Old Stars in Young Clusters: Lithium-depleted Low-Mass Stars of the Orion Nebula Cluster

Palla, F.; Randich, S.; Pavlenko, Ya. V.; Flaccomio, E.; Pallavicini, R.

doi:10.1086/516733

Cited by 77 publications

(101 citation statements)

References 23 publications

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“…6, the bulk of the measured pEWs above the chosen threshold is located around a median value of 560 mÅ with a dispersion of ∼100 mÅ. According to the curves of growth derived by Palla et al (2007) for a sample of stars observed by GIRAFFE and very similar to that described in this paper, this median pEW is compatible with the full preservation of lithium. In the σ Ori cluster, we found a few sources with pEWs between 250 and 400 mÅ.…”

Section: Membershipsupporting

confidence: 73%

FLAMES spectroscopy of low-mass stars in the young clusters σ Ori and λ Ori

Sacco

Franciosini²,

Randich

et al. 2008

A&A

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181

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Aims. We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1-10 Myr) clusters σ Ori and λ Ori. Methods. We observed 98 and 49 low-mass (0.2-1.0 M ) stars in σ Ori and λ Ori respectively, using the multi-object optical spectrograph FLAMES at the VLT, with the high-resolution (R ∼ 17 000) HR15N grating (6470-6790 Å). We used radial velocities, Li and Hα to establish cluster membership and Hα and other optical emission lines to analyze the accretion properties of members. Results. We identified 65 and 45 members of the σ Ori and λ Ori clusters, respectively, and discovered 16 new candidate binary systems. We also measured rotational broadening for 20 stars and estimated the mass accretion rates in 25 stars of the σ Ori cluster, finding values between 10 −11 and 10 −7.7 M yr −1 and in 4 stars of the λ Ori cluster, finding values between 10 −11 and 10 −10.1 M yr −1 . Comparing our results with the infrared photometry obtained by the Spitzer satellite, we find that the fraction of stars with disks and the fraction of active disks is larger in the σ Ori cluster (52 ± 9% and 78 ± 16%) than in λ Ori (28 ± 8% and 40 ± 20%). Conclusions. The different disk and accretion properties of the two clusters could be due either to the effect of the high-mass stars and the supernova explosion in the λ Ori cluster or to different ages of the cluster populations. Further observations are required to draw a definitive conclusion.

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Section: Membershipsupporting

confidence: 73%

FLAMES spectroscopy of low-mass stars in the young clusters σ Ori and λ Ori

Sacco

Franciosini²,

Randich

et al. 2008

A&A

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181

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“…6 the observed equivalent widths are also compared with curves of growth calculated by Zapatero Osorio et al (2002) and by Palla et al (2007). Palla et al (2007) provided the lithium abundance, A(Li), in steps of 0.5, and we show the curves for log g = 4.0 and 4.5. Zapatero Osorio et al (2002) covered a wider temperature range.…”

Section: Lithium Absorptionmentioning

confidence: 79%

X-shooter spectroscopy of young stellar objects

Stelzer

Frasca

Alcalá

et al. 2013

A&A

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Context. Traditionally, the chromospheres of late-type stars are studied through their strongest emission lines, Hα and Ca ii HK emission. Our knowledge on the whole emission line spectrum is more elusive as a result of the limited spectral range and sensitivity of most available spectrographs. Aims. We intend to reduce this gap with a comprehensive spectroscopic study of the chromospheric emission line spectrum of a sample of non-accreting pre-main sequence stars (Class III sources). Methods. We analyzed X-shooter/VLT spectra of 24 Class III sources from three nearby star-forming regions (σ Orionis, Lupus III, and TW Hya). We determined the effective temperature, surface gravity, rotational velocity, and radial velocity by comparing the observed spectra with synthetic BT-Settl model spectra. We investigated in detail the emission lines emerging from the stellar chromospheres and combined these data with archival X-ray data to allow for a comparison between chromospheric and coronal emissions. Results. For some objects in the sample the atmospheric and kinematic parameters are presented here for the first time. The effective temperatures are consistent with those derived for the same stars from an empirical calibration with spectral types. Small differences in the surface gravity found between the stars can be attributed to differences in the average age of the three star-forming regions. The strength of lithium absorption and radial velocities confirm the young age of all but one object in the sample (Sz 94). Both X-ray and Hα luminosity as measured in terms of the bolometric luminosity are independent of the effective temperature for early-M stars but decline toward the end of the spectral M sequence. For the saturated early-M stars the average emission level is almost one dex higher for X-rays than for Hα: log (L x /L bol ) = −2.85 ± 0.36 vs. log (L Hα /L bol ) = −3.72 ± 0.21. When all chromospheric emission lines (including the Balmer series up to H11, Ca ii HK, the Ca ii infrared triplet, and several He i lines) are summed up the coronal flux still dominates that of the chromosphere, typically by a factor 2−5. Flux-flux relations between activity diagnostics that probe different atmospheric layers (from the lower chromosphere to the corona) separate our sample of active pre-main sequence stars from the bulk of field M dwarfs studied in the literature. Flux ratios between individual optical emission lines show a smooth dependence on the effective temperature. The Balmer decrements can roughly be reproduced by an NLTE radiative transfer model devised for another young star of similar age. Future, more complete chromospheric model grids can be tested against this data set.

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“…Population A would need to be older (on average) by an amount which is dependent on the the way that EW(Li) is translated into a Li abundance. Because the Li i 6708 Å line is in the saturated part of the curve of growth, a small change in EW(Li) corresponds to a large change in Li abundance (Palla et al 2007), but Li-depletion is also very rapid at these masses, so a large change in abundance is expected in a small amount of time. Adopting the models of Baraffe et al (1998) and the isochrones shown in Fig.…”

Section: Lithium Depletionmentioning

confidence: 99%

TheGaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

Jeffries

Jackson

Cottaar

et al. 2014

A&A

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127

256

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Context. A key science goal of the Gaia-ESO survey (GES) at the VLT is to use the kinematics of low-mass stars in young clusters and star forming regions to probe their dynamical histories and how they populate the field as they become unbound. The clustering of low-mass stars around the massive Wolf-Rayet binary system γ 2 Velorum was one of the first GES targets. Aims. We empirically determine the radial velocity precision of GES data, construct a kinematically unbiased sample of cluster members and characterise their dynamical state. Methods. Targets were selected from colour-magnitude diagrams and intermediate resolution spectroscopy was used to derive radial velocities and assess membership from the strength of the Li i 6708 Å line. The radial velocity distribution was analysed using a maximum likelihood technique that accounts for unresolved binaries. Results. The GES radial velocity precision is about 0.25 km s −1 and sufficient to resolve velocity structure in the low-mass population around γ 2 Vel. The structure is well fitted by two kinematic components with roughly equal numbers of stars; the first has an intrinsic dispersion of 0.34 ± 0.16 km s −1 , consistent with virial equilibrium. The second has a broader dispersion of 1.60 ± 0.37 km s −1 and is offset from the first by 2 km s −1 . The first population is older by 1-2 Myr based on a greater level of Li depletion seen among its M-type stars and is probably more centrally concentrated around γ 2 Vel. Conclusions. We consider several formation scenarios, concluding that the two kinematic components are a bound remnant of the original, denser cluster that formed γ 2 Vel, and a dispersed population from the wider Vela OB2 association, of which γ 2 Vel is the most massive member. The apparent youth of γ 2 Vel compared to the older (≥10 Myr) low-mass population surrounding it suggests a scenario in which the massive binary formed in a clustered environment after the formation of the bulk of the low-mass stars.

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Old Stars in Young Clusters: Lithium-depleted Low-Mass Stars of the Orion Nebula Cluster

Cited by 77 publications

References 23 publications

FLAMES spectroscopy of low-mass stars in the young clusters σ Ori and λ Ori

FLAMES spectroscopy of low-mass stars in the young clusters σ Ori and λ Ori

X-shooter spectroscopy of young stellar objects

TheGaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

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