Protostars in Diverse Environments: Unraveling the
Role of Nature vs Nurture in Low Mass Star Formation
Results from the Herschel Orion Protostar Survey
Thomas Stanke
(ESO)
Tom Megeath (U. Toledo)
Joseph Booker (U.Toledo)
Will Fischer (GSFC)
Elise Furlan (IPAC)
Marina Kounkel (U. Michigan)
Amy Stutz (MPIA)
John Tobin (Leiden)
Mayra Osorio (IAA))
Babar Ali (SSI)
Lori Allen (NOAO)
Nuria Calvet (U.Michigan)
Lee Hartmann (U.Michigan)
Brian Mazur (U of Toledo)
Charles Poteet (RPI)
James Muzerolle (STScI)
3.6 micron
70 micron
160 micron
Dan Watson (U.Rochester)
P. Manoj (TIFR)
Beatriz Gonzalez (ESA)
Roland Vavrek (ESA)
David Neufeld (JHU)
Ted Bergin (U.Michigan)
Ruud Visser (ESO)
Melissa McClure (ESO)
Thomas Henning (MPIA)
James DiFrancesco (NRC)
Tom Wilson (NRL)
Phil Myers (CfA)
What controls mass
accretion onto
protostars?
1.6 μm image from WFC3
What controls mass
accretion onto
protostars?
Infalling Envelope
Fragmentation
Disk Accretion
Formation
Environment
1.6 μm image from WFC3
Artist conception
by Robert Hurt
Outflow
What controls mass
accretion onto
protostars?
Infalling Envelope
Fragmentation
Disk Accretion
Formation
Environment
1.6 μm image from WFC3
Artist conception
by Robert Hurt
Outflow
Use Large Sample of Protostars in Diverse
Environments in Orion to Probe these Factors
Protostellar Evolution in SEDs & Images
Class 0
Class 0 Protostar
+
+
–
+
+
–
Class I
Class I Protostar
Flat Spectrum
Protostar
2MASS
Spitzer
Spitzer/IRS
Herschel
APEX
Model (J. Tobin)
Pre-ms star
with disk
Evolution
WFC3 1.6 μm
Manoj et al. 2013
Stutz et al. 2013
Fischer et al. 2014 Kounkel et al. 2016
Furlan et al 2016 Booker et al. in prep.
Stutz et al. 2013
24 micron
70 micron
870 micron
How Fast Do Protosars Evolve?
Number
Fraction
Lifetime
PBRS
18
0.06
0.03 Myr
Class 0
84
0.26
0.13 Myr
Class I
125
0.39
0.20 Myr
Flat Spect.
102
0.32
0.16 Myr
Stutz et al. 2013
Dunham et 2014
Furlan et al 2016
Outflows demonstrate connection between
bolometric luminosity and accretion
CO lines dominated spectrum
Manoj et al. 2013, in prep.
Herschel Observations of HOPS, PBRS, and Digit samples
Show Correlation between bolometric luminosity and far-IR CO
Luminosity.
Evidence for Exponentially Decreasing Infall Rates
Fischer et al. in prep.
Flat distribution of Tbol and Menv + assumption of constant SFR
=> exponentially decreasing infall rate.
Decrease in Bolometric Luminosity Evidence for
Exponentially Decreasing Infall Rates
Fischer et al. in prep.
Decrease in luminosity can be explained by exponentially decreasing
infall (and accretion) rates – by factor 50 from Class0 to flat-spectrum.
But what factors are responsible?
Are Outflows Responsible for Halting Infall?
NICMOS 1.6 and 2.05 μm
Fischer et al. 2014
Booker et al. in prep.
Use 1.6 μm images to measure outflow cavities
Are Outflows Responsible for Halting Infall?
No evidence of
progressive
clearing
(CO, Arce & Sargent 2006)
Evolution
Protostars with
evolved envelopes
can have narrow
cavities.
HST answer:
probably not
Booker et al. in
prep.
How do disks regulate accretion?
A Class 0 Protostar Undergoing an Outburst
12
Safron, Fischer et al. 2015
How do disks regulate accretion?
V1647 or McNeil’s Nebula
(2004)
“New” HOPS 383
(2006)
V2775 or HOPS 223
(2007)
Three outbursts (10-40x increase) 2003 - 2010 =>
319 protostars => outburst every ~800 years.
Duration of bursts needed to find mass accreted.
Disks modulate accretion, but may not halt infall
What is the role
of
environment?
<L> = 7.6 Lsun
<spacing> = 8000 AU
<L> = 0.7 Lsun
<spacing> = 13000 AU
3.6 µm / 24 µm / 870 µm
(Dunham et al. PPVI,
Megeath, Stanke, et al. in
prep. Stutz et al. in prep., Ali
et al. in prep.)
3.6 µm / 24 µm / 870 µm
Herschel Gould Belt Survey 500 µm image (Polychroni et al. 2013; Roy et al. 2013)
Luminosity and Separation of Protostars
depend on Gas Column Density
(Megeath, Stanke, et al. in prep. Stutz
et al. in prep., Ali et al. in prep.)
Derive column density from
APEX and Herschel data
Slope = 2.3
Slope = – 0.9
With increasing gas density
• Protostellar luminosity increases
• Projected separation decreases
Evidence that Multiplicity Depends on
Formation Environment
Companion fraction between 100 and 1000 AU
2000 WFC3 1.6 AU μm
Envir.
Density
Proto
stars
>45 pc-2 < 45 pc-2
(high)
(low)
19.2%
10.8%
Pre-ms
stars
13.9%
10.2%
Merged
YSOs
15.6%
10.5%
+/- 1-2% uncertainty due to LOS
correction
Kounkel et al. 2016
Evidence of enhanced formation of companions in dense environments.
16
Large samples needed to rule out random fluctuations with high significance.
ALMA 13CO and C18O Mapping of Orion Edge-on
Protostars (12 m + ACA + TP) Zsofia Nagy
blue = 2.5 ­ 3.15 km s
−1 blue = 7.6­8.2 km s −1
green = 3.15­3.8 km s green = 8.9­10 km s red red = 3.8­4.45 km s
= 8.2­8.9 km s
−1
−1 −1 HST
1.6 μm
−1 What controls mass
accretion onto
protostars?
4. Environments with
higher densities of
stars and/or gas
show evidence for
faster accretion, more
massive objects, and
a higher incidence
of 100-1000 AU
binaries.
1. Depletion of envelope
reduces/stops mass
accretion. But what
depletes envelope?
2. Frequent
outburst from
disk regulation
modulates
accretion
3. Outflow may have <40%
reduction of mass accretion,
but not dominant. Trace
mass accretion through far-IR lines
The End?
“Riddles”:
●
Protostars stop accreting.
●
Only 1/3 of the core ends up in star.
●
IMF virtually identical in very different regions.
The End?
“Riddles”:
●
Protostars stop accreting.
●
Only 1/3 of the core ends up in star.
●
IMF virtually identical in very different regions.
Wildly speculative! Solution?
●
Filament forms core.
●
Protostar+envelope forms in core.
●
Filament+core move away from protostar+env.
(cf. Stutz+Gould 2016) (core magnetically attached to filament?
Protostar+envelope ballistic?)
●
Accretion stops.
Corona Australis
130 pc
60 AU Resolution
Within 1.4 kpc, tens of thousands of
dusty YSOs can be resolved and
spectra obtained in a wide range of
environments, these are a natural
laboratory for low mass SF.
Orion Nebula
400 pc
60 AU Resolution
Cygnus-X
1.4 kpc
NGC 3603
Extrapolate with
Model of Low Mass SF
WFIRST:
20 AU Resolution
Serpens South
400 pc
Galactic Center
Antennae Galaxy
200 AU
Resolution
How Do Companions Form?
Do they form in disks, by envelope fragmentation, or both?
Mass function of companions is constraint on mechanism.
HOPS 170 protostar
Pre-ms star
Spectral types from low
resolution spectrum.
WFC3 and WFIRST can
detect companions and
isolated objects down to
5 MJup at 1 Myr year.
WFIRST spectroscopy
over large areas can
find rare, very low mass
objects.
x2
Pre-ms star
x2
IRTF SpeX spectra
Pre-ms star
x8
B. Mazur
Role of Outflows?
Arce & Sargent 2006
Current Picture: clearing by outflows stops infall/accretion
and contributes to inefficiency.
Mass to Length Ratio x
Typical Seperaton = available
mass
What is the mass available per star
in filaments?
What controls mass
accretion onto
protostars?
What processes control the
luminosities and evolution of
protostars?
Why do we get a large range
of protostar densities but a
relatively constant IMF?
What is responsible for the
low efficiency of star
formation (30-40% for cores)?
1.6 μm image from WFC3
Luminosity and Separation of Protostars
depend on Gas Column Density
(Megeath, Stanke, et al. in prep. Stutz
et al. in prep., Ali et al. in prep.)
Derive column density from
APEX and Herschel data
Slope = 2.3
Slope = – 0.9
Faster star formation or more massive
star formation?
With increasing gas density
• Protostellar luminosity increases
• Projected separation decreases
Luminosity and Separation of Protostars
Depend on Mass to Length Ratio Preliminary!!
Class 0
Class I/flat
slope ~ 0.5
Class 0
Class I/flat
slope ~ 3.3
mass to length x spacing
between protostars
Derive mass to length ratio from
APEX and Herschel data
Suggests that this may be in
part the result of faster star
formation!