VOSA. Help and Documentation

Version 7.0, July 2021

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. Binary Fit
5.6. HR diagram
5.7. Upper Limits
5.8. 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
12.1. VOSA
12.2. Th. Spectra
12.3. Templates
12.4. Isochrones
12.5. VO Photometry
12.6. Coordinates
12.7. Distances
12.8. Dereddening
12.9. Extinction
13. Helpdesk
14. About
. Excess calculation
. Total flux calculation
. VOphot quality info


Version 6.0Version 5.1Version 5.0Version 3.2Version 3.0Version 2.2Version 2.0Version 1.0

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.

Version 5.0

Sep 2015

New architecture

This VOSA version includes major changes in the internal architecture.

The advent of new and more sensitive surveys providing photometry at many wavelength ranges and covering large sky areas (GAIA, GALEX, SDSS, 2MASS, UKIDSS, AKARI, WISE, VISTA...) is pushing astronomy towards a change of paradigm where small groups, and not only large consortia, need to analyze large multi-wavelength data sets as part of their everyday work.

We have redesigned VOSA architecture since version 5.0 to be ready to work with large user files, containing thousands of objects.

Now VOSA works in a distributed environment, with parallelized computing and an asynchronous architecture. Together with an improved web design for a better performance for large files.

In particular, from the user point of view, the fact that most jobs are executed asynchronously is relevant. Whenever you start a process (for instance, a model fit or a search for VO photometry, VOSA submits it to an external computation server. From time to time, or because a user requests it, VOSA checks the status of the process and, when it is finished, downloads the results, makes the final necessary processing and presents them to the user.

The main advantage of this is that you, the final user, do not need to wait, with the browser open, to the end of the process. You don't depend on the stability of your internet connection either. You can start a process, close the computer and come back later to see how it is going. If it is finished you will see the results. If not, you will see the status of the process and an estimation of the remaining time.

See more details about this in the corresponding Help page

These changes have implied a major revision of all the VOSA programming and, in most cases, visualization of results. So you will see minor changes everywhere that are not detailed here. Some other, more significant, improvements are explained below.

Infrared excess

Several improvements have been done in the automatic algorithm to detect the presence of infrared excess that was sometimes overestimated by VOSA in the past. See the corresponding Help page for details about the new algorithm.

Whenever you make a model fit (using models with only a photospheric component) points with infrared excess are not taken into account.

But, when the fit is completed, VOSA offers now the functionality of comparing the model photometry with the observed one and "refine" the point where the infrared excess starts as the point where the observed photometry starts being clearly above the model.


Plots generated by VOSA are now bigger.

Additional error bars (in dashed style) are displayed showing "3σ" uncertainties.

Model fit

A new functionality is optionally included in the model fit so that the parameter errors are calculated using an statistical approach instead of being calculated as half the grid step.

HR diagram

If several model collections are used (different collections for different objects), one HR diagram plot is generated for each collection, so that graphs are more clear.

You can now click in any of the plots (or any object name) to locate one object in a diagram.


Now, you can see a new tab in VOSA that allows you to visualize the references for all the services that have been efectively used so far (this list will probably change when you continue working with your file). Appart from this, you will download a similar text file and the corresponding bibtex whenever you download VOSA results.

Version 3.2

May 26th, 2014

Changes in the SED tab, about how building the final SED.

  • Handle multiple data corresponding to the same filter (from different catalogs or/and user input).
  • Information available in the VO catalog about observation date, object name, quality, etc. See the origin of each SED point.
  • See the origin of each SED point (user photometry, VO photometry, original value, average value from measurements at different epochs, ...).
  • SED manipulation (possibility of excluding individual photometric points or flagging them as "not usable in the fit" or "upper limit".

Possibility of excluding points with Blue/UV excess.


Better information about confidence ranges in chi-square fits and HR diagram.

Version 3.0

May 15th, 2012

In this version of VOSA a lot of changes have been made. Both internally and in its functionalities.

User input data.

  • Filter names and properties:
    • Now VOSA uses the filter names as defined in the SVO Filter Profile Service. And all the relevant properties for each filter are also the ones given by this service.
    • ~ 1800 filters available.
    • Most old VOSA filter names can be still used in the input files for backwards compatibility. They will be translated, on upload, to the corresponding new names.
  • Two new columns in the input file
    • Point options. In the 9th column of the input file several keywords can be specified for each photometric point separated by "," (no spaces). The options available are:
      • nofit: meaning theat this point will be part of the SED (and shown in plots) but will not be fitted.
      • uplim: the point is an upper limit. VOSA does not really use this information by now. But the keyword can be included as information (it should be combined with nofit if you want that this point is not used for the fit).
      • Other options will be probably defined in future versions of VOSA.
    • Object options. In the 10th column of the input file several keywords can be given specifying options for this object (they must be repeated in each line corresponding to the same object). The currently available options are:
      • Av:avmin/avmax: Range of values for Av. If you give a range here, the visual extintion will be considered as an additional parameter in chi-2 fit and bayes analysis for theoretical models.
      • Veil:value : value in Angstroms so that photometric points with smaller wavelength will be considered to present UV/blue excess.
      • excfil:FilterName : name of the filter where infrared excess starts for this object.
      • Several options can be given for the same object separating them by "," (with no spaces). For instance: "Av:0.5/1.5,Veil:6000"
      • Other options will be probably defined in future versions of VOSA.
  • Distance error.
    • Now you can optionally give a value for the error in the distances writing "D+-err" in the 4th column of the input file. For instance: 100+-20, without spaces (Remember to write both symbols, + and -, together, not a ± symbol or something else; otherwise vosa will not understand the value).
    • The error in the distance will be propagated to the error in the bolometric luminosity given in the model fit.
  • Fluxes in Jy.
    • Fluxes in the input file can be given in Jy (in that case, errors must be given in Jy too). If fluxes are given in Jy, please remember to mark the corresponding chackbox when uploading the file.

New functionalities.

  • Visual extinction as a fit parameter.
    • If a range of AV is given in the input file (or in the object:extinction tab), AV will be considered a fit parameter in the model fit (chi-2 and bayes). 20 different values of AV will be considered in that range for each model file and the best result will be delivered.
  • New observational templates
    • VOSA offers the possibility of performing both the chi-2 fitting and Bayes Analysis with standard objects. Four template collections covering M, L and T spectral types are now available.
  • Log file with a summary of all the work done.
    • VO services consulted, fit made, fit undone, models used, etc since the file was uploaded.
    • Web visualization and downloadable file.
  • References
    • Description of all the references for external services, models, etc used to obtain the results for a user file.
    • Bibtex file with the bibtex entries for those references.
    • Always included in downloads.
  • Single object search.
    • No need to create an input file.
    • Just one object coordinates.
    • Photometric data will have to be search for in the VO
  • Input files management.
    • No sessions anymore.
    • Easy access to old files.
    • Organization of files in user folders.

New theoretical models.

  • New Lyon models.
    • BT-Settl.
    • BT-COND.
    • BT-Dusty.
    • BT-NextGen (Both with the AGS2009 and GNS93 abundances)
    • BT-Settl are the most adequate for actually fitting observed data. The other ones should be used, mainly, to test some extreme theoretical cases.
    • These models make obsolete the previous AMES models, so they are not available in VOSA anymore.
  • Black Body flux.
  • Red supergiants and AGB stars
    • GRAMS C-Rich,
    • GRAMS O-rich.

New VO photometry catalogs.

  • DENIS,
  • MSX6C,
  • AKARI, IRC and FIS,
  • IRAS,
  • C2D, Taurus and GLIMPSE Spitzer catalogues,
  • WISE.
  • New releases of UKIDSS (DR5/7) and SDSS (DR8).

Version 2.2

Mar 15th, 2011

New capabilities

  • Search for object distance in VO catalogues.
    • The object coordinates can be used to search into VO catalogues for distance information.
    • The user can decide to incorporate the obtained info (if any) into the data or not.
  • Search for extinction properties in VO catalogues
    • The object coordinates can be used to search into VO catalogues for extinction information.
    • Some catalogues do not give information about AV but RV or E(B-V). The user can provide his own default values to complete the information and calculate the final AV.
    • The user can decide to incorporate the obtained info (if any) into the data or not. If so, the final sed will be deredden accondingly.
  • New theoretical models for hot and helium rich stars.
    • Husfeld et al models for non-LTE Helium-rich stars.
    • TLUSTY OSTAR2002+BSTAR2006 for hot stars.
  • Bayes analysis
    • This option provides an estimation of the statistical probability for each posible value of the model parameters.
  • Improvements in HR diagram
    • The isochrones and evolutionary tracks used for the HR diagram for each object are always the ones more adequate for the best fit model for that object. This is made explicit in this version.

Version 2.0

May 1st, 2010

VOSA 2.0 allows for two different workflows: "Stars and brown dwarfs" and "Galaxies". It also includes new functionalities.

  • Galaxies workflow:
    • New models:
    • New VO photometric services:
      • The 2MASS Extended sources (IPAC/UMass 2003-2006)
      • The GALEX catalogue (GR4/GR5 Data Release)

  • New capabilities
    • New "objects" section.
      • The observational SED (including user and VO photometry) can be visualized and edited.
      • In the "Stars and Brown dwarfs" workflow, the user can manually specify the wavelength where the infrared excess begins to affect the SED. Photometric points redwards will not be considered in the fitting process.
    • Download process improvement.
      • Objects coordinates included in final files where appropriate.
      • Improved headers.
      • New information included.
      • Encapsulated postscript version of graphs available.
      • Different directory structure in .tar file.

  • Source code improvement.
  • Cosmetic changes.

Version 1.0.2

March 27, 2009
  • New option to fit data with observational templates.
  • The results of these fits can be also downloaded in the Save Results section.

Version 1.0.1

September 5, 2008
  • New collection of isochrones and evolutionary tracks from Siess
  • The Siess isochrones/tracks are used in the HR diagram for the objects that have been fitted by a Kurucz model (before, the NextGen ones where used for these cases)
  • The observed SED, with both the photometry data uploaded by the user and the one retrieved from VO services can be downloaded in the Save Results section.

Version 1.0

July 1, 2008
  • First official release.