The use of PNe precursors in the study of Diffuse Interstellar Bands

Pedro GARCIA-LARIOPlanetary Nebulae as Astronomical Tools / Gdańsk, June 28/July 2 2005, Page 1

The use of PNe precursors in the The use of PNe precursors in the study of Diffuse Interstellar Bandsstudy of Diffuse Interstellar Bands

¹ ESA/ISO Data Centre. ESAC, Madrid, Spain ² E. Politécnica Superior de Alcoy, Spain

Pedro García-Lario¹, Ramon Luna² & M.A. Satorre²

In collaboration with:

H. van Winckel, M. Reyniers (K.U. Leuven);

O. Suárez (INTA/LAEFF);

B. Foing, N. Boudin (ESA/ESTEC)


– 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 1900’s ! but still unknown origin (presumed interstellar because of their correlation with dust extinction)

What are DIBs ?

From P.

Jenniskens

Adapted from P. Jenniskens


– 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

What do we know about DIBs ?


– 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)

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)



– 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


– 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)



– 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

What else can we do?


– 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

What about circumstellar DIBs?


– Diffuse Interstellar Bands (DIBs) are

Search for DCBs in AGBs

IRC +10º 216, Kendall 2002

12.4’2’


– 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)

A way around: post-AGB stars

post-AGB


DBs in post-AGB stars

(Zacs et al. 1999)


Not always so simple…

Not the 5850 Å DB !


– 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

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



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

EW = α· E(B-V)

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


ISM vs. CS extinction

Overall extinction = ISM contribution + CS contribution



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 06530-0213 IRAS 17097-3210 HD 172324 IRAS 22272+5435


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



t

t t


The DB at 6284 Å

IRAS 19500-1709

E(B-V) = 0.37

IRAS 22023+5249

E(B-V) = 0.52


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

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

DB strength vs. E(B-V)


The DB at 6284 Å


The DB at 5780 Å


The DB at 5797 Å


The DB at 6614 Å


The DB at 7224 Å


Analysis of radial velocities

Na D2 5896 Å


Analysis of radial velocities


– 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!

Conclusions

The use of PNe precursors in the study of Diffuse Interstellar Bands

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