Volume 530, June 2011
|Number of page(s)||45|
|Section||Stellar structure and evolution|
|Published online||17 May 2011|
We display all data for the post-AGB candidates in our final sample that have a spectrum in three tables subdivided into the three subclasses based on the shape of the SED.
Catalogue of the objects in our final sample that have a low-resolution, optical spectrum and an SED indicative of a disc.
Appendix B: Table of all objects that have a low-resolution, optical spectrum but are no longer part of the post-AGB sample
List of objects for which a low-resolution, optical spectrum or a spectral type was obtained but that are no longer part of the final sample.
Fourteen of the low-resolution, optical spectra we took, do not belong to post-AGB stars. We were able to identify nine galaxies, two PN-like objects and two WC-like objects.
We observed nine objects for which the spectrum does not correspond to a source in the LMC. They all have too high a redshift and are therefore galaxies. Some details on these sources can be found in Table C.1. All these objects are listed as galaxies on NASA/IPAC Extragalactic Database (NED)4. A redshift is noted only for J050303.97-663345.9 and J053308.25-722644.9 and both values agree with the ones we determined.
Spectra of the two PN-like objects – J051654.04-672005.1 and J051147.92-692342.3 – that occur in our sample. All spectra were normalised and displaced vertically by 15 units to increase the visibility of the plot. The vertical grey lines indicate the wavelengths at which spectral features of certain elements are expected, corrected for the average radial velocity of the LMC. These are: Balmer lines (solid), [O iii] (dash dotted), [N ii] (dashed), He ii (dotted), [Ar iii] (dash dot dotted) and [Ne iii] (long dashes).
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Two objects in our sample – J051654.04-672005.1 and J051147.92-692342.3 – show emission features of Hα, Hβ, [O ii], [O iii], [N ii], [S ii], [Ar iii] and [Ne iii] (see Fig. C.1). In addition, He ii emission can be seen from J051147.92-692342.3. Both spectra bear resemblance to spectra of H ii regions as well as PNe.
The spectrum of J051147.92-692342.3 contains emission features of elements like [O iii], [Ar iii] and [Ne iii] at higher levels of ionisation than can be found in H ii regions. The line intensity ratio of [O iii] 5007 Å to Hβ is about 5, which is somewhat lower than the theoretically expected value of 9 (Reid & Parker 2006), but still compatible with a PN. Since [N ii] 6583 Å ≥ Hα and He ii 4686 Å is also clearly visible, this object is probably a high excitation type I PN.
The most significant differences in the spectrum of J051654.04-672005.1 with respect to J051147.92-692342.3 are the less prominent features of [O iii] and [N ii] when compared to the Balmer lines. The line intensity ratio of [O iii] 5007 Å to Hβ for this object is 0.4, which is incompatible with both classical PNe and H ii regions. A very low excitation PN or an extremely compact, low-excitation H ii can explain these ratios, however. The latter possibility is supported by the [N ii]/Hα ratio which is well below 0.7 (Kennicutt et al. 2000).
Some of the most prominent features in J051654.04-672005.1 show a P Cygni profile which is indicative of a fast stellar wind. The low-resolution of the spectrum only allows for a rough estimation of the velocity of this wind which turns out to be between 650 and 1050 km s-1.
Of the two objects we identified as PNe-like objects, only J051147.92-692342.3 can be found in the PNe catalogue of Reid & Parker (2006).
Redshifts and types of the galaxies in our sample for which we obtained low-resolution optical spectra.
Spectra of the two possible WC stars – J053348.94-701323.5 and J055825.96-694425.8 – that occur in our sample. All spectra were normalised and translated vertically in steps of four units to increase the visibility of the plot. The vertical grey lines indicate the wavelengths at which spectral features of H I (solid lines), He i (dotted lines), C II (dashed lines) and O ii (dot-dashed lines) are expected, corrected for the average radial velocity of the LMC.
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The spectra of J053348.94-701323.5 and J055825.96-694425.8 are clearly distinct from the other spectra, but resemble each other (see Fig. C.2). Both spectra are similar to Wolf-Rayet carbon (WC) stars, but the emission lines are rather weak and they lack the C iii feature at 5696 Å which is still present even in WC stars of spectral types as late as WC10 (Crowther et al. 1998). The resemblance of both spectra to that of V 348 Sagitarii, a Galactic R CrB star with a very peculiar spectrum (e.g., Leuenhagen & Hamann 1994; Houziaux 1968), makes it plausible that our objects are also of spectral type [WC12]. One of these objects, J053348.94-701323.5, is also listed as an R CrB star by Soszyński et al. (2009b) even though it is not H deficient.
In addition to the 105 objects from our sample of post-AGB candidates, we observed 31 bright sources with IR detections, which were originally identified using the first release of the SAGE catalogue of only Epoch 1 data. These objects were not recovered while creating our final list. Most of them were lost due to the black-body luminosity-cut, but some simply do not have the required measurements in the different SAGE catalogues we used to define our final sample or are listed as a cool carbon star by Kontizas et al. (2001) or an AGB star with spectral type by Trams et al. (1999). For these objects, and some objects with a low-resolution, optical spectrum that were later on discarded from our final sample, we list the spectral types and the reason why they are no longer in our final catalogue in Table B.1.
SEDs of all post-AGB candidates with a known spectral type and an SED indicative of a disc. The dark and light grey line are the Kurucz atmosphere model used and the low-resolution, optical spectrum, respectively. All photometric datapoints are dereddened.
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Same as Fig. D.1, but for objects of which the SED is inconclusive on whether they have a disc or a shell.
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© ESO, 2011
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