| DATA_SET_DESCRIPTION |
Data Set Overview
=================
A High Spectral Resolution Atlas of Comet 122P/deVico
This data set presents an atlas of 12,219 identified and 4,055
unidentified spectral lines from high resolution spectra of comet
122P/deVico. The spectra were obtained at the McDonald
Observatory using the 2D Coude cross-dispersed echelle spectrograph
(CS2) at the Coude f/32.5 focus of the 2.7m Harlan J. Smith telescope.
The CS2 was used in R=60,000 mode through a 1.2x8.2 arcsec slit to
obtain the observations in this dataset. Continuous spectral
coverage was obtained between the wavelengths 3800-5776 Angstroms,
while increasing interorder gaps are present from 5776-10192
Angstroms. In addition to spectra on the optocenter, one spectrum
was obtained at a point 100 arcsec in the tailward direction.
The atlas identifies lines from five molecular species (C2, C3,
CH, CN and NH2), two atomic species (O, H) and three ions (CH+,
CO+ and H2O+), as well as listing the wavelengths of lines that
were not identified.
The manuscript describing the data set in detail can be found in
Cochran and Cochran (2002) [COCHRAN&COCHRAN2002].
Parameters
==========
The atlas is presented as a table of spectral lines. Each entry
contains the relevant parameters including the wavelength, vacuum
frequency, species name, electronic band, vibrational transition
and rotational transition.
Note that the authors devised an encoding scheme for translating
electronic transition notation, which involves superscipts,
subscripts, and non-ASCII characters, into a flat ASCII notation
for use in the data tables. The description of this transformation
is in Cochran and Cochran (2002) [COCHRAN&COCHRAN2002]. An HTML-
formatted excerpt from this document describing the transitional
states included and the flat ASCII notation used, is included with
the data set documents. (HTML format was used to preserve the
original subscripted and superscripted notation as far as possible.)
Processing
==========
Spectra of an incandescent lamp were used to flat field the data,
and wavelength calibration was done by fitting a two dimensional
function to observations of a ThAr hollow-cathode lamp. Over
3100 lines were fit, with a fourth order fit along an order and
a fifth order fit across orders, resulting in an rms error of
2.5 mAngstroms in the wavelength. The spectra presented here are
doppler shifted by a velocity equal to the comet's geocentric
radial velocity, so the listed wavelengths are in the comet's rest
frame. (Telluric lines in the spectrum are, therefore, shifted
relative to the rest frame.)
Spectra were extracted using variance weighting along the spatial
dimension, with no attempt to preserve the spatial information.
Information needed for an absolute calibration was not available,
so it was not possible to convert the spectra to absolute flux
units.
The spectra presented here are doppler shifted by a velocity equal
to the comet's geocentric radial velocity, so they are in the rest
frame of the wavelength scale. (Telluric lines in the spectrum are,
therefore, shifted relative to the rest frame.)
To minimize introduction of noise into the spectrum, the continuum
level was not removed. Fortunately, the high gas-to-dust ratio in
comet DeVico means that the continuum is essentially negligible at
all wavelengths.
Data
====
The line lists consist of ASCII tables that give the wavelength
and transition information for each entry, if known.
1) format.dat: format of line list tables
2) all.txt: combined list of all spectral lines
3) atomic.txt: list of atomic lines
4) c2.txt: list of C2 lines
5) c3.txt: list of C3 lines
6) ch.txt: list of CH lines
7) ch_plus.txt: list of CH+ lines
8) cn.txt: list of CN lines
9) co_plus.txt: list of CO+ lines
10) h2o_plus.txt: list of H2O+ lines
11) nh2.txt: list of NH2 lines
12) unid.txt: list of unidentified lines
Ancillary Data
==============
In addition to the line lists, this PDS submission includes a
large number of plots to help put the line lists into a broader
context. These plots are presented in two formats.
The first format, given in the 'identify' directory, consists of a
series of plots of each spectral order, with the y scale expanded
to emphasize the weaker features. Two spectra are shown in each
panel, one from 3 October 1995 and the other from 4 October 1995.
A feature must appear in both spectra to be considered real.
These 'ident' plots also include marks identifying the spectral
lines, with different species displayed in different colors.
The second series of plots, given in the 'context' directory,
shows the spectral orders with the y axis scaled to the maximum
strength line in that region. This allows the relative strengths
of the strong and weak lines to be compared.
Media/Format
============
The line list tables are given in the form of ASCII files. These
tables do not use any sub- or super-script characters, and so are
readable in any format. The plots are presented in both pdf and
postscript format.
Spectra
========
The spectra used to generate the atlas have not yet been submitted
to the PDS for archiving. Any researcher interested in using the
spectra should contact Anita Cochran directly (Anita Cochran,
Department of Astronomy, University of Texas, 78712).
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