Periodic Reporting for period 2 - GAIA-BIFROST (GAIA-BInaries: Formation and fundamental pRoperties Of Stars and planeTary systems)
Okres sprawozdawczy: 2023-06-01 do 2024-11-30
Binary stars are foundation stones for modern astrophysics: they give rise to key phenomena that we study at all energies and redshifts; also, they are precision clockworks for deriving fundamental parameters for Stellar Evolution and Galactic Archaeology; and their orbital characteristics still carry the imprints of the formation process and of later dynamical interactions. The GAIA satellite mission has provided the ultimate sample for studying binaries, providing millions of astrometric orbits. However, for the vast majority GAIA is not able to spatially resolve the components, but measures only the motion of the photocenter between the stars. This prevents GAIA from deriving dynamical masses and strongly limits what we can learn about star and planet formation. In the project we build on the GAIA sample to study the dynamical processes that shape system architectures, over the whole mass range from stellar-mass companions down to planets. This will reveal what mechanisms are common between binary formation and planet formation, and how they differ. To achieve this goal, we build a 4-telescope instrument for the Very Large Telescope Interferometer, called BIFROST. With each single pointing, BIFROST will turn a GAIA binary into a fully-characterised system, with 3-dimensional orbits, precision dynamical masses and precision ages. Also, BIFROST will be the only VLTI instrument optimised for high spectral resolution. This allows us to measure the alignment between the stellar spin axis and the orbital axis for wide-separation systems that are inaccessible with other techniques, providing a key diagnostic on their dynamical history. Third, we image young stars with discs that show evidence for companion-disc interactions. We conduct deep multi-wavelength, multi-epoch imaging and model the observed disc structures to better understand the hydrodynamical effects that shape discs. The BIFROST survey will explore the origin of the diversity that we see in binary and planetary systems. It will provide the largest ever sample of precision dynamical masses and ages, which will have a tremendous impact in Stellar Evolution and Galactic Archaeology. Finally, BIFROST will break new ground for VLTI, leading the way for short-wavelength characterisation of exoplanet atmospheres in the future.
In the initial 30 months of the project, we progressed both on the methodology and scientific objectives of the ERC project:
On methodology, a key deliverable of the ERC project is building the BIFROST beam combination instrument for the European Southern Observatory’s (ESO) Very Large Telescope Interferometer (VLTI). We finalised the optical design, triggered the key procurements, and started assembly in our purpose-built optics lab at Exeter. We also made progress negotiating with the facility owner to obtain permission for bringing our instrument to their world-leading telescope facility in Chile. We submitted a science whitepaper and a technical feasibility document to ESO in June 2022 and went through various technical reviews. In June 2023, ESO Council recommended the Asgard Suite and BIFROST for implementation as VLTI visitor instrument, and we are on track to deliver the first part of the instrument to Chile in mid-2025.
To progress with the astrophysics science objectives ahead of the completion of the BIFROST instrumentation work, we started the GAIA binary survey (WP1) using the CHARA Array. We validated our observing approach and developed software tools that allow us to select GAIA binaries for different object classes, and to derive dynamical masses using a Bayesian modelling approach.
The second scientific objective is to measure the spin-spin and spin-orbit alignment of binaries (WP2). Existing instruments offer only moderate spectral resolution, which strongly limits the number of sources where spin measurements are feasible. We initiated pilot programs with VLTI to attempt spin-orbit alignments on some sources that might be feasible, but focussed our efforts also on the aforementioned BIFROST instrumentation efforts and also on commissioning a R=6000 VPH grating for MIRC-X.
The third workpackage (WP3) is to image companion-disc interactions in young binary systems to improve our understanding of how companions form. We pursued observations with VLTI, CHARA, ALMA, and VLT adaptive optics imaging, to study a range of systems, including intermediate-mass and high-mass young stars, where the observed disc structures suggest that young companion might just be forming or have formed already and are just sculpting the disc. We study more than a dozen young stars, including the pre-main-sequence multiple systems HD104237A and GW Ori, and the intermediate-mass star HD143006.
On methodology, a key deliverable of the ERC project is building the BIFROST beam combination instrument for the European Southern Observatory’s (ESO) Very Large Telescope Interferometer (VLTI). We finalised the optical design, triggered the key procurements, and started assembly in our purpose-built optics lab at Exeter. We also made progress negotiating with the facility owner to obtain permission for bringing our instrument to their world-leading telescope facility in Chile. We submitted a science whitepaper and a technical feasibility document to ESO in June 2022 and went through various technical reviews. In June 2023, ESO Council recommended the Asgard Suite and BIFROST for implementation as VLTI visitor instrument, and we are on track to deliver the first part of the instrument to Chile in mid-2025.
To progress with the astrophysics science objectives ahead of the completion of the BIFROST instrumentation work, we started the GAIA binary survey (WP1) using the CHARA Array. We validated our observing approach and developed software tools that allow us to select GAIA binaries for different object classes, and to derive dynamical masses using a Bayesian modelling approach.
The second scientific objective is to measure the spin-spin and spin-orbit alignment of binaries (WP2). Existing instruments offer only moderate spectral resolution, which strongly limits the number of sources where spin measurements are feasible. We initiated pilot programs with VLTI to attempt spin-orbit alignments on some sources that might be feasible, but focussed our efforts also on the aforementioned BIFROST instrumentation efforts and also on commissioning a R=6000 VPH grating for MIRC-X.
The third workpackage (WP3) is to image companion-disc interactions in young binary systems to improve our understanding of how companions form. We pursued observations with VLTI, CHARA, ALMA, and VLT adaptive optics imaging, to study a range of systems, including intermediate-mass and high-mass young stars, where the observed disc structures suggest that young companion might just be forming or have formed already and are just sculpting the disc. We study more than a dozen young stars, including the pre-main-sequence multiple systems HD104237A and GW Ori, and the intermediate-mass star HD143006.
The project pushed beyond the state-of-the-art in our capability to measure dynamical masses for large number of stars across the Hertzsprung-Russell diagram (WP1), which will have an impact across different areas of stellar astrophysics. Also, we expect that our imaging studies will reveal intriguing cases of companion-disc interaction that will go beyond what has been done before.
The instrumentation that we conduct as part of the project pushes the state-of-the-art in infrared long-baseline interferometry. The BIFROST instrument will open the short-wavelength window for VLTI, which will provide access to important new diagnostic spectral lines. At the same time, it will offer higher spectral resolution than existing infrared interferometric instruments. Besides the proposed work on GAIA binaries and studying accretion in young systems, this will enable a broad range of other science applications in the future, including the atmospheric characterisation of exoplanets.
The instrumentation that we conduct as part of the project pushes the state-of-the-art in infrared long-baseline interferometry. The BIFROST instrument will open the short-wavelength window for VLTI, which will provide access to important new diagnostic spectral lines. At the same time, it will offer higher spectral resolution than existing infrared interferometric instruments. Besides the proposed work on GAIA binaries and studying accretion in young systems, this will enable a broad range of other science applications in the future, including the atmospheric characterisation of exoplanets.