CCD OBSERVING/RESEARCH PROJECT:

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CCD OBSERVING/RESEARCH PROJECT:

NGC 3953

By: Ekta Patel

Date: April 7
th
, 2011

Instructor: J. West

Course 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 Comparison

GAO Image


STSciI

DSS Image


Date/Time

May 7th, 1991/ 4:17:00

Location


Latitude: 33.356




Longitude: 116.863

Telescope Used

Oschin

Schmidt
-

D

Detector Used

Photographic Plate

Filter



RG610

Exposure Time

72 minutes

Field of View

7.0’
x

7.0’


Date/Time

Feb 8, 2011/ 22:05:00

Location


Latitude: 49 38 min 43
s





Longitude: 97
d
, 7min, 20
s

Telescope Used

Evans 40 cm

Detector Used

Apogee U47

Exposure Time

33 minutes

Field 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 background

2.
Rotate 180 degrees about the center point (brightest region in the middle)

3.
Subtract rotated image from original

4.
Square the pixels in residual image

5.
Divide the sum of pixels in residual image by 2 times the sum of the squared pixels
of original image


Equation:

A=0 Perfectly symmetric

A=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 180
o

SUBTRACT

NGC 3953 Measurements

Result of Subtraction


NGC 3953 Measurements

2 X (Original Image)
2


(Result of Subtraction)
2

DIVIDE

NGC 3953 Measurements

Calculations:



A
2
= (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
Techniques


1.
GIMP/Photoshop


levels adjustment (method from class)

2.
GIMP
Colourize

Tool


playing with hue/saturation

3.
Stack to RGB

4.
LUT 2.2

5.
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 GIMP

Advantages: Highest control

Disadvantage: 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 Tool


Stack To RGB






References

Association 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.