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. 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&

dobim:

zdaj mi je task display sam nastavil parametre prikaza, bolje bi bilo ročno nastaviti nivoje:

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 1400 enot, to je za belo barvo (negativ) sem pustil avtomatsko določeno vrednost, za zgornji pa sem dvignil in s tem zmanjšal kontrast slike:

Na sliki se zdaj bolje vidi center kopice. Najprej določim center kopice. To se naredi z metodo centroid, to je izračuna se težišče (fluksa) kopice. Za začetne koordinate 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")           
vo>

Vrednosti ra in dec zapišem v datoteko in jo imenujem M13.wcs :

250.423475 36.4613194 

Za določitev centra uporabim task center in nastaviti moram parametre v datapars: fwhm, sigma

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
...

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")           

Tu povečam vrednost 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 in 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