Navodila za obdelavo slik
Fotometrija
Kazalo vsebine
1. Primer 1: Diferencialna fotometrija, znane koordinate objektov
[uredi]
Primer 1: Diferencialna fotometrija, znane koordinate objektov
[uredi]
Imamo 8 slik asteroida (297) Caecilia posnetih z filtrom V in bomo izmeril njegov sij. Slike so:
bojan@lib:~/data/vdelu/Caecilia$ ll -rtNajprej 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:
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
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 ref1.tsvPomembno 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.
048.683756 +29.426051 Caecilia
048.797613 +29.349161 597-008152 12.030 11.302 11.107 10.944
048.717783 +29.260143 597-008142 12.626 12.031 11.896 11.743
048.538336 +29.477656 598-008585 14.886 14.040 13.770 13.475
048.715125 +29.549617 598-008623 16.172 15.292 14.947 14.577
048.779038 +29.553463 598-008634 16.163 15.341 15.003 14.692
Zdaj poženemo iraf :
$ ecl
Za kontrolo vhodne datoteke ref1.tsv najprej narišem v irafu
ecl> imcoordsin dobim sliko podobno kot prej v ds9, označene so primerjalne zvezde in asteroid. Zdaj lahko začnem pripravljati za fotometrijo. v komandni vrstici irafa naložimo pakete za fotometrijo
imcoords> wcsctran
The input images (Caecilia_V_222.fts):
The input coordinate files (ref1.tsv):
The output coordinate files (ref1.xy):
The input coordinate system (|logical|tv|physical|world|) (world):
The output coordinate system (|logical|tv|physical|world|) (logical):
imcoords> display Caecilia_V_222.fts
frame to be written into (1:16) (2): 1
z1=383.5378 z2=698.7778
imcoords> tvmark 1 ref1.xy mark=circle radii=7 color=204
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=5Vrednost za STDEV je 26.0 in vnesem kot parameter sigma v datapars
# 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.
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)
($nargs = 0)
Urejanje parametrov končam z tipko ctrl-D. Naslednja klučna nastavitev je velikost aperture. Če izberem premajhno, izgubim del svetlobe in s tem natančnost, če pa izberem preveliko potem zajamem v meritev še velik del neba, ki prinese tudi veliko šuma. Običajno izberemo za velikost nekoliko manjšo vrednost od FWHM, ki ga izmerim tako:
apphot> obsutil
bitcount cgiparse kpno. psfmeasure specfocus sptime
ccdtime findgain pairmass shutcor specpars@ starfocus
obsutil> psfmeasure Caecilia_V_222.fts
** Select stars to measure with 'm' and finish with 'q'.
** Additional options are '?', 'g', and :show.
qNOAO/IRAF V2.16.1 bojan@lib Thu 13:27:21 21-Jan-2016
Image Column Line Mag FWHM Ellip PA SAT
Caecilia_V_222. 948.44 1036.26 0.07 3.258 0.11 -26
1038.39 1058.44 1.52 3.320 0.17 -20
957.44 948.46 0.00 3.080 0.16 -28
1176.95 909.18 1.78 3.322 0.13 -26
1179.85 875.30 0.68 3.116 0.18 -37
722.36 811.29 2.53 3.070 0.11 10
695.00 794.91 1.71 2.898 0.23 -21
888.08 788.07 1.80 2.852 0.28 -33
888.08 788.07 1.80 2.852 0.28 -33
Average full width at half maximum (FWHM) of 3.1265
S tipko 'm' izberemo nekaj lepih zvezd v sredini polja in končamo s tipko 'q', grafično program prikaže:
Zdaj nastavim še aperturo in sicer na vrednost 1.5 (2 x 1.5 = 3.0 ). Za čim boljše rezultate priporočajo, da se obdelavo večkrat ponovimo z malo različnimi vrednosti aperture in izberemo najbolj optimalno vrednost:
apphot> photpars
PACKAGE = apphot
TASK = photpars
(weighti= constant) Photometric weighting scheme for wphot
(apertur= 1.5) List of aperture radii in scale units
(zmag = 25.) Zero point of magnitude scale
(mkapert= no) Draw apertures on the display
(mode = ql)
($nargs = 0)
Paket apphot nastavimo verbose yes, to pomeni, da program naredi več izpisa, hkrati zamenjamo še wcsin na world, kar pomeni da bodo vhodne koordinate ekvatorialne. Rektascenzija in deklinacija zvezde je invarjantna na morebitne premike slike.
apphot> epar apphot
PACKAGE = digiphot
TASK = apphot
(version= May00)
(wcsin = world) 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)
Še nastavim največji dovoljen premik pri centriranju maxshift , koordinate iz katalogov lahko namreč malenkost odstopajo od trenutne pozicije zvezde, recimo zaradi lastnega gibanja zvezde. Za asteroid pa še posebej, ker se giblje precej hitro in je lahko že v nekaj deset minutah izven območja centriranja:
PACKAGE = apphot
TASK = centerpars
(calgori= centroid) Centering algorithm
(cbox = 10.) Centering box width in scale units
(cthresh= 0.) Centering threshold in sigma above background
(minsnra= 1.) Minimum signal-to-noise ratio for centering alg
(cmaxite= 10) Maximum number of iterations for centering algo
(maxshif= 5.) Maximum center shift in scale units
(clean = no) Symmetry clean before centering ?
(rclean = 1.) Cleaning radius in scale units
(rclip = 2.) Clipping radius in scale units
(kclean = 3.) Rejection limit in sigma
(mkcente= no) Mark the computed center on display ?
(mode = ql)
Nastavim še parametre za phot:
PACKAGE = apphot
TASK = phot
image = Caecilia_V_222.fts The input image(s)
skyfile = The input sky file(s)
(coords = ref1.tsv) The input coordinate files(s) (default: image.c
(output = default) The output photometry file(s) (default: image.m
(plotfil= ) The output plots metacode file
(datapar= ) Data dependent parameters
(centerp= ) Centering parameters
(fitskyp= ) Sky fitting parameters
(photpar= ) Photometry parameters
(interac= no) Interactive mode ?
(radplot= no) Plot the radial profiles in interactive mode ?
(icomman= ) Image cursor: [x y wcs] key [cmd]
(gcomman= ) Graphics cursor: [x y wcs] key [cmd]
(wcsin = world) The input coordinate system (logical,tv,physica
(wcsout = )_.wcsout) The output coordinate system (logical,tv,physic
(cache = )_.cache) Cache the input image pixels in memory ?
(verify = )_.verify) Verify critical parameters in non-interactive m
(update = )_.update) Update critical parameters in non-interactive m
(verbose= )_.verbose) Print messages in non-interactive mode ?
(graphic= )_.graphics) Graphics device
(display= )_.display) Display device
(mode = ql)
Končno poženem fotometrijo:
apphot> phot
The input image(s) (Caecilia_V_222.fts):
Centering algorithm (centroid) (CR or value):
New centering algorithm: centroid
Centering box width in scale units (10.) (CR or value):
New centering box width: 10. scale units 10. pixels
Sky fitting algorithm (centroid) (CR or value):
Sky fitting algorithm: centroid
Inner radius of sky annulus in scale units (10.) (CR or value):
New inner radius of sky annulus: 10. scale units 10. pixels
Width of the sky annulus in scale units (10.) (CR or value):
New width of the sky annulus: 10. scale units 10. pixels
File/list of aperture radii in scale units (1.5) (CR or value):
Aperture radius 1: 1.5 scale units 1.5 pixels
Standard deviation of background in counts (26.) (CR or value):
New standard deviation of background: 26. counts
Minimum good data value (100.) (CR or value):
New minimum good data value: 100. counts
Maximum good data value (59000.) (CR or value):
New maximum good data value: 59000. counts
Caecilia_V_222.fts 948.52 1036.25 543.9628 17.680 ok
Caecilia_V_222.fts 1501.78 594.48 550.011 15.684 ok
Caecilia_V_222.fts 1101.89 97.68 543.6045 16.432 ok
Caecilia_V_222.fts 233.60 1345.29 548.2761 18.461 ok
Caecilia_V_222.fts 1112.74 1743.06 542.8564 19.977 ok
Caecilia_V_222.fts 1429.21 1761.70 545.3671 20.235 ok
apphot>
Rezultate fotometrije imam v datoteki Caecilia_V_222.fts.mag.1 vendar je datoteka mag precej neberljiva, po štiri vrstice raznih podatkov na zvezdo, zato je bolj praktično če naredim izvleček in izpišem samo stolpce ki me zanimajo:
apphot> pdump Caecilia_V_222.fts.mag.1
Fields to be extracted (id,mag,merr):
Boolean expression (yes):
ID MAG MERR
1 17.680 0.005
2 15.684 0.002
3 16.432 0.003
4 18.461 0.007
5 19.977 0.018
6 20.235 0.023
apphot>
ID številka meritve v prvem stolpcu je številka vrstice iz vhodne datoteke ref1.tsv. Magnitude v drugem stolpcu so instrumentalne, to pomeni, da so nedoločene za aditivno konstanto, ki ji rečemo tudi ničelna magnituda. Le to določim s pomočjo kataloških vrednosti magnitude V primerjalnih zvezd.