The Necklace: equatorial and polar outflows from the binary central star of the new planetary nebula IPHASX J194359.5+170901

Abstract

IPHASX J194359.5+170901 is a new high-excitation planetary nebula with remarkable characteristics. It consists of a knotty ring expanding at a speed of 28 km s −1 , and a fast collimated outflow in the form of faint lobes and caps along the direction perpendicular to the ring. The expansion speed of the polar caps is ∼100 km s −1 , and their kinematical age is twice as large as the age of the ring.Time-resolved photometry of the central star of IPHASX J194359.5+170901 reveals a sinusoidal modulation with a period of 1.16 d. This is interpreted as evidence for binarity of the central star, the brightness variations being related to the orbital motion of an irradiated companion. This is supported by the spectrum of the central star in the visible range, which appears to be dominated by emission from the irradiated zone, consisting of a warm (6000-7000 K) continuum, narrow C III, C IV and N III emission lines, and broader lines from a flat H I Balmer sequence in emission. IPHASX J194359.5+170901 helps to clarify the role of (close) binaries in the formation and shaping of planetary nebulae (PNe). The output of the common-envelope (CE) evolution of the system is a strongly flattened circumstellar mass deposition, a feature that seems to be distinctive of this kind of binary system. Also, IPHASX J194359.5+170901 is among the first post-CE PNe for which the existence of a high-velocity polar outflow has been demonstrated. Its kinematical age might indicate that the polar outflow is formed before the CE phase. This points to mass transfer on to the secondary as the origin, but alternative explanations are also considered.

Forming equatorial rings around dying stars

“…The ring expands with a velocity of 28 km s −1 , and the total ionized mass of the nebula, most of it in the ring, is 0.06 ± 0.03M . The ring was ejected ∼ 5000 yr ago and the two opposite polar caps, which were most likely formed by two opposite jets, are ∼ 9000 − 13, 000 yr old (Corradi et al 2011;Tocknell et al 2014). The ring does not seem to posses perfect symmetry around the central star; there seems to be more mass to the north-west direction.…”

“…The Necklace PN has been studied by Corradi et al (2011) and its central binary system was further explored by Miszalski et al (2013). The ring expands with a velocity of 28 km s −1 , and the total ionized mass of the nebula, most of it in the ring, is 0.06 ± 0.03M .…”

The post-common envelope central stars of the planetary nebulae Henize 2-155 and Henize 2-161

“…As such, it is more reasonable to use the morphological features identified by Miszalski et al (2009b), as being particularly prevalent amongst PNe with binary central stars, as selection criteria for targeted photometric searches for new binaries. These features include filamentary structures, rings, polar outflows and bipolarity, and have been successfully employed by our group in the discovery of several new binary central stars (Miszalski et al 2011a,b;Corradi et al 2011;Boffin et al 2012b;Jones et al 2014a;Santander-García et al 2015).…”

“…Sab 41, Miszalski et al 2009b;and Fg 1, Boffin et al 2012b). Once again, the central binary of the Necklace shows extremely strong variability and a relatively short period (1.16 day, Corradi et al 2011), but is of special interest due to the chemical peculiarity of the companion star in the system. The secondary in the Necklace has been shown to be a carbon dwarf star, indicating that it has been chemically polluted (with asymptotic giant branch (AGB) material) by the primary star -thus far the only direct evidence of mass transfer during or, much more likely, just prior to the CE phase in a PN (Miszalski et al 2013).…”

Are planetary nebulae derived from multiple evolutionary scenarios?

“…In these cases, the emission lines arise from the heated hemisphere of a cool companion to the true ionizing star (e.g. Corradi et al 2011).…”