We present observations of the most bright main sequence stars in the Small Magellanic Cloud stellar cluster NGC330 obtained with the integral field spectrograph MUSE@VLT. The use of this valuable instrument allows us to study both photometric and spectroscopic properties of stellar populations of this young star cluster.
The photometric data provide us a precise color magnitude diagram, which seems to support the presence of two stellar populations of ages of $\sim$ 18 Myr and $\sim$ 30 Myr assuming a metallicity of Z = 0.002. Thanks to the spectroscopic data, we derive helium abundance of 10 main sequence stars within the effective radius Reff= 20" of NGC330, thus leading to an estimation of $ε(He)$ = 10.93 $\pm$ 0.05 (1$σ$ ). The helium elemental abundances of stars likely belonging to the two possible stellar populations, do not show differences or dichotomy within the uncertainties. Thus, our results suggest that the two stellar populations of NGC330, if they exist, share similar original He abundances.
If we consider stellar rotation velocity in our analysis, a coeval (30 Myr) stellar population, experiencing different values of rotation, cannot be excluded. In this case, the mean helium abundance < $ε(He)$ >rot obtained in our analysis is 11.00 $\pm$ 0.05 dex. We also verified that possible NLTE effects cannot be identified with our analysis because of the spectral resolution and they are within our derived abundance He uncertainties.
Moreover, the analysis of the He abundance as a function of the distance from the cluster center of the observed stars do not show any correlation.
We present MUSE integral field data of two HII region complexes in the Large Magellanic Cloud (LMC), N44 and N180. Both regions consist of a main superbubble and a number of smaller, more compact HII regions that formed on the edge of the superbubble. For a total of 11 HII regions, we systematically analyse the radiative and mechanical feedback from the massive O-type stars on the surrounding gas. We exploit the integral field property of the data and the coverage of the HeII$λ$5412 line to identify and classify the feedback-driving massive stars, and from the estimated spectral types and lumi…
The multiple stellar populations (MPs) of $\sim$11-13 Gyr-old Globular Clusters (GCs) in our Galaxy are characterized by different content of several light elements. These elements describe well-defined patterns like the C-N and the Na-O anticorrelations and the He-N and Na-N correlations. The discovery of the MPs in Magellanic Cloud GCs opened up new paths for the investigation of chemical anomalies in clusters with different age and physical properties. In this context, we used Hubble Space Telescope photometry to investigate the MPs and constrain their chemical composition of four $\sim$6-1…
Intermediate-age star clusters in the Magellanic Clouds harbour signatures of the multiple stellar populations long thought to be restricted to old globular clusters. We compare synthetic horizontal branch models with Hubble Space Telescope photometry of clusters in the Magellanic Clouds, with age between ~2 and ~10 Gyr, namely NGC 121, Lindsay 1, NGC 339, NGC 416, Lindsay 38, Lindsay 113, Hodge 6 and NGC 1978. We find a clear signature of initial helium abundance spreads (delta(Y)) in four out of these eight clusters (NGC 121, Lindsay 1, NGC 339, NGC 416) and we quantify the value of delta(Y)…
We provide an overview of Science Verification MUSE observations of NGC 2070, the central region of the Tarantula Nebula in the Large Magellanic Cloud. Integral-field spectroscopy of the central 2' x 2' region provides the first complete spectroscopic census of its massive star content, nebular conditions and kinematics. The star-formation surface density of NGC 2070 is reminiscent of the intense star-forming knots of high-redshift galaxies, with nebular conditions similar to low-redshift Green Pea galaxies, some of which are Lyman continuum leakers. Uniquely, MUSE permits the star-formation h…
We have observed the oxygen-rich SNR 1E 0102.2-7219 with the integral field spectrograph WiFeS at Siding Spring Observatory and discovered sulfur-rich ejecta for the first time. Follow-up deep DDT observations with MUSE on the VLT (8100 s on source) have led to the additional discovery of fast- moving hydrogen as well as argon-rich and chlorine-rich material. The detection of fast-moving hydrogen knots challenges the interpretation that the progenitor of 1E 0102 was a compact core of a Wolf-Rayet star that had shed its entire envelope. In addition to the detection of hydrogen and the products …
We present adaptive optics (AO) assisted integral-field spectroscopy of the intermediate-age star cluster NGC 419 in the Small Magellanic Cloud. By investigating the cluster dynamics and the rotation properties of main sequence turn-off stars (MSTO), we demonstrate the power of AO-fed MUSE observations for this class of objects. Based on 1 049 radial velocity measurements, we determine a dynamical cluster mass of 1.4+/-0.2x10^5 M_sun and a dynamical mass-to-light ratio of 0.67+/-0.08, marginally higher than simple stellar population predictions for a Kroupa initial mass function. A stacking an…
We use HST observations to study the LMC's young cluster NGC1844. We estimate the fraction and the mass-ratio distribution of photometric binaries and report that the main sequence presents an intrinsic breadth which can not be explained in terms of photometric errors only, and is unlikely due to differential reddening. We attempt some interpretation of this feature, including stellar rotation, binary stars, and the presence of multiple stellar populations with different age, metallicity, helium, or C+N+O abundance. Although we exclude age, helium, and C+N+O variations to be responsible of the…
Excitation of radial pulsations in red supergiants of Magellanic Clouds is investigated using the stellar evolution calculations and the self-consistent solution of the equations of radiation hydrodynamics and turbulent convection. The stars with initial masses 6M_odot<=M_zams<=28 M_odot and the initial chemical composition X=0.7, 0.004<=Z<=0.008 are shown to be unstable against fundamental mode oscillations with periods from 17 to 1200 days as they become helium burning red supergiants. The period-luminosity relation slightly depends on the mass loss rate varying with a factor of three, where…
MASYS is the AKARI spectroscopic survey of Symbiotic Stars in the Magellanic Clouds, and one of the European Open Time Observing Programmes approved for the AKARI (Post-Helium) Phase-3. It is providing the first ever near-IR spectra of extragalactic symbiotic stars. The observations are scheduled to be completed in July 2009.
Using a combination of high-resolution Hubble Space Telescope/WFPC2 observations, we explore the physical properties of the stellar populations in two intermediate-age star clusters in the Large Magellanic Cloud, NGC 1831 and NGC 1868, based on their color-magnitude diagrams. We show that both clusters exhibit extended main-sequence turn-offs. To explain the observations, we consider variations in helium abundance, binarity, age dispersions, and fast rotation of the clusters' member stars. The observed narrow main sequence excludes significant variations in helium abundance in both clusters. W…
We present the spectroscopic analysis of 333 OB-type stars extracted from VLT-MUSE observations of the central 30 x 30 pc of NGC 2070 in the Tarantula Nebula on the Large Magellanic Cloud, the majority of which are analysed for the the first time. The distribution of stars in the spectroscopic Hertzsprung-Russell diagram (sHRD) shows 281 stars in the main sequence. We find two groups in the main sequence, with estimated ages of 2.1$\pm$0.8 and 6.2$\pm$2 Myr. A subgroup of 52 stars is apparently beyond the main sequence phase, which we consider to be due to emission-type objects and/or signific…
Ancient ($>$10 Gyr) globular clusters (GCs) show chemical abundance variations in the form of patterns among certain elements, e.g. N correlates with Na and anti-correlates with O. Recently, N abundance spreads have also been observed in massive star clusters that are significantly younger than old GCs, down to an age of $\sim$2 Gyr. However, so far N has been the only element found to vary in such young objects. We report here the presence of Na abundance variations in the intermediate age massive star clusters NGC 416 ($\sim$6.5 Gyr old) and Lindsay 1 ($\sim$7.5 Gyr old) in the Small Magella…
A quantitative spectral analysis of BA-type supergiants and bright giants in an inner spiral arm region of the nearby spiral galaxy NGC 300 is presented, based on observations with the Multi Unit Spectroscopic Explorer (MUSE) on the European Southern Obsevatory, Very Large Telescope (ESO, VLT). The flux-weighted gravity-luminosity relationship (FGLR), a stellar spectroscopic distance determination method for galaxies, is extended towards stars at lower luminosities. Point spread function fitting 3D spectroscopy was performed with PampelMUSE on the datacube. The 16 stars with the highest signal…
One of the most interesting results from the OGLE-III study of the LMC Cepheids is the large number of objects that pulsate simultaneously in the first and second overtone (denoted 1O/2O). Double-mode Cepheids yield important constraint on stellar evolution models. We show that great majority of the LMC 1O/2O Cepheids have masses M=3.0+/-0.5 Msun. According to current stellar evolution calculations, these masses are lower than needed for the blue loop in the helium burning phase to reach the instability strip. On the other hand, we found most of these stars significantly overluminous if they a…
$ω$ Cen is a rare example of a globular cluster where the iron abundance of the stars spans more than one order of magnitude. Many spectroscopic investigations of its red-giant- and sub-giant- branches have revealed multiple peaks in the iron abundance distribution. The metallicity distribution of main-sequence (MS) stars is not well characterized yet, due to the faintness of the stars and lack of data. So far, almost all studies of MS stars are based on photometric measurements. Our goal is to investigate the metallicity distribution of a statistically significant sample of MS stars in $ω$ Ce…
Nearly all of the well studied ancient globular clusters (GCs), in the Milky Way and in nearby galaxies, show star-to-star variations in specific elements (e.g., He, C, N, O, Na, Al), known as "multiple populations" (MPs). However, MPs are not restricted to ancient clusters, with massive clusters down to $\sim2$ Gyr showing signs of chemical variations. This suggests that young and old clusters share the same formation mechanism but most of the work to date on younger clusters has focused on N-variations. Initial studies even suggested that younger clusters may not host spreads in other elemen…
We started a photometric survey using the WFC3/UVIS instrument onboard the Hubble Space Telescope to search for multiple populations within Magellanic Cloud star clusters at various ages. In this paper, we introduce this survey. As first results of this programme, we also present multi-band photometric observations of NGC 121 in different filters taken with the WFC3/UVIS and ACS/WFC instruments. We analyze the colour-magnitude diagram (CMD) of NGC 121, which is the only "classical" globular cluster within the Small Magellanic Cloud. Thereby, we use the pseudo-colour C_(F336W,F438W,F343N)=(F336…
Massive stars at low metallicity are among the main feedback agents in the early Universe and in present-day star forming galaxies. When in binaries, these stars are potential progenitors of gravitational-wave events. Knowledge of stellar masses is a prerequisite to understanding evolution and feedback of low-metallicity massive stars. Using abundant spectroscopic and photometric measurements of an outstandingly bright eclipsing binary, we compare its dynamic, spectroscopic, and evolutionary mass estimates and develop a binary evolution scenario. We comprehensively studied the eclipsing binary…
Context. The evolution of massive stars is strongly influenced by internal mixing processes such as semiconvection, convective core overshooting, and rotationally induced mixing. None of these is currently well constrained. Aims. We investigate models for massive stars in the Small Magellanic Cloud (SMC). We aim to constrain the various mixing efficiencies by comparing model results to observations. Methods. We use the stellar evolution code MESA to compute more than 60 grids of detailed evolutionary models for stars with initial masses of 9 to 100 Msol, in each grid assuming different combina…
A majority of massive stars are part of binary systems, a large fraction of which will inevitably interact during their lives. Binary-interaction products (BiPs), i.e. stars affected by such interaction, are expected to be commonly present in stellar populations. BiPs are thus a crucial ingredient in the understanding of stellar evolution. We aim to identify and characterize a statistically significant sample of BiPs by studying clusters of 10-40 Myr, an age at which binary population models predict the abundance of BiPs to be highest. One example of such a cluster is NGC 330 in the Small Mage…
ABRIDGED: 2D spectroscopic MUSE data for the whole extent of NGC3132 have been reduced and analised. The dust extinction, electron densities and temperatures of the ionised gas and abundances were determined. The nebula presents a complex reddening structure with high values (c(Hb)~0.4) at the rim. Density maps are compatible with an inner high-ionisation plasma at moderate high density (~1000cm^-3) while the low-ionisation plasma presents a structure in density peaking at the rim with values ~700 cm^-3. Median Te using different diagnostics decreases according to the sequence [NII],[SII]->[SI…
Observations of massive stars in young open clusters (< ~8 Myr) have shown that a majority of them are in binary systems, most of which will interact during their life. Populations of massive stars older than ~20 Myr allow us to probe the outcome of such interactions after many systems have experienced mass and angular momentum transfer. Using multi-epoch integral-field spectroscopy, we investigate the multiplicity properties of the massive-star population in NGC 330 (~40 Myr) in the Small Magellanic Cloud to search for imprints of stellar evolution on the multiplicity properties. From six epo…
We have demonstrated the advantage of combining multi-wavelength observations, from the ultraviolet (UV) to near-infrared, to study Kron 3, a massive star cluster in the Small Magellanic Cloud. We have estimated the radius of the cluster Kron 3 to be 2.'0 and for the first time, we report the identification of NUV-bright red clump (RC) stars and the extension of the RCin colour and magnitude in the NUV vs (NUV-optical) colour-magnitude diagram (CMD). We found that extension of the RC is an intrinsic property of the cluster and it is not due to contamination of field stars or differential redde…
Nearly all the star clusters with ages of ~1-2 Gyr in both Magellanic Clouds exhibit an extended main-sequence turn off (eMSTO) whose origin is under debate. The main scenarios suggest that the eMSTO could be either due to multiple generations of stars with different ages or to coeval stellar populations with different rotation rates. In this paper we use Hubble-Space-Telescope images to investigate the ~80-Myr old cluster NGC1755 in the LMC. We find that the MS is split with the blue and the red MS hosting about the 25% and the 75% of the total number of MS stars, respectively. Moreover, the …
This is the second paper in a series aiming at the analysis of nitrogen abundances in O-type stars, to enable further constraints on the early evolution of massive stars. We investigate the NIV lambda4058 emission line formation, provide nitrogen abundances for a substantial O-star sample in the LMC, and compare our findings with recent predictions from stellar evolutionary models. Stellar and wind parameters are determined by line profile fitting of hydrogen, helium and nitrogen lines, based on synthetic spectra calculated by FASTWIND. We derive nitrogen abundances for 20 O- and 5 B-stars, by…
Massive star evolution at low metallicity is closely connected to many fields in high-redshift astrophysics, but poorly understood. The Small Magellanic Cloud (SMC) is a unique laboratory to study this because of its metallicity of 0.2 Zsol, its proximity, and because it is currently forming stars. We used a spectral type catalog in combination with GAIA magnitudes to calculate temperatures and luminosities of bright SMC stars. By comparing these with literature studies, we tested the validity of our method, and using GAIA data, we estimated the completeness of stars in the catalog as a functi…
Multiple Populations of the Large Magellanic Cloud Globular Cluster NGC 2257: No Major Environmental Effect on the Formation of Multiple Populations of the Old Globular Clusters in Large Magellanic Cloud
本研究通过 Ca–CN–CH 测光分析年老贫金属 LMC 球状星团 NGC 2257 的多族群，发现其族群比例、金属丰度及元素变化趋势与银河系普通球状星团一致，表明宿主星系环境对多族群形成演化无重大影响。
We discuss new photometry from high-resolution images of 7 intermediate-age (1-2 Gyr) star clusters in the Large Magellanic Cloud taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. We fit color-magnitude diagrams (CMDs) with several different sets of theoretical isochrones, and determine systematic uncertainties for population parameters when derived using any one set of isochrones. The cluster CMDs show several interesting features, including extended main sequence turnoff (MSTO) regions, narrow red giant branches, and clear sequences of unresolved binary stars. W…
The Stripped-Star Ultraviolet Magellanic Cloud Survey (SUMS): The UV Photometric Catalog and Stripped Star Candidate Selection
University of Toronto（多伦多大学）；KU Leuven（荷语鲁汶大学）；Institute of Science and Technology Austria (ISTA)（奥地利科学技术研究所）；Perimeter Institute for Theoretical Physics（理论物理珀西默研究所）
We present new theoretical stellar yields and surface abundances for asymptotic giant branch (AGB) models with a metallicity appropriate for stars in the Small Magellanic Cloud (SMC, $Z= 0.0028$, [Fe/H] $\approx -0.7$). New evolutionary sequences and post-processing nucleosynthesis results are presented for initial masses between 1$M_{\odot}$ and 7$M_{\odot}$, where the 7$M_{\odot}$ is a super-AGB star with an O-Ne core. Models above 1.15$M_{\odot}$ become carbon rich during the AGB, and hot bottom burning begins in models $M \ge 3.75 M_{\odot}$. We present stellar surface abundances as a func…
We performed a new and accurate fit of light and radial velocity curves of the Large Magellanic Cloud (LMC) Cepheid --OGLE-LMC-CEP-0227-- belonging to a detached double-lined eclipsing binary system. We computed several sets of nonlinear, convective models covering a broad range in stellar mass, effective temperature and in chemical composition. The comparison between theory and observations indicates that current theoretical framework accounts for luminosity --V and I band-- and radial velocity variations over the entire pulsation cycle. Predicted pulsation mass --M=4.14+-0.06 Mo-- and mean e…
Without doubt, mass transfer in close binary systems contributes to the populations of Wolf-Rayet (WR) stars in the Milky Way and the Magellanic Clouds. However, the binary formation channel is so far not well explored. We want to remedy this by exploring large grids of detailed binary and single star evolution models computed with the publicly available MESA code, for a metallicity appropriate for the Large Magellanic Cloud (LMC). The binary models are calculated through Roche-lobe overflow and mass transfer, until the initially more massive star exhausts helium in its core. We distinguish mo…
We present new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Eight out of the 14 are RR Lyrae (RRL) stars, four are Anomalous Cepheids (ACs) and two are geometrical variables. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dSphs and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties. This finding is also supported by the RRL…
Theoretical estimates of the pulsation period change rates in LMC Cepheids are obtained from consistent calculation of stellar evolution and nonlinear stellar pulsation for stars with initial chemical composition X=0.7, Z=0.008, initial masses 5M_\odot <= Mzams <= 9M_\odot and pulsation periods ranged from 2.2 to 29 day. The Cepheid hydrodynamical models correspond to the evolutionary stage of thermonuclear core helium burning. During evolution across the instability strip in the HR diagram the pulsation period of Cepheids is the quadratic function of the evolution time for the both fundamenta…
Models for the progenitor systems of Type Ia supernovae can be divided into double-degenerate systems, which contain two white dwarfs, and single-degenerate systems, which contain one white dwarf plus one companion star (either a red giant, a subgiant, or a >1.16 M_sol main sequence star). The white dwarf is destroyed in the supernova explosion, but any non-degenerate companion remains intact. We present the results of a search for an ex-companion star in SNR 0519-69.0, located in the Large Magellanic Cloud, based on images taken with the Hubble Space Telescope with a limiting magnitude of V =…
We present a clean, magnitude-limited (IRAC1 or WISE1$\leq$15.0 mag) multiwavelength source catalog for the LMC. The catalog was built upon crossmatching ($1''$) and deblending ($3''$) between the SEIP source list and Gaia DR2, with strict constraints on the Gaia astrometric solution to remove the foreground contamination. The catalog contains 197,004 targets in 52 different bands including 2 ultraviolet, 21 optical, and 29 infrared bands. Additional information about radial velocities and spectral/photometric classifications were collected from the literature. The bright end of our sample is …
The majority of Wolf-Rayet (WR) stars represent the stripped cores of evolved massive stars who lost most of their hydrogen envelope. In low metallicity environments, such as the Small Magellanic Cloud (SMC), stellar winds are weaker and binary interaction is expected to dominate WR-star formation. However, the WR binary fraction appears to be ~40% at any metallicity. We use the recently determined physical properties of the twelve known SMC WR stars to explore their possible formation channels through comparisons with grids of SMC models, simulated with the detailed stellar evolution code MES…
We report the detection of a black hole (NGC 1850 BH1) in the $\sim$100 Myr-old massive cluster NGC~1850 in the Large Magellanic Cloud. It is in a binary system with a main-sequence turn-off star (4.9 $\pm$ 0.4 M${_\odot}$), which is starting to fill its Roche Lobe and becoming distorted. Using 17 epochs of VLT/MUSE observations we detected radial velocity variations exceeding 300 km/s associated to the target star, linked to the ellipsoidal variations measured by OGLE-IV in the optical bands. Under the assumption of a semi-detached system, the simultaneous modelling of radial velocity and lig…
We report the first-ever discovery of a Wolf-Rayet (WR) star in the Large Magellanic Cloud via detection of a circular shell with the Spitzer Space Telescope. Follow-up observations with Gemini-South resolved the central star of the shell into two components separated from each other by approx 2 arcsec (or approx 0.5 pc in projection). One of these components turns out to be a WN3 star with H and He lines both in emission and absorption (we named it BAT99 3a using the numbering system based on extending the Breysacher et al. catalogue). Spectroscopy of the second component showed that it is a …
Revealing Optically Hidden Companions to Intermediate-Mass Stripped Stars with Radial Velocities
University of Toronto（多伦多大学）；Dunlap Institute for Astronomy & Astrophysics, University of Toronto（多伦多大学邓普天文学与天体物理研究所）；Institute of Science and Technology Austria (ISTA)（奥地利科学与技术研究院）
We exploit multi-band Hubble Space Telescope photometry to investigate multiple populations (MPs) along the red horizontal branches (HBs) and red clumps of fourteen metal-rich Globular Clusters (GCs), including twelve Milky Way GCs and the Magellanic Cloud GCs NGC 1978 and NGC 416. Based on appropriate two-color diagrams we find that the fraction of 1G stars in Galactic GCs correlates with cluster mass, confirming previous results based on red-giant branch (RGB) stars. Magellanic-Cloud GCs show higher fractions of 1G stars than Galactic GCs with similar masses, thus suggesting that the environ…
Recent studies have revealed that the Multiple Populations (MPs) phenomenon does not occur only in ancient and massive Galactic globular clusters (GCs), but it is also observed in external galaxies, where GCs sample a wide age range with respect to the Milky Way. However, for a long time, it was unclear whether we were looking at the same phenomenon in different environments or not. The first evidence that the MPs phenomenon is the same regardless of cluster age and host galaxy came out recently when an intermediate-age cluster from the Small Magellanic Cloud, Lindsay 1, and a Galactic GC have…
