Andrea Richichi (NARIT) Asiago Winter School, March 1, Photo copyright: Kwon, O Chul (S. Korea)

Transcription

1 Andrea Richichi (NARIT) Asiago Winter School, March 1, 2013 Photo copyright: Kwon, O Chul (S. Korea)

2 Outline of the Talk Basic Definitions General Considerations (timing, pros, cons) Types of Occultations and Transits Instrumentation Space results Small Break Lunar occultations Preparing a LO observation Data Processing Analysis of a close binary system 2

3 About myself and NARIT Andrea Richichi formerly at Arcetri Observatory (Italy), Steward Observatory (Arizona), Max- Planck Astronomy (Germany), ESO (Germany) Lunar Occultations, Speckle and Long-Baseline Interferometry,High Time Resolution, Infrared, Late-type and Evolved Giants, YSOs, Binaries Currently at National Astronomical Research Institute of Thailand Chiang Mai 3

4 Thai 2.4m National Telescope Doi Inthanon at 2,457 m above mean sea level Latitude : 18 deg N Longitude : 98 deg 29 7 E Observing window : October to May Average seeing : ~0.8 arcsecs Temperature range : -5 degc to 22 degc 4

5 Disclaimer I acknowledge that this presentation includes numerous images and media collected from the World Wide Web. It would be impractical to give full credits to each item. I apologize in advance. Please be careful if you choose to reuse some of this material. 5

6 Definitions Transit: a (smaller) object passing in front of a background source. Mostly periodic. Occultation: a (larger) object passing in front of a background source. Mostly occasional. And a few ambiguous mixed cases... 6

7 Why Occultations and Transits The quest for higher performance in astronomy has generally resulted in a push for larger and larger telescopes Expensive (and elitarian ) approach Occultations shift the emphasis to a natural, not a man-made, instrument. The telescope is reduced to a mere recording tool. Source Instrument 7

8 Pros and Cons Unique performance, largely unrelated to the telescope used Fixed-time events Not linked to major observatories Simple instrumentation (mostly photometry) Limited repeatability Limited (random) source selection Time efficient Limited observing modes 8

9 Taxonomy of Occs and Trans Solar Transits Why observe them? Subspecies: Mercury Venus 9

10 Taxonomy of Occs and Trans Satellites & Planets Why observe them? Subspecies: gaseous planets rocky/icy planets planetary rings by rocky satellites by satellites with atmosphere above or behind the planet 10

11 Taxonomy of Occs and Trans Lunar Occultations Why observe them? Subspecies: of gaseous planets of rocky planets of stars of asteroids of galaxies of the Sun! 11

12 Taxonomy of Occs and Trans Occultations by Solar System Bodies Why observe them? Subspecies: by asteroids by gaseous planets by planetary rings by rocky planets by minor bodies 12

13 Taxonomy of Occs and Trans Eclipsing Binaries 13

14 Taxonomy of Occs and Trans Star-Exoplanets Why observe them? Subspecies: Single Planets Multiple Planets Planets with Moons (Planets with Atmosphere) 14

15 Taxonomy of Occs and Trans Microlensing Subspecies: Binary stars Stellar atmospheres Stars with planets Isolated low-mass objects Why observe them? 15

16 Timing Considerations Why include Occultations & Transits in this School? 16

17 Instrumentation [1] Photometers, photomultipliers, InSb diodes Cheap, small, efficient ms Time Resolution Aperture integration (high background noise)...disappearing species! 17

18 Instrumentation [2] Avalanche Photo-Diodes (APD), SPAD ns Time Resolution Aperture integration (but small arrays are becoming available) IQUEYE 18

19 CCD (drift scanning) Instrumentation [3] affordable, if not cheap ms Time Resolution choice of pixel (low background noise) need correct pixel scale limited time range Fors et al (2001) 19

20 EMCCD (Electron Multiplying CCD) Instrumentation [4] 0.01s Time Resolution full frame switchable gain almost zero noise Gain register Secondary electrons are generated via an impact-ionization process Two outputs: normal and avalanche expensive sophisticated ROE ULTRASPEC (Dhillon et al) 20

21 NIR Arrays (subwindow) Instrumentation [5] ms Time Resolution gapless long time range expensive sophisticated ROE ARNICA (Richichi et al 1996) 21

22 The ISAAC burst mode

23 The ISAAC burst mode fast 64 x 64 slow 32 x 32

24 Instrumentation [6] Mid-Infrared Arrays ms Time Resolution intrinsic (full frame) expensive high RON sophisticated ROE extreme cooling Aquarius /Raytheon(ESO) 24

25 Specialized small format arrays (AO) Instrumentation [7] ms Time Resolution full frame long time range expensive sophisticated ROE 25

26 Occultation of Mira by Saturn s Rings 26

27 Initial Results Mira s angular size as a function of 1 < < 5 m Star/Shell flux ratio, Multiple Directions and dates Paper submitted 27

28 Exoplanet Transits Can unequivocally confirm RV detections Can yield radius of planet (ie density, rocky or not) Planets orbiting double stars Transit Timing Variations (multiple planets, moons) Kepler First Planet in Habitable Zone P ~ 290 days G5 ly Radius, Mass ~ 1 Earth T ~ 260 K ~ 6% D stars with HZP 28

29 Lunar Occultations The Moon s limb acts as a straight diffracting edge The diffraction phenomenon occurs in vacuum, no turbulence effects. High-angular information is embedded in the diffraction fringes. Lunar limb irregularities have marginal influence (Fresnel fringes). The resolution is independent from telescope diameter (but depends on SNR). Temporal scales (depending on wavelength and apparent limb velocity ) are ~0.1s. Diffraction patterns of two or more components add linearly. Combination of sensitivity and angular resolution that cannot be achieved by any other technique in the near-ir. But: lunar occultations are fixed-time events! 29

30 Simulations with Ks filter, noiseless, typical lunar rate, source at T=275ms Measuring Stars with Occultations Signature of diffraction fringes is linked to source size. Fringe contrast is maximum for an unresolved source. When source size (λ/d) transition to geometrical optics size ~ time Diffraction patterns of 2 or more sources add linearly 1ms time difference ~ 0.4mas angular separation 30

31 Extracting Light Curves millisecond rates are needed Photometers are fast, but collect more of the intense background 2-D images allow masking of the background, but arrays are slower 31

32 What we get at the end , source with K=6.6 mag, no optical counterpart, no literature SNR=110, point source with upper limit 0.75 mas (χ2 = 1.013)

33 Moon in the Pleiades, December 2010 K<10 mag Richichi et al A&A 541, A96 (2012) members +non-members

34 Detected Binaries

35 Detected Binaries

36 Example of a circumstellar shell 2MASS = ISOGAL-P J IR source K=5.3, J-K=3.7; no optical cross-id; SiO Maser probably fore-gc star ( low A K =1.1mag) 1kpc-> shell ~20AU 2 =7.0 2 =6.3 2 =1.6 R~16mas Richichi et al. (2008)

37 Practical Exercises

38 Some Considerations

39 Lunar Occultations Software Occult v4.1.0 Occultation Prediction Software

40 Lunar Occultations Software ALOP (Predictions generation) ALOS (Predictions selection) ALOR (Light curve Analysis) Occult v4.1.0 Occultation Prediction Software

41 Practical Exercises

42 Practical Exercises

43 Practical Exercises

44 Summary Occultations and Transits stand aside from standard astronomical observations: the telescope has only a passive photon-bucket role. They offer performance and opportunities which may not be attained by other conventional methods. Price to pay: fixed-time, random events. We have taken a stroll in the zoo of the occultations and transits, and met some of its many species High time resolution is needed, generally in the 1 to 0,001s range. We have seen some of the possible detectors. We have discussed some of the science that can result from occultations and transits, both from the ground and from space We have learned how Lunar Occultations work We got some experience in prediction and analysis of Lunar Occultations

45 The End Thank you Grazie ขอบค ณ คร บ Terima kasih Спасибо