| Astronomical photometry (photometry for short) is the measurement of radiant flux comingfrom celestial body in the range of limited band. The photometry can give the important physicalparameters such as apparent magnitude, colour index, the spectral energy distribution (SED) andso on. By analyzing the photometric results, it will take further investigations on their physicalcharacteristics, kinetics, the process of formation and evolution, theoretical model and so forth.Photometry has been an important method to study a variety of celestial bodies.According to the extension of celestial image, the photometric method can be divided intotwo kinds: aperture photometry, including PSF (Point Spread Function) photometry), and surfacephotometry. Aperture photometry is suitable for point source (such as stars, distant galaxies withtiny angular diameter). Surface photometry is used to study extended objects such as nearbygalaxies, nebula, planet etc. The aperture photometry is relatively simple, however, the surfacephotometry is relatively complicated. The methods of both aperture photometry and surfacephotometry have been well-studies at abroad at present. Most of photometric documents at homeare the introductions about aperture photometry. There is still no comprehensive introductionabout surface photometry.The Sloan Digital Sky Survey(SDSS) is one of the most ambitious and influentialastronomical in history. The survey maps one-quarter of the entire sky in detail, determining thepositions and absolute brightness of hundreds of millions of celestial objects. It also measuresdistances of more than a million galaxies and quasars. It is one of the most scientific researchoutput program in sky survey. With the restrictions of scientific aims and the time-cost limitedabout high-accuracy surface photometry, it takes simple handle (circular aperture and variableaperture) about the surface photometry by using SDSS image reduction software. This methoddoesn’t measure celestial body according to their isophotes, which can not accurately reflect theproperties of intrinsic structure of the celestial objects whose isophotes greatly deviate fromperfect circles.According to the above two aspects, this task is on the basic of Command Language(CL),byinvoking toolkit in astronomical data processing and analysis software-IRAF ( Image Reductionand Analysis Facility ) and SExtractor (Source-Extractor) and so on, we design a program toperform high-accuracy isophotal photometry for SDSS galaxy images. Basing on our photometryprocedure, we provide a comprehensive and systematic annotation to the isophotal photometryon SDSS galaxies image (r band) for the first time. It includes the preliminary preprocessing of images, sky background subtraction, the fitting method of isophotes, output results and meaningetc. We carefully analyze and examine the fitted results of galaxies with different morphology( elliptical, spiral, barred, ringed galaxies etc.) , and discuss the similarities and differences of theoutput parameters of different galaxies. It will extend to~ 26mag /arcsec~2(on the average~ 24mag /arcsec~2in SDSS) to r-band image photometry of SDSS nearby galaxies by ourmethod, which make it possible to study the outskirts of galaxies (such as faint stellar halo) byusing SDSS data.We also describe the installation and usage about the Linux operating system, IRAF,SExtractor, ds9/SAOimage, Xgterm and so on. This thesis fills up the blank of introduction aboutgalaxy surface photometry, which is helpful for astronomers with interested in galaxy physics. |
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