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Detailed Far-UV Spectral Atlas of O Main Sequence Stars

Myron A. Smith


The far-UV spectral atlas of O stars (Smith 2012) 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) [06], 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

Star Spectral Type Vsin i (km/s)
BI237 O2 V((f*)) 83
MPG355 O2 III((f*)) 112
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HD 93250 O3 V((f*)) 107
Sk-68 137 O3III(f*) 107
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HD 46223* O4 V((f)) 82
Sk-67 166 O4 If+ 97
AV 435 O4 V 96
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HD 46150* O5 V((f)) 111
HD 93843 O5 II 95
MPG 342 O5--O6 58
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HD 42088* O6.5 V 65
AV 377 O6 V 51
Sk-66 100 O6 II(f) 73
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HD 93222* O7 III 75
Sk 80 O7 Iaf 76
AV 207 O7 V 75
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HD 66788* O8 V 60
AV 469 O8 II 79
D301-NW8 O8 V 57
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HD 46202* O9 V 37
HD207198 O9 Ib-II 91
AV 378 O9 III 71
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HD 112784* O9.5 V 51
HD 152405 O9.7 Ib-II 77
AV 238 O9.5 II 71


TABLE NOTES:
• For each spectral subtype, row 1: main sequence;   row 2: supergiants;   row3: low metallicity.
• Spectra of asterisked stars are used for line identifications and extended plots (next page).
•MPG (NGC 346), AV, and Sk stars are located in the Magellanic Clouds. DW301-NW89 is also named LMC2-755.





It can be anticipated that the line lists may require occasional corrections or additions as new atomic line data become available. If so, these addenda will be noted under the "Revisions/Errata" link located on the next page. These additions will supercede the contents of the journal paper in those respects. Comments and questions concerning the atlas may be directed to the author help AT stsci.edu.





Available Data