arXiv subjects

Yasunori Fujii

Publications and source records attributed to Yasunori Fujii.

At least 19 recordsLinked to original sources

arXiv2024

Q-band Line Survey Observations toward a Carbon-chain-rich Clump in the Serpens South Region

We have conducted Q-band (30 GHz $-$ 50 GHz) line survey observations toward a carbon-chain emission peak in the Serpens South cluster-forming region with the extended Q-band (eQ) receiver installed on the Nobeyama 45 m radio telescope. Approximately 180 lines have been detected including tentative detection, and these lines are attributed to 52 molecules including isotopologues. It has been found that this position is rich in carbon-chain species as much as Cyanopolyyne Peak in Taurus Molecular Cloud-1 (TMC-1 CP), suggesting chemical youth. Not only carbon-chain species, but several complex organic molecules (CH$_3$OH, CH$_3$CHO, HCCCHO, CH$_3$CN, and tentatively C$_2$H$_3$CN) have also been detected, which is similar to the chemical complexity found in evolved prestellar cores. The HDCS/H$_2$CS ratio has been derived to be $11.3 \pm 0.5$ %, and this value is similar to the prestellar core L1544. The chemically young features that are similar to the less-dense starless core TMC-1 CP ($10^4$ cm$^{-3}$ $-$ $10^5$ cm$^{-3}$) and chemically evolved characters which resemble the dense prestellar core L1544 ($\sim 10^6$ cm$^{-3}$) mean that the clump including the observed position is a pre-cluster clump without any current star formation activity.

astro-ph.GA↗

arXiv2024

An ultra wide-band, high-sensitivity Q-band receiver for single-dish telescopes, eQ: rest frequency determination of CCS ($J_N$ = $4_3$-$3_2$) and SO ($J_N$ = $1_0$-$0_1$), and high-redshift CO ($J$ = 1-0) detection

We report on the development and commissioning of a new Q-band receiver for the Nobeyama 45-m telescope, covering 30--50 GHz with a receiver noise temperature of about 15 K. We name it eQ (extended Q-band) receiver. The system noise temperatures for observations are measured to be $\sim$ 30 K at 33 GHz and $\sim$ 75 K at 45 GHz. The Half-Power-Beam-Width (HPBW) is around 38\arcsec at 43 GHz. To enhance the observation capability, we tested the smoothed bandpass calibration technique and demonstrated the observation time can be significantly reduced compared to the standard position switch technique. The wide-bandwidth capability of this receiver provides precise determination of rest frequencies for molecular transitions with an accuracy of a few kHz through simultaneous observations of multiple transitions. Particularly, we determined the rest frequency of SO ($J_N$ = $1_0$--$0_1$) to be 30.001542 GHz, along with the rest frequency of CCS ($J_N$ = $4_3$--$3_2$) being 45.379033 GHz, adopting CCS ($J_N$ = $3_2$--$2_1$) at 33.751370 GHz as a reference line. The SO profile shows a double peak shape at the Cyanopolyyne Peak (CP) position of the Taurus Molecular Cloud-1 (TMC-1). The SO peaks coincide well with the CCS sub-components located near the outer parts of the TMC-1 filament. We interpret that the gravitational infall of TMC-1 generates shocks which enhance the SO abundance. The TMC-1 map shows that carbon-chain molecules are more abundant in the southern part of the filament, whereas SO is more abundant in the northern part. The eQ's excellent sensitivity allowed us to detect faint CO ($J$ = 1--0) spectra from the high-redshift object at a redshift of 2.442. Our receiver is expected to open new avenues for high-sensitivity molecular line observations in the Q-band.

astro-ph.GA↗

arXiv2022

DESHIMA 2.0: development of an integrated superconducting spectrometer for science-grade astronomical observations

Integrated superconducting spectrometer (ISS) technology will enable ultra-wideband, integral-field spectroscopy for (sub)millimeter-wave astronomy, in particular, for uncovering the dust-obscured cosmic star formation and galaxy evolution over cosmic time. Here we present the development of DESHIMA 2.0, an ISS for ultra-wideband spectroscopy toward high-redshift galaxies. DESHIMA 2.0 is designed to observe the 220-440 GHz band in a single shot, corresponding to a redshift range of $z$=3.3-7.6 for the ionized carbon emission ([C II] 158 $μ$m). The first-light experiment of DESHIMA 1.0, using the 332-377 GHz band, has shown an excellent agreement among the on-sky measurements, the lab measurements, and the design. As a successor to DESHIMA 1.0, we plan the commissioning and the scientific observation campaign of DESHIMA 2.0 on the ASTE 10-m telescope in 2023. Ongoing upgrades for the full octave-bandwidth system include the wideband 347-channel chip design and the wideband quasi-optical system. For efficient measurements, we also develop the observation strategy using the mechanical fast sky-position chopper and the sky-noise removal technique based on a novel data-scientific approach. In the paper, we show the recent status of the upgrades and the plans for the scientific observation campaign.

astro-ph.IM↗

arXiv2020

Development of the new multi-beam receiver and telescope control system for NASCO

We report the current status of the NASCO (NAnten2 Super CO survey as legacy) project which aims to provide all-sky CO data cube of southern hemisphere using the NANTEN2 4-m submillimeter telescope installed at the Atacama Desert through developing a new multi-beam receiver and a new telescope control system. The receiver consists of 5 beams. The four beams, located at the four corners of a square with the beam separation of 720$''$, are installed with a 100 GHz band SIS receiver having 2-polarization sideband-separation filter. The other beam, located at the optical axis, is installed with a 200 GHz band SIS receiver having 2-polarization sideband-separation filter. The cooled component is modularized for each beam, and cooled mirrors are used. The IF bandwidths are 8 and 4 GHz for 100 and 200 GHz bands, respectively. Using XFFTS spectrometers with a bandwidth of 2 GHz, the lines of $^{12}$CO, $^{13}$CO, and C$^{18}$O of $J$=1$-$0 or $J$=2$-$1 can be observed simultaneously for each beam. The control system is reconstructed on the ROS architecture, which is an open source framework for robot control, to enable a flexible observation mode and to handle a large amount of data. The framework is commonly used and maintained in a robotic field, and thereby reliability, flexibility, expandability, and efficiency in development are improved as compared with the system previously used. The receiver and control system are installed on the NANTEN2 telescope in December 2019, and its commissioning and science verification are on-going. We are planning to start science operation in early 2021.

astro-ph.IM↗

arXiv2020

DESHIMA on ASTE: On-sky Responsivity Calibration of the Integrated Superconducting Spectrometer

We are developing an ultra-wideband spectroscopic instrument, DESHIMA (DEep Spectroscopic HIgh-redshift MApper), based on the technologies of an on-chip filter-bank and Microwave Kinetic Inductance Detector (MKID) to investigate dusty star-burst galaxies in the distant universe at millimeter and submillimeter wavelength. An on-site experiment of DESHIMA was performed using the ASTE 10-m telescope. We established a responsivity model that converts frequency responses of the MKIDs to line-of-sight brightness temperature. We estimated two parameters of the responsivity model using a set of skydip data taken under various precipitable water vapor (PWV, 0.4-3.0 mm) conditions for each MKID. The line-of-sight brightness temperature of sky is estimated using an atmospheric transmission model and the PWVs. As a result, we obtain an average temperature calibration uncertainty of $1σ=4$%, which is smaller than other photometric biases. In addition, the average forward efficiency of 0.88 in our responsivity model is consistent with the value expected from the geometrical support structure of the telescope. We also estimate line-of-sight PWVs of each skydip observation using the frequency response of MKIDs, and confirm the consistency with PWVs reported by the Atacama Large Millimeter/submillimeter Array.

astro-ph.IM↗

arXiv2019

First light demonstration of the integrated superconducting spectrometer

Ultra-wideband 3D imaging spectrometry in the millimeter-submillimeter (mm-submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution. However, it is challenging to scale up conventional coherent heterodyne receivers or free-space diffraction techniques to sufficient bandwidths ($\geq$1 octave) and numbers of spatial pixels (>$10^2$). Here we present the design and first astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer, which covers 332-377 GHz with a spectral resolution of $F/ΔF \sim 380$. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs) with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine, and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to $\sim$1.1 THz. The miniature chip footprint of a few $\mathrm{cm^2}$ allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible.

astro-ph.IM↗

arXiv2015

A new estimate of the mass of the gravitational scalar field for Dark Energy

A new estimate of the mass of the pseudo dilaton is offered by following the funda- mental nature that a massless Nambu-Goldstone boson, called a dilaton, in the Einstein frame acquires a nonzero mass through the loop effects which occur with the Higgs field in the relativistic quantum field theory as described by poles of D, spacetime dimensionality off the physical value D = 4. Naturally the technique of dimensional regulairzation is fully used to show this pole structure to be suppressed to be finite by what is called a Classical-Quantum-Interplay, to improve our previous attempt. Basically the same anal- ysis is extended to derive also the coupling of a pseudo dilaton to two photons.

gr-qc↗

arXiv2014

Is the zero-point energy a source of the cosmological constant?

We discuss how we remove a huge discrepancy between the theory of a cosmological constant, due to the zero-point energies of matter fields, and the observation. The technique of dimensional regularization plays a decisive role. We eventually reach the desired behavior of the vacuum densities falling off like t^{-2}, allowing us to understand how an extremely small result comes about naturally. As a price, however, the zero-point energy vacuum fails to act as a true cosmological constant. Its expected role responsible for the observed accelerating universe is then to be inherited by the gravitational scalar field, dark energy, as we suggest in the scalar-tensor theory.

gr-qc↗

arXiv2011

An approach toward the laboratory search for the scalar field as a candidate of Dark Energy

The observed accelerating universe indicates the presence of Dark Energy which is probably interpreted in terms of an extremely light gravitational scalar field. We suggest a way to probe this scalar field which contributes to optical light-by-light scattering through the resonance in the quasi-parallel collision geometry. As we find, the frequency-shifted photons with the specifically chosen polarization state can be a distinct signature of the scalar-field-exchange process in spite of the extremely narrow width due to the gravitationally weak coupling to photons. Main emphasis will be placed in formulating a prototype theoretical approach, then showing how the weak signals from the gravitational coupling are enhanced by other non-gravitational effects at work in laser experiments.

gr-qc↗

arXiv2010

A Laboratory Search for Dark Energy

The discovery of the accelerating universe indicates strongly the presence of a scalar field which is not only expected to solve today's version of the cosmological constant problem, or the fine-tuning and the coincidence problems, but also provides a way to understand dark energy. It has also been shown that Jordan's scalar-tensor theory is now going to be re-discovered in the new lights. In this letter we suggest a way to search for the extremely light scalar field by means of a laboratory experiment on the low-energy photon-photon interactions with the quasi-parallel incident beams.

gr-qc↗

arXiv2009

Accelerating universe and the time-dependent fine-structure constant

Theoretical background of our proposed relation between the accelerating universe and the time-variability of the fine-structure constant is discussed, based on the scalar-tensor theory, with emphases on the intuitive aspects of underlying physical principles. An important comment is added on the successful understanding of the size of the effective cosmological constant responsible for the acceleration, without appealing to fine-tuning parameters.

astro-ph.CO↗

arXiv2009

How successful can the scalar-tensor theory be in understanding the accelerating universe?

The accelerating universe is closely related to today's version of the cosmological constant problem; fine-tuning and coincidence problems. We show how successfully the scalar-tensor theory, a rather rigid theoretical idea, provides us with a simple and natural way to understand why today's observed cosmological constant is small only because we are old cosmologically, without fine-tuning theoretical parameters extremely.

astro-ph.CO↗

arXiv2009

Attractor Universe in the Scalar-Tensor Theory of Gravitation

In the scalar-tensor theory of gravitation it seems nontrivial to establish if solutions of the cosmological equations in the presence of a cosmological constant behave as attractors independently of the initial values. We develop a general formulation in terms of two-dimensional phase space. We show that there are two kinds of fixed points, one of which is an attractor depending on the coupling constant and equation of state. In the case with a power-law potential in the Jordan frame, we also find new type of inflation caused by the coupling to the matter fluid.

hep-th↗

arXiv2009

Revised fits to $Δα/α$ in consistency with the accelerating universe

An attempt is made for a new type of analysis of the time-variability of the fine-structure constant trying to fit the most recent result from the laboratory measurements, the Oklo constraint and the data from the QSO absorption lines all in consistency with the accelerating universe.

astro-ph↗

arXiv2008

Accelerating universe, WEP violation and antihydrogen atoms

Apart from the suspected violation of the CPT invariance, we might expect if the measurements of antihydrogen atoms provide testing Weak Equivalence Principle (WEP) in the gravitational phenomena. We start with how its violation can be related to the expected idea of unification of particle physics and gravitation, an attempt beyond the standard theories, including general relativity of Einstein. A particular emphasis will be placed on the issue of an accelerating universe, a rather recent development since nearly 10 years ago, suggesting a strong motivation toward attempts beyond the conventional concepts of the traditional cosmology. We face today's version of the cosmological constant problem. A candidate of the new ingredient appears to be provided by a scalar field, sometimes under the names like quintessence or dark-energy. In this article, we discuss the subject from a point of view of a more theoretical approach based on the scalar-tensor theory of gravitation. By exploiting the concepts of conformal transformations and conformal frames unique to this type of approach, we show that a successful understanding of the observed cosmological acceleration entails an unexpected outcome of breakdown of WEP, which may show up as a distinct behavior between hydrogen and antihydrogen in the gravitational influence, from a further wider perspective including a vector field as well. We intended to introduce most of the new concepts as plainly and briefly as possible, according to the nature of the talk. On the other hand, however, we find it also useful to go into some more details, depending on the interests of individuals among the audience. For a compromise, we decided to add a number of footnotes which were not delivered during the presentation, but might be helpful in the proceedings published later.

gr-qc↗

arXiv2007

Possible time-variability of the fine-structure constant expected from the accelerating universe

We present a theoretical calculation on the time-variability of the fine-structure constant to fit the result of the recent precise analysis of the measurement of the QSO absorption lines. We find the parameters and initial values of the scalar-tensor theory to be determined much more accurately than fitting the accelerating universe itself, but leading not to easy detections of the effect on the equation of state of the dark energy in the earlier epochs.

astro-ph↗

arXiv2007

Conformal transformation in the scalar-tensor theory applied to the accelerating universe

The scalar-tensor theory is plagued by nagging questions if different conformal frames, in particular the Jordan and Einstein conformal frames, are equivalent to each other. As a closely related question, there are opposing views on which of the two conformal frames is physically acceptable. Reinforcing our previous claims, we offer replies based on a cosmological model of the scalar-tensor theory, believed to be a promising theory for understanding the accelerating universe, as well as today's version of the cosmological constant problem. Exploiting the advantage that this model admits analytical asymptotic solutions, our argument does not depend on whether the underlying theory is invariant under conformal transformations. Our argument provides partial support for the claimed "equivalence," but we also present examples that require more careful analyses exploiting field equations. We also point out that the Jordan conformal frame is suitable for an interpretation in terms of unification theories in physics, for example, string theory and the Kaluza-Klein approach, while the Einstein conformal frame may be acceptable as a physical conformal frame under two conditions: (i) the simplest constant $Λ$ term in the Lagrangian in the Jordan conformal frame; (ii) the revised form of the conventional Brans-Dicke model based on the validity of weak equivalence principle.

gr-qc↗

arXiv2006

Gravitational scalar field coupled directly to the Maxwell field and its effect to solar-system experiments

The effect of the massless gravitational scalar field assumed to couple directly to the Maxwell field to the solar-system experiments is estimated. We start with discussing the theoretical significances of this coupling. Rather disappointingly, however, we find that the scalar-field parameters never affect the observation in the limit of the geometric optics, indicating a marked difference from the well-known contribution through the spacetime metric.

astro-ph↗