Luminous Blue Variables

Weis, Karsten; Bomans, D. J.

doi:10.3390/galaxies8010020

Cited by 39 publications

(13 citation statements)

References 147 publications

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“…What we know about LBVs is that they are massive, hot stars with very high mass-loss rates, located near the Eddington limit. The only way to classify a star as LBV is by studying its variability (Weis & Bomans 2020), either photometric or spectroscopic. To be classified as classical LBV, a star must undergo S-Doradus (hereafter S-Dor) cycles, i.e., temperature changes at practically constant luminosity (Humphreys & Davidson 1994;Groh et al 2009b;Smith 2017), or giant eruptions.…”

Section: Introductionmentioning

confidence: 99%

Multiplicity of Galactic luminous blue variable stars

Mahy

Lanthermann

Hutsemékers

et al. 2021

A&A

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Context. Luminous blue variables (LBVs) are characterised by strong photometric and spectroscopic variability. They are thought to be in a transitory phase between O-type stars on the main sequence and the Wolf-Rayet stage. Recent studies also evoked the possibility that they might be formed through binary interaction. Only a few are known in binary systems so far, but their multiplicity fraction is still uncertain. Aims. We derive the binary fraction of the Galactic LBV population. We combine multi-epoch spectroscopy and long-baseline interferometry to probe separations from 0.1 to 120 mas around confirmed and candidate LBVs. Methods. We used a cross-correlation technique to measure the radial velocities of these objects. We identified spectroscopic binaries through significant radial velocity variability with an amplitude larger than 35 km s−1. We also investigated the observational biases to take them into account when we established the intrinsic binary fraction. We used CANDID to detect interferometric companions, derive their flux fractions, and their positions on the sky. Results. From the multi-epoch spectroscopy, we derive an observed spectroscopic binary fraction of 26−10+16%. Considering period and mass ratio ranges from log(Porb) = 0 − 3 (i.e. from 1 to 1000 days), q = 0.1 − 1.0, and a representative set of orbital parameter distributions, we find a bias-corrected binary fraction of 62−24+38%. Based on data of the interferometric campaign, we detect a binary fraction of 70 ± 9% at projected separations between 1 and 120 mas. Based on the derived primary diameters and considering the distances of these objects, we measure for the first time the exact radii of Galactic LBVs to be between 100 and 650 R⊙. This means that it is unlikely that short-period systems are included among LBV-like stars. Conclusions. This analysis shows for the first time that the binary fraction in the Galactic LBV population is large. If they form through single-star evolution, their orbit must be large initially. If they form through a binary channel, the implication is that either massive stars in short binary systems must undergo a phase of fully non-conservative mass transfer to be able to sufficiently widen the orbit to form an LBV, or that LBVs form through merging in initially binary or triple systems. Interferometric follow-up would provide the distributions of orbital parameters at more advanced stages and would serve to quantitatively test the binary evolution in massive stars.

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Section: Introductionmentioning

confidence: 99%

Multiplicity of Galactic luminous blue variable stars

Mahy

Lanthermann

Hutsemékers

et al. 2021

A&A

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“…In this section we provide a short description of the algorithms chosen for this work (for more details, see, e.g., Baron 2019;Ball & Brunner 2010). The development of a classifier for massive stars requires the inclusion of "difficult" cases, such as those that are short-lived (e.g., YSGs with a duration of a few thousand years; Neugent et al 2010;Drout et al 2009) or very rare (e.g., LBVs, Weis & Bomans 2020;SGs, Kraus 2019). To secure the training of the algorithms with specific targets, we preferred the use of supervised algorithms.…”

Section: Application Of Machine Learningmentioning

confidence: 99%

A machine-learning photometric classifier for massive stars in nearby galaxies

Maravelias

Bonanos

Tramper

et al. 2022

A&A

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Context. Mass loss is a key parameter in the evolution of massive stars. Despite the recent progress in the theoretical understanding of how stars lose mass, discrepancies between theory and observations still hold. Moreover, episodic mass loss in evolved massive stars is not included in models, and the importance of its role in the evolution of massive stars is currently undetermined. Aims. A major hindrance to determining the role of episodic mass loss is the lack of large samples of classified stars. Given the recent availability of extensive photometric catalogs from various surveys spanning a range of metallicity environments, we aim to remedy the situation by applying machine-learning techniques to these catalogs. Methods. We compiled a large catalog of known massive stars in M31 and M33 using IR (Spitzer) and optical (Pan-STARRS) photometry, as well as Gaia astrometric information, which helps with foreground source detection. We grouped them into seven classes (Blue, Red, Yellow, B[e] supergiants, Luminous Blue Variables, Wolf-Rayet stars, and outliers, e.g., quasi-stellar objects and background galaxies). As this training set is highly imbalanced, we implemented synthetic data generation to populate the underrepresented classes and improve separation by undersampling the majority class. We built an ensemble classifier utilizing color indices as features. The probabilities from three machine-learning algorithms (Support Vector Classification, Random Forest, and Multilayer Perceptron) were combined to obtain the final classification.Results. The overall weighted balanced accuracy of the classifier is ∼ 83%. Red supergiants are always recovered at ∼ 94%. Blue and Yellow supergiants, B[e] supergiants, and background galaxies achieve ∼ 50 − 80%. Wolf-Rayet sources are detected at ∼ 45%, while Luminous Blue Variables are recovered at ∼ 30% from one method mainly. This is primarily due to the small sample sizes of these classes. In addition, the mixing of spectral types, as there are no strict boundaries in the features space (color indices) between those classes, complicates the classification. In an independent application of the classifier to other galaxies (IC 1613, WLM, and Sextans A), we obtained an overall accuracy of ∼ 70%. This discrepancy is attributed to the different metallicity and extinction effects of the host galaxies. Motivated by the presence of missing values, we investigated the impact of missing data imputation using a simple replacement with mean values and an iterative imputer, which proved to be more capable. We also investigated the feature importance to find that r − i and y − [3.6] are the most important, although different classes are sensitive to different features (with potential improvement with additional features). Conclusions. The prediction capability of the classifier is limited by the available number of sources per class (which corresponds to the sampling of their feature space), reflecting the rarity of these objects and the possible physical links between these massive st...

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“…Both modes are characterized by luminosities near or above the Eddington limit and considerable mass loss, but so far there is no conclusive evidence that both phenomena can be consistently traced back to a singular physical mechanism or class of star (Davidson 2020). For a more detailed description of LBVs, we refer the reader to the reviews of Humphreys & Davidson (1994) and Weis & Bomans (2020). Some imposters exhibit a more complex pattern of variability.…”

Section: Introductionmentioning

confidence: 99%

Multi-epoch variability of AT 2000ch (SN 2000ch) in NGC 3432

Müller

Frohn

Dirks

et al. 2023

A&A

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Context. AT 2000ch is a highly variable massive star and supernova imposter in NGC 3432 first detected in 2000. It is similar and often compared to SN 2009ip, and it is therefore expected to undergo a core-collapse supernova (SN) -a SN imposter of similar brightness-in the near future. Aims. We characterize the long-term variability of AT 2000ch in the radio and optical regimes with archival data reaching back to the year 1984. We use these newly reduced observations in addition to observations in the literature to restrict the mass-loss rates of AT 2000ch at multiple epochs based on different approaches, and to infer the general properties of its circumstellar nebula with respect to the detected radio brightness. Methods. We extend the known optical light curve of AT 2000ch up to the beginning of 2022 by performing point spread function (PSF) photometry on archival data from the Palomar Transient Factory and the Zwicky Transient Facility. We reduced archival radio continuum observations obtained with the Very Large Array using standard calibration and imaging methods and complemented these with pre-reduced chang-es observations as well as observations obtained with the Westerbork Synthesis Radio Telescope and LOw Frequency ARray. For the analysis of AT 2000ch, we consider the optical light curve and color evolution, its radio continuum brightness at different frequencies and times, and the corresponding spectral indices. We estimated mass-loss rates and optical depths based on radio continuum brightnesses and Hα fluxes. Results. We report two newly detected outbursts of AT 2000ch similar to those found in the 2000s and 13 re-brightening events, of which at least four are not conclusively detected because of insufficient sampling of the light curve. The dates of all outbursts and significant, well-sampled re-brightening events are consistent with a period of ∼ 201 ± 12 days over a total time-span of two decades. Such a behavior has never been found for any SN imposter, especially not for candidate SN 2009ip analogs. During 2010 to 2012 and 2014 to 2018, we only have a few detections, which is insufficient to come to any conclusion as to a possible less eruptive phase of the transient. We find steady dimming after the most recent re-brightening events and possible evidence of porosity in the circumstellar envelope, suggesting AT 2000ch may currently be in transition to a state of relative calm. We identified a second, unrelated source at a projected distance of ∼ 23 pc (∼ 0.5 ) that has contaminated the optical measurements of AT 2000ch at its minimum luminosity over the last two decades probably on a 5%−10 % level, but this does not affect our overall findings and is negligible during re-brightening. We are able to restrict the mass-loss rate of AT 2000ch to range between several 10 −6 M /yr and several 10 −5 M /yr. The fresh ejecta appear to be optically thick to radio continuum emission at least within the first ∼ 25 days after significant re-brightening. Conclusions. We suggest that other SN imposter and proba...

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Luminous Blue Variables

Cited by 39 publications

References 147 publications

Multiplicity of Galactic luminous blue variable stars

Multiplicity of Galactic luminous blue variable stars

A machine-learning photometric classifier for massive stars in nearby galaxies

Multi-epoch variability of AT 2000ch (SN 2000ch) in NGC 3432

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