Ian J. Lewis

The 2dF galaxy redshift survey: clustering properties of radio galaxies

The clustering properties of local, S1.4GHz ≥ 1 mJy, radio sources are investigated for a sample of 820 objects drawn from the joint use of the FIRST and 2dF Galaxy Redshift surveys. To this aim, we present 271 new bJ ≤ 19.45 spectroscopic counterparts of FIRST radio sources to be added to those already introduced in Magliocchetti et al. (2002). The two-point correlation function for the local radio population is found to be entirely consistent with estimates obtained for the whole sample of 2dFGRS galaxies. From measurements of the redshift-space correlation function �(s) we derive a redshift-space clustering length s0 = 10.7 +0.8 0.7 Mpc, while from the projected correlation function �(rT) we estimate the parameters of the real-space correlation function �(r) = (r/r0) , r0 = 6.7 +0.9 1.1 Mpc and = 1.6±0.1, where h = 0.7 is assumed. Different results are instead obtained if we only consider sources that present signatures of AGN activity in their spectra. These objects are shown to be very strongly correlated,

GMOS: the GEMINI Multiple Object Spectrographs

The two Gemini multiple object spectrographs (GMOS) are being designed and built for use with the Gemini telescopes on Mauna Kea and Cerro Pachon starting in 1999 and 2000 respectively. They have four operating modes: imaging, long slit spectroscopy, aperture plate multiple object spectroscopy and area (or integral field) spectroscopy. The spectrograph uses refracting optics for both the collimator and camera and uses grating dispersion. The image quality delivered to the spectrograph is anticipated to be excellent and the design is driven by the need to retain this acuity over a large wavelength range and the full 5.5 arcminute field of view. The spectrograph optics are required to perform from 0.36 to 1.8 microns although it is likely that the northern and southern versions of GMOS will use coatings optimized for the red and blue respectively. A stringent flexure specification is imposed by the scientific requirement to measure velocities to high precision (1 - 2 km/s). Here we present an overview of the design concentrating on the optical and mechanical aspects.

Integral field spectroscopy with the Gemini Multiobject Spectrographs

The most innovative feature of the Gemini multiobject spectrographs (GMOS) is the capability for integral field spectroscopy. This will allow the Gemini telescopes to obtain spectra over a contiguous rectangular field of area 50 arcsec2 with a sampling of 0.2 arcsec. The field will be reformatted into two long slits so that each element in the field is dispersed into a long spectrum containing up to 900 resolution elements at spectral resolutions up to 10,000. Background subtraction will be carried out via a separate field with identical optical characteristics. This will support a number of background-subtraction techniques including beam-switching. The integral field unit will be loaded into the focal plane in the same way as a slit mask to allow a rapid changeover between integral field and aperture spectroscopy. The design employs a combination of optical fibers and microlens arrays with enlarging fore-optics. The fibers give the desired reformatting ability to maximize the length of the spectrum while the microlenses provide both contiguous field coverage and optimal matching to the slow telescope and spectrograph optics. The integral field capability may be augmented and upgraded by adding different units. Of particular interest are options for finer spatial sampling (0.1 arcsec) and for operation in the near-infrared.

Multiple‐Object and Integral Field Near‐Infrared Spectroscopy Using Fibers

We describe a new system for multiple-object spectroscopy and integral field spectroscopy at near-infrared wavelengths using optical fibers. Both modes of the SMIRFS instrument have been tested at the UK Infrared Telescope with the CGS4 infrared spectrograph. The modular system includes a common optical system to image the fiber slit onto the cold slit inside the CGS4 cryostat. The multiobject mode consists of 14 interchangeable fused silica or zirconium fluoride fibers each with a field of 4. The integral field mode consists of 72 fused silica fibers coupled with a lenslet array to give a contiguous field of 6 × 4 with sampling.We describe the performance of both modes. For the multiobject mode, the feasibility and desirability of using fluoride fibers to extend the wavelength range into the K band is discussed. For the integral field mode, the performance is compared with theoretical expectation with particular attention to the effect of focal ratio degradation in the fibers.These results demonstrate the feasibility of multiobject and integral field spectroscopy in the near-infrared using lenslet-coupled fiber systems. Although SMIRFS in an experimental system working with a spectrograph not designed for this purpose, the throughput and uniformity of response are good. SMIRFS points the way forward to systems with much larger numbers of elements.

Autofib--2: an automated fiber positioner for the prime focus of the William Herschel Telescope

We are currently testing an automated fibre positioner for the 4.2 m William Herschel Telescope (WHT). This instrument, known as Autofib-2, operates at the prime focus where it is able to utilize the full 1 degree field provided by the prime focus corrector (PFC). The robotic positioner is able to place 160 optical fibres in the focal plane of the WHT which feeds the light to a dedicated spectrograph (WYFFOS) located on the Nasmyth platform. This paper contains a description of the instrument which highlights the new techniques demanded by the prime focus plate scale and the scale distortions due to the PFC and its atmospheric dispersion compensator. These include robot vision to help achieve the high positioning accuracy and the use of two sky viewing probes to accurately determine the time dependent transformation from celestial coordinates to instrumental Cartesian coordinates. Also presented are the initial technical results on the performance of the instrument and the operational results of particular interest to the astronomical observer.

The GEMINI Multiobject Spectrographs

As the only two optical instruments appearing in its first fleet of instrumentation, the GEMINI MultiObject Spectrograph (GMOS) are indeed being developed as workhorse instruments. One GMOS will be located at each of the GEMINI telescopes to perform: a) exquisite direct imaging, b) 5.5 arcminute longslit spectroscopy, c) up to 600 object multislit spectroscopy, and d) about 2000 element integral field spectroscopy. The GMOSs are the only GEMINI instrumentation duplicated at both telescopes. The UK and Canadian GMOS team successfully completed their critical design review in February 1997. They are now well into the fabrication phase, and will soon approach integration of the first instrument. The first GMOS is scheduled to be delivered to Mauna Kea in the fall of99 and the second to Cerro Pachon one year later. In this paper, we will look at how a few of the more interesting details of the final GMOS design help meet its demanding scientific requirements. These include its transmissive optical design and mask handling mechanisms. We will also discuss our plans for the mask handling process in GEMINIs queue scheduled environment, from the taking of direct images through to the use of masks on the telescope. Finally, we present the status of fabrication and integration work to date.

The Gemini Multi-Object Spectrographs

Each GEMINI telescope will be equipped with a versatile optical/near-IR spectrographs which will fully exploit its large aperture and excellent image quality. The basic parameters of the GEMINI Multi-object Spectrographs (GMOS) are summarised in the table below.

Autofib-2: commissioning results of a robotic multiobject fiber system for the William Herschel Telescope

Autofib-2 is a robotic fiber system for the prime focus of the William Herschel telescope capable of placing up to 150 fibers in the 1 degree focal plane of the telescope. The fibers are fed to a purpose built spectrograph (WYFFOS) mounted on one of the Nasmyth platforms. Autofib-2 and WYFFOS are now entering a common user phase as fully commissioned instruments. We describe the novel techniques used to achieve the high precision in fiber placement delivered by this instrument and the quality control procedures devised to measure and monitor instrument stability. The characterization of the distortions of focal plane delivered by the prime focus corrector of the telescope was a vital procedure during the commissioning. We describe the methods of measuring these distortions and discuss the limitations of the instrument, telescope and astrometry.

The HARMONI/ELT spectrographs

HARMONI is an Integral Field Spectrograph (IFS) for ESO’s ELT. It has been selected as the first light spec- trograph and will provide the workhorse spectroscopic capabilities for the ELT for many years. HARMONI is currently at the PDR-level and the current design for the HARMONI IFS consists of a number of spaxel scales sampling down to the diffraction limit of the telescope. It uses a field splitter and image slicer to divide the field into 4 sub-units, each providing an input slit to one of four nearly identical spectrographs. All spectrographs will operate at near infrared wavelengths (0.81-2.45 micrometers), sampling different parts of the spectrum with a range of spectral resolving powers (3300, 7000, 18000). In addition, two of the four spectrographs will have a Visible capability (0.5-0.83 micrometers) operating with seeing-limited observations. This proceeding presents an overview of the opto-mechanical design and specifications of the spectrograph units for HARMONI.

Autofib--2 software control systems and user operation

The first part of this paper describes the microcomputer software that controls the individual mechanisms of the Autofib-2 instrument. All previous microprocessor systems built for the William Herschel Telescope used a variant of the Forth language to implement the control system; however, Autofib-2 is the first instrument to be controlled using a UNIX-style real-time operating system. Facets of the implementation will be discussed, including the reengineering of the interfaces in OS/9 C to allow connection to the existing interinstrument communications systems (Utility Network). The algorithms needed to successfully configure 160 fibers taking into account prime focus corrector (PFC) distortions are also discussed. The second part of this paper describes the astronomer-level control system running on the VAX System Computer. Details will be given of the way in which the astronomers target field is defined and converted into the configuration data to be sent to the microprocessor system, including the mapping of the PFC distortions and the acquisition of new target fields.