1. Photometric Analysis of M92 and Analysis Programming
Andrew Hankins, Trevor Simpkin, Kayla Furukawa, and Adriana Fukuzato, mentored by Dr. Joanne Hughes-Clark
Seattle University Department of Physics
S&E Summer Research Program 2011
Abstract
Background & Theory
Methods / Experimental Design
Conclusions
References
1. Mateo, L.L. 1998, AR&A, 36 435
2. Hughes et al. 2008, Age and Metallicity of Bootes I system
3. Greco et al. 2007 ApJ 675 L73
Dwarf spheroidal galaxies are as the name
describes, small spherically shaped galaxies.
Generally dSph’s have low luminosities and high
mass-to-light ratios, making them prime
candidates for the study of dark matter (Mateo
1998). Dark matter halos are a phenomenon that
suggests the presence of unseen matter which
would explain accelerated rotation in the outer
regions of the Milky Way.
Photometric analysis is the process of conducting
photometry, a technique which measures the flux
of a stellar object’s light, to determine stellar
properties, such as age, metallicity, mass,
formation history, etc. To conduct photometry we
reduced and processed our images using the
DAOPHOT package in IRAF (Image Reduction and
Analysis Facility).
We built our data analysis program using the
programming capabilities and language of Matlab.
This project is part of an ongoing study of eight
newly discovered dwarf spheroidal galaxies
(dSph) in the halo of the Milky Way observed
with the Apache Point Observatory (APO) 3.5–m
telescope. These eight objects, identified in the
Sloan Digital Sky Survey (SDSS) will have
photometric analysis completed in hopes of
determining the star formation histories,
masses, ages, chemical compositions, and dark
matter content. To date the analysis for the first
of the eight objects, Bootes I dSph, has been
completed and published.
The overall vision for this study is an
investigation into the dark matter halos
surrounding the Local Group galaxies.
Our project consisted of building a data analysis
program and conducting photometric analysis of
the M92 Globular cluster for use in comparing
with the UMaII and WLM Dwarf Galaxies.
•The first step in processing the M92 images is to flat-field the raw images so as to remove the
signal noise from the instruments and as much of the sky and background illumination and signal as
possible leaving only the signal from the stars. This is done using the IRAF program.
•We then used the DAOPHOT package in IRAF to identify and obtain magnitudes for the stars in the
M92 star fields to analyze. Each time the images were processed a layer of stars was stripped off to
get at more of the stars. The process was done twice to obtain most of the stars in the fields.
•Finally, we perform analysis of the data obtained from the star fields including creating a color-
magnitude diagram and fitting fiducials to determine age and point in life span. Once this is done the
data can be passed through our data analysis program for CMD and Isochrone fitting analysis.
Our analysis of M92 and UMaII/WLM is still
ongoing as we finish final photometric analysis of
the M92 data and begin comparing it to the
UMaII/WLM data. Once M92’s color-magnitude
diagram is complete and have been fit with
fiducials, we can begin analyzing the UMaII/WLM
data by means of our data analysis program.
From this data we can determine metallicity,
mass, age, chemical composition, star formation
history, and the dark matter content of the dwarf
galaxies. Comparing the M92 data with the UMaII
and WLM data will allow for a better
understanding of the UMaII and WLM dSph’s
since M92 is well understood.
Continued research of dwarf galaxies that
populate the local group is an ongoing effort to
catalogue and learn about galaxy formation that
will further help us to understand not only the
formation of our own galaxy but an even more
elusive concept the existence and function of
dark matter.
•The goal was to build a data analysis program
that takes in photometric data, creates a CMD,
obtains photometric indices, and performs
Isochrone fitting.
•We built the program in Matlab using the built in
programming language and functions of Matlab.
•The program is designed to scan in the
photometric data outputted from IRAF store the
information into a series of cell arrays and then
compute and plot the necessary data obtaining
the desired values.
•Finally the program scans in a file containing
model Isochrones and performs a fit of the
models to the CMD data.
The APO 3.5m Telescope
Above is a CMD with an Isochrone fit to the data that
was outputted from our analysis program.
Program Development
M92 IRAF Reduction and Photometry
Raw unprocessed M92 image
Processed and photometric subtraction image