Finding the velocity of a high-proper-motion star in IC2118

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needs refinement


This paper was a result of one of the very first NITARP teams, when it was still the Spitzer program.

IC2118 is also known as the Witch Head Nebula, and is off the knee of Orion.

When we were working on finding new YSOs in IC 2118, we found a high proper motion star.

You can find the high proper motion star!

In general, stars don't move very fast by human standards. In order to find stars that move easily, you need images taken over a long time baseline to give the stars time to move. Alternatively, you need to move your baseline and make very careful measurements (for related information on measuring parallax, which is easier than proper motions, see Gaia and the New Horizons parallax project).

Fortunately, you have easy access to a time baseline of more than 50 years -- POSS photographic plates were taken in the 1950s and the Spitzer data were taken in the mid-2000s. Use IRSA Viewer to pull "big enough" images of IC2118 from POSS and from Spitzer (use the SEIP). You will need to decide how big is "big enough." Use IRSA Viewer to make a 3-color image using one of the earliest POSS images for at least one plane and one of the Spitzer/IRAC images for another plane. Does the high-proper-motion star jump out at you?

Identify the position of the high proper motion star in at least two epochs. (You have easy access to a third epoch from the late 1990s from 2MASS.) Do this by hand or look up the derived (sub-arc-second) position for the star at each epoch.

Do the math!

Figure out how far it has moved in the available time. Calculate the spherical trig properly. Make a note of the dates precisely. Calculate the average proper motion (in RA and Dec directions). Do you get the same numbers we did in section 4.6 of the IC2118 paper?

Since we did this work, more data have been released. Can you find this star in Gaia DR2? What parallax and proper motion did they get? How does it compare to our value from the paper, or your calculated value? (Did we get it right, or at least close?) Advanced: use Bailer-Jones et al. 2018 to get the corrected distance for this thing, as opposed to just inverting the parallax.

Calculate the true space velocity of this star, or at least the projected space velocity assuming ~50 pc distance. Is it a runaway? (Will it escape the galaxy?) You'll need to look up a bunch of supporting information here to figure this out.

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