Astron_ObsII

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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 gt los radial
  velocities
• Imaging in JHK gt isophotes gt deprojection gt
  Vrad(r)
• gt rotation curve
• and gt stellar
  population from colours

http//www.astro.su.se/utbildning/kurser/astro_obs
2/
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Spectrograph Slit
Radial Distance, r (arcsec to kpc)
Error Bars ???!
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The Spiral Galaxy M83
in broad band R
in narrow band Ha
H II regions point like
Stellar pop - extended
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U B V R I
Ha
line-to-continuum contrast In narrow band filter
continuum
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supersonic jet flow
Example of long-slit observation (spatio-spectra
l mapping)
star
1 wide 2 long spectrograph slit
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star
2 slit
Spatial Domain
Spectral Domain
1 slit
K-spectrum of Serpens SMM1 jet (VLT-ISAAC)
rovibrational H2 lines
S(3) n2-1
S(2) n2-1
R 400
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R 400 (Dv 750 km s-1)
R 100 000 (Dv 3 km s-1)
Radial velocity measurement
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Observing our galaxies
1. ALFOSC Ha imaging
What Filter? l 6563 (z 1) Å
z l (Å)
10-4 l0
10-3 6570
10-2 6630
10-1 7220
http//www.not.iac.es/instruments/instruments.html

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Observing our galaxies
2. ALFOSC Ha spectroscopy
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

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Observing our galaxies
2. ALFOSC Ha spectroscopy
Sun at 8.5 kpc 250 km s-1
What spectral resolution?
Dl l Dv/c R l/Dl
Dv (km s-1) Dl (Å) R
30 0.65 10000
300 6.5 1000
3000 65 100
30000 gt 650 lt 10
http//www.not.iac.es/instruments/instruments.html

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Observing our galaxies
2. ALFOSC Ha spectroscopy
What integration times? 1. NOT (or ESO) Exposure
Time Calculator
http//www.not.iac.es/observing/forms/signal/
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Observing our galaxies
2. ALFOSC Ha spectroscopy
What integration times? 2. Manual Estimate
Quantify the ns . . . for t 1s and t (S/N) 2

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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
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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
(Kirchoffs law)
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2. Below telluric atmosphere
Atmosphere emission
extinction
scattering Optics emission
absorption Detector absorption
emission
Extinction, kl
Transmission, Tl
Efficiency, hl Detector Noise
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Collecting terms 1. Signal degradation Atmospher
e 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
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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
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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
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• 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

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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).
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Obs. Group Filter (type / ) Grism Slit (arcsec) Object (Name) RA 2000 (h m s) Dec 2000 (o ) Proposal .and. Finder chart (Y/N)
1 Jeanette Christoffer NGC 5984 15 42 53.18 14 13 53.4
2 Andrej Milan 76, 49, 51 8 0.5, 0.75, 1.0, 1.3, 2.5 NGC 6389 17 32 39.8 16 24 06 Y Y
3 Anna Thomas 78, 50 8 0.5, 1.0, 1.3, 2.5 NGC 5112 13 21 56.43 38 44 05 N N
4 Sven 12, 15, 17, 18, 19, 20, 44 14 1.0, 1.2, 1.3 SAO104782 NGC 7023 B 335 19 11 01.25 21 01 35.62 19 37 15.8 14 42 46.5 68 10 10.4 07 34 00 N N
ALFOSC admits MAX
check thickness!!!
7 Filters UBVRI
2 12 FASU
6 Grisms
5 Slits
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Preparing our NIRF
http//www.not.iac.es/observing/guide/preparation

http//www.not.iac.es/observing/forms/nirf/
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Before we go to the mountain...
http//www.not.iac.es/observing/cookbook
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meaning astronomical night
Day 147-152