Where Can I Find Raw Data for Galactic Curve Velocities?

[lenfromkits]

Hi. I have google'd for awhile but cannot seem to find this information (velocities of stars in the galactic curve). I need to work with the raw data observed before calculating the doppler shift and subtracting the Earth and sun radial movement out of it. I need the transverse velocities as well.

Does anyone know where this info can be found?

Thanks.

 

[marcus]

I don't understand what you are trying to do. What doppler shift are you talking about? What are you planning to "subtract out"? I might be able to answer better if you explained more.

It is simple and straightforward to measure the rotation curves of OTHER GALAXIES. You just focus on a nearby galaxy that is seen flat-edge on. With say the stars on the right side coming at you, and the stars on the left side going away from you. And you can measure the doppler shift of those stars and see how it depends on distance from center.

It's like looking at a transparent turning wheel, edge on. Doppler tells the whole story.

What's hard, I think, is trying to work out the rotation curve for OUR MILKYWAY GALAXY.

You could explain more what you are trying to do, what you want to calculate, and why.
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It sounded from your post that you might want data on our own galaxy, and the solar system's motion in our galaxy. That is more complicated. Different data. Or could you perhaps be talking about the doppler shift in the CMB (microwave background) that is caused by the solar system's motion relative to the universe as a whole?

If you are wondering about the sun's motion around the center of the galaxy, that was determined a long time ago from data on the radial velocities of stars that are nearer the center, and the radial velocities of stars that are farther out from center.

We tend to be overtaking stars that are farther out (and still "ahead" of us) and stars that are nearer in (but "astern" of us) tend to be catching up. So both those classes of stars, statistically on average, are getting closer to us.

I think this method was really not very good, but it was all people could do in the early 20th century. After around 1940 or 1950 there was RADIO ASTRONOMY, looking at the 21 centimeter radiation of huge clouds of hydrogen. They could tell the radial velocity (by doppler) very accurately. Clouds closer to center, and behind us, would be catching up---so they would be getting closer to us. Likewise clouds farther out from center, and ahead, would be getting closer because we were catching up with them. I think the whole thing is a massive game of fitting the model to the data----mostly radial velocity data (rates of something getting closer or getting farther away from us).

I don't have any expert knowledge so let my response here be merely a stopgap. Before long I hope someone with more expertise will come along and help you out.

My guess would be that there is a huge amoung of "raw data" on radial velocities and that it would have been a decades-long and very involved process to derive orbital speeds from that data.
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Better amplify your question some, are you interested in our home galaxy, or in the rotation curves of other galaxies?

 

[lenfromkits]

I don't understand what you are trying to do. What doppler shift are you talking about? What are you planning to "subtract out"? I might be able to answer better if you explained more.

HI, thanks for the thorough response. I am looking for the frequencies of the red-shift they observed when looking at stars in our galaxy - or in another galaxy (from the 21cm light). Also, since when calculating the velocities of these stars, they have to take both the radial and the transverse velocities into account to figure out the real speed and direction, I need those too.

Basically, I need to work with the raw data and recalculate the velocities based on the doppler shift formula. I'm obviously going to be interjecting a variation into these calcs, which is the point of my study. There's no point in elaborating on that, I just need the data that they worked with initially.

One tricky part will be that the observed velocities will be in part due to the star, and in part due to the Earth's movement at the time of the observations. They apparently have to remove the Earths movement in order to get the star's movement relative to the galactic centre. I would need to know those values as well.

This is hard information to come by.

Thanks.

 

[Chronos]

I would start with http://vizier.u-strasbg.fr/