LIINUS/SERPIL: a design study for interferometric imaging spectroscopy at the LBT

Abstract

LIINUS/SERPIL is a design study to augment LBTs interferometric beam combiner camera LINC-NIRVANA with imaging spectroscopy. The FWHM of the interferometric main beam at 1.5 micron will be about 10 mas, offering unique imaging and spectroscopic capabilities well beyond the angular resolution of current 8-10m telescopes. At 10 mas angular scale, e.g., one resolution element at the distance of the Galactic Center corresponds to the average diameter of the Pluto orbit (79 AU), hence the size of the solar system. Taking advantage of the LBT interferometric beam with an equivalent maximum diameter of 23 m, LIINUS/SERPIL is an ideal precursor instrument for (imaging) spectrographs at extremely large full aperture telescopes. LIINUS/SERPIL will be built upon the LINC-NIRVANA hardware and LIINUS/SERPIL could potentially be developed on a rather short timescale. The study investigates several concepts for the optical as well as for the mechanical design. We present the scientific promises of such an instrument together with the current status of the design study.

LIINUS/SERPIL: a design study for interferometric imaging spectroscopy at the LBT

“…This section describes the scientific rationale for building LIINUS/SERPIL. An introduction of the exciting possibilities that this instrument will offer has been discussed in [3]. The science cases range from binary stars, exoplanets, star forming regions and star clusters, to intermediate mass black holes (IMBH), the Galactic Center, nearby galactic nuclei and in particular nearby AGN.…”

“…1. the nucleus should be bright enough for fringe-tracking (K-band magnitude <10 within 1" aperture), 2. the galaxy should be easily observable at LBT's latitude, 3. the galaxy should be close enough so that small nuclear structures can be resolved at the near-infrared diffraction limit of an equivalent 28m-telescope, and 4. the galaxies should be "well-known" so that complementary data can be found in the literature These 10 objects in themselves will already yield invaluable insights into the detailed structure of AGN.…”

“…The several options for IFS in the context of LIINUS/SERPIL are discussed in a previous publication [3]. Soon after the project was started, it became obvious, that LIINUS/SERPIL would not replace LINC at the telescope and therefore it will be built within the LINC/NIRVANA hardware.…”

“…The spectrograph could then be placed either inside LINC or in a new cryostat by transporting the light via optical fibers. Since image slicer IFUs normally occupy a lot of space due to the long pseudo-slit formed [3], for a spectrograph fully integrated to LINC, a lenslet array IFU is the baseline. If the spectrograph is built in a separate cryostat, a lenslet+fibers IFU is the only realistic option.…”

“…This space was initially considered as a cylinder of 30 cm diameter, and length of 70 cm. In order to demonstrate that building a spectrograph inside this volume is feasible, a preliminary optical design employing a microlens array IFU was first developed [3]. However, as this volume has changed over the last two years, a new design of the spectrograph has been developed.…”