Testing the Disk Regulation Paradigm with Spitzer Observations. II. A Clear Signature of Star-Disk Interaction in NGC 2264 and the Orion Nebula Cluster

Observations of PMS star rotation periods reveal slow rotators in young clusters of various ages, indicating that angular momentum is somehow removed from these rotating masses. The mechanism by which spin-up is regulated as young stars contract has been one of the longest-standing problems in star formation. Attempts to observationally confirm the prevailing theory that magnetic interaction between the star and its circumstellar disk regulates these rotation periods have produced mixed results. In this paper, we use the unprecedented disk identification capability of the Spitzer Space Telescope to test the star-disk interaction paradigm in two young clusters, NGC 2264 and the Orion Nebula Cluster (ONC). We show that once mass effects and sensitivity biases are removed, a clear increase in the disk fraction with period can be observed in both clusters across the entire period range populated by cluster members. We also show that the long-period peak (P $\sim$8 days) of the bimodal distribution observed for high-mass stars in the ONC is dominated by a population of stars possessing a disk, while the short-period peak (P $\sim$2 days) is dominated by a population of stars without a disk. Our results represent the strongest evidence to date that star-disk interaction regulates the angular momentum of these young stars. This study will make possible quantitative comparisons between the observed period distributions of stars with and without a disk and numerical models of the angular momentum evolution of young stars.Comment: 31 pages, 7 figures, 2 tables. Accepted for publication in Ap

The Dispersal of Protoplanetary Disks

Protoplanetary disks are the sites of planet formation, and the evolution and eventual dispersal of these disks strongly influences the formation of planetary systems. Disk evolution during the planet-forming epoch is driven by accretion and mass-loss due to winds, and in typical environments photoevaporation by high-energy radiation from the central star is likely to dominate final gas disk dispersal. We present a critical review of current theoretical models, and discuss the observations that are used to test these models and inform our understanding of the underlying physics. We also discuss the role disk dispersal plays in shaping planetary systems, considering its influence on both the process(es) of planet formation and the architectures of planetary systems. We conclude by presenting a schematic picture of protoplanetary disk evolution and dispersal, and discussing prospects for future work.Comment: 23 pages, 6 figures. Refereed review chapter, accepted for publication in Protostars & Planets VI, University of Arizona Press (2014), eds. H.Beuther, C.Dullemond, Th.Henning, R.Klesse

Procesos organizativos y acceso a la tierra en el Valle Calchaqui : El caso "El Churcal" departamento de Molinos, Salta

En este trabajo se expone el producto final de un proceso de investigación centrado en un pequeño paraje rural denominado “el Churcal”, ubicado en el Valle Calchaquí de la provincia de Salta. El Churcal como caso de estudio y su inserción en el contexto zonal y regional, fue el punto de partida para profundizar sobre los procesos históricos que contribuyeron a un tipo de estructuración particular de los territorios rurales en el departamento de Molinos y el Valle Calchaquí. El caso del Churcal condensa múltiples variables de las problemáticas campesinas, que pueden ser encontradas en otras áreas rurales del Valle Calchaquí y el NOA, como son las relaciones históricas de la población campesina y las grandes explotaciones agropecuarias, la lucha por la tierra, los procesos organizativos y la intervención de distintos actores sociales en diferentes contextos socio- políticos.Facultad de Ciencias Agrarias y Forestale

Procesos organizativos y acceso a la tierra en el Valle Calchaqui : El caso "El Churcal" departamento de Molinos, Salta

En este trabajo se expone el producto final de un proceso de investigación centrado en un pequeño paraje rural denominado “el Churcal”, ubicado en el Valle Calchaquí de la provincia de Salta. El Churcal como caso de estudio y su inserción en el contexto zonal y regional, fue el punto de partida para profundizar sobre los procesos históricos que contribuyeron a un tipo de estructuración particular de los territorios rurales en el departamento de Molinos y el Valle Calchaquí. El caso del Churcal condensa múltiples variables de las problemáticas campesinas, que pueden ser encontradas en otras áreas rurales del Valle Calchaquí y el NOA, como son las relaciones históricas de la población campesina y las grandes explotaciones agropecuarias, la lucha por la tierra, los procesos organizativos y la intervención de distintos actores sociales en diferentes contextos socio- políticos.Facultad de Ciencias Agrarias y Forestale

The Masses of Transition Circumstellar Disks: Observational Support for Photoevaporation Models

We report deep Sub-Millimeter Array observations of 26 pre-main-sequence (PMS) stars with evolved inner disks. These observations measure the mass of the outer disk (r ~20-100 AU) across every stage of the dissipation of the inner disk (r < 10 AU) as determined by the IR spectral energy distributions (SEDs). We find that only targets with high mid-IR excesses are detected and have disk masses in the 1-5 M_Jup range, while most of our objects remain undetected to sensitivity levels of M_DISK ~0.2-1.5 M_Jup. To put these results in a more general context, we collected publicly available data to construct the optical to millimeter wavelength SEDs of over 120 additional PMS stars. We find that the near-IR and mid-IR emission remain optically thick in objects whose disk masses span 2 orders of magnitude (~0.5-50 M_Jup). Taken together, these results imply that, in general, inner disks start to dissipate only after the outer disk has been significantly depleted of mass. This provides strong support for photoevaporation being one of the dominant processes driving disk evolution.Comment: Accepted for publication by ApJL, 4 pages and 3 figure

Evidence for J and H-band excess in classical T Tauri stars and the implications for disk structure and estimated ages

We argue that classical T Tauri stars (cTTs) possess significant non- photospheric excess in the J and H bands. We first show that normalizing the spectral energy distributions (SEDs) of cTTs to the J-band leads to a poor fit of the optical fluxes, while normalizing the SEDs to the Ic-band produces a better fit to the optical bands and in many cases reveals the presence of a considerable excess at J and H. NIR spectroscopic veiling measurements from the literature support this result. We find that J and H-band excesses correlate well with the K-band excess, and that the J-K and H-K colors of the excess emission are consistent with that of a black body at the dust sublimation temperature (~ 1500-2000 K). We propose that this near-IR excess originates at a hot inner rim, analogous to those suggested to explain the near-IR bump in the SEDs of Herbig Ae/Be stars. To test our hypothesis, we use the model presented by Dullemond et al. (2001) to fit the photometry data between 0.5 um and 24 um of 10 cTTs associated with the Chamaeleon II molecular cloud. The models that best fit the data are those where the inner radius of the disk is larger than expected for a rim in thermal equilibrium with the photospheric radiation field alone. In particular, we find that large inner rims are necessary to account for the mid infrared fluxes (3.6-8.0 um) obtained by the Spitzer Space Telescope. Finally, we argue that deriving the stellar luminosities of cTTs by making bolometric corrections to the J-band fluxes systematically overestimates these luminosities. The overestimated luminosities translate into underestimated ages when the stars are placed in the H-R diagram. Thus, the results presented herein have important implications for the dissipation timescale of inner accretion disks.Comment: 45 pages, 13 figure