M57: Stellar motion, almost a century of data…

Recently I have been working on Hubble data of M57. When processing the data I found one of the stars moving between the images. Triggered by this I tried to find more data that could show the motion. I found some old images made in 1922 and around 1959 made by a 100-inch and a 200-inch telescope (Mount Palomar). I combined this data into an animation showing the motion in a period of 90 years. It’s clear that the motion of this star is quite fast (about 0.1”/yr) and very well detectable. The star showing the motion is 2Mass 18533272+3301234

I wanted to make a rough estimate of the distance of this star to calculate its velocity perpendicular to our solar system. Therefore I made some photometric measurements from the Hubble imagery. This gives a difference in magnitude for the V and I channels (V-I) of about 1.5 +/- 0.2.

According to Rucinsky (1987) this corresponds to a red dwarf star with a designation of about K5-K8. When using spectroscopic parallax this gives a distance of the star of about 650-950 lightyears. So it’s clearly closer by then the nebula which has a distance of about 1500-2500 lightyears.

A motion of 0.1”/yr corresponds with a speed of the star of about 95-140 km/s.

This is a very rough estimate, but clearly shows a scale of velocity.

In the time scale of the hubble images the nebula should have expanded about 0.08”. This image with two images of 2000 and 2008 shows the expansion of the nebula in these 8 years:

Using the central star to align the images from 1998 and 2008 the expansion is visible in these two images from the Hubble. They were just shifted and no scaling was performed.

Using photoshop scaling with the central star as a central point the scaling factor can be determined. This shows that the 2008 needs to be scaled with a factor 0.982x to fit the 1998 image. With a central diameter of the nebula of 87” this means a growth of about 0.15”/10 years, or 1.5”/century. Assuming a constant expansion this sets the age of the nebula around 5,5×10^3 years.

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