Kitt Peak YSO Research Project
Exploring A New Technique for Identifying Potential T-Tauri Stars
T-Tauri stars are very young sun-like stars in the early stages of development, and are important to astronomers. In order to better understand how our own sun developed and how our solar system came to be, we must study similar stars. T-Tauri stars are similar in mass to that of the sun, and therefore follow a similar evolutionary path. As a result, a better understanding of T-Tauri stars will lead to a better understanding of how our own sun came into being.
Stars form from collapsing clouds of gas and dust called protostar. Current models of these young stars in their early stages of formation contain a hot collapsing core surrounded by a cocoon of gas and dust. As the star matures the cloud of gas and dust slowly forms into planetary objects or is blown off into space exposing the young star.
As a result two pieces of evidence should be apparent in T-Tauri candidates. First, due to the excess gas and dust around the young star, T-Tauri stars should show significantly higher infrared emissions than older more stable stars. Second, T-Tauri stars tend to be very active and have a strong h-alpha emission line. Although, this alone would be insufficient evidence to conclude an object is indeed a T-Tauri star, it can go a long way in making such a determination.
One problem that astronomers and in particular students conducting research often run into is limited access to a spectroscope necessary to identify the h-alpha emission line in the T-tauri candidate. We believe we have a solution to this problem, and we are putting forward this proposed study to verify the validity of this new and simple technique.
NOTE: We have identified over 100 standard stars from the Landolt: UBVRI Standards and over 50 known or likely T-Tauri candidates. Depending on the time we are given for this project, our observation plan will change. If there are two full nights made available, we have a sufficient number targets that will consume this time. However, if less time is available we can narrow our target list significantly. We estimate the minimum amount of observation time necessary for this study is eight hours. If we are fortunate enough to have this proposal accepted, a final target list will be identified and submitted prior to our observation date. The targets range between 00 – 07 hours RA, and -1d - +40 d Declination, and magnitude 10 – 18.
Stars identified as standard stars are stable and rarely change in brightness. This means they should be relatively inactive and have small h-alpha emissions when compared to more active T-Tauri stars. In addition we would expect standard stars to have significantly less infrared emission when compared to T-Tauri stars.
The 0.9 Meter combined with the R Harris, I Harris, and H-alpha filters offers the sort of size and precision instrumentation necessary for this study.
Our method will be to image the standard stars and the T-Tauri stars in R, I, and H-alpha. The exposure times for each object will be determined by the estimated R exposure time. The R exposure times have been calculated using the exposure calculator at http://www.noao.edu/gateway/ccdtime/ . In each image the I exposure time will always be twice the R exposure time, and the H-alpha exposure time will always be ten times the R exposure time. These exposure times should be sufficient for us to achieve a SNR of 50 or better. The data will be reduced using MaxIm DL.
For each target we will end up with an intensity value (counts) at R, I, and H-alpha. Since we will only be comparing relative brightness’s through the different filters, and the ratio for exposure times remains the same for all images, there is no need to determine magnitude using this methodology. Intensity values will be sufficient.
The following x/y scatter plot will then be generated using Microsoft Excel.
X axis – log(Icounts/Rcounts)
Y axis – log(H-ALPHA counts/Rcounts)
Because the narrow band H-alpha filter is within the broad band R filter, very active stars (T-Tauri stars) should break away from less active stars (standard stars) in the X/Y scatter plot. In addition, because T-Tauri stars will show a significant excess in the infrared when compared to older main sequence stars, the T-Tauri stars will break away from the standard stars in the second axis as well.
If our theory is correct, the X/Y scatter plot should allow us to clearly identify T-Tauri stars from their position in the plot. We may also even be able to differentiate between class 1, 2, and 3 T-Tauri stars.
If this works, scientists and high school students without access to an astronomical grade spectroscope will have a new tool in their hands to identify potential T-Tauri stars.