SH2-174 The Valentine Rose Nebula

Second attempt at this object, now with faster optics so the result is more interesting; on single frames you can only guess that there is something there, and if the moon is shining then it's completely empty; to get a better result one needs to move under a dark sky.

The nebula Sh2-174, located in the constellation Cepheus at a distance of about 1000 light-years, is one of the northernmost nebulae in the sky and has an amazing feature: its true nature has still not been precisely established! Discovered in 1959 by the American astronomer Stewart Sharpless, it is the 174th entry in his catalog. A few years later his colleague Beverly T. Lynds observed it with the Mount Palomar telescope and added it to his catalog of bright nebulae ("LBN"). However, a problem soon arose: no star formation was observed in this nebula, and the star responsible for the ionization was not identified... Only in 1970 was this star, a white dwarf named GD 561, identified, and in 1993 two astronomers, R. Napiwotzki and D. Schönberner, established an obvious connection with the nebula and proposed classifying it as a "planetary nebula." Indeed, at first glance Sh2-174 possesses characteristics typical of planetary nebulae, with a noticeable signal in the Ha (hydrogen) and OIII (oxygen) lines — the filters used for this image. However, there are a number of mysterious details, and not least the morphology, which is unusual for a planetary nebula. Such nebulae are usually spherical or very symmetrical. But not in the case of Sh2-174, where the HII and OIII zones seem not even to overlap... What is even more curious is that the white dwarf — the star that gave rise to the planetary nebula when its outer layers were ejected at the end of its life — is usually located close to the "center" of the nebula; however, in the case of Sh2-174 the star is strongly offset to the west, so much so that the astronomers Tweedy and Napiwotzki in a 1994 paper establishing the physical connection between the white dwarf GD 561 and the nebula describe the latter as a "planetary nebula abandoned by its star." GD 561 is moving at a speed of 71 km/s relative to the surrounding interstellar medium.