High spectral-resolution interferometry down to 1 micron with Asgard/BIFROST at VLTI: science drivers and project overview

Abstract

We present science cases and instrument design considerations for the BIFROST instrument that will open the short-wavelength (Y/J/H-band), high spectral dispersion (up to R=25,000) window for the VLT Interferometer. BIFROST will be part of the Asgard Suite of instruments and unlock powerful venues for studying accretion & mass-loss processes at the early/late stages of stellar evolution, for detecting accreting protoplanets around young stars, and for probing the spin-orbit alignment in directly-imaged planetary systems and multiple star systems. Our survey on GAIA binaries aims to provide masses and precision ages for a thousand stars, providing a legacy data set for improving stellar evolutionary models as well as for Galactic Archaeology. BIFROST will enable off-axis spectroscopy of exoplanets in the 0.025-1" separation range, enabling high-SNR, high spectral resolution follow-up of exoplanets detected with ELT and JWST. We give an update on the status of the project, outline our key technology choices, and discuss synergies with other instruments in the proposed Asgard Suite of instruments.

Spectrograph design for the Asgard/BIFROST spectro-interferometric instrument for the VLTI

“…Thus, it ultimately helps achieve the required accuracy before every night of observation. The BIFROST design demands an accuracy up to 1 km s −1 (Kraus et al 1 ), so that the central wavelength of each spectral channel can be defined with sub-channel accuracy. Fig.…”

“…BIFROST (Beam-combination Instrument for studying the Formation & fundamental pRoperties Of Stars and planeTary systems) is an upcoming Very Large Telescope Interferometry (VLTI) visitor instrument as part of VLTI/Asgard instrument Suite. [1][2][3][4][5][6][7][8][9][10] BIFROST will operate in either a Y+J or a H band mode. The major components that we need to design for BIFROST include the spectrograph.…”

“…* In Kraus et al,1 the LR arm is referred to as YJH arm and the HR arm as YJ arm, as we might chose a close filter with a lower cut-off wavelength on the arm with the R=1000, R=5000, and R=25,000 grating for Y and J-band to reduce the thermal background and to enable very long effective integration times.…”

Beam combiner for the Asgard/BIFROST instrument

“…1 With its short wavelength (J band) and high spectral resolution (R = 25,000) will open up a new observational window at the VLTI. A few key science drivers include measuring precision dynamical masses and ages for GAIA binaries, measuring the spin-orbit alignment for directly imaged exoplanets and off-axis exoplanet spectroscopy (Kraus et al 2022). 2 The instrument itself is still in the design phase, a key part of which is identifying which subsystems are necessary for the instrument to function.…”

“…A few key science drivers include measuring precision dynamical masses and ages for GAIA binaries, measuring the spin-orbit alignment for directly imaged exoplanets and off-axis exoplanet spectroscopy (Kraus et al 2022). 2 The instrument itself is still in the design phase, a key part of which is identifying which subsystems are necessary for the instrument to function. In addition to this the implications of the different beam combination schemes, namely an All-In-One (AIO) or a Integrated Optics (IO) beam combiner must be considered.…”