This page contains a reverse chronological order of research activities that I have led. See the subpages for a categorized version for the research activites that I have led and participated in, including

• Finding the "missing planets" in high-contrast imaging (Dynamical search)

• Finding the planets that are embedded in disks (Direct imaging)

• Exo–Kuiper Belt characterization

• Post-processing methods for high-contrast imaging

• Imaging the host galaxies of quasars using coronagraphs

4. OCA/IPAG Research (2022 Apr - 2025 May)

I am a young researcher (French title: jeune chercheur) affililated with the PROTOPLANETS project lead by Dr. Myriam Benisty funded by European Research Council (ERC 101002188). We are based at the Côte d'Azur Observatory (Formerly known as Nice Observatory. French: Observatoire de la Côte d'Azur, OCA), and employed by the Grenoble Institute of Planetology and Astrophysics (French: Institut de Planétologie et d'Astrophysique de Grenoble).

With the support from Dr. Benisty, who listens to what young scientists think/suggest and adjusts research goals realistically accordingly (like all my prior official advisors/hosts), rather than dictates what you should do, I can dream big, aim high, and have fun in the nice Nice, France. I strive to be not only an excellent scientist, but also a good mentor/listener like all of my official hosts.

More updates to come...

Oct 2019 --- Nov 2022: Multi-wavelength imaging of debris disks using Hubble Space Telescope (HST) coronagraphs (Ren et al. 2023b; A&A, arXiv, ADS).

• Technical highlight: reduction, modeling, and analysis of debris disk reflectance in a systematic way.

• Scientific highlight: 

  • Debris disks in HST wavelenghts (0.6 µm, 1.1µm, and 1.6µm)  are predominantly blue. 

  • The more luminous the host star, the more neutral the disk scatters light.

  • The abedo-color distribution may resemble that of solar system minor objects.

  • This confirms a simulation study (Thebault & Kral 2019), in which the authors found it hard to explain an observed "red" system: the system is blue in my work!

• Non-science but management lessons learnt: while the results were already obtained by Aug 2021 (funding completion), the actual manuscript was not completed until Nov 2022. This is not due to further analysis or manuscript writing, but due to a waste of my 15 calendar months of free labor!  The primary obstacles are (1) to convince one collaborator who made me to align my blue results with a few studies on that "red" system, yet these studies' limitations were already clearly identified by a later paper from that team. This year-long distrust from that person triggered my initial plan to leave debris disk imaging. (2) To persuade the same person -- who wanted to use Mie theory to explain the observations -- that Mie theory has been rigorously shown to be not appropriate in explaining disk observations. This waste of ~another year (for both me and another young scientist) consolidated my determination to leave debris disk imaging, at least to cut ties with that person. Were it not for the unwavering support of my official PhD and postdoc advisors, I would not have had the courage to confront that individual and to say no.

• Personal suggestions to young scientists when encountering similar issues: if someone's behaviors make you uncomfortable, they are highly likely to be not appropriate. However, I was too timid to stand out until when I confirmed that individual's behavoirs on a few other scientists younger than me, then I decided to stand out for them. As a result, no means no, no matter in what environment and regardless of your gender/race/age. If you are in the United States, cite Title IX.

Oct 2019 --- Apr 2020: Direct imaging of a protoplanetary disk system (Wang, Ginzburg, Ren et al. 2020; AJ, arxiv, ADS).

• Technical highlight: I modeled the PDS 70 disk to reveal the planet c (while ignoring the contribution from c) using the DebrisDiskFM framework constructed here.

• Scientific highlight: we imaged the PDS 70 system in Keck/NIRC2 L'-band, and performed an astrometric and spectral analysis for the two planets. See Keck, NSF, etc. webpages.

Jun 2019 --- Jan 2020: Method study on extracting circumstellar signals using data imputation (ApJ, arXiv, ADS).

• Technical highlight: I developed a method for signal extraction, sequential Non-negative Matrix Factorization for the data imputation (DI-sNMF). Mathematically, this reaches a least-biased capture of star light, and thus enables robust circumstellar structure recovery for both planets and disks.

• Scientific highlight: for the HR 4796A debris disk, the first marginal evidence that dust scatters light along forward direction more when wavelength increases.

• DI-sNMF Python code: GitHub link.

Sep 2015 --- May 2019: Modeling of the circumstellar disks using the MCFOST software (HD 191089, ApJ, arXiv, ADS).

• Technical highlight: I used probability integral transform to prove that current simple dust models are unable to consistently produce observations at different wavelengths.

• Scientific highlight: the closest Kuiper Belt sibling was found. See NASA Astrobiology webpage, SciTechDaily webpage, CosmicDiary post, and the SETI institute tweet.

Sep 2017 --- Mar 2018: Quantification of the rotation of spiral arms around a star (MWC 758, ApJL, arXiv, ADS).

• Technical highlight: I generalized the ordinary least square approach with dummy variables, by taking into account of the input uncertainty.

• Scientific highlight: our measurement is consistent with theoretical prediction, that the spiral arms are driven by a hidden planet! See this featured image in AAS Nova.

• Explanation for the equation of the minimum stellocentrc distance: link (pdf).

Jun 2016 --- Dec 2017: Implementation of Non-negative Matrix Factorization (NMF) for the extraction of circumstellar disk images (ApJ, arXiv, ADS).

• NMF Python code: GitHub link.

• Technical highlight: I mathematically proved that the iteration of NMF will result into a stable construction of the components.

• Scientific highlight: our simulation demonstrates that NMF is able to better detect and preserve the light scattered by circumstellar disks.

Dec 2015 --- May 2016: Sub-pixel Dithering Strategy for STIS/BAR5 Occulter. Contrast curve calculation, performance analysis with the sub-pixel dither strategy (Debes, Ren & Schneider, 2019; JATIS, arXiv, ADS) and SPIE paper (arXiv, ADS). See also HST/STIS BAR5 imaging webpage.

• Technical highlight: I demonstrated that 3-by-3 sub-pixel dithering is able to perform using HST/STIS, and this strategy can detect 2x fainter planets.

• Scientific highlight: this is demonstrating the 25-year-old Hubble is competitive with the best ground-based telescopes in terms of point source contrast (STScI Newsletter link).

Dec 2014 --- Sept 2015: Direct imaging of exoplanetary disks using the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST), with the Extrasolar Planetary Systems Imaging Group in the Space Telescope Science Institute (STScI). SPIE paper (arXiv, ADS).

• Notes on KLIP/PCA: Principal Component Analysis. Center Determination based on Radon Transform (Pueyo et al. 2015; Improved code available).

• Technical highlight: we processed the whole HST/STIS proved using KLIP/PCA.

• Scientific highlight: a systematically reduction of the archive will lead to a systematic analysis of all the STIS circumstellar disks, which will contribute to the questions of what are their current status, where do they come from, and what will they evolve to, etc.

1. XiamenU Research (until 2014)

1. Astrophysics: Analyzed the XMM-Newton spectrum of Mkn 501 (ApJ, arXiv, ADS).

• First detection of a Galactic O VII absorption feature along the sightline.

• Marginal detection of an intergalactic O VII absorption in the Hercules Supercluster.

---  Senior Thesis