Eruptive phenomena in early stellar evolution

Herbig, G. H.

doi:10.1086/155615

Cited by 493 publications

(471 citation statements)

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“…and EXor outbursts in more evolved pre-main-sequence stars (Herbig 1977;Audard et al 2014). Episodic accretion can also affect processes such as disk fragmentation (Stamatellos et al 2011(Stamatellos et al , 2012 and lithium depletion (Baraffe & Chabrier 2010).…”

Section: And For Fuormentioning

confidence: 99%

Chemical tracers of episodic accretion in low-mass protostars

Visser

Bergin

Jørgensen

2015

A&A

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Aims. Accretion rates in low-mass protostars can be highly variable in time. Each accretion burst is accompanied by a temporary increase in luminosity, heating up the circumstellar envelope and altering the chemical composition of the gas and dust. This paper aims to study such chemical effects and discusses the feasibility of using molecular spectroscopy as a tracer of episodic accretion rates and timescales. Methods. We simulate a strong accretion burst in a diverse sample of 25 spherical envelope models by increasing the luminosity to 100 times the observed value. Using a comprehensive gas-grain network, we follow the chemical evolution during the burst and for up to 10 5 yr after the system returns to quiescence. The resulting abundance profiles are fed into a line radiative transfer code to simulate rotational spectra of C 18 O, HCO + , H 13 CO + , and N 2 H + at a series of time steps. We compare these spectra to observations taken from the literature and to previously unpublished data of HCO + and N 2 H + 6−5 from the Herschel Space Observatory. Results. The bursts are strong enough to evaporate CO throughout the envelope, which in turn enhances the abundance of HCO + and reduces that of N 2 H + . After the burst, it takes 10 3 -10 4 yr for CO to refreeze and for HCO + and N 2 H + to return to normal. The H 2 O snowline expands outwards by a factor of ∼10 during the burst; afterwards, it contracts again on a timescale of 10 2 -10 3 yr. The chemical effects of the burst remain visible in the rotational spectra for as long as 10 5 yr after the burst has ended, highlighting the importance of considering luminosity variations when analyzing molecular line observations in protostars. The spherical models are currently not accurate enough to derive robust timescales from single-dish observations. As follow-up work, we suggest that the models be calibrated against spatially resolved observations in order to identify the best tracers to be used for statistically significant source samples.

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Section: And For Fuormentioning

confidence: 99%

Chemical tracers of episodic accretion in low-mass protostars

Visser

Bergin

Jørgensen

2015

A&A

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“…The photometry in 2006 listed in Table 1 which covers almost 200 days shows only a marginal trend for a brightness decrease and no evidence for strong fluctuations. For comparison, the high-state of EX Lupi in 1955-1956 lasted about 250 days (Herbig 1977). Future brightness monitoring and spectroscopy will prove whether L1415-IRS belongs to the class of FUors or shares more similarities with EXors.…”

Section: Fuor-or Exor-like Activity Of L1415-irsmentioning

confidence: 99%

The new nebula in LDN 1415 – A cry from the cradle of a low-luminosity source

Stecklum¹,

Melnikov

Meusinger³

2006

A&A

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Aims.A survey for candidate Herbig-Haro objects was performed to search for evidence of star formation in Galactic dark clouds Methods. For this aim true colour images were created from blue, red, and infrared DSS2 plates and inspected. Follow-up I-band, Hα, and [S ii] CCD imaging as well as long-slit spectroscopy using the Tautenburg 2-m telescope was carried out to verify candidate objects.Results. In the case of LDN 1415, the presence of a Herbig-Haro flow could be revealed which is henceforth named HH 892. In addition, an arcuate nebula was found which is barely seen on the DSS2 infrared plate (epoch 1996) and not detected in archival Kiso Schmidt data (epoch 2001). Thus, this nebula must have brightened by about 3.8 mag in recent years. Conclusions. The nebula is associated with IRAS 04376+5413. The 2MASS images show a red counterpart of the IRAS source, designated as L1415-IRS. Its morphology resembles that of a bipolar young object. The luminosity of this source integrated from 0.9 µm to 60 µm in the low state amounts to 0.13 L for an assumed distance of 170 pc. Thus it seems to be a young very-low mass star or it might even be of substellar mass. The current brightness increase of the nebula is caused by a FUor-or EXor-like outburst as indicated by the presence of a P Cygni profile of the Hα line. L1415-IRS is by far the least luminous member of the sparse sample of FUor and EXor objects.

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“…Photometric variability in young stars is mostly due to dark (cool) and bright (hot) spots and flare activity, which are related to the strengthened magnetic activy due to fast rotation, and interactions with circumstellar discs, such as intense, variable accretion episodes or occultations (e.g. classical works : Joy 1945;Walker 1956;Herbig 1977-theoretical works: Koenigl 1991Collier Comeron & Campbell 1993;Shu et al 1994-modern observational works: Bouvier et al 1993Herbst et al 1994;Thé et al 1994;Hartmann & Kenyon 1996;Hamilton et al 2001;Eiroa et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

2010

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We look for high-amplitude variable young stars in the open clusters and associations of the Orion Belt. We use public data from the ASAS-3 Photometric V -band Catalogue of the All Sky Automated Survey, infrared photometry from the 2MASS and IRAS catalogues, proper motions, and the Aladin sky atlas to obtain a list of the most variable stars in a survey area of side 5 deg centred on the bright star Alnilam (ǫ Ori) in the centre of the Orion Belt. We identify 32 highly-variable stars, of which 16 had not been reported to vary before. They are mostly variable young stars and candidates (16) and background giants (8), but there are also field cataclysmic variables, contact binaries, and eclipsing binary candidates. Of the young stars, which typically are active Herbig Ae/Be and T Tauri stars with Hα emission and infrared flux excess, we discover four new variables and confirm the variability status of another two. Some of them belong to the well known σ Orionis cluster. Besides, six of the eight giants are new variables, and three are new periodic variables.

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Eruptive phenomena in early stellar evolution

Cited by 493 publications

References 0 publications

Chemical tracers of episodic accretion in low-mass protostars

Chemical tracers of episodic accretion in low-mass protostars

The new nebula in LDN 1415 – A cry from the cradle of a low-luminosity source

Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

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