Historical transmissions and modern data constrain the evolution of the supernova progenitors Betelgeuse and Antares through the Hertzsprung gap: When will they explode?

Given the large apparent extension on sky of nearby supergiants, the distances of Betelgeuse (alpha Ori) and Antares (alpha Sco) and, hence, their masses, ages, and lifetimes are not well known from astrophysics alone. The recent claim for a Betelgeuse lifetime as short as a few centuries (Saio et al. 2023) was shown to have intrinsic inconsistencies (Molnar et al. 2023). Historical transmissions on the colors of Betelgeuse and Antares from the last few millennia can be quantified in terms of the B-V color index, because they were given in comparison with planets and other stars; we could show that the precision in pre-telescopic color records is around ±0.1-0.2 mag. Betelgeuse: Several independent texts from China and the Mediterranean show that alpha Ori has evolved rapidly from B-V≈1.0 mag two millennia ago to its current B-V=1.78±0.05 mag; given its current location in the color-magnitude diagram (CMD), only the 14 solar mass MESA/MIST track is consistent with such a rapid and recent color evolution. This constrains distance, mass, and age of Betelgeuse and, hence, its remaining lifetime to ~1.5 Myr (Neuhäuser et al. 2022). Antares: The age of the ScoCenLup subgroup called `Antares' was determined to 10-13 Myr by comparison with the PARSEC models (Ratzenböck et al. 2023); it was called `Antares', because its distance and sky location is consistent with the star Antares (alpha Sco), which, however, has a large uncertainty in distance (170±30 pc) and, hence, mass (13-18 solar mass) and lifetime. From the roughly constant color of alpha Sco reported for at least two millennia (and its current location in the CMD and the MIST tracks), we concluded that it is either on the 2nd or 3rd crossing of the Hertzsprung gap with 13 solar masses (16-17 Myr), or on the first and only crossing with 15-16 solar masses (13-12 Myr), see Neuhäuser et al. (2022). Now, if Antares is a member of the `Antares' group (10-13 Myr), the former larger age can be excluded, while the latter younger would be consistent. In such a case (15-16 solar masses), we would expect a significant color change until some 2-4 millennia ago from the MIST tracks. In this presentation, we will consider possible historical sources on the color of Antares more than two millennia ago: E.g., the name Antares is Greek and means `like Mars' (in color), probably given to this star some time BC. If Antares had B-V=1.43±0.13 mag (i.e. like Mars) back then, it would be different from now (1.88±0.02 mag). Then, it has just finished the crossing of the Hertzsprung gap with 15-16 solar mass. Antares' remaining lifetime is then 1.4-1.0 Myr. To investigate the age of the `Antares' group with an alternative method, we trace back all `Antares' group members in 3D (with and without the star Antares) to find the time of the smallest extension is space and, hence, their age. Betelgeuse and Antares might well be the next two nearby supernovae that will affect Earth by deposition of 60-Fe.