Boller & Chivens Spectrograph at OAGH

Overview

The layout of a typical Boller & Chivens spectrograph is shown below The spectrograph is mounted at the f/12 Cassegrain focus of the telescope, and is equipped with a collimator of focal length 1080 mm and a camera of focal length 465 mm. At the image scale of 8.185''/mm, this amounts to approximately 0.463''/pix (New) along the spatial direction for the TK1024 CCD as the detector. Slit width can be changed manually at steps of 1 micron all the way up to 1000 microns. A typical slit width of 250 micron (or 2 arcsec) corresponds to 4 detector pixels. Maximum slit length allowed is around 3 arcmin. The spectrograph uses a reflection grating, whose orientation can be changed with a micrometer at steps of 5 arcmin. A HeAr lamp is available with the spectrograph for wavelength calibration. In the default mounting of the spectrograph the slit is oriented along east-west. This corresponds to a reading of 263 degrees on the scale of the mounting panel (well, there is more than one way of mounting and unfortunately it is not mounted always the same way). For any other slit orientation the entire panel needs to be rotated.

CCD

The CCD detector of the Boller & Chivens spectrograph is a back illuminated Tektronix chip of format 1024x1024 pixels (TK1024AB grade 1). The device specifications are tabulated below.

Tektronix TK1024 Device Specifications
Format	1024 X 1024
Pixel size	24 micron
Dark current	0.4 e-/hour
Operating temperature	-110 o C
Full Well Capacity	503,000 e-(at A/D converter limit)
Bias Mean level	1000 ADU at 1X gain
Response linearity	0.1%
ADC Resolution	16 bit
Readout rate	40 kHz

Gain/Noise measurements
Software gain	Gain (e-/ADU)	Noise (e- rms)
1X	7.68	8.4
4X (default)	1.85	3.7

A typical quantum efficiency curve for the TK1024 chip is shown below

This CCD is also used with the Direct Imaging Camera.

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Quick user's guide to PMIS

• Start-up

  To start PMIS, click on the PMIS logo on the acquisition PC. Before clicking, make sure that the PC time/date is the Universal Time/Date. You may use the following formula to set the PC clock:
  UT = Sonora Time + 7hr (both winter and summer).
  PMIS command window appears with a prompt "Cli>".

  PMIS is a menu driven acquisition software. Data acquisition can be done either in the command mode or using the menu options. You can choose CCD parameters such as CCDformat, binning, gain etc by following the Menu or giving the appropriate commands on the command window. Values set in one mode are available for all the subsequent images, irrespective of whether command line or menu option is used.

• Data Acquisition using Menu

  Open an image window by clicking on Image on the command window. To take images go to Acquire and then click on expose (and select intergration time), or bias for object or bias exposures. Once the exposure is over, you need to save the image using File followed by Export and FITS 16. You have the option to give a comment to be included in the header by clicking on File followed by Image Info before saving the image. The image header will not include none of the observational parameters.

• Data Acquisition using Macros

  In this mode, images are taken by typing the commands on the PMIS command window. Each command is driven by a macro. We have a growing set of macros to overcome the limitations (e.g. overscan, fits headers, multiple image acquisition) of menu driven data acquisition system. We recommend that you use these macros. The instructions for their use are as follows:
  Cli> imdir "directory" "[Observer]" "[S]"
  ----------------------------- Set-up observational parameters
  The command imdir sets the directory (e.g. "C:\usuarios\ydm\n1") in to which images will be written. The directory should have already been created. Optionally, the observer's name also can be entered, which will go directly into the header of all the files created in the session. In the default mode ("S" as the third parameter), a CCD format of 1124x560 with the origin at X=0 and Y=232, suitable for the B&C session is chosen. To open a session for direct imaging you should choose "I" as the third parameter. This opens an image window of 1124x1024 pixels. Note that both the CCD formats include 100 pixel overscan. The sessions are opened with default values of gain (value of 4) and no binning. If you wish to change these values, follow the "Acquire" and "Acquisition Area" on the image window menu. A logfile named "log.txt" is created in the image directory. Information such as exposure time, UT are directly written into this text file. The command also initializes the counter number of multiple observations of bias, HeAr lamp and images to 0. Root names for multiple bias and HeAr observations are defined as "bias" and "hear" respectively. These default parameters may be changed by redefining them on the command line as shown in the following examples:

  Cli> vdef biasnum 1	Cli> vdef biasfil "n1bias"	if using marco mltbias
  Cli> vdef hearnum 1	Cli> vdef hearfil "n1hear"	if using marco: mlthear
  Cli> vdef objnum 1	Cli> vdef objfil "n1obj"	if using marco: mltobs

  IMPORTANT: Please make sure that all the image and graphic windows are closed (i.e. only the command window should be open) before running "imdir". Also note that both the command line parameters should be written inside double quotes. Quantities enclosed inside square brackets such as [comment] are optional parameters.

  Cli> obj "file" t "[comment]" "[filter]"
  ---------------------------------- Take 1 exposure of t secs
  Obtains an exposure of "t" secs and stores the data in a FITS file called file.fit. If a filter name is given as the 4th parameter, it will be written into the FILTER header. There is protection against overwriting and hence if the file already exists or if the file name contains more than 8 characters, the program exits and you need to start with a new filename.

  Cli> nobj "file" t n n0 "[comment]" "[filter]"
  ---------------------------------- Take n exposures of t secs each
  Obtains n exposures of "t" secs each and stores the data in FITS files. Filenames are formed as fileXX.fit, where XX=n0,n0+ 1,....,n0+ n-1. If any of the files already exists or if the file name contains more than 6 characters, the program exits and you need to start with a new filename. Maximum value of n=99.

  Cli> ndark "file" t n n0 "[comment]"
  ---------------------------------- Take n exposures of t secs each
  Obtains n dark exposures of "t" secs each and stores the data in FITS files. Filenames are formed as fileXX.fit, where XX=n0,n0+ 1,....,n0+ n-1. If any of the files already exists or if the file name contains more than 6 characters, the program exits and you need to start with a new filename. Maximum value of n=99.

  Cli> mltbias n "[comment]"
  ---------------------------------- Take n biases
  Obtains "n" bias frames and stores them in the disk. Names are of the form biasfilXX.fit [n1bias1.fit, n1bias2.fit etc], where XX is an incremental number initialized by imdir or later set using vdef.

  Cli> mlthear t n "[comment]"
  --------------------- Take n HeAr arc spectra, each of duration t secs.
  Obtains n exposures of t secs each and stores the images in FITS format files named hearfilXX.fit [n1hear1.fit, n1hear2.fit etc], where XX is an incremental number initialized by imdir or later set using vdef.

  Cli> mltobs "file" t n "[comment]"
  --------------------- Take n object spectra, each of duration t secs.
  Obtains n exposures of t secs each and stores the images in FITS format files named fileXX.fit [n1file1.fit, n1file2.fit etc], where XX is an incremental number initialized by imdir or later set using vdef.

  Cli> note "comments"
  ---------------------------------- Write comment lines to "log.txt"

  About the macros: The macros are relatively new and hence may not be bug-free. Macros imdir, mltbias, mlthear and mltobs were the first macros and were developed by Alejandro Terlevich during (April 2000, October 2000) (text of the original macro release). Macros obj, nobj and ndark are improved variations of these macros and are developed by D. Mayya. All these macros write the data in FITS format files. Header KEYWORDS EXPTIME, DATE-OBS, DATA-TYP, UT-START, CGAINPAR, XBINNING, YBINNING, DISPAXIS, TELESCOP, OBSERVER, INSTRUME, FILTER and COMMENT are written into all the FITS files. The macros obj and nobj have protection against overwriting of files.

  IMPORTANT: When defining "imdir" make sure that the directory is empty or else you will risk erasing files such as bias0.fit, hear0.fit when using mltbias and mlthear. For some reason you want to continue writing data on an old directory, you can redefine the numbers using vdef command.

• Data storage

  Data from the PC are transfered by ftp to the SUN (Ultra1) computer for image analysis and storage. The SUN is equiped with a DAT drive (/dev/rmt/0n). A CD-writer on the data acquisition PC can also be used for data storage. 4-mm DATA tape and read & write CDROMS are usually available at the observatory.

• TIPS

  • Use "Acquire" on the image window menu to take test images.
    
  • You can use "obj" or "nobj" to take HeAr arc spectrum (instead of mlthear).
    
  • Use "nobj" to take multiple flat-field exposures.
    
  • Macros create .FIT images, but IRAF tasks do not recognize .FIT as a fits file. Hence use the unix command "mv" or the iraf command "rfits" on the sun to convert file name extension .FIT to .fits.

Guias en Español del software PMIS desde http://www.casleo.secyt.gov.ar/casleo/byc/byc.html
y macros desde San Pedro Martir, B.C., Mexico

The resolution is then given as:

with F = effective focal length of the spectrograph, which for the Cananea Boller & CHivens is equal to 465mm. Here is a web program which calculates dispersion angle and spectral resolution using the above formulae.

Off-set Autoguider

Sky Spectrum at OAGH

A typical sky spectrum at OAGH is shown below. This spectrum corresponds to December 1999 observations. Important atmosperic and city lines have been identified.

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About this Page:
This page is created and maintained by

Alberto Caraminana, Esperanza Carrasco, Sergio Noriega, Monica Rodriguez, Roberto Terlevich, Elena Terlevich, Alejandro Terlevich, Jose Ramon Valdes, Edgar Castillo, ......

Last Updated: 4 Feb 2003 ydm@inaoep.mx

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