The Astronomy and Astrophysics Review最新文献

{"title":"Solar wind current sheets and deHoffmann-Teller analysis. First results from Solar Orbiter's DC electric field measurements","authors":"K. Steinvall, Y. Khotyaintsev, G. Cozzani, A. Vaivads, E. Yordanova, A. Eriksson, N. Edberg, M. Maksimović, S. Bale, T. Chust, V. Krasnoselskikh, M. Kretzschmar, E. Lorfèvre, D. Plettemeier, J. Souvcek, M. Steller, vS. vStver'ak, A. Vecchio, T. Horbury, H. O’Brien, V. Evans, A. Fedorov, P. Louarn, V. G'enot, N. Andr'e, B. Lavraud, A. Rouillard, C. Owen","doi":"10.1051/0004-6361/202140855","DOIUrl":"https://doi.org/10.1051/0004-6361/202140855","url":null,"abstract":"Context. Solar Orbiter was launched on 10 February 2020 with the purpose of investigating solar and heliospheric physics using a payload of instruments designed for both remote and in situ studies. Similar to the recently launched Parker Solar Probe, and unlike earlier missions, Solar Orbiter carries instruments designed to measure low-frequency DC electric fields. Aims. In this paper, we assess the quality of the low-frequency DC electric field measured by the Radio and Plasma Waves instrument (RPW) on Solar Orbiter. In particular, we investigate the possibility of using Solar Orbiter’s DC electric and magnetic field data to estimate the solar wind speed. Methods. We used a deHo ff mann-Teller (HT) analysis, based on measurements of the electric and magnetic fields, to find the velocity of solar wind current sheets, which minimises a single component of the electric field. By comparing the HT velocity to the proton velocity measured by the Proton and Alpha particle Sensor (PAS), we have developed a simple model for the e ff ective antenna length, L e ff of the E-field probes. We then used the HT method to estimate the speed of the solar wind. Results. Using the HT method, we find that the observed variations in E y are often in excellent agreement with the variations in the magnetic field. The magnitude of E y , however, is uncertain due to the fact that the L e ff depends on the plasma environment. Here, we derive an empirical model relating L e ff to the Debye length, which we can use to improve the estimate of E y and, consequently, the estimated solar wind speed. Conclusions. The low-frequency electric field provided by RPW is of high quality. Using the deHo ff mann-Teller analysis, Solar Orbiter’s magnetic and electric field measurements can be used to estimate the solar wind speed when plasma data are unavailable.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"103 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77526530","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Energy partition in a confined flare with an extreme-ultraviolet late phase","authors":"Q. M. Zhang, J. Cheng, Y. Dai, K. Tam, A. Xu","doi":"10.1051/0004-6361/202038082","DOIUrl":"https://doi.org/10.1051/0004-6361/202038082","url":null,"abstract":"In this paper, we reanalyze the M1.2 confined flare with a large extreme-ultraviolet (EUV) late phase on 2011 September 9, focusing on its energy partition. The radiation ($sim$5.4$times$10$^{30}$ erg) in 1$-$70 {AA} is nearly eleven times larger than the radiation in 70$-$370 {AA}, and is nearly 180 times larger than the radiation in 1$-$8 {AA}. The peak thermal energy of the post-flare loops is estimated to be (1.7$-$1.8)$times$10$^{30}$ erg based on a simplified schematic cartoon. Based on previous results of Enthalpy-Based Thermal Evolution of Loops (EBTEL) simulation, the energy inputs in the main flaring loops and late-phase loops are (1.5$-$3.8)$times$10$^{29}$ erg and 7.7$times$10$^{29}$ erg, respectively. The nonthermal energy ((1.7$-$2.2)$times$10$^{30}$ erg) of the flare-accelerated electrons is comparable to the peak thermal energy and is sufficient to provide the energy input of the main flaring loops and late-phase loops. The magnetic free energy (9.1$times$10$^{31}$ erg) before flare is large enough to provide the heating requirement and radiation, indicating that the magnetic free energy is adequate to power the flare.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"85 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89438841","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stellar collisions in flattened and rotating Population III star clusters","authors":"M. Vergara, D. Schleicher, T. Boekholt, B. Reinoso, M. Fellhauer, R. Klessen, N. Leigh","doi":"10.1051/0004-6361/202140298","DOIUrl":"https://doi.org/10.1051/0004-6361/202140298","url":null,"abstract":"Fragmentation often occurs in disk-like structures, both in the early Universe and in the context of present-day star formation. Supermassive black holes (SMBHs) are astrophysical objects whose origin is not well understood; they weigh millions of solar masses and reside in the centers of galaxies. An important formation scenario for SMBHs is based on collisions and mergers of stars in a massive cluster with a high stellar density, in which the most massive star moves to the center of the cluster due to dynamical friction. This increases the rate of collisions and mergers since massive stars have larger collisional cross sections. This can lead to a runaway growth of a very massive star which may collapse to become an intermediate-mass black hole. Here we investigate the dynamical evolution of Miyamoto-Nagai models that allow us to describe dense stellar clusters, including flattening and different degrees of rotation. We find that the collisions in these clusters depend mostly on the number of stars and the initial stellar radii for a given radial size of the cluster. By comparison, rotation seems to affect the collision rate by at most 20%. For flatness, we compared spherical models with systems that have a scale height of about 10% of their radial extent, in this case finding a change in the collision rate of less than 25%. Overall, we conclude that the parameters only have a minor effect on the number of collisions. Our results also suggest that rotation helps to retain more stars in the system, reducing the number of escapers by a factor of 2− 3 depending on the model and the specific realization. After two million years, a typical lifetime of a very massive star, we find that about 630 collisions occur in a typical models with N = 104, R = 100 R and a half-mass radius of 0.1 pc, leading to a mass of about 6.3 × 103 M for the most massive object. We note that our simulations do not include mass loss during mergers or due to stellar winds. On the other hand, the growth of the most massive object may subsequently continue, depending on the lifetime of the most massive object.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"53 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85223957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The β\u0000Pictoris b Hill sphere transit campaign","authors":"M. Kenworthy, S. N. Mellon, J. Bailey, R. Stuik, P. Dorval, G. Talens, S. Crawford, E. Mamajek, I. Laginja, M. Ireland, B. Lomberg, R. Kuhn, I. Snellen, K. Zwintz, R. Kuschnig, G. Kennedy, L. Abe, A. Agabi, D. Mékarnia, T. Guillot, F. Schmider, P. Stee, Y. De Pra, M. Buttu, N. Crouzet, P. Kalas, J. Wang, K. Stevenson, E. de Mooij, A. Lagrange, S. Lacour, A. Lecavelier des Etangs, M. Nowak, P. Strøm, Z. Hui, L. Wang","doi":"10.1051/0004-6361/202040060","DOIUrl":"https://doi.org/10.1051/0004-6361/202040060","url":null,"abstract":"Aims. Photometric monitoring of β Pic in 1981 showed anomalous fluctuations of up to 4% over several days, consistent with foreground material transiting the stellar disk. The subsequent discovery of the gas giant planet β Pic b and the predicted transit of its Hill sphere to within a 0.1 au projected separation of the planet provided an opportunity to search for the transit of a circumplanetary disk (CPD) in this 21 ± 4 Myr-old planetary system. We aim to detect, or put an upper limit on, the density and nature of the material in the circumplanetary environment of the planet via the continuous photometric monitoring of the Hill sphere transit that occurred in 2017 and 2018.\u0000Methods. Continuous broadband photometric monitoring of β Pic requires ground-based observatories at multiple longitudes to provide redundancy and to provide triggers for rapid spectroscopic follow-up. These include the dedicated β Pic monitoring bRing observatories in Sutherland and Siding Springs, the ASTEP400 telescope at Concordia, and the space observatories BRITE and the Hubble Space Telescope (HST). We search the combined light curves for evidence of short-period transient events caused by rings as well as for longer-term photometric variability due to diffuse circumplanetary material.\u0000Results. We find no photometric event that matches with the event seen in November 1981, and there is no systematic photometric dimming of the star as a function of the Hill sphere radius.\u0000Conclusions. We conclude that the 1981 event was not caused by the transit of a CPD around β Pic b. The upper limit on the long-term variability of β Pic places an upper limit of 1.8 × 1022 g of dust within the Hill sphere (comparable to the ~100 km radius asteroid 16 Psyche). Circumplanetary material is either condensed into a disk that does not transit β Pic, condensed into a disk with moons that has an obliquity that does not intersect with the path of β Pic behind the Hill sphere, or is below our detection threshold. This is the first time that a dedicated international campaign has mapped the Hill sphere transit of an extrasolar gas giant planet at 10 au.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"39 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87054402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Measuring the masses and radii of neutron stars in low-mass X-ray binaries: Effects of the atmospheric composition and touchdown radius","authors":"Myungkuk Kim, Young-Min Kim, K. Sung, Chang-Hwan Lee, K. Kwak","doi":"10.1051/0004-6361/202038126","DOIUrl":"https://doi.org/10.1051/0004-6361/202038126","url":null,"abstract":"Context. X-ray bursts (XRBs) are energetic explosive events which have been observed in low-mass X-ray binaries (LMXBs). Some Type-I XRBs show photospheric radius expansion (PRE) and these PRE XRBs are used to simultaneously estimate the mass and the radius of a neutron star in LMXB. Aims. The mass and radius estimation depends on a few model parameters most of which are still uncertain. Among them, we focus on the effects of the chemical composition of the photosphere which determines the opacity during the PRE phase and the touchdown radius which can be larger than the neutron star radius. We investigate how these two model parameters affect the mass and radius estimation in a systematic way and whether there is any statistical trend for these two parameters including a correlation between them. Methods. We use both a Monte Carlo (MC) sampling and a Bayesian analysis to find the effects of the photospheric composition and the touchdown radius. We apply these two methods to six LMXBs that show PRE XRBs. In both methods, we solve the Eddington flux equation and the apparent angular area equation both of which include the correction terms. For the MC sampling, we have developed an iterative method in order to solve these two equations more efficiently. Results. We confirm that the effects of the photospheric composition and the touchdown radius are similar in the statistical and analytical estimation of mass and radius even when the correction terms are considered. Furthermore, in all of the six sources, we find that a H-poor photosphere and a large touchdown radius are favored statistically regardless of the statistical method. Our Bayesian analysis also hints that touchdown can occur farther from the neutron star surface when the photosphere is more H-poor. This correlation could be qualitatively understood with the Eddington flux equation. We propose a physical explanation for this correlation between the photospheric composition and the touchdown radius. Our results show that when accounting for the uncertainties of the photospheric composition and the touchdown radius, most likely radii of the neutron stars in these six LMXBs are less than 12.5 km, which is similar to the bounds for the neutron star radius placed with the tidal deformability measured from the gravitational wave signal.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"4 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87924717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The LOFAR Two Meter Sky Survey","authors":"F. Combes, D. Elbaz, T. Forveille, R. Kotak, L. Pentericci, S. Shore","doi":"10.1051/0004-6361/202140819","DOIUrl":"https://doi.org/10.1051/0004-6361/202140819","url":null,"abstract":"","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"5 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78857120","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Submillimeter imaging of the Galactic Center starburst Sgr B2","authors":"M. Santa-Maria, J. Goicoechea, M. Etxaluze, J. Cernicharo, S. Cuadrado","doi":"10.1051/0004-6361/202040221","DOIUrl":"https://doi.org/10.1051/0004-6361/202040221","url":null,"abstract":"We present 168 arcmin^2 spectral images of the Sgr B2 complex taken with Herschel/SPIRE-FTS. We detect ubiquitous emission from CO (up to J=12-11), H2O, [CI]492, 809 GHz, and [NII] 205 um lines. We also present maps of the SiO, N2H+, HCN, and HCO+ emission obtained with the IRAM30m telescope. The cloud environment dominates the emitted FIR (80%), H2O 752 GHz (60 %) mid-J CO (91%), and [CI] (93 %) luminosity. The region shows very extended [NII] emission (spatially correlated with the 24 and 70 um dust emission). The observed FIR luminosities imply G_0~10^3. The extended [CI] emission arises from a pervasive component of neutral gas with n_H~10^3 cm-3. The high ionization rates, produced by enhanced cosmic-ray (CR) fluxes, drive the gas heating to Tk~40-60 K. The mid-J CO emission arises from a similarly extended but more pressurized gas component (P_th~10^7 K cm-3). Specific regions of enhanced SiO emission and high CO-to-FIR intensity ratios (>10^-3) show mid-J CO emission compatible with shock models. A major difference compared to more quiescent star-forming clouds in the disk of our Galaxy is the extended nature of the SiO and N2H+ emission in Sgr B2. This can be explained by the presence of cloud-scale shocks, induced by cloud-cloud collisions and stellar feedback, and the much higher CR ionization rate (>10^-15 s-1) leading to overabundant H3+ and N2H+. Hence, Sgr B2 hosts a more extreme environment than star-forming regions in the disk of the Galaxy. As a usual template for extragalactic comparisons, Sgr B2 shows more similarities to ultra luminous infrared galaxies such as Arp 220, including a \"deficit\" in the [CI]/FIR and [NII]/FIR intensity ratios, than to pure starburst galaxies such as M82. However, it is the extended cloud environment, rather than the cores, that serves as a useful template when telescopes do not resolve such extended regions in galaxies.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"100 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85836351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Compact steep-spectrum and peaked-spectrum radio sources","authors":"Christopher P. O’Dea,&nbsp;D. J. Saikia","doi":"10.1007/s00159-021-00131-w","DOIUrl":"https://doi.org/10.1007/s00159-021-00131-w","url":null,"abstract":"<p>Compact steep-spectrum (CSS) and peaked-spectrum (PS) radio sources are compact, powerful radio sources. The multi-frequency observational properties and current theories are reviewed with emphasis on developments since the earlier review of O’Dea (PASP 110:493–532, https://doi.org/10.1086/316162, 1998). There are three main hypotheses for the nature of PS and CSS sources. (1) The PS sources might be very young radio galaxies which will evolve into CSS sources on their way to becoming large radio galaxies. (2) The PS and CSS sources might be compact, because they are confined (and enhanced in radio power) by interaction with dense gas in their environments. (3) Alternately, the PS sources might be transient or intermittent sources. Each of these hypotheses may apply to individual objects. The relative number in each population will have significant implications for the radio galaxy paradigm. Proper motion studies over long time baselines have helped determine hotspot speeds for over three dozen sources and establish that these are young objects. Multi-frequency polarization observations have demonstrated that many CSS/PS sources are embedded in a dense interstellar medium and vigorously interacting with it. The detection of emission line gas aligned with the radio source, and blue-shifted H<span>i</span> absorption, and [OIII] emission lines indicates that AGN feedback is present in these objects—possibly driven by the radio source. Also, CSS/PS sources with evidence of episodic AGN over a large range of time-scales have been discussed. The review closes with a discussion of open questions and prospects for the future.</p>","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"29 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1007/s00159-021-00131-w","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5162632","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multiscale behaviour of stellar activity and rotation of the planet host Kepler-30","authors":"D. B. de Freitas, Antonino Francesco Lanza, F. da Silva Gomes, M. L. das Chagas","doi":"10.1051/0004-6361/202140287","DOIUrl":"https://doi.org/10.1051/0004-6361/202140287","url":null,"abstract":"Context. The Kepler-30 system consists of a G dwarf star with a rotation period of ∼16 days and three planets orbiting almost coplanar with periods ranging from 29 to 143 days. Kepler-30 is a unique target to study stellar activity and rotation in a young solar-like star accompanied by a compact planetary system. Aims. We use about 4 years of high-precision photometry collected by the Kepler mission to investigate the fluctuations caused by photospheric convection, stellar rotation, and starspot evolution as a function of the timescale. Our main goal is to apply methods for the analysis of timeseries to find the timescales of the phenomena that affect the light variations. We correlate those timescales with periodicities in the star as well as in the planetary system. Methods. We model the flux rotational modulation induced by active regions using spot modelling and apply the Multifractal Detrending Moving Average algorithm (MFDMA) in standard and multiscale versions for analysing the behaviour of variability and light fluctuations that can be associated with stellar convection and the evolution of magnetic fields on timescales ranging from less than 1 day up to about 35 days. The light fluctuations produced by stellar activity can be described by the multifractal Hurst index that provides a measure of their persistence. Results. The spot modeling indicates a lower limit to the relative surface differential rotation of ∆Ω/Ω ∼ 0.02 ± 0.01 and suggests a short-term cyclic variation in the starspot area with a period of ∼ 34 days, virtually close to the synodic period of 35.2 days of the planet Kepler-30b. By subtracting the two timeseries of the SAP and PDC Kepler pipelines, we reduce the rotational modulation and find a 23.1-day period close to the synodic period of Kepler-30c. This period also appears in the multifractal analysis as a crossover of the fluctuation functions associated with the characteristic evolutionary timescales of the active regions in Kepler-30 as confirmed by spot modelling. These procedures and methods may be greatly useful for analysing current TESS and future PLATO data.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"11 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74375936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Properties of the brightest globular cluster in M 81 based on multicolour observations","authors":"S. Wang, J. Ma","doi":"10.1051/0004-6361/202140574","DOIUrl":"https://doi.org/10.1051/0004-6361/202140574","url":null,"abstract":"Context. Researching the properties of the brightest globular cluster (referred to as GC1) in M 81 can provide a fossil record of the earliest stages of galaxy formation and evolution. The Beijing–Arizona–Taiwan–Connecticut (BATC) Multicolour Sky Survey has carried out deep exposures of M 81.\u0000Aims. We derive the magnitudes in intermediate-band filters of the BATC system for GC1 and determine its age, mass, and structural parameters.\u0000Methods. GC1 was observed by BATC using 14 intermediate-band filters covering a wavelength range of 4000–10 000 Å. Based on photometric data in BATC and Two Micron All Sky Survey near-infrared JHKs filters, we constructed an extensive spectral energy distribution of GC1, spanning the wavelength range from 4000 to 20 000 Å. By comparing multicolour photometry with theoretical single stellar population synthesis models, we derived the age and mass of GC1. In addition, we obtained ellipticities, position angles, and surface brightness profiles for GC1 based on the images of deep observations with the Advanced Camera for Surveys on the Hubble Space Telescope. GC1 is better fitted by the Wilson model than by the King and Sérsic models in the F606W filter, and it is better fitted by the Sérsic model than by the King and Wilson models in the F814W filter. The ‘best-fit’ half-light radius of GC1 obtained here is 5.59 pc, which is larger than the majority of normal globular clusters (GCs) of the same luminosity.\u0000Results. The age and mass of GC1 estimated here are 13.0 ± 2.90 Gyr and 1.06 − 1.48 × 107 M⊙, respectively. The Rh versus MV diagram shows that GC1 occupies the same area as extended star clusters. Therefore, we suggest that GC1 is more likely an accreted former nuclear star cluster than a classical GC similar to most of those in the Milky Way.","PeriodicalId":785,"journal":{"name":"The Astronomy and Astrophysics Review","volume":"100 1","pages":""},"PeriodicalIF":25.8,"publicationDate":"2021-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78658371","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}