of stellar photospheres are generally described by a continuum
flux level with absorption lines superimposed upon it. The
absorption lines can be characterized by their wavelength,
depth and shape, which reflect plasma conditions (temperature,
pressure, chemical composition, magnetic field strength) and
atomic parameters (isotope structure, hyperfine structure,
Zeeman splitting, oscillator strengths). The FTS measurements
provide information on a spectral line’s wavelength,
intensity and structure and even the transition energy levels.
When coupled with experimental energy level lifetime measurements
the FTS data lead to transition oscillator strengths. These
data provide the necessary atomic line description that serves
as input for synthetic spectrum codes.
analysis of stellar spectra aims to determine the plasma conditions
using spectral lines having known atomic parameters. In particular,
the chemical composition of the plasma plays an important
role in revealing the dynamical processes at work in stellar
atmospheres and even the past history of the galaxy. Our analysis
of the solar spectrum is directed to quantifying elemental
abundances for use of the Sun as an abundance standard by
using improved atomic data.
many stars hotter than the Sun, the deviation of the chemical
abundance pattern from the solar distribution is marked by
peculiarities in both elemental abundances and isotopic ratios
that have their origins in the dynamics of the atmosphere.
It is theorized that a delicate balance of forces involving
radiation and gravity is responsible for creating the quiet
conditions in the stellar atmosphere that allow atom/ions
to diffuse to higher or lower atmospheric depths. Our observations
of these chemically peculiar stars are directed to defining
peculiar element abundance distributions as well as isotopic
anomalies for the various types of peculiar stars.
compositions in stellar atmospheres may also be different
from the solar distribution due to the original composition
of the star forming clouds. The early history of the Galaxy
can be studied from the spectra of halo stars. Our laboratory
data are being applied to revealing the age of the Galaxy,
through observation of spectral lines of radioactive elements,
and the mechanisms for the creation of elements from its earliest
generations of stars.