Transcript The use of PNe precursors in the ¹


The use of PNe precursors in the
study of Diffuse Interstellar Bands
Pedro García-Lario¹, Ramon Luna² & M.A. Satorre²
¹ ESA/ISO Data Centre. ESAC, Madrid, Spain
² E. Politécnica Superior de Alcoy, Spain
In collaboration with:
H. van Winckel, M. Reyniers (K.U. Leuven);
O. Suárez (INTA/LAEFF);
B. Foing, N. Boudin (ESA/ESTEC)
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What are DIBs ?
– Diffuse Interstellar Bands (DIBs) are bands of variable strength and
width of still unknown origin which appear overimposed on the
spectra of bright but heavily reddened stars
Adapted from P. Jenniskens
From P. Jenniskens
– Discovered in the early 1900’s ! but still unknown origin (presumed
interstellar because of their correlation with dust extinction)
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What do we know about DIBs ?
– More than 300 catalogued (McCall et al. 2002) from UV to nearinfrared wavelengths (3600 -10200 Å)
– The most studied ones:
• 4430 Å, 5780, 5797 Å, 6284 Å
– Many carriers proposed; none convincing
– A major challenge for spectroscopists, astronomers, and physicists
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What are their carrier(s) ?
– Detection of
substructures in the
profiles of several DIBs
indicates the molecular
nature of some DIB
carriers (e.g. 5797, 6379
and 6614 Å )
(Kerr et al. 1998)
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What are their carrier(s) ?
– Existence of `families’ of
DIBs suggest not a
unique carrier
(Krelowski &
Walker 1987)
Families of DIBS:
1: 4430, 6180
2: 5780, 6196, 6203, 6269,
6284
3: 5797, 5850, 6376, (2200)
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What are their carrier(s) ?
– Interstellar origin
supported by correlation
with reddening found in
galactic early-type
stars, measured as
E(B-V)
(Herbig 1995)
Prototypical star:
HD 183143
DB
EW/E(B-V)
FWHM
5780
0.44
2.2
5797
0.13
1.1
5850
0.045
1.1
6196
0.044
0.90
6284
1.1
4.5
6379
0.067
1.1
6614
0.20
1.2
6993
0.10
1.6
7224
0.20
1.3
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What are their carrier(s) ?
– They are ubiquitous; detected towards a wide variety of astronomical
sources
– Most promising hypothesis: large carbon-bearing molecules:
• Long carbon chains? (Douglas 1977)
• PAH cations? (Allamandola et al. 1998; Salama et al. 1999)
• Fullerenes? (Foing & Ehrenfreund 1997)
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What else can we do?
– There are strong evidences that the relative strength of DIBs are
correlated with the properties of the clouds in the line of sight
– Environmental dependence of DIBs may reflect an interplay of
ionization, recombination, dehydrogenation and destruction of
chemically stable, carbonaceous species (Salama et al. 1996)
– Investigations of DIBs in regions of different metallicity, chemical
properties and UV radiation field may allow us to constrain the
physico-chemical properties of the (different) DIB carriers.
– Difficult to probe the ISM along a given line of sight; usually this is a
combination of many different clouds with inhomogeneous properties
and complex morphologies
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What about circumstellar DIBs?
– Are there also Diffuse Circumstellar Bands (DCBs) ?
– First suggested by Le Bertre & Lequeux (1993)
– Circumstellar shells around low- and intermediate-mass evolved
stars are a ‘natural’ environment where DB carriers may form.
– They are among the most important contributors of gas and dust to
the ISM
– Dense outflows of cool C-rich AGB stars are the best candidates
– Observational problems because of the presence of strong molecular
bands in their optical spectra; difficult to model stellar continuum;
complex photospheres
– Thus…
No attempt yet made for a systematic search for DCBs
– Ways around to address the problems needed (IRC +10º216)
unsuccessful
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Search for DCBs in AGBs
– Diffuse Interstellar Bands (DIBs) are
12.4’
2’
IRC +10º 216, Kendall 2002
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A way around: post-AGB stars
post-AGB
– Diffuse Bands (DBs) may
potentially be detected also
towards post-AGB stars
– Post-AGB stars show a wide
range of spectral types (from M to
B) in their way to become PNe
– High galactic latitude helps!
– For many of them we know the
chemical composition of the dust
grains (ISO, mm/submm, radio)
– Some results on individual postAGB stars look promising (Zacs
et al. 1999, 2001; García-Lario et
al. 1999; Klochkova et al. 2000)
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DBs in post-AGB stars
(Zacs et al. 1999)
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Not always so simple…
Not the 5850 Å DB !
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A systematic search for DBs
– 9 of the strongest Diffuse Interstellar Bands (DIBs) were investigated
in a sample of 33 post-AGB stars
– Spectral types: B – G
– A mixture of C-rich and O-rich stars (chemistry derived from ISO data
in most cases; also from submm and/or radio observations)
– Wide range of galactic latitudes and overall extinction
– high-radial velocity stars were favoured (to help discrimination of ISM
vs. CSE features)
– Several runs using 5 telescopes at three different observatories
• ESO/La Silla (ESO 1.52m/FEROS + ESO NTT/EMM)
• ESO/Paranal (VLT/UVES)
• Roque de los Muchachos, La Palma (TNG/SARG + WHT/UES)
– Spectral resolution  50,000; most of the observations so far
analyzed were initially taken for other purposes
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A systematic search for DBs
Recalculation of EW / E(B-V)
dependence using a sample of
53 reddened stars of early
spectral type
(Thorburn et al. 2003)
At 5780, 5797, 6196,
6284, 6379 and 6614 Å
Original spectroscopic data
R  38000
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A systematic search for DBs
EW = α· E(B-V)
Recalculation of EW/E(B-V) dependence
DB
r
EW/E(B-V)
EW/E(B-V)
using 4 reddened early type stars
5780
0.65
0.46
0.44
5797
0.70
0.19
0.13
5850
0.96
0.050
0.045
6196
0.79
0.053
0.044
6284
0.74
1.05
1.1
6379
0.59
0.093
0.067
6614
0.78
0.21
0.20
6993
0.95
0.12
0.10
7224
0.99
0.25
0.20
(Jenniskens et al. 2003)
At 5850, 6196 and 7224 Å
Original spectroscopic data: R  20000
HD 183143
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ISM vs. CS extinction
Overall extinction = ISM contribution + CS contribution
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A systematic search for DBs
Old Observations available
IRAS 04296+3429
IRAS 12175-5338
IRAS 17436+5003
IRAS 20462+3416
IRAS 05113+1347
IRAS 16594-4656
IRAS 18025-3906
IRAS 22023+5249
IRAS 05341+0852
IRAS 17086-2403
IRAS 18062+2410
IRAS 22223+4327
IRAS 06530-0213
IRAS 17097-3210
HD 172324
IRAS 22272+5435
IRAS 07134+1005
IRAS 17150-3224
IRAS 19114+0002
IRAS 23304+6147
IRAS 08005-2356
IRAS 17245-3951
IRAS 19386+0155
IRAS 08143-4406
IRAS 17395-0841
IRAS 19500-1709
IRAS 08544-4431
IRAS 17423-1755
IRAS 20000+3239
September 2003 observations
IRAS 01005+7910
IRAS Z02229+6208
IRAS F05251-1244
IRAS 19200+3457
June 2004 observations (under analysis)
IRAS 17023-1534
IRAS 17364-1238
IRAS 18379-1707
IRAS 21153-6842
IRAS 17074-1845
IRAS 17381-1616
IRAS 18442-1144
IRAS 21190+5140
IRAS 17195-2710
IRAS 17542-0603
IRAS 20572+4919
IRAS 21546+4721
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A systematic search for DBs
t
t
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t
Pedro GARCIA-LARIO
The DB at 6284 Å
IRAS 19500-1709
E(B-V) = 0.37
IRAS 22023+5249
E(B-V) = 0.52
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DB strength vs. E(B-V)
No clear correlation between
EW and E(B-V) in P-AGB stars
Many stars show values well
below the expectations
Some DBs are not even detected
in strongly reddened P-AGB stars
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DB strength vs. E(B-V)
In general, DCS PAGB stars show
always the lower values
Non-detections at high E(B-V) are
only found in DCS PAGB stars
Non-DCS PAGB stars show values
which are in many cases
consistent with the values
expected for ISM DIBs
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The DB at 6284 Å
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The DB at 5780 Å
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The DB at 5797 Å
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The DB at 6614 Å
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The DB at 7224 Å
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Analysis of radial velocities
Na D2 5896 Å
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Analysis of radial velocities
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Conclusions
– The strength of 9 of the strongest DBs has been systematically
searched and analysed in a sample of 33 PAGB stars.
– They are found to be extremely weak as compared to the results
obtained in other samples of reddened stars
– The effect is more clearly observed in P-AGB stars dominated by
circumstellar extinction
– Our results suggest that DIBs are not formed (yet) in the
circumstellar shells around PAGB stars
– If connected with PAHs, as suggested in the literature, their carriers
must form at a later stage as the result of their processing by the
hard UV field in the ISM
– Their identification as strongly ionized PAHs and/or radicals liberated
from carbonaceous species as a consequence of photoevaporation
of dust grains in the ISM would be consistent with our observations
– Interesting to observe CSPNe with various dominant chemistries and
a lot of internal extinction!
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