Astronomy & Astrophysics Master Seminar

Zoom: https://tau-ac-il.zoom.us/j/81239615480?pwd=qynx9sGBcqWlo2fNUEbZrq1VibGgwM.1

Speaker 1: Zehava Zina Katabi (TAU)

The origin of Blue Supergiants: a multiplicity perspective

Abstract: Blue supergiants (BSGs) are evolved massive stars that populate a region of the Hertzsprung–Russell diagram (HRD) where standard single-star evolution predicts very few stars should be found. Stars are expected to cross this region quickly on a thermal timescale, yet observations consistently reveal a dense, persistent population. This is the Blue supergiant problem. Several solutions have been proposed, invoking either enhanced mixing in single stars or various types of binary interactions. In this talk, I will present the first bias-controlled constraints on the multiplicity properties of this population. We derive the binary fraction and orbital properties of 254 BSGs in the Small Magellanic Cloud (SMC), monitored over more than two years with VLT/FLAMES within the Binarity at LOw Metallicity (BLOeM) survey. I will show that BSGs carry a clear binary deficit relative to their likely main-sequence progenitors. Moreover, I will demonstrate that the population is a mix of two main populations: a hotter population consistent with an extended main sequence, and a cooler population likely dominated by binary interaction products.

Speaker 2: Tom Sayada (TAU)

Double-Lined B-type Binaries in the Small Magellanic Cloud: Orbital Solutions from the BLOeM Survey

Abstract: Massive stars (M > 8 M⊙) drive much of the chemical enrichment, ionising radiation, and mechanical feedback that shape their host galaxies. Studies in the Milky Way and the Large Magellanic Cloud have revealed that most of them are born in close pairs (periods shorter than a few years). The orbits of these binaries dictate their future evolution: from mass transfer and mergers to the supernovae and compact-object remnants they leave behind. At sub-solar metallicities, like that of the Small Magellanic Cloud, prior information on orbits of massive stars has come largely from eclipsing-binary surveys or spectroscopy of individual systems. The Binarity at LOw Metallicity (BLOeM) survey provides the first multi-epoch spectroscopic monitoring of nearly one thousand massive stars in the SMC, with enough cadence to systematically solve orbits with periods shorter than a few years. Here, I will present results obtained for 66 B-dwarf and B-giant double-lined spectroscopic binaries (SB2) in BLOeM. SB2 systems have the unique advantage of providing a direct empirical measure of the mass ratio, and provide crucial constraints on models of star formation and tidal interaction. In my talk, I will describe the analysis pipeline and present the global orbital properties of the population. We find that the orbits are typically very short (median 2.7 days), and that the components tend toward equal masses with a clear preference for near-twin pairs. In addition, clear evidence of circularisation via tidal interaction is observed for periods below 2 days. We further find that a non-negligible fraction of the SB2 sample (more than 10%) shows evidence of additional companions, placing them in triple or quadruple configurations. This sample is one piece of a larger puzzle, necessary to investigate the dependence of multiplicity on metallicity.

Seminar Organizer: Dr. Jonathan Stern