2 Observations

Deep optical long-slit spectra of the PN PB8 were obtained at Las Campanas Observatory (PI: M. Peña), using the 6.5-m Magellan telescope and the double echelle Magellan Inamori Kyocera Echelle (MIKE) spectrograph on 9 May 2006 (García-Rojas et al., 2009). An observational journal is presented in Table 1. The standard grating settings used yield wavelength coverage from 3350-5050Å in the blue and 4950-9400Å in the red. The mean spectral resolution is 0.15Å FWHM in the blue and 0.25Å FWHM in the red. The MIKE observations were taken with three individual exposures of 300, 600 and 900 sec using a slit of $ 1 \times 5$ arcsec$ ^2$ and a position angle (PA) of 345$ ^{\circ}$ passing through the central star. To prevent contamination of the stellar continuum, an area of $ 0.9 \times 1$ arcsec$ ^2$ on a bright knot located in the northern part of the slit was used to extract the nebular spectrum. However, there is no definite constraint on the location of the combined slit spectrum for the bright knot in the nebula, as the slit crossed over the nebula during the three different observations.1 The top and bottom panels of Figure 1 show the blue and red spectra of PB8 extracted from the 2D MIKE echellograms, normalized such that $ F$(H$ \beta $) = 100. As seen, several recombination lines from heavy element ions have been observed.

Table: IR line fluxes of the PN PB8.
Lines $ F(\lambda)$ $ I(\lambda)$
$ 10^{-12}$ ergcm$ ^{-2}$s$ ^{-1}$ [$ I($H $ \beta)=100$]
[Ar III] 8.99 $ \mu $m 2.95 14.97
12.82 $ \mu $m 4.80 24.37
15.55 $ \mu $m 21.60 110.66
18.68 $ \mu $m 10.80 54.82
33.65 $ \mu $m 5.98 30.36
36.02 $ \mu $m 1.45 7.36
Fig. 5 shows the Spitzer spectrum (SL & LL combined).

Figure 1: The observed optical spectrum of the PN PB 8 (García-Rojas et al., 2009), covering wavelengths of (top) 3500-5046 Å and (bottom) 5047-8451 Å, and normalized such that $ F$(H$ \beta $) = 100.

Infrared (IR) spectra of the PN PB8 were taken on 25 February 2008 with the IR spectrograph on board the Spitzer Space Telescope (programme ID 40115, PI: Giovanni Fazio). The flux calibrated IR spectra used in this paper have been obtained from the Cornell Atlas of Spitzer / Infrared Spectrograph Sources2 (CASSIS; Lebouteiller et al., 2015; Lebouteiller et al., 2011). The Spitzer observations were taken with two low-resolution modules: Short-Low (SL) and Long-Low (LL). The SL spectrum was taken with an aperture size of $ 3.7 \times 57$ arcsec$ ^2$ covering a wavelength coverage of 5.2-14.5$ \mu $m, whereas the LL spectrum has a wavelength coverage of 14.0-38.0$ \mu $m and an aperture size of $ 10.7 \times 168$ arcsec$ ^2$. As the LL aperture is larger than the SL aperture, the LL module collects more flux than the SL, including the surrounding background contamination. This causes a jump at around 14$ \mu $m between the SL and the LL. To correct it, the LL spectrum was scaled to match the SL spectrum, so the combined Spitzer spectrum describes the thermal IR emission of the nebula with little background contribution. Table 2 lists the line fluxes measured from the Spitzer IR spectra (see Fig. 5 for the Spitzer SL and LL combined spectrum). The intrinsic line fluxes presented in column 3 are on a scale where $ I($H $ \beta)=100$, and the dereddened flux $ I($H $ \beta)=19.7 \times 10^{-12}$ ergcm$ ^{-2}$s$ ^{-1}$ calculated using the total H$ \alpha $ flux (Frew et al., 2013), $ E(B-V)=0.41$ and $ R_{V} = 4$ (Todt et al., 2010).

Integral field unit (IFU) spectra were obtained at the Siding Spring Observatory on 21 April 2010 (programme ID 1100147, PI: Q.A. Parker), using the 2.3-m ANU telescope and the Wide Field Spectrograph (WiFeS; Dopita et al., 2007; Dopita et al., 2010). The settings used were the B7000/R7000 grating combination and the RT560 dichroic, giving wavelength coverage from 4415-5589Å in the blue and 5222-7070Å in the red, and mean spectral resolution of 0.83Å FWHM in the blue and 1.03Å FWHM in the red (see the observational journal presented in Table 1). The WiFeS IFU rawdata were reduced using the IRAF pipeline wifes, which consists of bias-reduction, sky-subtraction, flat-fielding, wavelength calibration using Cu-Ar arc exposures, spatial calibration using wire frames, differential atmospheric refraction correction, and flux calibration using spectrophotometric standard stars EG274 and LTT3864 (fully described in Danehkar et al., 2014; Danehkar et al., 2013).

Figure 2 shows the spatially resolved flux intensity and radial velocity maps of PB8 extracted from the emission line $ [$NII$ ]$ $ \lambda $6584 for spaxels across the WiFeS IFU field. The black/white contour lines depict the distribution of the emission of H$ \alpha $ obtained from the SuperCOSMOS H$ \alpha $ Sky Survey (SHS; Parker et al., 2005), which can aid us in distinguishing the nebular borders. The emission line maps were obtained from solutions of the nonlinear least-squares minimization to a Gaussian curve function for each spaxel. The observed velocity $ V_{\rm obs}$ was transferred to the local standard of rest (LSR) radial velocity $ V_{\rm LSR}$. The WiFeS IFU observations have recently been used for morpho-kinematic studies of PNe (Danehkar, 2015; Danehkar et al., 2016). Considering the spatial resolution of the WiFeS (1 arcsec), this PN is very compact for detailed morpho-kinematic modeling. Following Danehkar & Parker (2015), the tenuous lobes of PB 8 extending from its compact core can be used to determine its spatial orientation. As seen in Figure 2, the orientation of its faint lobes onto the plane of the sky has a position angle of $ 132^{\circ}\pm8^{\circ}$ relative to the north equatorial pole towards the east. Transferring into the Galactic coordinate system, its symmetric axis has a Galactic position angle of $ 114.6^{\circ}\pm8^{\circ}$, measured from the north Galactic pole towards the Galactic east, approximately aligned with the Galactic plane.

We obtained an expansion velocity of $ V_{\rm exp}=20\pm 4$kms$ ^{-1}$ from the $ [$NII$ ]$ $ \lambda $6584 flux integrated across the whole nebula in the WiFeS field, which is in agreement with $ V_{\rm exp}=19$kms$ ^{-1}$ from $ [$NII$ ]$ $ \lambda $6584 line derived by Todt et al. (2010). Moreover, García-Rojas et al. (2009) derived an expansion velocity of $ V_{\rm exp}=14 \pm 2$kms$ ^{-1}$ from the $ [$OIII$ ]$ $ \lambda $5007 line, which is associated with a different ionization zone. García-Rojas et al. (2009) obtained $ V_{\rm sys}=1.4$kms$ ^{-1}$ from $ [$OIII$ ]$ lines, in agreement with the value of $ V_{\rm sys}=2.4$kms$ ^{-1}$ given by Todt et al. (2010).

Figure: Maps of PB 8 in $ [$NII$ ]$ $ \lambda $6584 from the IFU observation. From left to right: spatial distribution maps of flux intensity and LSR velocity. Flux unit is in $ 10^{-15}$ ergs$ {}^{-1}$cm$ {}^{-2}$spaxel$ {}^{-1}$, and velocity in kms$ {}^{-1}$. North is up and east is toward the left-hand side. The white/black contour lines show the distribution of the narrow-band emission of H$ \alpha $ in arbitrary unit obtained from the SHS (Parker et al., 2005).

Ashkbiz Danehkar