Morphological and kinematic signatures of a binary central star in the planetary nebula Hu 2-1 |
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| Authors: | Luis F Miranda José M Torrelles Martín A Guerrero Roberto Vázquez Yolanda Gómez |
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| Institution: | Instituto de Astrofísica de Andalucía, CSIC, Apdo. Correos 3004, E-18080 Granada, Spain;Institut d'Estudis Espacials de Catalunya (IEEC/CSIC) and Instituto de Ciencias del Espacio (CSIC), Edifici Nexus, C/ Gran Capitá2-4, E-08034 Barcelona, Spain;Department of Astronomy, University of Illinois at Urbana-Champaign 1002 West Green Street, Urbana, IL 61801, USA;Instituto de Astronomía, UNAM, Apto. Postal 877, 22800 Ensenada, B.C., México;Instituto de Astronomía UNAM, Campus Morelia, A.P. 3-72 (Xangari), c.p. 58089 Morelia, Michoacán, México |
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| Abstract: | We present H α , N ii ] and O iii ] ground-based and HST archive images, VLA–A 3.6-cm continuum and H92 α emission-line data and high-resolution long-slit N ii ] spectra of the planetary nebula Hu 2-1. A large number of structural components are identified in the nebula: an outer bipolar and an inner shell, two pairs of collimated bipolar structures at different directions, monopolar bow-shock-like structures, and an extended equatorial structure within a halo. The formation of Hu 2-1 appears to be dominated by anisotropic mass ejection during the late-AGB stage of the progenitor and by variable, 'precessing' collimated bipolar outflows during the protoplanetary nebula and/or early planetary nebula phases. Different observational results strongly support the existence of a binary central star in Hu 2-1, among them (1) the observed point-symmetry of the bipolar lobes and inner shell, and the departures from axial symmetry of the bipolar lobes, (2) the off-centre position of the central star, (3) the detection of mass ejection towards the equatorial plane, and (4) the presence of 'precessing' collimated outflows. In addition, (5) an analysis of the kinematics shows that the systemic velocity of the bipolar outflows does not coincide with the systemic velocity of the bipolar shell. We propose that this velocity difference is a direct evidence of orbital motion of the ejection source in a binary system. From a deduced orbital velocity of ∼10 km s−1, a semimajor axis of ∼ 9–27 au and period of ∼ 25–80 yr are obtained, assuming a reasonable range of masses. These parameters are used to analyse the formation of Hu 2-1 within current scenarios of planetary nebulae with binary central stars. |
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| Keywords: | stars: mass-loss ISM: jets and outflows ISM: kinematics and dynamics planetary nebulae: individual: Hu 2-1 |
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