ABSTRACT
We present JWST images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6 to 25 $\, \mu$m. The bright shell is strongly fragmented with some 20 000 ...dense globules, bright in H2, with a characteristic diameter of 0.2 arcsec and density nH ∼ 105–106 cm−3. The shell contains a narrow ring of polycyclic aromatic hydrocarbon (PAH) emission. H2 is found throughout the shell and also in the halo. H2 in the halo may be located on the swept-up walls of a biconal polar flow. The central cavity is filled with high-ionization gas and shows two linear structures which we suggest are the edges of a biconal flow, seen in projection against the cavity. The central star is located 2 arcsec from the emission centroid of the cavity and shell. Linear features (‘spikes’) extend outward from the ring, pointing away from the central star. Hydrodynamical simulations reproduce the clumping and possibly the spikes. Around 10 low-contrast, regularly spaced concentric arc-like features are present; they suggest orbital modulation by a low-mass companion with a period of about 280 yr. A previously known much wider companion is located at a projected separation of about 15 000 au; we show that it is an M2–M4 dwarf. NGC 6720 is therefore a triple star system. These features, including the multiplicity, are similar to those seen in the Southern Ring Nebula (NGC 3132) and may be a common aspect of such nebulae.
We present new Herschel photometric and spectroscopic observations of Supernova 1987A, carried out in 2012. Our dedicated photometric measurements provide new 70 mu m data and improved imaging ...quality at 100 and 160 mu m compared to previous observations in 2010. Our Herschel spectra show only weak CO line emission, and provide an upper limit for the 63 mu m OI line flux, eliminating the possibility that line contaminations distort the previously estimated dust mass. The far-infrared spectral energy distribution (SED) is well fitted by thermal emission from cold dust. The newly measured 70 mu m flux constrains the dust temperature, limiting it to nearly a single temperature. The far-infrared emission can be fitted by 0.5 + or - 0.1 M sub(middot in circle) of amorphous carbon, about a factor of two larger than the current nucleosynthetic mass prediction for carbon. The observation of SiO molecules at early and late phases suggests that silicates may also have formed and we could fit the SED with a combination of 0.3 M sub(middot in circle) of amorphous carbon and 0.5 M sub(middot in circle) of silicates, totalling 0.8 M sub(middot in circle) of dust. Our analysis thus supports the presence of a large dust reservoir in the ejecta of SN 1987A. The inferred dust mass suggests that supernovae can be an important source of dust in the interstellar medium, from local to high-redshift galaxies.
Abstract
After becoming ionized, low-density astrophysical plasmas will begin a process of slow recombination. Models for this still have significant uncertainties. Recombination cannot normally be ...observed in isolation, because the ionization follows the evolutionary timescale of the ionizing source. Laboratory experiments are unable to reach the appropriate conditions because of the very long required timescales. The extended nebula around the very late helium pulse (VLTP) star V4334 Sgr provides a unique laboratory for this kind of study. The sudden loss of the ionizing UV radiation after the VLTP event has allowed the nebula to recombine free from other influences. More than 290 long-slit spectra taken with FORS1/2 at ESO’s Very Large Telescope between 2007 and 2022 are used to follow the time evolution of the lines of H, He, N, S, O, and Ar. Hydrogen and helium lines, representing most of the ionized mass, do not show significant changes. A small increase is seen in N
ii
(+2.8% yr
−1
; 2.7
σ
significance), while we see a decrease in O
iii
(−1.96% yr
−1
; 2.0
σ
significance). The S
ii
lines show a change of +3.0% yr
−1
(1.6
σ
significance). The lines of S
iii
and of Ar
iii
show no significant changes. For S
iii
, the measurement differs from the predicted decrease by 4.5
σ
. A possible explanation is that the fractions of S
3+
and higher are larger than expected. Such an effect could provide a potential solution for the sulfur anomaly in planetary nebulae.
After becoming ionized, low-density astrophysical plasmas will begin a process of slow recombination. Models for this still have significant uncertainties. Recombination cannot normally be observed ...in isolation, because the ionization follows the evolutionary timescale of the ionizing source. Laboratory experiments are unable to reach the appropriate conditions because of the very long required timescales. The extended nebula around the very late helium pulse (VLTP) star V4334 Sgr provides a unique laboratory for this kind of study. The sudden loss of the ionizing UV radiation after the VLTP event has allowed the nebula to recombine free from other influences. More than 290 long-slit spectra taken with FORS1/2 at ESO’s Very Large Telescope between 2007 and 2022 are used to follow the time evolution of the lines of H, He, N, S, O, and Ar. Hydrogen and helium lines, representing most of the ionized mass, do not show significant changes. A small increase is seen in N ii (+2.8% yr−1; 2.7σ significance), while we see a decrease in O iii (−1.96% yr−1; 2.0σ significance). The S ii lines show a change of +3.0% yr−1 (1.6σ significance). The lines of S iii and of Ar iii show no significant changes. For S iii, the measurement differs from the predicted decrease by 4.5σ. A possible explanation is that the fractions of S3+ and higher are larger than expected. Such an effect could provide a potential solution for the sulfur anomaly in planetary nebulae.
The Real-Time Evolution of V4334 Sgr van Hoof, Peter; Kimeswenger, Stefan; Van de Steene, Griet ...
Galaxies,
09/2018, Letnik:
6, Številka:
3
Journal Article
Recenzirano
Odprti dostop
V4334 Sgr (Sakurai’s object) is an enigmatic evolved star that underwent a very late thermal pulse a few years before its discovery in 1996. It ejected a new hydrogen-deficient nebula in the process. ...The source has been observed continuously since, at many wavelengths ranging from the optical to the radio regime. In this paper we evaluate these data and discuss the evolution of this object. We reach the conclusion that we have seen no evidence for photoionization of the nebula yet and that the spectral features we see are caused either by shocks or by dust. These shocks are an integral part of the hydrodynamic shaping that is now producing a new bipolar nebula inside the old planetary nebula (PN), implying that we have a detailed observational record of the very early stages of the shaping of a bipolar nebula.
Herschel observations of planetary nebulae Van de Steene, Griet C.
Proceedings of the International Astronomical Union,
10/2016, Letnik:
12, Številka:
S323
Journal Article
Recenzirano
Odprti dostop
This article presents an overview of the published results for planetary nebulae based on images and spectroscopy from the PACS, SPIRE, and HIFI instruments on board the Herschel satellite.
After becoming ionized, low-density astrophysical plasmas will begin a process of slow recombination. Models for this still have significant uncertainties. The recombination cannot normally be ...observed in isolation, because the ionization follows the evolutionary time scale of the ionizing source. Laboratory experiments are unable to reach the appropriate conditions because of the required very long time scales. The extended nebula around the very late helium flash (VLTP) star V4334 Sgr provides a unique laboratory for this kind of study. The sudden loss of the ionizing UV radiation after the VLTP event has allowed the nebula to recombine free from other influences. More than 290 long slit spectra taken with FORS1/2 at the ESO VLT between 2007 and 2022 are used to follow the time evolution of lines of H, He, N, S, O, Ar. Hydrogen and helium lines, representing most of the ionized mass, do not show significant changes. A small increase is seen in N II (+2.8 %/yr; significance 2.7 sigma), while we see a decrease in O III (-1.96 %/yr; 2.0 sigma). The S II lines show a change of +3.0 %/yr; 1.6 sigma). The lines of S III and of Ar III show no significant change. For S III, the measurement differs from the predicted decrease by 4.5 sigma. A possible explanation is that the fraction of S IV and higher is larger than expected. Such an effect could provide a potential solution for the sulfur anomaly in planetary nebulae.
We present JWST images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6\(\mu\)m to 25 \(\mu\)m. The bright shell is strongly fragmented with some 20 000 ...dense globules, bright in H\(_2\), with a characteristic diameter of 0.2 arcsec and density \(n_{\rm H} \sim 10^5\)-\(10^6\) cm\(^{-3}\). The shell contains a thin ring of polycyclic aromatic hydrocarbon (PAH) emission. H\(_2\) is found throughout the shell and in the halo. H\(_2\) in the halo may be located on the swept-up walls of a biconal polar flow. The central cavity is shown to be filled with high ionization gas and shows two linear structures. The central star is located 2 arcsec from the emission centroid of the cavity and shell. Linear features (`spikes') extend outward from the ring, pointing away from the central star. Hydrodynamical simulations are shown which reproduce the clumping and possibly the spikes. Around ten low-contrast, regularly spaced concentric arc-like features are present; they suggest orbital modulation by a low-mass companion with a period of about 280 yr. A previously known much wider companion is located at a projected separation of about 15 000 au; we show that it is an M2-M4 dwarf. The system is therefore a triple star. These features, including the multiplicity, are similar to those seen in the Southern Ring Nebula (NGC 3132) and may be a common aspect of such nebulae.
Herschel observations of NGC 7027 Exter, Katrina M.; van Hoof, Peter A.M; Van de Steene, Griet C. ...
Proceedings of the International Astronomical Union,
07/2011, Letnik:
7, Številka:
S283
Journal Article
Recenzirano
Odprti dostop
We present our analysis of the spectra of NGC 7027 taken with the PACS and SPIRE instruments of the Herschel satellite.
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