2025-02-19 TSO CT WG Meeting Notes

• Hannah Diamond-Lowe — discussion going on in MIRI to shifting LRS subarray to avoid software corrections on EMI.
  
  
  • There's questions about whether this is a huge factor or not. Hannah Diamond-Lowe's opinion is that moving the subarray is great so long as it doesn't introduce more problems in other time-varying way.
    
    
  • Moving the subarray could also help on getting faster readout time — brighter targets!
    
    
    • Michael Regan clarifies this would imply dropping wavelengths > 12 um.
  • Hannah Diamond-Lowe  will do a Jira ticket in terms of
    
    
    • Wishlists
    • What pros and cons this has.
    • Timescale.
      
      
  • Michael Regan also points out at the wavelength correction.
     
    • Bottom of the array (> 14 um) are actually not even wavelength calibrated.
      
      
  • Nestor Espinoza suggests to bring a presentation to the TSO CT.
  • Taylor Bell likes the idea of going brighter
    
    • Initial thought/pause on that would be what the impact of this would be in settling times for this.
    • His opinion is that chopping signal above > 12 um is fine — it's low SNR anyways. 
    • He also notes whether this change could help on the shadowing region > 10.6 um.

Achrene presents updates on NIRCam DHS wavelength and flux calibration

• She introduces the fact that to calibrate everything you also need to calibrate the filters, and these define in turn 2 combinations of DHS/long wavelength grism (because there are two field points to make everything match).
  
  
• For exoplanet science, likely the most interesting ones are the F150W2 (SW) + F322W2 (LW) — this one produces the widest wavelength range combo.
  
  
• She extracted flux from calibration data of DHS. However, she notes:
  
  
  • Shape is not exactly the same for all substripes.
    
    
  • Hard to make the calibration happen due to the lack of lines.
    • Should they change the calibrator?
      
      
  • Also, absolute flux is not matching the model for the different substripes.
    
    
• Line availability depends on the filter combination with DHS (ie, defined by the wavelength calibration).

Some questions:

• Michael Regan asks whether there are upcoming observations for Multistripe observations? 
  
  • John will update on this.
    
    
• Everett Schlawin 
• Nestor Espinoza notes an M-dwarf could be the way to calibrate:
  
  • Loic Albert suggests even combining wavelength calibration from, e.g., NIRSpec to cross-calibrate NIRCam targets.
• Nestor Espinoza suggests to look back at the detector-effect calibrated DHS spectra:
  
  • Relative shapes of spectra should not depend on the detector properties, so if this is related to the optics, you would see problems here too.
  • Probably useful to study this in detail before Multistripe because it can give you a heads-up on what to expect.
  • Michael Regannotes that the optics might be indeed slightly different for each DHS sub-aperture.
  • Nestor Espinozasuggests to indeed take a look at this, so we can separate what's unique to the multistripe mode.

John Stansberry sent some questions to the TSO CT (via e-mail):

• John: We need to figure out where to put reference rows – keep them interleaved between the substripe rows, or pull them out and put them along 1 edge. Mostly for level-1b (uncal.fits) since the reference pixels are (I think) set to NaN or removed for subsequent products.
  
  
• Loic Albertasks how many rows will be read for ref pixels.
  
  • Everett Schlawin suggests they be interleaved so you know which one goes to which substripe.
  • Michael Regan also suggests the same given his experience with IRS2 readout with NIRspec, which is a nightmare.
    
    
• Achrene Dyrek notes this will impact on the timing  of the substripes:
  
  
  • You will have to be careful to map timestamps correctly.
    
    • Nice thing of interleaving is that it will be easy to re-order things.
  • Snowballs concerns.

• John: We should divide this work into two categories: the minimum viable product in 11.3 and put the rest in 12.0. John will talk with Nestor and exoplanet group to see what they think.
  • Had no time to discuss this.