Notes on the JWST Workshop (Blue from Clampin)

Saturday, April 28, y

Notes on the JWST workshop (Blue from Clampin)

Day one Glad to see that the exoplanet community is thinking big in terms of what fraction of time they want i.e. 25%. I think that we also want to consider whether large team proposals for large data sets should be a discussion point for the community. This paradigm is certainly working well for the extragalatic community on HST - Laboratory astrophysics--need both data to improve uncertain lines lists for giant planets, but we also need to interpret correctly in terms of pressure broadening, etc. New lab astrophysics program? Put together an argument and give to Glen Walgren at NASA HQ, interested in lab astrophysics. - all agree that one should not attempt spectral observations that take a long time if the planet's mass is not known or poorly characterized. Is this an issue for M dwarfs? See Bean's talk tomorrow. (This discussion came about after Miller-Ricci's criticism of the Seager mass-from-spectra technique). - Need RVs -> this is a big issue and needs to be addressed before TESS. What do we need to do to orient NASA on this requirement. - Candidate identification and screening for JWST. Given what we have seen of super earth atmospheres so far, it is important to triage candidates. How do we do these with through to cycle 1 of JWST. CHEOPS ? Ground ? HST? - Thermal breathing lesson from HST. Once understood, along with other undesirable effects, HST given 10's ppm accuracy (30 ppm). Lesson for JWST? - Make JWST transit data from early on immediately publically available because one learns a lot by exposing the same data sets to different groups. Lesson from HST. - On information content and spectral resolution--better spectral resolution isn't better depending on the quality of the data set. Binning leads to some tricky effects. - Wobbles, pointing drifts, jitters, detector behaviors, variations while dithering, ramps in flux, slow decreases in flux, bright and dark latents from previous objects, a whole litany of unanticipated and undesirable effects from the lessons learned ses- sion. - Wavefront sensing and control measurement every two days..may be a problem for long term phase curve observations Saturday, April 28, y - Need decision on whether group needs the moving target capability for exoplanet observations...a scan strategy...but the moving target algorithm isn't really suitable for exoplanets (claim). - Allow transits to observe through HGA repointings? HGA repointing causes small disturbances to obs boresight. < 70 mas, < 1 min in time. Observing though these seems the best strategy. - Event-driven ops: Start of exposures uncertain to 5 minutes. This may cause a problem for planning your observations. - No dedicated ETC for exoplanets is in the works. Normal SNR predictions on host star are assumed to be ok. There is a bit more in the ETC for coronagraphs. There will be some suggestions from Pierre as to what to incorporate for exopl transits. - Clock corrections from Earth applied gradually, not as a jump...this might be a problem for observations requiring precise timing. Clampin will take an action to talk to the spacecraft people. Jesse will take action to explain what the realistic require- ments are for timing. - Bright source observations...small subarray has a short continuous obs time of 2.7 hours. - Note that subarray can be any size in 64 pixel bunches, and can be placed any- where. Stripe mode reads through 4 outputs but is less flexible. - Note telescope is diffraction limited at two microns but the best resolution is actu- ally at 1.5 microns. - Saturation limit not an issue for stars in the TES list. However, some bright stars are a problem. This can be solving by upping the back bias on the voltage. But then there is a wait time of 6 hours up and down, total of 12 hours of nonuse. - Stability in NIRCam is dominated by counting statistics... (can we get 10 ppm?) - Is a jitter tracking mode, using the short wavelength arm to observe the target star simul with a grism or filter in the long wavelength arm? Need to use the 1% filter or weak lens in this case. - Other issues--interpixel capacitance, arrays have random telegraph noise (popcorn), and small amounts of missing charge. The popcorn noise can simulate lines as they jump up and down. Saturday, April 28, y - MIRI arrays...the direct descendants of the IRAC arrays...so similar performance and problems. - Problem of cross-shaped star images at 5 microns thanks to the detector structure...may be a problem using MIRI at 5 microns for exoplanets. - MIRI has an excellent clock and timing within exposure is completely determinis- tic. Between frames, time not controlled and at the mercy of the ISIM. So within exposures the detectors are not interrupted, well controlled, etc. - Detector problems--drifts in apparent response, reset anomaly involving structure imprinted on the detector (fixable), latents (seconds to tens of minutes...considering thermal annealing for exoplanet bright star sources to restore latent-free imaging), other usual stuff... - Subarrays--reading a portion of the array is a very disruptive process in MIRI, leave their own latents...avoid using them unless absolutely required. - Good stuff--fantastically sensitive, excellent cosmetically, extensive calibration...the problems are the 1% stuff. Clear that the instruments offer a lot capability and there was some great discussion yesterday and what would be most useful for real observations.

JWST will be a stable observatory, in fact in the mid-IR i think understanding the detectors is clearly the main challenge. At shorter wavelengths stability is still something that will need to be understood, but there are mitigations.

I think that detectors are the key to early and rapid success with JWST in this field, so I would want data challenges to be focused on characterization detector issues from ground test data,

- full phase curve observations will require significant justification (see 6 below)

Day two - M dwarf surveys:

- RV studies down to 5 m/s; goal is 1 m/s by 2017.

- Kepler K

- 100 small exoplanets around M dwarfs in or near continuous zone for JWST, 20 with 5

- Also missions from ESA--CHEOPS, Gaia (latter for Saturn-mass + only). Note that Plato is too late.

- Peter McCullough "The fault is not in the stars but in ourselves"(Shakespeare). Stellar variability a problem. DO not pick stars that are too variable. UNOCCULTED starspots can also affect the apparent spectrum of the planet--in addition to the (rarer) occulted starspots.

- There is also the issue of ephemeris uncertainties making prediction of especially secondary transits very difficult. The eccentricities and longitudes of periastron cre- ate the problem. Kepler transits don't in general have eccentricity info (they are close to zero but still have some nonzero e). Without these, and indeed also i, you can observe the primary transit but cannot predict when a secondary transit will oc- cur. This problem will be even more so with TESS because they will have so many detections and no followups. Solution--get radial velocities or some way to predict/obs secondary eclipses--...otherwise obs won't pass TAC.

- The white paper should have an extensive analysis of availability of M dwarf tar- gets for JWST from these various experiments.

- There are too many modes for doing exoplanet transits. This will be a nightmare in terms of calibration, evaluation by TAC's, etc. SWG could help by selecting the most promising modes for doing exoplanet transits, codifying these as the official ones for calibration and for the proposal process (check a box that ays mode X for NIRCam exoplanet transit, etc. …) The data clearly, for me, show that spatial scanning' works very well for HST observations. Also, it is seems that NIRCam-GRism & MIRI-LRS are the only spectroscopic modes that would benefit on JWST. So, I would like the group to decide if they wish us to pursue spatial scanning for JWST, since it will come with a price and needs to be specified soon. - MIRI--don't want spectra with MRS, which is the longest wavelength, because of systematic errors...talk to George/Gillian about this!

Day three I think for gas giant comparative planetology low-res one transit surveys will provide a powerful capability. Saturday, April 28, y The debate about whether small planet atmospheres can be done with JWST needs to be broadened as well. Several speakers made the excellent point that multicolor transit photometry and light curves as well phase curves may be a good way to initially ap- proach observations of the smallest planets. - Considerable criticism of the JWST simulator....felt to be too pessimistic. People think they can get photon-limited performance, 10-20ppm. How good is the simulator?

- I also think a good data challenge would be to model what we could do for the smallest planets using photometry (e.g. multicolor transits) and phase curves.