The Porto Quiz Based on P. Tuthill’s idea (at the Michelson summer workshop 2006) Questions contributed by lecturers

Mizar: Northern binary, sky PA = 0º 126 Tau: Equatorial binary, sky PA = 0º Rigel: Equatorial star, resolved uniform disk Polaris: Polar star, resolved uniform disk Tuthill’s question 1: Santa finally gets the North Pole Optical Interferometer (NPOI) on line, and the Elves observe 4 stars but lost the night logs and did not fill the right FITS keywords. Match the stars with the data

Tuthill’s question 2: Can you associate each image to its Fourier transform ?

Tuthill’s question 3: You are an alien and are observing various observatories on the Earth, using your own interferometer. Which interferometer does have a null phase closure ? A.The VLTI B.The Keck interferometer C.CHARA D.NPOI

Millour’s question 1: You want to use PRIMA in 2 years with MIDI. You have identified some bright stars close to your targets to do fringe tracking. You have now to characterize these bright stars to check what would be their intrinsic phase. So you measure their visibilities with AMBER with one baseline (but letting it rotate over 24 hours). Associate each visibility curve to the object shape. A.elongated uniform disk B.binary with brightness ratio 1/1 C.binary with brightness ratio 1/5 D.elongated gaussian

Millour’s question 2: You want to observe a star with AMBER closure phase. You place the 3 telescopes on an equilateral triangle and let the Earth rotate over 24 hours. You observe the following closure phase curve. What could be your object shape ? a binary of brightness ratio 5:1 a binary of brightness ratio 1:1 a star with a hot Jupiter an elongated disk

Lodato’s question 1: Accretion disc 1 is identical to accretion disc 2, except that its temperature is two times larger. A.Disc 1 evolves 4 times faster than disc 2 B.Disc 1 evolves 2 times faster than disc 2 C.The two discs evolve on the same timescale D.Disc 1 evolves 4 times slower than disc 2

Lodato’s question 2: An accretion disc extends to 10 AU. Suddenly the disc outside 5 AU is istantaneously removed. Which of the following statements is correct? A.The viscous timescale of the system is reduced. The disc will evolve faster B.The viscous timescale at 5AU does not depend on the presence of the outer disc. The disc lifetime is not affected C.The disc at 5 AU will spread to larger radii where the viscous time is longer. It will evolve more slowly

The energy dissipated by viscosity in an annulus of width dR at radius R (far from the inner boundary) is This is 3 times larger than the energy gained by accretion due to potential energy losses. Where does the rest of the energy come from? Lodato’s puzzle 1

Lodato’s puzzle 2 Navier-Stokes equation imply that for a rotating flow the viscous stress tensor is proportional to d  /dR. How does this reconcile with the expectation from kinetic theory that angular momentum should flow in the direction of the gradient of the angular momentum itself (i.e., that viscosity should flatten the angular momentum gradient)?

Percheron’s question: You observe with MIDI a young stellar object to determine the diameter of the star and of its molecular disk (hydro-silicate). The calibrated visibilities that you obtain look like this: What does it mean ? A.The central star is resolved and you can extract the star and disk diameters from these data B.There is non-calibrated longitudinal dispersion that you have to remove first C.The diameter of your calibrator was over-estimated D.The diameter of your calibrator was under-estimated

Akeson’s question 1: You have a young stellar binary at 100 pc. The stars are separated by 2AU and each star has a disk at 0.3 AU. Which of the following baselines would you use at 2 microns to observe the binary orbit ? A.30 m B.80 m C.200 m D.600 m 2 AU 0.3 AU

Akeson’s question 1: You have a young stellar binary at 100 pc. The stars are separated by 2AU and each star has a disk at 0.3 AU. Which of the following baselines would you use at 2 microns to observe the disks ? A.30 m B.80 m C.200 m D.600 m 2 AU 0.3 AU

Tuthill’s question 4: You, an alien, realize that your planet is in imminent danger of discovery by PRIMA (or SIM). To prevent it, you recommend: A.painting your planet black, B.painting your planet silver, C.splitting your planet into two halves which orbit 180º apart or D.scattering clumpy clouds of dust in your solar system ?

Delplancke’s question: ESO has installed an interferometer at the South Pole (ESPOIR = Eso South Pole Optical InterfeRometer). You applied for time and received one full night to look for planets with astrometry. Here are the measurements on one of the stars: A.Success: you have detected a planet with a period of 24 h ! B.Bad: the telescope flexures have not been correctly taken into account by the data reduction C.You got a good measurement of the star parallax D.You are observing the ice tides

The answers

Mizar: Northern binary, sky PA = 0º 126 Tau: Equatorial binary, sky PA = 0º Rigel: Equatorial star, resolved uniform disk Polaris: Polar star, resolved uniform disk Tuthill’s question 1: Santa finally gets the North Pole Optical Interferometer (NPOI) on line, and the Elves observe 4 stars but lost the night logs and did not fill the right FITS keywords. Match the stars with the data

Tuthill’s question 2: Can you associate each image to its Fourier transform ?

Tuthill’s question 3: You are an alien and are observing various observatories on the Earth, using your own interferometer. Which interferometer does have a null phase closure ? A.The VLTI B.The Keck interferometer C.CHARA D.NPOI 

Millour’s question 1: You want to use PRIMA in 2 years with MIDI. You have identified some bright stars close to your targets to do fringe tracking. You have now to characterize these bright stars to check what would be their intrinsic phase. So you measure their visibilities with AMBER with one baseline (but letting it rotate over 24 hours). Associate each visibility curve to the object shape. A.elongated uniform disk B.binary with brightness ratio 1/1 C.binary with brightness ratio 1/5 D.elongated gaussian

Millour’s question 2: You want to observe a star with AMBER closure phase. You place the 3 telescopes on an equilateral triangle and let the Earth rotate over 24 hours. You observe the following closure phase curve. What could be your object shape ? a binary of brightness ratio 5:1 a binary of brightness ratio 1:1 a G star with a hot Jupiter an elongated disk 

Lodato’s question 1: Accretion disc 1 is identical to accretion disc 2, except that its temperature is two times larger. A.Disc 1 evolves 4 times faster than disc 2 B.Disc 1 evolves 2 times faster than disc 2 C.The two discs evolve on the same timescale D.Disc 1 evolves 4 times slower than disc 2 

Lodato’s question 2: An accretion disc extends to 10 AU. Suddenly the disc outside 5 AU is instantaneously removed. Which of the following statements is correct? A.The viscous timescale of the system is reduced. The disc will evolve faster B.The viscous timescale at 5AU does not depend on the presence of the outer disc. The disc lifetime is not affected C.The disc at 5 AU will spread to larger radii where the viscous time is longer. It will evolve more slowly  ???

Percheron’s question: You observe with MIDI a young stellar object to determine the diameter of the star and of its molecular disk (hydro-silicate). The calibrated visibilities that you obtain look like this: What does it mean ? A.The central star is resolved and you can extract its diameter from these data B.There is non-calibrated longitudinal dispersion that you have to remove first C.The diameter of your calibrator was over-estimated D.The diameter of your calibrator was under-estimated 

Akeson’s question 1: You have a young stellar binary at 100 pc. The stars are separated by 2AU and each star has a disk at 0.3 AU. Which of the following baselines would you use at 2 microns to observe the binary orbit ? A.30 m B.80 m C.200 m D.600 m 2 AU 0.3 AU 

Akeson’s question 1: You have a young stellar binary at 100 pc. The stars are separated by 2AU and each star has a disk at 0.3 AU. Which of the following baselines would you use at 2 microns to observe the disks ? A.30 m B.80 m C.200 m D.600 m 2 AU 0.3 AU 

Tuthill’s question 4: You, an alien, realize that your planet is in imminent danger of discovery by PRIMA (or SIM). To prevent it, you recommend: A.painting your planet black, B.painting your planet silver, C.splitting your planet into two halves which orbit 180º apart or D.scattering clumpy clouds of dust in your solar system ? 

Delplancke’s question: ESO has installed a 100-m baseline interferometer at the South Pole (ESPOIR = Eso South Pole Optical InterfeRometer). You applied for time and received one full night to look for planets with astrometry. Here are the measurements on one of the stars: A.Success: you have detected a planet with a period of 24 h ! B.Bad: the telescope flexures have not been correctly taken into account by the data reduction C.You got a good measurement of the star parallax D.You are observing the ice tides 