arXiv subjects

T. Takekoshi

Publications and source records attributed to T. Takekoshi.

11 recordsLinked to original sources

arXiv2026

DESHIMA 2.0: A 200-400 GHz Ultra-wideband Integrated Superconducting Spectrometer

DESHIMA (Deep Spectroscopic HIgh-redshift MApper) is a broadband integrated superconducting spectrometer (ISS) for millimeter (mm) / sub-millimeter (sub-mm) wave astronomy based on Kinetic Inductance Detectors (KIDs). This paper describes characterization of DESHIMA 2.0 in laboratory settings. The instrument features NbTiN superconducting microstrip (MS) filters with low-loss a-SiC:H dielectric and an ultra-wideband leaky-wave antenna. A laboratory setup was designed, incorporating the cryostat housing cryogenic optics and ISS chip comprising 339 KIDs connected to MS filters tuned for (sub-)mm wave frequencies. Room-temperature mirrors on a hexapod stage allowed precise positioning and alignment of optical elements. The sky-position chopper was positioned on a motor-controlled stage for fine-tuned control over its position and alignment. Thanks to the multiplexing capability of KIDs, we could simultaneously measure multiple performance metrics across the entire frequency range. We showed that DESHIMA 2.0 achieved significant improvements in performance compared to its predecessor (DESHIMA 1.0): measured instantaneous frequency coverage was 200$-$400 GHz with a mean filter $Q_{filter}$ of $340 \pm 50$; instrument efficiency reached $\sim8$ \%, indicating 4 times wider band coverage and 4 times higher sensitivity. The yield rate for MS filters exceeded 98 \%. The estimated aperture efficiency from measured beam patterns agreed well with the designed value of approximately 70 \%. The telescope far-field beam patterns calculated from measured beam patterns also exhibited good agreement with design specifications. We also demonstrated validity of a new method of absolute frequency calibration using the data from beam pattern measurement.

astro-ph.IM↗

arXiv2025

Alignment and optical verification of DESHIMA 2.0 at ASTE

We developed, characterized, and verified an alignment procedure for the DESHIMA 2.0 instrument, an ultra wide-band spectrometer operating between 200--400 GHz, at the ASTE telescope. To this end, we mounted the warm optics, consisting of a modified Dragonian dual reflector system, on a motor controlled hexapod. Crucial in the alignment procedure is our sky chopper, which allows fast beam switching. It has a small entrance and exit aperture coupling to (cold) sky, which creates a measurable signal with respect to the warm cabin environment. By scanning the instrument beam across the entrance aperture of the sky chopper using the hexapod, we found the hexapod configuration that produced the lowest signal on our detectors, implying the beam is coupled fully to cold sky and not the warm cabin. We first characterized the alignment procedure in the laboratory, where we used a vat containing liquid nitrogen as the cold source behind the sky chopper. Then, we applied the alignment procedure to DESHIMA 2.0 at ASTE. We found that the alignment procedure significantly improved the aperture efficiency compared to previously reported values of the aperture efficiency of DESHIMA at ASTE, which indicates the veracity of the alignment procedure.

astro-ph.IM↗

arXiv2024

Optimisation-based alignment of wideband integrated superconducting spectrometers for sub-mm astronomy

Integrated superconducting spectrometers (ISSs) for wideband sub-mm astronomy utilise quasi-optical systems for coupling radiation from the telescope to the instrument. Misalignment in these systems is detrimental to the system performance. The common method of using an optical laser to align the quasi-optical components requires accurate alignment of the laser to the sub-mm beam coming from the instrument, which is not always guaranteed to a sufficient accuracy. We develop an alignment strategy for wideband ISSs directly utilising the sub-mm beam of the wideband ISS. The strategy should be applicable in both telescope and laboratory environments. Moreover, the strategy should deliver similar quality of the alignment across the spectral range of the wideband ISS. We measure misalignment in a quasi-optical system operating at sub-mm wavelengths using a novel phase and amplitude measurement scheme, capable of simultaneously measuring the complex beam patterns of a direct-detecting ISS across a harmonic range of frequencies. The direct detection nature of the MKID detectors in our device-under-test, DESHIMA 2.0, necessitates the use of this measurement scheme. Using geometrical optics, the measured misalignment, a mechanical hexapod, and an optimisation algorithm, we follow a numerical approach to optimise the positioning of corrective optics with respect to a given cost function. Laboratory measurements of the complex beam patterns are taken across a harmonic range between 205 and 391 GHz and simulated through a model of the ASTE telescope in order to assess the performance of the optimisation at the ASTE telescope. Laboratory measurements show that the optimised optical setup corrects for tilts and offsets of the sub-mm beam. Moreover, we find that the simulated telescope aperture efficiency is increased across the frequency range of the ISS after the optimisation.

astro-ph.IM↗

arXiv2021

DESHIMA 2.0: Rapid redshift surveys and multi-line spectroscopy of dusty galaxies

We present a feasibility study for the high-redshift galaxy part of the Science Verification Campaign with the 220-440 GHz DESHIMA 2.0 integrated superconducting spectrometer on the ASTE telescope. The first version of the DESHIMA 2.0 chip has been recently manufactured and tested in the lab. Based on these realistic performance measurements, we evaluate potential target samples and prospects for detecting the [CII] and CO emission lines. The planned observations comprise two distinct, but complementary objectives: (1) acquiring spectroscopic redshifts for dusty galaxies selected in far-infrared/mm-wave continuum surveys; (2) multi-line observations to infer physical conditions in dusty galaxies.

astro-ph.IM↗

arXiv2021

Large format imaging spectrograph for the Large Submillimeter Telescope (LST)

We present a conceptual study of a large format imaging spectrograph for the Large Submillimeter Telescope (LST) and the Atacama Large Aperture Submillimeter Telescope (AtLAST). Recent observations of high-redshift galaxies indicate the onset of earliest star formation just a few 100 million years after the Big Bang (i.e., z = 12--15), and LST/AtLAST will provide a unique pathway to uncover spectroscopically-identified first forming galaxies in the pre-reionization era, once it will be equipped with a large format imaging spectrograph. We propose a 3-band (200, 255, and 350 GHz), medium resolution (R = 2,000) imaging spectrograph with 1.5 M detectors in total based on the KATANA concept (Karatsu et al. 2019), which exploits technologies of the integrated superconducting spectrometer (ISS) and a large-format imaging array. A 1-deg2 drilling survey (3,500 hr) will capture a large number of [O III] 88 um (and [C II] 158 um) emitters at z = 8--9, and constrain [O III] luminosity functions at z > 12.

astro-ph.IM↗

arXiv2019

Discovery of Shocked Molecular Clouds Associated with the Shell-Type Supernova Remnant RX J0046.5$-$7308 in the Small Magellanic Cloud

RX J0046.5$-$7308 is a shell-type supernova remnant (SNR) in the Small Magellanic Cloud (SMC). We carried out new $^{12}$CO($J$ = 1-0, 3-2) observations toward the SNR using Mopra and the Atacama Submillimeter Telescope Experiment. We found eight molecular clouds (A-H) along the X-ray shell of the SNR. The typical cloud size and mass are $\sim$10-15 pc and $\sim$1000-3000 $M_{\odot}$, respectively. The X-ray shell is slightly deformed and has the brightest peak in the southwestern shell where two molecular clouds A and B are located. The four molecular clouds A, B, F, and G have high intensity ratios of $^{12}$CO($J$ = 3-2) / $^{12}$CO($J$ = 1-0) $> 1.2$, which are not attributable to any identified internal infrared sources or high-mass stars. The HI cavity and its expanding motion are found toward the SNR, which are likely created by strong stellar winds from a massive progenitor. We suggest that the molecular clouds A-D, F, and G and HI clouds within the wind-blown cavity at $V_\mathrm{LSR} = 117.1$-122.5 km s$^{-1}$ are to be associated with the SNR. The X-ray spectroscopy reveals the dynamical age of $26000^{+1000}_{-2000}$ yr and the progenitor mass of $\gtrsim 30$ $M_{\odot}$, which is also consistent with the proposed scenario. We determine physical conditions of the giant molecular cloud LIRS 36A using the large velocity gradient analysis with archival datasets of the Atacama Large Millimeter/submillimeter Array; the kinematic temperature is $72^{+50}_{-37}$ K and the number density of molecular hydrogen is $1500^{+600}_{-300}$ cm$^{-3}$. The next generation of $\gamma$-ray observations will allow us to study the pion-decay $\gamma$-rays from the molecular clouds in the SMC SNR.

astro-ph.GA↗

arXiv2019

ALMA observations of layered structures due to CO selective dissociation in the $\rho$ Ophiuchi A plane-parallel PDR

We analyze $^{12}$CO($J$=2-1), $^{13}$CO($J$=2-1), C$^{18}$O ($J$=2-1), and 1.3 mm continuum maps of the $\rho$ Ophiuchi A photo-dissociation region (PDR) obtained with ALMA. Layered structures of the three CO isotopologues with an angular separation of 10 arcsec = 6.6$\times$10$^{-3}$ pc = 1400 au are clearly detected around the Be star, S1 (i.e., each front of emission shifts from the near to far side in order of $^{12}$CO, $^{13}$CO, and C$^{18}$O). We estimate the spatial variations of $X$($^{13}$CO)/$X$(C$^{18}$O) abundance ratios, and find that the abundance ratio is as high as 40 near the emission front, and decreases to the typical value in the solar system of 5.5 in a small angular scale of 4 arcsec = 2.6$\times$10$^{-3}$ pc = 560 au. We also find that the $I$($^{12}$CO(2-1))/$I$($^{13}$CO(2-1)) intensity ratio is very high ($>$21) in the flat-spectrum young stellar object, GY-51, located in the PDR. The enhancement of the ratios indicates that the UV radiation significantly affects the CO isotopologues via selective dissociation in the overall $\rho$ Ophiuchi A PDR, and that the $\rho$ Ophiuchi A PDR has a plane-parallel structure.

astro-ph.GA↗

arXiv2018

Nobeyama 45m Cygnus-X CO survey I: photodissociation of molecules revealed by the unbiased large-scale CN and C$^{18}$O maps

We present an unbiased large-scale (9 deg$^2$) CN ($N$=1-0) and C$^{18}$O ($J$=1-0) survey of Cygnus-X conducted with the Nobeyama 45m Cygnus-X CO survey. CN and C$^{18}$O are detected in various objects towards the Cygnus-X North and South (e.g., DR17, DR18, DR21, DR22, DR23, and W75N). We find that CN/C$^{18}$O integrated intensity ratios are systematically different from region to region, and are especially enhanced in DR17 and DR18 which are irradiated by the nearby OB stars. This result suggests that CN/C$^{18}$O ratios are enhanced via photodissociation reactions. We investigate the relation between the CN/C$^{18}$O ratio and strength of the UV radiation field. As a result, we find that CN/C$^{18}$O ratios correlate with the far-UV intensities, $G_0$. We also find that CN/C$^{18}$O ratios decrease inside molecular clouds, where the interstellar UV radiation is reduced due to the interstellar dust extinction. We conclude that the CN/C$^{18}$O ratio is controlled by the UV radiation, and is a good probe of photon-dominated regions.

astro-ph.GA↗

arXiv2011

Intermittent maser flare around the high mass young stellar object G353.273+0.641 I: data & overview

We have performed VLBI and single-dish monitoring of 22 GHz H$_{2}$O maser emission from the high mass young stellar object G353.273+0.641 with VERA (VLBI Exploration of Radio Astrometry) and Tomakamai 11-m radio telescope. Two maser flares have been detected, separated almost two years. Frequent VLBI monitoring has revealed that these flare activities have been accompanied by structural change of the prominent shock front traced by H2O maser alignments. We have detected only blue-shifted emissions and all maser features have been distributed within very small area of 200 $\times$ 200 au$^{2}$ in spite of wide velocity range (> 100 km s$^{-1}$). The light curve shows notably intermittent variation and suggests that the H$_{2}$O masers in G353.273+0.641 are excited by episodic radio jet. The time-scale of \sim2 yr and characteristic velocity of \sim500 km s$^{-1}$ also support this interpretation. Two isolated velocity components of C50 (-53 \pm 7 km s$^{-1}$) and C70 (-73 \pm 7 km s$^{-1}$) have shown synchronised linear acceleration of the flux weighted $V_{\rmn{LSR}}$ values (\sim-5 km s$^{-1}$ yr$^{-1}$) during the flare phase. This can be converted to the lower-limit momentum rate of 1.1 \times 10$^{-3}$ M$_{\sun}$ km s$^{-1}$ yr$^{-1}$. Maser properties are quite similar to that of IRAS 20126+4104 especially. This corroborates the previous suggestion that G353.273+0.641 is a candidate of high mass protostellar object. The possible pole-on geometry of disc-jet system can be suitable for direct imaging of the accretion disc in this case.

astro-ph.SR↗

arXiv2011

Hyperfine, rotational and Zeeman structure of the lowest vibrational levels of the $^{87}$Rb$_2$ $\tripletex$ state

We present the results of an experimental and theoretical study of the electronically excited $\tripletex$ state of $^{87}$Rb$_2$ molecules. The vibrational energies are measured for deeply bound states from the bottom up to $v'=15$ using laser spectroscopy of ultracold Rb$_2$ Feshbach molecules. The spectrum of each vibrational state is dominated by a 47\,GHz splitting into a $\cog$ and $\clg$ component caused mainly by a strong second order spin-orbit interaction. Our spectroscopy fully resolves the rotational, hyperfine, and Zeeman structure of the spectrum. We are able to describe to first order this structure using a simplified effective Hamiltonian.

physics.atom-ph↗

arXiv2011

Production of a dual-species Bose-Einstein condensate of Rb and Cs atoms

We report the simultaneous production of Bose-Einstein condensates (BECs) of $^{87}$Rb and $^{133}$Cs atoms in separate optical traps. The two samples are mixed during laser cooling and loading but are separated by $400 μ$m for the final stage of evaporative cooling. This is done to avoid considerable interspecies three-body recombination, which causes heating and evaporative loss. We characterize the BEC production process, discuss limitations, and outline the use of the dual-species BEC in future experiments to produce rovibronic ground state molecules, including a scheme facilitated by the superfluid-to-Mott-insulator (SF-MI) phase transition.

cond-mat.quant-gas↗