Understanding the physical properties of young M dwarfs: NIR spectroscopic studies

Abstract

ABSTRACT We present here medium resolution (λ/Δλ ∼ 1200) H- and K-band spectra of M-type dwarf stars covering the wavelength ranges 1.50–1.80 μm and 1.95–2.45 μm. The sample includes 53 dwarf stars (M0V–M7V) from new observations using the TIFR Near-Infrared Spectrometer and Imager instrument on the 2-m Himalayan Chandra Telescope. Using interferometrically measured effective temperature (Teff), radius and luminosity of nearby bright calibrator stars, we have created new empirical relationships among those fundamental parameters and spectral indices. The equivalent widths of H-band spectral features like Mg (1.57 μm), Al (1.67 μm) and Mg (1.71 μm), and the H2O–H index are found to be good indicators of Teff, radius and luminosity and we establish linear functions using these features relating to those stellar parameters. The root-mean-squared error of our best fits are 102 K, 0.027$\, \mathrm{R}_{\odot }$ and 0.12 dex respectively. Using spectral-type standards along with known parallaxes, we calibrate both H- and K-band H2O indices as a tracer of spectral type and absolute Ks magnitude. Metallicities of M-dwarf samples are estimated using the K-band calibration relationships. The masses of M dwarfs could be determined using the luminosity ($L/{\rm L_\odot }$) and we establish a new empirical relation for this. We also compare and contrast our results with other similar work from the literature.