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Evidence of cosmic-ray acceleration up to sub-PeV energies in the supernova remnant IC 443
Authors:
Zhen Cao,
F. Aharonian,
Y. X. Bai,
Y. W. Bao,
D. Bastieri,
X. J. Bi,
Y. J. Bi,
W. Bian,
A. V. Bukevich,
C. M. Cai,
W. Y. Cao,
Zhe Cao,
J. Chang,
J. F. Chang,
A. M. Chen,
E. S. Chen,
G. H. Chen,
H. X. Chen,
Liang Chen,
Long Chen,
M. J. Chen,
M. L. Chen,
Q. H. Chen,
S. Chen,
S. H. Chen
, et al. (291 additional authors not shown)
Abstract:
Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy $γ$-ray emission from the SN…
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Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy $γ$-ray emission from the SNR IC 443 using the Large High Altitude Air Shower Observatory (LHAASO). The morphological analysis reveals a pointlike source whose location and spectrum are consistent with those of the Fermi-LAT-detected compact source with $π^0$-decay signature, and a more extended source which is consistent with a newly discovered source, previously unrecognized by Fermi-LAT. The spectrum of the point source can be described by a power-law function with an index of $\sim3.0$, extending beyond $\sim 30$ TeV without apparent cutoff. Assuming a hadronic origin of the $γ$-ray emission, the $95\%$ lower limit of accelerated protons reaches about 300 TeV. The extended source might be coincident with IC 443, SNR G189.6+3.3 or the putative pulsar wind nebula CXOU J061705.3+222127, and can be explained by either a hadronic or leptonic model. The LHAASO results provide compelling evidence that CR protons up to sub-PeV energies can be accelerated by the SNR.
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Submitted 29 October, 2025;
originally announced October 2025.
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A Giant Peanut-shaped Ultra-High-Energy Gamma-Ray Emitter Off the Galactic Plane
Authors:
Zhen Cao,
Felix Aharonian,
Yunxiang Bai,
Yiwei Bao,
Denis Bastieri,
Xiaojun Bi,
YuJiang Bi,
Mr Bian WenYi,
A. Butkevich,
Chengmiao Cai,
Wenyu Cao,
Zhe Cao,
Jin Chang,
Jinfan Chang,
Mr Aming Chen,
Ensheng Chen,
Mr Guo-Hai Chen,
Mr Huaxi Chen,
Liang Chen,
Long Chen,
Mingjun Chen,
Mali Chen,
Qihui Chen,
Shi Chen,
Suhong Chen
, et al. (291 additional authors not shown)
Abstract:
Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts), γ-rays manifests extreme particle acceleration in astrophysical sources. Recent observations by γ-ray telescopes, particularly by the Large High Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE sources, indicating numerous Galactic sources capable of accelerating particles to PeV (10^15 electronvolts) energi…
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Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts), γ-rays manifests extreme particle acceleration in astrophysical sources. Recent observations by γ-ray telescopes, particularly by the Large High Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE sources, indicating numerous Galactic sources capable of accelerating particles to PeV (10^15 electronvolts) energies. However, discerning the dominant acceleration mechanisms (leptonic versus hadronic), the relative contributions of specific source classes, and the role of particle transport in shaping their observed emission are central goals of modern UHE astrophysics. Here we report the discovery of a giant UHE γ-ray emitter at -17.5° off the Galactic plane - a region where UHE γ-ray sources are rarely found. The emitter exhibits a distinctive asymmetric shape, resembling a giant "Peanut" spanning 0.45° \times 4.6°, indicative of anisotropic particle distribution over a large area. A highly aged millisecond pulsar (MSP) J0218+4232 is the sole candidate accelerator positionally coincident with the Peanut region. Its association with UHE γ-rays extending to 0.7 PeV, if confirmed, would provide the first evidence of a millisecond pulsar powering PeV particles. Such a finding challenges prevailing models, which posit that millisecond pulsars cannot sustain acceleration to PeV energies. The detection reveals fundamental gaps in understanding particle acceleration, cosmic-ray transport, and interstellar magnetic field effects, potentially revealing new PeV accelerator (PeVatron) classes.
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Submitted 25 October, 2025; v1 submitted 8 October, 2025;
originally announced October 2025.
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Mapping the Milky Way with Gaia Bp/Rp spectra II: The inner stellar halo traced by a large sample of blue horizontal branch stars
Authors:
Wenbo Wu,
Xianhao Ye,
C. Allende Prieto,
Yuqin Chen,
Xiang-Xiang Xue,
Gang Zhao,
Jingkun Zhao,
David S. Aguado,
Jonay I. González Hernández,
Rafael Rebolo
Abstract:
We selected BHB stars based on synthetic photometry and stellar atmosphere parameters inferred from Gaia Bp/Rp spectra. We generated the synthetic SDSS broad-band $ugr$ and Pristine narrow-band CaHK magnitudes from Gaia Bp/Rp data. A photometric selection of BHB candidates was made in the $(u-g, g-r)$ and $(u-\mathrm{CaHK},g-r)$ color-color spaces. A spectroscopic selection in…
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We selected BHB stars based on synthetic photometry and stellar atmosphere parameters inferred from Gaia Bp/Rp spectra. We generated the synthetic SDSS broad-band $ugr$ and Pristine narrow-band CaHK magnitudes from Gaia Bp/Rp data. A photometric selection of BHB candidates was made in the $(u-g, g-r)$ and $(u-\mathrm{CaHK},g-r)$ color-color spaces. A spectroscopic selection in $T_\mathrm{eff}-\log g$ space was applied to remove stars with high surface gravity. The selection function of BHB stars was obtained by using the Gaia DR3 photometry. A non-parametric method that allows the variation in the vertical flattening $q$ with the Galactic radius, was adopted to explore the density shape of the stellar halo. We present a catalog of 44,552 high latitude ($|b|>20^\circ$) BHB candidates chosen with a well-characterized selection function. The stellar halo traced by these BHB stars is more flattened at smaller radii ($q=0.4$ at $r\sim8$ kpc), and becomes nearly spherical at larger radii ($q=0.8$ at $r\sim25$ kpc). Assuming a variable flattening and excluding several obvious outliers that might be related to the halo substructures or contaminants, we obtain a smooth and consistent relationship between $r$ and $q$, and the density profile is best fit with by a single power law with an index $α=-4.65\pm0.04$.
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Submitted 12 August, 2025;
originally announced August 2025.
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Chemical abundances of seven stars in the GD-1 stream
Authors:
Jing-Kun Zhao,
Guang-Wei Li,
Wako Aoki,
Gang Zhao,
Guo-Chao Yang,
Jian-Rong Shi,
Hai-Ning Li,
Tadafumi Matsuno,
Miho Ishigaki,
Takuma Suda,
Satoshi Honda,
Yu-Qin Chen,
Qian-Fan Xing,
Hong-Liang Yan,
Yong Yang,
Xian-Hao Ye
Abstract:
We present the first detailed chemical abundances for seven GD-1 stream stars from Subaru/HDS spectroscopy. Atmospheric parameters were derived via color calibrations ($T\rm_{eff}$) and iterative spectroscopic analysis. LTE abundances for 14 elements ($α$, odd-Z, iron-peak, n-capture) were measured. Six stars trace the main orbit, one resides in a `blob'. All exhibit tightly clustered metallicitie…
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We present the first detailed chemical abundances for seven GD-1 stream stars from Subaru/HDS spectroscopy. Atmospheric parameters were derived via color calibrations ($T\rm_{eff}$) and iterative spectroscopic analysis. LTE abundances for 14 elements ($α$, odd-Z, iron-peak, n-capture) were measured. Six stars trace the main orbit, one resides in a `blob'. All exhibit tightly clustered metallicities ([Fe/H] = -2.38, {\bf intrinsic dispersion smaller than 0.05 dex, average uncertainty is about 0.13 dex}). While one star shows binary mass transfer signatures, the other six display consistent abundance patterns (dispersions $<$ uncertainties). Their iron-peak elements (Sc, Cr, Mn, Ni) match Milky Way halo stars. In contrast, Y and Sr are systematically lower than halo stars of similar [Fe/H]. Significantly, six stars show consistently enhanced [Eu/Fe] $\sim$ 0.60 ($σ$ = 0.08). A tight Ba-Eu correlation (r = 0.83, p=0.04) exists, with [Ba/Fe] = -0.03 $\pm$ 0.05, indicating a common r-process origin. This extreme chemical homogeneity strongly supports an origin from a single disrupted globular cluster. The lack of light-element anti-correlations may stem from our sample size or the progenitor's low mass.
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Submitted 1 August, 2025;
originally announced August 2025.
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All-sky search for individual Primordial Black Hole bursts with LHAASO
Authors:
Zhen Cao,
F. Aharonian,
Y. X. Bai,
Y. W. Bao,
D. Bastieri,
X. J. Bi,
Y. J. Bi,
W. Bian,
A. V. Bukevich,
C. M. Cai,
W. Y. Cao,
Zhe Cao,
J. Chang,
J. F. Chang,
A. M. Chen,
E. S. Chen,
G. H. Chen,
H. X. Chen,
Liang Chen,
Long Chen,
M. J. Chen,
M. L. Chen,
Q. H. Chen,
S. Chen,
S. H. Chen
, et al. (293 additional authors not shown)
Abstract:
Primordial Black Holes~(PBHs) are hypothetical black holes with a wide range of masses that formed in the early universe. As a result, they may play an important cosmological role and provide a unique probe of the early universe. A PBH with an initial mass of approximately $10^{15}$~g is expected to explode today in a final burst of Hawking radiation. In this work, we conduct an all-sky search for…
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Primordial Black Holes~(PBHs) are hypothetical black holes with a wide range of masses that formed in the early universe. As a result, they may play an important cosmological role and provide a unique probe of the early universe. A PBH with an initial mass of approximately $10^{15}$~g is expected to explode today in a final burst of Hawking radiation. In this work, we conduct an all-sky search for individual PBH burst events using the data collected from March 2021 to July 2024 by the Water Cherenkov Detector Array of the Large High Altitude Air Shower Observatory (LHAASO). Three PBH burst durations, 10~s, 20~s, and 100~s, are searched, with no significant PBH bursts observed. The upper limit on the local PBH burst rate density is set to be as low as 181~pc$^{-3}$~yr$^{-1}$ at 99$\%$ confidence level, representing the most stringent limit achieved to date.
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Submitted 2 November, 2025; v1 submitted 30 May, 2025;
originally announced May 2025.
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First Identification and Precise Spectral Measurement of the Proton Component in the Cosmic-Ray `Knee'
Authors:
The LHAASO Collaboration,
Zhen Cao,
F. Aharonian,
Y. X. Bai,
Y. W. Bao,
D. Bastieri,
X. J. Bi,
Y. J. Bi,
W. Bian,
A. V. Bukevich,
C. M. Cai,
W. Y. Cao,
Zhe Cao,
J. Chang,
J. F. Chang,
A. M. Chen,
E. S. Chen,
G. H. Chen,
H. X. Chen,
Liang Chen,
Long Chen,
M. J. Chen,
M. L. Chen,
Q. H. Chen,
S. Chen
, et al. (292 additional authors not shown)
Abstract:
We report the first high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and syst…
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We report the first high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and systematic accuracy comparable to satellite data at lower energies. The proton spectrum shows significant hardening relative to low-energy extrapolations, culminating at 3 PeV, followed by sharp softening. This distinct spectral structure - closely aligned with the knee in the all-particle spectrum - points to the emergence of a new CR component at PeV energies, likely linked to the dozens of PeVatrons recently discovered by LHAASO, and offers crucial clues to the origin of Galactic cosmic rays.
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Submitted 20 May, 2025;
originally announced May 2025.
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The Accretion Properties and Jet Mechanisms for the Low-Excitation Radio Galaxies
Authors:
Xu-Hong Ye,
Ranieri D. Baldi,
Yong-Yun Chen,
Denis Bastieri,
Jun-Hui Fan
Abstract:
Radio galaxies (RGs) are a subclass of active galactic nuclei, which are suggested to be the parent populations of blazars. According to the accretion-ejection paragram, RGs can be classified into low-excitation or high-excitation radio galaxies (LERGs or HERGs). In this paper, we compiled a distance-limited ($z<0.15$) sample of 431 LERGs (Fanaroff-Riley, or FR, type 0, I, and II RGs) to discuss t…
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Radio galaxies (RGs) are a subclass of active galactic nuclei, which are suggested to be the parent populations of blazars. According to the accretion-ejection paragram, RGs can be classified into low-excitation or high-excitation radio galaxies (LERGs or HERGs). In this paper, we compiled a distance-limited ($z<0.15$) sample of 431 LERGs (Fanaroff-Riley, or FR, type 0, I, and II RGs) to discuss their jet formation mechanism with the ADAF (advection-dominated accretion flow) scenario, and compare their accretion properties with Fermi BL Lacertae objects. We explored different jet mechanisms (Blandford-Znajek [BZ] model and a mixture of the BZ and Blandford-Payne, hybrid, model) within the framework of ADAF-type disc around a Kerr black hole for both LERGs and Fermi BL Lacs. Based on standard assumptions on the accretion-ejection coupling in RGs, the maximum kinetic jet and accretion power for FR 0s, FR Is, FR IIs can be, explained by an ADAF with the pure BZ mechanism or hybrid jet mechanism. In addition, for one third of the FR IIs, to account for their higher kinetic jet power than what is simply expected by the hybrid jet mechanism, the magnetic field could play an important role as in the form of magnetization-driven outflows or stronger magnetic structures, as observed in some BL Lacs with high jet powers. Similarities between BL Lacs and LERGs (e.g., accretion-ejection and clustering properties) suggest that high synchrotron peaked BL Lacs could be the beamed counterparts of FR 0s, and a potential general unification between LERGs and BL Lacs populations is discussed. However, a complete sample of BL Lacs is needed to robustly compare the jet and accretion properties with those of LERGs in the future.
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Submitted 30 March, 2025;
originally announced March 2025.
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Ultra-high-energy $γ$-ray emission associated with the tail of a bow-shock pulsar wind nebula
Authors:
Zhen Cao,
F. Aharonian,
Y. X. Bai,
Y. W. Bao,
D. Bastieri,
X. J. Bi,
Y. J. Bi,
W. Bian,
A. V. Bukevich,
C. M. Cai,
W. Y. Cao,
Zhe Cao,
J. Chang,
J. F. Chang,
A. M. Chen,
E. S. Chen,
H. X. Chen,
Liang Chen,
Long Chen,
M. J. Chen,
M. L. Chen,
Q. H. Chen,
S. Chen,
S. H. Chen,
S. Z. Chen
, et al. (274 additional authors not shown)
Abstract:
In this study, we present a comprehensive analysis of an unidentified point-like ultra-high-energy (UHE) $γ$-ray source, designated as 1LHAASO J1740+0948u, situated in the vicinity of the middle-aged pulsar PSR J1740+1000. The detection significance reached 17.1$σ$ (9.4$σ$) above 25$\,$TeV (100$\,$TeV). The source energy spectrum extended up to 300$\,$TeV, which was well fitted by a log-parabola f…
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In this study, we present a comprehensive analysis of an unidentified point-like ultra-high-energy (UHE) $γ$-ray source, designated as 1LHAASO J1740+0948u, situated in the vicinity of the middle-aged pulsar PSR J1740+1000. The detection significance reached 17.1$σ$ (9.4$σ$) above 25$\,$TeV (100$\,$TeV). The source energy spectrum extended up to 300$\,$TeV, which was well fitted by a log-parabola function with $N0 = (1.93\pm0.23) \times 10^{-16} \rm{TeV^{-1}\,cm^{-2}\,s^{-2}}$, $α= 2.14\pm0.27$, and $β= 1.20\pm0.41$ at E0 = 30$\,$TeV. The associated pulsar, PSR J1740+1000, resides at a high galactic latitude and powers a bow-shock pulsar wind nebula (BSPWN) with an extended X-ray tail. The best-fit position of the gamma-ray source appeared to be shifted by $0.2^{\circ}$ with respect to the pulsar position. As the (i) currently identified pulsar halos do not demonstrate such offsets, and (ii) centroid of the gamma-ray emission is approximately located at the extension of the X-ray tail, we speculate that the UHE $γ$-ray emission may originate from re-accelerated electron/positron pairs that are advected away in the bow-shock tail.
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Submitted 24 February, 2025; v1 submitted 21 February, 2025;
originally announced February 2025.
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The Influence of Sun's and Moon's Shadows on Cosmic-Ray Anisotropy
Authors:
Xuan'ang Ye,
Yi Zhang,
Jiayin He,
Shiping Zhao
Abstract:
Large-scale anisotropy, with amplitudes reaching approximately 0.1% at TeV energies, has been observed by multiple cosmic-ray experiments. The obstruction of cosmic rays by the Sun and Moon creates shadow effects, potentially impacting the observed cosmic ray anisotropy. To evaluate these effects, this study calculates the contributions of the Sun's and Moon's shadows to the overall cosmic-ray ani…
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Large-scale anisotropy, with amplitudes reaching approximately 0.1% at TeV energies, has been observed by multiple cosmic-ray experiments. The obstruction of cosmic rays by the Sun and Moon creates shadow effects, potentially impacting the observed cosmic ray anisotropy. To evaluate these effects, this study calculates the contributions of the Sun's and Moon's shadows to the overall cosmic-ray anisotropy in both local solar and sidereal time. The analysis reveals that in local sidereal time, the total 1D projection amplitude of the anisotropy is around 0.003%, which is significantly smaller than the observed cosmic-ray anisotropy. This indicates that the influence of the Sun's and Moon's shadows on cosmic-ray anisotropy analysis in local sidereal time is negligible. In contrast, in local solar time, the shadow-induced deficit appears in a very small time bin, with a magnitude comparable to that of the cosmic-ray solar anisotropy. This deficit could serve as a benchmark for validating anisotropy measurements in future facilities.
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Submitted 13 February, 2025;
originally announced February 2025.
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Broadband $γ$-ray spectrum of supernova remnant Cassiopeia A
Authors:
Zhen Cao,
F. Aharonian,
Y. X. Bai,
Y. W. Bao,
D. Bastieri,
X. J. Bi,
Y. J. Bi,
W. Bian,
A. V. Bukevich,
C. M. Cai,
W. Y. Cao,
Zhe Cao,
J. Chang,
J. F. Chang,
A. M. Chen,
E. S. Chen,
H. X. Chen,
Liang Chen,
Long Chen,
M. J. Chen,
M. L. Chen,
Q. H. Chen,
S. Chen,
S. H. Chen,
S. Z. Chen
, et al. (293 additional authors not shown)
Abstract:
The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $γ$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telesc…
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The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $γ$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telescopes (IACTs) and its flux near $\sim 1$ TeV is about two times higher. In combination with analyses of more than 16 years of \textit{Fermi}-LAT data covering $0.1 \, \mathrm{GeV} - 1 \, \mathrm{TeV}$, we find that the spectrum above 30 GeV deviates significantly from a single power-law, and is best described by a smoothly broken power-law with a spectral index of $1.90 \pm 0.15_\mathrm{stat}$ ($3.41 \pm 0.19_\mathrm{stat}$) below (above) a break energy of $0.63 \pm 0.21_\mathrm{stat} \, \mathrm{TeV}$. Given differences in the angular resolution of LHAASO-WCDA and IACTs, TeV $γ$-ray emission detected with LHAASO may have a significant contribution from regions surrounding the SNR illuminated by particles accelerated earlier, which, however, are treated as background by IACTs. Detailed modelling can be used to constrain acceleration processes of TeV particles in the early stage of SNR evolution.
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Submitted 7 February, 2025;
originally announced February 2025.
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Mapping the Milky Way with Gaia Bp/Rp spectra I: Systematic flux corrections and atmospheric parameters for 68 million stars
Authors:
Xianhao Ye,
Wenbo Wu,
Carlos Allende Prieto,
David S. Aguado,
Jingkun Zhao,
Jonay I. González Hernández,
Rafael Rebolo,
Gang Zhao,
Zhuohan Li,
Carlos del Burgo,
Yuqin Chen
Abstract:
Gaia Bp/Rp spectra for over two hundred million stars have great potential for mapping metallicity across the Milky Way. We aim to construct an alternative catalog of atmospheric parameters from Gaia Bp/Rp spectra by fitting them with synthetic spectra based on model atmospheres, and provide corrections to the Bp/Rp fluxes according to stellar colors, magnitudes, and extinction. We use GaiaXPy to…
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Gaia Bp/Rp spectra for over two hundred million stars have great potential for mapping metallicity across the Milky Way. We aim to construct an alternative catalog of atmospheric parameters from Gaia Bp/Rp spectra by fitting them with synthetic spectra based on model atmospheres, and provide corrections to the Bp/Rp fluxes according to stellar colors, magnitudes, and extinction. We use GaiaXPy to obtain calibrated spectra and apply FERRE to match the corrected Bp/Rp spectra with models and infer atmospheric parameters. We train a neural network using stars in APOGEE to predict flux corrections as a function of wavelength for each target. Based on the comparison with APOGEE parameters, we conclude that our estimated parameters have systematic errors and uncertainties in $T_{\mathrm{eff}}$, $\log g$, and [M/H] about $-38 \pm 167$ K, $0.05 \pm 0.40$ dex, and $-0.12 \pm 0.19$ dex, respectively, for stars in the range $4000 \le T_{\mathrm{eff}} \le 7000$ K. The corrected Bp/Rp spectra show better agreement with both models and Hubble Space Telescope CALSPEC data. Our correction increases the precision of the relative spectrophotometry of the Bp/Rp data from $3.2\% - 3.7\%$ to $1.2\% - 2.4\%$. Finally, we have built a catalog of atmospheric parameters for stars within $4000 \le T_{\mathrm{eff}} \le 7000$ K, comprising $68,394,431$ sources, along with a subset of $124,188$ stars with $\mathrm{[M/H]} \le -2.5$. Our results confirm that the Gaia Bp/Rp flux calibrated spectra show systematic patterns as a function of wavelength that are tightly related to colors, magnitudes, and extinction. Our optimization algorithm can give us accurate atmospheric parameters of stars with a clear and direct link to models of stellar atmospheres, and can be used to efficiently search for extremely metal-poor stars.
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Submitted 27 March, 2025; v1 submitted 28 November, 2024;
originally announced November 2024.
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The Pristine survey: XXV. The very metal-poor Galaxy: Chemodynamics through the follow-up of the Pristine-Gaia synthetic catalogue
Authors:
Akshara Viswanathan,
Zhen Yuan,
Anke Ardern-Arentsen,
Else Starkenburg,
Nicolas F. Martin,
Kris Youakim,
Rodrigo A. Ibata,
Federico Sestito,
Tadafumi Matsuno,
Carlos Allende Prieto,
Freya Barwell,
Manuel Bayer,
Amandine Doliva-Dolinsky,
Emma Fernandez-Alvar,
Pablo M. Galan-de Anta,
Kiran Jhass,
Nicolas Longeard,
Jose Maria Arroyo-Polonio,
Pol Massana,
Martin Montelius,
Samuel Rusterucci,
Judith Santos,
Guillaume F. Thomas,
Sara Vitali,
Wenbo Wu
, et al. (5 additional authors not shown)
Abstract:
The Pristine-\textit{Gaia} synthetic catalogue provides reliable photometric metallicities for $\sim$30 million FGK stars using the Pristine survey model and Gaia XP spectra. We perform the first low-to-medium-resolution spectroscopic follow-up of bright (G<15) and distant (up to 35 kpc) very and extremely metal-poor (V/EMP, [Fe/H]<-2.5) red giant branch stars from this. We use Isaac Newton Telesc…
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The Pristine-\textit{Gaia} synthetic catalogue provides reliable photometric metallicities for $\sim$30 million FGK stars using the Pristine survey model and Gaia XP spectra. We perform the first low-to-medium-resolution spectroscopic follow-up of bright (G<15) and distant (up to 35 kpc) very and extremely metal-poor (V/EMP, [Fe/H]<-2.5) red giant branch stars from this. We use Isaac Newton Telescope/Intermediate Dispersion Spectrograph (INT/IDS) observations centred around the calcium triplet region ideal for V/EMP stars. We find that 76\% of our stars indeed have [Fe/H]<-2.5 with these inferred spectroscopic metallicities and only 3\% are outliers with [Fe/H] > -2.0. We report a success rate of 77\% and 38\% in finding stars with [Fe/H]<-2.5 and -3.0 respectively. This will allow for 10,000-20,000 homogeneously analysed EMP stars using the WEAVE survey follow-up of Pristine EMP candidates. We associate 20\%, 46\%, and 34\% of the stars to be confined to the disc plane, or to have inner and outer halo orbits, respectively. We also associate these V/EMP stars to known accretion events such as Gaia-Enceladus-Sausage (GES), LMS-1/Wukong, Thamnos, Helmi streams, Sagittarius, Sequoia, etc. For the stars that orbit close to the disc plane, we find that the prograde region with low vertical action is overdense with a significance of 4$σ$ as compared to its retrograde counterpart. We also find three new (brightest) members of the most metal-poor stellar stream, C-19, one of which is 50$^\circ$ away from the main body of the stream. Our measured mean metallicity, velocity dispersion, and stream width are consistent with the literature, but our results favour a higher distance ($\sim$21.5 kpc) for the stream. We publish a catalogue (and 1D spectra) of 215 V/EMP stars from this spectroscopic follow-up and showcase the power of chemokinematic analysis of V/EMP end.
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Submitted 15 April, 2025; v1 submitted 21 May, 2024;
originally announced May 2024.
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Primordial Black Hole Formation in a Dust Bouncing Model
Authors:
E. J. Barroso,
L. F. Demétrio,
S. D. P. Vitenti,
Xuan Ye
Abstract:
Linear scalar cosmological perturbations have increasing spectra in the contracting phase of bouncing models. We study the conditions for which these perturbations may collapse into primordial black holes and the hypothesis that these objects constitute a fraction of dark matter. We compute the critical density contrast that describes the collapse of matter perturbations in the flat-dust bounce mo…
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Linear scalar cosmological perturbations have increasing spectra in the contracting phase of bouncing models. We study the conditions for which these perturbations may collapse into primordial black holes and the hypothesis that these objects constitute a fraction of dark matter. We compute the critical density contrast that describes the collapse of matter perturbations in the flat-dust bounce model with a parametric solution, obtained from the Lemaitre-Tolman-Bondi metric that represents the spherical collapse. We discuss the inability of the Newtonian gauge to describe perturbations in contracting models as the perturbative hypothesis does not hold in such cases. We carry the calculations for a different Gauge choice and compute the perturbations power spectra numerically. Finally, assuming a Gaussian distribution, we compute the primordial black hole abundance with the Press-Schechter formalism and compare it with observational constraints. From our analysis, we conclude that the primordial black hole formation in a dust-dominated contracting phase does not lead to a significant mass fraction of primordial black holes in dark matter today.
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Submitted 6 December, 2024; v1 submitted 30 April, 2024;
originally announced May 2024.
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The Spectacular Tidal Tails of Globular Cluster M3 (NGC 5272)
Authors:
Yong Yang,
Jing-Kun Zhao,
Xin-Zhe Tang,
Xian-Hao Ye,
Gang Zhao
Abstract:
We provide a detailed analysis on tidal tails of the globular cluster M3 (NGC 5272). We first discover clear extra-tidal structures with slight S-shape near the cluster. This inspires us to examine the existence of its long tidal tails. We highlight potential stream stars using proper motions (PMs) of a model stream combined with the cluster's locus in a color-magnitude diagram (CMD). A 35 deg lon…
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We provide a detailed analysis on tidal tails of the globular cluster M3 (NGC 5272). We first discover clear extra-tidal structures with slight S-shape near the cluster. This inspires us to examine the existence of its long tidal tails. We highlight potential stream stars using proper motions (PMs) of a model stream combined with the cluster's locus in a color-magnitude diagram (CMD). A 35 deg long leading tail and a 21 deg long trailing tail are successfully detected at the same time. Their corresponding overdensities can be recognized in CMD and PM space after subtracting background. We estimate stream width, star number density and surface brightness for both tails, as well as the distance variation along the entire stream. We then verify the connection of M3 and the Svöl stream. Finally, we tabulate 11 member stars belonging to the M3 tidal stream with available spectroscopic observations.
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Submitted 15 June, 2023;
originally announced June 2023.
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The beaming effect for Fermi-LAT-detected FR-I radio galaxies
Authors:
Xu-Hong Ye,
Xiang-Tao Zeng,
Dan-Yi Huang,
Zhuang Zhang,
Zhi-Yuan Pei,
Jun-Hui Fan
Abstract:
Our knowledge of Giga-electron volt (GeV) radio galaxies has been revolutionized by the Fermi-LAT Telescope, which provides an excellent opportunity to study the physical properties of GeV radio galaxies. According to the radio power and morphology, radio galaxies can be separated into Fanaroff-Riley Type I radio galaxies (FR-Is) and Type II radio galaxies (FR-IIs). In this paper, we consider the…
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Our knowledge of Giga-electron volt (GeV) radio galaxies has been revolutionized by the Fermi-LAT Telescope, which provides an excellent opportunity to study the physical properties of GeV radio galaxies. According to the radio power and morphology, radio galaxies can be separated into Fanaroff-Riley Type I radio galaxies (FR-Is) and Type II radio galaxies (FR-IIs). In this paper, we consider the unification of FR-Is and BL Lacertae objects (BL Lacs), and assume FR-Is to be a standard candle to discuss the beaming effect for Fermi-LAT-detected FR-Is. Our main conclusions are as follows: (1) The estimated Doppler factors for 30 Fermi-LAT-detected FR-Is are in a range of $δ_{\rm{I}}=0.88-7.49$. The average Doppler factor ($<δ_{\rm{I}}>=2.56\pm0.30$) of the 30 FR-Is is smaller than that ($<δ_{\rm{BL}}>=10.28\pm2.03$) of the 126 Fermi-LAT-detected BL Lacs, supporting the unification model that FR-Is are regarded as the misaligned BL Lacs with smaller Doppler factors; (2) We propose that different regions of FR-Is in the plot of the $γ$-ray luminosity against the photon spectral index $(\log L_γ-α_{\rm{ph}})$ may indicate the different beaming effects; (3) The average Doppler factor of the 6 TeV FR-Is is similar to that of the 24 non-TeV FR-Is, which implies that the difference between the TeV and GeV emissions is not driven by the beaming effect in the Fermi-LAT-detected FR-I samples.
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Submitted 17 May, 2023;
originally announced May 2023.
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Detection of multiple phase space overdensities of GSE stars by orbit integration
Authors:
WenboWu,
GangZhao,
JiangChang,
Xiang-XiangXue,
YuqinChen,
ChengdongLi,
Xianhao Ye,
Chengqun Yang
Abstract:
In N-body simulations, nearly radial mergers can form shell-like overdensities in the sky position and phase space ($r-v_r$) due to the combination of dynamical friction and tidal stripping. The merger event of Gaia-Sausage-Enceladus has provided a unique opportunity to study the shells in the phase space. To search for them, we integrate the orbits of 5949 GSE-related halo K giants from the LAMOS…
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In N-body simulations, nearly radial mergers can form shell-like overdensities in the sky position and phase space ($r-v_r$) due to the combination of dynamical friction and tidal stripping. The merger event of Gaia-Sausage-Enceladus has provided a unique opportunity to study the shells in the phase space. To search for them, we integrate the orbits of 5949 GSE-related halo K giants from the LAMOST survey and record their positions at all time intervals in $r-v_r$ diagram. After the subtraction of a smoothed background, we find six significant and complete thin chevron-like overdensities. The apocenters $r_\mathrm{apo}$ of stars in the six chevrons are around 6.75, 12.75, 18.75, 25.25, 27.25, and 30.25 kpc. These chevrons reveal the multiple pile-ups of GSE stars at different apocenters. The application of a different Milky Way mass $M_\mathrm{vir}$ will change the opening angles of these chevrons, while leave their apocenters almost unchanged. By comparing with a recent study of the phase space overdensities of local halo stars from Gaia RVS survey, our results are more inclined to a medium $M_\mathrm{vir}$ of $10^{12}\,M_\odot$. The application of a non-axisymmetric Galactic potential with a steadily rotating bar has a blurring effect on the appearance of these chevron-like overdensities, especially for the chevrons with $r_\mathrm{apo} > 20$ kpc.
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Submitted 11 May, 2023;
originally announced May 2023.
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A Dwarf Galaxy Debris Stream Associated with Palomar 1 and the Anticenter Stream
Authors:
Yong Yang,
Jing-Kun Zhao,
Xian-Hao Ye,
Gang Zhao,
Ke-Feng Tan
Abstract:
We report the discovery of a new stream (dubbed as Yangtze) detected in $Gaia$ Data Release 3. The stream is at a heliocentric distance of $\sim$ 9.12 kpc and spans nearly 27$°$ by 1.9$°$ on sky. The colour-magnitude diagram of Yangtze indicates a stellar population of Age $\sim$ 11 Gyr and [M/H] $\sim$ -0.7 dex. It has a number density of about 5.5 stars degree$^{-2}$ along with a surface brightn…
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We report the discovery of a new stream (dubbed as Yangtze) detected in $Gaia$ Data Release 3. The stream is at a heliocentric distance of $\sim$ 9.12 kpc and spans nearly 27$°$ by 1.9$°$ on sky. The colour-magnitude diagram of Yangtze indicates a stellar population of Age $\sim$ 11 Gyr and [M/H] $\sim$ -0.7 dex. It has a number density of about 5.5 stars degree$^{-2}$ along with a surface brightness of $Σ_G \simeq$ 34.9 mag arcsec$^{-2}$. The dynamics and metallicity estimate suggest that Yangtze may be closely related to Palomar 1 and the Anticenter stream.
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Submitted 10 February, 2023;
originally announced February 2023.
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Existence of Tidal Tails for the Globular Cluster NGC 5824
Authors:
Yong Yang,
Jing-Kun Zhao,
Miho N. Ishigaki,
Masashi Chiba,
Cheng-Qun Yang,
Xiang-Xiang Xue,
Xian-Hao Ye,
Gang Zhao
Abstract:
Context. Several dynamically cold streams have been associated with certain globular clusters (GCs) based on orbital energies and angular momenta. Some of these streams are surprisingly far apart from their progenitors and one such pair is Triangulum and NGC 5824. Triangulum can be considered as a piece of NGC 5824 leading tail since the cluster's future orbit matches with the stream's track well.…
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Context. Several dynamically cold streams have been associated with certain globular clusters (GCs) based on orbital energies and angular momenta. Some of these streams are surprisingly far apart from their progenitors and one such pair is Triangulum and NGC 5824. Triangulum can be considered as a piece of NGC 5824 leading tail since the cluster's future orbit matches with the stream's track well. The existence of the leading tail for NGC 5824 is the motivation behind the search for its trailing tail. Aims. Our goal is to confirm the connection between Triangulum and NGC 5824 and seek the trailing tail of the cluster. Methods. The selection of member stars of Triangulum is made through various cuts in metallicity, proper motions (PMs), radial velocity and color-magnitude diagram (CMD). The selected members are compared in phase space to a mock stream which models the disruption of NGC 5824. We then try to detect the trailing tail of the cluster based on a modified matched-filter technique. Stars are assigned weights using their color differences from the cluster's locus in CMD. These weights are further scaled based on stars' departures from expected PMs of the model stream. Results. A total of 26 member stars for Triangulum are obtained and 16 of them are newly identified. These members are consistent with the mock stream in the phase space and their metalicity and position on the CMD are in good agreements with NGC 5824. By applying the matched-filter, a tenuous trailing tail of the cluster is detected, spanning $\sim$ 50$^\circ$ long on sky. The signature matches with the mock stream's trajectory well. Conclusions. Our results support that Triangulum stream acts as a part of the leading tail for NGC 5824. On the trailing side, we have detected a 50$^\circ$ tail extended from the cluster. The existence of both leading and trailing tails for the GC NGC 5824 is verified.
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Submitted 10 August, 2022;
originally announced August 2022.
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A New Cold Stream near the Southern Galactic Pole
Authors:
Yong Yang,
Jing-Kun Zhao,
Xiang-Xiang Xue,
Xian-Hao Ye,
Gang Zhao
Abstract:
We report the discovery of a cold stream near the southern Galactic pole (dubbed as SGP-S) detected in $Gaia$ Early Data Release 3. The stream is at a heliocentric distance of $\sim$ 9.5 kpc and spans nearly 58$^\circ$ by 0.6$^\circ$ on sky. The colour-magnitude diagram of SGP-S indicates an old and metal-poor (age $\sim$ 12 Gyr, [M/H] $\sim$ -2.0 dex) stellar population. The stream's surface brig…
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We report the discovery of a cold stream near the southern Galactic pole (dubbed as SGP-S) detected in $Gaia$ Early Data Release 3. The stream is at a heliocentric distance of $\sim$ 9.5 kpc and spans nearly 58$^\circ$ by 0.6$^\circ$ on sky. The colour-magnitude diagram of SGP-S indicates an old and metal-poor (age $\sim$ 12 Gyr, [M/H] $\sim$ -2.0 dex) stellar population. The stream's surface brightness reaches an exceedingly low level of $Σ_G \simeq$ 36.2 mag arcsec$^{-2}$. Neither extant globular clusters nor other known streams are associated with SGP-S.
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Submitted 10 August, 2022;
originally announced August 2022.
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Revisit of open clusters UPK 39, UPK 41 and PHOC 39 : a new binary open cluster found
Authors:
Xianhao Ye,
Jingkun Zhao,
Terry D. Oswalt,
Yong Yang,
Gang Zhao
Abstract:
We investigate the three open clusters near Aquila Rift cloud, named as UPK 39 (\texttt{c1} hereafter), UPK 41 (\texttt{c2} hereafter) in Sim et al. (2019) and PHOC 39 (\texttt{c3} hereafter) in Hunt \& Reffert (2021), respectively. Using photometric passpands, reddening, and extinction from Gaia DR3, we construct the color-absolute-magnitude diagram (CAMD). Using isochrone fits their ages are est…
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We investigate the three open clusters near Aquila Rift cloud, named as UPK 39 (\texttt{c1} hereafter), UPK 41 (\texttt{c2} hereafter) in Sim et al. (2019) and PHOC 39 (\texttt{c3} hereafter) in Hunt \& Reffert (2021), respectively. Using photometric passpands, reddening, and extinction from Gaia DR3, we construct the color-absolute-magnitude diagram (CAMD). Using isochrone fits their ages are estimated as $6.3\pm0.9$, $8.1\pm1.4$ and $21.8\pm2.2$ Myr, respectively. Their proper motions and radial velocities, estimated using data from Gaia and LAMOST are very similar. From their orbits, relative distances among them at different times, kinematics, ages, and metallicities, we conclude that \texttt{c1} and \texttt{c2} are primordial binary open cluster, which are likely to have been formed at the same time, and \texttt{c3} may capture \texttt{c1}, \texttt{c2} in the future.
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Submitted 28 July, 2022;
originally announced July 2022.
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Neutral Stellar Winds Toward the High-Mass Star-Forming Region G176.51+00.20
Authors:
Li Yingjie,
Xu Ye,
Xu Jin-Long,
Liu Dejian,
Li Jingjing,
Lin Zehao,
Jiang Peng,
Bian Shuaibo,
Hao Chaojie,
Chen Xiuhui
Abstract:
We observed the high-mass star-forming region G176.51+00.20 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) with the 19-beam tracking observational mode. This is a pilot work of searching for neutral stellar winds traced by atomic hydrogen (i.e., HI winds) using the high sensitivity HI line toward high-mass star-forming regions where bipolar molecular outflows have been dete…
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We observed the high-mass star-forming region G176.51+00.20 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) with the 19-beam tracking observational mode. This is a pilot work of searching for neutral stellar winds traced by atomic hydrogen (i.e., HI winds) using the high sensitivity HI line toward high-mass star-forming regions where bipolar molecular outflows have been detected with high sensitivity by Liu et al. HI wind was detected in this work only in Beam 1. We find here that, similar to low-mass star formation, no matter how large the inclination is, the HI wind is likely sufficiently strong to drive a molecular outflow. We also find that the abundance of HI in the HI wind is consistent with that of the HI narrow-line self-absorption (HINSA) in the same beam (i.e., Beam 1). This implies that there is probably an internal relationship between HI winds and HINSA. This result also reinforces the assertion that HI winds and detected molecular outflows are associated with each other.
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Submitted 13 July, 2022;
originally announced July 2022.
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HI Narrow-Line Self-Absorptions Toward the High-Mass Star-Forming Region G176.51+00.20
Authors:
Li Yingjie,
Xu Ye,
Xu Jin-Long,
Liu Dejian,
Li Jingjing,
Lin Zehao,
Jiang Peng,
Bian Shuaibo,
Hao Chaojie,
Chen Xiuhui
Abstract:
Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) 19-beam tracking observational mode, high sensitivity and high-velocity resolution HI spectral lines have been observed toward the high-mass star-forming region G176.51+00.20. This is a pilot study of searching for HI narrow-line self-absorption (HINSA) toward high-mass star-forming regions where bipolar molecular outflows have…
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Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) 19-beam tracking observational mode, high sensitivity and high-velocity resolution HI spectral lines have been observed toward the high-mass star-forming region G176.51+00.20. This is a pilot study of searching for HI narrow-line self-absorption (HINSA) toward high-mass star-forming regions where bipolar molecular outflows have been detected. This work is confined to the central seven beams of FAST. Two HINSA components are detected in all seven beams, which correspond to a strong CO emission region (SCER; with a velocity of $\sim$ $-$18 km s$^{-1}$) and a weak CO emission region (WCER; with a velocity of $\sim$ $-$3 km s$^{-1}$). The SCER detected in Beam 3 is probably more suitably classified as a WCER. In the SCER, the HINSA is probably associated with the molecular material traced by the CO. The fractional abundance of HINSA ranges from $\sim 1.1 \times 10^{-3}$ to $\sim 2.6 \times 10^{-2}$. Moreover, the abundance of HINSA in Beam 1 is lower than that in the surrounding beams (i.e., Beams 2 and 4--7). This possible ring could be caused by ionization of HI or relatively rapid conversion from HI to H$_2$ in the higher-density inner region. In the WCER (including Beam 3 in the SCER), the HINSA is probably not associated with CO clouds, but with CO-dark or CO-faint gas.
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Submitted 13 July, 2022;
originally announced July 2022.
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Revisit NGC 5466 Tidal Stream with $Gaia$, SDSS/SEGUE and LAMOST
Authors:
Yong Yang,
Jing-Kun Zhao,
Miho N. Ishigaki,
Jian-Zhao Zhou,
Cheng-Qun Yang,
Xiang-Xiang Xue,
Xian-Hao Ye,
Gang Zhao
Abstract:
By mining the data from $Gaia$ EDR3, SDSS/SEGUE DR16 and LAMOST DR8, 11 member stars of the NGC 5466 tidal stream are detected and 7 of them are newly identified. To reject contaminators, a variety of cuts are applied in sky position, color-magnitude diagram, metallicity, proper motion and radial velocity. We compare our data to a mock stream generated by modeling the cluster's disruption under a…
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By mining the data from $Gaia$ EDR3, SDSS/SEGUE DR16 and LAMOST DR8, 11 member stars of the NGC 5466 tidal stream are detected and 7 of them are newly identified. To reject contaminators, a variety of cuts are applied in sky position, color-magnitude diagram, metallicity, proper motion and radial velocity. We compare our data to a mock stream generated by modeling the cluster's disruption under a smooth Galactic potential plus the Large Magellanic Cloud (LMC). The concordant trends in phase-space between the model and observations imply that the stream might have been perturbed by LMC. The two most distant stars among 11 detected members trace the stream's length to $60^\circ$ of sky, supporting and extending the previous length of $45^\circ$. Given that NGC 5466 is so distant and potentially has a longer tail than previously thought, we expect that NGC 5466 tidal stream could be a useful tool in constraining the Milky Way gravitational field.
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Submitted 24 March, 2022;
originally announced March 2022.
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Unification of BL Lac objects, FR I and FR II(G) radio galaxies and Doppler factor Estimation for BL Lac Objects
Authors:
Xu-Hong Ye,
Jun-Hui Fan
Abstract:
In this work, we collected a sample of BL Lacs, FR I and FR II(G) radio galaxies with available core and extended emissions from published works to discuss the unified schemes and estimate the Doppler factor for BL Lacs. Wilcoxon rank-sum test and Kolmogorov-Smirnov test both suggest that the probabilities for the distribution of the extended luminosity of BL Lacs and that of FR I and FR II(G) rad…
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In this work, we collected a sample of BL Lacs, FR I and FR II(G) radio galaxies with available core and extended emissions from published works to discuss the unified schemes and estimate the Doppler factor for BL Lacs. Wilcoxon rank-sum test and Kolmogorov-Smirnov test both suggest that the probabilities for the distribution of the extended luminosity of BL Lacs and that of FR I and FR II(G) radio galaxies to be from the same parent distribution are $p_{\rm{WRS}}=0.779$ and $p_{\rm{K-S}}=0.326$, suggesting they are unified. Based on this unified schemes, we propose to estimate the Doppler factors for BL Lacs. Comparing the Doppler factor estimated by the fitting/regression method with those for the common sources in the literatures, we found a good linear correlation for common sources.
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Submitted 17 November, 2021;
originally announced November 2021.
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A study of Intrinsic $γ$-ray Emission for {\it Fermi}/LAT-detected BL Lacs
Authors:
X. H. Ye,
X. T. Zeng,
W. X. Yang,
H. S. Huang,
Y. H. Xuan,
J. W. Huang,
Z. Zhang,
Z. Y. Pei,
J. H. Yang,
J. H. Fan
Abstract:
BL Lacs are one subclass of blazars with highly energetic $γ$-ray emission, which is strongly boosted by a relativistic beaming effect. The latest catalogue of the 10 years of {\it Fermi}/LAT data Abdollahi et al. (2020) and the $γ$-ray Doppler factors in Pei et al. (2020) provide us with a large BL Lac sample to study their jet emission morphologies and intrinsic properties. In this paper, we col…
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BL Lacs are one subclass of blazars with highly energetic $γ$-ray emission, which is strongly boosted by a relativistic beaming effect. The latest catalogue of the 10 years of {\it Fermi}/LAT data Abdollahi et al. (2020) and the $γ$-ray Doppler factors in Pei et al. (2020) provide us with a large BL Lac sample to study their jet emission morphologies and intrinsic properties. In this paper, we collected a sample of 294 {\it Fermi} BL Lacs and probed the correlations between the $γ$-ray emissions and luminosity distances. Our analyses give following conclusions: (1) the observed $γ$-ray emissions are really boosted by the $γ$-ray Doppler factor, and the intrinsic $γ$-ray emissions are closely correlated with luminosity distances. (2) the morphology of jet emissions for HBLs may be continuous, while that for IBLs may be the case of a moving sphere in the $γ$-ray bands.
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Submitted 17 November, 2021;
originally announced November 2021.
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Extended Tidal Tails of IC 4756 detected by {\it Gaia} EDR3
Authors:
Xianhao Ye,
Jinkun Zhao,
Jiajun Zhang,
Yong Yang,
Gang Zhao
Abstract:
We report the discovery of emerged tidal tails around open cluster IC 4756 ($\sim$ 1 Gyr) based on 644 members identified from {\it Gaia} EDR3. Three-dimensional spatial positions, two-dimensional tangential velocities $\left( x, y, z, κ\cdot μ_α^{*}/\varpi, κ\cdot μ_δ/\varpi \right)$ are utilized to determine the co-moving member candidates of IC 4756. Using a Bayesian method, we correct the dist…
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We report the discovery of emerged tidal tails around open cluster IC 4756 ($\sim$ 1 Gyr) based on 644 members identified from {\it Gaia} EDR3. Three-dimensional spatial positions, two-dimensional tangential velocities $\left( x, y, z, κ\cdot μ_α^{*}/\varpi, κ\cdot μ_δ/\varpi \right)$ are utilized to determine the co-moving member candidates of IC 4756. Using a Bayesian method, we correct the distance for each cluster member. Two tidal tails extend up to 180 pc and display a S-shape in $X^{\prime}Y^{\prime}$ space (Cartesian coordinates focused on cluster center). A clean sequence of our members in Color-Absolute-Magnitude Diagram (CAMD) indicates the coeval population and matches perfectly with the PARSEC isochrone with age from Bossini et al. (2019). Mass segregation is detected in this cluster as well. Finally, we derive the tidal radius and core radius of IC 4756 about $12.13$ pc and $4.33 \pm 0.75$ pc, respectively.
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Submitted 15 October, 2021;
originally announced October 2021.
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Tracing the Origin of Moving Groups. III. Detecting Moving Groups in The LAMOST DR7
Authors:
Yong Yang,
Jingkun Zhao,
Jiajun Zhang,
Xianhao Ye,
Gang Zhao
Abstract:
We revisit the moving groups (MGs) in the solar neighborhood with a sample of 91969 nearby stars constructed from LAMOST DR7. Using the wavelet technique and Monte Carlo simulations, five MGs together with a new candidate located at $V \simeq$ -130 km s$^{-1}$ are detected simultaneously in $V-\sqrt{U^2+2V^2}$ space. Taking into account the other known MGs, we conclude that MGs in the Galactic dis…
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We revisit the moving groups (MGs) in the solar neighborhood with a sample of 91969 nearby stars constructed from LAMOST DR7. Using the wavelet technique and Monte Carlo simulations, five MGs together with a new candidate located at $V \simeq$ -130 km s$^{-1}$ are detected simultaneously in $V-\sqrt{U^2+2V^2}$ space. Taking into account the other known MGs, we conclude that MGs in the Galactic disk are spaced by approximately 15 $\sim$ 25 km s$^{-1}$ along $V$ velocity. The origin of detected MGs is analysed through the distributions of [Fe/H]$-$[Mg/Fe] and ages. Our results support attributing the origin to the continuous resonant mechanisms probably induced by the bar or spiral arms of the Milky Way.
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Submitted 15 October, 2021;
originally announced October 2021.
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Nearly 30,000 late-type main-sequence stars with stellar age from LAMOST DR5
Authors:
Jiajun Zhang,
Jingkun Zhao,
Terry D. Oswalt,
Xilong Liang,
Xianhao Ye,
Gang Zhao
Abstract:
We construct a sample of nearly 30,000 main-sequence stars with 4500K $<T\rm_{eff}<$ 5000K and stellar ages estimated by the chromospheric activity$-$age relation. This sample is used to determine the age distribution in the $R-Z$ plane of the Galaxy, where $R$ is the projected Galactocentric distance in the disk midplane and $Z$ is the height above the disk midplane. As $|Z|$ increases, the perce…
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We construct a sample of nearly 30,000 main-sequence stars with 4500K $<T\rm_{eff}<$ 5000K and stellar ages estimated by the chromospheric activity$-$age relation. This sample is used to determine the age distribution in the $R-Z$ plane of the Galaxy, where $R$ is the projected Galactocentric distance in the disk midplane and $Z$ is the height above the disk midplane. As $|Z|$ increases, the percentage of old stars becomes larger. It is known that scale-height of Galactic disk increases as $R$ increases, which is called flare. A mild flare from $R$ $\sim$ 8.0 to 9.0 kpc in stellar age distribution is found. We also find that the velocity dispersion increases with age as confirmed by previous studies. Finally we present spiral-shaped structures in $Z-\upsilon_{Z}$ phase space in three stellar age bins. The spiral is clearly seen in the age bin of [0, 1] Gyr, which suggests that a vertical perturbation to the disk probably took place within the last $\sim$ 1.0 Gyr.
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Submitted 24 November, 2020;
originally announced November 2020.
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Estimating Atmospheric Parameters of DA White Dwarf Stars with Deep Learning
Authors:
Yong Yang,
Jingkun Zhao,
Jiajun Zhang,
Xianhao Ye,
Gang Zhao
Abstract:
The determination of atmospheric parameters of white dwarf stars (WDs) is crucial for researches on them. Traditional methodology is to fit the model spectra to observed absorption lines and report the parameters with the lowest $χ^2$ error, which strongly relies on theoretical models that are not always publicly accessible. In this work, we construct a deep learning network to model-independently…
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The determination of atmospheric parameters of white dwarf stars (WDs) is crucial for researches on them. Traditional methodology is to fit the model spectra to observed absorption lines and report the parameters with the lowest $χ^2$ error, which strongly relies on theoretical models that are not always publicly accessible. In this work, we construct a deep learning network to model-independently estimate Teff and log g of DA stars (DAs), corresponding to WDs with hydrogen dominated atmospheres. The network is directly trained and tested on the normalized flux pixels of full optical wavelength range of DAs spectroscopically confirmed in the Sloan Digital Sky Survey (SDSS). Experiments in test part yield that the root mean square error (RMSE) for Teff and log g approaches to 900 K and 0.1 dex, respectively. This technique is applicable for those DAs with Teff from 5000 K to 40000 K and log g from 7.0 dex to 9.0 dex. Furthermore, the applicability of this method is verified for the spectra with degraded resolution $\sim 200$. So it is also practical for the analysis of DAs that will be detected by the Chinese Space Station Telescope (CSST).
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Submitted 1 November, 2020; v1 submitted 2 October, 2020;
originally announced October 2020.
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Two Portions of Sagittarius Stream in the LAMOST Complete Spectroscopic Survey of Pointing Area at Southern Galactic Cap
Authors:
J. K. Zhao,
X. H. Ye,
H. Wu,
M. Yang,
Terry D. Oswalt,
X. X. Xue,
Y. Q. Chen,
J. J. Zhang,
G. Zhao
Abstract:
We constructed a sample of 13,798 stars with $T\rm_{eff}$, log $g$, [Fe/H], radial velocity, proper motions and parallaxes from LAMOST DR5 and Gaia DR2 in the LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) at the Southern Galactic Cap consisting of areas A and B. Using the distributions in both proper motions and radial velocity, we detected very significant overdensities in the…
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We constructed a sample of 13,798 stars with $T\rm_{eff}$, log $g$, [Fe/H], radial velocity, proper motions and parallaxes from LAMOST DR5 and Gaia DR2 in the LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) at the Southern Galactic Cap consisting of areas A and B. Using the distributions in both proper motions and radial velocity, we detected very significant overdensities in these two areas. These substructures most likely are portions of Sagittarius (Sgr) stream. With the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, 220 candidates stream members were identified. Based upon distance to the Sun and published models, 106 of these stars are likely to be the members of the Sgr stream. The abundance pattern of these members using [$α$/Fe] from Xiang et al. were found to be similar to Galactic field stars with [Fe/H] $<$ -1.5 and deficient to Milky Way populations at similar metallicities with [Fe/H] $>$ -1.0. No vertical and only small radial gradients in metallicity along the orbit of Sgr stream were found in our Sgr stream candidates.
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Submitted 24 September, 2020;
originally announced September 2020.
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A new moving group in the Local Arm
Authors:
Xilong Liang,
Jingkun Zhao,
Yuqin Chen,
Xiangsong Fang,
Xianhao Ye,
Jiajun Zhang,
Xiaoming Kong,
Gang Zhao
Abstract:
We present a new moving group clustered in kinematics, spatial position and elemental abundances. Its spatial position is around the center of the Local Arm of the Milky Way. A convergent point method was taken to select candidate member stars.\textbf{ Among 206 candidate member stars, 74 are pre-main-sequence stars and some of them have stellar disks.} We presume those pre-main sequence stars bel…
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We present a new moving group clustered in kinematics, spatial position and elemental abundances. Its spatial position is around the center of the Local Arm of the Milky Way. A convergent point method was taken to select candidate member stars.\textbf{ Among 206 candidate member stars, 74 are pre-main-sequence stars and some of them have stellar disks.} We presume those pre-main sequence stars belong to Orion nebula. We suggest this moving group is caused by density wave of the Local Arm passing by.
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Submitted 11 March, 2020;
originally announced March 2020.
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Stellar chromospheric activity and age relation from open clusters in the LAMOST Survey
Authors:
Jiajun Zhang,
Jingkun Zhao,
Terry D. Oswalt,
Xiangsong Fang,
Gang Zhao,
Xilong Liang,
Xianhao Ye,
Jing Zhong
Abstract:
We identify member stars of more than 90 open clusters in the LAMOST survey. With the method of Fang et al.(2018), the chromospheric activity (CA) indices logR'CaK for 1091 member stars in 82 open clusters and logR'Hα for 1118 member stars in 83 open clusters are calculated. The relations between the average logR'CaK, logR'Hα in each open cluster and its age are investigated in different Teff and…
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We identify member stars of more than 90 open clusters in the LAMOST survey. With the method of Fang et al.(2018), the chromospheric activity (CA) indices logR'CaK for 1091 member stars in 82 open clusters and logR'Hα for 1118 member stars in 83 open clusters are calculated. The relations between the average logR'CaK, logR'Hα in each open cluster and its age are investigated in different Teff and [Fe/H] ranges. We find that CA starts to decrease slowly from logt = 6.70 to logt = 8.50, and then decreases rapidly until logt = 9.53. The trend becomes clearer for cooler stars. The quadratic functions between logR' and logt with 4000K < Teff < 5500K are constructed, which can be used to roughly estimate ages of field stars with accuracy about 40% for logR'CaK and 60% for logR'Hα.
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Submitted 30 September, 2019;
originally announced September 2019.
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Detecting a physical difference between the CDM halos in simulation and in nature
Authors:
Weike Xiao,
Chang Peng,
Xianfeng Ye,
Heng Hao
Abstract:
Numerical simulation is an important tool to help us understand the process of structure formation in the universe. However many simulation results of cold dark matter (CDM) halos on small scale are inconsistent with observations: the central density profile is too cuspy and there are too many substructures. Here we point out that these two problems may be connected with a hitherto unrecognized…
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Numerical simulation is an important tool to help us understand the process of structure formation in the universe. However many simulation results of cold dark matter (CDM) halos on small scale are inconsistent with observations: the central density profile is too cuspy and there are too many substructures. Here we point out that these two problems may be connected with a hitherto unrecognized bias in the simulation halos. Although CDM halos in nature and in simulation are both virialized systems of collisionless CDM particles, gravitational encounter cannot be neglected in the simulation halos because they contain much less particles. We demonstrate this by two numerical experiments, showing that there is a difference on the microcosmic scale between the natural and simulation halos. The simulation halo is more akin to globular clusters where gravitational encounter is known to lead to such drastic phenomena as core collapse. And such artificial core collapse process appears to link the two problems together in the bottom-up scenario of structure formation in the $Λ$CDM universe. The discovery of this bias also has implications on the applicability of the Jeans Theorem in Galactic Dynamics.
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Submitted 21 August, 2005;
originally announced August 2005.