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- ID:
- ivo://CDS.VizieR/J/PASP/98/1133
- Title:
- The open cluster NGC 346
- Short Name:
- J/PASP/98/1133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD photometry and spectrographic observations for stars in the open cluster NGC 346, which excites the largest H II region in the Small Magellanic Cloud. These observations show that NGC 346 is an extremely young cluster, containing more than 20 hot O-type stars. A radial-velocity study of the brightest stars, and also of the nearby supergiant Of star Sk 80, discloses atmospheric expansion due to strong stellar winds, but no large-amplitude radial-velocity variations due to short-period binary motion. However, two stars are probably longer period binaries.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A65
- Title:
- The sHRD of OB stars in NGC 2070
- Short Name:
- J/A+A/648/A65
- Date:
- 06 Dec 2021 13:26:57
- Publisher:
- CDS
- Description:
- We present the spectroscopic analysis of 333 OB-type stars extracted from VLT-MUSE observations of the central 30x30pc of NGC 2070 in the Tarantula Nebula on the Large Magellanic Cloud, the majority of which are analysed for 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+/-0.8 and 6.2+/-2Myr. A subgroup of 52 stars is apparently beyond the main sequence phase, which we consider to be due to emission-type objects and/or significant nebular contamination affecting the analysis. As in previous studies, stellar masses derived from the sHRD are systematically larger than those obtained from the conventional HRD, with the differences being largest for the most massive stars. Additionally, we do not find any trend between the estimated projected rotational velocity and evolution in the sHRD. The projected rotational velocity distribution presents a tail of fast rotators that resembles findings in the wider population of 30 Doradus. We use published spectral types to calibrate the HeI{lambda}4921/HeII{lambda}5411 equivalent-width ratio as a classification diagnostic for early-type main sequence stars when the classical blue-visible region is not observed. Our model-atmosphere analyses demonstrate that the resulting calibration is well correlated with effective temperature.
- ID:
- ivo://CDS.VizieR/J/AJ/138/1243
- Title:
- The star formation history of the LMC
- Short Name:
- J/AJ/138/1243
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first ever global, spatially resolved reconstruction of the star formation history (SFH) of the Large Magellanic Cloud (LMC), based on the application of our StarFISH analysis software to the multiband photometry of 20 million of its stars from the Magellanic Clouds Photometric Survey (MCPS). The general outlines of our results are consistent with previously published results: following an initial burst of star formation, there was a quiescent epoch from approximately 12 to 5Gyr ago. Star formation then resumed and has proceeded until the current time at an average rate of roughly 0.2M_{sun}_/yr, with temporal variations at the factor of 2 level.
- ID:
- ivo://CDS.VizieR/J/ApJ/868/47
- Title:
- The 1st year of the Swift SMC Survey (S-CUBED)
- Short Name:
- J/ApJ/868/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Swift Small Magellanic Cloud (SMC) Survey, S-CUBED, is a high-cadence shallow X-ray survey of the SMC. The survey consists of 142 tiled pointings covering the optical extent of the SMC, which is performed weekly by NASA's Neil Gehrels Swift Observatory, with an exposure per tile of 60s. The survey is focused on discovery and monitoring of X-ray outbursts from the large known and unknown population of Be/X-ray binaries (BeXRBs) in the SMC. Given the very low background of Swift's X-ray telescope, even with a short exposure per tile, S-CUBED is typically sensitive to outbursts in the SMC at >1%-2% Eddington luminosity for a typical 1.4M_{sun}_ neutron star compact object. This sensitivity, combined with the high cadence and the fact that the survey can be performed all year round, makes it a powerful discovery tool for outbursting accreting X-ray pulsars in the SMC. In this paper we describe results from the first year of observations of S-CUBED, which includes the 1SCUBEDX catalog of 265 X-ray sources, 160 of which are not identified with any previously cataloged X-ray source. We report on bulk properties of sources in the 1SCUBEDX catalog. Finally, we focus on results of S-CUBED observations of several interesting sources, which includes discovery of three Type II outbursts from BeXRBs and the detection of Type I outbursts and orbital periods in six BeXRB systems.
- ID:
- ivo://CDS.VizieR/J/ApJS/224/21
- Title:
- The VMC survey. XIX. Classical Cepheids in SMC
- Short Name:
- J/ApJS/224/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The "VISTA near-infrared YJK_s_ survey of the Magellanic Clouds System" (VMC) is collecting deep K_s_-band time-series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y, J, K_s_ light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period-luminosity (PL), period-luminosity-color (PLC), and period-Wesenheit (PW) relationships, which are valid for Fundamental (F), First Overtone (FO), and Second Overtone (SO) pulsators. The relations involving the V, J, K_s_ bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge, we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near-infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V, K_s_) to estimate the relative SMC-LMC distance and, in turn, the absolute distance to the SMC. For the former quantity, we find a value of {Delta}{mu}=0.55+/-0.04mag, which is in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are {mu}_SMC_=19.01+/-0.05mag and {mu}_SMC_=19.04+/-0.06mag, based on two distance measurements to the LMC which rely on accurate CC and eclipsing Cepheid binary data, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/158/185
- Title:
- Three binary systems in the Large Magellanic Cloud
- Short Name:
- J/AJ/158/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the physical properties and apsidal motion elements of three eccentric eclipsing binaries in the Large Magellanic Cloud. The time-series photometric observations were carried out for a total of 41 nights between 2018 November and 2019 February using the KMTNet 1.6 m telescopes installed in South Africa and Australia. The radial velocities of binary components were measured using about 15 spectra per system collected from the ESO Science Archive Facility, which were observed with the Very Large Telescope 8.2 m telescope. The effective temperatures of the more massive binary components were determined to be 19000+/-500 K for OGLE-LMC-ECL-05797, 17000+/-500 K for OGLE-LMC-ECL-05861, and 19000+/-500 K for OGLE-LMC-ECL-06510 by comparing the observed spectra and the stellar atmosphere models obtained from the BOSZ spectral library. The absolute dimensions of each system were derived by analyzing the radial velocity curves together with the light curves obtained from the KMTNet, OGLE, and MACHO observations during about three decades. For the apsidal motion study, new eclipse timings were derived from the KMTNet and survey photometry. The apsidal motion elements of the three binaries were determined from both light curve and eclipse timing analysis. The periods of apsidal motion were 67+/-2 yr for OGLE-LMC-ECL-05797, 124+/-6 yr for OGLE-LMC-ECL-05861, and 39+/-1 yr for OGLE-LMC-ECL-06510 and their internal structure constants (ISCs) were log k_2,obs_=-2.3+/-0.1, -2.4+/-0.1, and -2.1+/-0.1 in the same order. The observed ISCs of OGLE-LMC-ECL-05797 and OGLE-LMC-ECL-05861 showed a good match to the theoretical ISC values, while the value of OGLE- LMC-ECL-06510 was somewhat larger than the theoretical one.
- ID:
- ivo://CDS.VizieR/J/ApJ/789/139
- Title:
- Three O-type binaries photometry in LMC
- Short Name:
- J/ApJ/789/139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper in a series devoted to the study of massive binary systems in the Large Magellanic Cloud (LMC). We mainly aim to provide accurate data that constrains the mass-luminosity relation for the most massive stars but also to address the long lasting problem known as the "mass discrepancy." We present here our results for three binaries (LMC 169782, LMC 171520, and [P93] 921) harboring the earliest O-type components-ranging from O4 V to O6.5 V-among our sample of 17 systems. Our photometry provided accurate periods for the studied systems, allowing the spectroscopic observations to be performed at selected phases where the radial velocity separation between binary components is larger. Following the procedure outlined in our first paper of this series, after solving the radial velocity curves for orbital parameters, we used tomographic reconstruction to obtain the individual spectra of each star, from which we determined effective temperatures via a model atmosphere fitting with FASTWIND. This information, combined with the light-curve analysis that was performed with GENSYN, enabled the determination of absolute masses, radii, and bolometric luminosities that are compared with those predicted by modern stellar evolutionary models finding that they agree within the uncertainties. Nevertheless, the comparison seems to confirm the small differences found in the first paper of this series in the sense that the evolutionary masses are slightly larger than the Keplerian ones, with differences averaging ~10%, or alternatively, the stellar evolutionary models predict luminosities that are somewhat lower than observed. Still, the overall agreement between the current evolutionary models and the empirically determined stellar parameters is remarkable.
- ID:
- ivo://CDS.VizieR/J/AJ/157/87
- Title:
- Times of minima for 21 early-type SMC eccentric EBs
- Short Name:
- J/AJ/157/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the apsidal motion and light-curve analyses of 21 eccentric eclipsing binaries located in the Small Magellanic Cloud. Most of these systems have never been studied before, hence their orbital and physical properties as well as the apsidal motion parameters are given here for the first time. All the systems are of early spectral type, having orbital periods up to 4 days. The apsidal motion periods were derived to be from 7.2 to 200 yr (OGLE-SMC-ECL-2194 having the shortest apsidal period among known main-sequence systems). The orbital eccentricities are usually rather mild (median of about 0.06), the maximum eccentricity being 0.33. For the period analysis using O-C diagrams of eclipse timings, in total 951 minima were derived from survey photometry as well as our new data. Moreover, six systems show some additional variation in their O-C diagrams, which should indicate the presence of hidden additional components in them. According to our analysis these third-body variations have periods from 6.9 to 22 yr.
- ID:
- ivo://CDS.VizieR/J/AJ/150/183
- Title:
- Times of minima for 18 LMC eclipsing binaries
- Short Name:
- J/AJ/150/183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New CCD observations for 13 eccentric eclipsing binaries from the Large Magellanic Cloud were carried out using the Danish 1.54 m telescope located at the La Silla Observatory in Chile. These systems were observed for their times of minimum and 56 new minima were obtained. These are needed for accurate determination of the apsidal motion. Besides that, in total 436 times of minimum were derived from the photometric databases OGLE and MACHO. The O - C diagrams of minimum timings for these B-type binaries were analyzed and the parameters of the apsidal motion were computed. The light curves of these systems were fitted using the program PHOEBE, giving the light curve parameters. We derived for the first time relatively short periods of the apsidal motion ranging from 21 to 107 years. The system OGLE-LMC-ECL-07902 was also analyzed using the spectra and radial velocities, resulting in masses of 6.8 and 4.4 M_{sun}_ for the eclipsing components. For one system (OGLE-LMC-ECL-20112), the third-body hypothesis was also used to describe the residuals after subtraction of the apsidal motion, resulting in a period of about 22 years. For several systems an additional third light was also detected, which makes these systems suspect for triplicity.
