The South Africa Near-infrared Doppler instrument (SAND) is a time-stable high-dispersion spectrograph, covering the z- and Y-bands simultaneously (849 - 1085 nm) with the maximum spectral resolution of ∼60,000. We aim to monitor the radial velocity of M-dwarfs with the precision of a few m/s level, which enables us to search for habitable exoplanets. Our another scientific motivation is the statistical investigation of young planets and stellar atmosphere to comprehensively understand the formation senario of stellar systems. We are planning to install the SAND to telescopes at the South African Astronomical Observatory (SAAO) in Sutherland, since the Southern sky covers plentiful stellar associations with young stars. The SAND is a fiber-fed spectrograph, and we can change telescope used to collect the star light by switching the fiber connection. It will be operated mainly with two telescopes: the Prime-focus Infrared Microlensing Experience telescope (PRIME) and the InfraRed Survey Facility (IRSF), which both are managed by universities in Japan. This strategy of using multiple telescopes gives us opportunities of frequent and long-term observations, which provides well phase coverage in radial velocity monitoring and results in non-bias search for exoplanets. Most of the components used in the spectrograph and the fiber injection module have been fabricated. We will present the detailed status and recent progress: designing the fiber injection module and the thermal control system, examination of fiber characteristics, and estimating our target candidates.
We have developed a simultaneous near-infrared camera, kSIRIUS, for the Kagoshima University 1m telescope. This camera has three focal planes created by two dichroic beam splitters for the J (λ = 1.21μm), H (λ= 1.65μm), and Ks (λ = 2.15μm) bands. kSIRIUS is designed to have three ∼ 10′ × 10′ fields of view with a seeing-limited resolution (∼ 1.5′′ at Kagoshima University Iriki Observatory) all over the fields. However, we have not yet obtained large format array detectors, so three small InGaAs array detectors are placed at the three focal planes. These detectors, which have 320×256 pixels, are newly manufactured for astronomy at Hamamatsu Photonics K. K., Japan, in collaboration with us, and cover three 3.7′ × 2.9′ fields of view with a pixel scale of 0.69′′. These three detectors enable a simultaneous imaging observation of the J, H, and Ks bands. We performed a test observation of kSIRIUS on the 1m telescope in January 2023. The stellar image quality is reasonably good compared to the typical site seeing. We have also determined the limiting magnitudes as J: 16.3, H: 15.3, and Ks: 14.5 (270 sec integration, S/N = 10, Vega magnitude), which are consistent with the expected values. We also have an optical g′ and i′ band camera covering 10′×10′ fields of view, working together with kSIRIUS. This setup allows us to acquire five (g′i′JHKs) images simultaneously, and will be particularly useful for studying any kind of time variable targets.
We present the current status of our development of a new near-infrared spectrometer for the InfraRed Survey Facility (IRSF) 1.4-m telescope, located in South Africa. The spectrometer is designed to cover the wavelength range of 1.0–1.6 μm with the spectral resolution of 550 at 1.2 μm and 730 at 1.6 μm and have a small number of optical surfaces to achieve a high optical throughput of 55%. The spectrometer is also equipped with a near-infrared slit viewer with a 3′×4′ field of view to perform precise spectral monitoring and mapping. We have tentatively completed the development of the instrument by using a commercial InGaAs detector and confirmed its expected sensitivity and spectral resolution by test observations with the Kagoshima University 1-m telescope. We now plan to replace the current detector with a new InGaAs detector developed for astronomical observations. The new detector covers the same wavelength range as the current one but has a significantly lower dark current and a larger array format, which enables us to upgrade the spectrometer to have higher sensitivity and spectral resolution. We plan to mount the spectrometer on the IRSF telescope by early 2025 after the detector is replaced and the second test observation with the Kagoshima University telescope is done.
We are developing a high-resolution near-infrared spectrograph for exoplanet searches with telescopes in Suther- land, South Africa; the South Africa Near-infrared Doppler (SAND) instrument. It covers the z- and Y -bands (0.83–1.10 µm) simultaneously with a maximum spectral resolution of 55, 000. This specification enables the precise radial velocity (RV) measurements to search for both giant planets around young stars and habitable planets around nearby M-dwarfs. The SAND is a fiber-fed instrument and, therefore, can be installed into several telescopes at the same site by changing the fiber connection. It will be operated mainly on the PRIME telescope, which is newly developed by Osaka University in Japan. The InfraRed Survey Facility (IRSF) and the Southern African Large Telescope (SALT) are also candidate telescopes for the installation. Inside the SAND spectrograph, a star image ejected from the fiber is sliced half and each sliced image is spectrally dispersed by an echelle grating. As a reference source for the wavelength calibration, light transmitted from a Fabry-Perot Etalon is simultaneously injected into the spectrograph and share the almost identical optical pass. The SAND is expected to realize RV-measurements for targets in large stellar associations at the southern sky, with exclusive and flexible use of the telescope time.
Narrow-band filters can detect emission and absorption line features from multiple sources in a field of view simultaneously without spectroscopy. However, it is difficult to estimate and subtract the continuum component from sources of different spectral slope, especially when the equivalent width of the target lines is small. For example, Cataclysmic Variables have equivalent widths of hydrogen recombination emission lines of about –10 to –100 angstroms, but many of the ones that have been detected by conventional NB filters so far have a large equivalent width. We have therefore constructed novel narrow-band filters with transmission bands on both sides of the central wavelengths of the Paβ (1.282 µm) and Brγ (2.167 µm) emission lines so that we can evaluate the continuum level more accurately than the conventional filters having transmission in only one side of the target line. We installed the narrow-band filters to the Simultaneous three-color InfraRed Imager for Unbiased Survey (SIRIUS) in the InfraRed Survey Facility (IRSF) telescope at South African Astronomical Observatory (SAAO), and evaluated their performance. We found that the narrow-band filters can detect emission line features with an equivalent width of several tens of angstroms. Thus, this filter set is useful for detecting emission line features from targets with small equivalent widths that have been difficult to detect with the conventional NB filter set.
We report the evaluation results of a commercially available InGaAs image sensor manufactured by Hamamatsu
Photonics K. K., which has sensitivity between 0.95μm and 1.7μm at a room temperature. The sensor format was
128×128 pixels with 20 μm pitch. It was tested with our original readout electronics and cooled down to 80 K by a
mechanical cooler to minimize the dark current. Although the readout noise and dark current were 200 e- and 20 e-
/sec/pixel, respectively, we found no serious problems for the linearity, wavelength response, and intra-pixel response.
I have developed a special ND filter (Local Attenuation Filter) for observing bright near-infrared stars. This filter is a 60mm diameter with a 4mm thickness, on which an attenuation (0.02% transparency) patch with an 8mm diameter is coated. This filter is expected to be installed near the focal plane of telescope, and the flux through this patch is attenuated. Using this filter, we can observe the attenuated bright star together with not affected field stars as reference for relative photometry. This filter has been installed to the IRSF 1.4m telescope and used for the monitoring of NIR bright stars, for example, η Car.
Focal Plane Arrays (FPA) are key items for modern astronomical observations in the near infrared wavelength, but it is very expensive and not easy to get them. Less expensive NIR FPAs with reasonable performance are very important to spread NIR observation extensively. FPA640×512 manufactured by Chunghwa Leading Photonics Tech is a 640×512 InGaAs detector covering the 0.9-1.7 μm wavelength. Since this array is significantly cheaper than the commonly used NIR FPAs in the astronomical observation, it is possible to be a good choice for particular projects which do not need many pixels, if FPA640×512 has acceptable performance for the purpose. We have evaluated one test grade array of FPA640×512 both in the room and low temperature environment. In order to evaluate the characteristics of this FPA in the low temperature environment, we cooled it down by the mechanical refrigerator and confirmed that it works at 100 K. We have found that the dark current reduces exponentially as the FPA temperature decreases, but it hits the bottom at~1000 e−/sec bellow 200 K with the default setting. We are trying to reduce the dark current by optimizing the bias voltage and the current to the MUX circuit. The latest experiments have shown the possibility that the dark current decreases to~200 e−/sec. This value is still higher than that of NIR FPAs used in the scientific observation, but it may be applicable for the particular purpose, for example, FPAs for slit viewer in spectrometers, wave front sensor, and so on.
We present our new optical and near-infrared (NIR) spectrometer for the IRSF 1.4m telescope. The concept
of it is an effective use of photons, and so we have designed it to obtain a spectrum of the 0.4-2.5μm range
simultaneously and have a small number of optical surfaces in order to reduce reflection loss. Light collected by
the telescope is separated into optical (0.45-0.90μm) and NIR (1.0-2.5μm) wavelengths by a dichroic entrance
window, and two spectrometers are prepared, one for the optical wavelengths and another for the NIR. We use a
sapphire prism in the NIR spectrometer, and a diffraction grating in the optical spectrometer. The optical design
is very simple and the number of optical surfaces is 9 for optical and 10 for NIR (not including the telescope
mirrors). A 1024×250 pixels CCD (optical) and a 1024×1024 HgCdTe detector array (NIR) are used. The
spectral resolution will be 470@0.70μm and 380@1.8μm with a 1” slit width. A NIR slit viewer with a 3’.5 ×
3’.5 field of view is also mounted. The development of the spectrometer will be complete by March 2013.
We have developed a control system for infrared array detectors with 16, 32 or more outputs. Our system consists of five boards (clock pattern generator, clock driver, A/D converter, parallel-in, and isolation), and is operated with a Linux (kernel 2.4 or 2.6) PC. It is capable of supplying 24 DC bias voltages and 16 clock voltages,
adjustable between -7.5V and +7.5V and the shortest clock width of 156 ns. One A/D board converts 16 analog array outputs to digital data simultaneously using 16 A/D converters. The rms of A/D conversions for fixed voltages is 2-3 ADU (or 150-200 μV) at a sampling rate of 250 kSPS. The parallel-in board has 32 optically
isolated input channels, and can receive data from 2 A/D boards simultaneously. The maximum data rate to
main memory of PC is 40 MB/sec, corresponding to 20 frames/sec of a 1024×1024 array. Our system is now
utilized for Aladdin 2 (InSb, 1024×1024, 32 outputs) of Wide Field Cryogenic Telescope 2 and SB-774 (Si:As, 320×240, 16 outputs) of 17μm Fabry-Perot spectrometer. The A/D boards have daisy-chain capability for next generation arrays with more than 32 outputs. In the daisy-chain mode, all A/D converters are triggered simultaneously, but the A/D boards make time-delayed data transfer. The parallel-in board receives data sequentially by every 32 A/D converters. When we apply our system for 2048×2048 detectors with 64 outputs, the frame rate will be 5 frames/sec.
We have developed Wide Field Cryogenic Telescope II (WFCT II) which contains a whole telescope-optics together with a detector in a vacuum case for cooling to suppress thermal emission from a telescope. The telescope inside is a Ritchey-Chretien system with an aperture of 220 mm and a focal length of 1540 mm. Light from celestial objects enters the telescope through a window, hits primary and secondary mirrors, passes through a filter, and reaches a detector. Spiders, baffles, and radiation shields are cooled down to ~80 K or lower by a refrigerator. All the optics reach a low temperature by exchanging heat with the radiation shields. A 1024×1024 InSb infrared array detector covers a field of view of 1 square degree with resolution of 3".5/pixel. The detector is also cooled by the refrigerator and is regulated at 29 ± 0.1 K. WFCT II is mounted on a small equatorial mounting whose size is 1 m in height, 1 m in width, and 1.2 m in length along the N-S direction. The main targets are diffuse emissions radiated from hydrogen atoms, molecules, and carbonaceous materials in star formation regions and the Galactic Center. We have started to obtain scientific data at Sutherland, South African Astronomical Observatory since December 2007.
We present our high spectral resolution tandem Fabry-Perot (FP) spectrometer for detecting the pure rotational
transition line of molecular Hydrogen S (1) at 17.035 μm. It is designed to be attached to a new dedicated 1
m telescope planned to be put at a dry and high-altitude site. The spectrometer has two sequentially placed
FP units (order 1000 and 99 with finesse >50) consisting of ZnSe etalons and one narrow band filter. We will
be able to obtain high spectral resolution of R=50,000 at 17.035 μm. The ZnSe etalons of 110mm diameter
with >94% reflectance are to be provided from Barr Associates. The interval and tilt of etalons are sensed and
regulated by piezo actuators and newly-developed capacitance sensors, which resolve 100nm in vacuum and 30K
environment. By changing the interval, we change the wavelength of transmission up to 17.2 μm, corresponding
toν = 3000 km/s. We adopt an on-axis catadioptric system, in which the two FP units are placed. The focal
plane detector is a Raytheon SB-774, 320×240 pixel array of Si:As, yielding 9.1 × 6.8 arcmin2 field of view with
1.7 arcsec pixel scale. To suppress the thermal background radiation and dark current of the Si:As detector, the
system is cooled down to 6K at the detector and 35K for the whole optical system by two refrigerators. The
development of spectrometer will be completed in 2007.
We describe a polarimeter for the near-infrared camera SIRIUS mounted on the IRSF 1.4 m telescope in South Africa. The polarimeter, SIRPOL, consists of an achromatic (1-2.5 μm) wave plate rotator unit and a polarizer located upstream of the camera, both of which are at a room temperature. This minimizes the effect of the mirrors in the camera on instrumental polarization. The combination of the polarimeter with the SIRIUS camera enables a deep (J = 19.2 mag, 5σ in one hour) and wide-field (7.7' × 7.7') imaging polarimetry at JHKs simultaneously. The three color near-infrared polarimetry is useful for understanding the properties of dust grains that cause scattering and absorption in various environments (e.g., star forming regions, late-type stars, and galaxies). Using IRSF and SIRPOL, wide-field near-infrared polarization surveys in various star-forming regions are being conducted, starting from 2006, which aim to study both reflection nebulae associated with young stars and interstellar polarizations of background stars. In this contribution, we describe the hardware and software of SIRPOL and report its first results on the telescope.
We developed a near infrared simultaneous three-band (J, H and Ks) camera, SIRIUS. The design of SIRIUS is optimized to deep, large area surveys in the three IR bands. SIRIUS is equipped with three 1024 x 1024 HgCdTe (HAWAII) arrays, providing simultaneous three-band images. SIRIUS has obtained its first light on the UH 2.2 m telescope in August 2000. SIRIUS is now mounted on the IRSF 1.4 m telescope in Sutherland and is dedicated to deep survey in the southern sky from November 2000. On this telescope, SIRIUS provides 7'.8 x 7'.8 field of view with a pixel scale of 0".45 in all bands. The typical limiting magnitudes are J = 19.2 mag, H = 18.6 mag, Ks = 17.3 mag (15 min. integration, S/N = 10 σ). The effective exposure time (30 sec exposure for each frame) in an hour is about 37 minutes (60%) for each band. Both the instrument and the 1.4 m telescope are in operation.
Some results from the near infrared camera SIRIUS are presented. SIRIUS is designed for deep and wide JHKs-bands simultaneous surveys, being equipped with three science-grade HAWAII (1024×1024) arrays. SIRIUS is attached on a dedicated 1.4m telescope (IRSF) at Sutherland observatory in South Africa. The field of view is 7.8'×7.8', the pixel scale is 0.45", and the limiting magnitude is J=19.2, H=18.6, Ks=17.3 (S/N=10σ and 15minutes integration) with the 1.4m telescope. The survey of southern sky began in November 2000. SIRIUS was also used on the University of Hawaii 2.2m telescope at Mauna Kea for three times in August 2000, October 2000, and September 2001. Surveys of several northern sky areas were done. Unbiased deep survey for 6 degree square area of Large Magellanic Cloud (LMC) is one of the key programs with the 1.4m telescope. Several clusters of intermediate mass YSO candidates have been discovered so far. Monitoring surveys of several selected areas of LMC have also been carried out for detection of variable stars. The other main science programs of SIRIUS are deep imaging surveys of star forming regions in our galaxy, brown dwarf surveys in clusters, search for galaxies behind the Milky way (the Zone of Avoidance), and surveys toward the galactic center.
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