National Astronomical Observatory Of Japan Research Articles

Optical Imaging Polarimetry of Comet 21P/Giacobini–Zinner during Its 2018 Apparition

We conducted polarimetric observations of comet 21P/Giacobini–Zinner in the optical wavelength region using the polarimetric imager PICO equipped with the 50 cm telescope for Public Outreach at the Mitaka Campus of the National Astronomical Observatory of Japan on UT 2018 September 16, at a solar phase angle of 77° for the comet. We used Gunn’s i′-band filter to cover the wavelength region where sunlight reflected by dust grains dominates cometary spectra. The intensity map of comet 21P/Giacobini–Zinner showed an elongated coma structure along the east–west direction. The linear polarization degree map was almost uniform and showed no evidence of jet or arc structures in the inner coma. The linear polarization degree was 22% in the coma, which is consistent with other optical polarization observations of 21P/Giacobini–Zinner for this and previous apparitions reported in the literature. The measured polarization angles (179°) were nearly perpendicular to the position angle of the scattering plane of 271°. There is no evidence of significant changes in the dust properties (composition, porosity, and size distribution) in the comet from its 1985 to 2018 apparitions. The spectral gradient of the linear polarization degree for the comet was nearly flat in the wavelength range of ∼510–830 nm at a solar phase angle of ∼77° during the 2018 apparition.

Ultradiffuse Galaxies (UDGs) with Hyper Suprime-Cam. I. Revised Catalog of Coma Cluster UDGs* * This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the universe from Maunakea, which has cultural, historical, and natural significance in Hawaii.

This is the first in a series of papers on the properties of ultradiffuse galaxies (UDGs) in clusters of galaxies. We present an updated catalog of UDGs in the Coma Cluster using g- and r-band images obtained with Hyper Suprime-Cam (HSC) of the Subaru telescope. We develop a method to find UDGs even in the presence of contaminating objects, such as halos and background galaxies. This study expands upon our previous works that covered about half the area of the Coma Cluster. The HSC observations covered the whole Coma Cluster up to the virial radius and beyond (an area twice as large as the previous studies) and doubled the numbers of UDGs (r eff, r ≥ 1.5 kpc) and sub-UDGs (1.0 ≤ r eff, r < 1.5 kpc) to 774 and 729, respectively. The new UDGs show internal properties consistent with those of previous studies (e.g., a Sérsic index of approximately 1), and are distributed across the cluster, with a concentration around the cluster center. The whole cluster coverage clearly revealed an excess of their distribution toward the east to southwest direction along the cluster center, where Coma connects to other large-scale structure, and where a known substructure exists (the NGC 4839 subgroup). The alignment of the UDG distribution along the large-scale structure around Coma supports the interpretation that most of them lie at the distance of the Coma Cluster and the NGC 4839 subgroup.

Predicting the 25th and 26th solar cycles using the long short-term memory method

Abstract Solar activities directly or indirectly affect space missions, geophysical environment, space climate, and human activities. We used the long short-term memory (LSTM) deep learning method to predict the amplitude and peak time of solar cycles (SCs) 25 and 26 by using the monthly relative sunspot number data taken from the National Astronomical Observatory of Japan (NAOJ). The dataset is divided into eight schemes of two to nine slices for training, showing that the five-slice LSTM model with root mean square error of 11.38 is the optimal model. According to the prediction, SC 25 will be about 21$\%$ stronger than SC 24, with a peak of 135.2 occurring in 2024 April. SC 26 will be similar to SC 25 and reach its peak of 135.0 in 2035 January. Our analysis results indicate that the sunspot data from NAOJ is highly credible and comparable.

UV and Lyα Halos of Lyα Emitters across Environments at z = 2.84* * This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

We present UV and Lyα radial surface brightness (SB) profiles of Lyα emitters (LAEs) at z = 2.84 detected with the Hyper Suprime-Cam on the Subaru Telescope. The depth of our data, together with the wide-field coverage including a protocluster, enable us to study the dependence of Lyα halos (LAHs) on various galaxy properties, including Mpc scale environments. UV and Lyα images of 3490 LAEs are extracted, and stacking the images yields SB sensitivity of in Lyα, reaching the expected level of optically thick gas illuminated by the UV background at z ∼ 3. Fitting of the two-component exponential function gives the scale-lengths of 1.56 ± 0.01 and 10.4 ± 0.3 pkpc. Dividing the sample according to their photometric properties, we find that, while the dependence of halo scale-length on environment outside of the protocluster core is not clear, LAEs in the central regions of protoclusters appear to have very large LAHs, which could be caused by combined effects of source overlapping and diffuse Lyα emission from cool intergalactic gas permeating the forming protocluster core irradiated by active members. For the first time, we identify UV halos around bright LAEs that are probably due to a few lower-mass satellite galaxies. Through comparison with recent numerical simulations, we conclude that, while scattered Lyα photons from the host galaxies are dominant, star formation in satellites evidently contributes to LAHs, and that fluorescent Lyα emission may be boosted within protocluster cores at cosmic noon and/or near bright QSOs.

Spectroscopic Study of Ba and CEMP-s Stars: Mass Distribution of AGB Progenitors* * Based [in part] on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. † †[Part of] the data are retrieved from the JVO portal (http://jvo.nao.ac.jp/portal) operated by the NAOJ.

We have performed detailed high-resolution spectroscopic analysis on seven metal-poor stars (BD+75 348, BD+09 3019, HD238020, HE0319–0215, HE0507–1653, HE0930–0018, HE1023–1504) and derived their atmospheric parameters T eff, log g, [Fe/H], and microturbulent velocity (ξ). The metallicity range is found to be –2.57 < [Fe/H] < –0.42. The elemental abundances of 17 light elements and 12 heavy elements are estimated. We have classified BD+75 348 and BD+09 3019 as strong Ba stars, HD238020 as a mild Ba star, and the remaining four objects as CEMP-s stars. We have estimated the masses of the stars from Hertzsprung–Russel (HR) diagram, and, compiling the data of 205 Ba stars from literature, estimated the mass distribution of Ba stars. We have also estimated the initial masses of the companion AGBs of the program stars as well as the masses of the companion AGBs of 159 Ba and 36 CEMP-s stars from literature, with the help of a parametric-model-based analysis using FRUITY models. While the primary mass distribution of mild Ba stars peaks at 3.7 M ⊙, for the strong Ba stars the peak appears at 2.5 M ⊙. We, therefore, propose that the initial masses of the progenitor AGBs dominantly control the formation of mild and strong Ba stars. However, a clear overlap, in the range 1.3–4.0 M ⊙, noticed between the progenitor masses of both the subclasses of Ba stars, may indicate that other factors, such as the metallicities and the orbital periods, may also have significant contributions. The progenitor AGBs’ mass distribution of CEMP-s stars is found to peak at 2.03 M ⊙.

Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-dwarf Companion in the Hyades* *Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Benchmark brown dwarf companions with well-determined ages and model-independent masses are powerful tools to test substellar evolutionary models and probe the formation of giant planets and brown dwarfs. Here, we report the independent discovery of HIP 21152 B, the first imaged brown dwarf companion in the Hyades, and conduct a comprehensive orbital and atmospheric characterization of the system. HIP 21152 was targeted in an ongoing high-contrast imaging campaign of stars exhibiting proper-motion changes between Hipparcos and Gaia, and was also recently identified by Bonavita et al. (2022) and Kuzuhara et al. (2022). Our Keck/NIRC2 and SCExAO/CHARIS imaging of HIP 21152 revealed a comoving companion at a separation of 0.″37 (16 au). We perform a joint orbit fit of all available relative astrometry and radial velocities together with the Hipparcos-Gaia proper motions, yielding a dynamical mass of , which is 1–2σ lower than evolutionary model predictions. Hybrid grids that include the evolution of cloud properties best reproduce the dynamical mass. We also identify a comoving wide-separation (1837″ or 7.9 × 104 au) early-L dwarf with an inferred mass near the hydrogen-burning limit. Finally, we analyze the spectra and photometry of HIP 21152 B using the Saumon & Marley (2008) atmospheric models and a suite of retrievals. The best-fit grid-based models have f sed = 2, indicating the presence of clouds, T eff = 1400 K, and . These results are consistent with the object’s spectral type of T0 ± 1. As the first benchmark brown dwarf companion in the Hyades, HIP 21152 B joins the small but growing number of substellar companions with well-determined ages and dynamical masses.

Development of highly selective compact high-temperature superconducting quad-band bandpass filter using interdigital feeding structure for radio astronomy

Astronomers at the Mizusawa Very Long Baseline Interferometry Observatory of the National Astronomical Observatory of Japan are promoting the development of broadband receivers in the ultra-high frequency (UHF) band. The presence of extensive radio frequency interferences (RFI) in the UHF band hinders continuous broadband radio observations in this band. A promising technical solution to this problem is to use a superconducting multi-band bandpass filter as it enables the bundling of several RFI-free bands. We have developed a high-temperature superconducting compact quad-band bandpass filter (QB-BPF) at 0.7, 1.4, 1.6, and 2.1 GHz with low loss and steep cutoff characteristics for broadband receivers. That consists of two six-pole dual-band bandpass filters. We have devised an interdigital feeding structure with a high degree of freedom that enables the external quality factor to be designed individually for each band. A compact QB-BPF was fabricated using double-sided YBa2Cu3Oy thin films on a 36.4 mm × 42.0 mm (0.22λ g × 0.25λ g) Al2O3 substrate. The measurement results agreed well with the simulated ones, indicating that the QB-BPF overcomes the problem of extensive RFI in the UHF band.

CASA, the Common Astronomy Software Applications for Radio Astronomy

CASA, the Common Astronomy Software Applications, is the primary data processing software for the Atacama Large Millimeter/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA), and is frequently used also for other radio telescopes. The CASA software can handle data from single-dish, aperture-synthesis, and Very Long Baseline Interferometery (VLBI) telescopes. One of its core functionalities is to support the calibration and imaging pipelines for ALMA, VLA, VLA Sky Survey, and the Nobeyama 45 m telescope. This paper presents a high-level overview of the basic structure of the CASA software, as well as procedures for calibrating and imaging astronomical radio data in CASA. CASA is being developed by an international consortium of scientists and software engineers based at the National Radio Astronomy Observatory (NRAO), the European Southern Observatory, the National Astronomical Observatory of Japan, and the Joint Institute for VLBI European Research Infrastructure Consortium (JIV-ERIC), under the guidance of NRAO.

Probing Photon Statistics in Adaptive Optics Images with SCExAO/MEC* * Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

We present an experimental study of photon statistics for high-contrast imaging with the Microwave Kinetic Inductance Detector (MKID) Exoplanet Camera (MEC) located behind the Subaru Coronagraphic Extreme Adaptive Optics System at the Subaru Telescope. We show that MEC measures the expected distributions for both on-axis companion intensity and off-axis intensity, which manifests as quasi-static speckles in the image plane and currently limits high-contrast imaging performance. These statistics can be probed by any MEC observation due to the photon-counting capabilities of MKID detectors. Photon arrival time statistics can also be used to directly distinguish companions from speckles using a post-processing technique called Stochastic Speckle Discrimination (SSD). Here, we give an overview of the SSD technique and highlight the first demonstration of SSD on an extended source—the protoplanetary disk AB Aurigae. We then present simulations that provide an in-depth exploration as to the current limitations of an extension of the SSD technique called Photon-Counting SSD (PCSSD) to provide a path forward for transitioning PCSSD from simulations to on-sky results. We end with a discussion of how to further improve the efficacy of such arrival-time-based post-processing techniques applicable to both MKIDs, as well as other high-speed astronomical cameras.

SCExAO and Keck Direct Imaging Discovery of a Low-mass Companion Around the Accelerating F5 Star HIP 5319* *Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT).

We present the direct imaging discovery of a low-mass companion to the nearby accelerating F star, HIP 5319, using SCExAO coupled with the CHARIS, VAMPIRES, and MEC instruments in addition to Keck/NIRC2 imaging. CHARIS JHK (1.1–2.4 μm) spectroscopic data combined with VAMPIRES 750 nm, MEC Y, and NIRC2 L p photometry is best matched by an M3–M7 object with an effective temperature of T = 3200 K and surface gravity log(g) = 5.5. Using the relative astrometry for HIP 5319 B from CHARIS and NIRC2, and absolute astrometry for the primary from Gaia and Hipparcos, and adopting a log-normal prior assumption for the companion mass, we measure a dynamical mass for HIP 5319 B of , a semimajor axis of au, an inclination of degrees, and an eccentricity of . However, using an alternate prior for our dynamical model yields a much higher mass of . Using data taken with the LCOGT NRES instrument we also show that the primary HIP 5319 A is a single star in contrast to previous characterizations of the system as a spectroscopic binary. This work underscores the importance of assumed priors in dynamical models for companions detected with imaging and astrometry, and the need to have an updated inventory of system measurements.

Atmospheric Monitoring and Precise Spectroscopy of the HR 8799 Planets with SCExAO/CHARIS* * Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

The atmospheres of gas giant planets are thought to be inhomogeneous due to weather and patchy clouds. We present two full nights of coronagraphic observations of the HR 8799 planets using the CHARIS integral field spectrograph behind the SCExAO adaptive optics system on the Subaru Telescope to search for spectrophomometric variability. We did not detect significant variability signals, but placed the lowest variability upper limits for HR 8799c and d. Based on injection-recovery tests, we expected to have a 50% chance to detect signals down to 10% H-band photometric variability for HR 8799c and down to 30% H-band variability for HR 8799d. We also investigated spectral variability and expected a 50% chance to recover 20% variability in the H/K flux ratio for HR 8799c. We combined all the data from the two nights to obtain some of the most precise spectra obtained for HR 8799c, d, and e. Using a grid of cloudy radiative–convective–thermochemical equilibrium models, we found all three planets prefer supersolar metallicity with effective temperatures of ∼1100 K. However, our high signal-to-noise spectra show that HR 8799d has a distinct spectrum from HR 8799c, possibly preferring more vertically extended and uniform clouds and indicating that the planets are not identical.

Constrained Reference Star Differential Imaging: Enabling High-fidelity Imagery of Highly Structured Circumstellar Disks * * Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

High-contrast imaging presents us with the opportunity to study circumstellar disks and the planets still embedded within them, providing key insights into the formation and evolution of planetary systems. However, the postprocessing techniques that are often needed to suppress stellar halo light typically result in significant and variable loss of circumstellar light, even when using relatively conservative approaches like reference star differential imaging (RDI). We introduce “constrained reference star differential imaging” (constrained RDI), a new class of RDI point-spread-function (PSF) subtraction techniques for systems with circumstellar disks. Constrained RDI utilizes either high-resolution polarized-intensity (PI) images or disk models to severely limit or even eliminate the signal loss due to oversubtraction that is common to RDI. We demonstrate the ability of constrained RDI utilizing polarimetric data to yield an oversubtraction-free detection of the AB Aurigae protoplanetary disk in total intensity. PI-constrained RDI allows us to decisively recover the spectral signature of the confirmed, recently discovered protoplanet, AB Aurigae b. We further demonstrate that constrained RDI can be a powerful analysis tool for soon-to-be-acquired James Webb Space Telescope coronagraphic imaging of disks. In both cases, constrained RDI provides analysis-ready products that enable more detailed studies of disks and more robust verification of embedded exoplanets.

Direct-imaging Discovery and Dynamical Mass of a Substellar Companion Orbiting an Accelerating Hyades Sun-like Star with SCExAO/CHARIS* *Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

We present the direct-imaging discovery of a substellar companion in orbit around a Sun-like star member of the Hyades open cluster. So far, no other substellar companions have been unambiguously confirmed via direct imaging around main-sequence stars in Hyades. The star HIP 21152 is an accelerating star as identified by the astrometry from the Gaia and Hipparcos satellites. We detected the companion, HIP 21152 B, in multiple epochs using the high-contrast imaging from SCExAO/CHARIS and Keck/NIRC2. We also obtained the stellar radial-velocity data from the Okayama 188 cm telescope. The CHARIS spectroscopy reveals that HIP 21152 B’s spectrum is consistent with the L/T transition, best fit by an early T dwarf. Our orbit modeling determines the semimajor axis and the dynamical mass of HIP 21152 B to be 17.5 au and 27.8 M Jup, respectively. The mass ratio of HIP 21152 B relative to its host is ≈2%, near the planet/brown dwarf boundary suggested by recent surveys. Mass estimates inferred from luminosity-evolution models are slightly higher (33–42 M Jup). With a dynamical mass and a well-constrained age due to the system’s Hyades membership, HIP 21152 B will become a critical benchmark in understanding the formation, evolution, and atmosphere of a substellar object as a function of mass and age. Our discovery is yet another key proof of concept for using precision astrometry to select direct-imaging targets.

Over seven decades of solar microwave data obtained with Toyokawa and Nobeyama Radio Polarimeters

AbstractMonitoring observations of solar microwave fluxes and their polarization began in Japan during the 1950s at Toyokawa and Mitaka. At present (April 2022), monitoring observations continues with the Nobeyama Radio Polarimeters (NoRP) at the Nobeyama campus of the National Astronomical Observatory of Japan (NAOJ). In this paper, we present a brief history of the solar microwave monitoring observations preceding those now carried out by NoRP. We then review the solar microwave flux and polarization measurements obtained at Toyokawa and Nobeyama, and their metadata. The datasets are publicly provided by the Solar Data Archive System (SDAS) operated by the Astronomy Data Center of the NAOJ, via http (https://solar.nro.nao.ac.jp/norp/) and FTP (ftp://solar‐pub.nao.ac.jp/pub/nsro/norp/) protocols.

Hemispheric asymmetry of long-term sunspot activity: sunspot relative numbers for 1939–2019

ABSTRACT Hemispheric asymmetry of solar magnetic structures is an important feature of solar cycles, and it involves dynamical processes in the interior of the Sun. For the first time, the data of the monthly sunspot relative numbers derived from the National Astronomical Observatory of Japan (NAOJ) is used to perform a long-term study (1939 March–2019 November) of the north–south asymmetry. The results show the following: (1) the sunspot relative numbers derived from NAOJ/Mitaka observatory are highly correlated with the international sunspot numbers obtained from the World Data Center Sunspot Index and Long-term Solar Observations, which justifies the use of Mitaka sunspot time series for hemispheric variation; (2) the change in the signs of the slopes of the regression lines fitted to the absolute asymmetry index suggest a kind of periodic variation in the hemispheric asymmetry, but the time interval of the current data base is not long enough to derive 8 or 12 cycles periodicity; and (3) for mid-term periods, there are enhanced powers for the period ranges around 3.7 yr, around 9 yr, between 30 and 50 yr. Our analysis results implicate a possible mechanism responsible for the generation and variation of the hemispheric coupling in the Sun.

Improving the stability of frequency-dependent squeezing with bichromatic control of filter cavity length, alignment, and incident beam pointing

Frequency dependent squeezing is the main upgrade for achieving broadband quantum noise reduction in upcoming observation runs of gravitational wave detectors. The proper frequency dependence of the squeezed quadrature is obtained by reflecting squeezed vacuum from a Fabry-Perot filter cavity detuned by half of its linewidth. However, since the squeezed vacuum contains no classical amplitude, co-propagating auxiliary control beams are required to achieve the filter cavity's length, alignment, and incident beam pointing stability. In our frequency dependent squeezing experiment at the National Astronomical Observatory of Japan, we used a control beam at a harmonic of squeezed vacuum wavelength and found visible detuning variation related to the suspended mirrors angular drift. These variations can degrade interferometer quantum noise reduction. We investigated various mechanisms that can cause the filter cavity detuning variation. The detuning drift is found to be mitigated sufficiently by fixing the incident beam pointing and applying filter cavity automatic alignment. It was also found that there is an optimal position of the beam on the filter cavity mirror that helps to reduce the detuning fluctuations. Here we report a stabilized filter cavity detuning variation of less than 10$\,$Hz compared to the 113$\,$Hz cavity linewidth. Compared to previously published results [Phys. Rev. Lett. 124, 171101 (2020)], such detuning stability would be sufficient to make filter cavity detuning drift induced gravitational wave detector detection range fluctuation reduce from $11\%$ to within $2\%$.

Size Distribution of Small Jupiter Trojans in the L5 Swarm* *This research is based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has the cultural, historical and natural significance in Hawaii.

We present an analysis of survey observations of the trailing L5 Jupiter Trojan swarm using the wide-field Hyper Suprime-Cam CCD camera on the 8.2 m Subaru Telescope. We detected 189 L5 Trojans from our survey that covered about 15 deg2 of sky with a detection limit of m r = 24.1 mag, and selected an unbiased sample consisting of 87 objects with absolute magnitude 14 ≲ H r ≤ 17 corresponding to diameter 2 km ≲ D ≲ 10 km for analysis of size distribution. We fit their differential magnitude distribution to a single-slope power law with an index α = 0.37 ± 0.01, which corresponds to a cumulative size distribution with an index of b = 1.85 ± 0.05. Combining our results with data for known asteroids, we obtained the size distribution of L5 Jupiter Trojans over the entire size range for 9 ≲ H V ≤ 17, and found that the size distributions of the L4 and L5 swarms agree well with each other for a wide range of sizes. This is consistent with the scenario that asteroids in the two swarms originated from the same primordial population. Based on the above results, the ratio of the total number of asteroids with D ≥ 2 km in the two swarms is estimated to be N L4/N L5 = 1.40 ± 0.15, and the total number of L5 Jupiter Trojans with D ≥ 1 km is estimated to be 1.1 × 105 by extrapolating the obtained distribution.

Subaru Telescope -History, active/adaptive optics, instruments, and scientific achievements.

The Subaru Telescopea) is an 8.2 m optical/infrared telescope constructed during 1991–1999 and has been operational since 2000 on the summit area of Maunakea, Hawaii, by the National Astronomical Observatory of Japan (NAOJ). This paper reviews the history, key engineering issues, and selected scientific achievements of the Subaru Telescope. The active optics for a thin primary mirror was the design backbone of the telescope to deliver a high-imaging performance. Adaptive optics with a laser-facility to generate an artificial guide-star improved the telescope vision to its diffraction limit by cancelling any atmospheric turbulence effect in real time. Various observational instruments, especially the wide-field camera, have enabled unique observational studies. Selected scientific topics include studies on cosmic reionization, weak/strong gravitational lensing, cosmological parameters, primordial black holes, the dynamical/chemical evolution/interactions of galaxies, neutron star mergers, supernovae, exoplanets, proto-planetary disks, and outliers of the solar system. The last described are operational statistics, plans and a note concerning the culture-and-science issues in Hawaii.

Broadband quantum noise reduction via frequency dependent squeezing for Advanced Virgo Plus

Quantum noise is limiting the sensitivity of ground based gravitational wave detectors both at high frequency, in the form of shot noise, and low frequency, in the form of radiation pressure noise. In the last observing run, the injection of frequency independent squeezing improved Virgo and LIGO sensitivities at high frequency, slightly worsening the performance at low frequency. A broadband quantum noise reduction can be achieved using frequency dependent squeezing, i. e. rotating the vacuum squeezed ellipse below 100 Hz by reflecting the squeezed vacuum off a Fabry–Perot cavity, called filter cavity. The frequency-dependent squeezed quadrature rotation with rotation frequency around a few tens of Hz has been proven at National Astronomical Observatory of Japan (NAOJ) and at Massachusetts Institute of Technology (MIT). The experiment at NAOJ uses the former TAMA facility, a 300 meter long filter cavity, reproducing in scale the ones planned to be installed in Virgo and LIGO. Once the frequency dependent squeezing is produced, it has to be injected into the interferometer. This interface is not trivial, since it requires the installation of additional benches and a 285 meter long cavity (in Advanced Virgo Plus) and also to couple the rotating squeezed vacuum with the detector. An important issue which can worsen the performance of frequency dependent squeezing or directly the interferometer sensitivity is the stray light. To avoid the propagation of additional stray light, we traced the ghost beam on squeezing benches, inside linking tubes and inside the filter cavity and several diaphragms and baffles will be installed to limit this problem.

Superconducting Receiver Technologies Supporting ALMA and Future Prospects

AbstractThis paper describes the development of superconductor–insulator–superconductor (SIS) receivers in the 787–950 GHz radio frequency (RF) range, which covers the highest frequency band of the Atacama Large Millimeter/submillimeter Array (ALMA) and is recognized as the most difficult band in terms of superconducting technology, because the conventional superconducting material of Nb cannot be used for the circuitry in the mixer devices at the frequencies. The development began at the National Astronomical Observatory of Japan (NAOJ) in 2005, and the manufacturing and testing of all the receivers to be installed in the 66 Cassegrain reflector antennas that compose ALMA was completed in 2013. This enabled the terahertz frequency observations with the highest sensitivity from the ground. To meet the stringent ALMA requirements, terahertz SIS mixers with high‐quality superconducting NbTiN films were developed, which successfully demonstrated an unpreceded noise performance less than 230 K (5 times the quantum noise) for all the receivers. After the construction of ALMA, NAOJ began development studies for ALMA enhancement such as wideband and multibeam SIS receivers according to top‐level science requirements. To increase instantaneous bandwidth of the receivers, a submillimeter‐wave multiband receiver concept with a waveguide multiplexer, wideband intermediate frequency SIS‐mixer‐amplifier, and multifrequency local oscillator (LO) source is presented. The multibeam receiver employs a planar‐integrated SIS mixer circuit that includes all the RF components except the LO distribution network and an SIS‐mixer‐based amplifier of low power consumption, which is expected to enable the wide field‐of‐view observations in the future.