Convective Energy Transport Boundary in Field Stars Dillon R. Foight Dr. Brian Rachford Embry-Riddle Aeronautical University April 28, 2007

Overview Objective of research Why the D3 line? Approach Results Conclusions and Future Work

Objectives Determine level of activity in late A and early F-type stars. The D3 absorption line (Helium) is used as an activity indicator. Determine the cutoff of convective activity, and possibly find factors involved in this boundary.

Why the D3 Line? The D3 line has been shown to be a reliable chromospheric activity indicator for early F-type stars. It is a indicator of convective activity. D3 measurements provide activity level measurements comparable to those found by space based observations.

Approach Each spectrum had to be corrected for telluric lines. Photospheric lines around the D3 region were divided out. Spectrum on right has visible telluric and photospheric lines.

Sample Group Data was available on over 50 field stars observed by Dr. Brian Rachford from 1995-2000 at Kitt Peak National Observatory. From these 30 were chosen based on the quality of spectra. The stars ranged in temperature from 6500 – 8500 K, corresponding to the region of late A and early F type stars.

Results

Results

Results From the temperature graph, it is evident that there is not a definite cut-off in temperature, as might be expected. There is a mixture of active and non-active stars in the same temperature region. This can also be seen on the H-R diagram. From this diagram, it is also evident that both stars on the ZAMS and more evolved stars exhibit activity.

Conclusions and Further Work The results suggest that the boundary is not abrupt, but instead spread over a range of temperatures and ages. Thus, there must be another parameter which contributes to the boundary. In future work, additional parameters will be investigated. In depth analysis of abundances will be done, to investigate any contributions. Also, cluster stars can be added to the sample, to see if they exhibit the same behavior.

Acknowledgements Dr. Brian Rachford – Mentor of project. Dr. Ron Madler – Space Grant Coordinator The Arizona Space Grant Consortium for financing this project.

Results Star EW (mA) EW Err. (mA) Temp (K) 31.5 1.6 7117 36.3 3.0 7185 Eta Lep 31.5 1.6 7117 HD 218396 36.3 3.0 7185 Alp Crv 26.0 3.3 6935 51 Eri 27.3 3.5 7352 Bet Cas 33.0 11.0 6869 HR 6237 22.6 3.2 6691 Rho Gem 31.4 1.0 7107 Sig Boo 16.1 2.9 6748

Results