我们利用文献中的Strömgren光度数据和年龄 dating 算法，推断了大麦哲伦星云（LMC）中R127和R128星团的年龄。单星演化模型分析显示，蓝巨星数量与低质量星数量与Salpeter质量函数的预期存在显著差异，且蓝巨星的年龄比其余恒星更年轻。这种不一致反映了本地组年轻星团中的新兴趋势。通常，解决方法可能是二元演化或极快的自转，但在R127和R128星团的情况下，数据不完整可能也影响低质量和高质量恒星的数量。不一致程度随光度减小而增加，表明数据集可能不完整。然而，当排除前五颗最亮的恒星后，观测和预期的计数变得一致，证明最亮的恒星是特殊的。这些发现对位于年轻恒星团中的唯一确认的LBV R127有直接意义。LBV通常被认为是由单星演化产生，但越来越多地认识到二元相互作用可能在它们的演化中起关键作用。需要更完整的数据集，特别是通过哈勃空间望远镜的深场成像，以确认是否最亮恒星的缺失仅源于观测不完整，还是年轻星团建模不一致的更广泛趋势。
英文摘要：
We infer the age of the R127 and R128 clusters in the Large Magellanic Cloud (LMC) using Strömgren photometry from the literature and the age-dating algorithm, Stellar Ages. Analysis using single-star evolutionary models shows a substantial discrepancy between the relative numbers of bright blue stars and lower-mass stars as compared to expectations from a Salpeter mass function, and yields a younger age for the brightest blue stars than for the rest of the cluster. This inconsistency reflects an emerging trend among young clusters in the Local Group. In general, the resolution may be binary evolution or very rapid rotation, although in the specific case of the R127 and R128 clusters, unknown incompleteness in the data may also affect the relative numbers of low- and high-mass stars. The discrepancy grows toward fainter magnitudes, suggesting that the dataset is likely incomplete. However, when the five brightest stars are excluded, the observed and expected counts become consistent, demonstrating that the brightest stars are peculiar. These findings have direct implications for the luminous blue variable (LBV) R127, which is the only confirmed LBV in the LMC located within a young stellar cluster. LBVs have traditionally been considered products of single-star evolution, although there is growing recognition that binary interactions may play a critical role in their evolution. A more complete dataset, particularly deeper imaging with the Hubble Space Telescope, is needed to confirm whether the apparent absence of coeval stars arises solely from observational incompleteness or the broader trend of inconsistency in young cluster modeling.
We perform a study on the optical and infrared photometric properties of known luminous blue variables (LBVs) in M31 using the sample of LBV candidates from the Local Group Galaxy Survey (Massey et al. 2007). We find that M31 LBV candidates show photometric variability ranging from 0.375 to 1.576 magnitudes in rP1 during a three year time-span observed by the Pan-STARRS 1 Andromeda survey (PAndromeda). Their near-infrared colors also follow the distribution of Galactic LBVs as shown by Oksala et al. (2013). We use these features as selection criteria to search for unknown LBV candidates in M31…
Observations show that luminous blue variables (LBVs) are far more dispersed than massive O-type stars, and Smith & Tombleson suggested that these large separations are inconsistent with a single-star evolution model of LBVs. Instead, they suggested that the large distances are most consistent with binary evolution scenarios. To test these suggestions, we modelled young stellar clusters and their passive dissolution, and we find that, indeed, the standard single-star evolution model is mostly inconsistent with the observed LBV environments. If LBVs are single stars, then the lifetimes inferred…
It remains unclear whether massive star evolution is facilitated by mass loss through stellar winds only, or whether episodic mass loss during an eruptive luminous blue variable (LBV) phase is also significant. LBVs exhibit unique photometric and spectroscopic variability (termed S Dor variables). This may have tremendous implications for our understanding of the first stars, gravitational wave events, and supernovae. A key question here is whether all evolved massive stars passing through the blue supergiant phase are dormant S Dor variables transforming during a brief period, or whether LBVs…
(shortened) It has been proposed that the envelopes of luminous stars may be subject to substantial radius inflation. The inflation effect has been discussed in relation to the radius problem of WR stars, but has yet failed to explain the large observed radii of Galactic WR stars. We wish to obtain a physical perspective of the inflation effect, and study the consequences for the radii of WR stars, and LBVs. For WR stars the observed radii are up to an order of magnitude larger than predicted by theory, whilst S Doradus-type LBVs are subject to humongous radius variations, which remain as yet …
We present two new luminous blue variable (LBV) candidate stars discovered in the M33 galaxy. We identified these stars (Valeev et al. 2010) as massive star candidates at the final stages of evolution, presumably with a notable interstellar extinction. The candidates were selected from the Massey et al. (2006) catalog based on the following criteria: emission in Halpha, V<18.5 and 0.35<(B-V)<1.2. The spectra of both stars reveal a broad and strong Halpha emission with extended wings (770 and 1000 km/s). Based on the spectra we estimated the main parameters of the stars. Object N45901 has a bol…
The luminous blue variable (LBV) phase is a poorly understood stage in the evolution of high mass stars, characterized for its brevity and instability. The surroundings of LBV stars are excellent test beds to study their dense stellar winds and eruptive mass-loss events. Aiming to improve our knowledge of the LBV phase, we observed the J=1-0 and J=2-1 lines of CO and $^{13}$CO in a field of 1.5'x1.5' around the recently identified candidate LBV MGE 042.0787+00.5084, using the IRAM 30-m radio telescope. We report the first detection of molecular emission associated with this source, tracing a s…
Luminous blue variables (LBVs) are suprisingly isolated from the massive O-type stars that are their putative progenitors in single-star evolution, implicating LBVs as binary evolution products. Aadland et al. (A19) found that LBVs are, however, only marginally more dispersed than a photometrically selected sample of bright blue stars (BBS) in the LMC, leading them to suggest that LBV environments may not exclude a single-star origin. In both comparisons, LBVs have the same median separation, confirming that any incompleteness in the O-star sample does not fabricate LBV isolation. Instead, the…
For the first time, the interior and spectroscopic evolution of a massive star is analyzed from the zero-age main sequence (ZAMS) to the pre-supernova (SN) stage. For this purpose, we combined stellar evolution models using the Geneva code and atmospheric models using CMFGEN. With our approach, we were able to produce observables, such as a synthetic high-resolution spectrum and photometry, aiding the comparison between evolution models and observed data. Here we analyze the evolution of a non-rotating 60 Msun star and its spectrum throughout its lifetime. Interestingly, the star has a supergi…
(Shortened) Luminous blue variable stars (LBVs) form dust as a result of episodic, violent mass loss. To investigate their contribution as dust producers in the Magellanic Clouds, we analyse 31 LBVs from a recent census. We built a maximally complete multi-wavelength dataset of these sources from archival data from near-IR to millimetre wavelengths. We review the LBV classification on the basis of the IR SED. To derive characteristic dust parameters, we fitted the photometry resulting from a stacking analysis. For comparison we also stacked the images of low- and intermediate-mass evolved star…
Luminous Blue Variables have been suggested to be the direct progenitors of supernova types IIb and IIn, with enhanced mass loss prior to explosion. However, the mechanism of this mass loss is not yet known. Here, we investigate the qualitative behaviour of theoretical stellar wind mass-loss as a function of Teff across two bi-stability jumps in blue supergiant regime and also in proximity to the Eddington limit, relevant for LBVs. To investigate the physical ingredients that play a role in the radiative acceleration we calculate blue supergiant wind models with the CMFGEN non-LTE model atmosp…
Probing the wind and evolutionary state of the quiescent luminous blue variable Var$\,$2 in the Galaxy M33: constraints from self-consistent non-LTE modeling
We present time series photometric and spectroscopic data for the transient SN 2009ip from the start of its outburst in September 2012 until November 2013. This data was collected primarily with the new robotic capabilities of the Las Cumbres Observatory Global Telescope Network, a specialized facility for time domain astrophysics, and includes supporting high-resolution spectroscopy from the Southern Astrophysical Research Telescope, Kitt Peak National Observatory, and Gemini Observatory. Based on our nightly photometric monitoring, we interpret the strength and timing of fluctuations in the …
Evolution of wide O star binaries through their LBV stage. Population synthesis with mass-ejection-driven orbital evolution
Tsung-Dao Lee Institute, Shanghai Jiao-Tong University（上海交大李政道研究所）；London Institute for Stellar Astrophysics（伦敦恒星天体物理学研究所）；University of Oxford, St Edmund Hall（牛津大学圣埃德蒙学堂）；Argelander-Institut für Astronomie, Universität Bonn（波恩大学阿格勒兰德尔天文学研究所）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education（南京大学现代天文与天体物理教育部重点实验室）；School of Physics and Astronomy, Monash University（蒙纳士大学物理与天文学院）；Dublin Institute for Advanced Studies, Astronomy & Astrophysics Section, DIAS Dunsink Observatory（都柏林高等研究院天文与天体物理部都柏林星象观测站）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）
We present a brief overview of the theory of stellar winds with a strong emphasis on the radiation-driven outflows from massive stars. The resulting implications for the evolution and fate of massive stars are also discussed. Furthermore, we relate the effects of mass loss to the angular momentum evolution, which is particularly relevant for the production of long and soft gamma-ray bursts. Mass-loss rates are not only a function of the metallicity, but are also found to depend on temperature, particularly in the region of the bi-stability jump at 21 000 Kelvin. We highlight the role of the bi…
Recent surveys of the Magellanic Clouds have revealed a subtype of Wolf-Rayet (WR) star with peculiar properties. WN3/O3 spectra exhibit both WR-like emission and O3 V-like absorption - but at lower luminosity than O3 V or WN stars. We examine the projected spatial distribution of WN3/O3 stars in the LMC as compared to O-type stars. Surprisingly, WN3/O3 stars are among the most isolated of all classes of massive stars; they have a distribution similar to red supergiants dominated by initial masses of 10-15 $M_{\odot}$, and are far more dispersed than classical WR stars or luminous blue variabl…
Dust formation in the winds of hot stars is inextricably linked to the classic eruptive state of luminous blue variables (LBVs) because it requires very high mass loss rates, Mdot>10^(-2.5) Msun/year, for grains to grow and for the non-dust optical depth of the wind to shield the dust formation region from the true stellar photosphere. Thus, dusty shells around hot stars trace the history of "great" eruptions, and the statistics of such shells in the Galaxy indicate that these eruptions are likely the dominant mass loss mechanism for evolved, M>40Msun stars. Dust formation at such high Mdot al…
The spin of Wolf-Rayet (WR) stars at low metallicity (Z) is most relevant for our understanding of gravitational wave sources such as GW 150914, as well as the incidence of long-duration gamma-ray bursts (GRBs). Two scenarios have been suggested for both phenomena: one of them involves rapid rotation and quasi-chemical homogeneous evolution (CHE), the other invokes classical evolution through mass loss in single and binary systems. WR spin rates might enable us to test these two scenarios. In order to obtain empirical constraints on black hole progenitor spin, we infer wind asymmetries in all …
The giant HII region W31 hosts the populous star cluster W31-CL and others projected on or in the surroundings. The most intriguing object is the stellar cluster SGR1806-20, which appears to be related to a Luminous Blue Variable (LBV) - a luminous supergiant star. We used the deep VVV J-,H-and K$_s$-bands photometry combined with 2MASS data in order to address the distance andother physical and structural properties of the clusters W31-CL, BDS 113 and SGR1806-20. Field-decontaminated photometry was used to analyse colour-magnitude diagrams and stellar radial density profiles, using procedures…
We have obtained far-infrared Herschel PACS imaging and spectroscopic observations of the nebular environment of the luminous blue variable WRAY 15-751. These images clearly show that the main, dusty nebula is a shell of radius 0.5 pc and width 0.35 pc extending outside the H-alpha nebula. They also reveal a second, bigger and fainter dust nebula, observed for the first time. Both nebulae lie in an empty cavity, likely the remnant of the O-star wind bubble formed when the star was on the main sequence. The kinematic ages of the nebulae are about 20000 and 80000 years and each nebula contains a…
In light of recently revised observational measurements of the radius and spectroscopic parameters of the extremely old and metal-poor Gaia benchmark star HD 140283 -- also known as the Methuselah star due to prior suggestions that its age is in tension with the age of the Universe -- we present new, best estimates for the star's mass and age from stellar modeling. These are derived using 1D stellar evolutionary tracks computed with MESA and the most up-to-date measurements from CHARA interferometry. Excluding modeling variance from the uncertainties, we report a mass of $0.809 \pm 0.001 M_{\o…
Very massive stars in the final phases of their lives often show unpredictable outbursts that can mimic supernovae, so-called, "SN impostors", but the distinction is not always straigthforward. Here we present observations of a luminous blue variable (LBV) in NGC 2770 in outburst over more than 20 years that experienced a possible terminal explosion as type IIn SN in 2015, named SN 2015bh. This possible SN or "main event" was preceded by a precursor peaking $\sim$ 40 days before maximum. The total energy release of the main event is $\sim$1.8$\times$10$^{49}$ erg, which can be modeled by a $<$…
Type IIn Supernovae (SNe IIn) are rare events, constituting only a few percent of all core-collapse SNe, and the current sample of well observed SNe IIn is small. Here, we study the four SNe IIn observed by the Caltech Core-Collapse Project (CCCP). The CCCP SN sample is unbiased to the extent that object selection was not influenced by target SN properties. Therefore, these events are representative of the observed population of SNe IIn. We find that a narrow P-Cygni profile in the hydrogen Balmer lines appears to be a ubiquitous feature of SNe IIn. Our light curves show a relatively long rise…
We used the Navy Precision Optical Interferometer to measure the limb-darkened angular diameter of the exoplanet host star kappa CrB and obtained a value of 1.543 +/- 0.009 mas. We calculated its physical radius (5.06 +/- 0.04 R_Sun) and used photometric measurements from the literature with our diameter to determine kappa CrB's effective temperature (4788 +/- 17 K) and luminosity (12.13 +/- 0.09 L_Sun). We then placed the star on an H-R diagram to ascertain the star's age (3.42 +0.32/-0.25 Gyr) and mass (1.47 +/- 0.04 M_Sun) using a metallicity of [Fe/H] = +0.15. With this mass, we calculated…
We present a chemical-composition analysis of 77 red-giant stars in Omega Centauri. We have measured abundances for carbon and nitrogen, and combined our results with abundances of O, Na, La, and Fe that we determined in our previous work. Our aim is to better understand the peculiar chemical-enrichment history of this cluster, by studying how the total C+N+O content varies among the different-metallicity stellar groups, and among stars at different places along the Na-O anticorrelation. We find the (anti)correlations among the light elements that would be expected on theoretical ground for ma…
About 20% out of the $>1000$ known exoplanets are Jupiter analogs orbiting very close to their parent stars. It is still under debate to what detectable level such hot Jupiters possibly affect the activity of the host stars through tidal or magnetic star-planet interaction. In this paper we report on an 87 ks Chandra observation of the hot Jupiter hosting star WASP-18. This system is composed of an F6 type star and a hot Jupiter of mass $10.4 M_{Jup}$ orbiting in less than 20 hr around the parent star. On the basis of an isochrone fitting, WASP-18 is thought to be 600 Myr old and within the ra…
Type Ibn supernovae (SNe Ibn) are intriguing stellar explosions whose spectra exhibit narrow helium lines with little hydrogen. They trace the presence of circumstellar material (CSM) formed via pre-SN eruptions of their stripped-envelope progenitors. Early work has generally assumed that SNe Ibn come from massive Wolf-Rayet (WR) stars via single star evolution. In this paper, we report ultraviolet (UV) and optical observations of two nearby Type Ibn SNe 2006jc and 2015G conducted with the Hubble Space Telescope (HST) at late times. A point source is detected at the position of SN 2006jc, and …
We performed a detailed study of the evolution of the luminosity of He-ignition stage and of the red giant branch bump luminosity during the red giant branch phase transition for various metallicities. To this purpose we calculated a grid of stellar models that sample the mass range of the transition with a fine mass step equal to ${\rm 0.01M_\odot}$. We find that for a stellar population with a given initial chemical composition, there is a critical age (of 1.1-1.2~Gyr) around which a decrease in age of just 20-30 million years causes a drastic drop in the red giant branch tip brightness. We …
In certain mass ranges, massive stars can undergo a violent pulsation triggered by the electron/positron pair instability that ejects matter, but does not totally disrupt the star. After one or more of these pulsations, such stars are expected to undergo core-collapse to trigger a supernova explosion. The mass range susceptible to this pulsational phenomena may be as low as 50-70 Msun if the progenitor is of very low metallicity and rotating sufficiently rapidly to undergo nearly homogeneous evolution. The mass, dynamics, and composition of the matter ejected in the pulsation are important asp…
The most accurate ages for the oldest stars are those obtained for nearby halo subgiants, because they depend almost entirely on just the measured parallaxes and absolute oxygen abundances. In this study, we have used the Fine Guidance Sensors on the Hubble Space Telescope to determine trigonometric parallaxes, with precisions of 2.1% or better, for the Population II subgiants HD 84937, HD 132475, and HD 140283. High quality spectra have been used to derive their surface abundances of O, Fe, Mg, Si, and Ca, which are assumed to be 0.1-0.15 dex less than their initial abundances due to the effe…
In the absence of constraints from the binary companion or supernova remnant, the standard method for estimating pulsar ages is to infer an age from the rate of spin-down. While the generic spin-down age may give realistic estimates for normal pulsars, it can fail for pulsars with very short periods. Details of the spin-up process during the low mass X-ray binary phase pose additional constraints on the period (P) and spin-down rates (Pdot) that may consequently affect the age estimate. Here, we propose a new recipe to estimate millisecond pulsar (MSP) ages that parametrically incorporates con…
The accuracy of masses of pre-main sequence (PMS) stars derived from their locations on the Hertzsprung-Russell Diagram (HRD) can be tested by comparison with accurate and precise masses determined independently. We present 29 single stars in the Taurus star-forming region (SFR) and 3 in the Ophiuchus SFR with masses measured dynamically to a precision of at least $10 \%$. Our results include 9 updated mass determinations and 3 that have not had their dynamical masses published before. This list of stars with fundamental, dynamical masses, M$_{dyn}$, is drawn from a larger list of 39 targets i…
Extended main-sequence turnoffs apparent in most young and intermediate-age clusters (younger than ~2 Gyr) are known features caused by fast rotating early-type (earlier than F-type) stars. Late-type stars are not fast rotators because their initial angular momenta have been quickly dispersed due to magnetic braking. However, the mass limit below which stars have been magnetically braked has not been well constrained by observation. In this paper, we present an analysis of the eMSTO of NGC 6819, an open cluster of an intermediate-age (~2.5 Gyr), believed to be comparable to the lifetime of sta…
Blue straggler stars have been proposeed as powerful indicators to measure the dynamical state of Galactic globular clusters. Here we examine for the first time if this framework of blue straggler stars as dynamical clocks, which was specifically developed for Galactic globular clusters, may also hold for younger globular clusters in the Large Magellanic Cloud. Using Hubble Space Telescope observations, we study seven Large Magellanic Cloud star clusters with ages between ~700 Myr and 7 Gyr. We confirm that our sample clusters are consistent with the empirical correlation previously derived fo…
Solar twins in Gaia DR3 GSP-Spec II. Age distribution and its implications for the Sun's migration
Tokyo Metropolitan University（东京都立大学）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学，蔚蓝海岸天文台，法国国家科学研究中心，拉格朗日实验室）；National Astronomical Observatory of Japan（日本国立天文台）；Department of Physics, Tokyo Metropolitan University（东京都立大学物理系）
We analyze age distributions of two nearby rich stellar clusters, the NGC 2024 (Flame Nebula) and Orion Nebula Cluster (ONC) in the Orion molecular cloud complex. Our analysis is based on samples from the MYStIX survey and a new estimator of pre-main sequence (PMS) stellar ages, AgeJX, derived from X-ray and near-infrared photometric data. To overcome the problem of uncertain individual ages and large spreads of age distributions for entire clusters, we compute median ages and their confidence intervals of stellar samples within annular subregions of the clusters. We find core-halo age gradien…
We study the relationship between coronal X-ray emission and stellar age for late-type stars, and the variation of this relationship with spectral type. We select 717 stars from 13 open clusters and find that the ratio of X-ray to bolometric luminosity during the saturated phase of coronal emission decreases from 10^-3.1 for late K-dwarfs to 10^-4.3 for early F-type stars (across the range 0.29<(B-V)_0<1.41). Our determined saturation timescales vary between 10^7.6 and 10^8.3 years, though with no clear trend across the whole FGK range. We apply our X-ray emission - age relations to the invest…
