(sub)Millimeter Emission Lines of Molecules in Born-again Stars

Abstract

The detection and study of molecular gas in born-again stars would be of great importance to understand their composition and chemical evolution. In addition, the molecular emission would be an invaluable tool to explore the physical conditions, kinematics and formation of asymmetric structures in the circumstellar envelopes of these evolved stars. However, until now, all attempts to detect molecular emission from the cool material around born-again stars have failed. We carried out observations using the APEX and IRAM 30m telescopes to search for molecular emission toward four well studied born-again stars, V4334 Sgr, V605 Aql, A30 and A78, that are thought to represent an evolutionary sequence. We detected for the first time emission from HCN and H${}^{13}$CN molecules toward V4334 Sgr, and CO emission in V605 Aql. No molecular emission was detected above the noise level toward A30 and A78. A first estimate of the H${}^{12}$CN/H${}^{13}$CN abundance ratio in the circumstellar environment of V4334 Sgr is $\approx$3, which is similar to the value of the ${}^{12}$C/${}^{13}$C ratio measured from other observations. We derived a rotational temperature of $T_{\mathrm{rot}}$=13$\pm 1$ K, and a total column density of $N_{\mathrm{HCN}}$=1.6$\pm 0.1\times$10${}^{16}$ cm${}^{-2}$ for V4334 Sgr. This result sets a lower limit on the amount of hydrogen that was ejected into the wind during the born-again event of this source. For V605 Aql, we obtained a lower limit for the integrated line intensities $I_{{}^{12}\mathrm{C}}$/$I_{{}^{13}\mathrm{C}}$>4.

7 pages, 4 figures and 3 tables. Accepted for publication in A&A

References in corpus (7)

• V605 Aql: The Older Twin of Sakurai's Object
• The hydrogen-deficient knot of the `born again' planetary nebula Abell 58 (V605 Aql)
• The onset of photoionization in Sakurai's Object (V4334 Sgr)
• The Spitzer IRS view of V4334 Sgr (Sakurai's Object)
• A dense disk of dust around the born-again Sakurai's object
• Expansion of hydrogen-poor knots in the born-again planetary nebulae A30 and A78
• The born-again planetary nebula A78: an X-ray twin of A30

Cited by in corpus (5)

• Carbon dust in the evolved born-again planetary nebulae A30 and A78
• The infrared view of dust and molecules around V4334 Sgr (Sakurai's Object): a 20-year retrospective
• WR 72: a born-again planetary nebula with hydrogen-poor knots
• First images of the molecular gas around a born-again star revealed by ALMA
• Common envelope evolution in born-again planetary nebulae -- Shaping the H-deficient ejecta of A30