1. Stellar Spectroscopy at Appalachian State University R.O. Gray
Department of Physics and Astronomy

3. Stellar spectrograph
mounted on 32”
telescope.

4. A look at our data

5. Spectral Types

6. The NASA Nearby Stars Project
Three year project to obtain Spectral Data for all 3600 Solar-type stars within 40 parsecs (130 light years) of earth. Use these data to determine:
Accurate stellar spectral classifications
Basic Physical Parameters
Levels of Stellar Activity

7. The Project
Program stars are located all over the sky – both Northern and Southern hemispheres
Telescopes enlisted for the Project:
Dark Sky Observatory 0.8m –10o to +50o
David Dunlap Observatory 1.8m (Canada) North Polar Cap
Steward Observatory 2.4m (Kitt Peak) –30o to -10o
Cerro Tololo Interamerican Observatory 1.5m (Chile): remainder of the southern sky.

8. David Dunlap Observatory

9. Steward Observatory (Kitt Peak) 2.4m Bok telescope

10. Cerro Tololo 1.5m telescope

11. Red-eye observing at Cerro Tololo

12. Preparatory science for …

13. SIM Spacecraft Launch Date 2008
SIM slide: Point out individual telescopes and explain what an optical interferometer does – it combines individual telescopes to simulate a single large telescope, with very high resolution. SIM will have such high resolution, that it will be able to directly see the wobbling of stars as Jupiter size planets orbit about them. Thus, it will be able to discover planets and thus solar systems around thousands of nearby stars. Our data will be used by the SIM team to select targets – I.e. stars – for the Space Interferometry mission. It will also be able to determine precise distances to millions of stars, thus greatly increasing our knowledge of astrophysics. Go back to previous slide.

14. TPF Spacecraft Launch Date 2012?
TPF: four freely flying telescopes linked together into an interferometer; NULLing optics are designed to greatly
Reduce the brightness of the star, thus revealing the much fainter planets.

15. TPF Detection of ExoPlanets via Nulling Interferometry

16. Recognition of Earth-like planets:

17. Computational Astrophysics …

18. Stellar Spectral Classification using xmk18

19. How do we determine basic physical parameters
for our stars?
This is done by computing synthetic stellar
spectra and then making a detailed comparison
between the synthetic and observed spectra.
The comparison yields the four basic stellar
parameters: Temperature, acceleration of
gravity at the surface, turbulent velocity,
and overall chemical abundance.

20. Stellar Spectral Synthesis using SPECTRUM … a 25000+ line code
to compute radiative
transfer in a stellar
atmosphere.

21. Spectral Synthesis Detail

22. Calculations are carried out on a three-node
Beowulf machine, called Hrothgar

24. The SIMPLEX algorithm is
a multi-dimensional mini-mization technique. We use it to minimize a 2 formed
from both the line spectrum and fluxes in comparison with a library of synthetic spectra. The SIMPLEX algorithm roams around in the 4-D library of synthetic spectra, interpolating as it goes, until it finds the best fit.
The figure shows how the SIMPLEX algorithm wanders like an amoeba around the (in this case) two dimensional
Space seeking the spot with the mimimum Chi-squared value. The red dot shows the actual minimum of the
test function. The simplex (in this case a triangle – the number of vertices on the simplex is always one greater
than the dimensionality of the function) expands, contracts and translates in its effort to find the minimum. In
our application, the library of synthetic spectra is 4 dimensional, according to the four basic parameters – the
Effective temperature, log(g), the microturbulent velocity and the metalicity [M/H]. Our algorithm can interpolate
Between the grid points for better accuracy.

26. An HR-diagram based
on our spectral types
and Hipparcos parallaxes.

27. An Astrophysical
HR-diagram based
on physical
parameters from the
NStars project.

28. Stars with exo-
planets:
<[M/H]> = -0.02
 = 0.14
Field stars:
<[M/H]> = -0.14
 = 0.16
Student’s t test:
means different to
a confidence of
99.9%