106 research outputs found
UV camera conceptual designs for TMT Fiber WFOS
This paper discusses refractive, reflective and catadioptric designs for the Thirty Meter Telescope Fiber Wide Field Optical Spectrograph (WFOS) instrument concept. Custom macros were written to evaluate performance at the detector plane with the grating at the pupil as a function of fiber position in the pseudo-slit and wavelength, and a tolerance analysis has been performed for each design based on best engineering practices to assess performance robustness against opto-mechanical errors. The catadioptric camera appears to provide the best compromise in this regard
Tachoastrometry: astrometry with radial velocities
Spectra of composite systems (e.g., spectroscopic binaries) contain spatial
information that can be retrieved by measuring the radial velocities (i.e.,
Doppler shifts) of the components in four observations with the slit rotated by
90 degrees in the sky. By using basic concepts of slit spectroscopy we show
that the geometry of composite systems can be reliably retrieved by measuring
only radial velocity differences taken with different slit angles. The spatial
resolution is determined by the precision with which differential radial
velocities can be measured. We use the UVES spectrograph at the VLT to observe
the known spectroscopic binary star HD 188088 (HIP 97944), which has a maximum
expected separation of 23 milli-arcseconds. We measure an astrometric signal in
radial velocity of 276 \ms, which corresponds to a separation between the two
components at the time of the observations of 18 milli-arcseconds. The
stars were aligned east-west. We describe a simple optical device to
simultaneously record pairs of spectra rotated by 180 degrees, thus reducing
systematic effects. We compute and provide the function expressing the shift of
the centroid of a seeing-limited image in the presence of a narrow slit.The
proposed technique is simple to use and our test shows that it is amenable for
deriving astrometry with milli-arcsecond accuracy or better, beyond the
diffraction limit of the telescope. The technique can be further improved by
using simple devices to simultaneously record the spectra with 180 degrees
angles.With tachoastrometry, radial velocities and astrometric positions can be
measured simultaneously for many double line system binaries in an easy way.
The method is not limited to binary stars, but can be applied to any
astrophysical configuration in which spectral lines are generated by separate
(non-rotational symmetric) regions.Comment: Accepted for publication in A&
The ESO Spectroscopic facility
We present the concept of a novel facility dedicated to massively-multiplexed
spectroscopy. The telescope has a very wide field Cassegrain focus optimised
for fibre feeding. With a Field of View (FoV) of 2.5 degrees diameter and a
11.4m pupil, it will be the largest etendue telescope. The large focal plane
can easily host up to 16.000 fibres. In addition, a gravity invariant focus for
the central 10 arc-minutes is available to host a giant integral field unit
(IFU). The 3 lenses corrector includes an ADC, and has good performance in the
360-1300 nm wavelength range. The top level science requirements were developed
by a dedicated ESO working group, and one of the primary cases is high
resolution spectroscopy of GAIA stars and, in general, how our Galaxy formed
and evolves. The facility will therefore be equipped with both, high and low
resolution spectrographs. We stress the importance of developing the telescope
and instrument designs simultaneously. The most relevant R\&D aspect is also
briefly discussed.Comment: 6 pages 4 figures , presented at IAU Symposium 334 "rediscovering our
galaxy
On-sky results of the adaptive optics MACAO for the new IR-spectrograph CRIRES at VLT
The adaptive optics MACAO has been implemented in 6 focii of the VLT
observatory, in three different flavors. We present in this paper the results
obtained during the commissioning of the last of these units, MACAO-CRIRES.
CRIRES is a high-resolution spectrograph, which efficiency will be improved by
a factor two at least for point-sources observations with a NGS brighter than
R=15. During the commissioning, Strehl exceeding 60% have been observed with
fair seeing conditions, and a general description of the performance of this
curvature adaptive optics system is done.Comment: SPIE conference 2006, Advances in adaptive optics, 12 pages, 11
figure
Concept and optical design of the cross-disperser module for CRIRES
This is the peer reviewed version of the following article: Oliva, Ernesto, A. Tozzi, D. Ferruzzi, L. Origlia, A. Hatzes, R. Follert, T. Loewinger et al. "Concept and optical design of the cross-disperser module for CRIRES+." In SPIE Astronomical Telescopes+ Instrumentation, pp. 91477R-91477R. International Society for Optics and Photonics, 2014, which has been published in final form at 10.1117/12.2054381
Toward the final optical design MOONS, the Multi-Object Optical and Near infrared Spectrometer for the VLT
MOONS (Multi-Object Optical and Near-infrared Spectrograph for the VLT) is entering into the final design phase. This paper presents and discusses the latest proposed version of the optical design of the cryogenic spectrograph. The main developments and modifications were aimed at minimizing the overall size and mass of the cryogenic spectrograph. The most remarkable new feature is the design of an extremely fast (F/0.95), light and compact (40 kg in less than 80 dm3) camera with superb image quality over a very large field of view (9 degrees on a collimated beam of 265 mm). The camera consists of only three optical elements: two lenses and one mirror. All elements are made of fused-silica. The optical performances are independent on the temperature, i.e. the camera can be fully characterized at room temperatures
Elliptic and hyperelliptic magnetohydrodynamic equilibria
The present study is a continuation of a previous one on "hyperelliptic"
axisymmetric equilibria started in [Tasso and Throumoulopoulos, Phys. Plasmas
5, 2378 (1998)].
Specifically, some equilibria with incompressible flow nonaligned with the
magnetic field and restricted by appropriate side conditions like "isothermal"
magnetic surfaces, "isodynamicity" or P + B^2/2 constant on magnetic surfaces
are found to be reducible to elliptic integrals. The third class recovers
recent equilibria found in [Schief, Phys. Plasmas 10, 2677 (2003)]. In contrast
to field aligned flows, all solutions found here have nonzero toroidal magnetic
field on and elliptic surfaces near the magnetic axis.Comment: 9 page
Challenges in optics for Extremely Large Telescope instrumentation
We describe and summarize the optical challenges for future instrumentation
for Extremely Large Telescopes (ELTs). Knowing the complex instrumental
requirements is crucial for the successful design of 30-60m aperture
telescopes. After all, the success of ELTs will heavily rely on its
instrumentation and this, in turn, will depend on the ability to produce large
and ultra-precise optical components like light-weight mirrors, aspheric
lenses, segmented filters, and large gratings. New materials and manufacturing
processes are currently under study, both at research institutes and in
industry. In the present paper, we report on its progress with particular
emphasize on volume-phase-holographic gratings, photochromic materials,
sintered silicon-carbide mirrors, ion-beam figuring, ultra-precision surfaces,
and free-form optics. All are promising technologies opening new degrees of
freedom to optical designers. New optronic-mechanical systems will enable
efficient use of the very large focal planes. We also provide exploratory
descriptions of "old" and "new" optical technologies together with suggestions
to instrument designers to overcome some of the challenges placed by ELT
instrumentation.Comment: (Proc. OPTICON Key Technology Network Workshop, Rome 20-21 October
2005
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