Webb Office Hours Session 4: March 28, 2024
Q&A's:
Q1: Where are the Webb Office Hours procedures and guidelines?
A1: Webb Office Hours. Type your question into the WebEx chat. We will asynchronously copy questions from the chat to this main page and work through them as a group. If you have images to share please give WebEx permission to share your screen (you may need to log out and log back in again to enable this feature.)
Q2:Question about the updated JWST Guide Star Catalogue. Program to observe SgrB2, can we pre-select the guide stars?
A2: The exact guide star used for an observation is not chosen until the week before the observation executes. You can contact your program coordinator to discuss your specific guide star needs. The Guide Star Catalogue now uses the Galactic Nucleus Catalogue, which significantly improves the number of stars and the accuracy of their positions in the galactic center region.
Fig 1: Target fields for the GALACTICNUCLEUS survey over-plotted on a Spitzer/IRAC image at 3.6 μm (Nogueras-Lara, F. et al. 2019, https://ui.adsabs.harvard.edu/abs/2019A%26A...631A..20N/abstract).
Astrometric accuracy and number of targets has greatly improved, see Fig. 2 and updates here: https://www.stsci.edu/contents/news/jwst/2024/updates-to-the-jwst-guide-star-catalogue
Fig 2: Simulated and observed FGS images of a guide star field for a SgrA* science program. Left: Simulation based upon the contents of GSC2.4.3.1 which was the operational guide star catalog at the time of these observations. Center: Image captured by the FGS as part of the guide star acquisition process, showing saturated cores of bright stars. Right: Simulation based upon the contents of the GNC, now part of the GSC3.0, demonstrating the remarkable correlation with the NIR sky observed by FGS in the neighborhood of SgrA*. These images cover a 48”x33” patch of sky, which is about 8% of the FGS detector.
Q3: I've reprocessed my MRS data with the pipeline following the recommendations to optimize the result. How do I know the data reduction is optimized? Is there any test you recommend running to ensure my data is up to scientific standards? I do worry about the negative fluxes I see on my spectra; maybe we are over-subtracting the background? Are we diving into detector noise or could it be result of background subtraction?
A3: It is good to keep a critical mind when looking at the data. Do the results make sense? Are they scientifically "sound". With respect to the negative flux values, as you said you are diving into the detector noise. If you are doing the pixel-based subtraction you could end up with negative fluxes; if you are using the model it could also happen but in general you can take it out. You know the flux is not negative, it is only the result of comaring it with other value.
Q4: When we collapse the cube in Channel 2 we find a bright bar-like structure on a dither pointing (see figure, right panel).
A4:
Q5: I have a program with MRS and simultaneous imaging. What is the box to the to left of the image? What are the structures/dark patch I am seeing on the MIRI imager FOV? The red dots are the source catalogue outputs. The program did not have an associated background.
A5: The top left "box" is the region of the MIRI Lyot Coronagraph, . The dark region looks like the result of subtracting the background and there is a positive source that is having that impact on the data. Will be interesting to look at the data. The filter used is F2100W, which is background dominated, and at that wavelength it is recommended to subtract a good background.
