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- Reichel, Martin, et al.
(author)
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Recombination of Hot Ionized Nebulae: The Old Planetary Nebula around V4334 Sgr (Sakurai’s Star)* * This investigation makes use of ESO data from program IDs 077.D-0394, 079.D-0256, 381.D-0117, 383.D-0427, 385.D-0292, 087.D-0223, 089.D-0080, 091.D-0209, 093.D-0195, 095.D-0113, 097.D-0146, 099.D-0045, and 0109.D-0060.
- 2022
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In: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 939:2
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Journal article (peer-reviewed)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; 2.7σ 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.
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- Tafoya, Daniel, 1981, et al.
(author)
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The heart of Sakurai's object revealed by ALMA
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 677
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Journal article (peer-reviewed)abstract
- We present high-angular-resolution observations of Sakurai's object using the Atacama Large Millimeter Array, shedding new light on its morpho-kinematical structure. The millimetre continuum emission observed at an angular resolution of 20 milliarcsec (corresponding to 70 AU) reveals a bright compact central component whose spectral index indicates that it is composed of amorphous carbon dust. Based on these findings, we conclude that this emission traces the previously suggested dust disc observed in mid-infrared observations, and therefore our observations provide the first direct imaging of this disc. The H12CN(J = 4 → 3) line emission observed at an angular resolution of 300 milliarcsec (corresponding to 1000 AU) displays a bipolar structure with a north- south velocity gradient. From the position- velocity diagram of this emission, we identify the presence of an expanding disc and a bipolar molecular outflow. The inclination of the disc is determined to be i = 72. The derived values for the de-projected expansion velocity and the radius of the disc are vexp = 53 km s-1 and R = 277 AU, respectively. On the other hand, the de-projected expansion velocity of the bipolar outflow detected in the H12CN(J = 4 → 3) emission is of approximately 1000 km s-1. We propose that the molecular outflow has an hourglass morphology with an opening angle of around 60. Our observations unambiguously show that an equatorial disc and bipolar outflows formed in Sakurai's object during the 30 years following the occurrence of the born-again event, providing important constraints for future modelling efforts of this phenomenon.
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