Twin Suns of Different Mothers

HIP 56948 (HD 101364)—an 8.7 magnitude star in Draco—is more like our Sun than any other star yet discovered. It is 194 light years away and located at α2000 = 11h 40m 28s and δ2000 = +69° 00′ 31″, near Gianfar (λ Draconis) and the Draco-Ursa Major border, above the Big Dipper’s bowl.

Solar twin HIP 56948 (circled) in Draco near Gianfar

With the exception of lithium, the elemental abundances are identical to that found in the Sun, within the observational uncertainties. As expected, lithium is severely depleted in HIP 56948, but not as much as in the Sun. This is to be expected for a solar twin about 1 Gyr younger than the Sun.

The temperature, luminosity, mass, and rotation of HIP 56948 almost exactly match that of the Sun. For example, HIP 56948 is only 17 ± 7 K hotter than the Sun, and its mass is 1.02 ± 0.02 M. Given all these similarities, it appears its most recently determined (1993) spectral type of G5 is incorrect. Or is it the spectral type of our Sun that is wrong (G2V)? Actually, it is quite difficult to make measurements of our Sun “as a star” because it is so incredibly close and bright.

HIP 56948 harbors no giant planets or “hot Jupiters” within or interior to its habitable zone, so there remains the enticing possibility that it may host a planetary system similar to our own, though no planets have yet been detected.

Incidentally, the next time you’ve got a good view of the Head of Draco and the “box” of Cepheus, cast your eyes toward a point halfway between the two. You’re looking towards where the rotational axis of the Sun points north. Like HIP 56948, it’s in Draco.

North Solar Pole in relation to HIP 56948

References
“The remarkable solar twin HIP 56948: a prime target in the quest
for other Earths”
J. Meléndez, et. al., A&A 543, A29 (2012)
https://www.aanda.org/articles/aa/pdf/2012/07/aa17222-11.pdf

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