ccd observing/research project: ngc 3953 by: ekta patel date: april 7 th, 2011 instructor: j. west...
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CCD OBSERVING/RESEARCH PROJECT:NGC 3953
By: Ekta PatelDate: April 7th, 2011Instructor: J. WestCourse No: PHYS 2070(NOAO, 2005)
Basic Info
My Images
Image Comparison
Research Area
Repeated Calculation
Focus Area
Table of Contents
Basic Information (Stellarium,
2010)•Barred spiral galaxy•Located 46 million light years away•Magnitude: 10.1•Angular Size: 6’36”
•Coordinates (Jan 1, 2001 @ 23:00) (Stellarium, 2010)• RA: 11 h 54 m 22.0s• DE: +52 D 16’ 20”
•Rising earlier each night between January – March (our observing period)• Best month is April
•Located in constellation Ursa Major• Use one of the stars from the constellation as a guide star
•Member of the M109 Group of galaxies• Over 50 galaxies
•Two supernovae have gone off in past decade • SN 2001 dp (Type Ia)• SN 2006 bp (Type II)
(Moromisato, 2011)
(Moromisato, 2011)
Image ComparisonGAO Image
STSciI DSS Image
Date/Time May 7th, 1991/ 4:17:00Location Latitude: 33.356
Longitude: 116.863Telescope Used Oschin Schmidt - DDetector Used Photographic PlateFilter RG610Exposure Time 72 minutesField of View 7.0’ x 7.0’
Date/Time Feb 8, 2011/ 22:05:00Location Latitude: 49 38 min 43 s
Longitude: 97 d, 7min, 20 sTelescope Used Evans 40 cmDetector Used Apogee U47 Exposure Time 33 minutesField of View 7.0’ x 7.0’
Image Processing
Background Information
Structural symmetry specifically in spiral arms of face-on spiral galaxies.
Symmetry: “The quality of being made up of exactly similar parts facing each other or around an axis.” (Oxford American Dictionary, 2010)
Asymmetry: “The lack of equivalence between parts or aspects of something; lack of symmetry.” (Oxford American Dictionary, 2010)
General assumption: face-on spiral galaxies are mainly axi-symmetric
(Foresman, 2007)
Background Information
•Fourier techniques show deviations in symmetry exist for spiral galaxies. (Zarisky, 1995)
•Use of symmetry of spiral arms as a morphological indicator:
•started by Elmegreen and Elmegreen in 1982 “symmetric images of galaxies …allowed for underlying
spiral structure to be examined closely…revealed many spirals have hidden features (ie: triple arm patterns)” (Conselice, 2007)
•Classification of galaxies includes high redshifted galaxies (ie: those seen in HDS telescope images) regular classification is not sufficient because they galaxies are faint and irregular.
• solution 1: automated classification through computer models to assign galaxies classical morphological types
•solution 2: use structural symmetry measurements for classification
•First we must study its usefulness and examine limitations on nearby galaxies
(Conselice, 1997)
Research Paper “The Symmetry, Color, and Morphology of Galaxies”
Christopher J. Conselice 1997
Research Topic: What symmetry in a galaxy can imply.
Objects Studied: •35 face-on spiral (early, intermediate and late types)•8 elliptical•selected from the public FTP site of galaxy images•large, nearby with high-surface brightness •various morphologies •Images in R (650 nm) and J (450 nm) bands used
•1.1 m Hall telescope @ Lowell Obs (March 24-April 4 1989)
•CCD camera: 320 X 512 pixel RCA
•30 min exposures for R band
•45 min exposure for J band
(Conselice, 1997)
Research Paper “The Symmetry, Color, and Morphology of Galaxies”
Christopher J. Conselice 1997
Method: 1. Subtract background stars + sky background2. Rotate 180 degrees about the center point (brightest region in the
middle)3. Subtract rotated image from original 4. Square the pixels in residual image5. Divide the sum of pixels in residual image by 2 times the sum of the
squared pixels of original image
Equation:
A=0 Perfectly symmetricA=1 Completely asymmetric
Research Paper “The Symmetry, Color, and Morphology of Galaxies”
Christopher J. Conselice 1997
Potential Limitations:
•Distant galaxies have lower resolution
•Closer galaxies have higher resolution
Are these limitations present?
•plot of symmetry vs. distance
•slight distance effect is noticed
•thus, caution should be used when
applying this method to galaxies in
different red-shift ranges
(Conselice, 1997)
Research Paper “The Symmetry, Color, and Morphology of Galaxies”
Christopher J. Conselice 1997
Results:
•J band images are more asymmetic on average than R band•Most galaxies were found to be not extremely asymmetric•NGC 3953 was right in the middle average asymmetry
•Strong correlation between asymmetry and morphological types:• Low #’s = early system• High #’s = late-type system• Trend noticeable between Hubble morphology
& sym.• As galaxies reach later- type spirals,
asymmetry increases. Suggests, Hubble Sequence is on increasing optical asymmetry.
(Conselice, 1997)
(Conselice, 2007)
Research Paper “The Symmetry, Color, and Morphology of Galaxies”
Christopher J. Conselice 1997
•Symmetry colour plot has a strong correlation
•Thus degree of symmetry can be used to measure global stellar
populations within a galaxy.
•asymmetric galaxies have stellar populations that are blue recently
formed massive young stars. Due to patchy star formation throughout
the disk
•older stellar populations are smoothed out through time, thus more
symmetric
•Global asymmetries affect R and J bands equally
•Asymmetries are causes by recently formed stars,
thus can be used to measure star formation rate.
(Conselice, 1997)
Research Paper Findings
“The Symmetry, Color, and Morphology of Galaxies”Christopher J. Conselice 1997
Conclusions:
•Strong correlation between asymmetry and colour useful for
finding one, when other is unknown
•Using symmetry, physical parameters of galaxies which otherwise
would not be measureable are reasonably estimated.
•Limited, but powerful for morphological and physical information of
a galaxy.
NGC 3953 Measurements
Original Image: Background & Star Subtracted
Background Subtracted & Star Subtracted + Flipped 180o
SUBTRACT
NGC 3953 Measurements
Result of Subtraction
NGC 3953 Measurements
2 X (Original Image)2 (Result of Subtraction)2
DIVIDE
NGC 3953 Measurements
Calculations:
A2= (73563 x 81283.44)/ 2(73563 x 8284.404)
A=0.20 (for 550 nm)
Sources of Error: •different wavelengths are being compared•Star subtraction method was not perfect•Background subtraction method was not 100% perfect
Focus Area: Colour Processing Techniques1. GIMP/Photoshop – levels adjustment (method from
class)2. GIMP Colourize Tool– playing with hue/saturation3. Stack to RGB4. LUT 2.25. RGB Composer Plugin
NOTE: All of the following images are taken from Sloan Digital Sky Survey.
Filters: Ultraviolet (u), Green (g), Red (r), Near Infrared (i), Infrared (z)Corresponding Wavelength (Angstroms): 3543, 4770, 6231, 7624, 9134
Level Control in GIMPAdvantages: Highest controlDisadvantage: Time consuming & multiple steps
Level Control in GIMP
Level Control in GIMP
Colourize Tool• Uses GIMP/Photo Shop• Disadvantage: Less control • Advantage: Simple and Quick
Colourize Tool
Stack to RGB•Open stake of 3 grey-scale images•Convert to 8-bit•Image Colour Stack to RGB
Stack to RGB
LUT Panel 2.2•Up to 3 gray-scale images•Each image can have multiple colors assigned
LUT Panel 2.2
RGB Composer Plugin•Works for up to 3 gray-scale images•Simple & easy to use.•Take only a few minutes!
RGB Composer Plugin
My Images
RGB Composer Plug-In GIMP Level Controls Stack To RGB
LUT Panel 2.2 Colour Processor ToolStack To RGB
ReferencesAssociation of Universities for Research in Astronomy, Inc. 1994. The Digitized Sky Survey http://stdatu.stsci.edu/cgi-bin/dss_form
Chereau F, Gates M, Kerr N, Marcos D, Marinov B. et al. 2010. Stellarium
Conselice C. 1997. The Symmetry, Color, and Morphology of Galaxies: Astronomical Society of the Pacific 1251-1255
Haynes G, Haynes. 2005. Best of AOP: NGC 3953: T.http://www.noao.edu/outreach/aop/observers/n3953.html
Moromisato G. 2011. NGC 3953 http://neurohack.com/astrotourist/NGC3953.html
This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.