2 Observations

Integral field spectroscopic observations of Th2-A were obtained using the Wide Field Spectrograph (WiFeS; Dopita et al., 2007; Dopita et al., 2010) on the Australian National University (ANU)2.3-m Advanced Technology Telescope (ATT) at the Siding Spring Observatory on 2010 April 20 under program number 1100147 (PI: Q.A. Parker). WiFeS is an image-slicing Integral Field Unit (IFU) feeding a double-beam spectrograph. WiFeS samples 0$\mbox{$.\!\!^{\prime\prime}$}$$5$ along each of twenty five $38\hbox{$^{\prime\prime}$}\times 1\hbox{$^{\prime\prime}$}$ slitlets, which provides a field of view of $25\hbox {$^{\prime \prime }$}\times 38\hbox {$^{\prime \prime }$}$ and a spatial resolution element of $1$$\mbox{$.\!\!^{\prime\prime}$}$$0\times0$$\mbox{$.\!\!^{\prime\prime}$}$$5$. The output is optimized to fit the $4096 \times 4096$ pixel format of the CCD detectors. Each slitlet is designed to project to 2 pixels on the detector. This yields a reconstructed point spread function with a FWHM of about 2 arcsec. The spectrograph uses volume phase holographic gratings to provide a spectral resolution of either $R \sim 3000$ or $R \sim 7000$. We used the spectral resolution of $R \sim 7000$, resulting in a linear wavelength dispersion per pixel of $0.45$Å for the red spectrum (5222-7070Å). This spectral resolution yields a resolution of $\sim 20$kms${}^{-1}$.

We reduced the data using the IRAF pipeline wifes to correct bias, correct pixel-to-pixel sensitivity using dome flat-field frames, calibrate spectra based on arc lamp exposures, calibrate space based on wire frames, correct differential atmospheric refraction, remove cosmic rays, and calibrate data to the absolute flux unit based on spectrophotometric standard stars (described in detail by Danehkar et al., 2014; Danehkar et al., 2013).

Figure: HST image of Th2-A on a squared scale taken with the F555W filter and WFPC2 on HST (observing program 6119). The rectangle shows the $25\hbox {$^{\prime \prime }$}\times 38\hbox {$^{\prime \prime }$}$ WiFeS field of view observed using the ANU2.3-m telescope at the Siding Spring Observatory in 2010 April. North is up and east is toward the left-hand side.

The Hubble Space Telescope (HST) image of Th2-A shown in Fig.1 was retrieved from the HST archive. The HST image was taken using the non-aberrated Wide Field Planetary Camera 2 (WFPC2) and the F555W (“V”) filter with an exposure time of 60s under program 6119 (PI: H. Bond) on 1995 September 23, which has a central wavelength of 5439Å and a bandwidth of 1228Å. The rectangle in Fig.1 shows the location and area of the WiFeS aperture in the nebula.

Figure: Kinematic maps of Th2-A in H$\alpha$ $\lambda$6563Å. From left to right: the integrated line flux, continuum flux, radial velocity map (LSR), and velocity dispersion map. The color bars of the panels showing flux measurements are in $10^{-15}$ ergs${}^{-1}$cm${}^{-2}$spaxel${}^{-1}$ unit, those showing continuum are in $10^{-15}$ ergs${}^{-1}$cm${}^{-2}$Å${}^{-1}$spaxel${}^{-1}$ unit, and those showing velocity measurements are in kms${}^{-1}$ unit. The white/black contours in the four maps are the narrow-band H$\alpha$ emission in arbitrary unit obtained from the SHS. North is up and east is toward the left-hand side.