K Line Shape
Photo credits: NASA/JPL-Caltech
Brown dwarfs are mysterious sub-stellar objects that possibly link between planets like Earth and Stars, such as the Sun. They are called “failed stars” because their masses are just below the critical values that can sustain fusion, leaving trace amounts of “un-burned” alkali metals in their H2/He-dominated atmospheres. The alkali resonance doublets, for example, potassium around 0.77 µm, lead to “fingerprint” absorption features in the spectral flux measured by space telescopes, and such distinctive observations can provide insight into the physical properties of their stellar atmospheres. Laboratory characterizations of the potassium absorption line shapes are crucial to explain these spectral
observations; yet they are difficult because of the dangers and difficulties in its sample handling and disposal.
I worked on a safe and effective seeding approach that uses potassium chloride as a precursor to produce potassium via shock wave-assisted processes of sublimation, dissociation, and deionization. To resolve the absorption line shapes of the ppb levels potassium in a highly-transient shock condition, tunable diode laser absorption spectroscopy (TDLAS) with >10kHz modulation frequencies was deployed.
Motivation
With better hardware and sensing technology mounted on state-of-the-art space telescopes, the quality of observations is better than ever. The extraction of useful information is, however, limited by our fundamental knowledge of absorption/emission.
Figure credits: Burrows, 2000
My approach
KCl seeding in a shock tube + TDLAS sensing solution
3D printed plug
3D printing is great in faster turnaround, cost reduction ($500 each to <$10 a pair) and better machinability.
Minimally-intrusive seeding strategy
I did not observe any variation in the shock tube's temperature and pressure profile due to the screw insert.
System integration
Results: highly-resolved line shape
The yielded spectra were fitted to a comprehensive list of line shape profiles and the measurements show small fitting residuals of less than 2%.
Results: temperature dependence
This is the very first characterization of potassium collisional broadening at brown dwarf temperatures (~2000 K), with ongoing collaborations with NASA Ames and SETI for simulation/analysis.
