ccd observing/research project: ngc 3953 by: ekta patel date: april 7 th, 2011 instructor: j. west...

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.