DGalanDieguez

Software

SPAMMS

Spectroscopic PAtch Model for Massive Stars: spectral synthesis for stars that are not spheres.

Code on GitHub Papers using SPAMMS

What it does

Rapid rotation and binary interaction distort massive stars, so their temperature and gravity change across the surface and shape the spectrum we observe. One-dimensional models cannot capture this. SPAMMS describes the star as a 3D mesh of surface elements, each with its own local conditions, and adds up their light to produce the spectrum an observer would see.

SPAMMS was created by Michael Abdul-Masih (Abdul-Masih et al. 2020). I extended it with new LTE and non-LTE specific-intensity grids, so that it now covers O- to K-type stars instead of O stars only (Galán-Diéguez et al. 2026).

How it works

Four panels: a triangulated mesh of a contact binary; the same mesh coloured by temperature; spectra assigned to three surface elements; the integrated line profile.
The four stages of SPAMMS for an overcontact binary.
  1. Build the mesh. PHOEBE 2 generates a triangulated surface that follows the rotational or Roche distortion of the star or binary.
  2. Assign local physics. Each triangle gets its own effective temperature and surface gravity from the Roche model and a gravity-darkening law (von Zeipel or Espinosa Lara & Rieutord).
  3. Attach a spectrum. Each triangle receives the specific intensity for its conditions and viewing angle, taken from a grid of model atmospheres (FASTWIND, TLUSTY or Kurucz).
  4. Integrate. SPAMMS sums the visible surface, accounting for projected area, Doppler shift and limb darkening, to produce the line profile. Wind and photosphere can both contribute.

Because each element is Doppler-shifted individually, rotational broadening comes out of the geometry itself instead of being applied afterwards as a convolution. That reproduces asymmetric, inclination-dependent line shapes that a single v sin i parameter cannot.

Key applications

Rapid rotators

Roche geometry and gravity darkening for single stars, with rotational broadening computed from the surface itself.

Binary systems

Tidal distortion and mutual irradiation of both components, phase by phase along the orbit.

Transits

A planet crossing a rotating star and the Rossiter–McLaughlin distortion of the lines.

Examples

Animation: temperature map of the contact binary VFTS 352 and its helium lines changing over the orbit.
Overcontact binary VFTS 352. Top: surface temperature, with differences above 10 000 K. Bottom: He I and He II lines through the orbit. Both stars and the neck between them are modelled together.
Animation: a star rotating at 90% of critical, coloured by temperature, and its helium lines as the inclination changes.
A star at 90% of critical rotation. Top: hot poles, cool equator. Bottom: the He lines as inclination changes. Seen pole-on, He II strengthens and He I weakens; a spherical fit would overestimate the temperature.
Animation: a planet crossing a rotating star and the distortion it produces in a spectral line.
Rossiter–McLaughlin effect. The same machinery handles a planet blocking part of a rotating star during transit.

New model atmospheres (2026)

With PRISMAS I computed specific-intensity grids from Kurucz ATLAS9 (LTE) and TLUSTY OSTAR2002/BSTAR2006 (non-LTE) atmospheres, spanning 3 500–55 000 K in Teff and 0–5 in log g, at 101 emergent angles. They are described in Galán-Diéguez et al. (2026) and available from the authors on request.

How to cite

If you use SPAMMS, please cite the original paper and, if you use the Kurucz or TLUSTY grids, the 2026 paper.

Abdul-Masih et al. (2020)

@ARTICLE{2020A&A...636A..59A,
       author = {{Abdul-Masih}, Michael and {Sana}, Hugues and {Conroy}, Kyle E. and {Sundqvist}, Jon and {Pr{\v{s}}a}, Andrej and {Kochoska}, Angela and {Puls}, Joachim},
        title = "{Spectroscopic patch model for massive stars using PHOEBE II and FASTWIND}",
      journal = {\aap},
         year = 2020,
       volume = {636},
          eid = {A59},
        pages = {A59},
          doi = {10.1051/0004-6361/201937341},
archivePrefix = {arXiv},
       eprint = {2003.09008},
 primaryClass = {astro-ph.SR},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2020A&A...636A..59A}
}

Galán-Diéguez et al. (2026)

@ARTICLE{2026arXiv260915331G,
       author = {{Gal{\'a}n-Di{\'e}guez}, D. and {Abdul-Masih}, M. and {Allende Prieto}, C. and {Berlanas}, S.~R. and {Herrero}, A. and {Sana}, H.},
        title = "{SPAMMS: 3D spectroscopic modelling of stellar surfaces. II. Implementation of Kurucz and TLUSTY model atmospheres}",
      journal = {arXiv e-prints},
     keywords = {Solar and Stellar Astrophysics, Earth and Planetary Astrophysics},
         year = 2026,
        month = sep,
          eid = {arXiv:2609.15331},
        pages = {arXiv:2609.15331},
archivePrefix = {arXiv},
       eprint = {2609.15331},
 primaryClass = {astro-ph.SR},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2026arXiv260915331G},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}