About Me

I'm a Postdoctoral fellow at Max-Planck Institute for Astronomy (MPIA, Heidelberg). My current research is mostly oriented towards understanding star clusters in galaxies, and primarily focusing on low-mass clusters to eventually constrain the dissolution theory of star clusters. However, I also contribute to many data modeling, especially using probabilistic inferences in astronomy but also other domains of physics.

My current main project is the construction of Gaia hyrid catalogs, a project that will combine all ancillary data with the most up to date Gaia measurements to infer the most precise information of objects in the Gaia Mission Survey and ultimately the to understand our own galaxy.

Recent Selected Research

A small selection of current projects and research.

Star Cluster in Stochastic Regime

The vast majority of clusters in the Universe are small, and it is well known that the integrated fluxes and colors of all but the most massive ones have broad probability distributions, owing to small numbers of bright stars.

Systematics and errors arising from the use of standard analysis methods, which are based on continuous population synthesis models are large. Systematic errors on ages and random errors on masses are large, while systematic errors on masses tend to be smaller.

Star Cluster Populations: Age and Mass Functions

Using the probabilistic technique from Fouesneau, M., Lançon, A., 2010, we derived ages, masses and extinction values of star clusters in the PHAT survey (Johnson et al., 2015).

We find that the cluster age distribution is consistent with being uniform over the past 100 Myr, which suggests a weak effect of cluster disruption within M31.

Fouesneau et al., 2014

We find that the mass distribution of the whole sample can be well-described by a single power-law with a spectral index of −1.9 ± 0.1 However, we find that the present day mass spectral index varies significantly with environment with the shallower slope in the highest star formation intensity regions.

Fouesneau et al., 2014

We currently work on infering the disruption processes and initial mass function with respect to environment and star formation intensity in M31

Dissolution of Star Clusters, Formation Histories and Mass Functions

(Coming soon)

We currently work on infering the disruption processes and initial mass function with respect to environment and star formation intensity in M31 from the PHAT survey.


A small selection of scientific codes


PyPegase is a stellar population synthesis suite in python that aims at generating integrated spectra of discrete populations. It may be easily used by anyone, familiar or not with spectral evolution questions. Further improvements will also be available as PEGASE is still under active development.

This code upgrades the latest version of the spectro-photometric model of galaxy evolution PEGASE.2 (Fioc and Rocca-Volmerange 1997) with a new initial mass function considerations which explicitly account for stochastic fluctuations due to finite and small number of stars in populations of stellar cluster scales.

The code sources, including input data, and stellar libraries are currently available on demand .


(Under construction)

the Bayesian Extinction and Stellar Tool (BEAST) is a probabilistic approach to infering stellar parameters and line of sight attenuation from the dust attenuated photometric spectral energy distribution of an individual star, which accounts for observational uncertainties common to large resolved star surveys. Specifically, the inference model accounts for measurement uncertainties and any correlation between them due to photon noise, stellar crowding (systematic biases and uncertainties in the bias), and absolute flux calibration.

Various Python Tools

(check github for more) All codes should work with python 2.6+ and 3.


Fast algorithms to do statistics
This package is my current exploration on how to make fast statistics on big data. Functions are typically several orders of magnitude faster, or so they claim.


direct interface to the PADOVA/PARSEC isochrone webpage It compiles the URL needed to query the website and retrives the data into a python table variable easy to manipulate.
Works with all their available models.


SAMPy Client package providing a very small VO interactivity using the SAMP protocol. This allows anyone to easily send and receive data to VO applications such as Aladin, Topcat or DS9.


make python parallel mapping even simpler Everything goes through the same command: map! which also includes a progress indicator.


No-U-Turn Sampler (NUTS) as in Hoffman and Gelman, (2011)

Differential Evolution

Differential evolution optimization method by Storn and Price (1997)


Bayesian Generalized Lomb-Scargle periodogram as in described in Mortier et al. (2014).

MPL contour add-on

a low-level contour computation for Matplotlib that could give me the polygones without the need to make an actual figure and extract the curves from the contour object.

Selected Publications

ADS search arXiv search

(updated: Aug 12 2015)
  • The High-mass Stellar Initial Mass Function in M31 Clusters
    Weisz, D. R., Johnson, L. C., Foreman-Mackey, D., Dolphin, A. E., Beerman, L. C., Williams, B. F., Dalcanton, J. J., Rix, H.-W., Hogg, D. W., Fouesneau, M., Johnson, B. D., Bell, E. F., Boyer, M. L., Gouliermis, D., Guhathakurta, P., Kalirai, J. S., Lewis, A. R., Seth, A. C., Skillman, E. D., 2015, The Astrophysical Journal, 806, 198 [1 citations]
  • A Global Star-forming Episode in M31 2-4 Gyr Ago
    Williams, B. F., Dalcanton, J. J., Dolphin, A. E., Weisz, D. R., Lewis, A. R., Lang, D., Bell, E. F., Boyer, M., Fouesneau, M., Gilbert, K. M., Monachesi, A., Skillman, E., 2015, The Astrophysical Journal, 806, 48 [3 citations]
  • The Panchromatic Hubble Andromeda Treasury. XI. The Spatially Resolved Recent Star Formation History of M31
    Lewis, A. R., Dolphin, A. E., Dalcanton, J. J., Weisz, D. R., Williams, B. F., Bell, E. F., Seth, A. C., Simones, J. E., Skillman, E. D., Choi, Y., Fouesneau, M., Guhathakurta, P., Johnson, L. C., Kalirai, J. S., Leroy, A. K., Monachesi, A., Rix, H.-W., Schruba, A., 2015, The Astrophysical Journal, 805, 183 [5 citations]
  • PHAT Stellar Cluster Survey. II. Andromeda Project Cluster Catalog
    Johnson, L. C., Seth, A. C., Dalcanton, J. J., Wallace, M. L., Simpson, R. J., Lintott, C. J., Kapadia, A., Skillman, E. D., Caldwell, N., Fouesneau, M., Weisz, D. R., Williams, B. F., Beerman, L. C., Gouliermis, D. A., Sarajedini, A., 2015, The Astrophysical Journal, 802, 127 [1 citations]
  • The Survey of Lines in M31 (SLIM): Investigating the Origins of [C II] Emission
    Kapala, M. J., Sandstrom, K., Groves, B., Croxall, K., Kreckel, K., Dalcanton, J., Leroy, A., Schinnerer, E., Walter, F., Fouesneau, M., 2015, The Astrophysical Journal, 798, 24 [3 citations]
  • The Supernova Progenitor Mass Distributions of M31 and M33: Further Evidence for an Upper Mass Limit
    Jennings, Z. G., Williams, B. F., Murphy, J. W., Dalcanton, J. J., Gilbert, K. M., Dolphin, A. E., Weisz, D. R., Fouesneau, M., 2014, The Astrophysical Journal, 795, 170 [4 citations]
  • Panchromatic Hubble Andromeda Treasury. IX. A Photometric Survey of Planetary Nebulae in M31
    Veyette, M. J., Williams, B. F., Dalcanton, J. J., Balick, B., Caldwell, N., Fouesneau, M., Girardi, L., Gordon, K. D., Kalirai, J., Rosenfield, P., Seth, A. C., 2014, The Astrophysical Journal, 792, 121 [3 citations]
  • The age distribution of stellar clusters in M83
    Silva-Villa, E., Adamo, A., Bastian, N., Fouesneau, M., Zackrisson, E., 2014, Monthly Notices of the Royal Astronomical Society, 440, L116 [9 citations]
  • The Panchromatic Hubble Andromeda Treasury. V. Ages and Masses of the Year 1 Stellar Clusters
    Fouesneau, M., Johnson, L. C., Weisz, D. R., Dalcanton, J. J., Bell, E. F., Bianchi, L., Caldwell, N., Gouliermis, D. A., Guhathakurta, P., Kalirai, J., Larsen, S. S., Rix, H.-W., Seth, A. C., Skillman, E. D., Williams, B. F., 2014, The Astrophysical Journal, 786, 117 [10 citations]
  • The Panchromatic Hubble Andromeda Treasury. VII. The Steep Mid-ultraviolet to Near-infrared Extinction Curve in the Central 200 pc of the M31 Bulge
    Dong, H., Li, Z., Wang, Q. D., Lauer, T. R., Olsen, K., Saha, A., Dalcanton, J., Gordon, K., Fouesneau, M., Bell, E., Bianchi, L., 2014, The Astrophysical Journal, 785, 136 [7 citations]
  • The Panchromatic Hubble Andromeda Treasury. IV. A Probabilistic Approach to Inferring the High-mass Stellar Initial Mass Function and Other Power-law Functions
    Weisz, D. R., Fouesneau, M., Hogg, D. W., Rix, H.-W., Dolphin, A. E., Dalcanton, J. J., Foreman-Mackey, D. T., Lang, D., Johnson, L. C., Beerman, L. C., Bell, E. F., Gordon, K. D., Gouliermis, D., Kalirai, J. S., Skillman, E. D., Williams, B. F., 2013, The Astrophysical Journal, 762, 123 [17 citations]
  • Supernova Remnant Progenitor Masses in M31
    Jennings, Z. G., Williams, B. F., Murphy, J. W., Dalcanton, J. J., Gilbert, K. M., Dolphin, A. E., Fouesneau, M., Weisz, D. R., 2012, The Astrophysical Journal, 761, 26 [12 citations]
  • The Panchromatic Hubble Andromeda Treasury. III. Measuring Ages and Masses of Partially Resolved Stellar Clusters
    Beerman, L. C., Johnson, L. C., Fouesneau, M., Dalcanton, J. J., Weisz, D. R., Seth, A. C., Williams, B. F., Bell, E. F., Bianchi, L. C., Caldwell, N., Dolphin, A. E., Gouliermis, D. A., Kalirai, J. S., Larsen, S. S., Melbourne, J. L., Rix, H.-W., Skillman, E. D., 2012, The Astrophysical Journal, 760, 104 [7 citations]
  • PHAT Stellar Cluster Survey. I. Year 1 Catalog and Integrated Photometry
    Johnson, L. C., Seth, A. C., Dalcanton, J. J., Caldwell, N., Fouesneau, M., Gouliermis, D. A., Hodge, P. W., Larsen, S. S., Olsen, K. A. G., San Roman, I., Sarajedini, A., Weisz, D. R., Williams, B. F., Beerman, L. C., Bianchi, L., Dolphin, A. E., Girardi, L., Guhathakurta, P., Kalirai, J., Lang, D., Monachesi, A., Nanda, S., Rix, H.-W., Skillman, E. D., 2012, The Astrophysical Journal, 752, 95 [24 citations]
  • The ACS Nearby Galaxy Survey Treasury. X. Quantifying the Star Cluster Formation Efficiency of nearby Dwarf Galaxies
    Cook, D. O., Seth, A. C., Dale, D. A., Johnson, L. C., Weisz, D. R., Fouesneau, M., Olsen, K. A. G., Engelbracht, C. W., Dalcanton, J. J., 2012, The Astrophysical Journal, 751, 100 [20 citations]
  • Analyzing Star Cluster Populations with Stochastic Models: The Hubble Space Telescope/Wide Field Camera 3 Sample of Clusters in M83
    Fouesneau, M., Lançon, A., Chandar, R., Whitmore, B. C., 2012, The Astrophysical Journal, 750, 60 [25 citations]
  • Spectroscopic constraints on the form of the stellar cluster mass function
    Bastian, N., Konstantopoulos, I. S., Trancho, G., Weisz, D. R., Larsen, S. S., Fouesneau, M., Kaschinski, C. B., Gieles, M., 2012, Astronomy and Astrophysics, 541, A25 [8 citations]
  • Accounting for stochastic fluctuations when analysing the integrated light of star clusters. I. First systematics
    Fouesneau, M., Lançon, A., 2010, Astronomy and Astrophysics, 521, A22 [58 citations]
  • Automatic detection and tracking of filaments for a solar feature database
    Aboudarham, J., Scholl, I., Fuller, N., Fouesneau, M., Galametz, M., Gonon, F., Maire, A., Leroy, Y., 2008, Annales Geophysicae, 26, 243 [7 citations]
2014 - present Postdoctoral at Max-Planck Institute for Astronomy (Heidelberg, Germany)
Gaia enabling science products - Hybrid catalogs / CU8 Validation
2011 - 2014 Postdoctoral at University of Washington (Seattle, WA)
The Panchromatic Hubble Andromeda Treasury (PHAT)
2007 - 2011 Ph.D. in Astronomy at University of Strasbourg (Strasbourg, France)
”Study of stellar cluster populations in galaxies: a Bayesian approach” under the supervision of Ariane Lancon.
2006 - 2007 Master degree at University of Strasbourg (Strasbourg, France)
Compact objects and high energy, inverse methods, galactic evolution, and ”big data”.
2004 - 2007 Engineer degree (ENSPS/Superior and National School of Physics of Strasbourg)
Fundamental physics, signal processing, data processing and databases.
Main projects
Gaia Hybrid Catalogs
As part of the Gaia collaboration (DPAC-CU9), the hybrid catalog aim to provide specific catalogs of Gaia sources combined with other wavelengths and information available.
Automated detection of star cluster in surveys
Algorithm combining of photometric and velocity measurements with density profiles. (Fouesneau et al, in prep)
Star cluster disruption from the photometric end-point
Statistical modeling and measurement of cluster disruption effect on present day cluster populations. (Fouesneau et al, in prep)
Inferring Dust Distribution on 20pc scale from resolved stellar populations in M31
Statistical modeling and measurement of dust distribution from CMD fitting of resolved stars in M31 through PHAT survey. (Dalcanton et al, submitted)
Stellar object characterization from spectro-photometric measurements
Calibrating spectra with photometry in order to derive more reliable stellar parameters (Weisz et al, in prep)
Bayesian extinction and stellar parameters fitting code (BEAST)
Determination of stellar parameters and dust properties using individual stars (Gordon et al, in prep)
Other projects
Characterization of Nuclear Deformations with AGATA
Statistical analysis of gamma detections and probabilistic modeling of uncertainties. Collaboration with Damian Ralet (PhD student, GSI)
Cross-correlation of inhomogeneous catalogs
Combining catalogs using positions and spectro-photometric measurements, Collaboration with Dr. François-Xavier Pinot (CDS, Observatoire de Strasbourg)
Machine learning to detect artifacts in astronomical images
Detecting effect of charge-transfer efficiency and cosmic rays in Hubble images Collaboration with Ms. Martina Unutzer and Prof. Magdalena Balazinska (University of Washington) conference poster
Percolation in Carbon Nanotube Networks
Statistical analysis of Carbon Nanotube Networks in the percolation context. Collaboration with Yann Leroy (ICube). paper
Photometry and Temporal analysis in the IRAC-CF
Master project at Harvard Smithonian Center for Astrophysics (Cambridge, MA) Photometry and temporal analysis in the photometric campaign of the Spitzer’s IRAC dark calibration field (IRACCF). Collaboration with Matthew Ashby (CfA) and Joseph Hora (CfA).
Automation of synoptic maps construction of the solar activity
Detecting and tracking solar features (spots, filaments, faculae) using multiwavelength imaging. Collaboration with Dr. Isabelle Scholl (ISU) and Dr. Jean Aboudarham, (LESIA/Paris Observatory) 2008AnGeo..26..243A
Teaching & Outreach
"Introduction to Bayesian statistics"
Lectures to Master student level, introducting the basics of statistical analysis in the most pragmatic way (if possible). online materials
"Introduction to MCMC and Nested sampling"
Improvised Blackboard lecture during the Gaia Challenge in 2014, covering the basis of Bayesian statistics and sampling for model fitting
"Introduction to python and object oriented programming"
Part of a workshop introducing python to astronomers and in particular basics of object oriented programming for science applications online materials
"Python for Astronomers and Curious"
Workshop introducing python to engineers, scientists from the observatory and university online materials
"Introduction to data reduction"
lectures to master of astrophysics students Cheat Sheet - Slides (french)
"Spectra of Stars to Stellar evolution in Layman's term"
Public talk reviewing our knowledge of stellar physics based on observations
2014 GESF2014 - Marseille, France, September - "Relation between environment and star cluster formation and evolution"
2013 Aspen Center for Physics, June - "Observational constraints on star and cluster formation"
Strasbourg, France, March - "Uncertainties when inferring the stellar mass function"
STScI, Baltimore, BA, January - "Clues in Environmental influence in cluster disruption in PHAT"
AAS, Long Beach, CA, January - "Star Clusters in PHAT, Early Science Review", M31 Special Session
2012 Sesto, Italy, July - "Star Clusters Populations in M31"
MPIA, Heidelberg, Germany, July - "Clusters Disruption from early science in PHAT"
AAS, Austin, TX, January - "Characterizing Cluster Populations in a Stochastic Regime"
2011 Strasbourg, France, December - "PHAT an HST large survey of M31"
Strasbourg, France, March - "Python for Astronomers" tutorial
2010 STScI, Baltimore, BA, May - "Estimating Cluster Properties in a Stochastic Context"
2009 Stockholm, November - "Unresolved Star Clusters Properties"
Next Generation Virgo Cluster Survey (NGVS), Paris, France, October - "Star cluster ages and masses analysis"
Johnson City, TN, July - "Bayesian Approach for Star cluster property determinations"
AAS, Passadena, CA, May - "Infrared-variable Objects in the IRAC-CF"
KITP, Santa Barbara, CA, January - "Stochastic fluctuations in cluster property analysis"
2008 Sheffield, United Kingdom, July "Stochastic Population Synthesis"
Illkirch, France, April Stellar evolution in Layman’s term
Geneva, Switzerland, February Spectra of populations dominated by supergiants



Max-Planck-Institut für Astronomie
Königstuhl 17
D-69117 Heidelberg, Germany