NutMaat: A Python package for stellar spectral classification on the MK system
Bibliographic record
Abstract
Stellar spectral classification according to the Morgan-Keenan (MK) system remains fundamental to astrophysical studies, yet modern surveys require automated, scalable tools. We present NutMaat, an open-source Python-based package inspired by MKCLASS, designed to automate MK classification while addressing scalability and usability limitations. It employs modern computational tools for batch processing and offers a modular architecture that enables efficient, platform-independent analysis of large spectral datasets. It also includes modules for detecting classical chemically peculiar stars, such as Am, Ap, and $λ$ Boo types, using internal consistency checks between different line diagnostics. Tested on the CFLIB and MILES libraries, NutMaat achieved spectral and luminosity classification accuracies comparable to MKCLASS, with minimal systematic offsets and a robust performance down to S/N $\le$ 10. NutMaat successfully identified chemically peculiar stars, tested on LAMOST DR7 ACV variables, and processed the SDSS-IV MaStar library -- which lacks native MK classifications -- to produce a stellar catalog, demonstrating survey readiness. Future development of NutMaat will focus on extending wavelength coverage beyond the 3800--5600 $Å$ range, computational acceleration via Cython, and refining peculiarity classification. Beyond its technical design, NutMaat can provide consistent, MK-standard classification across large-scale spectroscopic surveys, facilitating reliable stellar population analyses, identification of rare objects, and the construction of high-quality spectral catalogs essential for galactic archaeology and stellar evolution studies. As an open-source tool, NutMaat bridges traditional MK methods with modern data workflows, offering a scalable solution for current and future spectroscopic surveys.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.005 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.004 | 0.003 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.052 | 0.050 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".