- ID:
- ivo://CDS.VizieR/J/ApJ/348/98
- Title:
- LMC AGB stars IRAS fluxes
- Short Name:
- J/ApJ/348/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for optically obscured asymptotic giant branch (AGB) stars in the Large Magellanic Cloud (LMC), combining data obtained using the IRAS satellite with near-infrared photographic plate material of a 15deg^2^ region in the northern LMC. Of the 156 IRAS sources that are detected either in separate cross-scans or in more than one passband, 63 have [12-25] colors consistent with their being either stellar photospheres or circumstellar dust shells. Seventeen of these we identify with bright (I_c_<9) foreground stars in our own Galaxy, while a further 17 are associated with red supergiants in the LMC. Of the remaining stars, no more than five are likely to be optically visible AGB stars, while the rest have no obvious optical counterpart. This immediately rules out the presence of sufficient high-luminosity "cocoon" stars to explain the observed deficit of several hundred luminous (M_bol_<-6) AGB stars between the predictions of standard models of AGB evolution and the observed luminosity function. It remains possible that most of the unidentified sources are dusty AGB stars, evolving through a phase of enhanced mass loss toward becoming planetary nebulae. We infer bolometric magnitudes as low as M_bol_~-5 for these sources and suggest that this phase can be triggered at low luminosities, truncating AGB evolution and leading to the observed scarcity of asymptotic giant branch stars with bolometric magnitudes brighter than -6.0mag.
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- ID:
- ivo://CDS.VizieR/J/ApJ/825/59
- Title:
- LMC and Cen A 1.3-10GHz polarization behavior
- Short Name:
- J/ApJ/825/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a broadband polarization analysis of 36 discrete polarized radio sources over a very broad, densely sampled frequency band. Our sample was selected on the basis of polarization behavior apparent in narrowband archival data at 1.4GHz: half the sample shows complicated frequency-dependent polarization behavior (i.e., Faraday complexity) at these frequencies, while half shows comparatively simple behavior (i.e., they appear Faraday simple). We re-observed the sample using the Australia Telescope Compact Array in full polarization, with 6GHz of densely sampled frequency coverage spanning 1.3-10GHz. We have devised a general polarization modeling technique that allows us to identify multiple polarized emission components in a source, and to characterize their properties. We detect Faraday complex behavior in almost every source in our sample. Several sources exhibit particularly remarkable polarization behavior. By comparing our new and archival data, we have identified temporal variability in the broadband integrated polarization spectra of some sources. In a number of cases, the characteristics of the polarized emission components, including the range of Faraday depths over which they emit, their temporal variability, spectral index, and the linear extent of the source, allow us to argue that the spectropolarimetric data encode information about the magneto-ionic environment of active galactic nuclei themselves. Furthermore, the data place direct constraints on the geometry and magneto-ionic structure of this material. We discuss the consequences of restricted frequency bands on the detection and interpretation of polarization structures, and the implications for upcoming spectropolarimetric surveys.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/2307
- Title:
- LMC anomalous Cepheid Ks light curves
- Short Name:
- J/MNRAS/437/2307
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The VISTA near-infrared YJKs survey of the Magellanic Clouds System (VMC, PI M.-R. L. Cioni) is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper, we present for the first time Ks-band light curves for anomalous Cepheid (AC) variables. In particular, we have analysed a sample of 48 Large Magellanic Cloud ACs, for which identification and optical magnitudes were obtained from the OGLE III and IV catalogues. The VMC Ks-band light curves for ACs are well sampled, with the number of epochs ranging from 8 to 16, and allowing us to obtain very precise mean Ks magnitudes with errors on average of the order of 0.01mag. The <Ks> values were used to build the first period-luminosity and period-Wesenheit relations in the near-infrared for fundamental mode and first overtone ACs. At the same time we exploited the optical (V, I) OGLE data to build accurate period-luminosity, period-luminosity-colour and period-Wesenheit relations both for fundamental mode and first overtone ACs. For the first time, these relations were derived from a sample of pulsators which uniformly cover the whole AC instability strip. The application of the optical period-Wesenheit relation to a sample of dwarf galaxies hosting a significant population of ACs revealed that this relation is a valuable tool for deriving distances within the Local Group. Due to its lower dispersion, we expect the Ks period-Wesenheit relations first derived in this paper to represent a valuable tool for measuring accurate distances to galaxies hosting ACs when more data in near-infrared filters become available.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A21
- Title:
- LMC bar star clusters
- Short Name:
- J/A+A/606/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report results on star clusters located in the South-Eastern half of the Large Magellanic (LMC) bar fromWashington CT1 photometry. Using appropriate kernel density estimators we detected 73 star cluster candidates, three of which do not show any detectable trace of star cluster sequences in their colour-magnitude diagrams (CMDs).We did not detect other 38 previously catalogued clusters, which could not be recognized when visually inspecting the C and T1 images either; the distribution of stars in their respective fields do not resemble that of an stellar aggregate. They represent ~33 per cent of all catalogued objects located within the analysed LMC bar field. From matching theoretical isochrones to the cluster CMDs cleaned from field star contamination, we derived ages in the range 7.2<log(t[yr^-1^])<10.1. As far as we are aware, this is the first time homogeneous age estimates based on resolved stellar photometry are obtained for most of the studied clusters. We built the cluster frequency (CF) for the surveyed area, and found that the major star cluster formation activity has taken place during the period log(t[yr^-1^])~8.0-9.0. Since ~100Myr ago, clusters have been formed during few bursting formation episodes. When comparing the observed CF to that recovered from the star formation rate we found noticeable differences, which suggests that field star and star cluster formation histories could have been significantly different.
- ID:
- ivo://CDS.VizieR/J/AJ/154/102
- Title:
- LMC blue supergiants spectroscopic observations
- Short Name:
- J/AJ/154/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-quality spectra of 90 blue supergiant stars in the Large Magellanic Cloud are analyzed with respect to effective temperature, gravity, metallicity, reddening, extinction, and extinction law. An average metallicity, based on Fe and Mg abundances, relative to the Sun of [Z]=-0.35+/-0.09 dex is obtained. The reddening distribution peaks at E(B-V)=0.08 mag, but significantly larger values are also encountered. A wide distribution of the ratio of extinction to reddening is found ranging from R_V_=2 to 6. The results are used to investigate the blue supergiant relationship between flux-weighted gravity, g_F_=g/T_eff_^4^, and absolute bolometric magnitude M_bol_. The existence of a tight relationship, the Flux-weighted Gravity-Luminosity Relationship (FGLR), is confirmed. However, in contrast to previous work, the observations reveal that the FGLR is divided into two parts with a different slope. For flux-weighted gravities larger than 1.30 dex, the slope is similar to that found in previous work, but the relationship becomes significantly steeper for smaller values of the flux-weighted gravity. A new calibration of the FGLR for extragalactic distance determinations is provided.
- ID:
- ivo://CDS.VizieR/J/AJ/124/2039
- Title:
- LMC Blue variable stars from MACHO
- Short Name:
- J/AJ/124/2039
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the photometric properties of 1280 blue variable stars within the Large Megallanic Cloud. Photometry is derived from the MACHO database. The light curves of the sample exhibit a variety of quasi-periodic and aperiodic outburst behavior. A characteristic feature of the photometric variation is that the objects are reddest when at maximum outburst. A subset of 102 objects were examined spectroscopically. Within this subset, 91% exhibited Balmer emission in at least one epoch, in some cases with spectacular spectral variability. The variability observed in the sample is consistent with the establishment and maintenance of the Be phenomenon.
- ID:
- ivo://CDS.VizieR/J/AcA/58/313
- Title:
- LMC Cepheids in OGLE and MACHO data
- Short Name:
- J/AcA/58/313
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Pulsation period of Cepheids should change as stars evolve through the instability strip. Rates of these changes found by other authors based on the decades-long O−C diagrams show rather good agreement with theoretical predictions. We have checked the variability on the scale of a few years on the data recently published by the Optical Gravitational Lensing Experiment (OGLE) for the Large Magellanic Cloud Cepheids and found period changes for 18% of fundamental mode and 41% of first overtone pulsators. It suggest the overtone pulsations are less stable than the fundamental ones. For stars which had the cross-references in the MACHO catalog we have checked if the period change rates derived from the OGLE and the MACHO data are consistent.
- ID:
- ivo://CDS.VizieR/J/A+A/534/A95
- Title:
- LMC Cepheids radial velocities
- Short Name:
- J/A+A/534/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The extragalactic distance scale builds directly on the Cepheid Period-Luminosity (PL) relation as delineated by the sample of Cepheids in the Large Magellanic Cloud (LMC). However, the LMC is a dwarf irregular galaxy, quite different from the massive spiral galaxies used for calibrating the extragalactic distance scale. Recent investigations suggest that not only the zero-point but also the slope of the Milky Way PL relation differ significantly from that of the LMC, casting doubts on the universality of the Cepheid PL relation. We want to make a differential comparison of the PL relations in the two galaxies by delineating the PL relations using the same method, the infrared surface brightness method (IRSB), and the same precepts. The IRSB method is a Baade-Wesselink type method to determine individual distances to Cepheids. We apply a newly revised calibration of the method as described in an accompanying paper (Paper I, Cat. J/A+A/534/A94) to 36 LMC and five SMC Cepheids and delineate new PL relations in the V,I,J, & K bands as well as in the Wesenheit indices in the optical and near-IR. We present 509 new and accurate radial velocity measurements for a sample of 22 LMC Cepheids, enlarging our earlier sample of 14 stars to include 36 LMC Cepheids. The new calibration of the IRSB method is directly tied to the recent HST parallax measurements to ten Milky Way Cepheids, and we find a LMC barycenter distance modulus of 18.45+/-0.04 (random error only) from the 36 individual LMC Cepheid distances. In the J,K bands we find identical slopes for the LMC and Milky Way PL relations and only a weak metallicity effect on the zero points (consistent with a zero effect), metal poor stars being fainter. In the optical we find the Milky Way slopes are slightly shallower than the LMC slopes (but again consistent with no difference in the slopes) and small effects on the zero points. However, the important Wesenheit index in V,(V-I) shows a metallicity effect on the slope and on the zero point which is likely to be significant. We find a significant metallicity effect on the Wvi index gamma(Wvi)=-0.23+/-0.10mag/dex as well as an effect on the slope. The K-band PL relation on the other hand is found to be an excellent extragalactic standard candle being metallicity insensitive in both slope and zero-point and at the same time being reddening insensitive and showing the least internal dispersion.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A29
- Title:
- LMC classical Cepheids Fe and O content
- Short Name:
- J/A+A/658/A29
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Classical Cepheids are primary distance indicators and a crucial stepping stone to determining the present-day value of the Hubble constant Ho to the precision and accuracy required to constrain apparent deviations from the LCDM Concordance Cosmological Model. We have measured the iron and oxygen abundances of a statistically significant sample of 89 Cepheids in the LMC, one of the anchors of the local Distance Scale, quadrupling the prior sample and including 68 of the 70 Cepheids used to constrain Ho by the SH0ES program. The goal is to constrain the extent to which the Cepheid luminosity is influenced by their chemical composition, which is an important contributor to the uncertainty on the determination of the Hubble Constant itself and a critical factor in the internal consistency of the distance ladder. We have derived stellar parameters and chemical abundances from a self-consistent spectroscopic analysis based on Equivalent Width of absorption lines. The iron distribution of Cepheids in the LMC can be very accurately described by a single Gaussian with a mean [Fe/H]=-0.409+/-0.003dex and sigma=0.076+/-0.003dex. We estimate a systematic uncertainty on the absolute mean values of 0.1dex. The width of the distribution is fully compatible with the measurement error and supports the low dispersion of 0.069 mag seen in the NIR HST LMC period-luminosity relation. The uniformity of the abundance has the important consequence that the LMC Cepheids alone cannot provide any meaningful constraint on the dependence of the Cepheid Period-Luminosity relation on chemical composition at any wavelength. This revises a prior claim based on a small sample of 22 LMC Cepheids that there was little dependence (or uncertainty) between composition and NIR luminosity, a conclusion which would produce an apparent conflict between anchors of the distance ladder with different mean abundance. The chemical homogeneity of the LMC Cepheid population makes it an ideal environment to calibrate the metallicity dependence between the more metal poor SMC and metal rich Milky Way and NGC 4258.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A33
- Title:
- LMC 162 eccentric eclipsing binaries light curve
- Short Name:
- J/A+A/640/A33
- Date:
- 17 Dec 2021 07:53:18
- Publisher:
- CDS
- Description:
- We present an extensive study of 162 early-type binary systems located in the LMC galaxy that show apsidal motion and have never been studied before. For the ample systems, we performed light curve and apsidal motion modelling for the first time. These systems have a median orbital period of 2.2 days and typical periods of the apsidal motion were derived to be of the order of decades. We identified two record-breaking systems. The first, OGLE LMC-ECL-22613, shows the shortest known apsidal motion period among systems with main sequence components (6.6 years); it contains a third component with an orbital period of 23 years. The second, OGLE LMC-ECL-17226, is an eccentric system with the shortest known orbital period (0.9879 days) and with quite fast apsidal motion period (11 years). Among the studied systems, 36 new triple-star candidates were identified based on the additional period variations. This represents more than 20% of all studied systems, which is in agreement with the statistics of multiples in our Galaxy. However, the fraction should only be considered as a lower limit of these early-type stars in the LMC because of our method of detection, data coverage, and limited precision of individual times of eclipses.
