Lithium abundances among solar-type pre-main-sequence stars

Strom, K. M.; Wilkin, Francis P.; Strom, S. E.; Seaman, R.

doi:10.1086/115230

Cited by 46 publications

(35 citation statements)

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“…Observations of (mostly near-) infrared disk emission and gaseous accretion onto central stars show a strong decline in the frequency of these disk signatures between $1 and 10 Myr (Strom et al 1989;Skrutskie et al 1990;Hillenbrand et al 1998;Lada et al 2000;Muzerolle et al 2000;Haisch et al 2001;Briceño et al 2001;Sicilia-Aguilar et al 2005b, hereafter Paper II; Calvet et al 2005). This decrease in dust emission and gas accretion is plausibly related to giant planet formation, which is thought to take a few megayears or more in the core accretion picture (e.g., Podolak et al 1993 and references therein).…”

Section: Introductionmentioning

confidence: 99%

“…Grain growth, settling to the midplane, and formation of rocky planetesimals are thought to occur fastest in the inner disk (e.g., Hayashi et al 1985); the corresponding reduction in the abundance of small dust particles would result in a faster decline of disk emission at shorter wavelengths (Strom et al 1989;Skrutskie et al 1990). Of particular interest are ''transition disk'' objects, systems with strong mid-to far-infrared disk emission but very weak or absent near-infrared emission, and sometimes strongly reduced or absent gaseous accretion, such as TW Hya Uchida et al 2004) and CoKu Tau 4 (Forrest et al 2004;D'Alessio et al 2005b).…”

Section: Introductionmentioning

confidence: 99%

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Disk Evolution in Cep OB2: Results from theSpitzer Space Telescope

Sicilia‐Aguilar

Hartmann

Calvet

et al. 2006

ApJ

246

291

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We present the results of an infrared imaging survey of two clusters in the Cep OB2 Association, Tr 37 and NGC 7160, using the IRAC and MIPS instruments on board the Spitzer Space Telescope. Our observations cover the wavelength range from 3.6 to 24 m, allowing us to detect disk emission over a typical range of radii $0.1 to $20 AU from the central star. In Tr 37, with an age of about 4 Myr, about 48% of the low-mass stars exhibit detectable disk emission in the IRAC bands. Roughly 10% of the stars with disks may be ''transition'' objects, with essentially photospheric fluxes at wavelengths 4.5 m but with excesses at longer wavelengths, indicating an optically thin inner disk. The median optically thick disk emission in Tr 37 is lower than the corresponding median for stars in the younger Taurus region; the decrease in infrared excess is larger at 6-8 m than at 24 m, suggesting that grain growth and/or dust settling has proceeded faster at smaller disk radii, as expected on general theoretical grounds. Only about 4% of the low-mass stars in the 10 Myr old cluster NGC 7160 show detectable infrared disk emission. We also find evidence for 24 m excesses around a few intermediate-mass stars, which may represent so-called ''debris disk'' systems. Our observations provide new constraints on disk evolution through an important age range.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Disk Evolution in Cep OB2: Results from theSpitzer Space Telescope

Sicilia‐Aguilar

Hartmann

Calvet

et al. 2006

ApJ

246

291

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“…More than 80% of the low-mass stars aged $1 Myr have accreting disks, with accretion rates around 10 À8 M yr À1 ( Hillenbrand et al 1995;Haisch et al 2001;Gullbring et al 1998). By the age of $4 Myr, disk fractions drop to around $45%, and accreting disks are a rare feature in regions aged $10-12 Myr (Strom et al 1989;Skrutskie et al 1990;Lada et al 2000;Carpenter et al 1990;Armitage et al 2003;Sicilia-Aguilar et al 2006), suggesting that most of the disk dissipation (and probably planet formation) occurs within 1-10 Myr (Haisch et al 2001;Bergin et al 2004;Forrest et al 2004;D'Alessio et al 2005;Sicilia-Aguilar et al 2006). Moreover, the changes in the spectral energy distributions (SEDs) at these ages suggest that important dust evolution (via grain growth and/or dust settling) is taking place during these ages (Sicilia-Aguilar et al 2006).…”

Section: Introductionmentioning

confidence: 99%

High-Resolution Spectroscopy in Tr 37: Gas Accretion Evolution in Evolved Dusty Disks

Sicilia‐Aguilar¹,

Hartmann²,

Fürész³

et al. 2006

Astron J

147

155

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Using the Hectochelle multifiber spectrograph, we have obtained high-resolution (R $ 34; 000) spectra in the H region for a large number of stars in the 4 Myr old cluster Tr 37, containing 146 previously known members and 26 newly identified ones. We present the H line profiles of all members, compare them to our IR observations of dusty disks ( Two Micron All Sky Survey JHK + IRAC + MIPS 24 m), use the radial velocities as a membership criterion, and calculate the rotational velocities. We find a good correlation between the accretion-broadened profiles and the presence of protoplanetary disks, noting that a small fraction of the accreting stars presents broad profiles with H equivalent widths smaller than the canonical limit separating classical T Tauri stars (CTTSs) and weak-lined T Tauri stars (WTTSs). The number of strong accretors appears to be lower than in younger regions, and a large number of CTTSs have very small accretion rates (Ṁ 10 À9 M yr À1 ). Taking into account that the spectral energy distributions are consistent with dust evolution (grain growth/settling) in the innermost disk, this suggests a parallel evolution of the dusty and gaseous components. We also observe that about half of the ''transition objects'' (stars with no IR excesses at k 6 m) do not show any signs of active accretion, whereas the other half is accreting with accretion rates 10 À9 M yr À1 . These zero or very low accretion rates reveal important gas evolution and/or gas depletion in the innermost disk, which could be related to grain growth up to planetesimal or even planet sizes. Finally, we examine the rotational velocities of accreting and nonaccreting stars, finding no significant differences that could indicate disk locking at these ages.

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“…The star LkCa 4, a WTTS member of the Taurus Molecular Cloud (Herbig et al 1986;Strom et al 1989a; Downes & Keyes 1988;Strom et al 1989b) is an ideal exemplar for a spotted pre-MS star because it does not have any mid-IR or mm excess (e.g. Andrews & Williams 2005;Furlan et al 2006;Buckle et al 2015) and is not actively accreting (e.g.…”

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confidence: 99%

Placing the Spotted T Tauri Star LkCa 4 on an HR Diagram

Gully-Santiago

Herczeg

Czekala

et al. 2017

ApJ

135

111

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Ages and masses of young stars are often estimated by comparing their luminosities and effective temperatures to pre-main sequence stellar evolution tracks, but magnetic fields and starspots complicate both the observations and evolution. To understand their influence, we study the heavily-spotted weak-lined T-Tauri star LkCa 4 by searching for spectral signatures of radiation originating from the starspot or starspot groups. We introduce a new methodology for constraining both the starspot filling factor and the spot temperature by fitting two-temperature stellar atmosphere models constructed from Phoenix synthetic spectra to a high-resolution near-IR IGRINS spectrum. Clearly discernable spectral features arise from both a hot photospheric component T hot ∼ 4100 K and to a cool component T cool ∼ 2700 − 3000 K, which covers ∼ 80% of the visible surface. This mix of hot and cool emission is supported by analyses of the spectral energy distribution, rotational modulation of colors and of TiO band strengths, and features in low-resolution optical/near-IR spectroscopy. Although the revised effective temperature and luminosity make LkCa 4 appear much younger and lower mass than previous estimates from unspotted stellar evolution models, appropriate estimates will require the production and adoption of spotted evolutionary models. Biases from starspots likely afflict most fully convective young stars and contribute to uncertainties in ages and age spreads of open clusters. In some spectral regions starspots act as a featureless "veiling" continuum owing to high rotational broadening and heavy line-blanketing in cool star spectra. Some evidence is also found for an anti-correlation between the velocities of the warm and cool components.

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Lithium abundances among solar-type pre-main-sequence stars

Cited by 46 publications

References 0 publications

Disk Evolution in Cep OB2: Results from theSpitzer Space Telescope

Disk Evolution in Cep OB2: Results from theSpitzer Space Telescope

High-Resolution Spectroscopy in Tr 37: Gas Accretion Evolution in Evolved Dusty Disks

Placing the Spotted T Tauri Star LkCa 4 on an HR Diagram

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