Extended J-band spectroscopy of red supergiants: Parameter identifiability and metallicity robustness
Year: 2026
Type: article
Abstract: Red supergiants (RSGs) provide a near-infrared metallicity diagnostic complementary to optical hot-supergiant spectroscopy. Their low-resolution extragalactic use requires tests of parameter identifiability and modelling robustness. We quantified the information content of extended (J)-band RSG spectra at (R ≃ 2000) over (1.155)--(1.340,μ ) and assessed the recovery of effective temperature, surface gravity, microturbulence, and metallicity. m We evaluated MARCS/TURBOSPECTRUM spectra via an emulator. A six-node Fisher analysis maps the parameter geometry and wavelength distribution of information, while controlled mocks test recovery, continuum placement, and three fixed carbon, nitrogen, and oxygen (CNO) mixtures. We analysed 21 SpeX spectra of 20 RSG candidates towards Per OB1, using a model-guided continuum treatment, a luminosity-based gravity prior, and diagonal and regularised correlated-residual likelihoods. All four parameters yield measurable spectral responses, but only 8--10% of the raw metallicity information and 4--7% of the gravity information are independent of the other directions. Extending beyond (1.22,μ ) supplies median fractions of 60% of the raw and 66% of the nuisance-orthogonal metallicity information. Surface gravity dominates the weakest Fisher mode, though its prior choice shifts association means by at most 0.03 dex. Matched mocks recover metallicity with a root-mean-square error of (0.04) dex. Standard continuum treatment biases solar-metallicity mocks by about (-0.23) dex, reduced to about (-0.01) dex by our adopted treatment. Plausible CNO mismatch adds a zero-point sensitivity of 0.04--0.05 dex and regularised covariance changes association means by at most 0.03 dex. The preferred analysis gives (〈 ̊angle ≃ -0.10) dex, with a star-to-star dispersion of 0.09 dex. m Z Extended low-resolution (J)-band RSG spectra yield recoverable metallicity and temperature constraints once continuum placement and weak parameter directions are controlled. Per OB1 serves as a validation benchmark, though the absolute scale remains conditional on the adopted stellar-atmosphere and line-formation framework.
Source: Astronomy and Astrophysics
Authors: M. A. Urbaneja, R. P. Kudritzki
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7222924088