Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis in honor of David L. Lambert ASP Conference Series, Vol. 336, 2005 Thomas G. Barnes III and Frank N. Bash The of Arcturus from the through the Ultraviolet

Kenneth Hinkle, Lloyd Wallace National Optical Observatory, P.O. Box 26732, Tucson, AZ 85726

Abstract. The spectrum of the bright K giant Arcturus has been observed at high resolution over nearly a factor of 50 in from 1150 A˚ in the ultra- violet to 5 µm in the infrared. A compressed view of the spectrum is presented in the figures. The observations, from both ground and space based facilities, illustrate changes resulting from variations in optical depth and transition en- ergy with wavelength. The high resolution spectra as well as the digital data are available in a series of atlases published by Astronomical Society of the Pacific.

1. Overview of the Figures

The spectrum of the bright K giant Arcturus has been observed at high resolu- tion over nearly a factor of 50 in wavelength. A compressed view of the spectrum is presented in the figures. The 1000 to 3100 A˚ region was observed with STIS on HST. The 3100 to 9000 A˚ region was observed by the ´echelle spectrograph on the Kitt Peak coud´e feed telescope. The 0.9 to 5 µm region was observed with a Fourier transform spectrometer at the KPNO 4 m telescope. The observations were all obtained at resolving power 100000. From the mid-optical through th∼e infrared, telluric absorption lines are present in the observed spectrum. For observations with telluric contamination, a reference pure telluric spectrum has been computed by ratioing solar spectra. This reference spectrum has been divided into the observed Arcturus spectrum. In those areas where the telluric spectrum is optically thick, we have placed gaps in the plotted Arcturus spectrum. The Arcturus spectrum changes dramatically from atomic and molecular emission lines in the ultraviolet to dense absorption by atomic lines in the optical to dominance by diatomic molecular bands in the infrared. The impressive conversion from absorption to emission results from changing optical depth and contrast with the Teff 4300 K photosphere. Equally as interesting is the sorting of transition types∼ by wavelength. The typical 0.5 eV transition energy of infrared lines matches that of molecular vibration-rotation transitions while the energies typical of the violet match typical atomic and molecular electronic transitions. The spectra displayed here are high resolution observations plotted on a compressed scale so that individual spectral lines are shown as sharp unresolved lines. The abscissa is wavelength in Angstroms.˚ In the infrared and optical regions the ordinate is relative intensity normalized to the continuum. At wave- lengths shorter than 3100 A˚ the ordinate is in flux units displayed on a log-linear scale. 321 322 Hinkle & Wallace Arcturus Spectrum – IR to UV 323 324 Hinkle & Wallace Arcturus Spectrum – IR to UV 325 326 Hinkle & Wallace

Throughout only the major features are identified. The detailed spectra, plotted on a scale to resolve the spectral lines and with extensive line identifi- cations, can be found in a series of three atlases available from ASP (Hinkle et al. 1995, 2000, 2005).

2. Acknowledgements

This work is based on observations made with the NASA/ESA Hubble Space Telescope (HST), obtained from the data archive at the Space Telescope Science Institute (STScI). STScI is operated by AURA under NASA contract NAS 5- 26555. These observations are associated with programs GO-7263, GO-7733, and GO-8614. Support for programs GO-7263 [Valenti], GO-7733 [Ayres], and GO-8614 [Hinkle] was provided by NASA through grants from STScI. Program GO-7733 was a continuation of the failed program GO-6066.

References

Hinkle, K., Wallace, L., & Livingston, W. 1995, Infrared Atlas of the Arcturus Spectrum, 0.9 - 5.3 microns (San Francisco: ASP) Hinkle, K., Wallace, L., Valenti, J., & Harmer, D. 2000, Visible and Near Infrared Atlas of the Arcturus Spectrum, 3727 - 9300 A˚ (San Francisco: ASP) Hinkle, K., Wallace, L., Valenti, J., & Ayres, T. 2005, Ultraviolet Atlas of the Arcturus Spectrum, 1150 – 3800 A˚ (San Francisco: ASP), in press