Project #6 Asteroids
The purpose of this exercise is to observe
the motion of an asteroid against the background of stars and to detect its
light variation due to its orbital motion.
Preparation
UPDATE
There may be an easier way to get an asteroid finder. Go to heavens-above . Under Astronomy, right after Comets, they have 'Minor planets brighter than mag 10'. Pick one and see if it is visible for your observing run.
The coordinates for the night are given. You still might get a chart from the Navy (see below), but the Heavens-Above chart might do it. our CCD is about 1/10 the size of the H-A fine finder chart.
OR try this
From the following asteroids,
9 Metis, 40 Harmonia and 2 Pallas, choose one to observe. You want to observe
it for about two hours to see its motion and possible light variation.
Once you pick a possible
target use ASTFINDER to get a chart. Enter just the number OR the name not both.
Use observatory #764. Enter the beginning of your observation time. At the top
of the chart you will find the RA and Dec of the asteroid at your time of
observation. Make sure it will be up during your observation.
The ASTFINDER chart is great
for figuring out the asteroid placement and direction of motion BUT it shows
stars down to 19 magnitude.
We should be so lucky!
Go get another chart of the same
region at the Naval Observatory (Flagstaff Station)
You can use the defaults
except you have to enter the coordinates, of course, and choose 12 mag for the
R2 mag limit. (You can use I, for infrared, instead of R2, for red, if you
want. It will not make much difference. Hit retrieve data and you will get a
picture in the upper window, which will be what you are looking for. When you
take your CCD picture is will look something like this [maybe rotated] but with
the asteroid on it. Some of the fainter stars you will not see in the eyepiece and
may not see in the CCD picture depending on how faint you expose.
You should be able to
identify the brighter stars in ASTFINDER. Mark where the asteroid will be
on the USNO chart. You can also list the stars on the USNO chart by
clicking the USNO A2 Star List link to make sure they will be bright enough to
see. 11 mag is ok, 10 mag is
better and 9 mag not a problem. To get a good result you will need a CCD frame
(12x12 arcminutes) that has the asteroid and at least one other star in it for
which you can get good exposures. If this is not the case try another target. Preparing
two targets for the same night might give some security that you will get good
data.
Observations
To save time in the dome have your finder
chart and the coordinates for your offset star in hand. Move to the asteroid
field and take a picture. Check to see if you have an object not on the finder.
The magnitude should be a clue. That is, if the predicted magnitude is 10 and
you have other 10 magnitude stars on the finder they should be about the same.
Once you think you have start taking CCD
images. Your goal is to take about 2 hours of exposures. This is not to hard
since Maxim has a feature to take one after another. Under sequence change
number to 300 or so. Put a name like Juno in the space for names. Then when you
go back to expose and mark sequence it will take pictures Juno001.fit,
Juno002.fit, etc. When you want it to stop just click abort. Do this while
it is taking and exposure and it will
throw that one a way and be ready to start again. If you abort during download
it will lose count and you will have to go to the Sequence page and up the
start number by 1. You do not have to log every observation. Just note the
first one and the last one [before any abort].
The field may drift a bit. You can abort the
sequence, recenter a bit, and then start up the procedure. Don't be too picky.
You would like to keep the asteroid and one or two stars in the frame. You will
be using the reference stars to measure the asteroids brightness changes and
motion. The R or I filters are your best bets.
Another way to reduce drift is to change the
tracking rates. If you click on
the ‘55’ button at the top you will get a menu in which you can change the
track in ra and dec. For ra 15 is
the nominal rate. Changing it to
15.01 will speed it up and 14.99 will slow it down. Change it in small steps and see what it does. Dec should not matter much.
Reduction and analysis
You need to do two things:
Calculate
the distance traveled in pixels and then, using the scale of the telescope, in
arc seconds. How many arc seconds did the asteroid move in what amount of time?
Explain how this could be converted to the rate of motion in the asteroid's
orbit. Be clear about what other information you would need.
Remember,
smaller magnitude at the top.] (Star1- Star2) should remain constant. Why? Did
you get a change in brightness for (Star1-Asteriod)? How much in what amount of
time? Can you explain how a solid rock can change in brightness? Why is this
NOT a due to the changing distance?
Write-up
You need to have print outs of the beginning
and ending images you used to show the motion as well as your calculations.
Show the motion on the printouts. Which direction is it? Include the 'time
series' data [the time vs. magnitude] with your plots. Also include the finder
chart with the asteroid sketched on it. Did the table you printed out when
finding the asteroid on the web have a period of rotation for the asteroid? If
is did, how does this compare with the variation you found?