赤外線高分散ラボ:Laboratory of Infrared High-resolution spectroscopy

about WINERED

Top Overview For observers Gallery Technical detail

Observing modes

Observers can select one of the three modes (WIDE, HIRES-Y&J) depending on their priority on spectral resolution [1] and wavelength coverage. Three slits of 100 μm-width 140 μm-width, and 200 μm-width are available for WIDE and HIRES-Y&J modes.

[1] Note that the WIDE and HIRES-Y&J modes cannot be switched during the observing night to avoid any hardware trouble.


Mode

WIDE

HIRES-Y

HIRES-J

Wavelength coverage

0.91 - 1.35 μm
(z, Y, J bands)

0.96 - 1.11 μm
(Y band)

1.14 - 1.35 μm
(J band)

Spectral resolution
(R≡λ/ΔλFWHM)

28,000

70,000 [1]

Throughput

~ 50% [2]

~ 32% [2]

~ 42% [2]

Main disperser

Reflective echelle grating

Mosaicked high-blazed echelle grating

Array

1.7 μm cut-off HAWAII-2RG

Size

1.75 m (L) × 1.07 m (W) × 0.50 m (H)


[1] In the engineering observation on NTT, R∼55,000
[2] Including the throughput of optics and QE of the array.


Wavelength coverages

Overall picture

The wavelength coverages of each echell order for the WIDE, HIRES-Y, and HIRES-J modes are illustrated in the figure below. A model of atmospheric transmission curve is also indicated in the figure.

WINERED

For reference, the observed spectrum of atmospheric absorption with the WIDE mode at Kyoto is available here. [Click here for details]


Free spectral ranges

WIDE mode

m

Free spectral range (μm)

m

Free spectral range (μm)

61

0.912 – 0.928

51

1.089 – 1.110

60

0.928 – 0.942

50

1.110 – 1.132

59

0.942 – 0.958

49

1.132 – 1.156

58

0.958 – 0.976

48

1.156 – 1.180

57

0.976 – 0.992

47

1.180 – 1.205

56

0.992 – 1.010

46

1.205 – 1.232

55

1.010 – 1.028

45

1.232 – 1.260

54

1.028 – 1.048

44

1.260 – 1.290

53

1.048 – 1.068

43

1.290 – 1.319

52

1.068 – 1.089

42

1.319 – 1.351


HIRES-Y mode

m

Free spectral range (μm)

m

Free spectral range (μm)

184

0.957 – 0.962

171

1.030 – 1.036

183

0.962 – 0.968

170

1.036 – 1.042

182

0.968 – 0.973

169

1.042 – 1.048

181

0.973 – 0.978

168

1.048 – 1.055

180

0.978 – 0.984

167

1.055 – 1.061

179

0.984 – 0.989

166

1.061 – 1.067

178

0.989 – 0.995

165

1.067 – 1.074

177

0.995 – 1.001

164

1.074 – 1.080

176

1.001 – 1.007

163

1.080 – 1.087

175

1.007 – 1.012

162

1.087 – 1.094

174

1.012 – 1.018

161

1.094 – 1.101

173

1.018 – 1.024

160

1.101 – 1.108

172

1.024 – 1.030

159

1.108 – 1.115


HIRES-J mode

m

Free spectral range (μm)

m

Free spectral range (μm)

155

1.136 – 1.143

142

1.239 – 1.248

154

1.143 – 1.150

141

1.248 – 1.257

153

1.150 – 1.158

140

1.257 – 1.266

152

1.158 – 1.166

139

1.266 – 1.275

151

1.166 – 1.173

138

1.275 – 1.284

150

1.173 – 1.181

137

1.284 – 1.294

149

1.181 – 1.189

136

1.294 – 1.303

148

1.189 – 1.197

135

1.303 – 1.313

147

1.197 – 1.205

134

1.313 – 1.323

146

1.205 – 1.214

133

1.323 – 1.333

145

1.214 – 1.222

132

1.333 – 1.343

144

1.222 – 1.231

131

1.343 – 1.353

143

1.231 – 1.239


Limiting magnitudes

The following table gives estimated limiting magnitudes when the WINERED is attached to the 3.58-meter NTT.


Mode

WIDE

HIRES

Slit width [um]

100

140

200

100

140

200

Slit width [arcsec]

0.54

0.76

1.08

0.54

0.76

1.08

Slit width [pixel]

2.0

2.8

4.0

2.0

2.8

4.0

Pixel scale [arcsec/pixel]

0.27

Slit length [arcsec]

16.34

Resolution

28,000

24,000[1]

18,000

68,000[2]

58,000[3]

44,000[3]

z-band limiting magnitude (Vega)

14.08

14.40

14.69

-

-

-

Y-band limiting magnitude (Vega)

14.29

14.62

14.19

12.91

13.25

13.53

J-band limiting magnitude (Vega)

14.40

14.73

15.02

13.03

13.35

13.64


[1] Not measurement, but just expected value.
[2] In the engineering observation on NTT, R∼55,000
[3] Not measurement, but just expected value from an ideal case.


The assumptions made for calculating the above limiting magnitudes are as follows:

  • Integration time: 1 hour (900 sec * 4; ABBA sequence)
  • S/N: 30
  • Point source size: 1.2 arcsec
  • Atmospheric transmittance: 0.95
  • Throughput of the telescope: 0.55

Estimate of observing time

The following figures show roughly estimated required time as a function of the J-band magnitude. The time is calculated for the point-source observation.


WIDE mode

WINERED

HIRES-J mode

WINERED

Overheads

Action Time (minutes)
Acquisition 3 [1]
Read-out + writing data 0.2 [2]
Nodding to another slit position 0.5 [1]
Offset to sky 0.2 [1]

[1] In the case of being installed on Araki telescope.
[2] This is a typical time. Strictly speaking, it depends on the setting of non-destructive reading.


Observing sequences and necessary durations

A typical observing sequence is composed of four integrations at dithered position along the slit (known as an ABBA sequence) for a faint target or three integrations, two with the target within the slit and one for a blank sky (known as an OSO sequence) for a bright target whose PSF gets prominent over a wide area of the slit.


For each sequence, the following formula may be used for estimating a necessary observing time including the overheads. The overheads are estimated for observations with Araki telescope in Koyama observatory at Kyoto Sangyo University, and they may be slightly different when attached to other telescopes. We are going to give realistic estimates of these overheads for observations with NTT 3.6-m telescope after our first observing run(s).


  • ABBA: t(integ) + 3 + 4 * 0.2 + 2 * 0.5 [minutes]
  • OSO: t(integ) * (3/2) + 3 + 3 * 0.2 + 2 * 0.2 [minutes]

t(integ) is the integration time for a given magnitude.


Detector characteristics

Residual charge

The detector array used in WINERED exhibits a residual charge from bright sources. The residual will typically be ~1% of the originally detected signal.


In order to reduce the influence of the residual charge, bright and faint sources are usually observed at different slit positions [1]. Furthermore, dome flats and comparison lamp spectra will be taken only after observation.


[1] The O position is mainly used for bright sources, while the A and B positions are for faint sources.


Miscellaneous information

  • The shortest exposure time is 1.5 sec. In this case, the time to reset, read out and write data is about 10 sec. Therefore, the minimum amount of time between consecutive observation is about 10 sec.
  • The linearity limit is around 40000 ADU (or 48000 ADU may be acceptable to ~1.3% deviation) from laboratory experiments.

Data reduction pipeline

We developed the WINERED data-reduction pipeline, which automatically produces 1D spectra from raw data in less than 20 minutes/frame.


Automatic correction for telluric absorption, which is mandatory for infrared spectroscopy, is under development and is planned to be incorporated into the WINERED data-reduction pipeline.


Auxiliary information concerning the WINERED performance

Quality of spectra

The high-sensitivity of WINERED enables us to obtain NIR high-resolution spectra with high signal-to-noise ratio in much shorter time, or bring us to unexplored faint-end by NIR high-resolution spectroscopy. For example, WINERED mounted on a 10-m telescope equipped with AO can be used for the study of the absorption line systems of z > 6 QSOs or GRBs (J > 18 mag).


Background

The measured background radiation reaching the array for various the ambient temperatures is shown in the figure below. The difference of plots shows different season. The solid line is a predicted flux with an assumption that the ambient environment is the block body. The dashed lines is the level of measured stray light in the cryostat.



Optical performances

The measurement result of the total throughput of the WIDE-mode (filled circles) that does not include the slit loss is shown in the figure below. The solid line, dashed line, and dotted line are the model of atmospheric transmittance, the asuumed throughput of the 1.3-m Araki telescope, and the quantum efficiency of the array based on measurements by Teledein Inc., respectively.


WINERED