Free Astronomy Magazine May-June 2015

STELLAR EVOLUTION CK Vul, absent in other 17 novae remnants ob- served for comparison with APEX by Kami ń - ski's team. According to the researchers, such atypical scenario could be the end product of a Luminous Red Nova (LRN), a rather rare oc- currence, still subject to debate in the astro- nomical community, in which two main-se- quence stars (stars as normal as the Sun, but not necessarily of the same size) collide and merge, creating a very powerful, but not en- tirely destructive explosion. In practice, something half-way between the superno- vae, where the stars concerned do not sur- vive, and the novae, where only the surface layer explodes, without deeply destabilis- ing the stellar structure. As to the luminous red novae, or “red transients”, we essen- tially know that after the explosion – which also affects the deep layers of the two stars, and thus the richness of the chemical composition of the remnant – there occurs a very rapid expansion of the material, which ends up occupying a radius volume thousands or tens of thousands of times greater than that of the Sun. This expan- sion rapidly lowers the temperature of the bubble of gas and dust, pushing the light emitted towards greater wavelengths and causing therefore the remnant to assume a red hue, from which the name of this class of objects derives. That CK Vul may have effectively been a LRN is corroborated by a now confirmed red transient, OGLE-2002-BLG-360, observed on more occasions between 2002 and 2006, which has shown a light curve that is ac- tually a scaled down version of that of Nova Vul 1670. More generally, Kami ń ski and colleagues point out in an article pu- blished in Nature on 23 March 2015 (in which they show the results of their obser- vations), that most of the characteristics of CK Vul suits the luminous red novae model and that consequently that object could be considered the archetype of that class of stars. It remains to understand the type of star that nests at the centre of the remnant, but answering this question will not be an easy task, both for its low brightness and because it is still surrounded and thus ob- scured by the material processed in the thermonuclear reactions and scattered by the explosive fusion. R ight, false col- our images published in July 1985 in The Astro- physical Journal, as part of an arti- cle confirming the discovery of the remnant of Nova Vul 1670. The var- iable stellar source within it was named CK Vul. [Shara, Mof- fat, Webbink] Almost 30 years later, Kami ń ski and colleagues published in Na- ture the images below: “a” shows the entire nebular remnant shot in H-alpha and Nll, with out- lined in green the molecular emission newly discovered with the SMA; and “b” a close-up of the central region. [Kami ń ski et al.] n