Part 2: Retrieve your CCD Data
In this part, you will retrieve all of the CCD images for your night, and gather all the pieces you need to measure the brightnesses of the variable star and its nearby "comparison" stars. The data have already been through the basic YALO reduction pipeline, and thus have already had the following data-reduction procedures performed:
The result of the basic pipeline processing is a set of reduced CCD images showing the region of the sky around CY Aquarii in the B-band for a roughly 20 minute period on a particular night.
All notes you take during this step must be written into your lab notebooks.
Step 1: Retrieve your data
The data for your assigned night are packed into compressed Unix "tape archive" or "tar" files, stored on the main data disk on regulus in the Astronomy 350 Lab Data directory: /home/regulus/ast350/LabData/CYAqr/. For each of you, the tar file will be filed by your last name with the .tgz file extension. For example, student "Pogge" would have their data in a file named
/home/regulus/ast350/LabData/CYAqr/pogge.tgzThe assignments are as follows:
Person Date Observed --------------------------- Adkins 2000 Sep 25 Durben 2000 Sep 26 Gero 2000 Sep 27 Grilliot 2000 Sep 28 Heinrichs 2000 Sep 29 Lundell 2000 Sep 30 McFerran 2000 Oct 04 Payne 2000 Oct 05 Pitts 2000 Oct 06 Reed 2000 Oct 07 Scaife 2000 Oct 09 Shepherd 2000 Oct 08 Sutherland 2000 Oct 09 Walker 2000 Oct 11 ---------------------------The date above is for the "Observing Day", which at YALO is the date of the start of the night in local time (in this case, Chilean Standard Time). The "Observing Day" begins at Local Noon. This is not the UT date of the observations; that information must be derived separately from the observing logs (or the image headers).
Copy your tar file into your personal directory. For example:
cp /home/regulus/ast350/LabData/CYAqr/pogge.tgz .And you are ready to begin the next step.
Step 2: Unpack the "tarball" of data for your night
A compressed tar file is known colloquially as a "tarball". It contains all of your CCD image files in a single, self-contained archive file for ease of copying. To actually get at your files, you need to first unpack the tarball. Follow these steps:
cd working tar xzf ../pogge.tgzThe last command above uses the Unix "tar" command to extract ("x") and uncompress ("z") the tar file ("f") stored in "../pogge.tgz". After a short delay (it takes a little under a minute to extract and uncompress the 25 images).
ls -lto see a listing of your images, with their sizes. You should each have 25 files.
The CCD image files will all have names like:
ccd000925.0014.fitsThese are the names given to the files by the ANDICAM data-taking system. The filename format is as follows:
ccd = data are from the CCD detector channel of ANDICAM 000925 = date of the observation, in YYMMDD format. In this example, this image was taken on observing day 2000 Sept 25. 0014 = sequence number of the image (i.e., this was image #14 taken on observing day 2000 Sept 25) .fits = the file is a FITS format CCD image.More precise information is contained in the data headers and online observing logs. These data include the UTC time and date of the observation, telescope and instrument data, etc.
After unpacking the files, you should move your tarball of the original data in a "safe" directory so that if there is a problem later on and you need to retrieve the original data, you can just unpack it again as above and start over from a known step.
Step 3: Retrieve the data log and observing report for your night
Using the Web, go to the YALO Observing Web Page at OSU:
http://www.astronomy.ohio-state.edu/YALOand follow the "Nightly Observing Log Archive" link to find the observing logs from your observing night. Scroll down to find the log entries for "CY Aqr"
For example, for the log for the observations for Observing Date 2000 Sept 24, you would see entries like this:
Project ImType Object RA Dec ExpTime Filter SecZ LST UTDate UTC JD Filename [Logged@UT] ... O39901 OBJECT CY Aqr 22:37:47.9 +01:30:49 30.0 B 1.32 00:27:11 2000-09-25 04:53:10.3 2451812.7036 ccd000924.0021 [04:54:05] O39901 OBJECT CY Aqr 22:37:47.9 +01:30:49 30.0 B 1.33 00:28:09 2000-09-25 04:54:07.9 2451812.7043 ccd000924.0022 [04:55:02] ...and so forth. The heading of this table is at the top of the log file.
Copy the entries for CY Aqr for your night into a text file in your working directory for future reference. You will need this information to perform various tasks that follow.
Also retrieve the nightly observer's report for that night by returning to the YALO main page, following the "Observer's Reports" link and then downloading the the observer's report for your night. This file will tell you the weather and approximate seeing conditions on the night that your data were acquired.
Step 4: Compile a brief observing summary
Using the logs, make a brief narrative summary of the observations for your night. In this summary, provide the following information:
This information will eventually become part of your final write-up for this lab.
Advance to Part 3: Measure the Images
Go back to Part 1: Finding Catalog Data
Copyright © Richard W. Pogge, All Rights Reserved.