`OHANA - an interferometric Network at Mauna Kea Telescopes ----------------------------------------------------------- Progress meeting summary December 18th, 19th 2000, Waimea. The `Ohana concept considers interferometric coupling of 3 to 10 meter class telescopes of Mauna Kea taking advantage of two technological breakthroughs: adaptive optics and coherent transport of light with single mode optical fibers. This concept, proposed in 1996 (Mariotti et al, AASS, 116, 381-393, SPIE 3350, 785-792), was informally discussed at a first meeting in March 2000. It was considered worth pursuing by the participants and a number of preliminary actions was undertaken. A plan was drafted comprising three phases: - Phase I: demonstration of beam extraction from AO foci with fibers and routing to ground (year 2001). - Phase II: first coupling of a pair of telescopes leading to fringes acquisition, visibility measurements and scientific impact (2002- mid 2003). - Phase III: progressive implementation and completion of the array capability with full scientific program (from 2003 onwards). A follow up meeting was held on December 18th/19th 2000 in Waimea at CFHT headquarters, and was attended by the following participants: - Andy Adamson (UKIRT) - Jim Beletic (Keck) - Fred Chaffee (Keck) - Mark Chun (Gemini) - Vincent Coude du Foresto (Obs. de Paris) - Celine D'Orgeville (Gemini) - Catherine Dougados (CFHT) - John Gathright (Keck) - Olivier Guyon (UH) - Tim Hawarden (UKIRT) - Olivier Lai (CFHT) - Pierre Lena (Obs. de Paris) - Francois Menard (CFHT) - David Le Mignant (Keck) - Matt Mountain (Gemini) - Jun Nishikawa (NAOJ) - Dan O'Connor (IRTF) - Guy Perrin (Obs. de Paris) - Jacques Sebag (Gemini) - Helene Sol (Obs. de Paris) - Alan Tokunaga (IRTF) - Christian Veillet (CFHT) - Peter Wizinowich (Keck) - Julien Woillez (Obs. de Paris) Other invited participants had to decline because of other commitments but had expressed interest and wish to be kept informed: - Hiroyasu Ando (Subaru) - Chris Dainty (Imperial College) - Greg Fahlman (CFHT) - Wolfgang Gaessler (Subaru) - Don Hall (Ifa - UH) - Rolf Kudritzki (Ifa - UH) - Antoine Labeyrie (OHP) - Fabien Malbet (Obs. de Grenoble) - David St Jacques (Subaru) - Francois Reynaud (IRCOM) - Steve Ridgway (NOAO) - Francois Rigaut (Gemini) - Jean Rene Roy (Gemini) - Hideki Takami (Subaru) 1. Overview This meeting follows a first definition meeting that was held on March 16th and 17th 2000 at CFHT, at which a set of goal was defined: - get Ph.D. student (Julien Woillez) and funds in France, - begin implementation study, - inform and invite new potential partners, - inform the community (web site, SPIE), - think on science cases and - prepare a second meeting. All of these actions have been closed at the start of the meeting. The goals set forth for this second meeting were to: - Obtain instrument status and progress reports of different groups, - Establish a schedule for the upcoming year 2001 (Phase I) and define technical interfaces, - Expand the `Ohana committee with new partners, - Establish science cases, - Define phase II. Members of IRTF, UKIRT and Subaru were invited by the `Ohana committee and largely contributed to the progress of the meeting. They have been invited to join the `Ohana committee. The meeting was divided into two parts. The first day addressed technical issues and the second day was dedicated to science cases and to definition of action items. 2. Technical Progress 2.1 AO/Fiber coupling The conceptual design of the injection module was overviewed and the use of such a device as a diagnostic tool for adaptive optics was reviewed and offered for characterisation for existing or planned AO systems. 2.2 Fiber beam transport experiments The use of single mode fibers for beam transport over hectometric distances in the visible and near infrared has been demonstrated in laboratory experiments in Japan (MIRA) as well as in France (IRCOM), and will be pursued at Observatoire de Paris for K band fibers. 2.3 Fiber routing It is believed that the existence of an empty 4 inch duct linking telescopes could be available for a permanent link, but requires confirmation from UH. It appears that for a temporary connection of close observatories on the Eastern ridge, an overground solution is feasible and indeed preferable. However, for the western side, the wikaiu bug habitat may prevent overground routing of the fibers in which case an underground solution readily exists. 2.4 Detectors Several solutions have been discussed. For a baseline involving Keck telscopes the fringe tracker camera may be available, as long as the dedicated optics are provided for fiber focusing. The Meudon group is considering building a Nicmos array. The availability for an innovative detector at University of Hawaii should be investigated. 2.5 Other prospects to investigate - Integrated optics beam combination (IONIC) is now demonstrated on the sky and would simplify `OHANA's beam combination. - Pupil densification could provide a direct imaging capability when a number of telescopes are available (Labeyrie, Guyon). - In the case of imaging of complex sources, combining `Ohana data with KeckI and VLTI data will allow to fill out the UV plane more evenly and cover more spatial frequencies. 3. Science Four illustrative science cases were presented and they already proved to be strong science drivers for phase II of the instrument. 3.1 AGNs In AGNs, the topics of interest are the size of the Broad Line Region and the strucrure of the base of jets in the infrared. This will require baseline on the order of or greater than 200 meters. However, the sensitivity required will imply the need for the larger apertures. Significant results can be obtained by obtaining visibilities in H band and Pa{beta}; a moderate spectral resolution is needed for the determination of the size of the BLR. For the study of jets, calibrated fluxes and polarimetric measurements will be needed. A deeper study is necessary in order to examine the significance of a few visibility measurements for constraining models. 3.2 YSOs `Ohana will be able to probe the inner central AUs of the circumstellar environment, including the inner accretion disk, and star/disk interface region, which hold important clues on the accretion/ejection mechanism. Thermal emission from dust heated by the viscous accretion process dominates the near-infrared continuum. It will be possible to constrain the size of the disk truncation radius (expected to lie close to the corotation radius - 0.07 au) and discriminate between different disk models (magnetized versus purely hydro). Brgamma observations with moderate spectral resolution (a few 100) would constrain the geometry of the star/disk interface region and the wind formation regions. Baseline greater than 200 meters will be needed to answer these questions. However, the sensitivity is not an issue, and the smaller telescopes can be used for this program. Even a very limited number of visibilities constrain models. About 100 sources are accessible. K band is the most suited for this program. 3.3 Cepheids The distance ladder can be improved in two ways. First by indirect measurements: angular diameter measurement coupled with linear diameter derived from models. Second, by direct measurement: angular diameter variation coupled with spectroscopic photosphere velocity determination. The sample of sources for `Ohana comprises at least 100 targets for the indirect measurement and from 60 up to more than 100 for the direct measurement. Besides, the resolving power of `Ohana will allow to study the atmosphere of these stars and compare with current models which are a source of bias in the final distance ladder calibration. A large fraction of this program can be achieved with moderate baselines (~200 meters) and pupils (4 meters). 3.4 Brown dwarves The modeled diameter is on the order of 100 micro-as. However a measure of this diameter will strongly constrain the equation of state for cooling models. This is unique science as the full resolution of `Ohana is required as well as the largest pupils: the resolution of `Ohana is 425 micro-as in H band and so a diameter measurement translates into a 95% visibility measurement. The required accuracy on the visibility is 1% and there are half a dozen candidates within 10 pc. 4. Summary of plans for phase I and II 4.1 Phase I overview A modular injection device, the interfaces of which will have to be adapted to the f-ratio of each input beam, will be designed for Keck, CFHT and Gemini telescopes and possibly Subaru pending steric compatibility. It will verify the injection, measure the efficiency of AO to fiber coupling, investigate polarisation and fiber stability during the transport from focus to ground and give clues to the final sensitivity of the array. The tests, to begin on the telescopes in the fall of 2001, are expected to be completed by the end of that year. A large fraction of the tests will be done during daytime, while technical and/or discretionnary time could be considered for the sky validation. Both silica and fluoride glass fibers should be used for these tests and the injection modules should preserve compatibility for both types of fibers. Cost for phase I includes the construction of 2 injection modules (provision for phase II), a length of 50 meters of infrared fibers (and also silica fibers), laboratory measurement of beam transport in it and the assembly of an available IR detector. These costs can be beared by Meudon. New visits of Woillez to Hawaii will be necessary and it is wished to continue the arrangement which supported Woillez visit in November to December 2000. Phase I also includes the design and cost estimate of phase II for which the following goals and requirements were established. A requirement is the minimum achievement at which a task is said to be completed, while a goal is the ideal objective one would like to reach. 4.1 Requirements for Phase II - Demonstrate feasability of Phase III - Obtain fringes with 2 different telescopes equipped with AO on Mauna Kea - the diameter of the telescopes should be greater than 3 meters and the minimum baseline should be 150 meters. - Demonstrate coupling of telescopes of unequal diameter - The demonstrator source should be fainter than K = 8 - Meaningful visibilities should be obtained with 5% accuracy. - Meaningful results should be published as a refereed paper. - J or H or K bands - transit interferometer + "slew and clamp" delay line - delay line solution for phase III. 4.2 Goals for phase II - same as requirements but with 2 pairs (1 North/South, 1 East/West) - Baseline > 400 meters, - Limiting magnitude K > 12, - Unique science, - J, H and K, - sideral motion tracking, - fringe tracking. All this has to be achieved within the following constraints: - budget (cost and manpower), - telescope time, - demonstration by mid-2003. - telescope specifics (focii, mount, etc) 4.3 Plan for phase II Phase II should not only demonstrate the technical feasability of telescopes' coupling on Mauna Kea summit, but also lead to some unique science results beyond the VLTI and Keck Interferometer capabilities. Main parameters for the choice of telescopes are: telescope aperture, baseline length, baseline orientation (North/South orientation simplifies delay line problem). The science discussion led to the following potential objectives, ordered by probable increasing difficulty: - Cepheids require long (>200~400m) baselines and moderate apertures. Even one visibility at J, H, or K brings important information. - Young Stellar Objects require at least 150~200m baselines and moderate apertures. A few visibilities, using two different baselines (e.g. 200 and 400m) at J, H or K and possibly moderate spectral resolution (Br{gamma}) bring important information. - AGNs require at least 200 meters baselines with large apertures at H or K, possibly with moderate spectral resolution. Proper interpretation of a few visibilities in a complex object require more study. - Brown dwarves may require both largest baselines and apertures. Even one well calibrated visibility in H or K is important. Extending the VLTI and KI resolutions, any of those programs can bring unique science. Three baseline configurations satisfy the phase II requirements, offer the technical demonstration capability and contribute to these science goals. Among all possible configurations, this choice appears to select the simplest ones, which can be ordered by increasing difficulty: - CFHT-Gemini (~150m ~NS) with simple delay lines (slew and clamp) at Gemini or CFHT. - CFHT-UKIRT (~350m ~NS) with simple delay lines at Gemini. UKIRT having no AO for the moment, it will be equivalent to a 1.5 meter aperture if tip-tilt is corrected. - IRTF-Subaru (~405m ~EW) with Keck delay lines. IRTF should be equipped with AO by early 2003. For any of these baselines, the same pair of matched infrared and/or silica fibers ca. 450 meters in length can be used. Recombining equipment can be made available from existing systems for both infrared and silica fibers. Cost estimates for phase II will be consolidated in 2001 and discussed among partners. Yet, a significant fraction of the cost (beam combiner and possibly fibers) may be covered as the french contribution to the project. Phase II is likely to extend over 2002 and 2003. Its precise definition requires additional studies and will be the subject of the third `Ohana meeting to be held in the fall of 2001. 5. Action Items 1. Write summary (distribute) [PL, GP, OL, JW] 2. Date for next meeting [OL] 3. Obtain plan for ducts (Don Hall, Pui Hin) 4. String test/cable length [OL, OG] 5. Subaru AO injection interface [JN, JW] 6. cost and schedule analysis for phase II [GP, PL] 7. decide on silica fibers (for phase I and II) (F Reynaud) 8. Interferometric room in NPT [AT, OL] 9. Final design and fabrication of injection modules [JW] 10. Plan for 2x1month independant visits of JW. 11. Implementation and tests of modules (JW + technical contacts of each obs) 12. Schedule, temporal windows and deadlines for technical time 2001B [OL] 13. Light tunnels for phase II delay lines (GP, PW) 14. UKIRT direction and board information, AO possibilities [AA] 15. Paper for Liege July 2001 [`Ohana committee] 16. Operating modes (VLBI-like?) 17. Science cases for three configurations of phase II Cepheids [GP] YSOs [FMenard, CD, FMalbet] AGNs [HS, JW] Brown Dwarves [VCdF] 18. Preliminary Observations Fiber/AGN connection [JW] Possibility of AGN Collaboration on Gemini/Hokupa'a [OG, JW] 19. Three configurations of phase II: CFHT/Gemini CFHT/UKIRT (Gemini delay lines) Subaru/IRTF (Keck delay lines) 20. Ohana Committee (updated composition to be confirmed) Ukirt (Andy Adamson) IRTF (Alan Tokunaga) Subaru (Jun Nishikawa) UH contact update (Olivier Guyon, Don Hall, Rolf Kudritzki) 21. Technical contacts Keck (Peter Wizinowich) Gemini (Mark Chun and Jacques Sebag) Subaru (Jun Nishikawa, Hideki Takami) CFHT (Olivier Lai) IRTF (Dan O'Connor) UKIRT (Andy Adamson) UH (Olivier Guyon) 22. Contact the Canadian community [GF, OL, JP Veran] 6. Conclusion The meeting showed an extremely fruitful atmosphere of cooperation. The `Ohana committee remains informal, and will continue to inform the institutions interested by `Ohana.