VOSA. Help and Documentation

Version 6.0, Apr 2018

1. Introduction
2. Input files
2.1. Upload files
2.2. VOSA file format
2.3. Single object
2.4. Manage files
2.5. Archiving
2.6. Filters
3. Objects
3.1. Coordinates
3.2. Distances
3.3. Extinction
4. Build SEDs
4.1. VO photometry
4.2. SED
4.3. Excess
5. Analysis
5.1. Model Fit
5.2. Bayes analysis
5.3. Template Fit
5.4. Templates Bayes
5.5. HR diagram
5.6. Upper Limits
5.7. Statistics
6. Save results
6.1. Download
6.2. SAMP
6.3. References
6.4. Log file
6.5. Plots
7. VOSA Architecture
8. Phys. Constants
9. FAQ
10. Use Case
11. Quality
11.1. Stellar libraries
11.2. VO photometry
12. Credits
13. Helpdesk
14. About


Version 6.0

April 2018


  • Possibility of selecting the quantity to be plotted in the Y axis of the graphics (Flux vs lambda or lambda*Flux vs lambda).
  • Possibility of building a VOSA input file from a spectrum / list of spectra using SpecPhot.
  • New quality controls in the upload of the input file.
  • Asynchronous management of the input files to avoid long waits with heavy files.

Build SEDs / VO photometry

New catalogues:
  • Gaia DR2
  • Dark Energy Survey (DES), SVA1 Gold
  • The DECam Legacy Survey (DECaLS) DR3
  • Pan-Starrs PS1
  • VPHAS+ DR2

Build SEDs / SED edit/visualize

  • A new column (Delta_2 (VO)) has been added in the table of results. This column indicates the distance from the object position to the second closest result in the VO catalogue (within the given search radius).
  • A new column (Info) has been added in the table of results. This column allows to change the user photometry, either in flux units or in magnitudes. Remember that if the errors in flux / magnitudes are not given or set to zero, the associated photometric point will be given the least weight in the fitting process.
  • A new interactive graphic facility has been added.

Analyse SED

  • New goodness of fit criteria have been included.
  • A new collection (Kesseli et al.) has been added in the "Template fit" option.
  • New format of the table of results to efficiently manage long tables.
  • Possibility of customizing the table of results to visualize only the columns that you prefer.


  • New information added to the FAQ section.


  • Asynchronous management of the exchange of information between VOSA machines to avoid long waits.

Version 5.1

Oct 2016

Upper limits

New treatment of upper limits. They are adequately taken into account in the fit unless you don't want it. Better graphical representation in plots.

Upper limits are not automatically marked as "nofit" anymore.

Partial "refit"

After you have finished the fit process, sometimes it is useful to make small changes in the SED for some objects and repeat the fit.

VOSA keeps track of what SEDs have been changed in a significant way after the fit, so that the current fit results could be not valid for those objects anymore.

When you go back to the chi2 fit tab, VOSA will show you a message saying the the SED for some objects has been changed after the fit was finished and offers you the option of repeating the fit only for those objects. If you click in the "Repeat the fit process" button, the fit process will be done again with the same previous options (model choice, parameter ranges choices, etc) but only for the objects that have changed. The fit results for the other objects will remain the same.

This is also implemented for the Bayes analysis.

New statistical information

In the model fit, when the option of using a Monte Carlo method to estimate parameter uncertainties is selected, VOSA will calculate a full set of statistical properties on the distribution of parameter values including a normality test to check the probability of the distribution to be normal. Some of the obtained results will be shown in the table of bestfit results and the full list is offered when you see all the fit results for a given object.

In the case of Bayes analysis, the same statistical calculations are performed using the distribution of probabilities for each fit parameter.


The possibility of searching Gaia TGAS catalog for more accurate values for object distance is now offered.

Chi2 model fit

Two alternative calculations for the stellar mass and radius are done now using other fit results. $$R_1 \equiv \sqrt{D^2 M_d} $$ $$R_2 = \sqrt{L_{bol}/(4\pi\sigma_{SB} T_{eff}^4)}$$ $$ M_1 = 10^{logg} R_1^2 / G_{Nw} $$ $$ M_2 = 10^{logg} R_2^2 / G_{Nw} $$

(Caution is adviced on the values obtained for the mass, specially for low values of logg).

VO photometry

New catalogs: Gaia, Stromgren Paunzen (2015; J/A+A/580/A23), IPHAS DR2, APASS DR9

Quality flag for UKIDSS and VISTA photometry is now provided in the "SED" tab. If the catalog provides a flag ppErrBits>0 , the point is flagged as "nofit".

Theoretical models

7 new collections of theoretical models are now offered: NextGen, TMAP (Grid 1), Drift-Phoenix, Morley 2012, Morley 2014, Saumon 2012, Koester.

Vosa files

Large input data files are allowed now. If the file contains more than 10.000 objects it will be split in several files, each one containing up to 10.000 objects.

Improvement of the ASCII to VOSA conversor to handle large data files.


The footprints of VO catalogs offering extinction information are now shown using MOCs.


Better design of the VOSA workflow/menu. Tags are now more efficiently grouped.

Several bugs corrected in GALEX limiting magnitudes and Nextgen isochrones and evolutionary tracks.

Previous versions