The evolutionary state of chemically peculiar stars in NGC 2516 using GAIA data on singles and binaries

The origin of the magnetism in stars with radiative envelopes and the role the magnetic field plays in their evolution remain unknown. The most popular scenario involves a merging event or a common envelope evolutionary phase. Mass transfer in stellar merging may rejuvenate the mass gaining star, while the induced differential rotation is thought to be a key ingredient to generate a magnetic field. One of the observable manifestations of the presence of coalesced stars or stars experiencing a common envelope evolution is the existence of blue straggler stars. Studies of open clusters and associations have seen great improvement with the advent of Gaia DR3 data, allowing us to determine photometric and kinematic ages, including runaway status of upper-main sequence stars possessing magnetic fields. In our poster we discuss our assessment of the evolutionary state of eleven binary and single chemically peculiar stars, among them stars with strong magnetic fields previously classified as highly probable members of the open cluster NGC 2516

Searching for Magnetospheres around Herbig Ae/Be Stars

We describe four different approaches for the detection of magnetospheric accretion among Herbig Ae/Be stars with accretion disks. Studies of several unique objects have been carried out. One of the objects is the Herbig Ae star HD 101412 with a comparatively strong magnetic field. The second is the early-type Herbig B6e star HD 259431. The existence of a magnetosphere in these objects was not recognized earlier. In both cases, a periodicity in the variation of some line parameters, originating near the region of the disk/star interaction, has been found. The third object is the young binary system HD 104237, hosting a Herbig Ae star and a T Tauri star. Based on the discovery of periodic variations of equivalent widths of atmospheric lines in the spectrum of the primary, we have concluded that the surface of the star is spotted. Comparing our result with an earlier one, we argue that these spots can be connected with the infall of material from the disk onto the stellar surface through a magnetosphere. The fourth example is the Herbig Ae/Be star HD 37806. Signatures of magnetospheric accretion in this object have been identified using a different method. They were inferred from the short-term variability of the He I λ5876 line profile forming in the region of the disk/star interaction

Growing up -the completion of the VLTI

Abstract. The completed VLTI with eight Delay Lines and eight ATs forms the basis for the second generation instrumentation. We describe the events up to first fringes with the test instrument VINCI using the siderostats, and the planning for the immediate future. Multi beam combination for 'smoother images' will be briefly discussed as well as artificial guide stars for fringe tracking. New technological developments like fiber optics amplifiers and integrated optics in combination with STJ open the door for a new type of interferometric arrays. Baselines as long as a a few kilometres come into reach. Examples of these second generation interferometers will be given

GRAVITY: observing the universe in motion

GRAVITY is the second generation VeryLarge Telescope Interferometer instrument for precision narrow-angle as -trometry and interferometric imaging.With its fibre-fed integrated optics,wavefront sensors, fringe tracker, beamstabilisation and a novel metrologyconcept, GRAVITY will push the sensitivity and accuracy of astrometry andinterferometric imaging far beyond whatis offered today. Providing precisionastrometry of order 10 microarcseconds,and imaging with 4-milliarcsecondresolution, GRAVITY will revolutionisedynamical measurements of celestialobjects: it will probe physics close tothe event horizon of the Galactic Centreblack hole; unambiguously detect andmeasure the masses of black holesin massive star clusters throughout theMilky Way; uncover the details of massaccretion and jets in young stellarobjects and active galactic nuclei; andprobe the motion of binary stars, exoplanets and young stellar discs. Theinstrument capabilities of GRAVITY areoutlined and the science opportunitiesthat will open up are summarised

Multiple star systems in the Orion nebula

This is the author accepted manuscript. The final fersion is available from EDP Sciences via the DOI in this record.This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for θ1 Ori B, θ2 Ori B, and θ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary θ1 Ori C and we are able to derive a new orbit for θ1 Ori D. We find a system mass of 21.7 M⊙ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.Marie Skłodowska-Curie Grant AgreementFCT-PortugalERC Starting Gran