New Radial Velocity Experiment (RAVE) Data Release

[patmurris]

The new data release of the Radial Velocity Experiment (RAVE) is the fifth spectroscopic release of a survey of stars in the southern celestial hemisphere. It contains radial velocities for 520 781 spectra of 457 588 unique stars that were observed over ten years. With these measurements RAVE complements the first data release of the Gaia survey published by the European Space Agency ESA last week by providing radial velocities and stellar parameters, like temperatures, gravities and metallicities of stars in our Milky Way.

Read more at: http://phys.org/news/2016-09-dynamic-duo-rave-complements-gaia.html#jCp

The RAVE project site: https://www.rave-survey.org/project/

In the above image taken from one of the RAVE DR5 video, surveyed stars are shown in 3D and color coded according to their positive or negative radial velocity relative to the Sun.

I'm a bit puzzled that stars on one 'side' tend to run away from us whereas on the other 'side' they tend to come toward us. If the Sun is moving around the galactic center "with the flow" there should not be such a bias? Does that mean that the Sun moves noticeably faster (or slower) then the other stars or is this expected from the way velocities have been measured or computed?

Looking closer at the stars in one of the fly through video we can see that not all stars follow the same trend. Some go one way while others in the same vicinity go the other way. This reminds me of another video i saw a few years back showing a simulation of stars formation in a dust cloud where you could see them 'dancing' around in very chaotic orbits - a bit like fire flies above a camp fire.

If we keep surveying those stars, i guess that at some point in the future we will have enough data to actually infer their orbits - and create fascinating movies.

 

[mfb]

No bias would require the same angular velocity for all stars. Stars closer to the galactic center have a larger angular velocity: if they are "behind" us (relative to the orbital direction), they are approaching us, if they are "ahead" of us, they move away from us. The opposite happens to stars further away from the center.

There is a also some dipole effect from the random motion of our sun relative to the average flow of stars around us.

 

[patmurris]

No bias would require the same angular velocity for all stars. Stars closer to the galactic center have a larger angular velocity: if they are "behind" us (relative to the orbital direction), they are approaching us, if they are "ahead" of us, they move away from us. The opposite happens to stars further away from the center.

Thanks for the hint. That makes sense, and it should produce a cross pattern - like the BMW logo. However the RAVE survey only covers a portion of one hemisphere (looking back apparently) so we don't get the whole pattern, but a top view from one of the video does indeed show a 'blue shift' for stars closer to the galactic center as you explain it: