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Table of Contents
                            Clemson University
The Detection of a Light Echo from SN 2007af
	Dina Drozdov
		Recommended Citation
Title Page
List of Tables
List of Figures
	Type Ia Supernovae
	Light Curve
	Importance of SNe Ia to Astronomy
	Late-time Behavior
Light Echoes
	Light Echoes in SNe Ia
	Importance of Light Echoes
	Steward Observatory
	Swift UVOT
	Low- and High-Resolution Spectroscopy
SN 2007af
	Late-Time Observations with Hubble Space Telescope
	Light Echo
Dust Analysis and Modeling
	Dust Distance
	Dust Properties
	Future Work
Document Text Contents
Page 1

Clemson University

All Theses Theses


The Detection of a Light Echo from SN 2007af
Dina Drozdov
Clemson University

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Recommended Citation
Drozdov, Dina, "The Detection of a Light Echo from SN 2007af " (2013). All Theses. 2308.
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Page 2

The Detection of a Light Echo from SN 2007af

A Dissertation

Presented to

the Graduate School of

Clemson University

In Partial Ful�llment

of the Requirements for the Degree

Master of Science



Dina Drozdov

December 2013

Accepted by:

Dr. Mark D. Leising, Committee Chair

Dr. Dieter Hartmann

Dr. Jeremy King

Dr. Catalina Marinescu

Page 48

The \Supernovae and Ho for the Equation of State" (SH0ES) project began operations

during HST Cycle 15, with the aim to measure the expansion rate to more than 5% precision using

SNe Ia and Cepheids. The Wide Field Camera 3 (WFC3) was installed and began taking images

in Cycle 17. The SH0ES program was created to improve on the systematic error in calibrating the

luminosities of SNe Ia. Type Ia supernovae chosen for this cosmological study had to �t the following

criteria: modern photometric data (e.g. CCD), have observations before peak, low reddening (AV

< 0.5 mag), spectroscopically classi�ed as normal, and optical observations of Cepheid variables in

the host galaxy of the SN had to be made withHST (Riess et al., 2011). Cepheid variables have the

unique property that their absolute magnitude is directly related to their period of variability. From

measuring the magnitude they appear (called the apparent magnitude) a distance can be determined

using the distance modulus equation. This makes them especially powerful for cosmology.

NGC 5584, the host galaxy of SN 2007af, was discovered to have a wealth of Cepheids

(see Figure 4.2) inHST Cycle 17 and was observed with the Wide Field Camera 3 (WFC3). Over

250 Cepheid variable stars were observed from this galaxy alone. NGC 5584 was observed in the

F160W (wide H), F350LP (un�ltered long pass), F555W (wide V ), and F814W (wide I) �lters

from January to April 2010, three years after the explosion of the supernova. The composite image

was created from stacking multiple exposures in three �lters. The F350LP �lter transmits the most

visible light, and was colored white. The yellow/green �lter, F555W, was colored blue, and the near

infrared F814W �lter was colored red. The individual exposures were 400 { 700s in length with total

exposure time equaling 4926s. Integer and half-pixel dithering was enabled between exposures to

strengthen the point spread function (PSF). The total �eld of view was 2.4′ across.

The team developed an automated pipeline to calibrate the WFC3 images. First, they were

put through the STScI (Space Science Telescope Institute)calwf3 pipeline in the STDAS routines

in PyRAF to subtract the bias and darks and remove any stray cosmic rays. Pixel-to-pixel

�elding was also performed. Some anomalous depressions in the
ux covering∼1% of the image

area were corrected for in the
at �elding routine. These are due to spotting on the surface of

the WFC3 Channel Select Mechanism. The individual exposures were combined to create a master

image usingmultidrizzle. Corrections were made to account for geometric distortions in the camera.

The positions of Cepheids was performed by comparing the F814W and F160W images and deriving

geometric transformations. The photometry was accomplished with algorithms that used PSF �tting

to model the surrounding areas of the Cepheids (Riess et al., 2011).


Page 49

Figure 4.2: HST images of NGC 5584 showing the locations of the Cepheid variable stars. Red
circles are stars with period (P) > 60 days, blue circles have 30 days < P < 60 days, and green
circles have 10 days < P< 30 days. The location of SN 2007af (left of the center of the galaxy) is
marked with a yellow circle (Riess et al., 2011).


Page 95

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