Download Interstellar Extinction

Non-linear Effects of Atmospheric
Extinction on Observations in Astronomy
Frédéric Zagury
Institut Louis de Broglie
Paris - France
1
Contents
I.
Modifications of the night-sky spectrum in the vicinity of a star
I.1 The night-sky spectrum
I.2 Diffracted and scattered starlight
I.3 Intermediate distances
II.
The Red Horizon
III.
Analysis of the spectrum of the Red Rectangle nebula
III.1 Broad-band analysis
III.2 Fine structure: the Red Rectangle bands
IV.
Diffuse Interstellar Bands
V.
Conclusion
2
I. Modifications of the night-sky
spectrum in the vicinity of a star
3
I.1 The night-sky spectrum
 > a few arc-minute (3 10-4 rd)
Night-sky spectrum at Mt Wilson, USA
5700-6000 Å region
Massey et al., 1990, PASP, 112, 566
Massey & Foltz, 2000, PASP, 102, 1046
4
Night skies at La Silla-Paranal and Mount Wilson
Spectrum of the night sky at Mount Wilson (USA)
Spectrum of the night sky at La Silla-Paranal (Chili)
5
I.2 Diffracted and scattered starlight
10’’
 < a few arcsecond (5 10-6 rd)
5’’
10’’
6
I.3 Spectra at intermediate distances from the star
( ~ a few 10’’)
10’’
7
The Red Rectangle nebula
30 ’’
HST image of the RR nebula with
the WFPC2 camera
8
10’’
30 ’’
9
II The Red Horizon
10
Why is the horizon red?
Spectrum of a red horizon at sunrise
6000
7000
5500
5000
4700
Å
Rayleigh
extinction
ozone
(Observed spectrum)/(spectrum of the sun)
Fit: Cte x exp(-2.3 1020 oz) x exp(-b/4)/4
11
III. Analysis of the spectrum of the
Red Rectangle nebula
12
The spectrum of the Red Rectangle nebula
 = 5’’
30 ’’
 > 10’’
13
Spectrum of the Red Rectangle nebula close to HD44179
( = 5’’)
nebula
30 ’’
Diffracted light from HD44179
14
Spectrum of the Red Rectangle nebula away from HD44179
( > 10’’)
nebula
30 ’’
Diffracted light from HD44179
Nebula ( = 14’’)
Background (x 6)
Scattered starlight (1/ x HD44179)
15
Red slope of the Red Rectangle nebula spectrum
Nebula/(non reddened A0 star)
1/4
16
Ground-based spectrum of galaxy UGC 11917
17
Non-linearity of atmospheric extinction
galaxy, nebula
star
Atmosphere
Telescope
Telescope
Rayleigh
ozone
Rayleigh
ozone
18
Fine structure of the Red Rectangle spectrum:
the Red Rectangle bands
Spectrum of the nebula
Background x 7
19
Comparison of the Red Rectangle and
background spectra in the 5800 Å region
20
Comparison of the Red Rectangle and the
background spectra in the 6100 Å region
21
Comparison of the Red Rectangle and the
background spectra in the 6200 Å region
22
Temptative identification of the carriers for the atmospheric
absorption in the Red Rectangle nebula - 1
Red Rectangle spectrum
Sun occultation (SAOZ experiment)
23
Temptative identification of the carriers for the atmospheric
absorption in the Red Rectangle nebula - 2
24
Temptative identification of the carriers for the atmospheric
absorption in the Red Rectangle nebula - 3
25
Temptative identification of the carriers for the atmospheric
absorption in the Red Rectangle nebula - 3
26
IV. Diffuse Interstellar Bands (DIBS)
27
Star
Interstellar cloud
Telescope
From Jenniskens & Desert, 1994, A&ASS, 106, 39
28
The 6200 Å Diffuse Interstellar Band
29
Interstellar cloud
Atmosphere
Telescope
30
V. CONCLUSION
1. Consequences of the observed nonlinearity of atmospheric extinction
- Need for a review of the data reduction process
used in Astronomy
-The atmosphere may impose the most serious
limits to future deep observations of the
Universe from Earth
31
CONCLUSION
2. Synergies between Astronomy and
studies of the atmosphere
3. DIBs and Red Rectangle bands:
A need for observations with HST
32