We present a new tool for colour-magnitude diagram (CMD) studies, $Powerful~CMD$. This tool is built on the basis of the advanced stellar population synthesis (ASPS) model, in which single stars, binary stars, rotating stars, and star formation history have been taken into account. Via $Powerful~CMD$, the distance modulus, colour excess, metallicity, age, binary fraction, rotating star fraction, and star formation history of star clusters can be determined simultaneously from observed CMDs. The new tool is tested via both simulated and real star clusters. Five parameters of clusters NGC6362, NGC6652, NGC6838 and M67 are determined and compared to other works. It is shown that this tool is useful for CMD studies, in particular for those with the data of the Hubble Space Telescope (HST). Moreover, we find that the inclusion of binaries in theoretical stellar population models may lead to smaller colour excess compared to the case of single star population models.
In this fourth paper of a series on the precision of ages of stellar populations obtained through the full-spectrum fitting technique, we present a first systematic analysis that compare the age, metallicity and reddening of star clusters obtained from resolved and unresolved data (namely colour-magnitude diagrams (CMDs) and integrated-light spectroscopy) using the same sets of isochrones. We investigate the results obtained with both Padova isochrones and MIST isochrones. We find that there generally is a good agreement between the ages derived from CMDs and integrated spectra. However, for m…
We present a deep Blanco/DECam colour-magnitude diagram (CMD) for the large but very diffuse Milky Way satellite dwarf galaxy Crater II. The CMD shows only old stars with a clearly bifurcated subgiant branch (SGB) that feeds a narrow red giant branch. The horizontal branch (HB) shows many RR Lyrae and red HB stars. Comparing the CMD with [Fe/H] = -2.0 and [$α$/Fe] = +0.3 alpha-enhanced BaSTI isochrones indicates a mean age of 12.5 Gyr for the main event and a mean age of 10.5 Gyr for the brighter SGB. With such multiple star formation events Crater II shows similarity to more massive dwarfs th…
Two stellar clocks, one history: a Gaia colour-magnitude-diagram reconstruction of the solar-neighbourhood star-formation history tested against white dwarfs
Università di Pisa（比萨大学）；INFN（意大利国家核物理研究所）；INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（博洛尼亚天体物理学与空间科学天文台）
Virtual observatories allow the means by which an astronomer is able to discover, access, and process data seamlessly, regardless of its physical location. However, steep learning curves are often required to become proficient in the software employed to access, analyse and visualise this trove of data. It would be desirable, for both research and educational purposes, to have applications which allow users to visualise data at the click of a button. Therefore, we have developed a standalone application (written in Python) for plotting photometric Colour Magnitude Diagrams (CMDs) - one of the …
We perform a comprehensive study of the stellar populations in the young Large Magellanic Cloud cluster NGC 1866, combining the analysis of its best-studied Cepheids with that of a very accurate colour-magnitude diagram (CMD) obtained from the most recent Hubble Space Telescope photometry. We use a Bayesian method based on new PARSEC stellar evolutionary tracks with overshooting and rotation to obtain ages and initial rotation velocities of five well-studied Cepheids of the cluster. We find that four of the five Cepheids belong to an initially slowly rotating young population (of $ 176 \pm 5$ …
We present a new method for probabilistic generative modelling of stellar colour-magnitude diagrams (CMDs) to infer the frequency of binary stars and their mass-ratio distribution. The method invokes a mixture model to account for overlapping populations of single stars, binaries and outliers in the CMD. We apply the model to Gaia observations of the old open cluster, M67, and find a frequency $f_B(q > 0.5) = 0.258 \pm 0.019$ for binary stars with mass ratio greater than 0.5. The form of the mass-ratio distribution function rises towards higher mass ratios for $q > 0.3$.
We investigate the morphology of the colour-magnitude diagram (CMD) of the open cluster NGC 2509 in comparison with other Galactic open clusters of similar age using Gaia photometry. At $\sim900$ Myr Galactic open clusters in our sample all show an extended main sequence turn off (eMSTO) with the exception of NGC 2509, which presents an exceptionally narrow CMD. Our analysis of the Gaia data rules out differential extinction, stellar density, and binaries as a cause for the singular MSTO morphology in this cluster. We interpret this feature as a consequence of the stellar rotation distribution…
Stellar evolutionary tracks for $0.12 \le M/M_\odot \le 1.0$ have been computed for each of several variations in the abundances of C, N, and O, assuming mass-fraction helium abundances $Y = 0.25$ and $0.29$, and 11 metallicities in the range $-1.5 \le$ [Fe/H] $\le -0.5$, in 0.2 dex increments. Such computations are provided for mixtures with [O/Fe] between $+0.4$ and $+0.8$, for different C:N:O ratios at a fixed value of [CNO/Fe], and for enhanced C. Computer codes are provided to interpolate within these grids to produce isochrones for ages $> 7$ Gyr and to generate magnitudes and colours fo…
Astrometry and photometry from {\it Gaia} and spectroscopic data from the {\it Gaia}-ESO Survey (GES) are used to identify the lithium depletion boundary (LDB) in the young cluster NGC 2232. A specialised spectral line analysis procedure was used to recover the signature of undepleted lithium in very low luminosity cluster members. An age of $38\pm 3$ Myr is inferred by comparing the LDB location in absolute colour-magnitude diagrams (CMDs) with the predictions of standard models. This is more than twice the age derived from fitting isochrones to low-mass stars in the CMD with the same models.…
This work employs high-quality {\em Hubble Space Telescope} ({\em HST}) Advanced Camera for Surveys (ACS) F606W and F814W photometry to correct for the differential reddening affecting the colour-magnitude diagram (CMD) of the poorly-studied globular cluster (GC) Palomar\,2. Differential reddening is taken into account by assuming that morphological differences among CMDs extracted across the field of view of Palomar\,2 correspond essentially to shifts (quantified in terms of $δE(B-V)$) along the reddening vector due to a non-uniform dust distribution. The average reddening difference over all…
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters - XIV. Multiple stellar populations within M 15 and their radial distribution
在哈勃太空望远镜银河球状星团紫外巡天的背景下，我们推导出高精度，多波段测光，以调查在大质量和金属贫乏的GC M 15中的多个恒星星族。通过创建红巨星分支（RGB）恒星的集群的“染色体地图”，这是一个伪双色图与适当的组合的F275 W，F336 W，F438 W，和F814 W的星等，我们揭示了颜色传播周围的三个已知的恒星星族。这些扩散不能仅由光度误差产生，并且可能隐藏（两个）额外种群的存在。这一发现增加了M15中多种群现象的复杂性。我们的分析表明，M15表现出一个微弱的亚巨星分支（SGB），这也是在彩色星等图（CMD）中检测到的光学星等。这颗星的数量约占整个星的5%，并在m_F336 W-m_F814 WCMD中演化为红色RGB，表明M 15属于II型GC。我们测量了每个人口中恒星的相对数量在不同的径向距离从集群中心，显示所有这些人口共享相同的径向分布的统计不确定性。这些新的发现进行了讨论的背景下，形成和演变的多个种群的情况。
In order to characterize 22 new globular cluster (GC) candidates in the Galactic bulge, we present their colour-magnitude diagrams (CMDs) and Ks-band luminosity functions (LFs) using the near-infrared VVV database as well as Gaia-DR2 proper motion dataset. CMDs were obtained, on one hand, after properly decontaminating the observed diagrams from background/foreground disc stars and other sources. On the other hand, CMDs were also obtained based upon star selection in proper motion diagrams. Taking into account our deep CMDs and LFs analyses, we find that 17 out of 22 new GC candidates may be r…
[...] This paper presents a rigorous derivation of a goodness-of-fit statistics for colour-magnitude diagrams (CMD). We discuss the reliability of the underlying assumptions and their validity. We derived the distribution of the sum of squared Mahalanobis distances of stellar data and theoretical isochrone for a generic set of data and models. We applied this to the case of synthetic CMDs constructed to mimic real data of open clusters in the GAIA sample. We analysed the capability of distinguishing among different sets of input physics and parameters that were used to compute the stellar mode…
A growing disquiet has emerged in recent years that standard stellar models are at odds with observations of the colour-magnitude diagrams (CMDs) and lithium depletion patterns of pre main sequence (PMS) stars in clusters. In this work we select 1,246 high probability K/M-type constituent members of 5 young open clusters (5--125\,Myr) in the Gaia-ESO Survey to test a series of models that use standard input physics and others that incorporate surface magnetic fields or cool starspots. We find that: standard models provide systematically under-luminous isochrones for low-mass stars in the CMD a…
We present the UV photometry of the old open cluster NGC188 obtained using images acquired with Ultraviolet Imaging Telescope (UVIT) on board the ASTROSAT satellite, in two far-UV (FUV) and one near-UV (NUV) filters. UVIT data is utilised in combination with optical photometric data to construct the optical and UV colour-magnitude diagrams (CMDs). In the FUV images, we detect only hot and bright blue straggler stars (BSSs), one hot subdwarf, and one white dwarf (WD) candidate. In the NUV images, we detect members up to a faintness limit of ~22 mag including 21 BSSs, 2 yellow straggler stars (Y…
Chronology of our Galaxy from Gaia Colour-Magnitude Diagram-fitting (ChronoGal). I. The formation and evolution of the thin disk from the Gaia Catalogue of Nearby Stars
Stellar models for -2.5 <= [Fe/H] <= -0.5 that have been computed for variations in the C:N:O abundance ratio (for two different values of [CNO/Fe]) are compared with HST Wide Field Camera 3 (WFC3) observations of the globular clusters (GCs) 47 Tuc, NGC 6362, M5, M5, M55, and M92. The bolometric corrections used to transpose the models to the observed planes are based on new MARCS synthetic spectra that incorporate improved treatments of molecules that involve atoms of C, N, and O. On the assumption of well-supported distance moduli and reddenings, isochrones for [O/Fe] = 0.6 and [m/Fe] = 0.4 …
We recently found the globular cluster (GC) EXT8 in M31 to have an extremely low metallicity of [Fe/H]=-2.91+/-0.04 using high-resolution spectroscopy. Here we present a colour-magnitude diagram (CMD) for EXT8, obtained with the Wide Field Camera 3 on board the Hubble Space Telescope. Compared with the CMDs of metal-poor Galactic GCs, we find that the upper red giant branch (RGB) of EXT8 is about 0.03 mag bluer in F606W-F814W and slightly steeper, as expected from the low spectroscopic metallicity. The observed colour spread on the upper RGB is consistent with being caused entirely by the meas…
The open clusters NGC 2323 and NGC 2539 have been analysed using CCD UBV(RI)KC photometric data, observed at the San Pedro Martir Observatory. Cluster memberships have been determined with the proper motion and parallax measures from the GaiaDR2 astrometric data release. Photometric metal and heavy element abundances have been obtained as (M/H, Z) = (-0.10, 0.012) (NGC 2323) and (-0.31, 0.007) (NGC 2539), from the delta(U-B) technique in the two colour diagrams, which are used to select the appropriate PARSEC isochrones. The estimated reddening of NGC 2323 is E(B-V) = 0.23+-0.04 using 11 early…
We present the analysis of the colour-magnitude diagram (CMD) morphology of the ~ 800 Myr old star cluster NGC1831 in the Large Magellanic Cloud, exploiting deep, high-resolution photometry obtained using the Wide Field Camera 3 onboard the Hubble Space Telescope. We perform a simultaneous analysis of the wide upper main sequence and main sequence turn-off observed in the cluster, to verify whether these features are due to an extended star formation or a range of stellar rotation rates, or a combination of these two effects. Comparing the observed CMD with Monte Carlo simulations of synthetic…
Multiple stellar populations (MPs) in most star clusters older than 2 Gyr, as seen by lots of spectroscopic and photometric studies, have led to a significant challenge to the traditional view of star formation. In this field, space-based instruments, in particular the Hubble Space Telescope (HST), have made a breakthrough as they significantly improved the efficiency of detecting MPs in crowding stellar fields by images. The China Space Station Telescope (CSST) and the HST are sensitive to a similar wavelength interval, but it covers a field of view which is about 5-8 times wider than that of…
Multiple populations detection with the Chinese Space Station Survey Telescope main survey camera
School of Physics and Astronomy, Sun Yat-sen University（中山大学物理学院）；CSST Science Center for the Guangdong-Hong Kong-Macau Greater Bay Area（中国空间站巡天望远镜大湾区科学中心）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；Osservatorio Astronomico di Padova（帕多瓦天文台）；Dipartimento di Fisica e Astronomia “Galileo Galilei”, Univ. di Padova（帕多瓦大学伽利略物理学与天文学系）
We present a far-ultraviolet (FUV) study of the globular cluster M30 (NGC 7099). The images were obtained using the Advanced Camera for Surveys (ACS/SBC, F150LP, FUV) and the Wide Field Planetary Camera 2 (WFPC2, F300W, UV) which were both on board the Hubble Space Telescope (HST). The FUV-UV colour-magnitude diagram (CMD) shows a main sequence (MS) turnoff at FUV $\approx$ 22 mag and FUV-UV $\approx$ 3 mag. The MS extends 4 mag below the turnoff, and a prominent horizontal branch (HB) and blue straggler (BS) sequence can be seen. A total of 1218 MS stars, 185 red giant branch stars, 47 BS sta…
Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs
NGC 1984、NGC 1994和NGC 2011这三个大麦哲伦星云年轻星团的光学积分光谱显示出凹连续谱和突出的分子谱带，与单颗恒星星族（SSP）模型的预测结果有很大的偏差。为了了解这些光谱的外观，我们创建了一套年轻的恒星星族（英里）模型，我们提供给社会。我们使用档案国际紫外线探测器集成的紫外光谱独立约束的集群质量和消光，并排除强随机效应的光谱。此外，我们还分析了深颜色的星等图的集群提供独立的年龄测定等时线拟合的基础上。我们探讨的假设包括年龄蔓延的集群，头重脚轻的初始质量函数，不同的SSP模型和红超巨星（RSG）的作用。我们发现，在光学光谱中的强分子功能，只能通过建模增加约20%的RSG的光度以上的经典恒星演化模型预测的分数再现。由于在Myr年龄的恒星演化的不确定性，我们目前不能排除在这些星团中存在Myr年龄扩展。我们的工作结合了不同的波长以及不同的方法（解析数据以及同一样品的积分光谱），以揭示完整的图像。我们表明，每种方法提供了重要的信息，但结合起来，我们可以更好地了解集群恒星星族。
We made use of the Gaia DR2 archive to comprehensively study the Milky Way open cluster Collinder 347, known until now as a very young object of solar metal-content. However, the G versus G_BP-G_RP colour-magnitude diagram (CMD) of bonafide probable cluster members, selected on the basis of individual stellar proper motions, their spatial distribution and placement in the CMD, reveals the existence of a Hyades-like age open cluster (log(t /yr) = 8.8) of moderately metal-poor chemical content ([Fe/H] = -0.4 dex), with a present-day mass of 3.3x10^3 Mo. The cluster exhibits an extended Main-Sequ…
We present the UV photometry of the globular cluster NGC 1261 using images acquired with the Ultraviolet Imaging Telescope (UVIT) on-board ASTROSAT. We performed PSF photometry on four near-UV (NUV) and two far-UV (FUV) images and constructed UV colour-magnitude diagrams (CMDs), in combination with HST, Gaia, and ground-based optical photometry for member stars. We detected the full horizontal branch (HB) in NUV, blue HB in the FUV and identified two extreme HB (EHB) stars. HB stars have a tight sequence in UV-optical CMDs well-fitted with isochrones generated (12.6 Gyr age, [Fe/H] = -1.27 met…
