Correct a giant's light by its type, not by the cooler dwarf its colour reads as

3392f06 read every star's bolometric correction off the dwarf sequence at its colour, so a giant
got the correction of the cooler dwarf of that colour, which is larger. Antares, M1 Ib at B−V 1.87,
took an M5 dwarf's −3.26 and came out 172 023 L☉ and 1 516 R☉, a 7.06 AU sphere, against the 680 R☉
Ohnaka et al. (2013) measure; 119 Tau 2 838 against 587, Menkar 204 against 89.

isGiant (spectral.ts) reads luminosity class I to III off a type's primary component, or HYG's g
and c prefixes, and a giant keeps its type's correction. Drawn radius against the published one
(no planets, so derived), before and after: Antares 2.23 -> 1.01, 119 Tau 4.84 -> 1.43, Menkar 2.29
-> 1.80, Scheat 1.92 -> 1.42, Aldebaran 1.95 -> 1.10, Mirach 1.96 -> 1.27, 41 Com 2.14 -> 1.56;
Betelgeuse 0.76 -> 0.89. It is not better everywhere: Gacrux goes from 1.23 to 1.40 and Arcturus
from 1.02 to 0.88. 10 808 stars have a giant's type, 10 794 of them a colour. Against the archive's
own luminosity for the 130 giant hosts, the median error moves from 0.038 to 0.052 dex and the 90th
percentile from 0.246 to 0.204; 17 are off by over 1.5 times, against 19.

Controls, each failing its named test (1 of 781): the giant given the dwarf's correction, a giant
companion read as the primary, a IV read as a I, and the prefixes ignored.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/app/shared/astro/stellar.spec.ts

@@ -122,6 +122,18 @@ describe('luminositySolar', () => {
     expect(derived / 5.53e-4).toBeLessThan(1.5);
   });
 
+  it("gives a giant its type's correction, not the cooler dwarf's its colour reads as", () => {
+    // Antares, M1 Ib at B−V 1.87 and 170 pc, and Aldebaran, K5 III: 680 R☉ (Ohnaka et al. 2013)
+    // and 44.2 (Richichi & Roccatagliata 2005). As dwarfs they came out 1 516 and 86.
+    const antares = { magnitude: 1.06, distancePc: 169.78, spectralType: 'M1Ib + B2.5V', magnitudeBand: 'V', colorIndex: 1.865, colorSystem: 'B-V' } as const;
+    const aldebaran = { magnitude: 0.87, distancePc: 20.433, spectralType: 'K5III', magnitudeBand: 'V', colorIndex: 1.538, colorSystem: 'B-V' } as const;
+    for (const [star, published] of [[antares, 680], [aldebaran, 44.2]] as const) {
+      const radius = radiusFromLuminositySolar(luminositySolar(star)!, effectiveTemperatureK(star)!);
+      expect(radius / published).toBeGreaterThan(1 / 1.2);
+      expect(radius / published).toBeLessThan(1.2);
+    }
+  });
+
   it('clamps a pathological record instead of producing an absurd luminosity', () => {
     const absurd = luminositySolar({ magnitude: -40, distancePc: 5000, spectralType: 'O5V' })!;
     expect(Number.isFinite(absurd)).toBe(true);