AGO Teleskop

Posneli smo 12 slik krogralste kopice M13, čas osvetlitve smo nastavili na 60s. Vse slike smo najprej obdelali osnovne kalibracije, to je zero, dark in flat ten nato naredili še astrometrični fit. Nato smo slike sešteli in dobili končno sliko sM13_W.fts. Nadaljujem z obdelavo: najprej sliko pogledam v irafu:

vo> !ds9&
vo> display sM13_W.fts                                
frame to be written into (1:16) (1): 
z1=1379.238 z2=1914.297> !ds9&

vo> display sM13_W.fts zrange- zscale- z1=1400 z2=10000                      
frame to be written into (1:16) (1): 
z1=1400. z2=10000.

spodnji nivo z1=1400 enot, to je za belo barvo (negativ) sem pustil približno avtomatsko določeno vrednost, zgornji nivo pa sem dvignil in s tem zmanjšal kontrast in slika je tudi svetlejša:

Na tako prikazani sliki se bolje vidi center kopice. Najprej moram natančno določiti center kopice. To se naredi z metodo centroid, to je izračuna se težišče (fluksa) kopice. Za začetne koordinate kopice, da ne ugibam in klikam preveč, uporabim kar kataloško vrednost recimo iz Simbada, ali pa dam, da mi kar iraf poišče:

vo> sesame M13                                                            
16:41:41.63 +36:27:40.
vo> lpar sesame 
       target = "M13"           Target names to resolve
       (range = "")             Target range string
     (verbose = yes)            Print position to stdout?
        (long = no)             Long format?\n
         (pos = "16:41:41.63 +36:27:40.") Resolved position (sexagesimal string)
          (ra = 250.423475)     Resolved RA (J2000 decimal degrees)
         (dec = 36.461319)      Resolved Dec (J2000 decimal degrees)
      (ra_err = 0.)             Error on RA (arcsec)
     (dec_err = 0.)             Error on Dec (arcsec)
       (otype = "Gl")           Resolved object type description
      (status = 0)              Service status code
        (mode = "ql")           

Vrednosti ra in dec zapišem v datoteko in jo imenujem M13.wcs, datoteka izgleda tako:

250.423475 36.4613194 

Za določitev centra uporabim task center iz paketa apphot, še prej pa moram nastaviti parametre v datapars: fwhm, sigma

vo> imstat  sM13_W.fts  nclip=7                            
#               IMAGE      NPIX      MEAN    STDDEV       MIN       MAX
           sM13_W.fts   3679001     1645.     36.55     1533.     1759.
vo> datapars 
       (scale = 1.)             Image scale in units per pixel
     (fwhmpsf = 150.)           FWHM of the PSF in scale units
    (emission = yes)            Features are positive ?
       (sigma = 36.)            Standard deviation of background in counts
     (datamin = 1000.)          Minimum good data value
     (datamax = 58000.)         Maximum good data value
...

fwhm sem povečal na "širino" kopice, sigma pa izmerim z imstat, ostale parametre pustim privzete. Še centerpars:

 vo> centerpars
  (calgorithm = "centroid")     Centering algorithm
        (cbox = 250.)           Centering box width in scale units
  (cthreshold = 0.)             Centering threshold in sigma above background
  (minsnratio = 1.)             Minimum signal-to-noise ratio for centering algorithm
    (cmaxiter = 10)             Maximum number of iterations for centering algorithm
    (maxshift = 50.)            Maximum center shift in scale units
       (clean = yes)            Symmetry clean before centering ?
      (rclean = 50.)            Cleaning radius in scale units
       (rclip = 50.)            Clipping radius in scale units
      (kclean = 3.)             Rejection limit in sigma
    (mkcenter = no)             Mark the computed center on display ?
        (mode = "ql")           

Tudi tu povečam vrednosti cbox, maxshift, rclean in rclip, tako da zdaj iraf vidi celo kopico kot eno zvezdo in jo bo centriral:

vo> center sM13_W coords="M13.wcs" wcsin="world" interactive=no   

Centering algorithm (centroid) (CR or value): 
        New centering algorithm: centroid
Centering box width in scale units (250.) (CR or value): 
        New centering box width: 250. scale units  250. pixels
Standard deviation of background in counts (36.) (CR or value): 
        New standard deviation of background: 36. counts
Minimum good data value (0.) (CR or value): 
        New minimum good data value: 0. counts
Maximum good data value (58000.) (CR or value): 
        New maximum good data value: 58000. counts

sM13_W   846.80 1093.18   832.35 1078.20    0.02   0.02  err

Rezultat dobim v datoteki sM13_W.ctr.1, za kontrolo narišem na sliko:

vo> pdump sM13_W.ctr.1 fields="xc,yc" expr=yes > center.xy
vo> tvmark 1 centerW.xy col=204 radii=50

Nastavim še parametre za meritev ozadja fitskypar

vo> fitskypar
  (salgorithm = "centroid")     Sky fitting algorithm
     (annulus = 160.)           Inner radius of sky annulus in scale units
    (dannulus = 10.)            Width of sky annulus in scale units
...

Povečal sem annulus radij od kje naprej vzame vrednosti neba. Končno izmerimo profil kopice:

vo> radprof       
The input image(s) (sM13_W): 
The maximum radial profile radius in scale units (150.): 200
The step size for radial profile in scale units (3.): 1

Centering algorithm (centroid) (CR or value): 
        New centering algorithm: centroid
Centering box width in scale units (250.) (CR or value): 
        New centering box width: 250. scale units  250. pixels
Sky fitting algorithm (centroid) (CR or value): 
        Sky fitting algorithm: centroid
Inner radius of sky annulus in scale units (160.) (CR or value): 200
        New inner radius of sky annulus: 200. scale units 200. pixels
Width of the sky annulus in scale units (10.) (CR or value): 
        New width of the sky annulus: 10. scale units 10. pixels
Standard deviation of background in counts (36.) (CR or value): 
        New standard deviation of background: 36. counts
File/list of aperture radii in scale units (2) (CR or value): 
        Aperture radius 1: 2. scale units 2. pixels
Fitting radius in scale units (200.) (CR or value): 
        New fitting radius: 200. scale units  200. pixels
Step size in scale units (1.) (CR or value): 
        New step size: 1. scale units  1. pixels
Minimum good data value (0.) (CR or value): 1000
        New minimum good data value: 1000. counts
Maximum good data value (58000.) (CR or value): 
        New maximum good data value: 58000. counts

sM13_W    831.56  1078.19  2138.514 117.2   16.646  err
vo> 

Rezultat dobimo v datoteki sM13_W.prf.1 in še narišemo v gnuplotu:

gnuplot> set logscale
gnuplot> plot [2:200][0.05:2]'sM13_W.prf.5' u ($1*0.64):2
gnuplot> set ylabel "povrsinska svetlost I/Io"
gnuplot> set xlabel "radij /arcsec"
gnuplot> set grid 0
gnuplot> replot

in dobim: