1,762 research outputs found
Near Infrared Spectroscopy of M Dwarfs. I. CO Molecule as an Abundance Indicator of Carbon
Based on the near infrared spectra of 42 M dwarfs, carbon abundances are
determined from the ro-vibrational lines of CO 2-0 band. We use Teff values
based on the angular diameters if available or apply a logTeff - M3.4 (the
absolute magnitude at 3.4 micron based on the WISE W1 flux and the Hipparcos
parallax) relation to estimate Teff values of objects for which angular
diameters are unknown. Also, we discuss briefly the HR diagram of low mass
stars. On the observed spectrum of M dwarf, the continuum is depressed by the
numerous weak lines of H2O and only the depressed continuum or the pseudo-
continuum can be seen. On the theoretical spectrum of M dwarfs, we find that
the pseudo-continuum can be evaluated accurately thanks to the recent H2O line
database. Then quantitative analysis of the spectrum of M dwarf can be done by
referring to the pseudo-continua both on the observed and theoretical spectra.
Since the basic principle of the spectroscopic analysis should be the same
whether the true- or pseudo-continuum is referred to, the difficulty related to
the continuum in cool stars can in principle be overcome. Then, the numerous CO
lines can be excellent abundance indicators of carbon, since almost all the
carbon atoms are in stable CO molecules whose abundance remains almost
unchanged for the changes of physical condition in the photosphere and,
somewhat unexpectedly, carbon abundances in late-type stars can best be
determined in M dwarfs rather than in solar type stars. The resulting C/Fe
ratios for most M dwarfs are nearly constant at about the solar value based on
the classical high carbon abundance rather than on the recently revised lower
value. This result implies that the solar carbon abundance is atypical for its
metallicity among the stellar objects in the solar neighborhood if the downward
revised solar carbon abundance is correct.Comment: 33 pages, 17 figures, 13 tables + 1 table for electronic version
only, minor changes in abstract, errors corrected in Tables 5, 8, and 10,
corrected typos, accepted by PAS
Propagation of two short laser pulse trains in a -type three-level medium under conditions of electromagnetically induced transparency
We investigate the dynamics of a pair of short laser pulse trains propagating
in a medium consisting of three-level -type atoms by numerically
solving the Maxwell-Schr\"odinger equations for atoms and fields. By performing
propagation calculations with different parameters, under conditions of
electromagnetically induced transparency, we compare the propagation dynamics
by a single pair of probe and coupling laser pulses and by probe and coupling
laser pulse trains. We discuss the influence of the coupling pulse area, number
of pulses, and detunings on the probe laser propagation and realization of
electromagnetically induced transparency conditions, as well on the formation
of a dark state
- …