arXiv subjects

Abel de Burgos

Publications and source records attributed to Abel de Burgos.

10 recordsLinked to original sources

arXiv2026

Unveiling the Milky Way with a Gaia DR3 census of OB-type stars within 2 kpc. I. Tracing local Galactic structure, massive star-forming regions and core-collapse supernova progenitors

O- and B-type stars are young and hot, thereby serving as vital tracers of the star formation and spiral arm structure of the Milky Way. At the dusk of the \textit{Gaia} DR3 era, a high-confidence and accurate catalogue appears timely. We have characterized 105,971 OB-type stars (T$_{\rm eff} >$ 10,000 K) within 2 kpc from the Sun, using an astro-photometric Bayesian inference tool. Our map unveils a complex view of the young stellar populations across the thin disk, with prominent large-scale features such as the Cepheus Spur, the Giant Oval Cavity, and a segment the Sagittarius-Carina arm all visible. Their inhomogeneous spatial distribution implies that massive star formation has taken place clustered across a few highly concentrated regions. We find a correlation between the overdensities of OB-type stars and young open clusters, and attribute departure from it to extinction effects. We identify 4200 stars as model-dependent core-collapse supernova (ccSN) or direct-collapse black hole (BH) progenitor candidates, including 6 ccSN progenitor candidates within 125 pc -- the maximum radius within which a ccSN explosion could be harmful to Earth's biosphere -- but our analysis suggests none of them exploding within the next 5 Myrs. Finally, we anticipate more evolved OB-type stars to collapse to form BHs within the next 1 Myr than ccSN progenitors will explode, despite the former's much scarcer number. A possible interpretation is a recent star formation burst in the local Milky Way, consistent with overdensities of ccSN progenitor candidates in Cyg OB2 and the Sagittarius-Carina arm.

astro-ph.GA↗

arXiv2026

The IACOB project XIX. Revisiting massive-star evolution with empirical TAMS constraints: updated models, overshoot calibration, and the population of blue supergiants

Massive stars play a fundamental role in the evolution of the Universe. Yet, several physical processes governing their evolution remain poorly constrained. Notably, the main-sequence width is sensitive to the convective boundary mixing efficiency; it becomes necessary to account for binary interactions to explain some observed properties of massive-star populations. We constrain single-star models using recent observations of massive Galactic stars from the IACOB database. We use the latest proposed empirical location of the TAMS to calibrate the convective boundary mixing efficiency, and use this calibration to test single-star evolution by comparing various model predictions to the observed populations of the IACOB sample. We compute several GENEC grids with various overshoot calibrations, angular momentum transport (AMT) treatments, initial masses and velocities. Finally, we generate synthetic populations from the tracks with SYCLIST and perform a direct comparison with the observed population. The calibrated models at slow rotation reproduce the empirical TAMS location. We find that a mass-dependent overshoot efficiency is required to fit the observational constraints. The overall rotational properties of the observed populations are well reproduced with single-star models, independently of the AMT assumptions. Models accounting only for hydrodynamical instabilities are successful at reproducing the rotational properties, unlike previous genec grids, which we attribute to the choice of winds prescription. Although the empirical TAMS of slow rotators is well reproduced, we find that models are unsuccessful at explaining the velocity dependence of the TAMS location observed in the IACOB sample. Finally, we find that single-star models fail at explaining the population of blue supergiants to the right of the TAMS location.

astro-ph.SR↗

arXiv2026

You're Gonna Need a Bigger Core: Calibrating Massive Star Models against Galactic OB-type Stars

The evolution of massive stars above 8 M$_\odot$ depends critically on the amount of mixing above the convective core during the main sequence. However, current models typically extrapolate results from lower-mass stars, where constraints from asteroseismology and eclipsing binary systems are more readily available. A new opportunity to study the evolution of massive stars and their distribution in the Hertzsprung--Russell diagram arises by combining the IACOB spectroscopic sample of over 900 Galactic OB-type stars with Gaia distances. We use this homogeneously analyzed sample to place population-level constraints on main-sequence evolution. We analyze the data by forward modeling stellar evolution tracks with MESA and applying Bayesian inference. This enables us to 1) determine a physically-motivated, data-driven location of the terminal-age main sequence, 2) constrain convective boundary mixing and resulting core masses, and 3) provide a set of massive star models calibrated against modern data. We explore how boundary mixing depends on mass and find that it is well described by a constant overshooting parameter in the mass range of 12 to 40 M$_\odot$, with $α_{\mathrm{ov}} = 0.33 \pm 0.02$, or $f_{\mathrm{ov}} = 0.028 \pm 0.003$ in the step and exponential overshooting schemes respectively. We find evidence against a continuation of the trend to increase with mass that is found at lower masses. Instead, the data does not exclude a decreasing trend at the high mass end. We find that the resulting helium core masses are 10 to 40% larger than other commonly used overshooting prescriptions. Combining our findings with existing observational constraints for low- and intermediate-mass stars, we propose a new mass-dependent overshooting prescription for a wide range of masses. Our calibration and model set are particularly useful for population and spectral synthesis applications.

astro-ph.SR↗

arXiv2024

On the evolutionary nature of massive B-type supergiants: a modern empirical reappraisal using data from IACOB, Gaia and TESS

Massive stars are key contributors to the chemodynamical evolution of galaxies and the Universe. Despite their significance, discrepancies between observational data and theoretical models of massive stars challenge our understanding of these objects. A major uncertainty is the overdensity of B-type supergiants (BSGs) in the Hertzsprung-Russell diagram, where models predict the end of the main sequence phase (or TAMS). Is uncertain whether the TAMS needs to be redefined or if the overdensity results from overlapping populations following different evolutionary paths. Conceived as direct descendants of O-type stars, BSGs may include stars not only evolving in the main sequence but also returning from a post-red supergiant phase. A representative fraction of massive stars are predicted to be products of binary interaction, creating additional evolutionary channels. In addition, some fundamental properties of BSGs such as the spin- and mass-loss rates are not as well constrained as in O-type stars, having a significant impact on massive star evolution. To overcome this situation, statistically significant spectroscopic samples offer a unique opportunity to study the physical and chemical properties of BSGs. Moreover, the advent of space astrometry and photometry missions such as Gaia and TESS has brought a new era for studying additional properties in detail. This thesis comprises the study of 1000 Galactic blue supergiants (O- and B-type) combining multi-epoch high-resolution spectroscopic data from the IACOB project and the ESO archive with Gaia distances and TESS photometry, becoming the largest holistic empirical study of the physical, chemical, and pulsational properties of these objects performed to date. All these properties gathered into a unique volume-limited sample allowed to provide an empirical reassessment of the main properties of BSGs and investigate their intricate nature.

astro-ph.SR↗

arXiv2024

The IACOB project XII. A new grid of northern standards for the spectral classification of B-type stars

With the advent of large spectroscopic surveys, automated stellar parameter determination has become commonplace. Nevertheless, spectral classification still offers a quick and useful alternative for obtaining parameter estimates for large samples of spectra of varying quality. We present a new atlas of stellar spectra covering the B-type range, with the intention of providing detailed classification criteria valid for modern spectra and improving the grid of reliable standards. This new grid will be used in future works to provide classification criteria beyond the classical classification range and addressing, in particular, the use of Gaia/RVS spectra. We analysed historical standards by means of multiple high-resolution spectra, marking out problematic cases and complementing the grid with a new set of reliable comparators. We then elaborated on a new set of classification criteria based on high-quality R=4000 spectra. Our new classification grid is much thicker than any previous set of standards, presenting a high degree of self-consistency. Although it is based entirely on morphological criteria, the grid demonstrates a much better correlation with different physical parameters. The new grid can be used to study classification criteria in other spectral ranges, providing a valuable tool for the study of B-type stars that covers a very wide range of temperatures, luminosities, and stellar masses. The very process of classification also offers valuable insights into stellar evolution.

astro-ph.SR↗

arXiv2024

The IACOB project XI. No increase of mass-loss rates over the bistability region

The properties of blue supergiants are key for constraining the end of the main sequence (MS) of massive stars. Whether the observed drop in the relative number of fast-rotating stars below $\sim$21$\,$kK is due to enhanced mass-loss rates at the location of the bistability jump, or the result of the end of the MS is still debated. Here, we combine newly derived estimates of photospheric and wind parameters with Gaia distances and wind terminal velocities from the literature to obtain upper limits on the mass-loss rates for a sample of 116 Galactic luminous blue supergiants. The parameter space covered by the sample ranges between 35-15$\,$kK in $T_{\rm eff}$ and 4.8-5.8$\,$dex in log(L/L$_{\odot}$). Our results show no increase in the mass-loss rates over the bistability jump. Therefore, we argue that the drop in rotational velocities cannot be explained by enhanced mass loss. Since a large jump in the mass-loss rates is commonly included in evolutionary models, we suggest an urgent revision of the currently used default prescriptions.

astro-ph.SR↗

arXiv2024

The IACOB project X. Large-scale quantitative spectroscopic analysis of Galactic luminous blue stars

Blue supergiants (BSGs) are key objects for understanding the evolution of massive stars. However, discrepancies between theoretical predictions and empirical observations have opened up important questions yet to be answered. Studying statistically significant and unbiased samples of BSGs can help to improve the situation. We aim to perform a homogeneous and comprehensive quantitative spectroscopic analysis of a large sample of Galactic luminous blue stars (being the majority BSGs) from the IACOB spectroscopic database. We derive the projected rotational velocity ($v\sin i$) and macroturbulent broadening ($v_{\rm mac}$) using IACOB-BROAD. We used FASTWIND computations to derive effective temperatures ($T_{\rm eff}$), surface gravities, microturbulences ($ξ$), Si and He surface abundances, and the wind-strength parameter. We provide estimates of these quantities for the largest sample of Galactic luminous O9-B5 stars spectroscopically analyzed to date, with 527 targets. We find a drop in the relative number of stars at ~21 kK, coinciding with a scarcity of fast rotating stars below that temperature. We speculate that this feature might be roughly delineating the location of the Terminal-Age-Main-Sequence in the 15-85M$_\odot$ range. By investigating the main characteristics of the $v\sin i$ distribution as a function of $T_{\rm eff}$, we propose that an efficient mechanism transporting angular momentum from the stellar core to the surface might be operating along the main sequence. We find correlations between $ξ$, $v_{\rm mac}$ and the spectroscopic luminosity. We also find that no more than 20% of the stars in our sample have atmospheres clearly enriched in He, and suggest that the origin of this specific sub-sample might be in binary evolution. We do not find clear empirical evidence of an increase in the wind-strength over the wind bi-stability region towards lower temperatures.

astro-ph.SR↗

arXiv2023

The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366$-$959\,nm at $R\sim5000$, or two shorter ranges at $R\sim20\,000$. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for $\sim$3 million stars and detailed abundances for $\sim1.5$ million brighter field and open-cluster stars; (ii) survey $\sim0.4$ million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey $\sim400$ neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in $z<0.5$ cluster galaxies; (vi) survey stellar populations and kinematics in $\sim25\,000$ field galaxies at $0.3\lesssim z \lesssim 0.7$; (vii) study the cosmic evolution of accretion and star formation using $>1$ million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at $z>2$. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.

astro-ph.IM↗

arXiv2023

The IACOB project IX. Building a modern empirical database of Galactic O9-B9 supergiants: sample selection, description, and completeness

Blue supergiants (BSGs) are important objects to study the intermediate phases of massive star evolution, helping to constrain evolutionary models. However, the lack of a holistic study of a statistically significant and unbiased sample of these objects makes several long-standing questions about their nature to remain unsolved. The present and other upcoming papers of the IACOB series are focused in studying - from a pure empirical point of view - a sample of 500 Galactic O9 - B9 stars with luminosity classes I and II (plus 250 late O- and early B-type stars with luminosity classes III, IV and V) and covering distances up to 4 kpc from the Sun. We compile an initial set of 11000 high-resolution spectra of 1600 Galactic late O- and B-type stars. We use a new novel spectroscopic strategy based on a simple fitting of the Hbeta line to select stars in a specific region of the spectroscopic HR diagram. We evaluate the completeness of our sample using the Alma Luminous Star catalog (ALS III) and Gaia-DR3 data. We show the benefits of the proposed strategy for identifying BSGs descending from stellar objects born as O-type stars, in the context of single star evolution. The resulting sample reaches a high level of completeness with respect to the ALS III catalog, gathering the 80% for all-sky targets brighter than Bmag < 9 located within 2 kpc. However, we identify the need for new observations in specific regions of the Southern hemisphere. In conclusion, we have explored a very fast and robust method to select BSGs, providing a valuable tool for large spectroscopic surveys like WEAVE-SCIP or 4MIDABLE-LR, and highlighting the risk of using spectral classifications from the literature. Upcoming works will make use of this large and homogeneous spectroscopic sample to study specific properties of these stars in detail. We initially provide first results about their rotational properties.

astro-ph.SR↗

arXiv2023

Gaia colour-magnitude diagrams of young open clusters: Identification in the UBC catalogue and a comparison of manual and automated analysis

Automated analysis of Gaia astrometric data has led to the discovery of many new high-quality open cluster candidates. With a good determination of their parameters, these objects become excellent tools to investigate the properties of our Galaxy. We explore whether young open clusters can be readily identified from Gaia data alone by studying the properties of their Gaia colour-magnitude diagrams. We also want to compare the results of a traditional cluster analysis with those of automated methods. We selected three young open cluster candidates from the UBC catalogue, ranging from a well-populated object with a well-defined sequence to a poorly-populated, poorly-defined candidate. We obtained classification spectra for the brightest stars in each. We redetermined members based on EDR3 data and fitted isochrones to derive age, distance and reddening. All three candidates are real clusters with age below 100 Ma. UBC103 is a moderately populous cluster, with an age around 70 Ma. At a distance of $\sim$ 3 kpc, it forms a binary cluster with the nearby NGC6683. UBC114 is a relatively nearby ($\sim1.5$kpc) poorly-populated cluster containing two early-B stars. UBC587 is a dispersed, very young ($<$ 10 Ma) cluster located at $\sim3$ kpc, behind the Cygnus~X region, and may be a valuable tracer of the Orion arm. The OCfinder methodology for the identification of new open clusters is extremely successful, with even poor candidates resulting in interesting detections. The presence of an almost vertical photometric sequence in the Gaia colour-magnitude diagram is a safe way to identify young open clusters. Automated methods for the determination of cluster properties give approximate solutions, but are still subject to some difficulties. There is some evidence suggesting that artificial intelligence systems may systematically underestimate extinction, which may impact in the age determination.

astro-ph.SR↗