The physics of brown dwarfs

Program lead: Catarina Alves de Oliveira (ESA)

Collaborations with other GTO teams: the ONC observations are conducted in collaboration with JWST's inter-disciplinary scientist M. J. MacCaughrean.

Coordination with other GTO teams: the observations of WISE 0855-0714 are conducted in coordination with the NIRISS and MIRI EC GTO teams to share the slew overheads.

Program duration: 17 hours

Brown dwarfs represent by number a sizeable fraction of the stellar content of the Galaxy and their masses populate the transition between the stellar and planetary mass regime. There is not an accepted explanation for how they form, making them a key element in understanding the origin of stellar masses and their distribution. As brown dwarfs evolve and cool down, their atmospheres resemble those of gas giant extrasolar planets, providing easier targets to observe and investigate the physical and chemical processes in low-temperature atmospheres. The new observational frontier is therefore the discovery and spectral characterization of the coldest and least massive brown dwarfs to test formation theories and advance the physics of cool atmospheres. This is the main driver behind this NIRSpec/JWST GTO proposal, which we have divided into two complementary programs. In the first program, we propose to obtain low and medium resolution near-IR spectra of known and candidate brown dwarfs in two nearby star-forming clusters that are representative of different star formation environments. We will use these data to

  • search for brown dwarfs down to the mass of Jupiter to improve constraints on the minimum mass of the initial mass function and
  • search for spectroscopic signatures of formation mechanism (e.g., like a star via cloud core collapse vs. like a planet within a disk).

In the second program, we will perform near-IR spectroscopy on the coldest known brown dwarf (250 K), which is also the Sun’s 4th closest neighbor, to test model atmospheres at very low temperatures.

Observations and targets:

Orion Nebula Cluster (ONC)

15-minute (on-source) MOS observations in the CLEAR/PRISM and F290LP/G395M configurations and for 2 different sets of targets (2 different MSA configurations and pointings). Observations based on existing source catalogs.

NIRCam imaging observations will be obtained in parallel to these spectroscopic observations.

IC 348 cluster

This program is making use of the possibility of conducting a same-cycle imaging campaign from which the sources suitable for a spectroscopic follow-up will be extracted.

Imaging campaign: Shallow NIRCam imaging in three pairs of short/long wavelength filters (F140M+F227W, F162M-F150W2+F360M, F182M+F444W) with NIRISS slitless spectroscopy (F115W, F140M and F158M) conducted in parallel.

Spectroscopic follow-up campaign: 25-minute (on-source) MOS observations in the CLEAR/PRISM and F290LP/G395M configurations and for 2 different sets of targets (2 different MSA configurations).

NIRCam imaging observations will be obtained in parallel to these spectroscopic observations.

WISE 0855-0714

~5.2h (on-source) SLIT observations in the CLEAR/PRISM and F290LP/G395M configurations.

CAUTION: the observing strategy described here is not yet completely frozen and is subject to change between now and the submission of the consolidated observation proposal files in November 2017 when the official cycle-1 APT software version will become available.

Presentations:

"The physics of brown dwarfs and exoplanets - a JWST/NIRSpec GTO program overview", Stephan Birkmann, Catarina Alves de Oliveira and the NIRSpec GTO team, JWST min-session at the AAS 230th meeting (Austin, TX, June 2017).