We present a comprehensive analysis of the far UV spectrum of G191-B2B over
the range of 900-1700{\AA} using co-added data from the FUSE and STIS archives.
While previous identifications made by Holberg et al. (2003) are reaffirmed in
this work, it is found that many previously unidentified lines can now be
attributed to Fe, Ni, and a few lighter metals. Future work includes extending
this detailed analysis to a wider range of DA objects, in the expectation that
a more complete analysis of their atmospheres can be realised.Comment: 4 pages, 2 figures, 1 table: To appear in the proceedings of the
  "18th European White Dwarf Workshop" in Krakow, Poland, 201

Barstow, Martin A.

Dickinson, N J.

Holberg, Jay B.

Preval, Simon P.

English

arXiv

We present a comprehensive analysis of the far UV spectrum of G 191-B2B over the range of 900–1700Å using co-added data from the FUSE and STIS archives. While previous identifications made by Holberg et al. (2003) are reaffirmed in this work, it is found that many previously unidentified lines can now be attributed to Fe, Ni, and a few lighter metals. Future work includes extending this detailed analysis to a wider range of DA objects, in the expectation that a more complete analysis of their atmospheres can be realised

Preval, S. P.

Barstow, M. A.

Holberg, J. B.

Dickinson, N. J.

University of Strathclyde Institutional Repository

Strathprints Institutional RepositoryPreval, S. P. and Barstow, M. A. and Holberg, J. B. and Dickinson, N. J. (2013) Towards a standardized line list for G 191-B2B and other DA type objects. In: 18th European White Dwarf Workshop (EUROWD12). Astronomical Society of the Pacific Conference Series, 469 . Astronomical Society of the Pacific, San Francisco, pp. 193-196. ISBN 9781583818206 , This version is available at http://strathprints.strath.ac.uk/59469/Strathprints is  designed  to  allow  users  to  access  the  research  output  of  the  University  of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may  not  engage  in  further  distribution  of  the  material  for  any  profitmaking  activities  or  any commercial gain. You may freely distribute both the url (http://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge. Any  correspondence  concerning  this  service  should  be  sent  to  Strathprints  administrator: strathprints@strath.ac.uk18th EUROPEAN WHITE DWARF WORKSHOPASP Conference Series, Vol. 469Krzesin´ski, Stachowski, Moskalik, and Bajan, eds.c©2013 Astronomical Society of the PacificTowards a Standardized Line List for G 191-B2B and other DAType ObjectsS. P. Preval,1 M. A. Barstow,1 J. B. Holberg,1,2 and N. J. Dickinson11Physics Building, University of Leicester, University Road, Leicester, LE17RH, UK2Lunar and Planetary Laboratory, Gould-Simpson Building, University ofArizona, Tucson, AZ 85721, USAAbstract. We present a comprehensive analysis of the far UV spectrum of G 191-B2B over the range of 900–1700Å using co-added data from the FUSE and STISarchives. While previous identifications made by Holberg et al. (2003) are reaffirmedin this work, it is found that many previously unidentified lines can now be attributed toFe, Ni, and a few lighter metals. Future work includes extending this detailed analysisto a wider range of DA objects, in the expectation that a more complete analysis of theiratmospheres can be realised.1. IntroductionG 191-B2B is one of the best studied objects of its kind. However, while we haveextensive knowledge of the composition of the white dwarf’s atmosphere, some as-pects remain unknown. For example, the majority of the absorption features presentin the object’s UV spectrum have been identified, while some features remain elusive.For white dwarfs whose effective temperature Teff exceeds 50 000 K, determination ofTeff becomes ambiguous due to the Lyman-Balmer line problem (Barstow et al. 2003),where determinations of Teff using Lyman or Balmer line profiles can differ by thou-sands of Kelvin. A similar effect is not seen in determining the surface gravity log g.The Lyman-Balmer line problem may be due to incompleteness in the models used incalculating Teff and log g, and it is suggested in this paper that a solution may be toinclude additional opacities in model atmosphere calculations.2. New high quality data2.1. High signal to noise spectraUsing the Mikulski Archive for Space Telescopes1 (MAST), Barstow et al. (2010) co-added all available low resolution (LWRS) FUSE exposures, and Holberg et al. (2003)co-added all of the high resolution eschelle STIS spectra to cover the entire NUV andFUV range. Wavelength ranges, number of exposures, and gratings are summarised in1 http://archive.stsci.edu193194 Preval et al.Instrument: Range (Å) No. of Data reductionFilter exposures referenceFUSE:LWRS 910 – 1185 57 Barstow et al. (2010)STIS:E140H 1150 – 1700 22 Holberg et al. (2003)STIS:E230H 1600 – 3165 40 Holberg et al. (2003)Table 1. A summary of the data used in the co-addition process. The referencesprovided detail how the data was reduced.Table 1. The resulting spectra had exceptionally high signal to noise (≈ 200 at somewavelengths), allowing features with equivalent widths as small as 2mÅ to be detected.2.2. New atomic dataIn this analysis, two line lists were compiled using different data releases from theKurucz and Kentucky atomic databases. The first line list makes use of the 2006 datarelease from Kurucz (2006), while the second line list combines the 2011 and 2012 datareleases from the Kurucz2 and Kentucky3 atomic databases respectively. Where entriesof the Kurucz and Kentucky databases conflicted, the Kurucz entry was favoured owingto the greater accuracy of the oscillator strengths ( f -value) provided. Lines which didnot have a corresponding f -value in the Kentucky database were nominally set at 1.00×10−6. The combined line list increases the number of transitions considered in thesynthetic spectrum calculation, while also improving on the accuracy of transitions inprevious data releases.3. Modeling743 absorption features were measured in the near and far UV spectrum of G 191-B2B to greater than 5σ. Line identification has been performed by comparing syntheticspectrum calculations to observed spectral flux distributions from G 191-B2B. A modelatmosphere using abundances from Barstow et al. (2003) was calculated by TLUSTY(Hubeny 1988), and synthesised with SYNSPEC (Hubeny & Lanz 2011) using the twoline lists described in §2.2 from different data releases. A comparison of the synthe-sised spectra using the two line lists is depicted in Figure 1, where the top and bottomplots compare the synthetic and observed spectra using the old and new line lists re-spectively (all plots were produced using an IDL package called SYNPLOT4). In thetop plot of Figure 1, there are few similarities between the predicted and observed lineprofiles, whereas the bottom plot depicts the tentative identifications of several Fe lines2 http://kurucz.harvard.edu/3 http://www.pa.uky.edu/ peter/newpage/4 http://nova.astro.umd.edu/Synspec43/synspec.htmlTowards a Standardized DA Line List 195Figure 1. A comparison between the 2006 Kurucz and the 2012 combined Ken-tucky +Kurucz 2011 datasets. The bottom and top lines in each plot are the observedand synthetic spectra respectively, where the latter has been offset for clarity.among others. The line positions appear to correspond quite accurately with obser-vation, however, the line depths for the new list occasionally descend deeper than theobserved absorption profiles. This disagreement is likely to be due to the f -values(described in §2.2) assigned to transitions whose real f -value is unknown. Some ab-sorption features however have remained unidentified. One example is a line measuredat λ1273.069, depicted in Figure 2. One possible identification originates from that ofV IV λ1272.972. The top and bottom plot in Figure 2 depicts the synthetic spectrumwith V at abundances of 1.07 × 10−9 and 1.00 × 10−6 relative to H respectively.4. ConclusionWe have performed an in-depth survey of the near and far UV spectrum of G 191-B2B.We have measured 743 absorption features to 5σ confidence, whose identifications willbe detailed in future work. Utilising a new line list combining the 2011 and 2012 datareleases from Kurucz and Kentucky, we have identified the majority of these lines tooriginate from Fe IV, V, and VI, with occasional detections of lighter metals. Usingthe newly identified lines, it is now possible to calculate revised abundances of Feand Ni in future model atmosphere calculations. The obvious increase in identified Feabsorption features presents the question of opacity consideration in model atmospherecalculations. With the resulting changes in the atmospheric structure from the inclusionof additional opacities, it may also be possible to explain the discrepancies betweenthe measured values of Teff obtained from Lyman and Balmer lines by Barstow et al.(2003).196 Preval et al.Figure 2. An unidentified line at λ1273.069, a potential identification being V IV.The top plot shows a non detection when a V abundance of 1.07 × 10−9 is assumed.The bottom plot shows the V line when an abundance of 1.00×10−6 is assumed. Thebottom and top lines in each plot are the observed and synthetic spectra respectively,where the latter has been offset for clarity.Acknowledgments. SPP, MAB, and NJD gratefully acknowledges the continuedsupport of the Science and Technology Facilities Council (STFC). JBH acknowledgesa visiting professorship from the University of Leicester.ReferencesBarstow, M. A., Boyce, D. D., Welsh, B. Y., Lallement, R., Barstow, J. K., Forbes, A. E., &Preval, S. 2010, ApJ, 723, 1762Barstow, M. A., Good, S. A., Burleigh, M. R., Hubeny, I., Holberg, J. B., & Levan, A. J. 2003,MNRAS, 344, 562Holberg, J. B., Barstow, M. A., Hubeny, I., Sahu, M. S., Bruhweiler, F. C., & Landsman, W. B.2003, in Hubble’s Science Legacy: Future Optical/Ultraviolet Astronomy from Space,edited by K. R. Sembach, J. C. Blades, G. D. Illingworth, & R. C. Kennicutt, vol. 291of Astronomical Society of the Pacific Conference Series, 383Hubeny, I. 1988, Computer Physics Communications, 52, 103Hubeny, I., & Lanz, T. 2011, in Astrophysics Source Code Library, record ascl:1109.022, 9022Kurucz, R. L. 2006, in EAS Publications Series, edited by P. Stee, vol. 18 of EAS PublicationsSeries, 129

Towards a standardized line list for G 191-B2B and other DA type objects

Towards a standardised line list for G191-B2B, and other DA type objects

Towards a standardised line list for G191-B2B, and other DA type objects

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