I am a postdoc researcher at the Johns Hopkins Univerisity (JHU) and now visiting the École Normale Supérieure, Paris (ENS). I just got my Ph.D. in astrophysics this summer at JHU. I love physics, math, philosophy, classical music, kendo, and anime.

Research

I am interested in using statistical analysis to understand our Universe. My interests range from observational cosmology to stellar physics and planets. My work led to the discovery of special stars that shine out of gravitational sedimentation and the cosmological applications of a new statistic that borrows ideas from convolutional neural networks.

How to quantify fields or textures?

Textures and patterns are ubiquitous in astronomical data but challenging to quantify. The scattering transform provides a new powerful statistic for these features. It borrows ideas from convolutional neural nets (CNNs), but shares advantages of traditional statistics. In my recent papers ([1], [2], [3]), I discussed in depth how to intuitively understand this new statistic which is unfamiliar to most physicists, and I showed that on weak lensing mass maps it outperforms classic statistics and is on a par with CNNs. The first paper won an award of astrostatistics and was reported by this astrobites blog.

To advocate the use of the scattering transform, I also wrote a publicly available module ST.py based on pytorch, which can implement 1D and 2D scattering transform in a fast and transparent way.

Discoveries about white dwarfs from Gaia satellite

I also work on white dwarfs, the destiny of most stars in the universe. Using data from the Gaia space mission, I discovered a new population of white dwarfs that cool extremely slowly and some others that are merger products. My work has led to two papers (click the figures below), one of which was highlighted by astrobites and AAS Nova and considered a major discovery in Gaia data.

To make white dwarf research easier, I also built a publically available package WD_models in python for transformation between white dwarf photometry and physical properties.

Spectra of meteors

In high school, my twin brother (who is studying philosophy now) and I found an efficient way to take spectra of meteors with digital camera. We designed a prism device that can screw in front of a lens. We ordered several from a factory, and sold them to other amateurs of astronomy. Shown below is one spectrum of the Geminid meteor shower, taken in 2010. We have made a new batch of such prism devices with a cost of less than 200 dollars each. If you are interested, please contact us or buy it here!

C.V.

École Normale Supérieure, Paris

The Centre for Sciences of Data
2021- now, visiting fellow
Advisor: Prof. Stéphane Mallat

Johns Hopkins University

Department of Physics and Astronomy
2021- now, postdoc fellow
2017-2021, M.A., Ph.D. (Thesis)
Advisor: Prof. Brice Ménard

Peking University (北京大学)

Department of Astronomy
2012-2016, B.S.
Advisor: Prof. Eric Peng (彭逸西)

Publications

First author:

Cheng, S. & Ménard, B., How to quantify fields and textures? A guide to the scattering transoform, 2021, arXiv:2112.01288

Cheng, S. & Ménard, B., Weak lensing scattering transform: dark energy and neutrino mass sensitivity, 2021, MNRAS, 507, 1012

Cheng, S., Ting, Y.-S., Ménard, B., & Bruna, J., A new approach to observational cosmology using the scattering transform, 2020, MNRAS, 499, 5902

Cheng, S., Cummings, J. D., Ménard, B., & Toonen, S., Double White Dwarf Merger Products among High-mass White Dwarfs, 2020, ApJ, 891, 160

Cheng, S., Two delays in white dwarf evolution revealed by Gaia, 2019, Proceedings of IAU, 15(S357), 175

Cheng, S., Cummings, J. D., Ménard, B., A Cooling Anomaly of High-mass White Dwarfs, 2019, ApJ, 886, 100

Cheng, S., Cheng, S., Meteor spectral observation with DSLR, normal lens and prism, 2011, JIMO, 39, 39

Others:

Camisassa, M., et al., Forever young white dwarfs: when stellar ageing stops, 2021, A&A Letters, 649, 7

Lu, C. X., Schlaufman, K. C., Cheng, S., An Increase in Small-planet Occurrence with Metallicity for Late-type Dwarf Stars in the Kepler Field and Its Implications for Planet Formation, 2020, AJ, 160, 253

Bauer, E. B., Schwab, J., Bildsten, L., and Cheng, S., Multi-Gigayear White Dwarf Cooling Delays from Clustering-Enhanced Gravitational Sedimentation, 2020, ApJ, 902, 93

Chandra, V., Hwang, H.-C., Zakamska, N. L., Cheng, S., A Gravitational Redshift Measurement of the White Dwarf Mass–Radius Relation, 2020, ApJ, 899, 146

Marigo, P., Cummings, J. D., et al., Carbon star formation as seen through the non-monotonic initial–final mass relation, 2020, Nature Astronomy, full text here

Contacts

s.cheng@jhu.edu
+1 443 207 1532
Bloomberg 506
3400 N. Charles St., Johns Hopkins University
Baltimore, MD21218, USA

Sky Altas (Aladin)