Stellar Winds of Central Stars of the LMC PNe

Abstract

˙MV ∞R 0.5 is proportional to the stellar luminosity. If this relation is confirmed, it can be used as a distance indicator for the central stars (CSs) of the Galactic planetary nebulae. This relation for the massive O stars was established in [3] and [4]. An attempt to extend the relation to the Galactic central stars in planetary nebulae (CSPNe) did not show any convincing relation [6]. In this work we investigate the relation between the modified wind momentum Π versus the luminosity of the CSPNe in the Large Magellanic Cloud (LMC) taking advantage of the less uncertain distances to these objects. We show that these winds obey a similar relation as the Galactic O stars, thus are subject to the same physics, and that their momentum can be used as a distance indicator. 2 Observations and Analysis The present work is based on observations designed to study the nebular physics of planetary nebulae in the LMC. The observations were made with Space Telescope Imaging Spectrograph (STIS) in ultraviolet slitless spectroscopy mode, with gratings G140L, G230. The data are described in [5]. Here we have selected 12 of the target nebulae, those that show a stellar continuum in the UV spectra. The 1D extraction from the 2D spectral images were performed using a small aperture around the location of the central star spectra. The spectra were then corrected for the Galactic and LMC extinction. The temperature and radius were derived by the approximation of the stellar continuum with a black body using a method described in [1]. The luminosities were calculated base on these parameters and they are in agreement with those derived by Zanstra analysis for the same objects [7]. The nebular contribution to the continuum was estimated via CLOUDY modeling. Some of the objects show P Cygni profiles corresponding to the C IV 1548/1551 ˚ Si IV 1394/1403 ˚ and N V 1239/1243 ˚ lines. We fit these lines using a line transfer code together with a genetic minimization algorithm [2]. As a result we obtained the mass loss rates and the terminal velocities for these stars.