Spectral Type: L

Abstract

The characteristic properties of type L stars – including spectra, mass, and luminosity – are briefly described, followed by notes about a few well-known examples.

Keywords: Spectral type L

Introduction

“As mass and luminosity drop, so does the surface temperature, making low-end stars (and brown dwarfs) so cool that they radiate most of their light in the infrared. Cameras designed to observe in the infrared reveal them easily, allowing the discovery of bodies so cool that astronomers have had to invent a whole new spectral class for them, class L (a letter originally used by Pickering and co-workers, but dropped as un-needed). In keeping with classical spectral taxonomy, the “L-stars” are characterized not by temperature but by spectral characteristics. They are so cool that titanium and vanadium oxide bands weaken and disappear (as the metals condense onto solid grains) and are replaced by metallic hydrides, chromium hydride (CrH) and iron hydride (FeH) being prominent. Absorptions of neutral metals – sodium, rubidium, cesium, even lithium – become important as well, depending on temperature, and the L stars [are] decimalized like the others. Temperature of stars with such complex spectra are difficult to measure. The coolest M stars hover around 2000 K. At L2 the temperature seems to be around 1900 K, dropping to perhaps as low as 1800 K by L4 and to 1500 K at L9” (Kaler 2001, p. 46).

Characteristics

Spectra

Occurrence

SAO# = SAO catalogue number, HD# = Henry Draper catalogue number, Bayer = Bayer (or Flamsteed) reference, R.A. = right ascension, Dec = declination, Type = spectral type, Lum = luminosity class, Mag(V) = apparent visual magnitude, #Components = number of visual components in multiple systems (after Ochsenbein & Halbwachs 1987, except where otherwise noted). < /p >

Mass and Luminosity

Variability/Mass Loss

Summary

Interpretation

Examples

References

Kaler, James B. 2001: Extreme stars. Cambridge University Press, 236 pp.

Ochsenbein F.; Halbwachs J.L. 1987: Le Catalogue des Etoiles les Plus Brillantes (Catalogue of the Brightest Stars). Bull. Inform. CDS 32, 83.  NASA Astronomical Data Centre, catalogue 5053A.

Smith, W.B. 1996: FK5 – SAO – HD – Common Name Cross Index.  NASA Astronomical Data Centre, catalogue 4022.