Navodila za obdelavo slik

Fotometrija

Ogled različice #9
(Obnovi to različico) 

Spremenjeno: 22 januar 2016, 12:01 PM   Uporabnik: Bojan Dintinjana  → Bojan

Primer 1:

Imamo 8 slik asteroida  (297) Caecilia posnetih z filtrom V in bomo izmeril njegov sij. Slike so:

bojan@lib:~/data/vdelu/Caecilia$ ll -rt
total 82136
-rw-rw-r--  1 bojan bojan 8406720 Dec  9 15:36 Caecilia_V_222.fts
-rw-rw-r--  1 bojan bojan 8406720 Dec  9 15:36 Caecilia_V_224.fts
-rw-rw-r--  1 bojan bojan 8406720 Dec  9 15:36 Caecilia_V_223.fts
-rw-rw-r--  1 bojan bojan 8406720 Dec  9 15:36 Caecilia_V_225.fts
-rw-rw-r--  1 bojan bojan 8406720 Dec  9 15:36 Caecilia_V_227.fts
-rw-rw-r--  1 bojan bojan 8406720 Dec  9 15:36 Caecilia_V_226.fts
-rw-rw-r--  1 bojan bojan 8406720 Dec  9 15:36 Caecilia_V_229.fts
-rw-rw-r--  1 bojan bojan 8406720 Dec  9 15:36 Caecilia_V_228.fts

Najprej preverim ali je asteroid na sliki. V ds9 File->Open in odprem prvo sliko. Nato Analysis->Catalogs->Database->SkyBot in mi na sliki označi pozicijo asteroida, če želim v rdeči barvi Symbol->Color->Red:


Izberem še primerne primerjalne zvezde, Analysis->Catalogs->Search for catalog in za iskanje UCAC4 in kontrolnik Catalog:

Uporabim filter $Vmag<15.5 & $Vmag>0 & ($Bmag-$Vmag)>0.5 & ($Bmag-$Vmag)<0.9 ki mi izbere samo zvezde, ki imajo v katalogu podano V magnitudo, ki so svetlejše od 15.5 in ki imajop barvni indeks B-V med 0.5 in 0.9. Torej čimbolj podobno barvo kot jo ima asteroid.  Tako se tudi izognem zelo rdečim zvezdam, ki so pogosto spremenljivke.
Krogce obarvam v modro barvo in končni izgled je:


Še podatke o zvezdah izvoziml v tekstovno datoteko File-Export->Tab-Separated-Value. Datokoteki asteroid in zvezde združim in v urejevalniku teksta preuredim, da izgledajo takole:

$ cat ref.wcs 
048.73007   +29.43533  Caecilia 
048.7976127 +29.3491614 597-008152 12.030 11.302 11.107 10.944 
048.7177833 +29.2601428 597-008142 12.626 12.031 11.896 11.743 
048.5830383 +29.3559573 597-008123 14.847 14.361 14.242 14.129
Pomembno je, da sta prva dva stolpca rektascenzija in deklinacija  (podano v decimalnih stopinjah), potem sledi ime (mora biti brez presledkov) ter magnitude Bmag, Vmag,rmag,imag.

Zdaj poženemo iraf : 
$ ecl

in v komandni vrstici irafa naložimo pakete za fotometrijo

   NOAO/IRAF PC-IRAF Revision 2.16.1 EXPORT Mon Oct 14 21:40:13 MST 2013
      This is the EXPORT version of IRAF V2.16 supporting PC systems.

  Welcome to IRAF.  To list the available commands, type ? or ??.  To get
  detailed information about a command, type `help <command>'.  To run  a
  command  or  load  a  package,  type  its name.   Type  `bye' to exit a
  package, or `logout' to get out  of the CL.    Type `news' to find  out
  what is new in the version of the system you are using.  

  Visit http://iraf.net if you have questions or to report problems.

      color.      gemini.     lists.      optic.      softools.   utilities.
      ctio.       gmisc.      mscred.     phist.      stecf.      vo.
      dataio.     guiapps.    mtools.     plot.       stsdas.     wcstools.
      dbms.       images.     noao.       proto.      system.     xdimsum.
      fitsutil.   language.   obsolete.   rvsao.      tables.     

ecl> noao
      airvac        astutil.      ll            observatory   surfphot.
      artdata.      digiphot.     mtlocal.      obsutil.      twodspec.
      astcat.       focas.        nobsolete.    onedspec.     
      astrometry.   imred.        nproto.       rv.           

noao> digiphot
      apphot.   daophot.  photcal.  ptools.

digiphot> apphot
      aptest        findpars@     pconvert      polymark      psort
      center        fitpsf        pdump         polypars@     qphot
      centerpars@   fitsky        pexamine      polyphot      radprof
      daofind       fitskypars@   phot          prenumber     wphot
      datapars@     pcalc         photpars@     pselect

Sledi nastavitev parametrov, najprej izračunam vrednost sigma neba, izmerim več slik, recimo sliko na začetku, na sredini in na koncu opazovaja: 

apphot>  imstat Caecilia_V_22*.fts nclip=5
#               IMAGE      NPIX      MEAN    STDDEV       MIN       MAX
   Caecilia_V_222.fts   4173484     539.5     26.05      462.      617.
   Caecilia_V_225.fts   4172849      549.     26.17      471.      627.
   Caecilia_V_227.fts   4172156      547.     26.18      469.      625.

Vrednost za STDEV je 26.0 in vnesem kot parameter sigma v datapars
apphot> datapars
PACKAGE = apphot
   TASK = datapars

(scale  =                   1.) Image scale in units per pixel
(fwhmpsf=                  2.5) FWHM of the PSF in scale units
(emissio=                  yes) Features are positive ?
(sigma  =                  26.) Standard deviation of background in counts
(datamin=                 100.) Minimum good data value
(datamax=               57000.) Maximum good data value
(noise  =              poisson) Noise model
(ccdread=              RDNOISE) CCD readout noise image header keyword
(gain   =                 GAIN) CCD gain image header keyword
(readnoi=                   0.) CCD readout noise in electrons
(epadu  =                   1.) Gain in electrons per count
(exposur=             EXPOSURE) Exposure time image header keyword
(airmass=              AIRMASS) Airmass image header keyword
(filter =               FILTER) Filter image header keyword
(obstime=                   JD) Time of observation image header keyword
(itime  =                   1.) Exposure time
(xairmas=                INDEF) Airmass
(ifilter=                INDEF) Filter
(otime  =                INDEF) Time of observation
(mode   =                   ql)
($nargs =                    0)

Urejanje parametrov končam z tipko ctrl-D. Naslednja klučna nastavitev je velikost aperture. Če izbere premajhno, izgubim del svetlobe, če pa izberem preveliko potem zajamem v meritev še velik del neba, ki prinese tudi veliko šuma. Običajno izberemo za velikost nekoliko manjšo vrednost od FWHM,  ki ga izmerim tako:

apphot> obsutil
      bitcount    cgiparse    kpno.       psfmeasure  specfocus   sptime
      ccdtime     findgain    pairmass    shutcor     specpars@   starfocus

 psfmeasure Caecilia_V_222.fts
** Select stars to measure with 'm' and finish with 'q'.
** Additional options are '?', 'g', and :show.
qNOAO/IRAF V2.16.1 bojan@lib Thu 13:27:21 21-Jan-2016

          Image  Column    Line     Mag    FWHM   Ellip      PA SAT
Caecilia_V_222.  948.44 1036.26    0.07   3.258    0.11     -26
                1038.39 1058.44    1.52   3.320    0.17     -20
                 957.44  948.46    0.00   3.080    0.16     -28
                1176.95  909.18    1.78   3.322    0.13     -26
                1179.85  875.30    0.68   3.116    0.18     -37
                 722.36  811.29    2.53   3.070    0.11      10
                 695.00  794.91    1.71   2.898    0.23     -21
                 888.08  788.07    1.80   2.852    0.28     -33
                 888.08  788.07    1.80   2.852    0.28     -33

  Average full width at half maximum (FWHM) of 3.1265

Zdaj nastavim še aperturo in sicer na vrednost 1.5  (2 x 1.5 = 3.0 )

apphot> photpars
PACKAGE = apphot
   TASK = photpars

(weighti=             constant) Photometric weighting scheme for wphot
(apertur=                  1.5) List of aperture radii in scale units
(zmag   =                  25.) Zero point of magnitude scale
(mkapert=                   no) Draw apertures on the display
(mode   =                   ql)
($nargs =                    0)

apphot> epar apphot
PACKAGE = digiphot
   TASK = apphot

(version=                May00)
(wcsin  =              logical) The input coordinates wcs
(wcsout =              logical) The output coordinates wcs
(cache  =                   no) Cache image in memory ?
(verify =                  yes) Verify critical parameters ?
(update =                  yes) Update critial parameters ?
(verbose=                  yes) Print verbose output ?
(graphic=             stdgraph) Default graphics device
(display=             stdimage) Default display device
(mode   =                   ql)
($nargs =                    0)