A photometry and multiplicity study of young brown dwarfs in the Taurus star formation region with HST
I am conducting a direct imaging survey of young brown dwarfs in the Taurus star formation region. The data were taken with HST. I am detecting potential companions of these objects.
An extremely wide-orbit exoplanet candidate imaged around two enigmatic stars
I detected a low-mass planet candidate (3-5 Mj) located more than 760 au from its central stars. The central star was resolved to be a closely separated binary. This work was submitted. More details in the future.
Weather on brown dwarfs - a near-infrared variability survey of young planetary-mass objects
Variability is common in brown dwarfs. As they rotate, inhomogeneous atmospheric structures can be probed by variability monitoring. Young brown dwarfs share similar mass, temperature and age with direct-imaged exoplanets. These free-floating planetary-mass objects are exoplanet analogues. Decade-long observations have revealed that brown dwarfs have complicated atmospheric structures possibly due to clouds, hotspots, and chemical-thermo instability. It has been found that young L-dwarfs are more likely to be variable than field L dwarfs which is attributed to lower surface gravity. To complete the statistical study on the effects of surface gravity on the variability of brown dwarfs from L to T spectral types, I conducted the first near-infrared variability survey of 18 young planetary-mass objects with spectral types from L5 to T8. I detected four new variables and two variable candidates. Combining previous variability surveys of field and young L and T objects, I find that young objects tend to be more variable than field objects. I constrained the variability rate of young T dwarfs for the first time and found that young T dwarfs are also more likely to be variable than field T dwarfs. Both field and young samples have higher variability rates at the L/T transition than outside the L/T transition. This work supports the critical role of surface gravity on the atmospheric structures of brown dwarfs and planetary-mass objects. This work was published in Liu et al.2024.
TRAP for vAPP - Applying a temporal systematics model to vector Apodizing Phase Plate coronagraphic data
The vector Apodizing Phase Plate (vAPP) is a pupil-plane coronagraph that produces a dark hole with a certain shape in its point spread function (PSF). The unconventional and non-axisymmetrical PSF arising from the phase modification applied by this coronagraph presents a special challenge to post-processing techniques. To develop algorithms for the vAPP coronagraphic data, I implemented a temporal systematics model, TRAP (Samland et al.2021). I applied the TRAP algorithm to two types of vAPP datasets, gvAPP180 which produces two complementary PSFs with two 180-degree dark holes and dgvAPP360 which produces one PSF with a 360-degree dark hole. The property of TRAP using non-local reference pixels combined with the two PSFs of gvAPP180 produces plenty of freedom to select reference pixels to build the noise model. I found that the systematic noise between the two D-shaped PSFs is not as temporally associated as expected. Conversely, a significant number of systematic noise sources are shared by the dark hole and the bright side in the same PSF. We should choose reference pixels from the same PSF when reducing the dgvAPP360 dataset or the gvAPP180 dataset with TRAP. In these datasets, TRAP achieves results consistent with previous best detections, with an improvement of 43% for companion detection in the gvAPP180 dataset compared to cADI. This work was published in Liu et al.2023.