[Heig] [HighEnergyObscoreExtension Note] comments about section 6

[Dr. Ian N. Evans]

Hi Mireille,

I think this would depend on the characteristics of the data.  For example, if a data collection were to consist solely of datasets from a single instrument obtained with a single set of instrument settings, then I can imagine the ref_energy and ref_oaa values could be the same for the entire collection.

For Chandra Source Catalog data products, I expect these values to be different for different datasets.  For example, datasets with different energy bands will have different ref_energy values; ref_energy will also vary depending on which instrument is used and can vary depending on certain instrument parameter settings that alter the energy response of the observation.  “Cutout” datasets extracted for each X-ray detection will have different ref_oaa values.

For some Chandra datasets with calib_level <=2 that utilize the full field of view and full energy coverage, we may choose the same values for all of those datasets (although again ref_energy will vary with instrument choice and some instrument parameter settings when required).

obs_mode, tracking_type, and scan_mode will depend on the individual observation parameters (and target in the case of tracking_mode).  I think this is similar to the case for the radio extension.  Chandra doesn’t require the use of pointing_mode or analysis_mode.

Thanks,
—Ian

> On Mar 29, 2026, at 12:52, Mireille Louys via heig <heig at ivoa.net> wrote:
> 
> 
> Hi HEIG members, 
> 
> I have read again the content of this section :
> section 6 Proposal of the ivoa.obscore_hea attributes
> 
> It appears to me that the features in this table  may be applicable to a group of data sets , or to an obs_collection. 
> I guess there is a global decision to define the reference system of the data like s_ref_energy, em_ref_energy, s_ref_oaa, s_ref_oaa,
>  so may be this metadata can be factorized at the level of a part of an obs_collection. 
> 
> Are their groups , data releases, that would share the same reference systems? the same observing conditions like obs_mode, tracking_mode, etc...
> 
> It relates to the way the Obs_collection is defined and possibly organized  as sub-groups. 
> 
> Of course if it may change for every dataset, there would be no gain to group these . 
> 
> Best wishes, Mireille
> 
> 
> 
> -- 
> --
> Mireille Louys, MCF (Assistant Professor)
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—

Dr. Ian Evans
Astrophysicist
Chandra X-ray Center
Center for Astrophysics | Harvard & Smithsonian

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