A disc inside the bipolar planetary nebula M2-9

Abstract

Aims. Bipolarity in proto-planetary and planetary nebulae is associated with events occurring in or around their cores. Past infrared observations have revealed the presence of dusty structures around the cores, many in the form of discs. Characterising those dusty discs provides invaluable constraints on the physical processes that govern the final mass expulsion of intermediate mass stars. We focus this study on the famous M2-9 bipolar nebula, where the moving lighthouse beam pattern indicates the presence of a wide binary. The compact and dense dusty core in the centre of the nebula can be studied by means of optical interferometry. Methods. M2-9 was observed with VLTI/MIDI at 39-47 m baselines with the UT2-UT3 and UT3-UT4 baseline configurations. These observations are interpreted using a dust radiative transfer Monte Carlo code. Results. A disc-like structure is detected perpendicular to the lobes, and a good fit is found with a stratified disc model composed of amorphous silicates. The disc is compact, 25 × 35 mas at 8 μm and 37 × 46 mas at 13 μm. For the adopted distance of 1.2 kpc, the inner rim of the disc is ∼15 AU. The mass represents a few percent of the mass found in the lobes. The compactness of the disc puts strong constraints on the binary content of the system, given an estimated orbital period 90-120 yr. We derive masses of the binary components between 0.6-1.0 M for a white dwarf and 0.6-1.4 M for an evolved star. We present different scenarios on the geometric structure of the disc accounting for the interactions of the binary system, which includes an accretion disc as well.

The evolution of M 2–9 from 2000 to 2010

“…This is consistent with the value of 2500 L in Lykou et al (2011), and reopens the possibility -compared to the low luminosity estimated in Schwarz et al (1997) -that the central source in M 2-9 hosts an AGB or luminous post-AGB star.…”

“…This makes M 2-9 even more unusual, and the discussion of its nature more complex. The ∼90-yr period of the rotating pattern, the presence of a jet, the nuclear spectrum, and the recent discovery of circumstellar discs (Lykou et al 2011), suggest the presence of a symbiotic binary star at its centre: a compact star, perhaps a relatively cool white dwarf, accreting from the wind of a giant and producing the rotating jet. System parameters for our revised distance of 1.3 kpc, such as the bolometric luminosity or the circumbinary disc properties in the models by Lykou et al (2011), are consistent with this hypothesis.…”

“…In the innermost few arcseconds from the central star (bottom panels of Fig. 4), the [N ii] and [O iii] emission show a faint, diffuse east-west structure that is aligned with infrared dust emission (Lykou et al 2011). In the vertical direction, the structure is thinnest in [O iii], and near the centre is not resolved at the HST resolution (0.…”

“…Livio & Soker 2001) made several authors suggest that M 2-9 contains a symbiotic star at its centre. Schmeja & Kimeswerner (2001) Movie is only available in electronic form at http://www.aanda.org several authors have pointed out that these colours can also be produced by dusty discs (Chesneau et al 2007;Cohen et al 2011;Lykou et al 2011). Figure 1 illustrates the morphology of M 2-9.…”

Dust shell model of the water fountain source IRAS 16342–3814

“…The most plausible definition of a disk should be a region where the matter is gravitationally bounded by the central star and has a Keplerian rotating motion. Although dusty disk structures have been spatially resolved in several evolved stars (e.g., Matsuura et al 2006;Lykou et al 2011), the dynamics are not well known or much less understood than accretion disks of young stellar objects. Therefore, we regarded the disk simply as a geometrically thin, optically thick dust structure.…”