Star Formation in a Crossing Time

Elmegreen, Bruce G.

doi:10.1086/308361

Cited by 548 publications

(628 citation statements)

References 69 publications

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“…As most of the stars used in this study are located in the S Mon region or halo region, and given the embedded population in the Spokes and Cone nebula regions, the formation timescale of the entire region of NGC 2264 is likely to be about 4-5 Myr. The extremely extended star formation scenarios (Herbig 1962;Palla & Stahler 1999, 2000 can be ruled out, at least for NGC 2264.…”

Section: Discussionmentioning

confidence: 99%

“…He presumed that lowmass star formation occurred prior to the formation of highmass stars, and that star formation within a cluster could be prolonged for up to~10 8 years. Palla & Stahler (1999, 2000 suggested a revised version of the sequential star formation speculated by Herbig (1962) using their own PMS evolutionary models. According to their argument, star formation started at an early epoch (about 10 Myr ago), and then the star formation rate accelerated in the present epoch (1-2 Myr ago).…”

Section: Introductionmentioning

confidence: 99%

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A Constraint on the Formation Timescale of the Young Open Cluster NGC 2264: Lithium Abundance of Pre-Main Sequence Stars

Lim

Sung

Kim

et al. 2016

ApJ

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The timescale of cluster formation is an essential parameter in order to understand the formation process of star clusters. Pre-main sequence (PMS) stars in nearby young open clusters reveal a large spread in brightness. If the spread were considered to be a result of a real spread in age, the corresponding cluster formation timescale would be about 5-20 Myr. Hence it could be interpreted that star formation in an open cluster is prolonged for up to a few tens of Myr. However, difficulties in reddening correction, observational errors, and systematic uncertainties introduced by imperfect evolutionary models for PMS stars can result in an artificial age spread. Alternatively, we can utilize Li abundance as a relative age indicator of PMS star to determine the cluster formation timescale. The optical spectra of 134 PMS stars in NGC 2264 have been obtained with MMT/Hectochelle. The equivalent widths have been measured for 86 PMS stars with a detectable Li line (). Li abundance under the condition of local thermodynamic equilibrium (LTE) was derived using the conventional curve of growth method. After correction for non-LTE effects, we find that the initial Li abundance of NGC 2264 is. From the distribution of the Li abundances, the underlying age spread of the visible PMS stars is estimated to be about 3-4 Myr and this, together with the presence of embedded populations in NGC 2264, suggests that the cluster formed on a timescale shorter than 5 Myr.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Constraint on the Formation Timescale of the Young Open Cluster NGC 2264: Lithium Abundance of Pre-Main Sequence Stars

Lim

Sung

Kim

et al. 2016

ApJ

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“…Elmegreen 2000;Hartmann, Ballesteros-Paredes & Bergin 2001;Lada & Lada 2003). Since τcross will almost invariably be shorter than τ disc , the realistic probability of encounter has an upper bound of P∆ t =τcross .…”

Section: Discussion: Are Disc Encounters Likely In Star-forming Regions?mentioning

confidence: 99%

Stellar orbit evolution in close circumstellar disc encounters

Muñoz

Kratter

Vogelsberger

et al. 2014

Monthly Notices of the Royal Astronomical Society

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The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3-D, focusing on disc-disc interactions that result from stellar fly-bys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3-D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericenter separation r p , disc orientation and disc-star mass ratio (M d /M * ) on the orbital evolution of the host stars. Close encounters (2r p disc radius) can truncate discs on very short time scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that for realistic primordial disc masses M d 0.1M * , non-colliding encounters induce minor orbital changes, which is consistent with analytic calculations of encounters in the linear regime. The same disc masses produce entirely different results for grazing/colliding encounters. In the latter case, rapidly cooling discs lose orbital energy by radiating away the energy excess of the shock-heated gas, thus causing capture of the host stars into a bound orbit. In rare cases, a tight binary with a circumbinary disc forms as a result of this encounter.

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“…There has been evidence for the photoevaporation process decreasing the disc fraction of PMS stars within a few parsecs (Guarcello et al 2010;Roccatagliata et al 2011). Alternatively, ionising fronts of O-stars are thought to trigger star formation by collapsing molecular clouds (see Elmegreen 2000;Sicilia-Aguilar et al 2010;Barentsen et al 2011;Karr, Manoj & Ohashi 2009;Snider et al 2009). …”

Section: Accretion Properties With Respect To O Starsmentioning

confidence: 99%

Classical T Tauri stars with VPHAS+ – I. H α andu-band accretion rates in the Lagoon Nebula M8

Kalari

Drew

Barentsen

et al. 2015

Mon. Not. R. Astron. Soc.

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We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using ugriHα photometry from the VPHAS+ survey. Our sample consists of stars displaying Hα-excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the u-band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using Hα and u-band intensities to be ∼ 0.17 dex, agreeing with previous estimates (0.04-0.4 dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star forming processes suggested in the literature.

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Star Formation in a Crossing Time

Cited by 548 publications

References 69 publications

A Constraint on the Formation Timescale of the Young Open Cluster NGC 2264: Lithium Abundance of Pre-Main Sequence Stars

A Constraint on the Formation Timescale of the Young Open Cluster NGC 2264: Lithium Abundance of Pre-Main Sequence Stars

Stellar orbit evolution in close circumstellar disc encounters

Classical T Tauri stars with VPHAS+ – I. H α andu-band accretion rates in the Lagoon Nebula M8

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