Mission Statement
Use and develop Statistics-, Mathematics-, and Instrumentation-Led approaches to understand Extrasolar/extragalactic Systems (SMILES) at high contrast.
Vision Statement
Find and Characterize Earth 2.0 with SMILES.
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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
4. OCA/IPAG Research (2022 Apr - 2025 May)
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...
Jun 2023 --- May 2025, I am an European Fellow funded by the Marie S.-Cuire Actions (MSCA).
Mar 2023 --- Mar 2025 (expected): I am leading the exploration of the inner working angle limit for Hubble Space Telescope's STIS coroangraph (HST GO-17135).
Technical highlight: demonstration of the reduction of inner working angle in HST/STIS coronagraphic imaging.
Scientific highlight: imaging towards ~0.1 arcsec, a region previous behind the coronagraph.
Stay tuned.
Jan 2022 --- Jan 2024: first application of the Hubble Space Telescope's STIS coroangraph on extragalactic studies (HST GO-16715; Ren et al. 2024). See more on the Coronagraphic Quasar Imaging page.
Technical highlight: (1) Demonstration of coronagraphic imaging from HST/STIS using the iconic quasar 3C 273. (2) Two-dimensional dummy variables for motion calculation and offset calibration. (3) Full procedure for STIS coronagraph usage for future users. (4) Obtained STIS imaging long-term rotation over the course of two decades.
Scientific highlight: Reavealed host galaxy image for 3C 273 down to ~0.2 arcsec.
Other: When I started as a postdoc in Caltech in 2019, the office of Marteen Schmidt – who identified 3C 273 as the first quasar in history – was assigned to me. While I was planning to show off this image to him, he passed away a few months after me arriving at France. However, this sense of connection in space-time encourages me to keep moving forward and explore the unknown!
Oct 2021 --- Jul 2023: planet-forming disks imaging with VLT/SPHERE (Ren et al., 2023). See this ADS entry for a presentation in an ESO conference for some intemediate results.
Technical highlight: Data imputation, a concept that I started developing since 2018 summer (Ren et al. 2020), finds its perfect application to star hopping observations of SPHERE.
Scientific highlight: (1) Planet-forming disks in total intensity. (2) Polarization fraction. (3) Trends, etc.
Highlighted as a Cover Photo for A&A's Volume 680: volume link, or A&A's tweet, or the photo below.
3. Caltech Research (2019 Oct - 2022 Mar)
3. Caltech Research (2019 Oct - 2022 Mar)
Sept 2021 --- Jul 2022: Planet imaging for Vega using Keck/NIRC2 in Ms-band (Ren et al. 2023a; A&A, arXiv, ADS).
Technical highlight: for the phoeometric stars, we used a combination of direct imaging and radial velocity to determine the detectability of substellar companions.
Scientific highlight: (1) with nearly an order of magnitude better in imaging companions than existing studies (in terms of mass), yet still no planets. (2) Keck is unparalleled at close-in regions (better than JWST!), so one should use JWST for the >20 au regions around Vega.
Fun fact: Vega is Zhinü 织女 (weaver girl) in Chinese. Zhinü the weaver girl is a goddess in the Chinese (east Asian) mythology The Cowherd and the Weaver Girl, which can be traced back to more than 2600+ years before and it is one of the four great folktales in the ancient Chinese culture. Zhinü (Vega) the godess and Niulang (Altair) the cowherd love each other, but their love was forbidden and they were separated by the Heavenly River (Milky Way). They can only reunite on every July 7th in the Chinese Lunar Canlender, through a bridge formed by a flock of magpies. July the 7th (in Chinese Lunar Canlendar) is the Qixi Festival, now recognized by the young as the most romantic and modern Valentine's Day in China.
Left: painting at Yiheyuan (Summer Palace) in Beijing on the mythology between Niulang and Zhinü. Source: link.
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.
Nov 2019 --- Jul 2020: Formation mechanism of spiral arms in protoplanetary disks (Ren et al. 2020; ApJL, arXiv, ADS). See AAS Nova feature here.
Technical highlight: I tested the formation mechanism of the MWC 758 spiral arms using a precise measurement of their rotation pattern speeds.
Scientific highlight: our measurement rules out one leading formation mechanism -- gravitational instability -- for the first time, which in turn supports the hypothesis that a hidden planet is responsbile for driving the spirals. We also observe shadowing effects at a global scale.
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.
2. Johns Hopkins / STScI Research (2014 Sept -2019 May)
2. Johns Hopkins / STScI Research (2014 Sept -2019 May)
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.
Sep 2014 --- Dec 2014: Direct imaging of exoplanets apprentice. Use the data of Near Infrared Camera and Multi-Object Spectrometer (NICMOS) onboard the Hubble Space Telescope (HST), with the Extrasolar Planetary Systems Imaging Group in the Space Telescope Science Institute (STScI).
Double checked the results of my implementation of the KLIP algorithm on HR8799 and HD202917, against the pipeline developed by STScI post-doctoral fellow Dr. Elodie Choquet.
Related papers: ADS Library.
2. Computational Biophysics: Simulated the process of HIV infection using a 3-dimensional lattice model (Physica A, ADS).
Scientific highlight: we modeled the HIV infection procedure with a 3D cellular automata, which provided a mathematically solid background for HIV infection.
--- Group Member
3. Image Processing: Detected the defects in LED chips using OpenCV with C++ (Collaborator: G-First OEIC CO., Ltd. Xiamen, Fujian, China). I managed a group of three undergraduate students, communicated with our collaborator, then distributed tasks to us. We three are able to not only increase the chip detection time for a 500 Megapixel image from ~15s to 0.3s, but also
Technical highlight: I found and implemented an algorithm to binarize LED chip images, this increased the efficiency by a factor of ~10.
--- Group Leader
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