Innovations Foresight Astronomical Seeing The AstroImaging Channel Dr

Innovations Foresight Astronomical Seeing The Astro-Imaging Channel Dr. Gaston Baudat Innovations Foresight, LLC (c) Innovations Foresight 2015 - Dr. Gaston Baudat 1

Seeing Innovations Foresight • Astronomical seeing is the blurring of astronomical objects caused by Earth's atmosphere turbulence and related optical refractive index variations (air density fluctuations). • It impacts the intensity (scintillation) and the shape (phase) of the incoming wave front. • This presentation will ignore scintillation. (c) Innovations Foresight 2015 - Dr. Gaston Baudat 2

Wavefront and phase distortion Innovations Foresight An incoming plane wave is perturbed by the Earth atmosphere turbulent structure leading to phase errors. (c) Innovations Foresight 2015 - Dr. Gaston Baudat 3

Fluid dynamics Innovations Foresight The Reynolds’s (O. Reynolds 1883) number Re predicts flow patterns. Density Velocity Characteristic length Viscosity For air flow with velocity of few km/h and for length scales of 0. 1 km to 1 km Re > 106. Therefore the atmosphere is almost always turbulent. (c) Innovations Foresight 2015 - Dr. Gaston Baudat 4

Source of optical turbulence Innovations Foresight Energy is transferred by a turbulence cascade form the outer scale L 0 to the inner scale l 0 until heat dissipation (friction). Eddies exhibit different air density -> different refraction index (c) Innovations Foresight 2015 - Dr. Gaston Baudat 5

Phase structure function Innovations Foresight (25 l) Some r (-15 l) (c) Innovations Foresight 2015 - Dr. Gaston Baudat 6

The Fried’s parameter Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 7

Atmospheric turbulence strength Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 8

Seeing versus diffraction limit Innovations Foresight FWHM [“] 1 1. 5 2 2. 5 3 110 / 4. 3 74 / 2. 9 56 / 2. 2 44 / 1. 7 37 / 1. 5 (c) Innovations Foresight 2015 - Dr. Gaston Baudat 9

Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 10

Innovations Foresight Credit Tokovinin (c) Innovations Foresight 2015 - Dr. Gaston Baudat 11

Innovations Foresight 30 0. 93 50 1. 5 70 2. 2 100 3. 1 300 9. 3 (c) Innovations Foresight 2015 - Dr. Gaston Baudat 12

Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 13

Aberrations and seeing Innovations Foresight Type of aberration removed (inclusive) Zernike’s polynomials Tilt/tip 36% Defocus 33% Astigmatism 25% Coma (3 rd order) 23% Spherical (4 th order) 21% Trefoild (3 rd order) 19% (c) Innovations Foresight 2015 - Dr. Gaston Baudat 14

Innovations Foresight Tilt/tip removed (c) Innovations Foresight 2015 - Dr. Gaston Baudat 15

Isoplanatic patch Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 16

Effect of the isoplanatic angle on AO Innovations Foresight AO operation is usually only effective in a very narrow FOV. IR bands: 1200 nm, 1600 nm, and 2200 nm Credit R. Dekany, Caltec Palomar AO system (c) Innovations Foresight 2015 - Dr. Gaston Baudat Guide star offset FWHM [“] 0 0. 2 5. 5 0. 3 13 0. 45 0. 59 23 0. 51 0. 68 17

Temporal behavior of seeing Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 18

Residual tilt/tip and centroid error Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 19

Lucky imaging and seeing Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 20

Lucky imaging and PSF shape Innovations Foresight Set of 10 short exposure frames (tilt/tip removed): (c) Innovations Foresight 2015 - Dr. Gaston Baudat 21

Seeing and wavelength Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 22

Limitations of the standard Kolmgorov’s model Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 23

The Von Karman’s (VK) model Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 24

FWHM and the VK’s model Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 25

Finite OST and guide star wander Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 26

Auto-guiding Innovations Foresight • The goal of auto-guiding is to correct for setup tracking errors. • Those errors are independent of the seeing effect and are fully correlated across the FOV (unlike seeing). • Long term errors: PE, King’ rate, flexure, model, polar alignment, …, require a slow correction rate (10 s to minutes). • Short term errors: Mount mechanics (gear box), wind burst, vibrations, …, require a faster correction rate (few seconds). • Short term corrections may be prone to seeing effects. (c) Innovations Foresight 2015 - Dr. Gaston Baudat 27

Auto-guiding and seeing Innovations Foresight Seeing Excellent 0. 5” Good 1. 0” Average 2. 0 ” Bad 3. 0” rms error 0. 13” 0. 25” 0. 50” 0. 75” (c) Innovations Foresight 2015 - Dr. Gaston Baudat 28

Auto-guiding/AO rates Innovations Foresight (c) Innovations Foresight 2015 - Dr. Gaston Baudat 29

NIR versus visible auto-guiding Innovations Foresight Mario Motta’s relay telescope 32” (0. 8 m) @ f/6 M 86 images with STL 11000 + AO-L (few Hz) M 83 with full spectrum guiding (OAG) M 83 with NIR guiding (ONAG) (c) Innovations Foresight 2013 2015 - Dr. Gaston Baudat 30

Thank you! Innovations Foresight, LLC Clear skies! (c) Innovations Foresight 2015 - Dr. Gaston Baudat 31