Observations unveil an ionized halo of planetary nebula IC 5148

Observations unveil an ionized halo of planetary nebula IC 5148
The [O iii] image of the halo region of IC 5148: Left: after masking the main nebula and removing a Gaussian shaped decline representing the normal halo intensity distribution. Right: same image with two circles centered exactly at the CSPN at 115 and 128''. Credit: Barría et al., 2018.

Using ESO's Very Large Telescope (VLT), astronomers have performed observations of the planetary nebula IC 5148. The new study, described in a paper published October 2 on the arXiv pre-print server, unveils the presence of IC 5148 ionized halo and provides fundamental parameters of its central star.

Planetary nebulae (PNe) are expanding shells of gas and dust that have been ejected from a star during the process of its evolution from main sequence star into a red giant or white dwarf. They are relatively rare, but important for astronomers studying the chemical evolution of and galaxies. Although IC 5148, a round , was discovered in 1894, it is still not well investigated in detail. The is located in the constellation of Grus, some 3,000 light years away from the Earth. With an expansion rate of about 50 km/s, it is one of the fastest planetary nebulae known to date.

In order to reveal more properties of IC 5148, a team of researchers led by Daniela Barría of the Catholic University of the North in Chile, has conducted spectroscopic observations of this nebula. For their observational campaign, the astronomers employed VLT's FORS2 and X-SHOOTER spectrographs. "We obtained long-slit low resolution spectroscopy (FORS2@VLT) of the nebula in two position angles, which we used to investigate the nebular and its in the optical range from 450 to 880 nm. In addition, we used medium resolution spectra taken with X-SHOOTER@VLT ranging from 320 nm to 2.4 μm to derive atmospheric parameters for the central star," the researchers wrote in the paper.

Via the observations, the astronomers discovered extended emission features around IC 5148 and collected essential data about the nebula's central star. In particular, the scientists found that IC 5148 showcases a set of unusual halo structures. These structures appear clearly as hot, ionized material.

"IC 5148 shows a perfect shock structure at its outermost edge of the main nebula, as predicted in the hydrodynamic models (e.g. Perinotto et al. 2004) It is only visible by using the high ionized species as already suggested and discussed in Guerrero et al. (2013)," the authors of the paper noted.

However, the researchers added that their discovery of structured halo emission in IC 5148 remains puzzling. They emphasized that while the inner halo region resembles the perfect circular shape as that of the main nebula, further out, a bow-like structure is seen at one side of the nebula only. Hence, the astronomers propose further deeper spectroscopic observations of this nebula to resolve the puzzle.

Moreover, the team derived essential parameters of IC 5148's . They found that the age of this star is about 8,500 years, its average temperature is approximately 11,500 K, and its metallicity is at a level of 0.02 dex. The researchers calculated that the star's initial mass was around 1.5 solar masses.


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Researchers spot an inside-out planetary nebula

More information: The planetary nebula IC 5148 and its ionized halo, arXiv:1810.01350 [astro-ph.SR] arxiv.org/abs/1810.01350

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Oct 15, 2018
The Spare-tyre nebula

Nicknamed the Spare-tyre nebula IC 5148 a planetary nebula 1 degree west of Lambda Gruis in the constellation of Grus The Crane discovered by Australian amateur astronomer Walter Gale in 1894. 3000 light-years away, expanding at 50km/s is one of the fastest of all planetary nebulae.
IC 5148's central star is 8,500 years, its temperature is 11,500 K, and its metallicity is at a level of 0.02 dex. The star's initial mass was around 1.5 solar masses
These planetary nebulae form in the end of the star's life over 10,000years which is a puzzle as this star is 8,500 years old
Once most of the red giant's atmosphere is dissipated, ultraviolet radiation from the hot luminous core, ionizes the ejected material in its planetary nebula, absorbed ultraviolet light then energises the shell of nebulous gas around the central star, causing it to appear as a brightly coloured planetary nebula. https://en.wikipe...y_nebula

Oct 15, 2018
Roughly copied from the paper:
Table 2.
Main derived nebular properties and nebular parameters obtained from the best Cloudy model. The independent model regions are labeled from in to out as Region I, II and III.
Nebular parameter Value
Expansion velocity 47.9±1.5 [km s−1]
Model age 8 500 years
Average Te 11 500 [K]
Main nebula angular radius 68'′
Main nebula linear radius 1.32×10^18[cm] = 0.43 [pc]
Total H mass 0.34 [M(insertsolarmasssymbolhere)]

The paragraphs in the paper do indicate they modeled the star at 8500 but they also add "The latter measured from the point where the post-AGB object has a log(Teff)=3.85." Once you get to table 2 it does indicate that as the age of the nebula rather than the progenitor. I don't know what a post-AGB object is but context seems to agree with the idea that the star itself is not 8500 years old rather the nebula is... This is just my uneducated reading of the subject.

Oct 17, 2018
That is correct Enthusiastic Fool, those are the parameters derived for the nebula. Table 1 gives the parameters for the central star, which is modeled to be 130,000 K (not 11,000 K like this article states). The object (a PN) as a whole consists of the central star and the nebula together (the central star is essentially the core of a dying star and the nebula is the outer layers of that star being blown out into space) so both parts of the object have the same age because they are technically the same object or part of the same object (they central star and nebula evolve separately but the temperature and brightness of the central star largely dictates how the nebula expands and is ionized). A planetary nebula in general is a type of post-AGB object, which just means the stage of evolution that comes after the AGB stage that all stars go through as they die, but not all stars go through a planetary nebula stage.

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