1. A Study of Accretion Disks Around Young Binary Star Systems
Paula Johns, Northern Arizona University
Mentor: Lisa Prato, Lowell Observatory

2. Why is the Study of Accretion Disks Important?
Can determine parameters such as efective temperatures, spectral types, luminosities, And masses, as well as accretion properties and near-infrared excesses for the individual binary components.
Contain the material for the formation of planetary systems. Is evolution different than for single star systems?

3. What are T Tauri Stars? Characterized by… Vigorous activity
Strong stellar winds
Variable and irregular light curves
Found in nebulous regions
< 2 solar masses
< 10 million years old
Newly formed low-mass stars that have recently become visible in the optical range
Pre main sequence
First one percent

4. Data Collection University of Hawaii 88”
800 spectral resolution in K-band
Low resolution infrared spectroscopy and photometry
Talk about moving telescope to center on object, grating changes wavelengths received, talk about how system works
Kspec=name of spectrograph

5. Aspects to Take into Consideration…
Extinction ~ Reddening attributable to dust
Infrared Excess~ Infrared flux in excess of that expected by assuming star is a black body
Veiling~ Filling in of spectral absorption lines by an IR excess
Rk=veiling, star is not perfect black body as a result of the dust in disk
Extinction=dust absorbs/scatters more frequently at shorter wavelengths

6. Spectra result from a combination of the young star photosphere and excess IR radiation from circumstellar disk material and IR emission from accretion processes and interstellar extinction along the line of sight

7. Spectral Standards Hotter Cooler
Create a model spectra of the underlying young star photosphere, beginning with an observed young star spectrum and varying the parameters of extinction amplitude of the k band excess and in some cases the slope of the excess
Water lines “eat” away at line on right side causing curve
Av affects shape of line, increase in extinction increases slope
Cooler

8. Br gamma line (Hydrogen) emission indicates that objects have active accreting circumstellar disks
Larger Rk(veiling) make spectra flatter
Mention that physically separated to see difference

9. LK Ca 7 Secondary K5 M5 Top is K5, av= 9.2, cc=.66, rk=0
Bottom is M5, av=0, cc=1.62, rk=0
Black line is Lk Ca 7
Least squares fit / X fit

10. LK Ca 7 Secondary Averaged K5 and M5
Lk Ca 7 2* M5,K5 spectral type
Av=0, rk=0, ratio=.24
Ang sep 0.25” fcn of telescope, .22wavelength/D

11. Results
Determined the spectral types of stars in 11 systems by comparing them to spectral standards
Determined extinction and K band excess
No significant correlation has been found between stellar spectral type and the K band excess, implying that the mass of a star is independent of the size or presence of a circumstellar disk
Future work: Mass and age of stars will be determined by comparing fit to H-R diagram
Luminosities, and effective temperature?

12. Acknowledgments N.A.S.A. Space Grant Consortium Lowell Observatory
Northern Arizona University
Tom Greene

13. Thank You