Observational Astrophysics II (L2)

1. Observational Astrophysics II (L2) http://www.astro.su.se/utbildning/kurser/astro_obs2/ Observational Astrophysics II: May-June, 2005

2. Observational Astrophysics II (L2) Getting our NIRF • What do we 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 Observational Astrophysics II: May-June, 2005

3. Spectrograph Slit Radial Distance, r (arcsec to kpc) Error Bars ???! VGalaxy Observational Astrophysics II: May-June, 2005

4. 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, 2005

5. UBVRI Ha line-to-continuum contrast In narrow band filter continuum Observational Astrophysics II: May-June, 2005

6. supersonic jet flow Example of long-slit observation (spatio-spectral mapping) star 1´´ wide 2´ long spectrograph slit Observational Astrophysics II: May-June, 2005

7. 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, 2005

8. R = 400 (Dv = 750 km s-1) R = 100 000 (Dv = 3 km s-1) Radial velocity measurement Observational Astrophysics II: May-June, 2005

9. 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, 2005

10. 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, 2005

11. 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, 2005

12. 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, 2005

13. Exposure Time Calculator • Instrument ALFOSC Spectroscopy • Detector CCD8 (CCD7) • Grism http://www.not.iac.es/instruments/alfosc/grisms/ • Band • Bandwidth • Slitwidth • Source Extended • Mag • FWHM • Exptime • Airmass • Extinction http://www.ast.cam.ac.uk/~dwe/SRF/camc_extinction.html • Sky Brightness B Observational Astrophysics II: May-June, 2005

14. 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, 2005

15. 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, 2005

16. 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, 2005

17. 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, 2005

18. 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, 2005

19. Observational Astrophysics II: May-June, 2005

20. 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, 2005

21. 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, 2005

22. Worked example: NOT-ALFOSC Ha image • Galaxy R = 13 mag • E(B-V) = 0.02 mag • kR = 0.02 • Airmass = 2 • Seeing = 1´´ • filter #49 Dl = 50 Å leff = 6607 Å • Line-to-continuum = 1 • Sky background = 18 mag Observational Astrophysics II: May-June, 2005

23. 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, 2005

24. ALFOSC admits MAX check thickness!!! 7 Filters: UBVRI +2 12 FASU: 6 Grisms: 5 Slits: Observational Astrophysics II: May-June, 2005

25. Preparing our NIRF http://www.not.iac.es/observing/guide/#preparation Before we go to the mountain... http://www.not.iac.es/observing/cookbook Observational Astrophysics II: May-June, 2005