SDSS-V OBA Stars
Most massive stars live with a close companion and often exchange matter during their lives. We use SDSS-V spectra to map how common these companions are and to find unusual systems—some of which could be the ancestors of the black-hole and neutron-star mergers seen in gravitational waves.
Overview
Massive stars rarely live alone. Because many orbit each other closely, they can pull material from one another; these interactions set up the systems that later become pairs of black holes or neutron stars. With SDSS-V we observe each star several times and look for small shifts in their spectral lines. Those shifts reveal hidden companions and let us measure how frequent binaries are across different masses, ages, environments and metallicities. From these data we flag special cases—like stars that have been stripped by a companion or candidates that may host a black hole—and then follow them with high-resolution spectroscopy to confirm their nature. Seeing these “in-between” stages helps us connect everyday massive binaries to the gravitational-wave sources detected today.
• Role: Leading author on the multiplicity of OBA stars
• Data: SDSS-V
mwm_ob_core, three epochs per star• Telescope instrument: The Sloan Foundation 2.5m Telescope at Apache Point Observatory / The Irénée du Pont Telescope at Las Campanas Observatory. BOSS spectrographs • Method: Radial-velocity changes to identify close binaries and interaction products
• Follow-up: High-resolution spectroscopy of top candidates
• Goal: Constrain how massive binaries evolve toward GW-source progenitors
My contributions
- 01.2024 - present: SDSS-V Collaboration Council (MPIA representative): membership and policy reviews; architect/external-collaborator applications; support for collaboration meetings and guidelines.
- Organised the 2025 collaboration meeting in Heidelberg (LOC chair; SOC member).
- Lead author on the first multiplicity paper (in prep).
Key results (so far)
- First large-scale young-disc map: Zari, Villaseñor, Kounkel, Rix, et al. (2025) used roughly 50,000 young OB stars from SDSS-V to build a first 3D kinematic map of the Milky Way disc out to ~5 kpc from the Sun.
- Coherent radial motions at kiloparsec scale: the young-star velocity field shows alternating inward and outward patterns with amplitudes of about ±30 km s⁻¹, substantially stronger than those seen in older red-giant populations.
- Young stars do not simply trace spiral structure: the radial-velocity patterns correlate only weakly with spiral-arm overdensities, pointing instead to a mix of spiral structure, bar-driven dynamics, resonances, or phase mixing.
- Age matters: about 85% of the sample is younger than ~300 Myr, while the very youngest stars (≲30 Myr) line up more clearly with density enhancements, showing that the youngest disc populations carry different spatial and kinematic information.