en:praktikum:sternspektren

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en:praktikum:sternspektren [2024/12/06 09:39] – [N1 - Stellar spectra of different spectral types (DADOS)] rhainichen:praktikum:sternspektren [2024/12/10 11:00] (current) – rhainich
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 These instructions are currently being revised as part of the move to enhanced evaluation software. However, the manual is currently complete. It can be used without further ado to evaluate the data. Just don't be surprised if you see "transition" or "transition_version" somewhere.  These instructions are currently being revised as part of the move to enhanced evaluation software. However, the manual is currently complete. It can be used without further ado to evaluate the data. Just don't be surprised if you see "transition" or "transition_version" somewhere. 
 </WRAP> </WRAP>
- 
  
 The aim of this observation is to obtain an overview of different spectral types. Thus, we will give you the coordinates and the apparent magnitude of four stars of different spectral type that are well visible during the night of your observation. Take spectra of these stars in order to classify them by means of the spectral lines and the shape of the continua.  The aim of this observation is to obtain an overview of different spectral types. Thus, we will give you the coordinates and the apparent magnitude of four stars of different spectral type that are well visible during the night of your observation. Take spectra of these stars in order to classify them by means of the spectral lines and the shape of the continua. 
  
- 
-/*The aim of this observation is to obtain an overview of different spectral types. Thus, choose at least one star of each spectral type (O, B, A, F, G, K, M, special classes after consultation) that is well visible ($m_\mathrm{V} \le 9\,$mag). Take spectra of these stars in order to classify them by means of the spectral lines and the shape of the continua. To find suitable stars, use pages like [[http://simbad.u-strasbg.fr/simbad/|Simbad]] - a help page for the parameter query at Simbad can be found [[en:etc:simbad|here]].*/ 
  
 ===== Observation ===== ===== Observation =====
-Nightly observations at the OST in Golm with the DADOS spectrograph are required. The scientific and technical background for this observation are presented in the seminary talks. A list with objects will be provided by us.+Nightly observations at the OST in Golm with the DADOS spectrograph are required. The //DADOS// with a 900 lines/mm grid is currently used in combination with the //QHY 268M//. The scientific and technical background for this observation are presented in the seminary talks. A list with objects will be provided by us.
  
 **Note**: The following exposures are needed //for every// star: **Note**: The following exposures are needed //for every// star:
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   * calibration spectra with a discrete light source   * calibration spectra with a discrete light source
   * calibration spectra with a continuous light source (flatfield)   * calibration spectra with a continuous light source (flatfield)
-  * darkframes for the exposures of the stellar spectra and the continuous light source+  * darkframes
  
 The calibration exposures are needed to calculate the pixel scale (wavelength calibration) and to remove the instrument signatures and possible artifacts. The calibration exposures are needed to calculate the pixel scale (wavelength calibration) and to remove the instrument signatures and possible artifacts.
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 The following variables need to be set in the script: The following variables need to be set in the script:
-<code>+<code Python>
 ### ###
 #   Path to the directories with the images #   Path to the directories with the images
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 There are several tools for viewing 2D images in FITS format. //ds9// is easy to use and can be started from the terminal: There are several tools for viewing 2D images in FITS format. //ds9// is easy to use and can be started from the terminal:
  
-   ds9 filename.fit +  ds9 filename.fit 
  
 Tasks: Tasks:
-  * determine the range of CCD rows that contains the stellar spectrum (master_spectrum.fit). +  * determine the range of camera chip rows that contains the stellar spectrum (master_spectrum.fit). 
-  * determine the range of CCD rows that can be used as background. Important: The background region must be outside the spectrum, but still within the used slit of the spectrograph. If the latter cannot be distinguished from the black background, compare with the images of the lamp spectra (master_wave.fit).+  * determine the range of camera chip rows that can be used as background. Important: The background region must be outside the spectrum, but still within the used slit of the spectrograph. If the latter cannot be distinguished from the black background, compare with the images of the lamp spectra (master_wave.fit).
  
  
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 === Basic principle === === Basic principle ===
-The script searches for the maxima in the calibration spectrum, marks them and notes the pixel number where the intensity maxima are located. It then assigns a wavelength to each of these values. This creates a pixel-wavelength mapping that is used to analyse the star's spectrum. +The script searches for the maxima in the calibration spectrum, marks them and notes the pixel number where the intensity maxima are located. It then assigns a wavelength to each of these values. This creates a pixel-wavelength mapping that is used to analyze the star's spectrum. 
  
 === Parameter === === Parameter ===
 The corresponding script is called **2_findcaliblines.py**. In this file, using an editor of your choice (e.g. //Kate//), you only need to edit the line region where the calibration spectrum is to be found (''specRegionStart'' and ''specRegionEnd''; can be the same as the one you want to extract the star spectrum from) and a line region that is **outside the slits** (''bgRegionStart'', ''bgRegionEnd''): The corresponding script is called **2_findcaliblines.py**. In this file, using an editor of your choice (e.g. //Kate//), you only need to edit the line region where the calibration spectrum is to be found (''specRegionStart'' and ''specRegionEnd''; can be the same as the one you want to extract the star spectrum from) and a line region that is **outside the slits** (''bgRegionStart'', ''bgRegionEnd''):
-   + 
-  # name of the file with the wavelength calibration spectrum  +<code Python> 
-  calibFileName   = "calib_wave.FIT" +# region (rows on the image) containing the calibration spectrum 
-   +specRegionStart = 495 
-  # region (rows on the image) containing the calibration spectrum +specRegionEnd   = 600
-  specRegionStart = 495 +
-  specRegionEnd   = 600 +
-   +
-  # background region (rows on the image), which needs to be outside of the slits +
-  bgRegionStart   = 0 +
-  bgRegionEnd     = 200+
    
 +# background region (rows on the image), which needs to be outside of the slits
 +bgRegionStart   = 0
 +bgRegionEnd     = 200
 +</code>
 +
 The calibration is designed such that lines of mercury and argon are identified. The strongest lines that can be expected are marked in the following plot. The calibration is designed such that lines of mercury and argon are identified. The strongest lines that can be expected are marked in the following plot.
  
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 [{{ :ost:spektrograph:spectra:calib_lines_dados.jpg?direct&800 | Emission spectrom of our calibration lamp. The strongest mercury and argon lines are identified.}}] [{{ :ost:spektrograph:spectra:calib_lines_dados.jpg?direct&800 | Emission spectrom of our calibration lamp. The strongest mercury and argon lines are identified.}}]
 ++++ ++++
 +
 === Execution of the script === === Execution of the script ===
 Now run the script by executing: Now run the script by executing:
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 === Basic principle === === Basic principle ===
-Once the wavelength-pixel mapping has been determined, the actual star spectrum can be evaluated. By default, the spectrum is divided by the flat field and then the wavelength calibration is performed. It is also possible to normalise the spectrum and mark the spectral lines identified in the spectrum.+Once the wavelength-pixel mapping has been determined, the actual star spectrum can be evaluated. By default, the spectrum is divided by the flat field and then the wavelength calibration is performed. It is also possible to normalize the spectrum and mark the spectral lines identified in the spectrum.
  
 === Parameters === === Parameters ===
 This associated script is named ''3_extractspectrum.py''. The script has a number of parameters, similar to the previous scripts, along with some additional parameters. The parameter section usually looks like this: This associated script is named ''3_extractspectrum.py''. The script has a number of parameters, similar to the previous scripts, along with some additional parameters. The parameter section usually looks like this:
  
-<code>+<code Python>
 #   Name of the object #   Name of the object
 object_name: str = "star" object_name: str = "star"
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 The name of the observed star can be specified in ''object_name''. The variables ''spec_region_start'' and ''spec_region_end'' define the lines of the camera chip containing the spectrum to be read out. From this star spectrum the sky background has to be subtracted. This is done by selecting a region that lies **within the slit** but **does not contain a spectrum**. This region is defined by the variables ''background_sky_start'' and ''background_sky_end''. The options ''lambda_min'' and ''lambda_max'' as well as ''flux_min'' and ''flux_max'' can be used to restrict the plot area on the X or Y axis. If ''?'' is written in these variables, the plot range is automatically defined. The name of the observed star can be specified in ''object_name''. The variables ''spec_region_start'' and ''spec_region_end'' define the lines of the camera chip containing the spectrum to be read out. From this star spectrum the sky background has to be subtracted. This is done by selecting a region that lies **within the slit** but **does not contain a spectrum**. This region is defined by the variables ''background_sky_start'' and ''background_sky_end''. The options ''lambda_min'' and ''lambda_max'' as well as ''flux_min'' and ''flux_max'' can be used to restrict the plot area on the X or Y axis. If ''?'' is written in these variables, the plot range is automatically defined.
  
-/* 
-++++ Additional parameter | 
  
-**Reduction method:**  
-The variable ''mode'' allows to specify the reduction method. An average over all extracted CCD rows will be calculated, if the method //mean// is set. A median function will be applied, if //median// is selected.  The latter method should be used as the default.  
- 
-   ### Image reduction mode ### 
-   #mode = 'mean' 
-   mode = 'median' 
- 
-**Line identifications:** 
-The line identifications can be switched on and off via the variable ''plotident'': 
- 
-   ### Idents ### 
-   # plot idents yes or no 
-   plotident = 'yes' 
-   #plotident = 'no' 
- 
-The file with line identifications, which by default is simply denoted by ''absorption_lines'', is not required for a successful script run, i.e. the variable ''lineFile'' can be an empty string or point to an empty file: 
- 
-   # file containing line identifications 
-   lineFile = "" 
-   # or 
-   lineFile = "directory/empty_file.dat" 
- 
-See below for an explanation how to adjust the line identification file for the individual stars.  
- 
-**File names:** 
-It also exists the possibility to change the names of the output files as well as to adjust the names of the files from the first step of the data reduction that are now needed as input for the wavelength calibration. 
-++++ 
-*/ 
 === Execution of the script === === Execution of the script ===
 Now run the script: Now run the script:
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   * ''{object_name}_spectrum_total.dat'' - with the spectrum in tabular form    * ''{object_name}_spectrum_total.dat'' - with the spectrum in tabular form 
   * ''{object_name}_spectrum_total.csv'' - with the tabulated spectrum in CSV format   * ''{object_name}_spectrum_total.csv'' - with the tabulated spectrum in CSV format
- 
  
  
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 | ''manual_lines'' | By means of this variable further line identifications can be added manually. An identification string such as "HeI", the wavelength and the alignment parameter ("center", "left" or "right") must be set for each line. | | ''manual_lines'' | By means of this variable further line identifications can be added manually. An identification string such as "HeI", the wavelength and the alignment parameter ("center", "left" or "right") must be set for each line. |
 | ''percentage_line_flux_must_be_below_continuum'' | This variable determines how deep lines must be in comparison to the continuum so that line identifications are displayed for the corresponding lines. The higher this value, the fewer line identifications are displayed, since only the stronger lines then fulfill this criterion. **Note:** If the radial velocity is wrong and a value greater than zero is set here, then the line identification often does not work. Therefore this variable should be set to zero if the radial velocity is unknown. | | ''percentage_line_flux_must_be_below_continuum'' | This variable determines how deep lines must be in comparison to the continuum so that line identifications are displayed for the corresponding lines. The higher this value, the fewer line identifications are displayed, since only the stronger lines then fulfill this criterion. **Note:** If the radial velocity is wrong and a value greater than zero is set here, then the line identification often does not work. Therefore this variable should be set to zero if the radial velocity is unknown. |
- 
  
  
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