ZTF Ia Phone-con: 2021-Oct-27

Meeting Agenda:

1. SNe of the week [Joel J]

2. AMPEL/IPAC FP [Jakob N]

3. Light-curve visualisation [Jacco T]

4. AOB / Close

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Participants (17):

• Adam M, Alice T, Ariel G, Bastien C, Benjamin R, Georgios D, Jacco T, Jakob N, Joel J, Kate M, Luke H, Mat S, Maxime D, Melissa A, Philippe R, Remy J, Suhail D, Young-Lo K
  • (apologies if I missed you!)

Transients of the Week:

• Limited data last week: the camera had to be warmed up
• ZTF21acfabut: Spectroscopically a Ia; photometrically -20.2. Could be a SLSN? More spectra needed
• ZTF21acdkydg: A 91bg sibling (in the same host as a SN from 2010
• Observing: Suhail has triggered the 3.6m (in India) on 5 objects for J,H photometry.
  • There is more time at the weekend, so bring on extra targets
  • The plan is to get 3 epochs around max to constrain RV / dust.

DR2 Updates:

• Mat has hacked IPAC photometry flags into the DR2 light-curve files
  • This is ongoing, but he doesn't have all of the information
• Adam: has figured out how to infer flags from other flags - exactly what Mat is looking for!

FP Pipelines:

• Jakob walked us through the FP schema within AMPEL.
• This is based on IPAC photometry. Each object is individually queried and downloaded.
• Joel: (Q) can this be done in bulk?; Adam did you do it in bulk?
  • (A) Adam: No; special permission was given to do everything (in BTS) once.
  • (A) Suhail: Rhaul had developed a query to bulk query and download FP: would this be useful (A: Yes!)
• AMPEL has several modules:
  • Positions are estimated from detections and then FP is queried for
  • FP errors are scaled based on the PSF (as recommended); cuts are made on 'infobitsci', 'zp_err' and 'n_calib', but not on 'procstatus'
  • FP errors are not scaled based on the photometry (as recommended).
  • A baseline correction is calculated (using outlier rejection and a weighted mean) and then applied
    • This is optimised by hand
    • BTS (Adam M) likely uses a longer baseline and more cuts to determine their correction
  • SALT2 is then fit.
• ZTF19acpfath is our test object of the day.
  • The FP photometry is offset from Alert by ~0.02 mag.
  • The FP between different merthods (FPbot; IPAC; IPAC with different centroids for different filters) show agreement at the 0.001 level. (good, but not stunning)
• What to do next?
  • Test with a sample seems to be the consensus. Alternative plans are to compare to external measurements (PS1), but that's complicated.
  • Remark (Mat): this is not cosmology, so let's not go over-board 'yet'
  • Let's pick ~100 objects and do the test.
  • Suhail and Jacco to help out
• Misc:
  • IPAC (Frank M) actually recommend using Alert over forced.
    • (Q): Do we know why? (A): Nope, but presumably it's to do with requiring stringent cuts.
    • (Q): Are the FP errors underestimated (they are recommended to be scaled)? (A): unclear. Could be weather dependent too?
• General:
  • This is all done in a schema: let's all work in the schema. Mat: yes; soon.

FP Visualisation:

• Jacco showed off some really nice visualisations of the ZTF data
• He's looking for late time excesses in the light-curves (for the 2018 sample), but as a consequence, he's getting very close to seeing if the data is any good!
• The input images for his study come out of ZTFquery => are the IPAC subtractions
• He sees two issues:
  • Long term negative fluxes due to the SNe being in the template
  • Awful subtractions when the object is on the edge of the CCD.
• Let's use the visualisations to help identify the problem (i.e. highlight bad images), and determine when it's been fixed :).

• Joel: the team are circulating a spreadsheet looking for volunteers to talk at these meetings: sign up!
• Next week: more photometry discussions (and maybe some actual comparisons), general updates and maybe some science :).