The use of PN precursors to study DIBs

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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
• Discovered in the early 1900s ! but still
  unknown origin (presumed interstellar because of
  their correlation with dust extinction)

Adapted from P. Jenniskens
From P. Jenniskens
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What do we know about DIBs ?

• More than 300 catalogued (McCall et al. 2002)
  from UV to near-infrared 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

• 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 post-AGB stars look
  promising (Zacs et al. 1999, 2001 García-Lario
  et al. 1999 Klochkova et al. 2000)

post-AGB
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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 a E(B-V)
Recalculation of EW/E(B-V) dependence using 4
reddened early type stars (Jenniskens et al.
2003) At 5850, 6196 and 7224 Å Original
spectroscopic data R ? 20000
DB r EW/E(B-V)
5780 0.65 0.46
5797 0.70 0.19
5850 0.96 0.050
6196 0.79 0.053
6284 0.74 1.05
6379 0.59 0.093
6614 0.78 0.21
6993 0.95 0.12
7224 0.99 0.25
EW/E(B-V)
0.44
0.13
0.045
0.044
1.1
0.067
0.20
0.10
0.20
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 Old Observations available Old Observations available Old Observations available
IRAS 042963429 IRAS 12175-5338 IRAS 174365003 IRAS 204623416
IRAS 051131347 IRAS 16594-4656 IRAS 18025-3906 IRAS 220235249
IRAS 053410852 IRAS 17086-2403 IRAS 180622410 IRAS 222234327
IRAS 06530-0213 IRAS 17097-3210 HD 172324 IRAS 222725435
IRAS 071341005 IRAS 17150-3224 IRAS 191140002 IRAS 233046147
IRAS 08005-2356 IRAS 17245-3951 IRAS 193860155
IRAS 08143-4406 IRAS 17395-0841 IRAS 19500-1709
IRAS 08544-4431 IRAS 17423-1755 IRAS 200003239
September 2003 observations September 2003 observations September 2003 observations September 2003 observations
IRAS 010057910 IRAS Z022296208 IRAS F05251-1244 IRAS 192003457
June 2004 observations (under analysis) June 2004 observations (under analysis) June 2004 observations (under analysis) 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 211905140
IRAS 17195-2710 IRAS 17542-0603 IRAS 205724919 IRAS 215464721
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A systematic search for DBs
t
t
t
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The DB at 6284 Å
IRAS 19500-1709 E(B-V) 0.37
IRAS 220235249 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!