Mission Overview
The "BOSZ" Synthetic Stellar Spectral Library ("BOSZ") -
New 2024 Version + Legacy 2017 Version
Primary Investigator: Ralph Bohlin, Szabolcs Mészáros
HLSP Authors: Ralph Bohlin, Szabolcs Mészáros, Scott Fleming
Released: 2017-04-04
Updated: 2024-07-16
Primary Reference(s): Bohlin et al. 2017, Mészáros et al. 2024
DOI: 10.17909/T95G68
Citations: See ADS Statistics
BOSZ 2017 and 2024 Figures
Top panel: Teff - log(g) diagram of the new BOSZ grid, middle panel: [α/M] as a function of [M/H], bottom panel: [C/M] as a function of [M/H]. There are 336 chemical composition combinations, each with 322 MARCS and 173 ATLAS9 model atmospheres. Star density from APOGEE DR17 (Abdurro’uf et al. 2022) is represented as a heat map in the background, showing that the selected parameters cover most of the stars that are observed in the Milky Way.
Top panel: The log(g) vs. effective temperature of model atmospheres used for synthesis. Middle panel: [C/M] abundances as a function of metallicity. Bottom panel: [alpha/M] abundances for each [C/M] value as a function of metallicity.
Overview
"BOSZ" synthetic stellar spectra are based on the ATLAS9-APOGEE (Mészáros et al. 2012) and MARCS (Gustafsson et al. 2008) model atmospheres, and cover a broad range of effective temperature, surface gravity, metallicity, carbon abundance, and alpha-element abundance. The name "BOSZ" comes from a combination of letters in the first and second authors' names. Versions at different instrumental broadenings are provided. See the tables in this section that describe the parameter ranges. Two versions are available, the original 2017 version and a newer 2024 version. The 2024 version supersedes the legacy 2017 version.
2024 Version
The new BOSZ synthetic spectral grid has been calculated with Synspec using LTE approximation covering metallicities [M/H] from -2.5 to 0.75 dex, alpha-element abundances [α/M] from -0.25 to 0.5 dex, and carbon abundances [C/M] from -0.75 to 0.5 dex, providing spectra for 336 unique compositions. Calculations for stars between 2800 and 8000 K use MARCS model atmospheres; and ATLAS9 is used between 7500 and 16,000 K. Continuous opacities and molecular line lists have also been updated. See Figure 1 in Mészáros et al. 2024 and on this page for the grid coverage compared to stars observed by the APOGEE survey.
The new BOSZ grid includes 628,620 synthetic spectra from 50 nm to 32 microns with models for 495 Teff, log(g) parameter pairs per composition and per microturbulent velocity. Each spectrum has eight different resolutions spanning a range from R = 500 to 50,000 and also at the original resolution of the synthesis. The original resolutions vary between 200,000 and 600,000 depending on the main atmospheric parameters. Parameter ranges are summarized in the table below.
The filenames of these original resolution spectra contains the "rorig" string and have three columns: the wavelength in Angstroms, the Eddington first moment (H, surface brightness) of the spectra, and the continuum. The flux (F) at the stellar surface is calculated as:
F = 4πH , where H is in erg s-1 cm-2 Å^-1.
To save disk space, each of the seven sets of lower resolutions has its own equally sampled logarithmic wavelength space that is not stored within the files, only the fluxes and continuum values are stored at these lower instrumental broadenings. These can be downloaded from the table in the Data Access section on this webpage, or calculated by adding Equations 3 and 4 from Mészáros et al. 2024.
Included in the original resolution ("rorig") collection are line identification files for each microturbulence v=0.0 synthetic spectrum. These files have three columns: wavelength in Angstroms, a string of line identifications, and the equivalent width (W) in Angstroms. Weak lines with W < 0.1 Angstroms are not listed.
NOTE: The published spectra were generated using an eight-level H atom, which results in a lack of higher-level H lines above 5.8 microns. The team is currently working on recalculating the 5.8 and 32 micron region, and will update the database after the availability of these new spectra. It is important to note that the 50 nm - 5.8 micron region is not affected by this issue.
Parameter Ranges
| Parameter | Values |
|---|---|
| Instrumental Broadening | 500, 1000, 2000, 5000, 10000, 20000, 50000, original |
| Temperature (K); log(g) |
MARCS ("ms" or "mp"):
ATLAS9 ("ap"):
|
| Metallicity | -2.50 to +0.75, in steps of 0.25 |
| Carbon Abundance [C/M] | -0.75 to +0.50, in steps of 0.25 |
| alpha Element Abundance [α/M] | -0.25 to +0.50, in steps of 0.25 |
| Microturbulence (km/s) | 0, 1, 2, 4 |
2017 Version - Legacy (Superseded by 2024 Models)
For historical information about the legacy 2017 version, expand the section below.
The models are fit to O,B,A,F,G stars observed with HST/STIS, and those results were compared to fits for the LTE grid from Castelli & Kurucz (2004). The primary reference that describes the model synthesis for this version of the BOSZ models is Bohlin et al. 2017. Two version of the files are available, an ASCII text table zipped using bzip2, and a FITS version with the data stored in a binary FITS table.
The models include wavelengths from 1000 Å < λ < 32 μm. The ASCII files contain the wavelengths (measured in vacuum) in Å, surface brightness (H_BOSZ), and theoretical continuum level. The FITS files have these data in the first extension, in columns called "WAVELENGTH", "SPECIFICINTENSITY", and "CONTINUUM". Note that to convert from surface brightness to flux, use the equation:
F = π * H_BOSZ
where H_BOSZ is the surface brightness in the file. Normally the equation includes a factor of 4*π, but the BOSZ models are already four times larger, so it is only necessary to multiply the surface brightness values by π to convert to flux in erg cm-2 s-1 Å-1.
Parameter Ranges
| Parameter | Values |
|---|---|
| Instrumental Broadening | 200, 500, 1000, 2000, 5000, 10000, 20000, 50000, 100000, 300000 |
| Temperature (K); log(g) |
|
| Metallicity | -2.5 to +0.75, in steps of 0.25 |
| Carbon Abundance [C/M] | -0.75 to +0.5 in steps of 0.25 |
| alpha Element Abundance [α/M] | -0.25 to +0.5 in steps of 0.25 |
Data Products
2024 Version
The files are organized into subdirectories based on parameter grouping as follows:
<insbroad>/<metallicity>/
where:
- <insbroad> is the instrumental broadening, one of {r500, r1000, r2000, r5000, r10000, r20000, r50000, rorig}
- <metallicity> is the metallicity used, one of {m+0.00, m+0.25, m+0.50, m+0.75, m-0.25, m-0.50, m-0,75, m-1.00, m-1.25, m-1.50, m-1.75, m-2.00, m-2.25, m-2.50}
For example, ASCII models with an instrumental broadening R of 500 and solar metalicity can be found in:
/r500/m+0.00/
Filesnames are consistent, so that the parameters of any spectra can be easily recovered. The following naming scheme applies:
bosz2024_<atmos>_<teff>_<logg>_<metal>_<alpha>_<carbon>_<micro>_<insbroad>_<prod>.txt.gz
where:
- <atmos> = model atmosphere: "mp" = MARCS plane-parallel model, "ms" = MARCS spherical model, "ap" = ATLAS9 plane-parallel model
- <teff> = "t####[#]" indicating the effective temperature, e.g., "t5000" for 5000 K or "t16000" for 16000 K; ranges from 2800-16000 K
- <logg> = "g{+,-}#.#" indicating the surface gravity, e.g., "g+4.5" for log(g) = 4.5; ranges from -0.5 to +5.5
- <metal> = "m{+,-}#.##" indicating the metallicity, e.g, "m-2.50" for metallicity = -2.50; ranges from -2.50 to +0.75
- <alpha> = "a{+,-}#.##" indicating the alpha element enrichment, e.g, "a+0.25" for α/M = +0.25; ranges from -0.25 to +0.50
- <carbon> = "c{+,-}#.##" indicating the carbon abundance, e.g, "c-0.75" for [C/M] = -0.75; ranges from -0.75 to +0.50
- <micro> = "v#" indicating microturbulence velocity, either 0, 1, 2, or 4 km/s
- <insbroad> = "r###[#][#]" indicating the instrumental broadening, e.g., "r2000" for R = 2000; either 500, 1000, 2000, 5000, 10000, 20000, 50000, or it is set to "rorig" indicating the original resolution; the original resolution depends on the other main atmospheric parameters, but ranges from ~200000 to ~600000
- <prod> = type of product, either "resam" indicating the spectra are resampled to a given instrumental broadening, "noresam" for the original resolution spectra indicating no resampling of the wavelength spacing was done, or "lineid" for files containing the line identifications
An example file name of a spectrum with Teff = 5000 K, logg = 5, [M/H] = 0, vmicro = 0, R = 500, and solar scaled [A/M], [C/M] abundances is:
bosz2024_mp_t5000_g+5.0_m+0.00_a+0.00_c+0.00_v0_r500_resam.txt.gz
Data file types:
| _wave<res>.txt | BOSZ 2024 wavelength grids. |
| _resam.txt.gz |
BOSZ 2024 synthetic stellar spectrum |
| _lineid.txt.gz | BOSZ 2024 line IDs (only for "rorig" resolution) |
2017 Version - Legacy (Superseded by 2024 Models)
For historical information on the file organization and naming convention of the legacy 2017 version, expand the section below.
The files are organized into subdirectories based on parameter grouping as follows:
<u>/insbroad_<w>/metal_<x>/carbon_<y>/alpha_<z>/
where:
- <u> is either "ascii" or "fits", depending on the data format
- <w> is a 6-digit, zero-padded instrumental broadening
- <x> is the metallicity value, including '+' or '-'
- <y> is the carbon abundance value, including '+' or '-'
- <z> is the alpha-element value, including '+' or '-'
For example, ASCII models with an instrumental broadening R of 200, solar metalicity, solar carbon abundance, and solar alpha-element abundance can be found in:
ascii/insbroad_000200/metal_+0.00/carbon_+0.00/alpha_+0.00/
The format for each part of the file name is described in detail in the Appendix of Bohlin et al. 2017, since, for example, decimals are avoided and some values are rounded in the file names. One minor change is the prepending of "bosz2017" to the front, to ensure they are differentiated from newer model versions, An example file name is:
bosz2017_amm13cp00op00t3500g45v20modrt0b50000rs.asc.bz2
where:
- mm13 represents [M/H] = -1.25
- cp00 represents [C/H] = 0.00
- op00 represents [α/H] = 0.00
- t3500 represents Teff = 3500 K
- g45 represents log(g) = 4.5 K
- v20 represents Microturbulent velocity = 2.0 km/s
- rt0 represents Rotational broadening = 0.0 km/s
- b50000 represents Instrumental broadening = 50,000
Data file types:
| *rs.asc.bz2 | BOSZ 2017 ASCII version. |
| *rs.fits | BOSZ 2017 FITS version. |
Data Access
Single Model
If you want to retrieve a specific model, following the file naming formula above, you can create your own download command using the following as the URL to retrieve the file from:
https://archive.stsci.edu/hlsps/bosz/bosz2024/<insbroad>/<metallicity>/<filename>
For example, the link to retrieve the model with Teff = 5000 K, logg = 5, [M/H] = 0, vmicro = 0, R = 500, and solar scaled [A/M], [C/M] abundances is:
Bulk Download Scripts
The bulk download scripts in the table below can be used to retrieve all models for a particular instrumental broadening and metallicity. Each script will download all available carbon abundances and alpha abundances within that broadening+metallicity combination.