We present an analysis of the photometric and spectroscopic observations of the split comet C/2019 Y4 (ATLAS). Observations were carried out on 2020 April 14 and 16, when the heliocentric distance of the comet was 1.212 and 1.174 au, its geocentric distance 0.998 and 0.991 au, and the phase angle 52.°9 and 54.°5, respectively. The comet was observed with the 6-m BTA (Big Telescope Alt-azimuth) telescope of the Special Astrophysical Observatory (Russia) with the SCORPIO-2 (Spectral Camera with Optical Reducer for Photometric and Interferometric Observations) multimode focal reducer. The narrow-band BC and RC cometary filters in the continuum were used. We identified numerous emissions of CN, C2, C3, and NH2 molecules within the range of 3750–7100 Å. The C2/CN and C3/CN production rate ratios coincide with those of typical comets. Four fragments belonging to the coma were detected in both observational runs. We compared and analysed temporal variations of the visual magnitudes, gas productivity, and dust colour. Based on our dynamical investigation of the orbits of comets C/1844 Y1 (Great comet) and C/2019 Y4 (ATLAS), we can claim that, with high probability, the two comets do not have a common progenitor.

中文翻译：

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分裂彗星 C/2019 Y4 (ATLAS) 的光度测量和长缝光谱

我们对分裂彗星 C/2019 Y4 (ATLAS) 的光度和光谱观测进行了分析。观测于2020年4月14日至16日进行，彗星的日心距分别为1.212和1.174 au，地心距0.998和0.991 au，相位角分别为52.°9和54.°5。这颗彗星是用特殊天体物理天文台（俄罗斯）的 6 米 BTA（大望远镜 Alt-azimuth）望远镜和 SCORPIO-2（带有用于光度和干涉观测的光学减焦器的光谱相机）多模减焦器进行观测的。使用了连续谱中的窄带 BC 和 RC 彗星滤光片。我们确定了在 3750-7100 Å 范围内的大量 CN、C2、C3 和 NH2 分子的排放。C2/CN 和 C3/CN 产率比与典型彗星的产率比一致。在两次观测运行中都检测到四个属于昏迷的碎片。我们比较和分析了视觉大小、气体产量和尘埃颜色的时间变化。根据我们对彗星 C/1844 Y1（大彗星）和 C/2019 Y4（ATLAS）轨道的动态调查，我们可以断言，这两颗彗星很有可能没有共同的祖先。