Ultraviolet imaging of planetary nebulae with $\mathit{}$

Astrophysics and Space Science, Apr 2018

Over four hundred Galactic Planetary Nebulae (PNe) have been imaged by \(\mathit{GALEX}\) in two ultraviolet (UV) bands, far-UV (FUV, 1344–1786 Å, \(\lambda _{eff}= 1528~{\mathring{\mathrm{A}}}\)) and near-NUV (NUV, 1771–2831 Å, \(\lambda _{eff} = 2271~{\mathring{\mathrm{A}}}\)). We present examples of extended PNe, for which UV spectroscopy is also available, to illustrate the variety in UV morphology and color, which reflects ionization conditions. The depth of the GALEX imaging varies from flux \(\approx 0.4/5\times 10 ^{-18}~\mbox{ergs}\,\mbox{cm}^{-2}\,\mbox{s}^{-1}\,{\mathring{\mathrm{A}}}^{-1}\,\square ^{\prime\prime\,-1}\) (\(\mathit{FUV}/\mathit{NUV}\)) for exposures of the order of \(\sim 100\) seconds, typical of the survey with the largest area coverage, to \(\sim 0.3/8.3\times 10^{-19}~\mbox{ergs}\,\mbox{cm}^{-2}\,\mbox{s}^{-1}\,{\mathring{\mathrm{A}}}^{-1}\,\square ^{\prime\prime\,-1}\) (\(\mathit{FUV}/\mathit{NUV}\)) for \(\sim 1500~\mbox{sec}\) exposures, typical of the second largest survey (see Bianchi in Astrophys. Space Sci. 320:11, 2009; Bianchi et al. in Adv. Space Res. 53:900, 2014). \(\mathit{GALEX}\) broad-band FUV and NUV fluxes include nebular emission lines and in some cases nebular continuum emission. The sensitivity of the \(\mathit{GALEX}\) instrument and the low sky background, especially in FUV, enable detection and mapping of very faint ionization regions and fronts, including outermost wisps and bow shocks. The \(\mathit{FUV}\mbox{-}\mathit{NUV}\) color of the central star provides a good indication of its \(T_{eff}\), because the \(\mathit{GALEX}\) FUV-NUV color is almost reddening-free for Milky Way type dust (Bianchi et al. in Astrophys. J. Suppl. Ser. 230:24, 2017; Bianchi in Astrophys. Space Sci. 335:51, 2011, Bianchi in Astrophys. Space Sci. 354:103, 2014) and it is more sensitive to hot temperatures than optical colors.

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Ultraviolet imaging of planetary nebulae with $\mathit{}$

Astrophys Space Sci Ultraviolet imaging of planetary nebulae with GALEX Luciana Bianchi 0 1 David Thilker 0 1 B L. Bianchi 0 1 0 Department of Physics and Astronomy, The Johns Hopkins University , Baltimore, MD 21210 , USA 1 This article belongs to the Topical Collection: UV Surveys, the Needs and the Means. Guest Editors: Ana I. Gómez de Castro , Noah Brosch Over four hundred Galactic Planetary Nebulae (PNe) have been imaged by GALEX in two ultraviolet (UV) bands, far-UV (FUV, 1344-1786 Å, λeff = 1528 Å) and near-NUV (NUV, 1771-2831 Å, λeff = 2271 Å). We present examples of extended PNe, for which UV spectroscopy is also available, to illustrate the variety in UV morphology and color, which reflects ionization conditions. The depth of the GALEX imaging varies from flux ≈ 0.4/5 × 10−18 ergs cm−2 s−1 Å−1 −1 (FUV/NUV) for exposures of the order of ∼ 100 seconds, typical of the survey with the largest area coverage, to ∼ 0.3/8.3 × 10−19 ergs cm−2 s−1 Å−1 −1 (FUV/NUV) for ∼ 1500 sec exposures, typical of the second largest survey (see Bianchi in Astrophys. Space Sci. 320:11, 2009; Bianchi et al. in Adv. Space Res. 53:900, 2014). GALEX broad-band FUV and NUV fluxes include nebular emission lines and in some cases nebular continuum emission. The sensitivity of the GALEX instrument and the low sky background, especially in FUV, enable detection and mapping of very faint ionization regions and fronts, including outermost wisps and bow shocks. The FUV-NUV color of the central star provides a good indication of its Teff , because the GALEX FUV-NUV color is almost reddening-free for Milky Way type dust (Bianchi et al. in Astrophys. J. Suppl. Ser. 230:24, 2017; Bianchi in Astrophys. Space Sci. 335:51, 2011, Bianchi in Astrophys. Space Sci. 354:103, 2014) and it is more sensitive to hot temperatures than optical colors. Astronomical data bases; surveys; Stars; white dwarfs; ISM; planetary nebulae; general; ISM; planetary nebulae; individual 1 Introduction Planetary Nebulae (PN) are the evolved descendants of intermediate mass stars, the major providers of important chemical elements such as carbon and nitrogen. The expanding layers of gas, shed in the previous Red Giant phases and then ionized by the hot central star (CSPN), offer clues about the progenitor’s evolution, in particular about the chemical elements produced by nucleosynthesis and brought up to outer layers, about the temperature and luminosity of the stellar remnant, through their ionization, and about massloss and wind momentum in subsequent phases, through their complex expansion kinematics and density structure. Studies of both the nebula and the central star benefit by observations in the Ultraviolet (UV), where crucial diagnostic transitions of important chemical elements, and trace elements, abound (e.g., Bianchi 2016, 2012) . CSPNe, the hottest stars known, emit most of their light at UV wavelengths or shortwards. IUE and HST spectrographs have collected UV spectra of a few hundred PNe, mostly of their central stars. FUSE has provided high resolution spectra at shorter UV wavelengths (905–1187 Å) for several objects. The FUSE observations, although difficult to obtain and limited to the brightest sources, have enabled major discoveries, such as highly ionized neon in the wind of CSPNe (Herald et al. 2005; Herald and Bianchi 2009, 2011; Keller et al. 2011, among others) , whose lines are a crucial diagnostics for the hottest (Teff > 85000 K) CSPN; the brightest PNe in the Magellanic Clouds were also observed by FUSE (Herin portion of the image, and a plot of archival IUE spectra taken in the bright part of the nebula, with the GALEX transmission bands overplotted, suggesting that the FUV flux mostly originates from HeII emission in the inner regions ald and Bianchi 2004, 2007) . For a review of the role of UV observations in the understanding of CSPNe see Bianchi uniquely complement ground-based and HST imaging in optical emission lines, and spectroscopic information. (2012). A completely different, new type of information has become available thanks to the deep sensitivity and wide field of view of the GALEX instrument. In this work we show examples of UV images of Planetary Nebulae, which 2 The data: UV imaging Figures 1 to 3 show FUV and NUV imaging data of selected PN obtained with GALEX. The instrument was first described by Martin et al. (2005) , and its performance by Morrissey et al. (2007) . The characteristics of the data and the sky surveys are described by Bianchi (2009) , Bianchi et al. (2011a, 2011b, 2014) ; in depth discussion of data quality and an updated version of science-enhanced catalogs of UV sources are presented in Bianchi et al. (2017, 2018). GALEX imaged the field in two bands simultaneously: FUV (1344–1786 Å, λeff = 1528 Å) and NUV (1771– 2831 Å, λeff = 2271 Å), with a field of view of 1.28/1.24◦ [FUV/NUV] diameter, and resolution of ≈ 4.2/5.3 [FUV/ NUV]. The images, reconstructed from photon counting (...truncated)


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Luciana Bianchi, David Thilker. Ultraviolet imaging of planetary nebulae with $\mathit{}$, Astrophysics and Space Science, 2018, pp. 85, Volume 363, Issue 5, DOI: 10.1007/s10509-018-3300-7