X-Rays Surveys and the Post-T Tauri Problem

Briceño, César; Hartmann, L.; Stauffer, J. R.; Gagné, Marc; Stern, Robert; Caillault, J. P.

doi:10.1086/118293

Cited by 114 publications

(106 citation statements)

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“…In subjecting HD 105 to the ( Randich et al 2001) and stronger than that found in $120 Myr old Pleiades stars (Soderblom et al 1993). Finally, the X-ray luminosity of HD 105 [log (L X ) ¼ 29:4 ergs s À1 ; Cutispoto et al 2002] is similar to what is expected for early-G stars with ages of 10-100 Myr ( Briceño et al 1997). Therefore, we conclude that HD 105 is a likely member of the Tuc-Hor association.…”

Section: The Samplesupporting

confidence: 70%

Constraining the Lifetime of Circumstellar Disks in the Terrestrial Planet Zone: A Mid‐Infrared Survey of the 30 Myr old Tucana‐Horologium Association

Mamajek¹,

Meyer²,

Hinz³

et al. 2004

ApJ

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We have conducted an N-band survey of 14 young stars in the $30 Myr old Tucana-Horologium association to search for evidence of warm, circumstellar dust disks. Using the MIRAC-BLINC camera on the Magellan I (Baade) 6.5 m telescope, we find that none of the stars have a statistically significant N-band excess compared to the predicted stellar photospheric flux. Using three different sets of assumptions, this null result rules out the existence of the following around these post-T Tauri stars: (1) optically thick disks with inner hole radii of P0.1 AU, (2) optically thin disks with masses of less than 10 À6 M È (in $1 m sized grains) within P10 AU of these stars, and (3) scaled-up analogs of the solar system zodiacal dust cloud with more than 4000 times the emitting area. Our survey was sensitive to dust disks in the terrestrial planet zone with fractional luminosity of log (L dust =L Ã ) $10 À2:9 , yet none were found. Combined with results from previous surveys, these data suggest that circumstellar dust disks become so optically thin as to be undetectable at N band before age $20 Myr. We also present N-band photometry for several members of other young associations and a subsample of targets that will be observed with

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Section: The Samplesupporting

confidence: 70%

Constraining the Lifetime of Circumstellar Disks in the Terrestrial Planet Zone: A Mid‐Infrared Survey of the 30 Myr old Tucana‐Horologium Association

Mamajek¹,

Meyer²,

Hinz³

et al. 2004

ApJ

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“…These optical and IR data are consistent with ages older than Taurus ( > 2 Myr) and younger than typical field dwarfs ( < 1 Gyr). These three sources may represent low-mass members of the population of young field stars ( $ 100 Myr) that Briceño et al (1997) used to explain the wide-field distribution of X-ray sources in the direction of Taurus. In this case, 2MASS 04203904+2355502 could be a young field L dwarf like the one recently discovered by Kirkpatrick et al (2006).…”

Section: Comments On Individual Sourcesmentioning

confidence: 99%

The Spatial Distribution of Brown Dwarfs in Taurus

Luhman

2006

ApJ

185

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By combining photometry from the 2MASS Point Source Catalog and the USNO-B1.0 catalog with optical and infrared spectroscopy, I have performed a search for young brown dwarfs in an area of 225 deg 2 encompassing all of the Taurus star-forming region ( $ 1 Myr). From this work, I have discovered 22 new members of Taurus, 5 of which were independently found by Guieu and coworkers. Sixteen of these new members have spectral types later than M6 and thus are likely to be brown dwarfs according to the theoretical evolutionary models of Chabrier and Baraffe. After adding these new members to the previously known members of Taurus, I have compared the spatial distributions of stars and brown dwarfs across the entire region. I find no statistically significant difference between these two distributions. Taurus does not contain the large, extended population of brown dwarfs that has been predicted by some embryo ejection models for the formation of brown dwarfs. However, these results are consistent with other ejection models, as well as models in which stars and brown dwarfs share a common formation mechanism.

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“…While there is some evidence for a "saturation" of magnetic activity among young stars (e.g., Briceño et al 1997 and references therein), there is no indication of a substantial decrease of such activity in the very youngest objects; detecting rotational periods requires the presence of large, presumably magnetic, starspots. Higher mass accretion rates in the ONC are even less likely to explain the difference (see § 3), at least at a level sufficient to increase f by the factors that may be needed to reconcile the ONC and Taurus distributions.…”

Section: Disk Lockingmentioning

confidence: 99%

On Disk Braking of T Tauri Rotation

Hartmann

2002

The Astrophysical Journal

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The rotation of T Tauri stars is thought to be slowed by coupling between the stellar magnetosphere and the circumstellar disk. Stassun and collaborators have recently questioned this picture, based on their observations of young stars in and near the Orion Nebula Cluster (ONC) that indicate little evidence for disk-mediated spindown. However, stellar spin-down can occur no faster than the rate at which angular momentum is removed from the inner disk, either through viscous processes associated with accretion or by a wind. Observational estimates of these processes suggest that the timescales for angular momentum loss may be comparable to the ages of the ONC stars, so that disk braking may not be completely effective, at least among the lowest mass stars. Testing this hypothesis will require further measurements of mass accretion and mass-loss rates as well as determinations of rotational periods as a function of age.

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X-Rays Surveys and the Post-T Tauri Problem

Cited by 114 publications

References 0 publications

Constraining the Lifetime of Circumstellar Disks in the Terrestrial Planet Zone: A Mid‐Infrared Survey of the 30 Myr old Tucana‐Horologium Association

Constraining the Lifetime of Circumstellar Disks in the Terrestrial Planet Zone: A Mid‐Infrared Survey of the 30 Myr old Tucana‐Horologium Association

The Spatial Distribution of Brown Dwarfs in Taurus

On Disk Braking of T Tauri Rotation

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