Lost in Space

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Lost in Space

• ASTR1001 Assignment 5

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Introduction

• The Starship USS Drongo was rescued from planet
  Ziggy by a benevolent race of aliens.
• Unfortunately, just after the rescue, the aliens
  happened to notice the music video collection of
  one of the junior engineering officers.
• Enraged that they had rescued life-forms with
  such disgusting musical taste, the aliens
  immediately flung the USS Drongo through a
  wormhole.

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USS Drongo in the Wormhole
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Lost in Space!

• The USS Drongo is now floating somewhere in
  space.
• You do not know if you are in some remote part of
  our own universe, or some quite different
  universe.
• Captain Howard has called you, the astrophysics
  team, together.
• Your task work out whether we are in our own
  universe, or whether we are in a different one.
• Investigate our surroundings. If we are in our
  own universe, what sort of environment could we
  be in?
• If we are in a different universe, try and work
  out its cosmology, as this will help the computer
  calculate a way home.

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The View

• The view around the spacecraft looks quite empty
  there do not appear to be any nearby planets,
  asteroids, suns etc.
• The space surrounding your ship is a hard vacuum.
• With the naked eye, you can see several thousand
  stars about the same number that you could see
  from Earth.

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Funny Colours

• The sky is not, however, quite like that seen
  from Earth.
• The stars seem to be rather more colourful than
  those seen from Earth. In particular, they seem
  to show bright primary colours, rather than the
  more subtle shades seen from Earth.
• Red stars seem to outnumber blue ones by quite a
  bit.
• There is no sign of a Milky Way.
• Curiously, the stars appear to twinkle, which
  they should not do in the absence of an
  atmosphere.
• Just like from Earth, however, the stars appear
  as dots, even through the best on-board
  telescopes no disks are seen

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Radio Signals

• Curiously, the signals division are reporting
  many sudden, sharp bursts of radio emission.
• These bursts mostly occur at wavelengths of 20cm
  or slightly longer.
• They are extremely intense while they occur, but
  last for only microseconds.
• Many bursts are very intense. They occur several
  times a day.
• There also appear to be a much larger number of
  faint bursts, at somewhat longer wavelengths.

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Spectroscopy

• The instrumentation division have just
  jury-rigged a spectrograph, and obtained spectra
  of some stars.
• The spectra are VERY unusual.
• All emission seems to occur at one particular
  wavelength.

Flux
Wavelength
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Wavelengths

• Each different star appears to radiate at a
  different wavelength.
• The wavelengths can lie anywhere in the whole
  wavelength range that the detector is sensitive
  to 400 - 800nm, though they do show a bias
  towards redder wavelengths.
• As far as we can tell, the flux from a given star
  could be purely monochromatic all the radiation
  comes at precisely one wavelength. The line width
  in the previous graph is due to the limited
  instrumental resolution of the spectrograph. We
  place an upper limit on the line width of 1nm.
• No other emission lines are seen from any stars
  down to a flux limit of 0.1 the intensity of the
  main line.

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Twinkling

• Why do the stars twinkle, in the absence of any
  atmosphere?
• You rigged up a multichannel photoelectric
  photometer to measure the brightness of some
  stars as a function of time.

Flux
Time
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Rapid Pulsation

• It appears that all the stars around you are
  pulsing rapidly. Pulse periods are typically a
  few seconds, and pulse amplitudes a few percent
  or less.
• Not all stars have the same periods and the same
  amplitudes.
• You have measured the pulse periods and
  amplitudes (maximum flux minus minimum flux
  divided by the average flux). The results are
  found in a separate Excel data table.

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The Parallax Probe

• To aid your investigation, Captain Howard sent
  out a robotic space-probe.
• The probe travelled 10,000 km away, and then
  stopped and deployed a small telescope.
• It measured the positions of dozens of bright
  stars with an accuracy of 0.2 arcseconds.
• At the same moment, you performed the same
  measurement using the USS Drongos main telescope.

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The Geometry
You studied stars in this direction
10,000 km
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The Data Table

• Between your two measurements you were able to
  measure whether the stars appeared to lie in
  exactly the same direction from the USS Drongo
  and from the probe.
• You found that many of the brightest stars
  appeared in slightly different directions.
• So the light from these stars was not coming in
  quite parallel to you and to the probe you
  measured the difference in angle (the parallax)
  with an accuracy of about 0.2 arcsec.
• Data from these observations can also be found in
  the separate Excel spreadsheet.

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Your Mission.

• Captain Howard has called you, the astrophysics
  team, together.
• Your task work out whether we are in our own
  universe, or whether we are in a different one.
• Investigate our surroundings. If we are in our
  universe, where could we be? What is our
  environment like?
• If we are in a different universe, try and work
  out its cosmology, as this will help the computer
  calculate a way home.

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Assessment

• This assignment is due by 10am on Thursday 29th
  May.
• It is worth 10 of the marks for ASTR1001.
• You should describe what you have learned about
  the universe in which you now find yourselves.
• Word limit 2000 words.
• You should describe the most important things you
  have learned, and describe how you learned them.
  There is no need to show mathematical working.
• You should also briefly describe what future
  observations would be most useful.

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More assessment details

• As usual, you can work by yourselves or in
  groups.
• You can submit your assigments electronically via
  WebCT e-mail, or in person to me in class, or
  into my mailbox in the physics department.
• As usual, please use the bulletin board to
  exchange ideas. I may hand out a few bonus marks
  to those who make particularly good postings.

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Assignment 6

• Once your assignments are in, I will release more
  data on the USS Drongo and its surrounds.
• This further data will be the subject of
  Assignment 6.
• I will also release a model answer to Assignment
  5, to make sure that you are in a good position
  to attempt Assignment 6, even if you stuffed this
  one up.

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Marking

• To get maximum marks, you should deduce as much
  as possible from the data, but not deduce more
  from the data than is possible!
• Im after hard numbers and not just waffly text
  (this is a science course, after all)
• Feel free to speculate, but make it clear what is
  speculation and what is solid deduction.
• Ive put some numerical data in a spreadsheet to
  facilitate playing with it. If youd like it in
  some other format, let me know (eg. text files
  for plotting/processing using MATLAB). You may or
  may not find this data useful.

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The Data

• The data file contains information on a bunch of
  bright stars that you have observed.
• For each star it lists
• A catalogue number
• The parallax (angular difference between the
  position measured by you and by the probe)
• Wavelength at which it is emitting.
• How strong the average emission you detect from
  that star is.
• How rapidly it pulses.
• By how much its intensity changes during a
  pulsation.