ESI: ESIRedux Cookbook

ESIRedux Cookbook

Echellette Suggested Calibrations

five Bias (0s) frames
five Pin Hole images (dome?)
ten QTZ Flats (Dome preferred) (each slit size)
Arc Calib: five CuAr (600s) + five HgXe (each slit size)
one Standard star (each slit size)

Pre-Reduction Setup

Computer Resources
- >300 MHz processor
- 5G disk space / night
- 750M RAM (1G on Solaris)
- Linux or Solaris
Solaris WARNINGS (These do not apply to Linux)
- Solaris+IDL does not release memory until IDL is exited
- Consider exiting IDL occasionally and monitor memory usage
- IDL+Solaris freezes up on the CPU intermittently
  - Most likely a bug in licensing software
  - Forced to kill IDL process and restart
Software
- gcc or cc
- IDL v5.4 or later
- IDL packages
  1. idlutils SDSS package (Schlegel)
  2. idlspec2d SDSS package (Sloan public)
  3. xidl IDL package (JXP)
Log sheets [somewhat optional]
This cookbook

Initial Setup (Repeat for each night)

Create a new directory for the night (e.g. 06aug02) and enter it
Create a 'Raw/' directory and put all the raw data in it.
If the filenames do not read esi####.fits, it is quite likely the code will be unhappy
gzip the data (gzip *.fits)
Create a 'pro/' directory and copy the files from $XIDL_DIR/ESI/pro/redux into it (e.g. proc_ech.pro, extract_ech.pro).
These files can and should be used to run most of the steps that follow.
Launch idl in the directory above Raw/

esi_strct :: Create the esi structure.

This structure organizes the entire night of data and is the most important file created. The structure is listed on the next page.
The routine creates a few things:
1. An IDL structure in memory with whatever name you choose (e.g. esi);
2. The file 'esistrct.fits' which is a fits version of the structure;
3. The file 'esi.list' which is an ASCII version of the fits file which lists the values of some but not all tags.
To view the structure outside of IDL, I recommend the program 'fv' which I think stands for fitsview. It allows you to examine binary fits tables.
If the EDIT keyword is set, a gui will launch which allows some editing of the esi structure (see below).
    Example: IDL> esi_strct, esi, /MKDIR, [/EDIT]
    Example: IDL> proc_ech, esi, /MKSTRCT
    Time : 1s per image

esistrct

Tag Type Comment

frame 0 FRAME Number

flg_anly 0 Analysis flag 0=Don't Analyse, 2 = bias sub, 4=scatt

Obj ' ' Object Name

obj_id 0L Obj ID

type ' ' ObjTyp : OBJ,STD,DRK,ZRO,IFLT,DFLT,ARC,MSK,IMG,TWI

slit 0. Slit width

exp 0.d Exposure time

imfilt ' ' Image Filter : U,B,V,R,I, C

mode 0L Mode: 0=Image, 1=LowD, 2=Echellette

CCD ' ' CCD

TEL ' ' Telescope

namp 0 Number of Amps

arclamp 0 Arc Lamps: (Binary flag) 1=CuAr, 2=Xe, 4=HgNe

qtzlamp 0 QTZ Lamp: 0=off, 1=On

rotmode 0 Rotation mode: 0=Stationary

ccdspeed ' ' CCD Speed

gain 0. Gain

readno 0. Read Noise

date 0.0d Date of Obs

UT ' ' UT

RA ' ' RA

DEC ' ' DEC

Equinox 0. EQUINOX

refordr 0L Reference order (ECH only)

rootpth ' ' Path of the Root

img_root ' ' Root name (usually in Raw directory)

flg_ov 0 OV FILE? 0=No, 1=Yes

img_ov ' ' Name of OV file (with directory)

flg_final 0 Final File? 0=No

img_final ' ' Name of Final img

ystrt 0L Column for initiating the trace

arc_fil ' ' Name of the Arc image file (fits)

map_fil ' ' Name of the Map image file (fits)

flat_fil ' ' Name of the Flat image file (fits)

obj_fil ' ' Name of object structure (fits)

esi_editstrct :: Modify the ESI structure. The previous step creates the structure and takes a guess at the initial values of many of the tags based on the header card info. It is difficult, however, to automate all of the values for the tags and therefore the user should carefully edit the structure. For most of the important tags, one can use esi_editstrct. The rest must be done from the command line by hand. The obvious tags to modify are:
- Obj :: Object name (this propagates into the final spectra and should have no spaces!)
- flg_anly :: Include in analysis (defaulted to 1 for yes)
- type :: ARC, IFLT, TWI, OBJ, STD, etc.
- mode :: ECH, LWD, IMG
Example: IDL> esi_editstrct, esi
Time : User interaction
Writing the ESI structure to disk:: In IDL you can modify the values of any of the tags. You can then save the structure in fits form and rewrite the ASCII file with the routine esi_wrstrct.
Example: IDL> esi_wrstrct, esi, FITS='name'
Time : fast
Reading the ESI structure from disk:: esi_ar
    Example: IDL> esi = esi_ar()
    Example: IDL> esi = esi_ar('esi_name.fits')
    Time : fast
esi_echsetup :: ECH Setup
- This routine examines the esi structure and looks for calibration files associated with the various slit widths of your ECH files. It groups together exposures with identical Obj name and ESI mode and sets the obj_id tags accordingly. A summary of the ECH exposures is put in 'esiECH_summ.txt'.
      Example: IDL> esi_echsetup, esi
      Example: IDL> proc_ech, esi, /SETUP
      Time : Fast

Create Bias (Zero) frame

esi_mkzero We have found that creating a Zero frame is preferred over an overscan subtraction. If you have taken Bias (0s) frames, the process is straightforward. If you haven't, you can copy the image (or make a soft link) 'BiasS.fits' from $XIDL_DIR/ESI/CALIBS into the 'Bias/' directory.
    Example: IDL> esi_mkzero, esi
    Example: IDL> proc_ech, esi, /MKZERO
    Time : 3-5min
To check the Bias frame : xatv, 'Bias/Bias1x1S.fits'

Pinhole Map

One may have taken a series of pinhole traces using the pinhole mask and the QTZ lamp to trace out the light path along the CCD. If so, the following task can be used to fit the pinhole traces and create a MAP which is required for the data reduction. In lieu of your own pinhole images, you will need to copy the files (or make soft links) hole_fit.idl, ECH_map.fits, img_hole.fits from $XIDL/ESI/CALIBS to Maps/.
At this point, I would recommend using the CALIBS files over creating new ones.
esi_echtrcholes :: This routine will combine all pinhole images (denoted by the 9.99 slit width) and then trace the pinholes. Output is 'Maps/img_hole.fits' and 'Maps/hole_fit.idl'
    Example: IDL> esi_echtrcholes, esi
    Example: IDL> proc_ech, esi, /MKMAP
    Time : <10min
esi_echmkmap :: This routine takes all of the good pinhole traces and makes an optical map. This is used to rectify the arcs for 2D fitting.
Example: IDL> esi_echmkmap, esi
Time : <5min

Process Flats

These routines processes your QTZ calibration frames to (1) trace the edges of each order, (2) calculate the gain mismatch between multiple amplifiers, and (3) correct pixel-to-pixel variations. Dome flats show significantly less scattered light than the internal flats and should be used when possible. Use the /IFLAT switch to use internal flats.
esi_echmkflat :: The first routine simply combines the flats. The output is a bias subtracted, median flat placed in 'Flats/'. If one does not specify the slit size, the program loops through all sizes.
    Example: IDL> esi_echmkflat, esi, [slit], [/IFLAT]
    Example: IDL> proc_ech, esi, [slit], /MKFLAT [/IFLAT]
    Time : 30s per flat
esi_echfltsct :: The next step is to subtract scattered light and normalize the flat. The scattered light is quite significant for Internal flats but also important for Dome flats. This code requires the slit size explicitly. The routine also normalizes the flat and also matches the gain on the two halves of the amplified CCD. If you are using the archived pinhole map (most likely), then you should use the keyword /KLUDGEOR to deal with an anomoly in Order 14. The output is 'Flats/FlatECHslit_{bin}N.fits' where slit = 50, 75, or 10 and bin = 1x1, 2x1, etc.
    Example: IDL> esi_echfltsct, esi, slit, [/IFLAT], [/KLUDGEOR]
    Example: IDL> proc_ech, esi, slit, /NRMFLAT, [/IFLAT]
    Time : 1min
Check the Flat: xatv, 'Flats/FlatECHslitN.fits'

Arc Image

This is the most important set of steps. The sky subtraction algorithm will only succeed with a good Arc Image. It should be emphasized that we only create one Arc Image per slit size and apply this to all of the exposures taken with that slit size. The following routines are well automated but should be checked carefully if you are doing a 'final' reduction. I think it is possible that one could use an Arc image from a previous run or the CALIBS database but wouldn't recommend it just yet. All of the following routines require a specific slit size.

esi_echmkarc :: Process the Arcs. This step bias subtracts and flat fields the arc images. If there is an image taken with all the lamps on (arclamp = 7) then the code will take that. Otherwise, it will the Arcs together to make a CuAr+HgNe+Xe image. Output is: 'Arcs/ArcECH_slit.fits'
    Example: IDL> esi_echmkarc, esi, slit
    Example: IDL> proc_ech, esi, slit, /MKARC
    Time : 1-15min
esi_echfitarc :: This routine extracts a 1D spectrum down the center of each order and determines the wavelength solution. There are two levels of interatction with this routine. The most interaction (not recommended) is to use /INTER which prompts the user to identify and fit the Arc lines. I recommend using the option /PINTER which has the program attempt to identify a set of lines in each order. The user than interactively fits the lines using the routine x_identify which calls x1dfit. As long as your arc lines are within several pixels of my solution, things ought to run smoothly. The output is an IDL file containing the polynomial fits for each order: 'Arcs/ArcECH_slitfit.idl'. The program also creates a ps file to examine the quality of fits. One can input their own set of linelists or restrict the code to use only CuAr lines (/CUAR).
    Example: IDL> esi_echfitarc, esi, slit, /PINTER
    Example: IDL> proc_ech, esi, slit, /FITARC
    Time : 2min per order
esi_fit2darc :: This routine takes the good lines from esi_echfitarc and then performs a 2D fit to the lines. This is useful for interpolating through the edges of the blaze.
    Example: IDL> esi_fit2darc, esi, slit
    Example: IDL> proc_ech, esi, slit, /FIT2DARC
    Time : 2min per order
esi_echtrcarc :: This routine traces arc lines in each order. It first straightens the curved orders, but does not rectify the arc lines. It simply traces them and then maps back to the original data frame in the following step. I recommend interactively choosing the lines the program uses to trace but on can also let the program choose (/AUTO). Output is a series of files in the 'Arcs/TRC' directory (1 per order) including ps files for rough inspection.
    Example: IDL> esi_echtrcarc, esi, slit, /AUTO
    Example: IDL> proc_ech, esi, slit, /AIMG (This does the following step too)
    Time : 2min (>10 min interactively)
esi_echmkaimg :: This routine takes the arc traces and uses them to create a full Arc Image in the data frame. The final wavelength image is then converted to vacuum wavelengths. Output is : 'Arcs/ArcECH_slitIMG.fits'
    Example: IDL> esi_echmkaimg, esi, slit, /CHK
    Time : 5min
    Check output with: xatv, 'Arcs/ArcECH_slitIMG.fits'

Process the Standard

This step is not necessary but will help with tracing the data and fluxing. Alternatively, one can grab the standard trace from the CALIBS directory.
esi_echtrcstd :: Process the standard star (bias, flatten), centroid it using a small region in order 11 (this can be modified), skysubtract, and then trace it through the 10 orders. The output are a processed image in 'Final/', an Obj structure in 'Extract' (see below), and the file 'Extract/STD_ECHslit_TRC.fits' which is the trace for the standard star.
    Example: IDL> esi_echtrstd, esi, slit
    Example: IDL> proc_ech, esi, slit, /PROCSTD
    Time : 10min (mainly sky sub)

0. Extraction

The following routines all apply to a single object, i.e. multiple exposures of that object will be reduced together.
I suggest you use a .pro file like extrct_ech.pro to guide the process. It provides a convenient way of stepping through the reduction.
Most of the following routines take the esi structure and obj_id.

Process the Image

esi_echproc :: Bias subtract and flat field the Raw image. This routine takes the index number of the esi structure as input. This is the integer in the first column of the file 'esi.list'. One can subtract scattered light with the flag (/SUBSCAT), but I currently don't recommend it. The contribution is small for almost all objects. Output is in 'Final/' and is a flattened flux and variance fits file (one gzipped fits file with two exentsions per image).
    Example: IDL> esi_echproc, esi, indx, [/SUBSCAT]
    Example: IDL> extrct_ech, esi, obj_id, /PROCOBJ, [/SUBSCAT]
    Time : 1min per image
    Check : xatv, 'Final/f_esi#.fits'

specobjstrct

Tag	Type	Comment
field	' '	Name of field
slit_id	0L	Used to store the order number (0-9) corresponding to physical order (15-6)
obj_id	' '	ID value (a=primary, b-z=serendip, x=NG)
flg_anly	0	0=No analysis
exp	0.
xcen	0L	Column where obj was id
ycen	0.
flg_aper	0	0=boxcar
aper	fltarr(2)	Widths of aperture, 0/1 = bottom/top (pixels)
skyrms	0.	RMS of sky fit
trace	fltarr(5000)
npix	0L
wave	fltarr(5000)
fx	fltarr(5000)
var	fltarr(5000)	rejected pix
flg_flux	0	0=f $_\lambda$ , 1=f $_\nu$
flux	fltarr(5000)	Fluxed data
sig	fltarr(5000)	Err in fluxed data
date	0.0d
UT	' '
img_fil	' '
slit_fil	' '
instr_strct	' '	e.g. wfccdstr fits file

Identify the Object

esi_echfndobj :: Allows the user to interactively identify the science objects (default is auto selection). It smashes a region of the spectrum and finds all peaks containing 4 continuous pixels with 3 sigma significance. The region is taken to be from 5600-5610A in order 4L (physical 11) by default. These can be changed via the keyword REFWV=fltarr(2) and REFORDR=#L. If not interactive, the program chooses the brightest object within 20 pixels of the center of the slit. Set the keyword /INTER to interactively identify the object and a an aperture to mask for sky subtraction (recommended). It then creates an object structure which stores the spectra of all objects identified in the slit. The IDL structure created is described below.
The routine also does a pseudo-trace to the object based on the paths of the pin-hole traces. This trace is used to mask out the object for sky subtraction. At present the code assumes that there are no serendipitous objects in the slit to mask.
Output is 'Extract/Obj_esi##.fits'
    Example: IDL> esi_echfndobj, esi, obj_id, [exp], [REFORDR=, REFWV= /NOCLOB, /INTER, /CHK, /STD]
    Example: IDL> extrct_ech, esi, obj_id, /FNDOBJ
    Time : fast
esi_echcopyfnd :: If desired, the user can copy the trace from another object using this routine. The program takes the trace from the alternate object and allows the user to choose a different aperture for masking. The keyword CPYIDX is required and refers to the index number of the template object. An offset can also be applied to this trace using OFFSET=.
Example: IDL> esi_echcopyfnd, esi, obj_id, [exp], CPYIDX=, [APER=, OFFSET=]
Time : fast

Sky Subtraction

esi_echskysub :: This procedure subtracts the sky from each order, one by one for each exposure with a given obj_id. The main recipe adopts either (a) a series of low order POLYNOMIALS row by row for orders 0 to 5 (physical orders 15 to 11) or (b) a 1D Bspline fit to the wavelength, flux pairs for orders 6-9. I have found that the polynomials work best in the low sky regions and the BSPLINE works significantly better in the orders with strong sky lines. There are some fancy features added in to deal with bright sky lines which get switched off or reduced for short exposures.
Current issues:: One current failing of the code is sky subtraction in order 11 where the amplifiers meet. The ratio of the gain is calculated from the Flat image and this ratio is not constant in time. This sometimes leads to over subtraction of sky in some regions.
Options ::
- BORDR= 5L :: Sets the order (non-physical) where the Bspline routine takes over.
- ORDR= [0L, 9L] :: Sets the first and last order for sky subtraction. This is useful for repeating sky subtraction in an order or two with improved parameters.
- SKLFIL= ' ' :: Input file for fine tuning skyline subtraction with the Bspline routine. Entires have this format:
  ordr # wvmin wvmax flag
  where the flag = 1 places breakpoints at the center of each row and 2 places one at each end. One usually turns on /NOVAC with this keyword
- /NOVAC :: Does not apply a vacuum correction to the skyline info. This probably would only be used with SKLFIL
Output is the sky subtracted 2D image appended to the unsubtracted flux and the variance 2D images (e.g. 'Final/f_esi#.fits')
    Example: IDL> esi_echskysub, esi, obj_id
    Example: IDL> extrct_ech, esi, obj_id, /SKYSUB, [/SKY_FCHK]
    Time : 10min per exposure
Examine the final product (and get wavelength info) by:
IDL> xatv, 'Final/f_esi#.fits', getsky=2, WVIMG='Arcs/ArcECH_slitIMG.fits'

Trace OBJ

esi_echtrcobj :: This procedure carefully traces the science objects. By default, it will combine multiple exposures to improve tracing. It uses the Standard star as a guide and a crutch. This new trace overwrites the one in the Obj structure. Turn the keyword /FAINT on for faint objects. This step can (should) be skipped if you have used esi_echcopyfnd for the trace above.
    Example: IDL> esi_echtrcobj, esi, obj_id, [exp], [/FAINT, /CHK, /USESTD, STDFIL=]
    Example: IDL> extrct_ech, esi, obj_id, [exp], /TRCOBJ, [/USESTD, STDFIL=, /TRCCHK, /FAINT]
    Time : fast

Extraction

esi_echextobj :: This procedure performs a boxcar (default) or optimal extraction of the object in each order. It then rebins to a 1D spectrum using linear interpolation of the wavelength solution. This is the only binning of the data during the entire reduction scheme. All spectra are also shifted to zero heliocentric velocity and placed on a wavelength array with 33000 pixels, w0 = 3900 Ang and constant velocity pixels at 10km/s.
All of the output is written to the Obj structure
    Example: IDL> esi_echextobj, esi, obj_id, [/OPTIMAL, /CHK]
    Example: IDL> extrct_ech, esi, obj_id, /EXTOBJ, [/OPTIMAL]
    Time : 3min (box), 10min (optimal)
Examine the final product:
IDL> esi_echspecplt

Combine Multiple Exposures (REQUIRED)

esi_echcombspec :: This procedure adds up multiple exposures of the same object, order by order, weighting by S/N after scaling each exposure to have the same flux as the first. It appropriately deals with CR's. For objects with more than 2 exposures, it clips 5 sigma outliers as well. Even if you have only a single exposure, you need to run this routine prior to fluxing and collapsing to a 1D spectrum as it creates the final spectrum structure that is necessary for fluxing and coadding to 1D.
Output is a fits file in 'FSpec' named 'Obja_ech.fits' where Obj is the name in the Obj tag and the letter 'a' signifies the primary science object. In the future, I might allow multiple objects to be extracted and would label them 'b', 'c'..
    Example: IDL> esi_echcombspec, esi, obj_id
    Example: IDL> extrct_ech, esi, obj_id, /COMBOBJ
    Time : fast

Flux the Spectra

esi_echflux :: This procedure fluxes each order of the combined frame. Generally, I'd suggest using the flux calibration that is defaulted (i.e. ECH_FLUX#.fits in CALIBS).
This program overwrites the fx array in the file created by esi_echcombspec.
    Example: IDL> esi_echfluxfin, esi, obj_id
    Example: IDL> extrct_ech, esi, obj_id, /FLUX, [/CLOBBER]
    Time : fast
Examine the final product:
IDL> esi_echspecplt, /fspec

Collapse to 1D

esi_echcoaddfin :: This procedure coadds the various orders into a 1D spectrum. It does weight by S/N but is otherwise rather simple minded. This includes the fact that various regions of the spectra are ignored, especially data in the lower left hand of the CCD.
Output is two fits files in 'FSpec' with names 'Obja_F.fits' and 'Obja_E.fits'.
    Example: IDL> esi_echcoaddfin, esi, obj_id
    Example: IDL> extrct_ech, esi, obj_id, /COADD
    Time : fast
Examine the final product:
IDL> x_specplot, 'FSpec/Name_F.fits', 'FSpec/Name_E.fits'

0. LWD Reduction

The following routines setup and then proceed through the reduction of data taken in the LWD mode with ESI.
I suggest you use a .pro files like proc_lwd.pro,extrct_lwd.pro to guide the process.
Most of the following routines take the esi structure, and the slit size or the obj_id.

Create Bias (Zero) frame

We have found that creating a Zero frame is preferred over an overscan subtraction. If you have taken Bias (0s) frames, the process is straightforward. If you haven't, you can copy the image 'BiasbinS.fits' from $XIDL_DIR/ESI/CALIBS into the 'Bias/' directory.
    Example: IDL> esi_mkzero, esi
    Example: IDL> proc_lwd, esi, /MKBIAS
    Time : 3-5min
To check the Bias frame : xatv, 'Bias/BiasS.fits'

LWD Setup

:: esi_lwdsetup

This routine examines the esi structure and looks for calibration files associated with the various slit widths of your LWD files. It groups together exposures with identical Obj name and ESI mode and sets the obj_id tags accordingly. A summary of the LWD exposures is put in 'esiLWD_summ.txt'.
    Example: IDL> esi_lwdsetup, esi
    Example: IDL> proc_lwd, esi, /SETUP
    Time : Fast

Arc Image

This is the most crucial step. The sky subtraction algorithm will only succeed with a good Arc Image. It should be emphasized that we only create one Arc Image per slit size and apply this to all of the exposures taken with that slit size. The following routines are well automated but should be checked carefully if you are doing a 'final' reduction. I think it is possible that one could use an Arc image from a previous run but wouldn't recommend it just yet. All of the following routines require a specific slit size.
For LWD mode, only the HgNe and Xe lamps are useful. Therefore we focus on these images (i.e. arclamp = 6).
esi_lwdmkarc :: Process the Arcs. This step bias subtracts, trims and combines all of the Arc images. Note that we find it is best not to flat field the Arc, at least not with an unnormalized arc. Output is: 'Arcs/ArcLWD_slit.fits'
Example: IDL> esi_lwdmkarc, esi, slit
Time : 2min
esi_lwdfitarc :: This routine extracts a 1D spectrum along row 820 (default) of Arc image and determines the wavelength solution. Currently, I recommend using the /INTER mode although you can try and let the code run automatically. As long as your arc lines are within 3 pixels of my solution, things ought to run smoothly in AUTO mode. The output is an IDL file containing the polynomial fits for each order: 'Arcs/AFIT_LWDslit.fits'. The program also creates a ps file to examine the quality of fits.
Example: IDL> esi_lwdfitarc, esi, slit, [/INTER]
Time : 2min
esi_lwdtrcarc :: This routine traces arc lines throughout the image. It will parse out the ends of traces where the algorithm tends to have trouble. Output is an anonymous structure written to the binary fits file 'Arcs/ATRC_LWDslit.fits'.
Example: IDL> esi_lwdtrcarc, esi, slit
Time : 2min
esi_lwdmkaimg :: This routine takes the arc traces and uses them to create a full Arc Image in the data frame. The main routine performs a 2D polynomial surface fit to the traces from the previous step. This is very expensive but needs to be only run once per night per slit width. Output is : 'Arcs/ArcECH_slitIMG.fits'
    Example: IDL> esi_lwdmkaimg, esi, slit, [/CHK]
    Time : 20min
    Check output with: xatv, 'Arcs/ArcECH_slitIMG.fits'
To run all three steps at once, use:
IDL> proc_lwd, esi, slit, /MKAIMG, [/INTER]

Process Flats

esi_lwdmkflat :: This routine processes the QTZ calibration frames, producing a normalized flat useful to correcting pixel-to-pixel variations. The routine bias subtracts and combines individual exposures. It then fits a high order bspline to a strip of the flat in order to normalize to unity.
Output is 'Flats/FlatLWD_slit.fits'     Example: IDL> esi_lwdmkflat, esi, slit
    Example: IDL> proc_lwd, esi, slit, /MKFLAT
    Time : 5-10min
Check the Flat: xatv, 'Flats/FlatLWD_slit.fits'

Extract

esi_lwdproc :: This routine bias subtracts and flattens the science frame.

Output is 'Final/f_esi####.fits'
    Example: IDL> esi_lwdproc, esi, obj_id, [/CLOBBER]
    Example: IDL> ext_lwd, esi, obj_id, /PROCOBJ
    Time : 1min/image
Check: xatv, 'Final/f_esi####.fits'

esi_lwdproc :: This routine finds the science object and any other serendips in the slit. I highly recommend you use the INTER mode. With this, you need to set the aperture size around the obj for sky subtraction (not extraction!). The routine also creates the Obj structure in Extract.

Output is 'Extract/Obj_esi####.fits'
    Example: IDL> esi_lwdfndobj, esi, obj_id, [/CLOBBER]
    Example: IDL> ext_lwd, esi, obj_id, /FNDOBJ
    Time: fast

esi_lwdskysub :: Sky subtract the image.

Output is in 'Final/f_esi####.fits'
    Example: IDL> esi_lwdskysub, esi, obj_id, [/CHK]
    Example: IDL> ext_lwd, esi, obj_id, /SKYSUB, [/SKYCHK]
    Time: fast