分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In modified gravity theories, the gravitational waves propagation are presented in nonstandard ways. We consider a friction term different from GR and constrain the modified gravitational waves propagation from observations. The modified gravitational waves produce anisotropies and polarization which generate measurable tensor power spectra. We explore the impact of the friction term on the power spectrum of B-modes and the impact on the constraints on the other parameters (e.g., $r$ or $A_t$) when $\nu_0$ is allowed to vary in the Monte Carlo analyses from Planck+BK18 datasets. If we assume the result of the scalar perturbations is unchanged, the inflation consistency relation alters with the friction term. In the $\Lambda$CDM+$r$+$\nu_0$ model, the tensor-to-scalar ratio and the amplitude of tensor spectrum are influenced obviously.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We constrain the primordial gravitational waves from cosmic microwave background (CMB) and stochastic gravitational wave background (SGWB) observations. SGWB provides the latest way to explore the early universe and the cosmological evolution which can be reflected by primordial gravitational waves. We not only combine LIGO observations with CMB to measure primordial gravitational waves, but also forecast the potential abilities of the LISA detector and PTA projects. In the $\Lambda$CDM+$r$+$n_t$ model, the standard six parameters change slightly from SGWB observations. While the constraints on tensor-to-scalar ratio and tensor spectral index are improved obviously from SGWB observations. FAST projects have a significant impact on tensor-to-scalar ratio and tensor spectral index, namely $r<0.028$ and $n_t=-0.41^{+0.64}_{-0.96}$ at $95\%$ confidence level.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Dust extinction law is crucial to recover the intrinsic energy distribution of celestial objects and infer the characteristics of interstellar dust. Based on the traditional pair method, an improved pair method is proposed to model the dust extinguished spectral energy distribution (SED) of an individual star. Instead of the mathematically parameterizing extinction curves, the extinction curves in this work are directly from the silicate-graphite dust model, so that the dust extinction law can be obtained and the dust properties can be analyzed simultaneously. The ATLAS9 stellar model atmosphere is adopted for the intrinsic SEDs in this work, while the silicate-graphite dust model with a dust size distribution of $dn/da \sim a^{-\alpha}{\rm exp}(-a/a_c),~0.005 < a < 5~\mu{\rm m}$ for each component is adopted for the model extinction curves. One typical extinction tracer in the dense region (V410 Anon9) and one in the diffuse region (Cyg OB2 \#12) of the MW are chosen to test the reliability and the practicability of the improved pair method in different stellar environments. The results are consistent with their interstellar environments and are in agreement with the previous observations and studies, which prove that the improved pair method is effective and applicable in different stellar environments. In addition to the reliable extinction results, the derived parameters in the dust model can be used to analyze the dust properties, which cannot be achieved by other methods with the mathematical extinction models. With the improved pair method, the stellar parameters can also be inferred and the extinction law beyond the wavelengths of observed data can be predicted based on the dust model as well.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The unusual extinction curves of SN 2010jl provide an excellent opportunity to investigate the properties of dust formed by core-collapse supernovae. By using a series of dust models with different compositions and grain size distributions, we fit the extinction curves of SN 2010jl and find that a silicate-graphite mixture dust model characterized by exponentially cutoff power-law size distributions can well reproduce its unusual extinction curves. The best-fit results show that the extinctions derived from the dust models are consistent with the observed values at all epochs. However, the total-to-selective extinction ratio $R_V$ is about 2.8 - 3.1, which is significantly smaller than the value of $R_V \approx 6.4$ derived by Gall et al. The best-fit models indicate that the dust grains around SN 2010jl are possibly composed of small-size astronomical silicate grains and micron-size graphite grains. In addition, by fitting the optical to mid-infrared spectral energy distribution, we find that the dust mass around SN 2010jl increases with time, up to $0.005\,M_{\odot}$ around 1300 days after peak brightness, which is consistent with previous estimates.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Dust extinction law is crucial to recover the intrinsic energy distribution of celestial objects and infer the characteristics of interstellar dust. Based on the traditional pair method, an improved pair method is proposed to model the dust extinguished spectral energy distribution (SED) of an individual star. Instead of the mathematically parameterizing extinction curves, the extinction curves in this work are directly from the silicate-graphite dust model, so that the dust extinction law can be obtained and the dust properties can be analyzed simultaneously. The ATLAS9 stellar model atmosphere is adopted for the intrinsic SEDs in this work, while the silicate-graphite dust model with a dust size distribution of $dn/da \sim a^{-\alpha}{\rm exp}(-a/a_c),~0.005 < a < 5~\mu{\rm m}$ for each component is adopted for the model extinction curves. One typical extinction tracer in the dense region (V410 Anon9) and one in the diffuse region (Cyg OB2 \#12) of the MW are chosen to test the reliability and the practicability of the improved pair method in different stellar environments. The results are consistent with their interstellar environments and are in agreement with the previous observations and studies, which prove that the improved pair method is effective and applicable in different stellar environments. In addition to the reliable extinction results, the derived parameters in the dust model can be used to analyze the dust properties, which cannot be achieved by other methods with the mathematical extinction models. With the improved pair method, the stellar parameters can also be inferred and the extinction law beyond the wavelengths of observed data can be predicted based on the dust model as well.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： A large class of Laboratory, Space, and Astrophysical plasmas is nearly collisionless. When a localized energy or particle sink, for example, in the form of a radiative cooling spot or a black hole, is introduced into such a plasma, it can trigger a plasma thermal collapse, also known as a thermal quench in tokamak fusion. Here we show that the electron thermal conduction in such a nearly collisionless plasma follows the convective energy transport scaling in itself or in its spatial gradient, due to the constraint of ambipolar transport. As the result, a robust cooling flow aggregates mass toward the cooling spot and the thermal collapse of the surrounding plasma takes the form of four propagating fronts that originate from the radiative cooling spot, along the magnetic field line in a magnetized plasma. The slowest one, which is responsible for deep cooling, is a shock front.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Extinction in ultraviolet is much more significant than in optical or infrared, which can be very informative to precisely measure the extinction and understand the dust properties in the low extinction areas. The high Galactic latitude sky is such an area, important for studying the extragalactic sky and the universe. Based on the stellar parameters measured by the LAMOST and GALAH spectroscopy and the ultraviolet photomery by the \emph{GALEX} space telescope, the extinction of 1,244,504 stars in the \emph{GALEX}/NUV band and 56,123 stars in the \emph{GALEX}/FUV band are calculated precisely. \textbf{The error of color excess is 0.009, 0.128 and 0.454 mag for $E_{\rm G_{BP}, G_{RP}}$, $E_{\rm NUV,G_{BP}}$ and $E_{\rm FUV,G_{BP}}$ respectively.} They delineates the \emph{GALEX}/NUV extinction map of about a third of the sky mainly at the high Galactic latitude area with an angular resolution of $\sim 0.4\,\, \rm deg$. The mean color excess ratio in the entire sky areas is derived to be 3.25, 2.95 and -0.37 for $E_{{\rm NUV,G_{BP}}} / E_{{\rm G_{BP},G_{RP}}}$, $E_{{\rm FUV,G_{BP}}} / E_{{\rm G_{BP},G_{RP}}}$ and $E_{{\rm FUV,NUV}} / E_{{\rm G_{BP},G_{RP}}}$ respectively, which is in general agreement with the previous works, and their changes with the Galactic latitude and the interstellar extinction are discussed.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The dust temperature and mass of the supernova remnants (SNRs) in M31 are estimated by fitting the infrared spectral energy distribution calculated from the images in the Spitzer/IRAC4 and MIPS24, Herschel/PACS70, 100, 160, and Herschel/SPIRE250, 350$\mu$m band. Twenty SNRs with relatively reliable photometry exhibit an average dust temperature of $20.1^{+1.8}_{-1.5}$K, which is higher than the surrounding and indicating the heating effect of supernova explosion. The dust mass of these SNRs ranges from about 100 to 800$ M_{\odot}$, much bigger than the SNRs in the Milky Way. On the other hand, this yields the dust surface density of $0.10^{+0.07}_{-0.04}{ M_{\odot} \rm pc^{-2}}$, about half of the surrounding area, which implies that about half dust in the SNRs is destroyed by the supernova explosion. The dust temperature, the radius, and thus the dust mass all demonstrate that the studied SNRs are old and very likely in the snowplow or even fade away phase because of the limitation by the far distance and observation resolution of M31, and the results can serve as a reference to the final effect of supernova explosion on the surrounding dust.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The scalar induced gravitational waves are produced from primordial curvature perturbations in the second order of perturbations. We constrain the fractional energy density of scalar induced gravitational waves from gravitational waves observations. If there is no detection of the scalar induced gravitational waves, the fractional energy density of scalar induced gravitational waves is constrained by some upper limits. Depends on these upper limits, we can obtain the constraints on the power spectrum of the primordial curvature perturbations. For a power-law scalar power spectrum, the constraints on the power spectrum are affected by adding the upper limit of scalar induced gravitational waves from Square Kilometer Array (SKA). In the standard model, the mean values of the scalar amplitude and the spectral index shift to lower values when SKA is added to the combination of Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillation (BAO) datasets, namely $\ln(10^{10}A_s)=3.038\pm0.013$ and $n_s=0.9589^{+0.0021}_{-0.0011}$ at $68\%$ confidence level. We also consider the effects of the existing ground-based gravitational-wave detectors, the existing Pulsar Timing Arrays (PTAs) and Five-hundred-meter Aperture Spherical radio Telescope (FAST), while the constraints from CMB+BAO datasets are totally within their upper limits of scalar induced gravitational waves. Furthermore, we characterize the scalar fluctuation spectrum in terms of the spectral index $n_s$ and its first two derivatives. We calculate corresponding power spectrum of scalar induced gravitational waves theoretically and give the constraints on the running of the spectral index and the running of the running of the spectral index.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The scalar induced gravitational waves are produced from primordial curvature perturbations in the second order of perturbations. We constrain the fractional energy density of scalar induced gravitational waves from gravitational waves observations. If there is no detection of the scalar induced gravitational waves, the fractional energy density of scalar induced gravitational waves is constrained by some upper limits. Depends on these upper limits, we can obtain the constraints on the power spectrum of the primordial curvature perturbations. For a power-law scalar power spectrum, the constraints on the power spectrum are affected by adding the upper limit of scalar induced gravitational waves from Square Kilometer Array (SKA). In the standard model, the mean values of the scalar amplitude and the spectral index shift to lower values when SKA is added to the combination of Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillation (BAO) datasets, namely $\ln(10^{10}A_s)=3.038\pm0.013$ and $n_s=0.9589^{+0.0021}_{-0.0011}$ at $68\%$ confidence level. We also consider the effects of the existing ground-based gravitational-wave detectors, the existing Pulsar Timing Arrays (PTAs) and Five-hundred-meter Aperture Spherical radio Telescope (FAST), while the constraints from CMB+BAO datasets are totally within their upper limits of scalar induced gravitational waves. Furthermore, we characterize the scalar fluctuation spectrum in terms of the spectral index $n_s$ and its first two derivatives. We calculate corresponding power spectrum of scalar induced gravitational waves theoretically and give the constraints on the running of the spectral index and the running of the running of the spectral index.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The dust mass of the well-known supernova remnant (SNR) IC 443 is estimated from both the infrared emission and the visual extinction. With photometry to the images taken by \emph{Spitzer}, \emph{WISE}, \emph{IRAS}, \emph{AKARI} and \emph{Planck}, the spectral energy distribution (SED) of the dust is obtained after subtracting the synchrotron radiation and considering the spectral line emission. The dust mass is derived from fitting the SED by a two-component model, which results in a warm component of the temperature of $\sim$ 53 K and the mass of 0.1 $M_\odot$, and a cold component of the temperature of $\sim 17$ K and the mass of 46 $M_\odot$. On the other hand, the dust mass is derived to be $\sim$ 66 $M_\odot$ from the visual extinction of IC 443 which is identified from the 3D Bayestar extinction map and its coincidence with the infrared emission morphology. Roughly the dust mass derived from the infrared emission and the extinction agree mutually. However, the dust mass derived from the infrared emission can be adjusted to be more consistent with that from the extinction by using different dust opacity property or considering optically thick radiation. In addition, the distribution of dust temperature and mass is analyzed by fitting the SED pixel by pixel.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Yong Yu
Peng-Fei Sun
Yu-Zhe Zhang
Bing Bai
Yu-Qiang Fang
Xi-Yu Luo
Zi-Ye An
Jun Li
Jun Zhang
Feihu Xu
Xiao-Hui Bao
Jian-Wei Pan
摘要： In this paper we report an experiment that verifies an atomic-ensemble quantum memory via a measurement-device-independent scheme. A single photon generated via Rydberg blockade in one atomic ensemble is stored in another atomic ensemble via electromagnetically induced transparency. After storage for a long duration, this photon is retrieved and interfered with a second photon to perform joint Bell-state measurement (BSM). Quantum state for each photon is chosen based on a quantum random number generator respectively in each run. By evaluating correlations between the random states and BSM results, we certify that our memory is genuinely entanglement-preserving.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Jun Li
Shimei Chen
Shangyuan Wang
Miao Lei
Xiaofang Dai
Chuangxue Liang
Kunyuan Xu
Shuxin Lin
Yuhui Li
Yuer Fan
Ting Zhong
摘要： We presented an optical system to perform imaging interested objects in complex scenes, like the creature easy see the interested prey in the hunt for complex environments. It utilized Deep-learning network to learn the interested objects's vision features and designed the corresponding "imaging matrices", furthermore the learned matrixes act as the measurement matrix to complete compressive imaging with a single-pixel camera, finally we can using the compressed image data to only image the interested objects without the rest objects and backgrounds of the scenes with the previous Deep-learning network. Our results demonstrate that no matter interested object is single feature or rich details, the interference can be successfully filtered out and this idea can be applied in some common applications that effectively improve the performance. This bio-inspired optical system can act as the creature eye to achieve success on interested-based object imaging, object detection, object recognition and object tracking, etc.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： A unique perspective approach based on an analogy method is presented to solve the ray equation in a model of a continuous inhomogeneous medium, which has a spherically symmetric distribution. Basically, in the standard undergraduate physics teaching, the curved ray path caused by refraction in a medium with a continuously varying refractive index has always been a relatively difficult problem to solve. The equation is usually expressed in terms of partial differential equations (PDEs), which cannot be solved by analytical methods. Based on the analogy method, this work proposes the correspondence between ray refraction in an established medium model and the inverse-square central force system, succinctly obtaining their relation equations mathematically. We also verify the correctness of the method by qualitative and quantitative analysis. In terms of theoretical validation, we analyse the relation between Fermat's principle and Hamilton's principle, which lays a theoretical foundation for the analogy method. In addition, ray paths in the medium model were also simulated by numerical calculations based on COMSOL Multiphysics, and the results are in perfect agreement with the conclusions.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Xinyue Long
Wan-Ting He
Na-Na Zhang
Kai Tang
Zidong Lin
Hongfeng Liu
Xinfang Nie
Guanru Feng
Jun Li
Tao Xin
Qing Ai
Dawei Lu
摘要： In open quantum systems, the precision of metrology inevitably suffers from the noise. {In Markovian open quantum dynamics, the precision can not be improved by using entangled probes although the measurement time is effectively shortened.} However, it was predicted over one decade ago that in a non-Markovian one, the error can be significantly reduced by the quantum Zeno effect (QZE) [Chin, Huelga, and Plenio, Phys. Rev. Lett. \textbf{109}, 233601 (2012)]. In this work, we apply a recently-developed quantum simulation approach to experimentally verify that entangled probes can improve the precision of metrology by the QZE. Up to $n=7$ qubits, we demonstrate that the precision has been improved by a factor of $n^{1/4}$, which is consistent with the theoretical prediction. Our quantum simulation approach may provide an intriguing platform for experimental verification of various quantum metrology schemes.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Xi-Yu Luo
Yong Yu
Jian-Long Liu
Ming-Yang Zheng
Chao-Yang Wang
Bin Wang
Jun Li
Xiao Jiang
Xiu-Ping Xie
Qiang Zhang
Xiao-Hui Bao
Jian-Wei Pan
摘要： Quantum internet gives the promise of getting all quantum resources connected, and it will enable applications far beyond a localized scenario. A prototype is a network of quantum memories that are entangled and well separated. Previous realizations are limited in the distance. In this paper, we report the establishment of remote entanglement between two atomic quantum memories physically separated by 12.5 km directly in a metropolitan area. We create atom-photon entanglement in one node and send the photon to a second node for storage. We harness low-loss transmission through a field-deployed fiber of 20.5 km by making use of frequency down-conversion and up-conversion. The final memory-memory entanglement is verified to have a fidelity of 90% via retrieving to photons. Our experiment paves the way to study quantum network applications in a practical scenario.
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