I am glad to introduce the latest version of iSpec, available for download at the v2023.08.04 release page. This update brings some small new features, compatibility improvements, and bug fixes. Here’s a detailed breakdown of what's new:


  • Doyle et al. (2014) Vmac Relation for Dwarfs: This implementation complements the already existing one based on the Gaia-ESO Survey.
  • Enhanced ESO Spectra Support: We've added new flux and wavelength keys for ESO spectra FITS files.
  • Disable SME for Apple Silicon: To avoid confusion and errors, SME will be disabled when the GUI is used on Macs with Apple Silicon chips (M1/M2).

Compatibility Updates:

  • Python Package Alignments: We've ceased the use of the deprecated np.int in favor of the builtin int.
  • Matplotlib adaptations: We've adjusted to how the latest versions of matplotlib manage line removals.
  • Cython & gfortran compatibility: The code has been updated for seamless integration with the latest versions of Cython (3.0) and gfortran (12.2).

Bug Fixes:

  • Resolved an issue where the "correct velocity" function modified the input spectrum.
  • Addressed the complication of fitting loggf and abundances simultaneously.
  • Streamlined the "create_filter_cosmic_ray" function by removing an unused parameter.
  • Addressed the MOOG compilation failure in Mac due to BSD sed.
  • Rectified the GUI's inability to properly run and synthesize spectra from a different directory.
  • Ensured the GUI fit continuum doesn't ignore the resolution parameter.

Stay updated with the latest enhancements by downloading the new version!

We are happy to announce the online PhD School "Stellar Spectroscopy and Astrophysical parameterization", Sept. 21-23, 2021, in the framework of the EU COST action MW-Gaia.

The Gaia mission is revolutionizing Galactic astrophysics in many ways and, although this is not generally perceived, Gaia is also a formidable spectroscopy machine. However, the best results are obtained by combining Gaia abilities and ground based high resolution spectroscopy. Advantages and limitations must be understood for a better synergy.

The school will discuss the derivation of stellar parameters from spectroscopy and large survey pipelines using classical, high precision and data driven methods. Tutorial sessions are foreseen. The final lecture will be on publication skills. Space for participants to present their research is granted, either as poster or oral presentation.

All sessions will be on-line. Registration is free of charge, but participant number will be limited. Dead-line for registration and abstract submission: Sept. 5th, 2021

The main subjects and the speakers are:

  • Large spectroscopic surveys: Angela Bragaglia (INAF-Bologna), Elena Pancino (INAF-Arcetri), Antonella Vallenari (INAF-Padova)
  • "Classical" spectroscopic analysis (equivalent widths, spectral synthesis, differential spectroscopy): Jorge Melendez (Univ. São Paulo), Chris Sneden (Univ. of Texas, Austin), Maria Tsantaki (INAF-Arcetri), Sergi Blanco-Cuaresma (Harvard-Smithsonian CfA)
  • Data driven methods: advantages and limitations René Andrae (MPIA), Alejandra Recio-Blanco (OCA), Lorenzo Spina (INAF-Padova)
  • Publication skills: Chris Sneden (Univ. of Texas, Austin)

More information at the web site:


Registration is now open!

iSpec now exclusively uses Python 3 (previous versions of Python were deprecated on January 1st 2020). The v2020.10.01 release does not remove or modify any of iSpec functionalities. It should be completely compatible with user written scripts as far as they are converted to Python 3.

In addition, most radiative transfer codes were updated, as well as the external Equivalent Width measurement tool (ARES), and the Gaia-ESO linelist version 6 was added. Regarding the input file, pre-computed grids were re-computed using the latest radiative transfer code versions, and line selections were re-done for a resolution of 47,000.


  • Python 3
  • Updated SPECTRUM to v2.77
  • Updated Turbospectrum to v19.1
  • Updated MOOG to November 2019 version
  • Updated SME to v574
  • Updated ARES to June 28th 2020 commit
  • Added Gaia-ESO linelist v6

Multiple codes are available to derive atmospheric parameters and individual chemical abundances from high-resolution spectra of AFGKM stars. Almost every spectroscopist has its own preferences regarding which code and method to use. But intrinsic differences between codes and methods lead to complex systematics that depend on multiple variables such as the selected spectral regions and the radiative transfer code used. I expanded iSpec, the popular open source spectroscopic tool, to support the most known radiative transfer codes and I assessed their similarities and biases when using multiple setups based on the equivalent width method and the synthetic spectral fitting technique (interpolating from a pre-computed grid of spectra or synthesizing with interpolated model atmospheres). This work shows that systematics on atmospheric parameter and abundances between most of the codes can be reduced when using the same method and a careful spectral feature selection is executed, but it may not be possible to ignore the remaining differences depending on what is the scientific case and the required precision. Regarding methods, equivalent width-based and spectrum fitting-analyses exhibit large differences that emerge due to their intrinsic differences, which is relevant given the popularity of these two methods. The results help us identify the key caveats of modern spectroscopy that any scientist should be aware of before trusting its own results or being tempted to combine atmospheric parameters and abundances from the literature.

Access to the article preprint and the ADS record.

The University of Wroclaw (Poland) is pleased to announce the international summer school "Spectroscopic data analysis with iSpec". That will take place in Wroclaw, Poland between 26 and 29 June 2018.

The aim of this school is to give participants a thorough introduction into the treatment and analysis of stellar spectra, including deriving the atmospheric parameters and the chemical abundances. The tool which will be used for this purpose is the code iSpec.

iSpec is a tool for the treatment and analysis of stellar spectra. Some of the main functionalities for spectra treatment and library creation that are integrated into iSpec are the following: cosmic rays removal, continuum normalization, resolution degradation, radial velocity determination and correction, telluric lines identification, re-sampling. iSpec is also capable of determining atmospheric parameters (i.e effective temperature, surface gravity, metallicity, micro/macroturbulence, rotation) and individual chemical abundances for FGKM stars by using two different approaches: synthetic spectra fitting technique or equivalent widths method. iSpec integrates MARCS and ATLAS model atmospheres together with the following radial transfer codes: SPECTRUM (R. O. Gray), Turbospectrum (Bertrand Plez), SME (Valenti & Piskunov), MOOG (Chris Sneden), and Synthe/WIDTH9 (Kurucz/Atmos). The user-friendly interface is perfect for learning and testing. However, to take advantage of the full potential, iSpec can be used from Python. This is the recommended way to use iSpec for complex scientific studies, it ensures reproducibility and give access to a wider range of functionalities and options.

The participants of the school "Spectroscopic data analysis with iSpec" will be given introductory lectures to iSpec and some hands-on experience with determination of the atmospheric parameters of A, F, G, K, and M type stars. The exercises will be based on publicly available stellar spectra as well as on pre-computed synthetic spectra.