LDAD (36), AAVSO observer BFX (36), AAVSO observer PKV (35), AAVSO observer SVI (35), AAVSO observer WKE (34), AAVSO observer FGIA (32), AAVSO observer UMAA (31), AAVSO observer TYS (30), AAVSO observer SABB (29), AAVSO observer PRI (29), AAVSO observer BVE (29), AAVSO observer MNIC (29), AAVSO observer WMG (29), AAVSO observer PSW (27), AAVSO observer SFK (27), AAVSO observer GTZ (27), AAVSO observer WCR (26), AAVSO observer CANG (26), AAVSO observer HPIA (25), AAVSO observer CRR (24), AAVSO observer HGUA (24), AAVSO observer OAD (24), AAVSO observer SKRC (24), AAVSO observer CXR (23), AAVSO observer SSTA (22), AAVSO observer RMQ (22), AAVSO observer KTHA (20), AAVSO observer LGO (20), AAVSO observer WJD (20), AAVSO observer CK (20), AAVSO observer MAV (20), TESS (340885)
- **WARN** Does AAVSO start at the star's normal brightness?: first 60 days of V: median 11.21; Gaia DR3 (2014-17 mean) implies V = 11.96; difference -0.75 mag. The series begins mid-event: its own median is not the star's normal state.
- **PASS** Multi-band consistency of the main event: deepest V event at MJD 57442: change vs. out-of-event median per band B -1.95, V -1.63
- **PASS** Periodicity vs survey rhythms (AAVSO V): strongest period 55.66 d is not a known survey/Earth rhythm (not yet evidence it is real)
- **PASS** Periodicity vs survey rhythms (TESS TESS): strongest period 50.35 d is not a known survey/Earth rhythm (not yet evidence it is real)
- **FAIL** TESS dips vs spacecraft events (S15): 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 (S16): 2 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): 5 dip(s); 4 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge
- **WARN** Gaia astrometric wobble (RUWE): RUWE = 2.33 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-0006. 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.