Observational Techniques

Samenvattingen

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Algemeen

2023-2024: This course is taught by Denis Defrère. He uses the same material as prof. Van Winckel. There are two guest lectures on interferometry, given by Dr. Marc-Antoine Martinod. We still need to prepare the same two exercises as Van Winkel gave: SED and HERMES. The exam was fully oral. In total, each report counted for 1/3 of the points, and the last 1/3 was on the course material. We got 1 hour preparation time to write out about 12 questions (where 3 of them are theory questions). Then, we had 10 minutes to do the examination.

before 2023-2024: This course is given by prof. H. Van Winckel. It consists of 11 two-hour lectures given in the first semester. As course material, there is a 80 pages course, plus slides, plus some copies from other books. During the year, two exercises are given. You have to send in the answers in form of a paper before Newyear. The examination is personal: the professor prepares different questions about everyone's paper, which you can prepare and then you have to defend your paper during the oral part of the examination. Be sure to bring a print out of your reports and a calculator!

In 2020-2021, the first exercise was about plotting the SED of a post-AGB star given its location. For the second report, we had to analyse the aspects of HERMES's echelle given reduced data of some night of observations. Both of the exercises were quite unclear as you'll likely be unfamiliar with the tools you have to use and the goals of the exercise are not made very clear, these papers can be rather frustrating. It is highly recommended you regularly ask the professor/fellow students questions and start early. At least gather data and make sure you can use the python programs provided by the prof before the exam period so you don't have to deal with technical difficulties under stress.

Exams

Some example questions:

Prof. Defrère

Theory

• Given the altitude of an observatory and the declination of a particular star, is this star circumpolar? Explain why you think so.
• What is an Echelle spectrograph?
• What are the main reasons modern telescopes uses mirrors instead of lenses?
  • Help from prof.: there are two main reasons. Solution: no chromatic abberations + nowadays telescopes big: only applicable for mirrors.
• What is the Littrow condition?
• What do we measure with an interferometer?
• Explain the calibration steps used in CCD's.

Reports

--> Also see question of Hans Van Winckel: this document Exams Observational Techniques Van Winckel.pdf has many questions Defrère asks.

• SED: You obtain a relatively low uncertainty on the obtained E(B-V), but still your minimal chi square is large. What would you conclude from that? Is that not a contradiction?
  • Subquestion: What is a typical 'good' chi square value?
• SED: What kind of object is J... ?
  • Subquestion: What is a post-AGB star?
• SED: List three things to make your report better.
• HERMES: What is spectral sampling in spectroscopy? How can you obtain it from the HERMES data?
• HERMES: The efficiency you calculated for HERMES and the one of the ETC is not very high. Can you give some improvements we can make to the instrumentation of HERMES to boost its efficiency, if it is still possible?
• HERMES: List three things to make your report better.

Prof. Van Winckel

• What are three things you would like to improve about your report
• (Interferometry) Given a plot of the closure phase to baseline over wavelength and squared visibility to baseline over wavelength, determine what sort of object was measured.
• Can you tell which month will be ideal to observe the star you discussed in your paper?
• Given the outflow speed of dust from an AGB star, and the temperature of the dust, can you calculate the time till the outburst? (This is an exercise that was solved in the course Radiative Processes)
• Why are spectroscopic measurements seldom flux calibrated unlike photometric observations?
• Explain some figure in your report in detail.