Detailed Far-UV Spectral Atlas of O Main Sequence Stars
Myron A. Smith
The far-UV spectral atlas of O stars
contains high resolution data in the far-UV wavelength region (defined here
as the range 930-1188 Ångstroms) for 25 O stars in the Galaxy and Magellanic
clouds between spectral types O2 and O9.5
were obtained from the MAST/FUSE data archives (Far Ultraviolet Spectroscopic Explorer).
The star list consists of three parallel
spectral type sequences, Galactic main sequence (luminosity classes III-I),
Galactic supergiants, and low metallicity stars in the Small or Large Magellanic clouds.
This atlas has been published
by the IOP (Institute of Physics) Press as an Astrophysical Journal Supplement
both in paper and on-line formats.
The FITS-formatted data on which the atlas is based as well as the complete
spectral line identification tables are available only through this website.
The conception of this atlas is similar to that of the far-UV spectral atlas of B
stars (Smith 2010).
The atlas actually consists of three parts. The first is the FITS data files of
25 stars given in the table below. These are comprised of merged spectra in each
of the two FUSE detector "sides." The files consist of two FITS extensions, each
representing the spectrum sampled in the original wavelength sampling (0.075Å)
Each FITS extension gives wavelength, fluxes, and FUSE pipeline-generated errors.
Of these stars six "spectral templates" were chosen for detailed study. These
selected O9.5, O8, O7, O6, O5, and O4 main sequence stars are shown with an
asterisk symbol in the table. Clicking on the Available Data link will
take you to tables where you can click on links to examine detailed plots and
detailed line identifications of these spectra and download the FITS data. The
identified lines are all the photospheric and Interstellar Medium atomic and
molecular features in the far-UV spectrum. These lists were compiled from line
synthesis of model atmospheres appropriate to the stars' spectral types from
a theoretical and empirical set of line libraries. All lines for which our
intrinsic line depths (unbroadened) of 10% are predicted from our synthesis.
The methodology behind, line library sources for, and details about the use of
the SYNSPEC line synthesis program (after Lanz and Hubeny, 2003, ApJS, 417) are
given in the the cited paper). The line library we constructed for this and
the B star atlases are available upon request to the author.
The atlas spectra are enhanced with respect to the data in the MAST archives, first, in that wavelength irregularities for the FUSE Side 1 and Side 2 spectra have been removed to the extent possible and corrections made for the stars' radial velocities. The spectra were then resampled to restore the wavelength zeropoints and increments of the original spectra. Second, the depressed fluxes in the FUSE 1B LiF detector segment due to the primary "worm" have been corrected by means of the quasi-continuum fluxes in the 2A LiF segment.
As with the preceeding FUV spectral atlas on B stars this work is practically unique among stellar spectral atlases in its attempt to identify all visible photospheric and interstellar lines in this wavelength region. For this reason it is called a "detailed" spectral atlas. These identifications are shown in a long table containing three subtables. These are referred to as Tables 3a-c in the Journal paper, and each includes about two thousand line identifications. The lines are designated as either "primary" or "secondary" for each of three spectral types, B0, B2, and B8, where the attached secondary lines have smaller equivalent widths than the primary lines within a common wavelength instrumental resolution of 0.05Å and 0.075Å for Copernicus and FUSE, respectively.
The line identification tables list wavelengths and ions from which they arise for 821 (500) [type O4], 992 (663) [O5], 1077 (749) , 1178 (847) [O7], 1359 (1001) [O8], and 1798 (1392) [O9.5]. Here the numbers in parentheses are the totals of lines formed in the atmospheres. These numbers reflect the advancing ionizations of the elements; at least half the lines are Fe V features. The number of Fe V and Fe VI lines peak at types O6-O7 and O5, respectively.
The FUSE Side 1 and 2 spectra are shown in the 3-panel plots large dots and green lines, respectively. The detailed wavelengths and ions also give the numbers of significant blended features within (±0.08Å) of dominant features. Molecular hydrogen and atomic ISM features are represented as vertical red bars or with green wavelength annotations, respectively. A README file is also provided, which describes the contents of these files.
List of Spectral Types of Far-UV Atlas Stars