A user's guide to SOPHIE real-time data products
We remind users that, in addition to the on-line DRS software running on the
sophiedrs worsktation which processes SOPHIE data automatically, all
data products can be displayed and analyzed using
the off-line DRS software running on the same machine. The raw data for a given night are stored in a sub-directory bearing the name
of the night (format: YYYY-MM-DD) in the /data/raw
directory. The reduced data are stored in a similar subdirectory in the
Raw CCD images
The CCD images containing the raw SOPHIE spectral information have 2154x4102
pixels and are stored in FITS files bearing a name constructed using the date
and time of their creation (to the millisecond), for example :
The 40 échelle orders lie in the vertical direction, with red to the
left and blue to the right and wavelength increasing towards the bottom. These
images have overscan areas of 53 pixels on both long sides where the bias values
are systematically measured.
At present no allowance is made either for dark counts or for scattered light.
The level of scattered light is small (<1%) but plans are to reduce it as
much as possible. The dark level is very small (< 8 e-/pixel/hour).
A future release of the DRS software will include both these corrections.
The bias noise pattern visible when using the "fast" readout mode has now been
considerably reduced. We do not recommend at this time using the
"medium" readout mode due to irregular banding in the bias.
All FITS keywords now contain valid information.
Tungsten lamp exposures
The DRS software extracts information from 39 orders in the raw images using
localization information derived from continuous spectra exposed using the Tungsten lamp
(a halogen lamp) using any of the templates:
The results are stored in FITS files having dimensions 4077x39,
where the orders are horizontal and wavelength increasing to the right,
and, in addition to the fiber name (_A or _B), the following information
is appended to the original file name
For the single-fiber exposures:
loco: This file contains the Y coordinates of the 39 extracted
orders in pixel-order space
- fwhm_order :
This file contains the FWHM of the extracted orders, perpendicular to the
dispersion, in pixel-order space
For the two-fiber exposures:
- blaze :
This file contains the results of fitting low-order polynomials
to the extracted orders, in pixel-order space
- flat :
This file contains the residuals from the low-order fit and corresponds to
the "spectrum of the flat-field", that is the flat-field averaged across the
pixels perpendicular to the main dispersion, in pixel-order space
Thorium lamp exposures
The Thorium lamp exposures, always exposed using the two apertures:
are analyzed to extract the pixel-to-wavelength conversion polynomial coefficients.
The results are given for each fiber in three separate 4077x39 FITS files :
- e2ds :
This file contains the extracted Thorium spectrum, in pixel-order space
- wave :
This file contains the wavelengths of all the pixels in the extracted e2sd
files (calibration or science exposures)
- th_lines :
This ASCII file contains the list of all Thorium lines used to derived
the wavelength solution as well as associated information
If science observations are made using a simultaneous Thorium exposure using
the B fiber, the Thorium information is
automatically processed in order to correct for any instrument velocity drifts.
Users should be aware that spectra using this mode are contaminated by
spurious reflections within the spectrograph due to strong infrared emission
lines due to Argon.
A special filter
was installed on 10 April 2007 in the Cassegrain bonnette to suppress those
lines. Previous to that date all spectra taken in the simultaneous Th mode were
subject to this contamination and are not suitable for continuum studies.
Spectra corresponding to templates :
are processed by an on-line pipeline. The results are stored in the FITS files :
For science observations using both fibers A and B, for example if
the sky spectrum is needed, each fiber is reduced separately.
No automatic sky subtraction is done (but see below for the ccf).
This 4077x39 file contains the extracted spectrum (converted in
electrons) in pixel-order space. The associated 'wave' file
giving the wavelengths for each pixel is
specified in the header by the OHP DRS CAL TH FILE keyword.
The 'e2ds' file is the result of bias subtraction, optimal
extraction using the Horne algorithm, cosmic-ray rejection and division
by the spectrum of the flat-field (whose file is specified by the
OHP DRS CAL FLAT FILE keyword). No scattered light or dark count corrections
are applied at present. In addition to the standard information
the file header also contains: order localization
information, FWHM of orders, RMS of flat used, S/N for center of each order,
number of noise spikes removed, wavelength transformation coefficients and
the barycentric radial velocity correction. Note that this file has not been
corrected for the blaze function.
s1d : In this file, containing 307125 flux values, the orders have
been divided by the blaze function, order by order, and reconnected. The
resulting spectrum, now relative to the Tungsten lamp, has been re-sampled
with a constant wavelength step of 0.01 Å and includes the barycentric
radial-velocity correction. Note that this step is smaller than the original
The file header contains values for the signal-to-noise ratio of
individual order centers. At present there is no correction for scattered
light nor for dark counts.
See examples of e2ds and
s1d files in the case
of a hot star (HD 34078) observed in HR mode.
In case the user needs to work with spectra having the original sampling, a
MIDAS procedure is available to create a file
(in table format) for each échelle order, from the e2ds,
wave and blaze files. In this procedure the
blaze file is normalized to 1 at order 20.
The science exposures are subjected to an automatic cross-correlation process
using the spectral type information given in the relevant catalog entry. If
no spectral type is specified, or none corresponds, it is correlated with
a G2 mask. The CCF is calculated over a ± 30 km/s interval around the
deepest peak detected and a gaussian is fitted to the profile. The derived
velocity includes the barycentric correction.
The results are written as two
ccf_mm_fiber files :
One set is written for fiber A and another for fiber B, if it was used.
Here mm stands for the mask used (F0, G2, K0, K5, M4 and M5).
The file headers include the average barycentric radial velocity as well as the
S/N ratio for each spectral order and the wavelength transformation
If any additional cross-correlations are done off-line on the DRS machine, with a different
velocity interval and resolution, the
results are written into three newccf_mm_A files :
- a 40-line FITS file with a CCF for each of the 39 orders (plus one for the average),
- a 39-line ASCII (.tbl) file with detailed CCF information for each order,
- an ASCII (.txt) file with the average CCF.
If fiber B was used for the sky spectrum, a newccf_G2_B is
also written with the result of cross-correlation with a G2 mask. In addition, the observer can
obtain another newccf_mm_C for the sky-subtracted stellar spectrum.
Here also mm stands for the mask used (F0, G2, K0, K5, M4 and M5).
Errors on measured radial velocities are given in two FITS keywords :
For high S/N (>100) spectra DVRMS is a reliable estimate based on the photon noise in the spectrum itself.
For low S/N (<100) spectra a more realistic error estimate is given by CCF ERR
which is based on the width and depth of the CCF profile and the S/N level.
For very accurate radial velocities (down to 2 m/s), a zero-point drift correction as a
function of time (since mid-2011) is available for SOPHIE
(see Courcol et al. (2015)).
Night summary files
Several ASCII .tbl files
summarizing results from different parts of the reduction process
are created in the sub-directory for a given night :
- cal_BIAS_result : This file gives means and RMS values for the bias
- cal_FF_result : This file gives information on the flat-field
twin-fiber exposures (RMS values and S/N)
- cal_loc_ONE_result : This file gives information on the
order-localization single-fiber Tungsten exposures
- cal_TH_result : This file summarizes all wavelength calibration
information derived from the Thorium exposures
- CCF_results : Here are given the results from the on-line
mask, number of lines used in mask, contrast, radial velocity and
FWHM of CCF dip.
- NEWCCF_results : In this file are given the results of any
new off-line cross-correlations made by the observer
- drift_result : For spectra taken with simultaneous Thorium calibration in fiber B,
this file is a summary of the velocity drift (m/s) for the Thorium spectrum, expressed relative
to a previous spectrum taken as a reference.
Other ASCII files (one with an .r extension) are
located in a special /data/msg directory are:
- DRS-sophiedrs.obs-hp.fr.YYYY-MM-DD : This ASCII file (not a .tbl)
contains a complete log of the reduction DRS pipeline for a given night
- YYYY-MM-DD.r : This file gives a list of all exposures with the
raw file name, the exposure time, the number of the exposure in a given
multiple-exposure sequence and the template used. A list of all raw data
exposures for a given night can be generated manually
using the off_list_raw.py YYYY-MM-DD command.
- TRIG-sophiedrs.obs-hp.fr.YYYY-MM-DD : This file gives an account of the
on-line reduction pipeline process
- OFFDRS-sophiedrs.obs-hp.fr.YYYY-MM-DD : This file gives an account
in the case of an off-line process
A copy of all valid reduced Tungsten and Thorium
calibration files is kept in the /data/calibDB directory.