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?
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