PPVI Talk 9: Amelia Stutz

THE EVOLUTION OF PROTOSTARS: INSIGHTS FROM TEN YEARS OF INFRARED SURVEYS WITH SPITZER AND HERSCHEL

M. Dunham (Yale University, New Haven, CT, United States), A. Stutz (MPIA, Germany), L. Allen (NOAO, United States), N. Evans (UT Austin, United States), W. Fischer (University of Toledo, United States), S.T. Megeath (University of Toledo, United States), P. Myers (Harvard-Smithsonian Center for Astrophysics, United States), S. Offner (Yale University, United States), C. Poteet (Rensselaer Polytechnic Institute, United States), J. Tobin (National Radio Astronomy Observatory, United States), E. Vorobyov (University of Vienna, Austria)

Stars and planets form from the gravitational collapse of dense molecular cloud cores. The protostellar phase is the period during which mass accretes from the core, through an accretion disk formed by conservation of angular momentum, and onto a hydrostatically supported protostar. It is the phase during which the initial masses of stars and the initial conditions for planet formation are set, thus understanding how protostars evolve is a crucial ingredient for developing a general understanding of star and planet formation. Identification and characterization of protostars has traditionally been hindered by the embedded nature of these objects. Over the past ten years, new observational capabilities provided by the Spitzer Space Telescope and Herschel Space Observatory have enabled wide-field infrared surveys of entire star-forming clouds with high sensitivities, leading to remarkable progress in our understanding of protostellar evolution. We review several key advances in the field over the past decade, focusing both on the observations themselves and the constraints these large-area surveys are placing on theoretical models of star formation and protostellar evolution. We also emphasize several open questions and debates and outline the future observational and theoretical work necessary to further advance the field.

Intro

Core -> First hydrostatic core -> protostar

Luminosity problem
  • Low-luminosity discrepancy, maybe sensitivity
Review of Classes: submillimeter vs bolometric luminosity, temperature
  • Classes don't necessarily correspond to Stages because of, e.g., geometry
  • Lifetimes of classes - consistent
  • L_submm / L_bol vs T_bol: L_smm/L_bol is a better envelope diagnostic
  • Monotonic evolution may not be true
  • Deviants from "cartoon picture" are at least 10% of all protostars
PACS Bright Red Sources
  • 18 reddest sources in Orion
  • 70um-bright, consistent with Stage 0
  • VeLLOs not a unique evolutionary stage
  • Too many VeLLOs: they can't be first hydrostatic cores (implies too long a lifetime)
How do protostars get their mass?
  • The protostellar luminosity problem: Theoretical accretion luminosity ~10x observed
  • None of the inputs are observationally directly constrained
  • m-dot provides the most lever arm, with order-of-magnitude uncertainty
Core-regulated vs disk-regulated accretion
  • Can rule out isothermal sphere
  • cannot rule out any other models
Low-luminosity bursts
  • episode accretion
  • How common are they?
Fossil evidence:
  • Arce ALMA HH46
  • prompt entrainment by episodic jet
  • 100-year spacing between clumps
DiGiT double-peaked CO2 ice feature
  • irreversible chemical process
  • observed towards vellos: vellos were warm in the past

What fraction of final protostellar mass is accreted in bursts?

What happens in disks?
  • Disk rotation is only direct means for measuring protostellar mass
The role of environment
  • B335 vs. OMC 2/3
  • Luminosities higher, mean separations lower in more active regions

Questions

  • Q: Mark Krumholz: Can you use the environmental dependence to distinguish disk physics from environmental = core accretion physics?
  • A: disk physics not environmentally dependent, but feeding through envelopes...
  • Krumholz: not external feeding that drives burstiness. Burstiness shouldn't know about environment
  • Q: Multiplicity?
  • A: Tom & student working on constraining with HST data.
  • Q: How do you check?
  • A: I dunno.
  • A: Neal - ???
  • Q: Structure in HH46. May be formed by... something else?????
  • A: Hard to make link between outflows and accretion. This is one nice example of some evidence but is not conclusive on its own.
  • Q: Lifetime of class I's. Maybe lifetimes have 2-order-of-magnitude variation; can't reference to Class II.
  • A: I agree.
  • Q: Inclination. SED models for diskey stars. Any method that can disentangle geometry from other effects?
  • A: avoid the issue by looking at direct detection of cold emission in envelope
  • Ewine: Centrally concentrated HCO+ emission can separate inclined Class I from Class 0. Best is large samples with ALMA though.
  • Q: IRS spectra from protostars. Amount of silicate lines as signature of episodic accretion.
  • A: Don't have a good answer. Don't necessarily look at those features. Only CO2 ice is clear-cut irreversible process. [missed one question]
  • Q: Ewine - what is the key observational distinction between VeLLOs and true first hydrostatic cores.
  • A: Catch young outflows. ALMA.
  • Q Mike Dunham: First cores - lifetimes. 10^4 years is the strict, absolute upper limit for first hydrostatic cores. 0.06-6 first cores in Perseus. No large-scale surveys for first cores.

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