Spitzer/IRS survey of heavily obscuredSpitzer/IRS survey of heavily obscured planetary nebula precursorsplanetary nebula precursors

D. A. García-Hernández (McDonald Observatory, UT, USA)D. A. García-Hernández (McDonald Observatory, UT, USA)J. V. Perea-Calderón (ESAC-INSA, Spain)J. V. Perea-Calderón (ESAC-INSA, Spain)

D. Engels (Hamburg Observatory, Germany)D. Engels (Hamburg Observatory, Germany)P. García-Lario (Herschel Science Centre-ESAC, Spain)P. García-Lario (Herschel Science Centre-ESAC, Spain)

APN IV, La Palma, June 19 2007APN IV, La Palma, June 19 2007

Project SummaryProject Summary

• Scientific Goal:Scientific Goal: Characterization of the IR properties of the Characterization of the IR properties of the Galactic Population of heavily obscured transition sources Galactic Population of heavily obscured transition sources (AGB(AGBPN)PN)

• The sample:The sample: a complete flux-limited sample of ~80 hidden a complete flux-limited sample of ~80 hidden post-AGB candidates selected from the GLMP catalog post-AGB candidates selected from the GLMP catalog (García-Lario 1992) according to their IRAS colors:(García-Lario 1992) according to their IRAS colors:

- No OPC; many obscured also at NIR wavelengths - No OPC; many obscured also at NIR wavelengths - ~40 non-variable OH/IR + ~40 of unknown chemistry- ~40 non-variable OH/IR + ~40 of unknown chemistry - Plus a few young PNe & variable TP-AGB stars- Plus a few young PNe & variable TP-AGB stars

• The Spitzer observations:The Spitzer observations: 5 537 37 m IRS spectra m IRS spectra (SL+SH+LH when possible). S/N > 50 (two 6 s cycles)(SL+SH+LH when possible). S/N > 50 (two 6 s cycles)

Project StatusProject Status

• 41 spectra (9 non-variable OH/IRs + 27 unknown 41 spectra (9 non-variable OH/IRs + 27 unknown chemistry + 2 PNe + 3 variable OH/IRs) reduced and chemistry + 2 PNe + 3 variable OH/IRs) reduced and analysedanalysed

• Here we present the first results and a qualitative Here we present the first results and a qualitative analysis of these 41 spectra (e.g. dominant analysis of these 41 spectra (e.g. dominant chemistry, dust composition, identification of new chemistry, dust composition, identification of new young PNe and peculiar sources) young PNe and peculiar sources)

• Unfortunately, the rest of the sample (47) was Unfortunately, the rest of the sample (47) was scheduled in the period Mayscheduled in the period MayJune 2007 and the data June 2007 and the data has not been released yethas not been released yet

Dominant chemistryDominant chemistry

• The variety of the spectra found is amazing:The variety of the spectra found is amazing:

- 6 non-variable OH/IRs show strong O-rich solid state 6 non-variable OH/IRs show strong O-rich solid state features as expected & 3 featurelessfeatures as expected & 3 featureless

- Among the pAGBs with unknown chemistry we find Among the pAGBs with unknown chemistry we find 8 O-rich, 9 C-rich & 8 featureless8 O-rich, 9 C-rich & 8 featureless

- We find some stars showing very clearly the moment We find some stars showing very clearly the moment of transition from amorphous (aliphatic) to of transition from amorphous (aliphatic) to crystalline (aromatic) dust features (in both chemical crystalline (aromatic) dust features (in both chemical branches) branches)

- We identify 1 new young PNe which is a possible We identify 1 new young PNe which is a possible double-dust chemistry (C-rich & O-rich) PNdouble-dust chemistry (C-rich & O-rich) PN

O-rich PN precursorsO-rich PN precursors

Different strengths of the Different strengths of the amorphous silicate amorphous silicate absorption features at absorption features at 9.7 and 18 9.7 and 18 mm

The crystalline silicatesThe crystalline silicatesfeatures at features at >15>1520 20 m arem areseen emerging from the seen emerging from the underlying continuum while underlying continuum while the amorphous silicate the amorphous silicate absorptions decrease inabsorptions decrease instrengthstrength

C-rich PN precursorsC-rich PN precursors

Bumps at 11Bumps at 1115 & 1515 & 1520 20 m,m,and sometimes strong andand sometimes strong andbroad features centred at broad features centred at 21, 26 and 30 21, 26 and 30 m and them and the‘‘classical’ set of PAHclassical’ set of PAHfeatures (6.2, 7.7, 8.6features (6.2, 7.7, 8.6and 11.3 and 11.3 m)m)

The 11The 1115 & 1515 & 1520 20 mmbumps dissapear whilebumps dissapear whilethe PAH features emerge the PAH features emerge at shorter wavelengthsat shorter wavelengths

Young PNeYoung PNe2 PNe as indicated 2 PNe as indicated by the detection of nebular by the detection of nebular emission lines (e.g. [Ar II], emission lines (e.g. [Ar II], [Ar III], [Ne II], [S III])[Ar III], [Ne II], [S III])

- I14079 is a poorly known - I14079 is a poorly known young and dusty PN. It is young and dusty PN. It is O-rich showing amorphous O-rich showing amorphous and crystalline silicatesand crystalline silicates

- I19176 is a new PN- I19176 is a new PN(possible double-chemistry)(possible double-chemistry)displaying crystalline displaying crystalline silicates & 6.3 silicates & 6.3 m emissionm emission

O-rich transition sourcesO-rich transition sources

2 O-rich PN precursors 2 O-rich PN precursors where the transition from where the transition from amorphous to crystalline amorphous to crystalline dust structure isdust structure istaking placetaking place

The crystalline silicate The crystalline silicate features are detected in features are detected in emission inside the emission inside the amorphous silicate amorphous silicate absorptions at 9.7 & 18 absorptions at 9.7 & 18 mm

C-rich transition sourcesC-rich transition sources5 sources displaying C5 sources displaying C22HH22

at 13.7 at 13.7 m and other m and other molecular absorptionsmolecular absorptions

I21525 and I15038 show a I21525 and I15038 show a broad C-based feature (SiC?) broad C-based feature (SiC?) at 11.3 at 11.3 m but I15038 alsom but I15038 alsodisplays Cdisplays C22HH22, PAHs & the , PAHs & the

26 and 30 26 and 30 m features! m features! Previously observed in some Previously observed in some Galactic & MC pAGBs Galactic & MC pAGBs (e.g. MSX (e.g. MSX SMC 029; Kraemer et al. 2006)SMC 029; Kraemer et al. 2006)

Other C-rich molecular Other C-rich molecular absorptions detected absorptions detected in the region 12in the region 1216.5 16.5 mm

IRAS 22036+5306IRAS 22036+5306

Sahai et al. 2003Sahai et al. 2003HST/ACS F814W (HST Data Archive)HST/ACS F814W (HST Data Archive)

Spitzer shows an O-rich chemistry, being Spitzer shows an O-rich chemistry, being consistent with previous ISO observations. consistent with previous ISO observations. HST images show a spectacular bipolar HST images show a spectacular bipolar morphology (knotty & jetlike structures & morphology (knotty & jetlike structures & a central disk). This suggest that I22036 a central disk). This suggest that I22036 may be a massive (>4may be a massive (>45 M5 M) HBB PN ) HBB PN

precursor.precursor.

SummarySummary

• 41 Spitzer/IRS (541 Spitzer/IRS (537 37 m) spectra of heavily obscured PN m) spectra of heavily obscured PN precursors have been qualitatively analysedprecursors have been qualitatively analysed

• Most of the non-variable OH/IRs are O-rich but both C-rich Most of the non-variable OH/IRs are O-rich but both C-rich & O-rich sources are found among the pAGBs with & O-rich sources are found among the pAGBs with unknown chemistry. A new young PNunknown chemistry. A new young PN

• The IR spectra display a variety of dust compositions The IR spectra display a variety of dust compositions (amorphous and crystalline structures in both C-rich & O-(amorphous and crystalline structures in both C-rich & O-rich environments)rich environments)

• We identify for the first time O-rich PN precursors where We identify for the first time O-rich PN precursors where the transition from amorphous to crystalline dust structure the transition from amorphous to crystalline dust structure is taking place including the first clear detection of Cis taking place including the first clear detection of C66HH66 in in

Galactic post-AGB starsGalactic post-AGB stars

I19176: a double-chemistry PN?I19176: a double-chemistry PN?

Crystalline silicates Crystalline silicates in the 9in the 913 13 m m spectral range spectral range together with a 6.3 together with a 6.3 m m feature. A 6.4 feature. A 6.4 m m feature has beenfeature has beenatrributed to C-C atrributed to C-C stretch transitions in stretch transitions in extremely H-deficient extremely H-deficient carbonaceous grains carbonaceous grains (e.g. Abell 78; Harrington (e.g. Abell 78; Harrington et al. 1998)et al. 1998)

Molecular AbsorptionsMolecular AbsorptionsMolecular absorption of Molecular absorption of CC22HH22, HCN, C, HCN, C44HH22, & C, & C66HH22::

the building blocks of the building blocks of PAHs!PAHs!

Benzene (CBenzene (C66HH66) is clearly) is clearly

detected in I19566 (only detected in I19566 (only two other detections two other detections reported by Cernicharo reported by Cernicharo et al. 2001 in CRL 618et al. 2001 in CRL 618– – tentative – andtentative – and BernardBernardSalas et al. 2006Salas et al. 2006in SMP LMC 11)in SMP LMC 11)