# Synthesis

Through the menu "Spectra - Synthesize spectrum", iSpec can compute synthetic spectra using one of the following radiative transfer codes:

The user can specify the different parameters and select a line list among different options:

• VALD: two line lists extracted from the VALD database (February 2015) with a wavelength range:
• From 300 to 11000 nm
• From 1100 to 24000 nm
• GES line list (version 5.0): they are used in the Gaia-ESO Survey (GES). It covers the wavelength range from 420 to 920 nm.
• With hyperfine structure (HFS) and isotopes (recommended)
• Without HFS and isotopes

The solar abundance can be also chosen from different authors and publications:

• Asplund 2005/2009
• Grevese 1998/2007
• Anders 1989

Additionally, iSpec incorporates several different grids of model atmospheres:

• MARCS GES/APOGEE models [paper] (plane-parallel + spherical).
• Effective temperatures (Teff): [ 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4250, 4500, 4750, 5000, 5250, 5500, 5750, 6000, 6250, 6500, 6750, 7000, 7250, 7500, 7750, 8000 ] K
• Gravities (Logg): [ 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 ] dex
• Metallicities ([M/H]): [ -5.00 , -4.00 , -3.00 , -2.50, -2.00 , -1.50, -1.00 , -0.70, -0.50, -0.20, 0.00 , 0.20, 0.50, 0.70, 1.00 ] dex
• Standard abundance composition, 30\% of all models
[Fe/H] [$\alpha$/Fe] [C/Fe] [N/Fe] [O/Fe]
+1.00 to 0.00 0.00 0.00 0.00 0.00
−0.25 +0.10 0.00 0.00 +0.10
−0.50 +0.20 0.00 0.00 +0.20
−0.75 +0.30 0.00 0.00 +0.30
−1.00 to -5.00 +0.40 0.00 0.00 +0.40
• ATLAS9 Kurucz/Castelli/Apogee/Kirby models [paper] (plane-parallel)
• Effective temperatures (Teff): [ 3500, 3750, 4000, 4250, 4500, 4750, 5000, 5250, 5500, 5750, 6000, 6250, 6500, 6750, 7000, 7250, 7500, 7750, 8000, 8250, 8500, 8750 ] K
• Gravities (Logg):[ 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 ] dex
• Metallicities ([M/H]): [ -5.00, -4.50, -4.00, -3.50, -3.00, -2.50, -2.00, -1.50, -1.00, -0.50, -0.30, -0.20, -0.10, 0.00, 0.10, 0.20, 0.30, 0.50, 1.00 ] dex
• Standard abundances (no enhanced).

iSpec will use linear interpolation with the previous models to compute spectra with any atmospheric parameters that fall inside the grids.

Apart from the astrophysical parameters, the model atmospheres and linelists, iSpec ask for other parameters like the projected rotational velocity ($V\sin(i)$), micro/macroturbulence, resolution and wavelength range/steps.

It is recommended not to use too narrow wavelength ranges and wavelength steps not smaller of 0.01 nm (being 0.001 nm the optimum value).