Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21546408g&link_type=abstract
American Astronomical Society, AAS Meeting #215, #464.08; Bulletin of the American Astronomical Society, Vol. 42, p.499
Astronomy and Astrophysics
Astronomy
2
Scientific paper
We present a preliminary analysis of the line spread function (LSF) of the Cosmic Origins Spectrograph (COS) using FUV and NUV stellar spectra acquired during the SM4 Servicing Mission Observatory Verification (SMOV). Our results indicate that the on-orbit shape of the COS LSF with the HST optical telescope assembly (OTA) deviates from the profile measured in ground testing due to the appearance of broad non-Gaussian wings. The wings are caused by mid-frequency wave-front errors (MFWFEs) that are produced by the zonal (polishing) errors on the HST primary and secondary mirrors; these errors could not be simulated during ground testing. The MFWFE effects are particularly noticeable in the FUV. While the pre-launch LSF is well described by a Gaussian, the on-orbit LSF has up to 40% of its total power distributed in non-Gaussian wings. The power in these wings is largest at the shortest wavelengths covered by the COS medium-resolution gratings ( 1150 A). The effect decreases with increasing wavelength but has a non-negligible effect on encircled energies even at the longest wavelengths. Optical models incorporating the MFWFE effects into the LSF have been calculated for the whole spectral range covered by the FUV and NUV medium-resolution gratings. We show that for the FUV, the convolution of these model LSFs with high-resolution STIS echelle spectra yields an excellent match to the on-orbit COS spectra of the same targets. The model LSFs are available online and can be used by COS observers to assess the impact of the MFWFE broadening on their COS spectra.
We address the impact of the on-orbit LSF on various types of COS scientific investigations.
Aloisi Alessandra
COS/STIS STScI Team
Delker Thomas
Ghavamian Parviz
Hartig George
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