Probing Episodic Accre0on Process inVery Low Luminosity Objects
Tien-Hao Hsieh1,2, Nadia M. Murillo3, Arnaud Belloche4, Naomi
Hirano1, Catherine Walsh5, Ewine F. van Dishoeck3,6, Shih-Ping Lai2
1Academia Sinica Ins0tute of Astronomy & Astrophysics (ASIAA)
2Na0onal Tsing Hua University (NTHU)

3Leiden Observatory, Leiden University, Netherlands

4Max-Planck-Ins0tut für extraterrestrische Physik (MPE)
5University of Leeds
6Max-Planck-Ins0tut für Radioastronomie (MPIfR)

EAYAM 2017, Ishigaki

submi[ed to ApJOrigin of episodic accre0onfragment

Vorobyov & Basu (2005, 2010)

Origin of episodic accre0on
Mini0al = 1.1 Msun
Class 0Class IClass II

Mini0al = 1.5 Msun
Class 0Class I

Class II

Vorobyov & Basu (2013, 2015)

Evidence of episodic accre0on
Before 2004
Aaer 2004

V1647 Ori

[CFT93]216-2

Luminosity varia0on can only bedetected via long-turn obs.
Andrew+ (2004); Àbrahàm+ (2004)

OO Serpen0s

Carah o Garah+ (2011)ḱospál+ (2007)

Chemical Probes (CO/N2H+)

Lstar = LCO

Lstar+Lacc,burst = LCO

N2H+Jørgensen et al. (2015)

Lbol<<LCO !!Chemical Probes (CO/N2H+)

Lstar+Lacc,burst = LCO
Lstar = LCO
Lbol<<LCO !!
N2H+ dele0on + extended CO is asignature of past episodic accre0on.
N2H+Jørgensen et al. (2015)

Chemical Probes toward Class 0/I objects
VeLLO-IRAM 04191

Belloche+ 2002

Jørgensen et al. (2013,2015)
Frieman et al. (2016, 2017)
Lee 2007, JKASChemical Probes toward Class 0/I obj.
VeLLO-IRAM 04191

Belloche+ 2002

Jørgensen et al. (2013,2015)
Jørgensen (2013,2015)

Sample:• 8 Very Low Luminosity Objects (VeLLOs)
Lint ≤ 0.1 L¤ (Di Francesco et al. 2007)• The natures of VeLLOs (Dunham+ 2014)u Protostars at a quiescent accre0on phaseSample:• 8 Very Low Luminosity Objects (VeLLOs)
Lint ≤ 0.1 L¤ (Di Francesco et al. 2007)• The natures of VeLLOs (Dunham+ 2014)
IRAS16253

André et al. (1999)
ICE348-SMM2
u Protostars
ataquiescentaccre0onphase
Hsieh+(2016);
Belloche et al. (2002)

IRAM 04191:

Palau et al. (2014)

Cha – MMS1:

Protostars in a very
early stage

Belloche et al. (2006)
Tsitali et al. (2013)

Hsieh et al. (2015, 2017)

Yen+ (2015, 2017);
Tobin+ (2011)

Very low mass stars
or Brown Dwarfs

C18O/13CO (1—0) on con0nuum maps

Chemical probe C18O/N2H+ pairChemical probe CO/N2H+ pair

C18O/13CO/C17O/N2H+?

Chemical probe CO/N2H+ pair

C18O/13CO/C17O/N2H+?

Chemical probe CO/N2H+ pairChemical models

CO snowline radius vs Luminosity

CO snowline radius vs Luminosity
Macc=10-6-10-5 Msun yr-1

5/8: a past accre0on burst occur in 10,000 yr
2/8: Unclear
1/8: without a past accre0on burst=> Time interval ~ 12,000-16,000 yr

Conclusions• 5/8 with con0nuum detec0ons (no mul0ple sources at ~250 au)• 5-7 out of 8 targets in our VeLLOs shows an recent accre0on bursts.
– N2H+ depleted/CO evaporated in center– Frac0on: similar or slightly larger than that of Class 0/I in
Jorgensen+ (2015)/Frimann+ (2017) => interval of accre0on
burst ~12,000-16,000 yrs– Episodic accre0on may start at very early stage if VeLLOs areextremely young• Mass accre0on rates of 5×10-5-5×10-6 Msun yr-1 during burst. To forma typical mass star (0.5 Msun), it takes 3--5% of 0me in the burstphase.

Thank you for your a[en0on

Chemical probes (CH3OH) of Episodic Accre0on
CH3OH
H2COIRAS 15398

Jørgensen+ (2013)

Luminosity problem

Lbol ~ Lstar,disk + Lenv + Lacc
(Ṁ ~ 2 x 106 Msun yr-1)

Lbol (Lsun)

Lacc ~ a few tens Lsun

Tbol (K)Evans et al. (2009), Kenyon et al. (1990)

A solu0on of Luminosity problem Episodic accre0on => varia0on in Lacc

Dunham et al. (2010)

A solu0on of Luminosity problem Episodic accre0on => varia0on in Lacc

Dunham et al. (2010)

Extremely young protostars:
IRAM 04191:

André et al. (1999)
Belloche et al. (2002)

Very low-mass stars:
ICE348-SMM2

IRAS16253
APEX CO (6—5)H2

IRAC1

Cha – MMS1:

Belloche et al. (2006)
Tsitali et al. (2013)
Palau et al. (2014)

Hsieh et al. (2015, 2017)

Hsieh+ (2016);
Yen+ (2015, 2017);
Tobin+ (2011)