The Herschel Orion Protostar Survey: Luminosity and Envelope Evolution

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1 The Herschel Orion Protostar Survey: Luminosity and Envelope Evolution Will Fischer STScI Tom Megeath (University of Toledo) Emily Safron (Louisiana State University) Elise Furlan (IPAC) Babar Ali (Space Science Institute) Amy Stutz (Universidad de Concepción) John Tobin (University of Oklahoma) Mayra Osorio (Instituto de Astrofísica de Andalucía) Thomas Stanke (ESO) P. Manoj (Tata Institute of Fundamental Research) Image: Herschel Gould Belt Survey

2 Key question: Do stars mainly accumulate Stochastic: their main-sequence masses through A sudden luminosity outburst secular or stochastic processes? Secular: Gradual envelope infall onto a disk, then accretion onto the star due to rapid disk accretion HOPS 136 (NICMOS) HOPS 383 (MIPS) Fischer et al. (2014) Safron et al. (2015)

3 Class 0 L bol = 20 L T bol = 44 K Class I L bol = 6 L T bol = 115 K HOPS allows a statistical look at how protostars accumulate their masses 315 protostellar SEDs tabulated & modeled by Furlan et al. (2016) Far IR data: accurate bolometric luminosities and temperatures Flat L bol = 15 L T bol = 457 K Class II L bol = 3 L T bol = 833 K

4 The Orion BLT Diagram Fischer et al. (2017) 1) Factor of 1000 spread in L bol ) Roughly flat T bol histogram: 29% in Class 0 Class I Class 0 EVOLUTION 3) L bol declines with evolution 2.3 L in Class L in Class I

5 Luminosity outbursts are known to play a role in the BLT distribution McNeil s Protostar V883 Ori V883 Ori Cieza et al. (2016) McNeil s Protostar HOPS 383 Reipurth & Aspin (2004) V2775 Ori Fischer et al. (2012) V2775 Ori = HOPS 223 Safron et al. (2015) HOPS 383

6 Outburst Search: Comparison of Spitzer and WISE IRAC 1 IRAC 2 MIPS 1 Variability survey with 7 yr baseline Look for sources with 1 mag brightening in all 3 bands WISE 1 WISE 2 WISE 4 Spitzer observed Orion in outbursts in 319 protostars in 7 yrs Implies each protostar has an outburst every ~1000 yr (but with large uncertainty) Outbursts were not as extreme as the famous FU Ori examples WISE observed Orion in 2010

7 EVOLUTION To compare to models, convert observed L bol, T bol to physical parameters From SED models, we get Total luminosity (corrected for inclination angle) Envelope mass (< 2500 AU) Three main features of the BLT diagram persist: Large spread in luminosities Flat mass histogram Lower luminosities at late times

8 Approximately flat histogram below 1 M suggests exponential decline in envelope mass (if starformation rate is constant) Total luminosity vs. envelope mass Three main features of the BLT diagram persist: Large spread in luminosities Flat mass histogram Lower luminosities at late times

9 EVOLUTION Total luminosity vs. envelope mass Three main features of the BLT diagram persist: Large spread in luminosities Flat mass histogram Lower luminosities at late times

10 EVOLUTION Interpretation Luminosity is mainly due to accretion:! ~ $% % ( Quick drop in luminosity suggests quick decline in accretion rate This and the flat mass histogram motivate models of exponentially declining envelope masses

11 Tracks show example protostars that reach the main sequence at 0.12, 0.58, 2.8 M 2.8 M 0.58 M 0.12 M Star-Formation Models Exponentially declining envelope mass Envelope infall rate is mass / free-fall time (~ exponential) Luminosity has accretion component ( infall rate) and stellar component (from pre-ms models) Asterisks: models at 1, 2,, yr

12 Tracks show example protostars that reach the main sequence at 0.12, 0.58, 2.8 M 2.8 M 0.58 M 0.12 M Model Results Exponentially declining infall reproduces quick drop in luminosity and flat mass histogram Formation of a realistic range of stellar masses reproduces spread in luminosities Major implication: stars are half-formed in < 10 5 yr Asterisks: models at 1, 2,, yr

13 Conclusions We assembled µm SEDs and 7 yr variability data for 315 protostars in the Orion molecular clouds Evolutionary Diagrams from SEDs Large spread in luminosity 30% of protostars are in Class 0 Decline in luminosity with evolution Survey for Outbursts Protostars have 1 mag outbursts every ~1000 yr Explains part of scatter in diagrams Secular or Stochastic Evolution? Evolutionary diagrams can be explained with exponentially declining infall rates that form a range of stellar masses Outbursts clearly happen, but they are not a major factor in the evolutionary diagrams