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Telescope & Instruments

The Near Infrared High Resolution Spectrograph



Overview

GIANO is a near IR high resolution spectrograph mounted at the Nasmyth A focus of the TNG in July 2012. In October 2013 the Commissioning has been completed and in September 2014 the Science Verification has been successfully carried out.
The instrument provides cross dispersed echelle spectroscopy at a resolution of 50,000 over the 0.95-2.45 micron spectral range in a single exposure. It is fiber-fed with two fibers of 1 arcsec angular diameter at a fixed angular distance of 3 arcsec on sky. GIANO has only one observing mode (R~50,000) and it can acquire spectra either of astrophysical objects and sky simultaneously, or of calibration lamps (halogen for flat-field and U-Ne for wavelength calibration) and dark frames.

The Near IR High Resolution Spectrograph Dewar
Figure 1. Picture of Giano dewar in the TNG Nasmyth A.

Table 1. GIANO detector and spectral characteristics
Detector HAWAII-2 2048x2048
Pixel size 18 microns
Gain 2.2 e-/ADU
Readout Noise 5 e-
Dark Current 0.05e-/s/pixel
Spatial resolution 0.25 arsec/pixel
Wavelength Coverage 0.95 - 2.45 microns
Spectral resolution 50000
Fiber Size 85 microns - 1.0 arsec on the sky
Slicer 2x

Performance

First estimates of the overall GIANO performance as measured during the Commissioning and Science Verification runs.

Table 2. GIANO spectral accuracy and sensitivities
Wavelength calibration accuracy with U-Ne lamp 300 m/s (r.m.s)
Radial velocity accuracy with telluric lines 7 m/s (r.m.s)
Maximum S/N on flat field (about photon-noise limited) ~1000 (Y, J), ~300 (H, K)
Maximum S/N on stars (limited by fiber modal noise*) ~70 (Y, J), ~50 (H, K)
Zero point in J-band (Vega mag for 1 ADU/s) 10.1
Zero point in H-band (Vega mag for 1 ADU/s) 10.3
Zero point in K-band (Vega mag for 1 ADU/s) 10.2
Limiting magnitude z-band (Vega mag) of the guiding camera 15

* Fibers suffers of modal noise, whose amplitude increases with increasing wavelength. The maximum signal-to-noise achievable in the K-band is about 20 (without fiber-agitator) and 50 (with fiber-agitator). The maximum signal-to-noise is slightly higher at shorter wavelengths.

For more detailed information and clarification about the sensitivity and the spectral accuracy see the Cookbook for 2015A proposers

Recommended on-source integration times to reach S/N~50 per spectral pixel (about modal noise limited) for stars of different magnitudes, seeing < 1, are listed in Table 3.

Table 3.Recomended on-souce integration times
10
9
3600 sec
8 2400 sec
7 1800 sec
6 1200 sec
5
4
3
600 sec
2
1
0
200 sec
Vega mag. On source Integration Times (seeing < 1arsec)

More detailed information and more explanation about procedure and method of observation are in Cookbook for 2015A proposers

Manuals


A complete list of technical and scientific documents can be found at the Giano webpage (Bologna)

For any comments please contact Francesca Ghinassi.