FUors: the smoking gun for episodic accretion, or misfit young stars?

Courtesy: R. Hurt, SSC

Ábrahám et al., 2009, Nature, 459, 224

FUors: the smoking gun for episodic accretion, or misfit young stars?

The FU Orionis Eruption: 1936Hartmann & Kenyon, 1996, ARAA, 34, 207

Courtesy: C. Briceno

Kenyon et al. (2000, ApJ 531, 1028)

Zhu et al. 2008, ApJ 684, 1281

Much wider than blackbody

Additional FUors 1950-1978

A few other stars with similar properties to FU Orionis were discovered, forming the “classical” FUor group (Herbig, 1977, ApJ, 217, 693; Elias, 1978, ApJ, 223, 859)

V1057 Cyg V1515 Cyg

Hartmann & Kenyon, 1996, ARAA, 34, 207

Dissecting the Electromagnetic Spectrum

Modified from Hartmann & Kenyon, 1996, ARAA, 34, 207

X-rayUV

OpticalNear-IR

Mid-IR

Far-IRSubmm

Radio

Millimeter

FUors as of 2013 Audard+14

FUor and EXor timescales are classically separable

Herbig G. H., 1977, AJ., 217, 693

Generic FUor

Variability-Typical periodic variability attributed to stellar rotation-Remaining few % color variations in UBVRI typical of FUors (Kenyon et al. 2000,Kenyon et al. 2009, Clarke et al. 2005, Green et al. 2013) – flickering/accretion event related (seen in T Tauri stars as well)

FU Ori

Kenyon+09

HBC 722

Green+13

Optical Spectroscopy• Broad blueshifted absorption in Na and Balmer lines (although

sometimes P Cygni or weak emission in Hα)– Drive powerful winds

• Magnetospheric accretion lines usually disappear during burst, or are not observed

• Optical F-G supergiant in many cases; in others (HBC 722?) stellar continuum may still dominate, and contribute to lines

Equivalent Width of Hβ absorption line jumped almost instantly-- uncorrelated with anything interesting happening in the overall lightcurve

Park, Lee, Green, Cochran et al., in prep.

Near-IR Spectroscopy

• CO absorption (often double-peaked) at 2.2 μm (disk), H2O absorption; characteristic of M atmospheres (3000 K)

• Some show CO in emission; whether this is the photosphere of the central star is unclear

• *HBC 722 was actually not detected in CO in one try with NIRSPEC (C. Salyk, priv. comm.)

Mid-IR (Spitzer)uncorrected for reddening: silicate dust is pristine

Amorphous silicates

Water vapor – disk photosphere?

Hot water screening an even hotter disk?

Sargent et al, subm.

Mid-IR Ices

Quanz+07Audard+10,12

H2O+CH3OH+CO2 mixtures from White et al. (2009)

FUor Subgroups

Figure from Quanz et al., 2007, ApJ, 668, 359;see also Green et al., 2006, ApJ, 648, 1099

Inclination effect?

“Embedded” “Flared Disk”

Ábraham et al., 2009, Nature, 459, 224

The Mid-IR: Long-Term Outburst Effects

Does dust processing from flash heating (or vertical transport and stirring of dust grains) occur on few month timescales?Unknown in FUors, which have yet to return to quiescence.

Herschel-eye View

Green+13

Far-IR Diagnostics

Green et al., in prep. Green et al., 2013, ApJ, 772, 117

Class I Protostar Classical FUor

Previously noted similarities at submillimeter wavelengths (e.g. Sandell & Weintraub, 2001, ApJS, 134, 155);--And from ISO: Lorenzetti et al., 2000, A&A, 357, 1035

Consistent with the Spitzer/Herschel perspective

CO Similarities

Other molecular emission consistent with protostars

Green+13c Green+14 in prep.

[OI] vs. CO spatially discrepant in HBC 722Line emissionLocal Continuum

Millimeter – PdBI/SMA

Kóspál (2010)

r (scattered light) vs. 13CO J=1-0

Pre-existing nebular material highlighted by burst; might even the “embedded” stage FUors be relatively evolved?

V1515 Cyg

The Millimeter Environs of FUorsDunham+12

CO J=2-1

Dunham+12, Green+11 1.3 mm

Dunham+ in prep.

Large spread in disk properties!

FUor stage?

YesV1057 CygV1515 CygV1735 CygHBC 722 (confused)

HCO+ 3-2(from CSO/Green+13)

NoFU Ori

Within 1 kpc of the Sun:

104 – 105 T Tauri stars x avg. accretion rate 10-8 M ⊙yr−1 = 10-3 M ⊙yr−1 8 FUors, combined accretion rate ~ few x 10-4 M ⊙yr−1

-FUors are responsible for ~ 10-50% of the current nearby accretion in Class II objects (decreased if we include Class I)

About 8 FUors since 1936; average star formation rate 1 / 50 yr (FUor list updated from Reipurth & Aspin 2010, Evolution of Cosmic Objects through their Physical Activity, 19; SFR from Miller & Scalo 1979, ApJS, 41, 513; see also Offner & McKee 2011, ApJ, 736, 53)

-FUors occur at several times the rate of star formation; averaging multiple bursts per star

(Updated from Hartmann & Kenyon, 1996, ARAA, 34, 207)

FUors are rarely seen…but they are common events!

So is FU Ori a typical FUor?