- ID:
- ivo://CDS.VizieR/J/ApJ/297/582
- Title:
- NGC 2213 BR photometry
- Short Name:
- J/ApJ/297/582
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The age of the LMC red globular cluster NGC 2213 has been estimated as 1.3+/-0.5x10^9^yr from a color-magnitude diagram, derived from CCD photometry, that reveals the cluster main sequence. The accuracy of the age estimate, however, is limited by uncertainly in the LMC distance modulus, by uncertainty in the cluster metal abundance which appears to lie in the range one-half to one-sixth solar, by uncertainty in the reddening of the cluster, and by uncertainty in the extent to which the theoretical isochrones used for the age dating are affected by the neglect, in standard stellar models, of the interior mixing caused by convective overshoot in the stellar cores. Using the adopted reddening of E(B-V)=0.09 and assuming Y=0.2, isochrone best fits to the cluster main sequence are found for [M/H]=-0.3 if (m-M)0=18.7 and for [M/H]=-0.7 if (m-M)0=18.2. After allowance for the possible effects of convective overshoot, the corresponding ages are 0.9^+0.5^_-0.3_ and 1.6^+0.8_^-0.4_x10^9^yr. Plausible alterations in the adopted reddening value and the adopted helium abundance also yield ages within these limits.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/298/544
- Title:
- NGC 121 BR photometry
- Short Name:
- J/ApJ/298/544
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The age of the SMC globular cluster NGC 121 is found from main-sequence isochrone fitting to be 12+/-2x10^9^yr if a distance modulus that assumes Mv=+0.6 for the field RR Lyrae variables near the cluster is used. If instead (m-M)o = 19.3, then the cluster age is 9+/-2x10^9^yr. The cluster is known to contain both RR Lyrae variables and a marginal carbon star; comparison with theoretical models indicates no significant inconsistencies in this joint occurrence at either modulus. The color-magnitude diagram for the nearby field also shows a faint, blue main-sequence turnoff and, in contrast to previous Magellanic Cloud field studies, the field lacks any evidence for the existence of a significant intermediate-age component. A new look at the chemical evolution of the Small Magellanic Cloud suggests that, unlike the Galaxy, where the rate of enrichment has been steady after the initial phase, the enrichment in the SMC remained small for a long interval before increasing rapidly sometime in the last 1-2x10^9^yr.
- ID:
- ivo://CDS.VizieR/J/A+A/351/526
- Title:
- NGC 2172 CCD BVI photometry
- Short Name:
- J/A+A/351/526
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new CCD photometry for the young LMC cluster NGC 2172, giving B, V, I magnitudes for more than 600 stars within 70" from the cluster center, down to -approximately- V=21mag. After correction for completeness and field stars contamination, we discuss the cluster HR diagram and the MS luminosity function in the light of current evolutionary theories and in connection with the problem of cluster age.
- ID:
- ivo://CDS.VizieR/J/AJ/133/44
- Title:
- NGC 346 HST VI photometry
- Short Name:
- J/AJ/133/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the quest to understand how star formation occurs and propagates in the low-metallicity environment of the Small Magellanic Cloud (SMC), we acquired deep F555W (~V) and F814W (~I) Hubble Space Telescope ACS images of the young and massive star-forming region NGC 346. These images and their photometric analysis provide us with a snapshot of the star formation history of the region. We find evidence for star formation extending from ~10Gyr in the past until ~150Myr in the field of the SMC. The youngest stellar population (~3+/-1Myr) is associated with the NGC 346 cluster. It includes a rich component of low-mass pre-main-sequence stars mainly concentrated in a number of subclusters spatially colocated with CO clumps previously detected by Rubio and coworkers. Within our analysis uncertainties, these subclusters appear coeval with each other.
- ID:
- ivo://CDS.VizieR/J/A+A/515/A56
- Title:
- NGC 346/N66 JHKs photometry
- Short Name:
- J/A+A/515/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The emission nebula N66 is the brightest HII Region in the Small Magellanic Cloud (SMC), with the stellar association NGC 346 located in its center. The youthfulness of the region NGC 346/N66 is well documented by studies of the gas and dust emission, and the detection in the optical of a rich sample of pre-main sequence (PMS) stars, and in the mid- and far-IR of Young Stellar Objects (YSOs). However, there is a lack of a comprehensive study of this region in the near-IR that will bridge the previous surveys. We perform a photometric analysis on deep, seeing-limited near-IR VLT images of the region NGC 346/N66 and a nearby control field of the SMC in order to locate the centers of active high- and intermediate-mass star formation through the identification of near-IR bright objects as candidate stellar sources under formation. We use archived imaging data obtained with the high-resolution camera ISAAC at VLT of NGC 346/N66 and we construct the near-IR color-magnitude (CMD) and color-color diagrams (C-CD) of all detected sources. We investigate the nature of all stellar populations in the observed CMDs, and we identify all stellar sources that show significant near-IR excess emission in the observed C-CD. We select, thus, the best candidates for being young stellar sources. Results. Based on their near-IR colors we select 263 candidate young stellar sources. This sample comprises a variety of objects such as intermediate-mass PMS and Herbig Ae/Be stars and possibly massive YSOs, providing original near-IR colors for them. The spatial distribution of the selected candidate sources shows that they are located along the dusty filamentary structures of N66 seen in mid- and far-IR dust emission and agrees very well with that of previously detected candidate YSOs and PMS stars.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A147
- Title:
- NGC 2070 point sources radial velocities
- Short Name:
- J/A+A/614/A147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We introduce VLT-MUSE observations of the central 2'x2' (30x30pc) of the Tarantula Nebula in the Large Magellanic Cloud. The observations provide an unprecedented spectroscopic census of the massive stars and ionised gas in the vicinity of R136, the young, dense star cluster located in NGC 2070, at the heart of the richest star-forming region in the Local Group. Spectrophotometry and radial-velocity estimates of the nebular gas (superimposed on the stellar spectra) are provided for 2255 point sources extracted from the MUSE datacubes, and we present estimates of stellar radial velocities for 270 early-type stars (finding an average systemic velocity of 271+/-41km/s). We present an extinction map constructed from the nebular Balmer lines, with electron densities and temperatures estimated from intensity ratios of the [SII], [NII], and [SIII] lines. The interstellar medium, as traced by H{alpha} and [NII] {lambda}6583, provides new insights in regions where stars are probably forming. The gas kinematics are complex, but with a clear bi-modal, blue- and red-shifted distribution compared to the systemic velocity of the gas centred on R136. Interesting point-like sources are also seen in the eastern cavity, western shell, and around R136; these might be related to phenomena such as runaway stars, jets, formation of new stars, or the interaction of the gas with the population of Wolf-Rayet stars. Closer inspection of the core reveals red-shifted material surrounding the strongest X-ray sources, although we are unable to investigate the kinematics in detail as the stars are spatially unresolved in the MUSE data. Further papers in this series will discuss the detailed stellar content of NGC 2070 and its integrated stellar and nebular properties.
387. NGC 330 seen by MUSE
- ID:
- ivo://CDS.VizieR/J/A+A/634/A51
- Title:
- NGC 330 seen by MUSE
- Short Name:
- J/A+A/634/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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 10-40Myr, 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 Magellanic Cloud. Using MUSE WFM-AO observations of NGC 330, we resolve the dense cluster core for the first time and are able to extract spectra of its entire massive star population. We develop an automated spectral classification scheme based on the equivalent widths of spectral lines in the red part of the spectrum. We characterize the massive star content of the core of NGC 330 which contains more than 200 B stars, 2 O stars, 6 A-type supergiants and 11 red supergiants. We find a lower limit on the Be star fraction of 32+/-3% in the whole sample. It increases to at least 46+/-10% when only considering stars brighter than V=17mag. We estimate an age of the cluster core between 35 and 40Myr and a total cluster mass of 88^+17^_-18_*10^3M_{sun}_. We find that the population in the cluster core is different than the population in the outskirts: while the stellar content in the core appears to be older than the stars in the outskirts, the Be star fraction and the observed binary fraction are significantly higher. Furthermore, we detect several BiP candidates that will be subject of future studies.
- ID:
- ivo://CDS.VizieR/J/A+A/652/A70
- Title:
- NGC 330 seen by MUSE. II.
- Short Name:
- J/A+A/652/A70
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Observations of massive stars in open clusters younger than 8 Myr have shown that a majority of them are in binary systems, most of which will interact during their life. While these can be used as a proxy of the initial multiplicity properties, studying populations of massive stars older than ~20Myr allows us to probe the outcome of such interactions after a significant number of systems have experienced mass and angular momentum transfer and possibly even merged. Using multi-epoch integral-field spectroscopy, we aim to investigate the multiplicity properties of the massive-star population in the dense core of the ~40Myr-old cluster NGC 330 in the Small Magellanic Cloud in order to search for possible imprints of stellar evolution on the multiplicity properties. We obtained six epochs of VLT/MUSE observations operated in wide-field mode with the extended wavelength setup and supported by adaptive optics.We extract spectra and measure radial velocities for stars brighter than m_F814W_=19. We identify single-lined spectroscopic binaries through significant RV variability with a peak-to-peak amplitude larger than 20km/s. We also identify double-lined spectroscopic binaries, and quantify the observational biases for binary detection. In particular, we take into account that binary systems with similar line strength are difficult to detect in our data set. The observed spectroscopic binary fraction among the stars brighter than m_F814W_=19 (~5.5M_{sun}_ on the main sequence) is f^obs^_SB_=13.2+/-2:0%. Considering period and mass ratio ranges from log(P)=0.15-3.5 (about 1.4 to 3160d), and q=0.1-1.0, and a representative set of orbital parameter distributions, we find a bias-corrected close binary fraction of f_cl_=34^+8^_-7_%. This fraction seems to decline for the fainter stars, which indicates either that the close binary fraction drops in the B-type domain, or that the period distribution becomes more heavily weighted towards longer orbital periods.We further find that both fractions vary strongly in different regions of the color-magnitude diagram that corresponds to different evolutionary stages. This probably reveals the imprint of the binary history of different groups of stars. In particular, we find that the observed spectroscopic binary fraction of Be stars (f^obs^_SB_=2+/-2%) is significantly lower than the one of B-type stars (f^obs^_SB_=9+/-2%). In this work we provide the first homogeneous RV study of a large sample of B-type stars at a low metallicity ([Fe/H]<~-1.0). The overall bias-corrected close binary fraction (log(P)<3.5d) of the B-star population in NGC 330 is lower than the one reported for younger Galactic and LMC clusters in previous works. More data are, however, needed to establish whether the observed differences result from an age or a metallicity effect.
- ID:
- ivo://CDS.VizieR/J/AJ/153/126
- Title:
- NIR polarimetric study in the LMC N159/N160 field
- Short Name:
- J/AJ/153/126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared polarimetric results for the N159/N160 star-forming complex in the Large Magellanic Cloud with SIRPOL, the polarimeter of the Infrared Survey Facility. We separated foreground sources using their visual extinction derived from near-infrared photometric data. The 45 young stellar candidates and 2 high-excitation blobs were matched with our sources, and 12 of them showed high polarization that did not originate from the interstellar dust. We made a polarimetric catalog of 252, 277, and 89 sources at the J, H, and K_s_ bands, respectively. Based on the ratios of the polarization degree between these bands, we verify that the origin of these polarized sources is the dichroic extinction from the interstellar dust aligned by the magnetic field and that the ratios follow a power-law dependence of P_{lambda}_~{lambda}^-0.9^. The linear polarization vectors projected onto the H{alpha} image of the complex turned out to follow the local magnetic field structure. The vector map overlaid on dust and gas emissions shows the close correlation between the magnetic field structure and surrounding interstellar medium. We suggest that the derived magnetic field structure supports the sequential formation scenario of the complex.
- ID:
- ivo://CDS.VizieR/J/ApJS/222/2
- Title:
- NIR sources in the northeastern part of LMC
- Short Name:
- J/ApJS/222/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a near-infrared band-merged photometric and polarimetric catalog for the 39'x69' fields in the northeastern part of the Large Magellanic Cloud (LMC), which were observed using SIRPOL, an imaging polarimeter of the InfraRed Survey Facility. This catalog lists 1858 sources brighter than 14mag in the H band with a polarization signal-to-noise ratio greater than three in the J, H, or K_s_ bands. Based on the relationship between the extinction and the polarization degree, we argue that the polarization mostly arises from dichroic extinctions caused by local interstellar dust in the LMC. This catalog allows us to map polarization structures to examine the global geometry of the local magnetic field, and to show a statistical analysis of the polarization of each field to understand its polarization properties. In the selected fields with coherent polarization position angles, we estimate magnetic field strengths in the range of 3-25{mu}G using the Chandrasekhar-Fermi method. This implies the presence of large-scale magnetic fields on a scale of around 100 parsecs. When comparing mid- and far-infrared dust emission maps, we confirmed that the polarization patterns are well aligned with molecular clouds around the star-forming regions.
