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Observational Astrophysics II (L2)

Observational Astrophysics II (L2). Getting our NIRF. What do want to do? Image a selected spiral galaxy in H a 6563 (HII/slit position) Spectroscopy of HII regions => los radial velocities Imaging in JHK => isophotes => deprojection => V rad (r)

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Observational Astrophysics II (L2)

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  1. Observational Astrophysics II (L2) Getting our NIRF • What do want to do? • Image a selected spiral galaxy in Ha 6563 (HII/slit position) • Spectroscopy of HII regions => los radial velocities • Imaging in JHK => isophotes => deprojection => Vrad(r) • => rotation curve • and => stellar population from colours http://www.astro.su.se/utbildning/kurser/astro_obs2/ Observational Astrophysics II: May-June, 2004

  2. Spectrograph Slit Radial Distance, r (arcsec to kpc) Error Bars ???! Observational Astrophysics II: May-June, 2004

  3. The Spiral Galaxy M83 in broad band R in narrow band Ha Stellar pop - extended H II regions – point like Observational Astrophysics II: May-June, 2004

  4. UBVRI Ha line-to-continuum contrast In narrow band filter continuum Observational Astrophysics II: May-June, 2004

  5. supersonic jet flow Example of long-slit observation (spatio-spectral mapping) star 1´´ wide 2´ long spectrograph slit Observational Astrophysics II: May-June, 2004

  6. star 2´ slit Spatial Domain Spectral Domain 1´´ slit K-spectrum of Serpens SMM1 jet (VLT-ISAAC) rovibrational H2 lines S(3) n=2-1 S(2) n=2-1 R = 400 Observational Astrophysics II: May-June, 2004

  7. R = 400 (Dv = 750 km s-1) R = 100 000 (Dv = 3 km s-1) Radial velocity measurement Observational Astrophysics II: May-June, 2004

  8. 1. ALFOSC Ha imaging Observing our galaxies What Filter? l = 6563 (z + 1) Å http://www.not.iac.es/instruments/instruments.html Observational Astrophysics II: May-June, 2004

  9. 2. ALFOSC Ha spectroscopy Observing our galaxies What slit width? ALFOSC Slits The following slits are available for use with ALFOSC: Simple, long-slit, covering the full spatial field of view of the instrument (in arcsec): 0.4, 0.5, 0.75, 1.0, 1.2, 1.3, 1.8, 2.5, 5.0, 10.0 Long-slit spectra are oriented vertically on the detector. The 1.8" slit is not very smooth and shows considerable flux variations along the slit. http://www.not.iac.es/instruments/instruments.html Observational Astrophysics II: May-June, 2004

  10. 2. ALFOSC Ha spectroscopy Observing our galaxies Sun at 8.5 kpc 250 km s-1 What spectral resolution? Dl = l Dv/c R = l/Dl http://www.not.iac.es/instruments/instruments.html Observational Astrophysics II: May-June, 2004

  11. 2. ALFOSC Ha spectroscopy Observing our galaxies What integration times? 1. NOT (or ESO) Exposure Time Calculator http://www.not.iac.es/observing/forms/signal/ Observational Astrophysics II: May-June, 2004

  12. 2. ALFOSC Ha spectroscopy Observing our galaxies What integration times? 2. Manual Estimate Quantify the ns . . . [ for t =1s and t ~ (S/N)2 ] Observational Astrophysics II: May-June, 2004

  13. source Two Domains: Above & Below Atmosphere spherical coherent - incoherent cow IS transport Plane Wave telluric atmospheric transport-turbulence diffraction aha... Obs. analysis: Reduction Calibration Informatics coherent – incoherent detection electronics Observational Astrophysics II: May-June, 2004

  14. 1. Above telluric atmosphere Photons gained Source - direct emission - scattered into beam Extra-Galactic Background Galactic Background Zodiacal Background Photons lost Source - direct abs/extinction -scattered out of beam Extra-Galactic Extinction Galactic Extinction (IS) Zodiacal Extinction A good emitter is also a good absorber (Kirchoff’s law) Observational Astrophysics II: May-June, 2004

  15. 2. Below telluric atmosphere Atmosphere emission extinction scattering Optics emission absorption Detector absorption emission Extinction, kl Transmission, Tl Efficiency, hl Detector Noise Observational Astrophysics II: May-June, 2004

  16. Collecting terms: 1. Signal degradation Atmosphere transmission Tatm (%) Telescope reflectivity Ttel (%) Filter transmission Tfilter (%) Spectrograph throughput Tspec (%) Detector efficiency QE (%) 2. Noise sources Source Photons Poisson Background Photons Sky + Telescope Detector emission Thermal or Dark Current Detector Read Noise Read out noise Observational Astrophysics II: May-June, 2004

  17. Observational Astrophysics II: May-June, 2004

  18. Signal = Source flux Fltel for given V, E(B-V) Similar can be done at any other filter wavelength, e.g. in the R band Observational Astrophysics II: May-June, 2004

  19. Sky Backgrounds are generally given in mag/arcsec2 (surface intensity) and are treated similar to source fluxes Dark current and read-out-noise are device specific normally provided externally (manufacturer/observatory) ALFOSC CCD # 8 2048 x 2048 13.5 mm pixels image scale 0.19´´/pxl dark current 0.4 e- / pxl / hr ron 5.3 e- / pxl (read time 90 s) conversion* 0.765 e- / ADU (high gain) well capacity 63 000 ADU (~216, high gain) non-linearity 0.3 % QEV 0.75 * Analogue-to-Digital Unit Observational Astrophysics II: May-June, 2004

  20. Worked example: NOT-ALFOSC Ha image • Galaxy R = 13 mag • E(B-V) = 0.02 mag • kR = 0.02 • Airmass = 2 • Seeing = 1´´ • Airmass = 2 • Filter #49 Dl = 50 Å leff = 6607 Å • Line-to-continuum = 1 • Sky background = 18 mag Observational Astrophysics II: May-June, 2004

  21. Worked example: NOT-ALFOSC Ha image, ctnd. Normally, one makes the computation in electrons and converts at the end. However, at the telescope, the student should watch the ADUs (linearity check). Observational Astrophysics II: May-June, 2004

  22. ALFOSC admits MAX check thickness!!! 7 Filters: UBVRI +2 12 FASU: 6 Grisms: 5 Slits: Observational Astrophysics II: May-June, 2004

  23. Preparing our NIRF http://www.not.iac.es/observing/guide/#preparation http://www.not.iac.es/observing/forms/nirf/ Observational Astrophysics II: May-June, 2004

  24. Before we go to the mountain... http://www.not.iac.es/observing/cookbook Observational Astrophysics II: May-June, 2004

  25. meaning astronomical night Day #147-152 Observational Astrophysics II: May-June, 2004

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