Joan Oró Telescope | Instrumentation

LAIA and ARES

The TJO is equipped with two instruments:

An imaging camera (LAIA) and a medium resolution spectrograph (ARES). It also has a second imaging camera (MEIA2) as a backup camera.

LAIA

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ARES

The ARES instrument (Astronomical mid-REsolution Spectrograph) is a fibre spectrograph installed in a dedicated room on the ground floor of the TJO building.

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LAIA

Large Area Imager for Astronomy

The LAIA instrument (Large Area Imager for Astronomy) is the optical imaging camera of the TJO, operational since December 2018. It consists of two components: the CCD camera and the filter wheel. Please read all the information presented here when preparing submissions with the TJO.

CCD camera

The CCD camera is an Andor iKon XL with a 4kx4k back-illuminated sensor:

R Model: CCD230-84
R Manufacturer of the sensor: e2v
R Sensor type: back-illuminated
R Coating: BV
R Number of pixels: 4096 x 4096
R Pixel size: 15 x 15 um (0.4 x 0.4 arcsec at the TJO)
R FOV at the TJO: 30 arcmin
R Sensor size: 61.4 x 61.4 mm
R Quantum efficiency: >90% from 500 to 650 nm; >50% in all the range from 400 to 850 nm
R Typical working temperature: -50ºC
R Dark current: <0.01 e-/pixel/sec at -50ºC
R Readout noise: <9e- RMS a 1 MHz
R Redout channels: 4
R Non-linearity: <1%
R Readout time: 8 sec

Filter wheel

The filter wheel is physically attached to the telescope, behind the primary mirror mount. It can accommodate up to 12 3-inch filters that are positioned on the optical axis of the telescope using the rotating filter wheel. There are currently 5 Johnson-Cousins photometric filters (manufactured by Custom Scientific) installed: U, B, V, Rc and Ic, 4 Sloan Digitized Sky Survey photometric filters (manufactured by Asahi Spectra): g, r, i and z; and an H-alpha filter (Asahi Spectra).

Vignetting

LAIA is designed to cover the entire field of the TJO focal plane. With its 4096 x 4096 pixels, LAIA can cover a head of 27.3 x 27.3 arc minutes. On the other hand, the focal plane covers a circular field of 30 minutes of arc. This causes the edges of the LAIA images to be vignetting. Additionally, the ARES pick-off mirror is also seen in the LAIA field of view with vignetting at the northern end of the field. As a result, the LAIA images will look similar to the one shown below:

Standard calibration procedure

The TJO control system is designed to periodically execute the acquisition of calibration images, including bias, darks and flats:

R Bias: They are usually taken in multiples of 5 before the start and at the end of each night. Observers are given a minimum of 10 bias images.

R Darks: They are obtained just before or after the bias images. The exposure time of the dark images will correspond to the maximum exposure time of the night science images.

R Sky flats: These are routinely taken at the beginning and end of the night under suitable sky lighting conditions. When sky conditions do not permit, observers are provided with the most recent flat images available.

ARES

Astronomical mid-REsolution Spectrograph

The ARES instrument (Astronomical mid-REsolution Spectrograph) is a fibre spectrograph installed in a dedicated room on the ground floor of the TJO building. ARES allows the observation of bright stars with a resolution of R=12000 in two spectral windows centred at 512 nm and 656 nm.

Limiting magnitude: S/N=10 for V=13 mag in 1-hour exposure time
Global transmissivity: >10%
Spectral resolution: R=12000
Two spectral windows: green (from 405 to 530 nm), red (from 630 to 673 nm)

In order to achieve a high global transmissivity (>10%) two telescopes (manufactured by Takahashi) and two VPHs in Littrow configuration are used.

VPHs

The dispersion system of the ARES spectrograph is composed of two VPHs developed by Wasatch Photonics, providing the two spectral windows and maintaining a high transmissivity. Both VPHs are mounted on a rail (prepared to accommodate an additional one) which allows a quick change between them.

CCD camera

The CCD detector used by ARES is an Andor Newton DU940P CCD camera with the following characteristics:

R Sensor type: BV- back-illuminated, optimised for VIS
R Number of pixels: 2048 x 512
R Pixel size: 13.5 x 13.5 um
R Sensor size: 26.7 x 6.9 mm
R Minimum working temperature: -100ºC
R Readout noise: 2.8 e-
R Dark current: 0.0002 e-/pixel/s
R Linearity: better than 99%

Spectra with simultaneous calibration

ARES is equipped with three fibres, providing 3 simultaneous spectra in each exposure. One of the fibres is centred on the stellar-type object of interest, another is used in order to obtain the spectrum of the sky background, and the third fibre, positioned between the other two, can be used both to obtain flats of a calibration lamp or to obtain calibration arcs in wavelength. The observer can choose which type of calibration spectrum will be inserted into the image when defining the configuration of the observations.

Below are two examples, one showing the two sky fibres illuminated, and the other with a star centred on a sky fibre and a simultaneous calibration arc.

Standard calibration procedure

Apart from the calibration of the spectrum obtained simultaneously with the images, the TJO control system is designed to periodically obtain the calibration images, including bias, darks and spectroscopic flats:

R Bias:They are usually taken in multiples of 5 before the start and at the end of each night. Observers are given a minimum of 10 bias images.

R Darks: They are obtained just before or after the bias images. The exposure time of the dark images will correspond to the maximum exposure time of the night science images.

R Spectroscopic flats: The optimal calibration strategy for ARES is still under evaluation. The main purpose of spectroscopic flats is to trace the position of the spectrum and correct the intra-pixel response. For this reason, 4 options can be studied: direct illumination of the CCD, dome flats, illumination of the fibres with LEDs, and standard stars. The solution that provides the optimal result will be used for the spectra images delivered to the observers.