Hera: Using NASA Astronomy Data in Your Classroom

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Hera Using NASA Astronomy Data in
Your Classroom
Dr. Jim Lochner (USRA) NASA/GSFC Astrophysics
Science Division
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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.

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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
  users 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.

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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!

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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.

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Exploring Student Hera

• Its 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
  youre ready to go!
• Lets find the period of GX301-2 using Student
  Hera!

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Exploring Student Hera
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Exploring Student Hera

• Student Hera offers a variety of tools and data
  to explore.

Skip to Folding the Data
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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.

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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!

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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.

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File Plot Light Curve

• This light curve is for 50 rows of data. You can
  see
• that such a small sample of data doesnt show
  much!

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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
  doesnt show the periodic motion, but plotting
  too much will make the peaks close together and
  hard to see.

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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)!

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Finding a better period

• Now youve 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.

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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.

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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.

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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.

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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.

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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.
• Lets imagine some simple data

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What is folding?

• Lets guess a reasonable period.

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What is folding?

• Lets 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

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What is folding?
Plot the data from that chart.

• If your plotted data makes a straight line or
  doesnt look like the original lightcurve the
  period youve guessed is wrong. Youll need to
  start over with a new period.

• If your plotted data makes a curve that resembles
  the original data, youve guessed a good period!

Skip to What Type of Orbit?
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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 signal-to-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).

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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!

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Folded light curve

• Our folded light curve shows clear periodic
• motion! We have found a period of 41.5 days.

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What type of orbit does the light curve suggest?
?

• What type of orbit does this light curve suggest ?

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Orbital Properties of GX301-2
More Mass - More X-rays

• 41.5 d period in an eccentric orbit.

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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!

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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

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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.

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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_co
  llege/
• Developed by Dr. Beth Hufnagel, Anne Arundel
  Community College, Maryland

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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.

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Links and Resources

• Student Hera on Imagine the Universe!http//imagi
  ne.gsfc.nasa.gov/docs/teachers/lessons/hera/
• Student Hera Teachers ManualTeachersManual.pdf
  in above directory
• The RXTE Learning Centerhttp//rxte.gsfc.nasa.gov
  /docs/xte/learning_center/
• Contact Lochner_at_milkyway.gsfc.nasa.gov

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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.