W. Reis | Searcharxiv

arXiv2026

Pre-main Sequence B Stars Surrounding the Orion Nebula

Pre-main sequence (PMS) early-type stars are rare due to their rapid evolution. Confirming PMS B stars is accordingly valuable for constraining higher mass star formation scenarios. Although the Orion Nebula (ON) region offers an ideal laboratory for such studies, its population of B stars remains poorly characterized. We aim to determine spectral types, masses, and ages of B and early A stars surrounding the ON, to identify robust PMS candidates. We combine optical and near-infrared spectroscopy to estimate spectral types using Brackett, He, Si, and Mg lines. Photometry from Gaia, 2MASS, and WISE is used to construct colour-magnitude diagrams to fit isochrones via chi-square minimisation, yielding stellar ages and masses. Dynamical masses from eclipsing binaries are employed as independent constraints on the mass range allowed for each spectral subtype. We derive stellar ages and masses for 53 stars and spectral classifications for 48 of them, identifying 30 PMS candidates, including some that were previously assigned to luminosity classes I-III. Several stars show spectroscopic variability, potentially linked to circumstellar material or binarity. Our combined spectroscopic and photometric approach identifies robust PMS B-star candidates and provides a validated framework for distinguishing them from evolved counterparts - in this instance, refining the census of early-types young stars in Orion. The age distribution of the PMS candidates offers preliminary clues about the star formation history of the ON region.

astro-ph.SR↗

arXiv2008

Mapping the interface between the Local and Loop I bubbles using Stromgren photometry

The Sun is located inside an extremely low density region of quite irregular shape called the Local Bubble. Close to the Local Bubble, there is an even larger cavity known as Loop I. A ring-like feature observed in X-ray and HI has been proposed as the contour of the bubbles interaction zone around 70 pc. Our goal is to identify the interface between the Local and Loop I Bubbles and discuss the ring's existence using Stromgren uvbyHβdata. We have used the uvbyHβdata of the General Catalogue of Photometric Data, covering the region defined by the Galactic coordinates: 250\degr <= l <= 50\degr and -60\degr <= b <= 60\degr to obtain E(b-y) colour excess and distances. The final sample is composed of 4346 stars located up to 500 pc from the Sun. The expected transition to E(b-y) ~ 0.070 - 0.100 mag, corresponding to the ring's column density, occurs on the western part of the ring at d = 110 +/- 20 pc, whereas on the eastern side it is not clearly seen before d = 280 +/- 50 pc. Near the Galactic plane the presence of the dark clouds is clearly established by E(b-y) >= 0.100 mag on the western side at about 100 - 150 pc and about 120 - 180 pc on the eastern side. In the southernmost part of the ring the reddening remains very low, typically E(b-y) = 0.020 in all its extension, except towards the Mensa constellation where a possible transition is observed at d = 200 +/- 20 pc. In the northernmost part the colour excess increases with distance in a gradual way, such that 0.020 <= E(b-y) <= 0.040 mag becomes predominant only after d=120 +/-15 pc. If the ring really exists the colour excess distribution indicates that it is very fragmented and distorted. However, the different characteristics of the reddening inside and along the ring do not support the existence of a ring.

astro-ph↗