Stellar Secrets: Mapping M Dwarfs with SAPP

M dwarfs, making up over 70% of stars in the solar neighborhood, are central to the search for Earth-like exoplanets. Their small sizes and low luminosities make it easier to detect orbiting planets using radial velocity and transit methods. Despite their significance, analyzing M dwarfs is a challenge due to their complex spectra filled with molecular lines, especially in the optical range. The Stellar Abundances and atmospheric Parameters Pipeline (SAPP), originally designed for FGK stars, has been adapted to handle M dwarfs using spectroscopic data primarily in the near-infrared (NIR) H-band, where fewer molecular lines allow clearer analysis.

The SAPP Adaptation for M Dwarfs

The modified SAPP focuses on deriving three key parameters for M dwarfs: effective temperature (Teff), surface gravity (log g), and metallicity ([Fe/H]). Unlike FGK stars, M dwarfs lack detectable pulsations, making it necessary to use photometry and stellar models to constrain log g. The spectroscopic module relies on a machine learning algorithm called The Payne, which fits synthetic spectra to observed data to estimate these stellar parameters.

Sample Selection and Data

To test the pipeline, the researchers used 26 M dwarfs from the APOGEE survey, part of the Sloan Digital Sky Survey (SDSS-IV). The sample includes a variety of M dwarfs, along with a few binary stars and K dwarfs for comparison. APOGEE’s high-resolution spectrographs provided spectra in the H-band, which the modified SAPP analyzed to derive stellar parameters.

Methods and Modifications

A key feature of the modified SAPP is the use of a synthetic pseudo-continuum to account for molecular absorption in M dwarfs. The spectroscopic module iteratively adjusts the observed spectra to match this pseudo-continuum, improving the accuracy of parameter estimates. The pipeline also incorporates photometric data to refine the surface gravity estimates and reduce parameter degeneracies common in M dwarf spectra.

Results and Validation

The pipeline was validated by comparing its results with reference values from interferometric measurements and previous studies. The effective temperature estimates were typically within 100 K of reference values, while surface gravity and metallicity had uncertainties of 0.1 dex and 0.15 dex, respectively. These results indicate that the modified SAPP performs well on M dwarfs, with future improvements expected to enhance its precision.

Conclusion

This study demonstrates the feasibility of adapting the SAPP for M dwarfs, an important step in preparing for upcoming missions like ESA’s Plato, which will survey thousands of M dwarfs for habitable planets. The researchers identified areas for further development, including the addition of Bayesian inference and a full chemical abundance analysis, to maximize the pipeline’s potential.

Source: Olander