IfA: Robotically Discovering Earth’s Nearest Neighbors

[bystander]

Robotically Discovering Earth’s Nearest Neighbors
Institute for Astronomy | University of Hawaii | 2015 Apr 28

[attachment=0]hd7924_1576x927labels.jpg[/attachment]

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A team of astronomers using ground-based telescopes in Hawaii, California, and Arizona recently discovered a planetary system orbiting a nearby star that is only 54 light-years away. All three planets orbit their star at a distance closer than Mercury orbits the sun, completing their orbits in just 5, 15, and 24 days.

Astronomers from the University of Hawaii at Manoa, the University of California, Berkeley, the University of California Observatories, and Tennessee State University found the planets using measurements from the Automated Planet Finder (APF) Telescope at Lick Observatory in California, the W. M. Keck Observatory on Maunakea, Hawaii, and the Automatic Photometric Telescope (APT) at Fairborn Observatory in Arizona.

The team discovered the new planets by detecting the wobble of the star HD 7924 as the planets orbited and pulled on the star gravitationally. APF and Keck Observatory traced out the planets’ orbits over many years using the Doppler technique that has successfully found hundreds of mostly larger planets orbiting nearby stars. APT made crucial measurements of the brightness of HD 7924 to assure the validity of the planet discoveries. ...

Astronomers Discover Three Super-Earths Orbiting Nearby Star
University of California Observatories | 2015 Apr 28

Robotic telescope discovers three super-Earth planetary neighbors
University of California, Berkeley | 2015 Apr 28

Three Super-Earths Orbiting HD 7924 - Benjamin J. Fulton et al

• arXiv.org > astro-ph > arXiv:1504.06629 > 24 Apr 2015

[Ann]

The picture caption wrote:
Artist’s impression of a view from the HD 7924 planetary system looking back toward our sun, which would be easily visible to the naked eye. Since HD 7924 is in our northern sky, an observer looking back at the sun would see objects like the Southern Cross and the Magellanic Clouds close to our sun in their sky. Art by Karen Teramura & BJ Fulton, UH IfA.

That is quite a creative rendering of the Southern Cross (Crux). Of course, HD 7924 is 54 light-years away from us, and the sky would not look the same from the vantage point of that solar system as it does to us. Nevertheless, Alpha, Beta and Delta Crucis are all around 300 light-years away from us, and would presumably stay in moderately similar relative positions when seen from HD 7924. Alpha, Beta and Delta are also all quite blue, with very negative B-V indexes. So where is the third blue star in Crux in the illustration here?

Epsilon Crucis, a yellow-orange K2-type giant, is a bit closer than Alpha, Beta and Delta, but still more than 200 light-years away. Epsilon might be the yellow star seen in the illustration (but it looks suspiciously bright to me). Gamma Crucis, the M-type red giant, is only about 90 light-years away from us, and would likely change position quite noticeably when seen from HD 7924, probably more so than in the illustration.

So Crux would look different from the position of HD 7924 than it does from us, but it wouldn't look like it does in the Karen Temura and BJ Fulton's illustration.

Ann