Peering into the physics of brown dwarfs: spectroscopy with JWST/ - - PowerPoint PPT Presentation

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Peering into the physics of brown dwarfs: spectroscopy with JWST/ NIRSpec

Catarina Alves de Oliveira, European Space Agency Understanding the Nearby Star-forming Universe with JWST

27 Aug 2019

ESA UNCLASSIFIED – Releasable to the public Catarina Alves de Oliveira| 27/ 08/ 2019 | Slide 2

The NIRSpec GTO program

• GTO program built for scientific excellent, but

also ensuring that the observations probe key modes, strategies and regimes to provide early feedback to the community https: / / www.cosmos.esa.int/ web/ jwst-nirspec-gto

• 17h (~ < 2% ) dedicated to the ‘Physics of

Brown Dwarfs” program, with focus-team:

• C. Alves de Oliveira, K. Luhman, R.

Parker, P. Tremblin, I. Baraffe, G. Chabrier Collaboration w/ M. McCaughrean for ONC program

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Science case: The Physics of Brown Dwarfs

• Physics of brown dwarfs challenge several areas from the theory of star and

planet formation to the physics of cool atmospheres

• Goal: Discovery and spectral characterization of the coldest and least

massive brown dwarfs to advance these fields

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Science case: The Physics of Brown Dwarfs

Program is divided into two parts aimed at:

• I. Testing star formation models by finding and

characterizing the lowest mass young planetary- mass brown dwarfs (IC 348 and ONC)

• II. Testing models of cool atmospheres by

studying the coldest known brown dwarf in the solar neighborhood (WISE0855)

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• I. Testing star formation models with young,

planetary-mass brown dwarfs

Obtain spectra of low mass young brown-dwarfs in nearby star-forming regions to: i. probe the cut-off mass limit of star formation, and the mass function across the planetary-mass regime, ii. investigate the presence of heavy elements enrichment as a clue to the formation process

Atmospheric models from P . Tremblin, I. Baraffe,

• G. Chabrier

The effect of m etallicity: Young Jupiter-mass object: Teff: 1200K, logg: 4, log Kzz: 0 Metallicity: Solar vs 5 xSolar

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Target selection: IC 348

Distance: 316 pc Size: ~ 2.6x2.3 pc (~ 34’x28’) Age: 2Myr Population: 478 spectroscopically confirmed members

Caltech Aladin/WISE

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What is the dynamical history of IC 348?

Minimum-spanning-tree method to quantify degree of mass segregation* : ‘mass segregation ratio’ (ΛMSR) = average random path length path length of massive stars (or brown dwarfs) ! No evidence that m ass segregation has occurred at 2 Myr in I C3 4 8 .

Parker & Alves de Oliveira 2017

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What were the initial conditions for star and planet formation in IC348?

N-body simulations of the dynamical evolution of star-forming regions with varying initial densities to characterize spatial structure and density* . !-parameter = mean distance between stars mean length of the minimal spanning tree

quantifies and distinguishes between substructured and centrally concentrated regions.

, ! Observational value suggests less-dense initial conditions in I C3 4 8 , and a m odest degree of dynam ic evolution.

Parker & Alves de Oliveira 2017

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What was the impact of dynamical evolution on star and planet formation in IC348?

N-body simulations of a young cluster with the dynamical history and initial conditions of IC348, to examine the direct effects of interactions in the cluster on stars and planetary systems. Sim ulation set-up:

• Cluster: based on our findings of most likely initial conditions
• Prim ary stars: 400 stars randomly drawn from an IMF
• Stellar com panions: assigned based on binary fractions associated with the

primary mass

• Planetary com panions: 1 Jupiter mass planet on a 30 AU orbit is assigned to

single stars

Parker & Alves de Oliveira 2017

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What was the impact of dynamical evolution on star and planet formation in IC348?

è After ~ 2 Myr, ~ 3 to 7 planets initially

• rbiting their parent star at 30AU,

have been liberated and became free- floating planets è This is significantly less than what was found for an Orion-like simulation, where ~ 10% of planetary companions were liberated

Parker & Alves de Oliveira 2017

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Spectroscopy with JWST

Near-IR MOS/ NI RSpec (vs slitless NIRCam & NIRISS)

+ More sensitive by ~ 2-5x + Reduces contamination/ confusion + Can block saturating sources within field + Higher spectral resolution options + Larger wavelength range coverage

• No blind searches possible
• Requirements on targets’ astrometric accuracy
• Needs target acquisition
• PSF truncation
• Aperture corrections

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JWST/ NIRSpec: MOS observing mode

Multi-Object spectroscopy (MOS) ➡ Rich fields, extended targets

FOV: ~ 9 arcmin2 Apertures: ~ 0.2x0.4 arcsec, ~ 1/ 4 million micro-shutters Resolution: ~ 100, ~ 1000 (~ 2700, partial truncation)

Credit: NASA Credit: NASA Credit: NASA

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JWST/ NIRSpec: wavelength coverage and resolution

Fixed Slits (FS) ➡ Single sources, bright stars Multi-Object spectroscopy (MOS) ➡ Rich fields, extended targets Integral Field Spectroscopy (IFS) ➡ Sources with few arcsec extent Bright Object Time Series (BOTS) ➡ Exoplanets

JWST spectroscopy comes in many flavours!

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JWST/ NIRSpec: field of view

Fixed Slits (FS) ➡ Single sources, bright stars Multi-Object spectroscopy (MOS) ➡ Rich fields, extended targets Integral Field Spectroscopy (IFS) ➡ Sources with few arcsec extent Bright Object Time Series (BOTS) ➡ Exoplanets

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JWST/ NIRSpec: multiplexing

Slitlet configuration

Shutter availability for an

• bservation depends on its
• perability status, avoidance
• f spectral overlap, or

spectral truncation

Density of targets Viable shutters Target centering

Multiplexing depends strongly on the density of targets in the input catalog Constraints on target centering are relevant for spectro-photometric accuracy, but impact multiplexing Length of slitlet and dithering strategy place constraints on the number of observable

• bjects and therefore multiplex

Credit: NASA Credit: P. Jakobsen Credit: P. Jakobsen Credit: JWST User documentation (STScI)

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JWST/ NIRSpec: multiplexing

Courtesy of P. Jakobsen (DAWN, former ESA/ JWST Project Scientist)

On the densest target fields, estimated maximum number of targets that can be

• bserved in single exposure without their

spectra overlapping: ~ 200 targets for R~ 100 PRISM ~ 60 targets for R~ 1000 gratings

R~100 R~1000

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JWST: same-cycle NIRCam-NIRSpec/ MOS follow-up

Submit combined proposal

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JWST: same-cycle NIRCam-NIRSpec/ MOS follow-up

Submit combined proposal NIRCam images are acquired Select targets and prepare NIRSpec MSA configurations

Image constructed with Spitzer data, not a NIRCam simulation.

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JWST: same-cycle NIRCam-NIRSpec/ MOS follow-up

Submit combined proposal NIRCam images are acquired Select targets and prepare NIRSpec MSA configurations NIRSpec MOS spectroscopy acquired

Credit: ESA/ JWST SOT

same JWST cycle

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JWST/ NIRSpec: parallel observations

NIRSpec in MOS-mode and NIRCam can be used simultaneously to observe adjacent fields

JWST FIELD OF VIEW EXAMPLE PLAN FROM NIRSpec & NIRCam GTO programs

Credit: JWST User documentation (STScI) Courtesy of the NIRSpec and NIRCam GTO teams

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Observations: IC 348

Sam e cycle NI RCam im aging + NI RSpec MOS

Target selection

NIRCam imaging to select candidate brown dwarfs NIRSpec MOS follow-up on targets with colours consistent with young low mass brown dwarfs Experimental Design Candidate selection based on colour-colour magnitude diagrams and expected colours for substellar objects Low and medium-resolution spectra to assess youth and membership to the cluster, surface gravity, temperature, presence of heavy elements enrichment Instrument setup 2 NIRCam tiles with module A+ B F140M, F162M, F182M short filters (F277W, F360M, and F444W long filters) NIRSpec/ MOS observations w/ PRISM and G395M 3-point nodding on a 3-shutter slitlet Parallels NIRcam imaging -> NIRISS imaging NIRSpec/ MOS -> NIRCam imaging Total time 7 hours

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Target selection: ONC-shallow

• HST/ WFC3 images from Hubble Treasury Program of the centre of Orion (r< 200”)
• Use color-magnitude diagram to select the targets based on the expected m130 −

m139 colors of late-type low mass brown dwarfs, complemented by other data

• Selected 200 new brown dwarf candidate members, ~ 90 known cluster members

will be observed as fillers

• 5.300
• 5.320
• 5.340
• 5.360
• 5.380
• 5.400
• 5.420
• 5.440
• 5.460

ONC

Candidate Selection Area

NIRSpec FoV

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Observations: ONC-shallow

NI RSpec MOS

Target selection

Candidate brown dwarfs selected from HST/ WFC3 Treasury program on the ONC Experimental Design Low and medium-resolution spectra to assess youth and membership to the cluster, surface gravity, temperature, presence of heavy elements enrichment Instrument setup NIRSpec/ MOS observations w/ PRISM and G395M 3-point nodding on a 3-shutter slitlet Parallels NIRSpec/ MOS -> NIRCam imaging Time 8 hours: 3h (NIRSpec GTO) + 5h (M. McCaughrean)

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• II. Testing models of cool atmospheres

Near-IR spectroscopy of the coldest known brown dwarf, to test model atmospheres at

very low temperatures to: i. constrain whether atmospheres are shaped by chemical disequilibrium driven by vertical transport or the formation of water clouds, ii. constrain the gravity, hence the mass of this object. The effect of clouds: atmospheric models from Tremblin + 2015 (no clouds) & Morley+ 2014 (with clouds) Y dwarf: Teff: 450K logg: 4 distance: 5 pc

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JWST/ NIRSpec: Fixed-slit observing mode mode

Multi-Object spectroscopy (MOS) ➡ Rich fields, extended targets Integral Field Spectroscopy (IFS) ➡ Sources with few arcsec extent

Slits: 0.2” and 0.4”-wide slits 1.6”x1.6” aperture for time-series Resolution: ~ 100, ~ 1000, ~ 2700

Fixed Slits (FS) ➡ Single sources, bright stars Bright Object Time Series (BOTS) ➡ Exoplanets

Credit: JWST User documentation (STScI)

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• II. Observations: WISE 0855-0714

NI RSpec fixed-slit

Target selection coldest object discovered outside the Solar System (250 K) and the 4th closest neighbor to the Sun (2.2 pc) Experimental Design Low and medium resolution spectroscopy to constrain: temperature, gravity, degree of turbulence, chemical equilibrium/ desiquilibrium, clouds Instrument setup S200A1 PRISM and G395M Time 7 hours

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Conclusion

By studying the lowest mass and coolest brown dwarfs, JWST has the potential to:

• place one of the most stringent observational constrains on star formation theories by

unveiling the low-mass end and cut-off of the IMF

• peer into the fate of embryonic planetary systems and their chances for survival in the

parent cluster environment

• unveil the ingredients and the physics of the coolest brown dwarf atmospheres

NIRSpec capabilities are well suited to facilitate such observations. Synergy with other JWST capabilities (e.g., MIRI spectroscopy, NIRCam photometry, NIRISS spectroscopy or AMI) will further complement and enlarge the scientific results.

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Catarina Alves de Oliveira, European Space Agency

Thank you for your attention.

Understanding the Nearby Star-forming Universe with JWST

27 Aug 2019