XCSAO Templates

Selection of templates is crucial to the quality of the velocities produced by xcsao. While single spectra with a known velocity may be used as templates, the RVSAO package includes two tasks which create templates. sumspec combines spectra of known velocities into asingle template, taking care to correct velocities to the solar system barycenter. linespec creates a spectrum from a list of emission and/or absorption lines.

The templates we use at the Center for Astrophysics are here.

In order to correlate object spectra against both absorption line templates and emission line templates in one xcsao run, the following header parameters in the template spectrum files can be used to affect the cross-correlation process: ABSREJ, CHOPEM, DIVCONT, EMREJ, FI-FLAG, FRACPEAK, OVERLAP, SUBCONT, and ZEROPAD. The numbers at the end of each parameter description indicate the version of RVSAO in which that parameter was first implemented. xcsao adds appropriate flags to the per-template lines in the summary display.

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ABSREJ = #sig
If CHOPEM is true and xcsao.s_emchop=tempfile, this limit is used as the minimum instead of contpars.s_abs_reject. It does not override contpars.t_abs_reject for the template spectrum. [1.7]

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CHOPEM = T or F
If true and xcsao.s_emchop=tempfile, replace all pixels in the object spectrum which are less than contpars.s_abs_reject times the standard deviation of the continuum fit (sigma) or greater than contpars.s_em_reject sigma with the value of the continuum fit at that wavelength. If true and xcsao.t_emchop=tempfile, replace all pixels in the template spectrum which are less than contpars.t_abs_reject sigma or greater than contpars.t_em_reject sigma with the value of the continuum fit at that wavelength. [1.6]

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DIVCONT = T or F
If true, divide, instead of subtract, the continuum from template and spectrum. The /c flag is then set on the xcsao summary display for this template.

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EMREJ = #sig
If CHOPEM is true and xcsao.s_emchop=tempfile, this limit is used as the maximum instead of contpars.s_em_reject. It does not override contpars.t_em_reject for the template spectrum. [1.7]

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FI-FLAG = 0 or 1 or 2 or 3
This flag determines how the Fourier transforms are filtered
=0 or not present: Filter both the template and the object spectrum transforms using xcsao.low_bin, xcsao.top_low, xcsao.top_nrun, and xcsao.nrun to define a cosine-bell. [1.6]
=1: Do not filter the template spectrum transform, but filter the object spectrum transform. The -f flag is printed on the xcsao summary display for this template.
=2: Do not filter the high frequencies of the object and template spectrum transforms. The +h flag is printed on the xcsao summary display for this template.
=3: Do not filter the high frequencies of the object spectrum transform and do not filter the template spectrum transform at all. The -f flag and the +h flag are printed on the xcsao summary display for this template. on the xcsao summary display for this template.

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FRACPEAK = number between 0.0 and 1.0
Override the pkfrac parameter for just this template by fitting the correlation peak from its maximum value down to this fraction of the maximum. The most common use of this parameter is to fit only the top quarter (set to ) of a correlation with an emission line template to avoid fitting side lobes caused by close emission lines in the template, such as N1 and N2 next to H-alpha. [1.8]

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OVERLAP = T or F
If true, the entire wavelength space which is shared by the spectra and this template spectrum is used. The wavelength limit parameters in xcsao, st_lambda and end_lambda, are ignored when spectra are cross-correlated against this template.

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SUBCONT = T or F
If true or not present, fit and remove the continuum from the template; if false, do not fit or remove continuum from template. This flag does not affect removal of the continuum from the object spectrum. If false, the +tc flag is set on the xcsao summary display for this template. [1.7]

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ZEROPAD = T or F
If the ZEROPAD parameter in XCSAO is set to tempfile instead of yes or no, and this template spectrum header parameter is T, the spectrum and template transforms are both padded with an equal number of zeroes before being cross-correlated. If it is F, the transforms are not zero-padded. [1.7]

Last updated October 20, 2011 by Doug Mink Telescope Data Center