Over 20 years ago Valenti & Piskunov developed the stellar spectral synthesis library Spectroscopy Made Easy (SME) [8,11] to simplify stellar spectral analysis, and it has been used in hundreds of works since.

PySME is a new Python frontend to the same library, developed with the same goal in mind: Making spectroscopy easier for everyone.

PySME creates accurate, high-resolution synthetic spectra, based on a range of stellar parameters, a linelist and a model atmosphere. It can also be used the other way around. Give PySME an observation and it will determine the best fit stellar parameters for that spectrum.

This is also useful for Exoplanet research. It is important to understand the host star, to properly understand the workings of the orbiting planet.

Fast and Reliable

PySME uses the latest version of the spectral synthesis code that incorporates 20 years of development

Open Source

PySME (and all its components) are completely open source

Easy to Use

PySME comes with a custom GUI to make inspecting your spectra easy

Example: The Sun

Here we display the capabilities of PySME on a small sample of the solar spectrum. For this we used a VALD linelist as input, set the abundances to solar abundances of Asplund 2009, and started with solar temperature and surface gravity.

To illustrate the difference between LTE and non-LTE calculations both are shown in this plot. Non-LTE calculations are performed for Ca, Mn, and Si. Notice that the Non-LTE Ca line is much deeper than the LTE calculation.


A section of the input image from the X-shooter instrument at the VLT. Red lines mark the position of spectral lines. Credit: Data from VLT/X-Shooter

PyReduce - A Data Reduction Pipeline for Echelle Spectrographs

PyReduce is the new and improved version of REDUCE, now rewritten in Python. it creates wavelength calibrated and continuum normalized 1D spectra, based on raw observation images from various instruments. From high resolution instruments like HARPS, to low resolution observations with the JWST. This makes it the perfect companion tool to SME. Reduce your observations with PyREDUCE then analyse them with PySME.


[1] Asplund, Martin, Nicolas Grevesse, A. Jacques Sauval, and Pat Scott. 2009. “The Chemical Composition of the Sun.” Annual Review of Astronomy and Astrophysics 47 (1): 481–522.

[2] Buder, Sven, Martin Asplund, Ly Duong, Janez Kos, Karin Lind, Melissa K. Ness, Sanjib Sharma, et al. 2018. “The GALAH Survey: second data release.” Monthly Notices of the RAS 478 (4): 4513–52.

[3] Gustafsson, B., B. Edvardsson, K. Eriksson, U. G. Jørgensen,. Nordlund, and B. Plez. 2008. “A grid of MARCS model atmospheres for late-type stars. I. Methods and general properties.” Astronomy and Astrophysics 486 (3): 951–70.

[4] Kupka, F. G., T. A. Ryabchikova, N. E. Piskunov, H. C. Stempels, and W. W. Weiss. 2000. “VALD-2 – the New Vienna Atomic Line Database.” Baltic Astronomy 9 (January): 590–94.

[5] Kupka, F., N. Piskunov, T. A. Ryabchikova, H. C. Stempels, and W. W. Weiss. 1999. “VALD-2: Progress of the Vienna Atomic Line Data Base.” Astronomy and Astrophysics, Supplement 138 (July): 119–33.

[6] Loss, RD. 2003. “Atomic Weights of the Elements 2001 (Iupac Technical Report).” Pure and Applied Chemistry 75 (8). De Gruyter: 1107–22.

[7] Piskunov, N. E., F. Kupka, T. A. Ryabchikova, W. W. Weiss, and C. S. Jeffery. 1995. “VALD: The Vienna Atomic Line Data Base.” Astronomy and Astrophysics, Supplement 112 (September): 525.

[8] Piskunov, Nikolai, and Jeff A. Valenti. 2017. “Spectroscopy Made Easy: Evolution.” Astronomy and Astrophysics 597 (January): A16.

[9] Ryabchikova, T. A., N. E. Piskunov, F. Kupka, and W. W. Weiss. 1997. “The Vienna Atomic Line Database : Present State and Future Development.” Baltic Astronomy 6 (March): 244–47.

[10] Ryabchikova, T., N. Piskunov, R. L. Kurucz, H. C. Stempels, U. Heiter, Yu Pakhomov, and P. S. Barklem. 2015. “A major upgrade of the VALD database.” Physica Scripta 90 (5): 054005.

[11] Valenti, J. A., and N. Piskunov. 1996. “Spectroscopy made easy: A new tool for fitting observations with synthetic spectra.” Astronomy and Astrophysics, Supplement 118 (September): 595–603.