Arcetri Solar Physics Group: Instrumentation

The Interferometric BIdimensional Spectrometer (IBIS) is a next generation bidimensional spectrometry instrument based on a dual Fabry-Perot interferometric system. It combines high-spectral resolution with short exposure times and a large field of view, as well as the ability to work in polarized light. This will allow it to address a variety of observational programs in solar physics. IBIS is based on the experience gained in the construction and operation of the Italian Panoramic Monochromator (IPM). The IPM, which is still an almost unique instrument for bidimensional solar spectroscopy, has high spectral resolution and high wavelength stability, but it suffers from low transparency and low temporal resolution, as well as a somewhat limited field of view.

IBIS esentially consists in two piezo-scanned, capacity servo-controlled Fabry-Perot interferometers (Queensgate Model ET50), used in series in the classical mount configuration and axial-mode, with a set of narrow-band interference filters (FWHM = 3 - 5 Å). This instrument, preserving the high spectral resolution ( λ / Δ&lambda ≥ 200,000) and the high wavelength stability (maximum drift ˜ 10 ms^-1 in 10 hours) typical of IPM, has improved characteristics. It allows observations over a larger wavelength range, in the red part of the spectrum (from 5800 Å to 8600 Å), and on a larger field of view (80" diameter vs. 51" diameter of IPM). Moreover, thanks to a high overall transparency ( ˜ 18 % vs. ˜ 1 % of IPM), IBIS allows the use exposure times sufficiently short to freeze the seeing ( ≤ 20ms vs. 200 - 300 ms of IPM, for S/N ≥ 100). By using post facto restoring procedures, such as the phase diversity technique, it is therefore possible to obtain high spatial resolution, near to the nominal limit of the telescope. Finally, due to the short exposure time and to the rapid wavelength positioning ( ˜ 20 ms vs. ˜ 1 s of IPM), a high temporal resolution (3 frames per second vs. ˜ 0.5 frames per second with the IPM) can also be obtained.

This instrument has been built by the Arcetri Astrophysical Observatory and the Department of Astronomy and Space Science of the Florence University, in collaboration with the Department of Physics of the Roma "Tor Vergata" University, to replace IPM at the THEMIS telescope. In 2003 IBIS will be provisionally installed to the Dunn Solar Telescope of the Sacramento Peak Observatory.


Wavelength range	5800 Å - 8600 Å

Available spectral lines	5896 Å Na D1 6302 Å Fe I 7090 Å Fe I 7224 Å Fe II 8542 Å Ca II

Range width	2.0 Å (5800 Å - 7500 Å) 3.5 Å (7500 Å - 8600 Å)

Spectral resolving power	212,000 - 274,000

Spectral inhomogeneity of the image plane (radial)	60 mÅ - 90 mÅ

Wavelength drift of the instrumental profile	≤ 10 ms^-1 on 10 h

Field of view (circular)	80"

Peak transparency	15% - 20%

Image scale	0.08" pixel^-1

Exposure time (for S/N ~ 100 and 2 pixels/resolved element)	7 - 18 ms

Wavelength setting time	~ 20 ms

Acquisition rate (1024 x 1024 pix @5 Mpixels/sec)	3 frames s^-1

Cavallini, F.: 1998, Purely Interferometric Solar Bidimensional Spectroscopy, Recent Results of Italian Solar Research, Roma, 18-20 March 1998, eds. I. Ermolli, F. Berrilli and B. Caccin, Memorie SAIt, 69, p. 627.

Cavallini, F., Berrilli, F., Cantarano, S., Egidi, A. and Baffa, C.: 1999, IBIS: A New Instrument for Solar Bidimensional Spectroscopy, JOSO Annual Report 1999, 29, p. 99

Cavallini, F., Berrilli, F., Cantarano, S. and Egidi, A.: 2000, IBIS: A New Instrument for Solar Bidimensional Spectroscopy, II Convegno sulla Ricerca Solare Italiana, L'Aquila, 3-5 July 2000, eds. P. Francia, E. Pietropaolo, B. Caccin, Memorie SAIt, 72, p. 554

Cavallini, F., Berrilli, F., Cantarano, S. and Egidi, A.: 2000, IBIS: A Purely Interferometric Instrument for Solar Bidimensional Spectroscopy, Proc. 1st Solar & Space Weather Euroconference, The Solar Cycle and Terrestrial Climate, Santa Cruz de Tenerife, 25-29 September 2000, ed. A. Wilson - ESA Publications Division, ESA SP-463, p. 607

Cavallini, F.: 2001, IBIS (Interferometric Bidimensional Spectrometer), Proc. of the Second Solar Cycle and Space Weather Conference, Vico Equense, 24-29 September 2001, ed. H. Sawaya-Lacoste, ESA-SP477, p. 585

Cavallini, F., Berrilli, F., Cantarano, S. and Egidi, A.: 2001, IBIS (Interferometric BIdimensional Spectrometer), THEMIS and the New Frontiers of Solar Atmosphere Dynamics, Roma, 19-21 March 2001, Il Nuovo Cimento (in press)

Cavallini, F., Berrilli, F., Cantarano, S., Egidi, A., Baffa, C. and Reardon K.: 2002, IBIS: Present Status, THEMIS Workshop, Toulouse, 17-19 April 2002 (in press)