Testing Pre-main-sequence Evolutionary Models with Gaia and SPHEREx Observations of Canis Major North

Abstract

Pre-main-sequence (PMS) evolutionary models can assign different ages across stellar mass within the same population. We use joint Gaia and SPHEREx spectral energy distributions to infer effective temperatures, radii, and luminosities for members of Canis Major North (CMaN), a nearby association with independent lithium and kinematic age constraints near 23 Myr. The SPHEREx fluxes agree with 2MASS and WISE photometry to 3--6\%, and we anchor the absolute flux scale to Gaia, 2MASS, and WISE. Using the revised temperatures, we obtain a lithium age of $22.4^{+2.8}_{-1.5}$ Myr. For a 29-star PMS sample, population-wide HR-diagram fits yield $20.5^{+1.5}_{-1.4}$ Myr for unspotted SPOTS models, consistent with the external constraints, $18.4^{+1.4}_{-1.3}$ and $18.7^{+1.3}_{-1.2}$ Myr for the Feiden nonmagnetic and BHAC15 models, and substantially older ages of $32.2^{+2.3}_{-2.1}$ and $55^{+5}_{-5}$ Myr for the Feiden magnetic and PARSEC models. No grid returns a temperature-independent age. The Feiden, SPOTS, and BHAC15 models assign older ages to stars above $4000$ K, whereas PARSEC assigns increasingly older ages toward lower temperatures. The intrinsic luminosity dispersion is also mass dependent, approximately $0.14$ dex below $3450$ K but $0.05$ dex at intermediate temperatures. At a fixed age of 23.0 Myr, a single SPOTS filling factor cannot reproduce the width of the low-temperature sequence, whereas the empirical filling-factor distribution of young stars overpredicts it. Spotted isochrones can enclose every cool member only at ages of 37--50 Myr, inconsistent with the lithium and kinematic ages.