# OS-0010: The young star nobody classified > Listed as a 'suspected variable' for decades. Gaia, ZTF and NEOWISE agree: a young star in Perseus whose own disk keeps blotting it out. - **Star:** NSV 1302 (TIC 26438706, Gaia DR3 219832339066395776, NSV 1302, 2MASS J03474294+3500441, Gaia DR2 219832339066395776) - **Position (J2000, deg):** RA 56.92895976487, Dec 35.01226990153 - **Status on the discovery ladder:** interpreted (observation → anomaly → reproduced → interpreted → validated; exits: artifact, closed) - **Web page:** https://oddsky.ai/case/OS-0010 - **All data (JSON, ~0.1-0.5 MB):** https://oddsky.ai/data/cases/OS-0010.json - **Case directory in git:** https://github.com/oddsky-org/oddsky/tree/main/cases/OS-0010 ## Gaia DR3 | quantity | value | |---|---| | Gaia G mag | 12.56 | | BP−RP | 1.188 | | Teff (K) | 5265.815 | | distance (pc) | 388.809 | | absolute G | 4.611 | | RUWE | 0.991 | | non_single_star | 0 | ## Where the argument stands NSV 1302 surfaced from Oddsky hunt H-0001 as the only unexplained survivor of 22,125 Gaia-selected fading Sun-like stars. It is a known young star in Per OB2; its data show an irregular disk-occultation 'dipper': 1.2 mag swings in ZTF, chromatic Gaia dips, and a warm infrared excess. A modest result, recorded honestly. ## Light curves Each light curve is `series[":"]` 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 | |---|---|---|---| | `GAIA:BP` | 44 | 2014-09-04 to 2017-03-15 | 4 | | `GAIA:G` | 49 | 2014-09-04 to 2017-03-15 | 4 | | `GAIA:RP` | 44 | 2014-09-04 to 2017-03-15 | 4 | | `NEOWISE:W1` | 21 | 2014-02-19 to 2024-01-31 | 4 | | `NEOWISE:W2` | 21 | 2014-02-19 to 2024-01-31 | 4 | | `TESS:TESS` | 41 | 2019-11-04 to 2024-12-18 | 4 | | `ZTF:ZTF_g` | 450 | 2018-07-14 to 2025-10-20 | 4 | | `ZTF:ZTF_i` | 33 | 2018-09-26 to 2024-01-15 | 4 | ## The Skeptic (deterministic artifact checks) 0 fail, 3 warn, 9 pass, 0 skipped - **PASS** Neighbours inside the NEOWISE beam (6.1"): no Gaia source within 6.1" - **PASS** Neighbours inside the TESS beam (42.0"): 6 Gaia source(s) within 42.0"; brightest contributes 0.8% of the target's G flux at 13.4" - **PASS** Neighbours inside the ZTF beam (2.0"): no Gaia source within 2.0" - **PASS** WISE saturation: all visits fainter than the W1/W2 saturation limits - **PASS** NEOWISE single-exposure quality cuts: 276 exposures; cuts removed up to 28 (10%) per band; 0 visits kept with fewer than 3 exposures - **WARN** Independent optical confirmation: optical data from 1 independent source(s): ZTF (483). One instrument or observer is a single point of failure; seek a second. TESS is not counted: it is normalised per sector, so it confirms an event only if a sector overlaps it, and never its absolute depth. - **PASS** Periodicity vs survey rhythms (GAIA_EPOCH G): strongest period 200.56 d is not a known survey/Earth rhythm (not yet evidence it is real) - **PASS** Periodicity vs survey rhythms (TESS TESS): strongest period 2.19 d is not a known survey/Earth rhythm (not yet evidence it is real) - **WARN** Periodicity vs survey rhythms (ZTF ZTF_g): strongest period 0.99 d coincides with: matches spectral-window peak at 1.00 d; sidereal day; solar day; best period above 2 d: 179.9 d (half year (NEOWISE cadence); matches spectral-window peak at 181.78 d; matches spectral-window peak at 184.01 d) - **PASS** TESS dips vs spacecraft events (S18): 3 dip(s); 0 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge - **WARN** TESS dips vs spacecraft events (S86): 3 dip(s); 1 sit within 0.3 d of a momentum dump or 1 d of a sector/orbit edge - **PASS** Gaia astrometric wobble (RUWE): RUWE = 0.99 (single-star-like astrometry) ## Claims so far - **C1** `observed` Found by Oddsky hunt H-0001 (Gaia-selected fading Sun-like stars) as one of 18 stars with Gaia dips deeper than 0.8 mag on 2+ transits, and the only one of them not already catalogued as an eclipsing binary, a blend, or a variable of known type. - **C2** `computed` ZTF g (450 points, 2018-2025) varies irregularly by 1.2 mag (2nd-98th percentile) about a 13.26 median, with no long-term trend (0.004 mag/yr) and no significant period between 1 and 60 days (top power 0.05). (receipts: K2, K4) - **C3** `computed` On Gaia transits BP and RP dim together, dBP/dRP = 1.32 with r = 0.98: chromatic, as dust is, but greyer than interstellar dust, which hints at large grains. (receipts: K8) - **C4** `computed` NEOWISE W1-W2 = 0.43 (median of 21 visits): a strong excess from warm dust, as an inner disk produces. (receipts: K7) - **C5** `inferred` TESS shows 'dips' of 0.7-2.5 mag lasting only 1-3 hours in two sectors. Disk occultations last longer than that; these are treated as probable systematics until checked against target pixels. (receipts: K6, K9) - **C6** `observed` SIMBAD lists the star only as a generic star (''). It appears in a 2015 WISE census of young stellar objects in Per OB2 and in membership lists of young Perseus groups, but no SIMBAD-indexed paper describes its dimming. (receipts: K1) ## Hypotheses - **H1** (yso_dipper, live): A young star in Per OB2 whose inner disk intermittently blocks it (an irregular 'dipper'). - *Would falsify:* A strict period (spots or an eclipsing companion), or no infrared excess. - **H2** (rotation_spots, live): Spots on a young, active star. - *Would falsify:* Spots give periodic, low-amplitude (<0.3 mag) modulation; ZTF shows no period and 1.2 mag swings. - **H3** (eclipse_companion, live): Eclipses by a companion. - *Would falsify:* Needs periodic dips; none found. - **H4** (artifact_instrumental, live): The variability is instrumental. - *Would falsify:* Gaia and ZTF independently show chromatic dimming; only the TESS hour-long dips are suspect. ## 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-0010. 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.