We present an observational study of the planetary nebula (PN) NGC?7354 consisting of narrowband Hα and [N II]λ6584 imaging as well as low- and high-dispersion long-slit spectroscopy, and VLA-D radio continuum. According to our imaging and spectroscopic data, NGC?7354 has four main structures: a quite round outer shell and an elliptical inner shell, a collection of low-excitation bright knots roughly concentrated on the equatorial region of the nebula, and two asymmetrical jet-like features, not aligned either with the shells' axes, or with each other. We have obtained physical parameters like electron temperature and electron density as well as ionic and elemental abundances for these different structures. Electron temperature and electron density slightly vary throughout the nebula going from 11, 000 to 14, 000 K, and from 1000 to 3000 cm–3, respectively. The local extinction coefficient c Hβ shows an increasing gradient from south to north and a decreasing gradient from east to west consistent with the number of equatorial bright knots present in each direction. Abundance values show slight internal variations but most of them are within the estimated uncertainties. In general, abundance values are in good agreement with the ones expected for PNe. Radio continuum data are consistent with optically thin thermal emission. Mean physical parameters derived from the radio emission are electron density ne = 710 cm–3 and M(H II) = 0.22 M ☉. We have used the interactive three-dimensional modeling tool SHAPE to reproduce the observed morphokinematic structures in NGC?7354 with different geometrical components. Our observations and model show evidence that the outer shell is moving faster (35 km s–1) than the inner one ( 30 km s–1). Our SHAPE model includes several small spheres placed on the outer shell wall to reproduce equatorial bright knots. Observed and modeled velocity for these spheres lies between the inner and outer shells velocity values. The two jet-like features were modeled as two thin cylinders moving at a radial velocity of 60?km?s–1. In general, our SHAPE model is in very good agreement with our imaging and spectroscopic observations. Finally, after modeling NGC?7354 with SHAPE, we suggest a possible scenario for the formation of the nebula.
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机译：我们介绍了由窄带Hα和[N II]λ6584成像以及低分散和高分散长缝光谱以及VLA-D无线电连续体组成的行星状星云（PN）NGC？7354的观察性研究。根据我们的成像和光谱数据，NGC？7354具有四个主要结构：一个相当圆的外壳和一个椭圆形的内壳，一系列低激发亮结，大致集中在星云的赤道区域，以及两个不对称的射流。相似的特征，既不与壳体的轴对齐，也不与壳体的轴对齐。我们已经获得了这些不同结构的物理参数，如电子温度和电子密度，以及离子和元素丰度。在整个星云中，电子温度和电子密度分别略有变化，分别为11、000至14、000 K和1000至3000 cm–3。局部消光系数cHβ从南到北呈逐渐增加的梯度，从东向西呈递减的梯度，这与每个方向上存在的赤道明亮结的数量一致。丰度值显示出微小的内部变化，但大多数在估计的不确定性范围内。通常，丰度值与PNe的预期值高度吻合。无线电连续体数据与光学上薄的热辐射一致。由无线电发射得出的平均物理参数是电子密度ne = 710 cm–3和M（H II）= 0.22 M☉。我们已经使用交互式三维建模工具SHAPE来重现NGC？7354中观察到的具有不同几何成分的形态动力学结构。我们的观察和模型表明，外壳运动的速度（35 km s-1）比内壳的运动（30 km s-1）快。我们的SHAPE模型包括放置在外壳壁上的几个小球体，以再现赤道明亮的结。这些球体的观测速度和建模速度位于内壳和外壳速度值之间。这两个喷射状特征被建模为两个细圆柱体，它们以60？km？s–1的径向速度运动。总的来说，我们的SHAPE模型与我们的成像和光谱观察非常吻合。最后，在使用SHAPE对NGC？7354进行建模之后，我们提出了可能的星云形成方案。
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