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Hera: Using NASA Astronomy Data in
Your Classroom
Dr. Jim Lochner (USRA)
NASA/GSFC Astrophysics Science Division
Welcome to Student Hera!
 Student Hera brings real astronomy into the classroom!
 Students use the same software and methods as
scientists to study objects in space such as black holes,
pulsars, and binary stars.
 One small download brings the universe to your fingertips.
What are Hera and Student Hera?
 Hera provides an interface to satellite data and
analysis tools which are used by scientists.
– Neither tools or data need to be downloaded to user’s
local computer.
 Hera is used by scientists around the world.
 Student Hera is a scaled-down interface which
provides selected data sets and tools for teachers
and students.
– Web pages provide walk-through of the tools for students.
Studying pulsars with Student Hera
 Looking at objects with an
X-ray telescope can teach
us about their structure,
features, and behavior.
 Pulsars are neutron stars
(very small, dense stars)
that “pulse” with radiation
through the rotation of
intense magnetic fields.
 Observing these pulses
can teach us about the
rotation, period, and other
features of the pulsar!
GX301-2
 GX301-2 is an X-ray binary system -- a pulsar in orbit
with a supergiant star. Mass is transferred from the
supergiant to the pulsar.
 The more mass dumped onto
the pulsar, the more X-rays it
will emit.
From the data, we can calculate the orbital
period and determine the type of orbit.
Exploring Student Hera
 It’s easy to get started with Student Hera in the
classroom. The website will lead you through installation
and getting started.
 Student Hera requires one 10MB download from the
website. The Windows program has an installation wizard
to guide you through set-up. Just click on the Student
Hera icon on your desktop, and you’re ready to go!
Let’s find the period of GX301-2
using Student Hera!
Exploring Student Hera
Exploring Student Hera
Student Hera offers a variety of tools and data to explore.
Skip to Folding the Data
File Utilities
 There are three tools available for
viewing the data:
• File Dump - Display FITS file in
text format.
• File List - List specific data in a
formatted text table.
• Column List - List the type of data in
the columns of the FITS file (the
variables and their units).
 These tools give information about
the contents of the data file.
 Data Statistics calculates the max,
min, mean, and standard deviation of
any column.
Light Curves and Periods
 A light curve is a graph which
shows the brightness of an
object over a period of time.
 In the study of objects which
change their brightness over
time, the light curve can help
us determine the rotational
period of an object, or the
orbital period of two objects
in a binary system!
File Utilities: File Plot
 The File Plot tool will create a light curve from the data you
select.
 Choose the variables for the axes (in this case, RATE and
TIME), and the rows from the data file that you want to plot.
This allows you to limit the amount of data plotted.
File Plot: Light Curve
This light curve is for 50 rows of data. You can see
that such a small sample of data doesn’t show much!
File Plot: Light Curve
50 rows
1000 rows
3000 rows
 Comparing plots of 50, 1000, and 3000 rows, you can see a definite
periodic pattern of brightness appearing.
 Plotting a the right time span can show the behavior of the system.
Plotting too little doesn’t show the periodic motion, but plotting too
much will make the peaks close together and hard to see.
Estimating the Period
 By identifying the peaks in the
light curve, you should be able
to estimate the orbital period for
the system.
 From this plot of 3000 rows, it
looks like the peaks are around
40 days apart.
 The error in this estimate is
quite large -- plus or minus 10
days (or more)!
Finding a better period
Now you’ve looked at the periodic motion of
GX301-2… but our period is a very rough
estimate. We need a more accurate number!
The File Utilities are tools to help you view the
data and make an initial assessment.
For a more thorough analysis of the data, we can
use another suite of tools: Timing Analysis Tools.
Exploring Student Hera
Timing Analysis Tools:
 This robust set of
utilities offers more
precise manipulation
and analysis of the
data.
 The timing analysis
tools (XRONOS Tools)
provide specialized
plots and statistics.
Plot Light Curve
 The Plot Light Curve tool in
the Timing Analysis utilities is
different than the basic File
Plot tool.
 This tool does not just plot
raw data points. It averages
the data points into time
“bins” (which you specify) in
order reduce the noise.
 Binning helps to emphasize
the peaks in the light curve.
Binning and plotting data
 You can experiment with the Plot Light Curve tool using different
parameters. Changing the size of the data bins, span of the data,
and averaging of the intervals chosen, you can work your way
toward the best parameters for a clear picture!
 Again, plotting too little or too much can affect the clarity of your
plots -- that perfect amount will make the periodic motion stand out.
Folding the data
 Binning reduces some of the noise in the plot, but the
data is still very messy. A precise period can still be
difficult to see.
 We can determine the period with a process called
folding.
 Since the period repeats indefinitely, imagine if we could
add all of the periods on top of each other. The peaks
would build up, one on top of the next, so the signal
would get stronger and the noise would cancel out.
 We will use folding to amplify the peaks so we can
clearly see the periodic behavior of GX301-2.
What is folding?
Folding is a way to add together, or fold, the
periods of a light curve in order to determine
an accurate period.
Let’s imagine some simple data…
What is folding?
Let’s guess a reasonable period.
What is folding?
Let’s do a little binning.
The y-axis value for Time Bin 1 would be the mean of
the y-axis values for the 1st data point in the red curve
and the 1st data point in the blue curve. And so on…
What is folding?
Plot the data from that chart.
 If your plotted data makes a
straight line or doesn’t look
like the original lightcurve…
the period you’ve guessed is
wrong. You’ll need to start
over with a new period.
 If your plotted data makes a
curve that resembles the
original data, you’ve
guessed a good period!
Skip to “What Type of Orbit?”
Search With Fold
 The trick to folding data is figuring out the
best period for the data. Otherwise, the
periods will not match up when folded.
 Search With Fold is a tool that can help you
discover the best value for the period.
 With Search With Fold, you can try different
periods (close to your original estimate),
and see which value gives the best signalto-noise ratio when folded.
 The software uses a statistical test called
chi-squared to assess this signal-to-noise
ratio. The period that provides the largest
chi-squared is the best match for the data.
Search With Fold will create a chi-squared
histogram (at right is one for 41.5 days).
Epoch Folding
Search With Fold provided a “best” period of
41.5 days. Now that we have this value, we
can create a folded light curve!
The final utility we will use is Epoch Fold.
Our folded light curve will tell us if the period
we found is correct -- will our plot look like a
periodic light curve?
It is time for the moment of truth!
Folded light curve
Our folded light curve shows clear periodic
motion! We have found a period of 41.5 days.
What type of orbit
does the light curve suggest?
?
What type of orbit does this light curve suggest ?
Orbital Properties of GX301-2
More Mass - More X-rays
41.5 d period in an eccentric orbit.
GX301-2 Conclusions
 You just successfully analyzed X-ray data just like a
professional astrophysicist! You employed the same
tools and methods used at NASA and other research
institutions.
 Nearly everything we know about GX301-2 has been
found using the same techniques that you use in
Student Hera.
With Student Hera, you can be an astrophysicist!
What did we learn?
Science topics
– Binary star systems, periodic motion, orbits
Math Topics
– Pattern recognition, interpreting graphs
Data Analysis Skills
– Investigating the nature of a data set
– Using software to view and analyze data
Science process skills
– Making mathematical models and testing
Classroom uses for Student Hera
 Use software and exercises within lessons on related
concepts, such as light curves, X-ray astronomy, or binary
stars. Plotting tools can create useful visual aids!
 Assign students individual or group projects using Student
Hera. Projects can be based on the guided activities on
the website -- many variations are possible.
 Integrate into lessons on mission design and technology.
Student Hera offers a look at the real data that comes
back from satellites, as well as the specialized analysis
and manipulation that scientists perform.
 Use with related lessons and activities from online
learning resources such as Imagine the Universe! and
mission-related sites like the RXTE Learning Center.
College Hera
Hera is also available as a 2-hour lab
experience for 1st year college astronomy
courses.
– http://imagine.gsfc.nasa.gov/docs/teachers/hera_college/
Developed by Dr. Beth Hufnagel, Anne Arundel
Community College, Maryland
The future of Student Hera
The File Utilities and Timing Analysis Tools, plus
all related lesson plans and materials, are
currently available online.
We appreciate any feedback you may have!
Student and teacher evaluation questionnaires
are available.
An Imaging module is available. Spectroscopy
module under development.
Links and Resources
Student Hera on Imagine the Universe!
http://imagine.gsfc.nasa.gov/docs/teachers/lessons/hera/
Student Hera Teacher’s Manual
TeachersManual.pdf in above directory
The RXTE Learning Center
http://rxte.gsfc.nasa.gov/docs/xte/learning_center/
Contact: [email protected]
Conclusions
 Using a series of qualitative
and quantitative
measurements, we have
discovered that the neutron
star and supergiant in
GX301-2 orbit each another
once every 41.5 days.
The orbital period we have found using Student Hera
matches the period published by British scientists in 1982.
The scientists also used their data (from a different
instrument) to examine the eccentric orbit of the binary
system and the interactions between the two stars.