1. INTRODUCTION

2. Ly α OBSERVATIONS AND REDUCTIONS

3. MCMC

3.3. Systematic effects

3.4. Comparison of fitting techniques

3.5. Time variability

3.6. Extreme-UV Spectrum

4. GJ 832

4.2. GJ 876

4.3. GJ 436

4.5. GJ 667C

4.6. GJ 176

4.7. GJ 1214

4.8. HD 85512

4.9. HD 97658

4.10. HD 40307

5. DISCUSSION
5.1. The Ly α line profile
5.2. Comparison with other chromospheric and transition region lines

6. SUMMARY