It has been a while since I have written a general review of the tass project. I notice that people are joining the tass mail list and new people must wonder what is going on. This is also being sent out to other lists that might find it interesting. Sorry it is so long. You may want to meander through the TASS home page at http://www.tass-survey.org.
Tass (The Amateur Sky Survey) does what the name says. We have set out to measure all the stars in the sky as often as possible in several filters. While we get some astrometry, measuring where stars are, we are primarily doing photometry. This is measuring how bright the stars are. To be useful to professionals, the brightness measurements need to made with calibrated filters. To start, we are using Johnson-Cousins V and I filters. Later we will add B (if we can afford the CCD) and R.
We hope to measure a large number of stars frequently. This will allow the detection of many as yet unknown variable stars. With the planned equipment, and if someone else does not get there first, we should more than double the number of known variable stars. Further, we are performing our measurements through calibrated filters. Many of the possible competing programs are not using filters. Understanding and studying our errors is a significant part of this project.
This whole mess was started by me (Tom Droege). I am paying most of the hardware bills. There is no government or foundation sponsorship. The work, much more valuable than the hardware, is being done by anyone who wants to join in.
The first stage of this program used the Mark III drift scan system wich was made out of cheap camera lenses and Kodak KAF- 0400 CCD detectors. Most were operated as triplets which made an I, V, and I measurement. The measurements of any one star were spaced at one hour intervals by the physical construction of the cameras. These cameras were operated in 6 locations with most of the locations equipped with triplet cameras. A large number of measurements were made. The result of these measurements is the 10XCAT which is described in some detail TASS Technical Note 56.
The drift scan mode has a fixed sensitivity due to an exposure time determined by the rotation rate of the earth. This resulted in a maximum sensitivity of about magnitude 12.5.
The Mark III program taught us all a lot. We developed software techniques, and learned how to take measurements. It seemed to be a productive line of research so the Mark IV system was planned. More important, we developed a group that seems to want to do this work.
We are building 20 Mark IV camera systems. Each will contain two telescopes and each of the telescopes will be equipped with a 2k x 2k CCD camera. The lens systems were designed especially for this project by one of the tass "members" (remember anyone can be a member). They are 4" diameter f/4 five element refractors. There are four designs each optimized for use with one of the BVRI filters.
The mount is a balanced equatorial. With everything, the Mark IV setup is table top size. About 30" wide by 30" deep by 36" tall.
Most of the cameras will operate with V and I cameras. The arrangement is such that both cameras track the same piece of sky. The simultaneous exposures help to remove cosmic ray hits. Few surveys take data simultaneously in several filters. While not likely to reveal anything spectacular, the data will be unique. Depending on the location and operating mode, these systems should reach magnitude 15.
These systems can produce a lot of data. The images each require 8MBytes of storage. A good night will produce 3 GBytes of data. One location will make 1-10 Million star measurements an evening.
The Mark IV test system saw first light October of 1998, and stars that November. An improved mechanical design was then produced. The first tests of this design on stars was made in March of 1999. The rest of the year 1999 was spent working out the production problems. By mid 1999 we had a prototype dual system operating every clear night. There were many problems, particularly with the RA drive. After many modifications we are able to take several hundred second exposures with minimal error contribution by the RA drive.
At present, we have the dual camera prototype system running and six additional systems on the production line. Two, which will go to NY and AZ are nearly complete. Two more will go to OH, and one to MD and one to CA. An eighth system has not yet been started but is destined for South Africa. 20 sets of electronics have been built. Each electronics set can operate 4 cameras, but most will be run as dual systems. Forty lens systems have been purchased (some parts more than once). There are 4 working 2k x 2k cameras, however, 19 more are in the final stages of construction. I have so far purchased 15 2k x 2k CCDs.
The camera systems are given away to those that convince us that they will operate them and take and process data. We are particularly looking for those in the south that would be interested in operating a system.
To join in this work, send mail to:
In the body of the message put:
subscribe tass
You will get a few messages a day. When a person is active, and I get to know them by their work on the list, I will then consider them for a camera installation. Many work without interest in running an installation. We welcome all.
Much of the work involves software. That is the big problem for a project like this. We are very happy to have people join who just work on software projects. Since the prototype has been running, I have been sending out data sets on CD ROM. Many are doing useful work for tass analyzing this CD ROM Data.