²⁸SiOv= 0J= 1–0 emission from evolved stars

Abstract

Aims. Observations of 28 SiO v = 0 J = 1-0 line emission (7-mm wavelength) from asymptotic giant branch (AGB) stars show in some cases peculiar profiles, composed of a central intense component plus a wider plateau. Very similar profiles have been observed in CO lines from some AGB stars and most post-AGB nebulae and, in these cases, they are clearly associated with the presence of conspicuous axial symmetry and bipolar dynamics. We aim to systematically study the profile shape of 28 SiO v = 0 J = 1-0 lines in evolved stars and to discuss the origin of the composite profile structure. Methods. We present observations of 28 SiO v = 0 J = 1-0 emission in 28 evolved stars, including O-rich, C-rich, and S-type Mira-type variables, OH/IR stars, semiregular long-period variables, red supergiants and one yellow hypergiant. Most objects were observed in several epochs, over a total period of time of one and a half years. The observations were performed with the 40 m radio telescope of the Instituto Geográfico Nacional (IGN) in Yebes, Spain. Results. We find that the composite core plus plateau profiles are systematically present in O-rich Miras, OH/IR stars, and red supergiants. They are also found in one S-type Mira (χ Cyg) and in two semiregular variables (X Her and RS Cnc) that are known to show axial symmetry. In the other objects, the profiles are simpler and similar to those observed in other molecular lines. The composite structure appears in the objects in which SiO emission is thought to come from the very inner circumstellar layers, prior to dust formation. The central spectral feature is found to be systematically composed of a number of narrow spikes, except for X Her and RS Cnc, in which it shows a smooth shape that is very similar to that observed in CO emission. These spikes show a significant (and mostly chaotic) time variation, while in all cases the smooth components remain constant within the uncertainties. The profile shape could come from the superposition of standard wide profiles and a group of weak maser spikes confined to the central spectral regions because of tangential amplification. Alternatively, we speculate that the very similar profiles detected in objects that are known to be conspicuously axisymmetric, such as X Her and RS Cnc, and in O-rich Mira-type stars, such as IK Tau and TX Cam, may be indicative of the systematic presence of a significant axial symmetry in the very inner circumstellar shells around AGB stars; such symmetry would be independent of the presence of weak maser effects in the central spikes.

A study of C4H3N isomers in TMC-1: Line by line detection of HCCCH2CN

“…The data presented here are part of a deep spectral line survey in the Q band towards TMC-1 that was performed at the Yebes 40 m radio telescope 1 (de Vicente et al 2016), located at an altitude of 990 m near Guadalajara (Spain). The observed position corresponds to the cyanopolyyne peak (CP) in TMC-1, at α J2000 = 4 h 41 m 41.9 s and δ J2000 = +25 • 41 27.0 .…”

Full-Dimensional Quantum Dynamics of SiO in Collision with H2

“…GHz with the 11 m Kitt Peak telescope toward Sgr B2(OH). 13 de Vicente et al 47 presented observational results of 28 SiO v 1 =0, j Since silicon is depleted onto grains, it is not detected in protoplanetary disks, though CO is. It is proposed, 52 however, that in the outflows of young stellar objects (YSOs), that the grains are disrupted, allowing for the formation of SiO.…”

Studies of stellar evolution using masers

“…Maser emission is used to study the dense regions surrounding evolved stars. Using the Yebes radio telescope, single-dish monitoring of the 43 GHz SiO emission from evolved stars suggests that the emission comes from the innermost circumstellar layers [43]. More VLBI observations would be helpful to clarify details, however, these are challenging due to a large amount of flux density being resolved out [9].…”