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
4.1.1. VO Search
4.1.2. Outlier detection
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
 
Appendixes
. Excess calculation
. Total flux calculation
. VOphot quality info

VO photometry

Search for photometry in VO catalogues.

The tool offers the possibility of searching in the VO for catalog photometry for the objects in the user file.

In order to do that, the object coordinates must be known as precisely as possible. Either the user can provide these coordinates in the input file or they can be obtained also from the VO.

VOSA offers access to several catalogs with observed photometry from the infrared to the ultraviolet.

You can choose which catalogs to use and the search radius within each one.

For each catalog, you have the option to establish magnitude limits, so that only photometry values in that range will be retrieved.

For each object in the user file, each catalog will be queried specifying the given radius, and the best result (the one closer to the object coordinates) will be retrieved. For some catalogs there are special restrictions. For instance, for the UKIDSS surveys, the search is restricted to class -1 (star) or -2 (probable star) objects. These special restrictions, when applied, are explicitly commented in the brief catalog description in the VOSA form.

When you click the "Search" button, VOSA starts the operation of querying VO catalogs.

This search is performed asynchronously so that you don't need to stay in front of the computer waiting for the search results. You can close your browser and come back later. If the search is not finished, VOSA will give you some estimation of the status of the operation and the remaining time.

When the search process is finished you will see the photometric values obtained for each object (if any).

If the catalog provides magnitude values, these are automatically converted to fluxes.

Take a look to the Credits section for information about the available VO catalogs.

Detection of outliers in VO data

When new data are found in VO catalogues and before incorporating them to the object SED, VOSA tries to identify the presence of outliers, that is, photometric points that, for one or another reason, seem not to be part of the real SED.

In particular, VOSA looks for V patterns and inverted V patterns, that is:

V pattern

VOSA looks for points that seem to be clearly below the main SED, that is points so that both the previous and next points have much higher fluxes. To be more precise, if all these criteria are met:

  • Fn-1/Fn > 5
  • Fn+1/Fn > 5
  • λnn-1 < 2500A
  • λn+1n < 2500A
     
    Although in the infrared, when 10000> ≤ λn-1 ≤ λn < 26000A, the criteria above is changed to:
  • λnn-1 < 6000A
  • λn+1n+1 < 6000A

the point (λn,Fn) is considered suspicious and thus is marked as 'bad'. A 'lowflux' flag will also be included in the vosa and SED files if they are downloaded later.

Take into account that to make these calculations only the points (both from VO catalogues or User data) that are not flagged as 'bad' or 'upper limit' will be considered.

A simple example can be seen in this image:

We can see a first suspicious point for CTIO/DECam.g:

But VOSA will not flag it as bad because it does not meet the criteria

  • Fn-1/Fn = 5.141e-15/1.050e-15 = 4.89 < 5
  • Fn+1/Fn = 1.366e-14/1.050e-15 = 13.00 > 5
  • λnn-1 = 4770.83 - 4671.78 = 99.05 < 2500A
  • λn+1n = 4810.88 - 4770.83 = 40.05 < 2500A

But the point for CTIO/DECam.Y will be marked as bad:

  • Fn-1/Fn = 1.807e-14/1.175e-15 = 15.37 > 5
  • Fn+1/Fn = 1.291e-14/1.175e-15 = 10.98 > 5
  • λnn-1 = 9886.35 - 9613.45 = 272.9 < 2500A
  • λn+1n = 12350 - 9886.35 = 2463.65 < 2500A

because all the criteria are met.

 

Inverse V pattern

VOSA looks for points that seem to be clearly above the main SED, that is points so that both the previous and next points have much lower fluxes. To be more precise, if all these criteria are met:

  • Fn/Fn-1 > 5
  • Fn/Fn+1 > 5
  • λnn-1 < 2500A
  • λn+1n < 2500A

the point (λn,Fn) is considered suspicious and thus is marked as 'bad'. A 'highflux' flag will also be included in the vosa and SED files if they are downloaded later.

Take into account that to make these calculations only the points (both from VO catalogues or User data) that are not flagged as 'bad' or 'upper limit' will be considered.

A simple example can be seen in this image:

The point for will be marked as bad:

  • Fn/Fn-1 = 3.142e-15/1.297e-16 = 24.22 > 5
  • Fn/Fn+1 = 3.142e-15/1.385e-16 = 22.68 > 5
  • λnn-1 = 7457.89 - 6156.36 = 1301.53 < 2500A
  • λn+1n = 7503.68 - 7457.89 = 45.79 < 2500A