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Post-AGB Weirdos

Here some ongoing work and plots of the stranger post-AGB sources in our sample:

The following stars will be discussed:

• IRAS06338 = HD46703: PAHs, CO2 gas emission, C60
• HD52961: PAHs?, CO2, C60
• IRAS13258: PAHs
• EPLyr: PAHs, CO2

Plot of all stars, showing the PAH and CO2 emission: plot_pahslines.ps

IRAS06338+5333:

General information:

• HD46703
• Spec.type = F3I
• Teff = 6250K
• log g = 1.0
• [Fe/H] = -1.5
• Porb = 600d
• e = 0.3
• Ppuls = 29d
• C/O = +0.74
• [C/H] = -0.3: no carbon/s-process enhancement
• depleted: [Zn/Fe] = +0.82 IRAS06338_depletie.ps

Spectral energy distribution iras06338_SED.ps

Spitzer spectrum: IRAS06338.txt

The reduced Spitzer spectrum shows a misalignment around 14-15micron. This due to bad overlap matching of the different spectral orders there. I think the spectrum longwards of 15micron should actually be shifted up a bit. Looking at the raw data and the Spitzer pipeline reduction, I think the spectrum longwards of 14micron needs to be shifted up around 0.045Jy. This results in the following spectrum: IRAS06338_rescaled.ps IRAS06338_rescaled.txt

The longer wavelength spectrum shows clear features of crystalline silicates: forsterite + enstatite

Fullerenes:

Used simple spline to subtract 'continuum', overplotted with scaled c60_T500_R120 as a test: IRAS06338contsub_c60_T500_R120.00.ps

The feature at 18.7micron is clear, the 17.4micron feature is probably blended with some CO2 gas emission.

The 18.7micron feature appears to be somewhat less broad than the models you send me:

The main problem will be determining the underlying continuum of the 17.4micron feature, depending on how you choose this, the ratio of the two features changes a bit, as can be seen in the following plots: IRAS06338_contsub1.ps IRAS06338_contsub2.ps IRAS06338_contsub3.ps

The resulting continuumsubtracted txt-files of the two models can be found here: IRAS06338_contsub1.txt IRAS06338_contsub2.txt IRAS06338_contsub3.txt

The best fit to IRAS06338_contsub2 is with: c60_T1000_R120.00.xdr

PAHS:

General:

This star shows strong PAH emission at6 and 11.3micron, with also some little features around 7micron: plot_7micron.ps. The big feature around 9micron is sofar unidentified, but probably also has some PAH emission around 8micron. A feature around 12.6micron could also be PAH emission.

To identify the PAH emission in the big feature we tried to remove this feature, but this is difficult since we do not know the type of emission, and thus the underlying shape of the feature. Still after removing a simple shape (see second plot), the features that remain are very similar to the emission seen in IRAS13258 (IRAS06338=black, scaled IRAS13258=blue/red): featsub3_iras13258.ps IRAS06338_featcont3.ps

Text file of continuumsubtracted spectrum of IRAS06338, as used in the above plots: IRAS06338_featsub.txt

Text file of the underlying feature, which peaks around 9.2micron, used as continuum in plots above: IRAS06338_cont3.txt

PAH emission of IRAS06338 compared to the PAH classes of Els Peeters (A=red, B=blue, C=green): IRAS06338_pahs.ps

Same plot but zoomed in on 6micron PAH feature: IRAS06338_pahs_zoom.ps

The underlying feature is not amorphous silicates, I think it is some sort of silica, maybe quartz. Still looking for a spectrum to compare with.

Spectral Fit: Amorphous Silica

Made a fit to the 5-12micron region, found a good fit using: pyroxene,silica,forst,enst and PAHs: IRAS06338.txt.ps

Made a plot of the feature, but removed pyroxene+silica contributions of the fit (red), and everything but the PAHs (blue): IRAS06338_nopyroxsilica_onlypah.ps nopyroxsilica.txt onlypah.txt

The 11.3micron PAH feature is broader than the template of Els, and in the fit this is solved by adding forsterite. Still I think the PAH is broad, this broad 11.3micron feature is also seen in the other sources, and so it is to me not entirely clear if we really need a lot of forsterite to broaden the feature. Jan, could you maybe try if you can model the 11.3micron feature with PAHs alone?

Spectral Fit: Quartz

Michiel provided some kappa files for quartz, redid the fit with them but gave a poorer fit....
IRAS06338_fit_quartz.ps

Spectral Fit: Na-Silicates

Looking at the spectrum, Michiel suspected the feature to be Na-based silicates, more specifally NaAlSi4O10. This indeed gives a very good fit to the central wavelength, but I am not sure if the residual spectrum is now still easily modelled. Made a plot where I subtract the NaSilicate emission, the PAH feature around 8micron now lies somewhere inbetween class B and C. IRAS06338_NaSil_sub.ps

The fit can considerable be improved if we dont force the PAHs to be class C. A good fit is obtained using NaSil, forst and enstatite, resulting in the following plot, and residual spectrum. IRAS06338_NaSil_pahresid.ps IRAS06338_NaSil_pahresid.txt

I then compared the residual spectrum with class B and C pahs of Els: IRAS06338_NaSil_pahresid_els.ps

The 8micron PAH feature now peaks at 7.9-8.0micron, and not 8.2 as in the class C case.

Comparison EPLyr:

The PAH emission is also similar to that observed in EPLyr. In the next plot we subtract the scaled spectrum of EPLyr (green) from IRAS06338 (black) to get the resulting spectum = red. As you can see, the feature around 11.3 and the shoulder around 8 micron are almost gone. There probably is also some emission due to forsterite around 11.3micron. plot_iras06338-eplyr0.7.ps

Made a similar fit as above, but now I used the observed PAH emission of EPLyr as PAH template: IRAS06338_eplyrPAHs.ps

CO2:

I made a plot comparing the CO2 of IRAS06338, EPLyr, HD52961 and HR4049. I tried to identify some of the features (12C16O2=dotted, 13C16O2=dashed, 16O12C18O=dot-dashed) co2_overview.ps

As you can see, the fullerene feature at 17.4 is contaminated by CO2 emission, for both HD52961 and IRAS06338...

The CO2 emission seems to be lying on a big feature. This is too broad to be just forsterite. Could it be optically think CO2? Or some ices? I have no idea? JAN?

HD52961:

General information:

• Spec.type = F6I
• Teff = 6000K
• log g = 0.5
• [Fe/H] = -4.8
• depleted: [Zn/Fe] = +3.1 HD52961_depletie.ps
• Porb = 1297d
• e = 0.22
• Ppuls = 72d
• no C2, CN, CH+ in optical spectra (Bakker et al. 1997)
• C/O = +0.76

Spectral energy distribution: hd52961_SED.ps

Spitzer spectrum: HD52961.txt

Fullerenes:

Used simple spline to subtract 'continuum', overplotted with scaled c60_T500_R120 as a test: HD52961contsub_c60_T500_R120.00.ps

Again here infection of CO2 gas lines in the 17.4micron feature. Two peaks can be seen (17.22-17.35micron). The first is, I think, a CO2 feature, since it is seen in a lot of sources (see co2_overview.ps ). The second feature is also seen in EPLyr, but not in IRAS06338. Not sure if it is a CO2 feature, or just the C60 feature itself (although the peak wavelength is slightly different)...

Plot of the continuum subtraction HD52961_contsub.ps and txtfile of resulting spectrum HD52961_contsub.txt

The best fit to HD52961_contsub is with: c60_T100_R600.00.xdr

CO2 gas emission:

The CO2 emission was modelled by Mikako, results can be found in Gielen et al. 2009: HD_CO2.ps

IRAS13258-8103:

General information:

• Spec.type = G5
• Teff = 5000-5500?
• log g= ?
• [Fe/H] = ?

Spectral energy distribution: iras13258_SED.ps

Spitzer spectrum: IRAS13258.txt

PAHs:

This star also shows the small features around 7micron: plot_overeen.ps plot_7micron.ps

The PAH emission between 8-11micron seems to be laying on a 'plateau'. We tried to remove this with a simple spline: IRAS13258_featcont.ps

A text file with the resulting continuum subtracted spectrum can be found here: IRAS13258_featsub.txt

PAH emission of IRAS13258 compared to the PAH classes of Els Peeters: IRAS13258_pahs.ps

Same plot but zoomed in on 6micron PAH feature: IRAS13258_pahs_zoom.ps

EPLyr:

General information:

• Spec.type = A4I
• Teff = 7000K
• log g = 2.0
• [Fe/H] = -1.5
• Ppuls = 84d
• Porb = ?
• 12C/13C = 9
• depleted: [Zn/Fe] = 1.1 EPLyr_depletie.eps

Spectral energy distribution: EPLyr_SED.ps

Spitzer spectrum: EPLyr.txt

PAHs:

This stars shows strong classC PAH emission, see Gielen et al. 2009.

PAH emission of EPLyr compared to the PAH classes of Els Peeters: EPLyr_pahs.ps

In the following we plot the PAH emission of IRAS06338 (black), IRAS13258 (red) and EPLyr (green). We used the continuum subtracted spectra as discussed above: IRAS06338_IRAS13258_EPLyr_featsub.ps

CO2 gas emission:

The CO2 emission was modelled by Mikako, results can be found in Gielen et al. 2009: EPLyr.ps

co2_overview.ps