-
Notifications
You must be signed in to change notification settings - Fork 3
Discussion of FOBOS Fiber Microlens R&D efforts, 6 Mar 2018
Reni: Developing a fiber test stand at UCO for an Akamai intern. Basic goal is to understand the wave-front phase coming out of the fiber. Optical design has been started and the budget is available for this small project. Improvements will be made after the summer, particularly with TMT-WFOS development in mind. UCO has a permanent bench at UCO for future development.
Other UCO fiber development includes the Automated Planet Finder (APF) at Lick observatory and fluoridic fiber development for an infrared instrument, among other fiber-based instruments being developed by Andy Skemer. Also interests in other fiber-based instruments for Lick Observatory, including a large-format IFU on the Shane 3m. If TMT selects the fiber-based WFOS design, there will be significant development needs that will happen at UCO (10 year horizon), and FOBOS can benefit from that. Nick McDonald is also involved in SDSS V development for the Local Volume Mapper project (large format IFUs on <1m class telescope for high-spatial-resolution (~10-100 pc) maps of mostly the star-forming galaxies in the Local Group). Unclear where the fiber development for LVM will happen, possibly by Sara Tuttle at UW.
At UC Berkeley Space Sciences Lab (SSL) and LBL, production for DESI is winding down. In particular, Claire will have more time for other projects after Sept. Other projects at SSL include the Keck Planet Finder (KPF), which pushes to very high spectral resolution so much of the development is in understanding gains made by scrambling in the near- and far-field. KPF uses much larger fibers than DESI (225 micron core) and the fibers are octagonal. Would be good to understand need for scrambling at the lower resolution of FOBOS; also interest in this at UCO for both FOBOS and TMT-WFOS.
Some funds (25% of Tim Miller's time for the next 2 months) available to work on the microlens development for FOBOS. Work to-date presented at the LBL meeting and M. Bershady pointed out possible telecentricity issues at the fiber entrance. Work still preliminary, but Tim has sent out the short-term goals for that development.
Important to keep in mind that SSL is project funded; i.e., on soft money. For SSL's involvement in FOBOS, need funds in place. Are there scientists at SSL that we can interest in helping us pursue funding for FOBOS?
- Details need to be worked out about whether or not an ADC is needed. Should have relevant data, just need to construct a report. The report should consider the three different possible observing modes (single fibers, mini-IFUs, monolithic IFU). This can be part of the work done during the conceptual study.
- Details of how the ADC affects the focal-plane axis and what that means for the instrument were unclear. Maureen passed on a report from Drew Phillips about this. E.g., the ADC imposes constraints on the size of the focal plane, the focal-plane is offset from the nominal Nasmyth axis and has to rotate during observations, and the positioners need to piston in z as well as move within the focal plane. It's possible that a (cheap) hexapod could be used to gimble the focal plane.
- FOBOS will nominally have 7-fiber mini-bundles used at integral collectors (not necessarily spatially resolved 7-fiber elements). - Nick M. developed this technology for MaNGA and is obvious choice to help/lead this development.
- However, a different camera design (like being developed for fiber-WFOS) and some additional foreoptics could yield an on-sky aperture of ~1" for a single fiber. Can we leverage this development for FOBOS? What's most scientifically advantageous?
- Regardless of the above, we envision multiple observing modes that could include single-fiber observations, resolved small-bundle observations, and single monolithic IFU observations. Each needs to be considered and weighed based on scientific merit.
- Main concern raised was about controlling for telecentricity. Are the current WFOS and FOBOS microlens designs telecentric? Reni and Tim to be in communication about this.
- Both here and for the ferules, we need to continually assess propagated effects on the science cases due to fiber bundle geometry and angle effects vs. changing f/# and pupil / vignetting over the field. The both near (image) and far field (FDR) can be impacted if there is not strong scrambling
- Format needs to consider:
- Phased development (see below)
- Science enabled
- Need scientifically motivated decisions on the following:
- Add a 4th arm that push the spectral range to ~1.3 micron; a design is in hand but not a trivial implementation; possible with advent of Germanium CCDs (1-2 years out); adding this wavelength range could entice JPL cosmologists to join the project.
- Is an increase of the resolution, particularly in the blue, scientifically useful. DESI spectrograph has R~2500 in the blue. Galactic archeology case discussed by Evan Kirby suggests only factor of
2 gain (R5k) becomes interesting. What about nearby galaxy case? - Critical to decide soon if we want to design a purpose built spectrograph vs. repeat the DESI design. One break point could be to keep the current DESI camera designs but redesign the bench. Need to assess the risk in adopting a new multiple camera design. Advantage of using a fiber-WFOS spectrograph design is both the increase in resolution and the possibility of having single-fiber apertures of ~1".
- Unclear that there is room on Keck II to place the instrument.
- Claire Max suggested an additional structure could be built to hold the spectrographs below the Nasmyth deck.
- Nasmyth FOV limited by K1DM3 on Keck I.
- Will need a mechanical design in place to assess feasibility.
- Secondary mirror slots on Keck-2 for a Phase-I instrument
- Is there scientific interest in (and unique capability gained by) having a "FOBOS-I" be a single, large-format IFU feeding a single DESI spectrograph with no ADC?
- What is the minimum amount of funding required to produce something interesting? $4M?
- Significant synergy with LVM (Nick M.), FOBOS, and fiber-WFOS (if it is selected) development. Nick has laid out a plan for this development that we need to consider.
- How do we sell a phased development to the community and funding agencies? How do we avoid descoping to a phase-I instrument that never implements future phases? What are the risks involved?
- Need to produce a document with the schedule of known funding opportunities over the course of a year.
- Current scheme looks like:
- 0.5M private donor to get us through PDR
- 4M NSF-MRI
- 10M NSF-MSIP (warning that this much money may not be available)
- Other opportunities include:
- DOE; interested in Euclid/LSST/WFIRST follow-up? Maybe expect $fewM
- CalTech, JPL if scientifically interested
- It's possible that the horizon of the DESI and SDSS-V surveys could mean that DESI spectrographs become available by 2025-ish. Should we bank on expanding FOBOS on this timescale by buying these spectrographs once the surveys are finished? What's the benefit, scientifically and budget-wise?