Observing Techniques: exercises and assignments

Exercises will be assigned in class, to be handed in one week later.
You may be asked to elucidate your answer and you may be asked to give a short presentation at one week's notice.
All of this contributes to your grade.
If you feel more information is needed to answer the question, say so in your answer and explain why.
Where you can, use sensible values to complete the answer.

THE ELECTROMAGNETIC SPECTRUM and associated objects.
Problem set 1:

Problem set 2:

Problem set 3:
  • In the section "adaptive optics" on the web page, mention is made of real-time "tip-tilt" image correction. How might you do this post-hoc rather than in real-time, and without the mechanical device to correct the x-y error?
  • Which measurables enable us to determine the absolute magnitudes of stars? Describe possible strategies.

  • What is the Julian date at the start of the first lecture (to the nearest minute).

    Problem set 5:

    1. Consider a grating with 600 grooves/mm which is illuminated at 10 degrees from the normal - the blaze gives the grating high efficiency over a large wavelength range in this configuration. You decide to make a spectrograph using this arrangement, i.e. fixing the input angle at 10 degrees. Which orders propagate at 500nm? In the m=+2 order, work out the focal length of the camera you would need to have a linear dispersion such that a wavelength increment of 0.1nm corresponds to two pixels (pixel size 20 micron) at the detector.
      2pt bonus How would you set up the collimator? Let us say you want the spectrograph to be "fed" by light from a D=4m telescope at the f/8 focus of the telescope. In principle you want the spectrograph to accept all the light in the seeing spot (also called the seeing disk) without degrading the spectrum quality.

    2. It is said that most spectrographs require a collimated beam. But the beam from a star is perfectly collimated... Give as many reasons as you can for the formation of a focus followed by recollimation. The main exception to the rule is the "objective prism spectrograph", in which the starlight indeed is allowed to fall on the dispersing element. What is it about this application that makes this viable?

    3. Calculate the line-of-sight velocity with respect to the Earth of a star when the Balmer H-alpha line in its spectrum is observed to be at a wavelength of 655.2 nm. Present the answer with the appropriate level of precision. In this calculation should you use the rest wavelength of the line in air or in vacuum? The observation was made at La Palma Observatory on a certain date. Using the iraf task rvcorrect, or any other tool or formula, convert the line-of-sight velocity you have calculated to one of the standard systems, such as Heliocentric.
      You will need the following data:
      date of observation:   1/1/2003
      time of observation:  UT=0
      coordinates of object:  RA 7h, Dec +3o
      observatory: lapalma (this will be recognised by rvcorrect, for other programs you may need the observatory latitude and longitude, 28:46 N, 17:53 W). Describe why this correction is necessary.


    ASSIGNMENTS (We will work on these together)

    1. Observing Write and defend an observing proposal for the 2m INT telescope at La Palma. The winning proposal will be carried out. Be prepared to criticise your peers, and to defend your own proposal.

    2. Optical Practicum: directly measure the rotation speed of the sun in km/s.

    Additional information:
    we have a 20cm f/10 reflector with a CCD detector having 600x600 square pixels of size 9 microns
    1 William Herschel Telescope, a 4.2m alt-az telecope.

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