06 ashish mahabal bse1

06 ashish mahabal bse1

• 1.
  BigSkyEarth I: Sensors inAstronomy Ashish Mahabal Center for Data-Driven Discovery, Caltech Apr 5, 2016
• 2.
  Ashish Mahabal -BSE I Sundial and friends Samrat Yantra at IUCAA 3
• 3.
  Ashish Mahabal -BSE I Ignoring Galileo to embracing Gravitational-Waves 4
• 4.
  Ashish Mahabal -BSE I The EM spectrum 5
• 5.
  Ashish Mahabal -BSE I Photographic plates • Silver salt emulsions - light sensitive • Same principle as older (pre-digital cameras) but on glass plates [palomar story] • large collections exist (Harvard computers) [great for archival searches of variables - DASCH] 6
• 6.
  Ashish Mahabal -BSE I Carina Nebula on a 1951 plate by Karl Heinze held by Thurburn Baker (ADAP). 38cm x 38cm 7
• 7.
  Ashish Mahabal -BSE I Photomultiplier tubes • 1% photometry (0.01 mag accuracy) • variable stars • set of electrodes multiply number of electrons through higher voltages: gain of a million • resolution not great • used extensively in cosmic-ray and neutrino detectors [super-kamiokande has 11200 50cm tubes looking for Cerenkov radiation] 8
• 8.
  Ashish Mahabal -BSE I Charge-Coupled Devices (CCDs) • Workhorse of modern-day astronomy • Typically a 2D set of light-sensitive pixels (picture elements) • photons -> electrons • CSS 10k x 10k chip 9
• 9.
  Ashish Mahabal -BSE I features • Great dynamic range (twice that of CMOS) [but is it good enough? problems with bright objects] • Great quantum efficiency (can reach 95%) • compare solar cells • Good spectral range • Needs to be cooled for astronomical purposes (LN2) [Orion challenge] • a bit slow 10
• 10.
  Ashish Mahabal -BSE I PQ CCDs 112-CCD, 161 Mpix camera • multiple amplifiers for readouts (either faster on same chip, or multiple chips): crosstalk [PQ] • gaps between adjacent CCDs to accomodate attendant electronics: leads to more complex cadence 11
• 11.
  Ashish Mahabal -BSE I CRTS-II •  Same telescopes •  Bigger cameras and FOVs: MLS 1.5m, 1.2 -> 5 sq. deg CSS 0.7m, 8.2 -> 19 sq. deg Spectral Instruments camera with Imager Labs thinned 10.5K2 CCD. Upgrades funded and underway. 8/27/14 51Ashish Mahabal 12
• 12.
  Ashish Mahabal -BSE I CCD pipeline • Bias subtraction (ambient noise) • Flat fielding (detector response - per pixel) • cosmic ray removal (grazing incidences) Big Picture at Griffith 13
• 13.
  Ashish Mahabal -BSE I spectroscopes • filters are low-res spectrographs • to capture emission and absorption lines, we need real spectroscopes • series of mirrors - fraction refracts; different angle depending on wavelength • limited resolution • gelatin and Bragg’s diffraction can be used for better • not below 3000 Angstrom 14
• 14.
  Ashish Mahabal -BSE I DBSP at palomar • two arms • wider wavelength coverage at better resolution • separate gratings 15
• 15.
  Ashish Mahabal -BSE I Spectroscopy pipeline • 1d response through polynomial fits • arcs for wavelength calibration • spectrophotometric standards for flux calibration • selection of appropriate wavlength range for best science (e.g H-alpha or L-alpha) 16
• 16.
  Ashish Mahabal -BSE I integral field units • SDSS example • hundreds of thousands of quasar spectra17
• 17.
  Ashish Mahabal -BSE I NIR spectroscopy • more challenging - water vapour and CO2 absorption • keck spectrographs (NIRSPEC, MOSFIRE) • above the atmosphere 18
• 18.
  Ashish Mahabal -BSE I radio detectors • large wavelengths - so larger receivers (lambda/d) • can have bigger gaps (mesh) • arrays for Fourier domain coverage • SKA and path-finders NEP uv coverage 19
• 19.
  Ashish Mahabal -BSE I subMM detectors • molecular clouds • Star formation: H2, CO • dark clouds: Frozen CO, N • water vapor limitation (dry/cool/stable site needed) • Mauna Kea, Chile, Hanle, South Pole, (Greenland) Balloons (BLAST), Stratosphere (SOFIA) LDN 1768 20
• 20.
  Ashish Mahabal -BSE I X-ray detectors • focussing: higher resolution/sensitivity • collimating: coded masks, large FOV Swift: GRB finder 21
• 21.
  Ashish Mahabal -BSE I Polarimeters • To measure polarized light BL Lac with RoboPol 22
• 22.
  Ashish Mahabal -BSE I Gravitational-wave detectors 23
• 23.
  Ashish Mahabal -BSE I Summary • Wide variety of sensors • Immense variety of science • Many recent/ongoing innovations • Better/vaster data accumulating 24