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W.P. Blair, R. Sankrit, S.I. Torres, P. Chayer (JHU/CAS), C.W. Danforth (UCol), J.C. Raymond (SAO)
We report the first observation of an FUV source behind the Cygnus Loop supernova remnant, using the Far Ultraviolet Spectroscopic Explorer satellite (FUSE). The star, KPD2055+3111, lies behind the NE Cygnus Loop filaments known as the Veil Nebula (NGC 6995) and was identified as UV-bright in an image from the Ultraviolet Imaging Telescope. Modeling of an optical spectrum of the star indicated an sdOB type and parameters consistent with a distance of 600 pc to the star. Recent distance estimates for the Cygnus Loop place it at less than 500 pc away.
The FUSE observation took place in late November 2003. The MDRS (4\arcsec\ \times 20\arcsec) aperture was placed on the star and then adjacent to the star on either side to sample the absorption and emission properties of the sight line separately. Due to thermal drifts, only the LiF1 channel was pointed with precision, producing spectra from 1000 -- 1187 Å. The spectrum of the sdOB star is complicated by numerous metal lines, but the imprint of molecular hydrogen is clearly present in the data, as is a broad absorption at the position of O~VI \lambda1032. The O~VI line is clearly due to absorption by the SNR, indicating that the star is indeed behind the Cygnus Loop. The H2 absorption is most likely due to gas in the foreground interstellar medium but could be associated with clouds around the remnant. FUSE spectra of the emission adjacent to the line of sight to the star show strong OVI emission. The combination of absorption and emission line spectra allows us to estimate the density of the gas in the SNR filaments.
This work is supported by NASA grants NAG-512423 and NAG-511581 to the Johns Hopkins University.
The author(s) of this abstract have provided an email address for comments about the abstract: wpb@pha.jhu.edu
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Bulletin of the American Astronomical Society, 36 #2
© YEAR. The American Astronomical Soceity.