MHD simulations of disk-star interaction

We discuss a number of topics relevant to disk-magnetosphere interaction and how numerical simulations illuminate them. The topics include: (1) disk-magnetosphere interaction and the problem of disk-locking; (2) the wind problem; (3) structure of the magnetospheric flow, hot spots at the star's surface, and the inner disk region; (4) modeling of spectra from 3D funnel streams; (5) accretion to a star with a complex magnetic field; (6) accretion through 3D instabilities; (7) magnetospheric gap and survival of protoplanets. Results of both 2D and 3D simulations are discussed.Comment: 12 pages, 10 figures, Star-Disk Interaction in Young Stars, Proceedings of the International Astronomical Union, IAU Symposium, Volume 243. See animations at http://astro.cornell.edu/~romanova/projects.htm and at http://astro.cornell.edu/us-rus

The Magnetic Fields of Classical T Tauri Stars

We report new magnetic field measurements for 14 classical T Tauri stars (CTTSs). We combine these data with one previous field determination in order to compare our observed field strengths with the field strengths predicted by magnetospheric accretion models. We use literature data on the stellar mass, radius, rotation period, and disk accretion rate to predict the field strength that should be present on each of our stars according to these magnetospheric accretion models. We show that our measured field values do not correlate with the field strengths predicted by simple magnetospheric accretion theory. We also use our field strength measurements and literature X-ray luminosity data to test a recent relationship expressing X-ray luminosity as a function of surface magnetic flux derived from various solar feature and main sequence star measurements. We find that the T Tauri stars we have observed have weaker than expected X-ray emission by over an order of magnitude on average using this relationship. We suggest the cause for this is actually a result of the very strong fields on these stars which decreases the efficiency with which gas motions in the photosphere can tangle magnetic flux tubes in the corona.Comment: 25 pages, 5 figure

No disks around low-mass stars and brown dwarfs in the young sigma Orionis cluster?

We report on the analysis of 2MASS near-infrared data of a sample of low-mass stars and brown dwarfs in the sigma Orionis cluster. Youth and cluster membership have been spectroscopically confirmed using the Li I spectral line. We find little evidence in the JHKs colour-colour diagram for near-infrared excess emission for these cluster members. By comparison with model expectations, at most 2 out of 34 stars show (H-K) colour consistent with a near-infrared excess. This scarcity of near-infrared signatures of circumstellar disks in the lower-mass and substellar regimes of this cluster contrasts with findings in younger clusters, hinting at an age dependence of the disk frequency. Taking into account the apparent cluster age, our result supports the idea of a relatively fast (few Myr) disk dissipation and extends this conclusion to the substellar regime. We also find some evidence that, in this cluster, the disk frequency as measured by the Ks-band excess may be mass dependent.Comment: 4 pages, 2 eps figures, accepted by Astronomy and Astrophysics Letter

Accretion in Brown Dwarfs: an Infrared View

This paper presents a study of the accretion properties of 19 very low mass objects (Mstar .01-0.1 Msun) in the regions Chamaeleon I and rho-Oph For 8 objects we obtained high resolution Halpha profiles and determined mass accretion rate Macc and accretion luminosity Lacc. Pabeta is detected in emission in 7 of the 10 rho-Oph objects, but only in one in Cha I. Using objects for which we have both a determination of Lacc from Halpha and a Pabeta detection, we show that the correlation between the Pabeta luminosity and luminosity Lacc, found by Muzerolle et al. (1998) for T Tauri stars in Taurus, extends to objects with mass approx 0.03 Msun; L(Pab) can be used to measure Lacc also in the substellar regime. The results were less conclusive for Brgamma, which was detected only in 2 objects, neither of which had an Halpha estimate of Macc. Using the relation between L(Pab) and Lacc we determined the accretion rate for all the objects in our sample (including those with no Halpha spectrum), more than doubling the number of substellar objects with known Macc. When plotted as a function of the mass of the central object together with data from the literature, our results confirm the trend of lower Macc for lower Mstar, although with a large spread. Some of the spread is probably due to an age effect; our very young objects in rho-Oph have on average an accretion rate at least one order of magnitude higher than objects of similar mass in older regions. As a side product, we found that the width of Halpha measured at 10% peak intensity is not only a qualitative indicator of accretion, but can be used to obtain a quantitative estimate of Macc over a large mass range, from T Tauri stars to brown dwarfs. Finally, we found that some of our objects show evidence of mass-loss.Comment: 11 pages, 8 figures, A&A in pres

A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G6

Aims. The aim of this paper is to characterise the star formation activity in the poorly studied embedded cluster Serpens/G3-G6, located ~ 45' (3 pc) to the south of the Serpens Cloud Core, and to determine the luminosity and mass functions of its population of Young Stellar Objects (YSOs). Methods. Multi-wavelength broadband photometry was obtained to sample the near and mid-IR spectral energy distributions to separate YSOs from field stars and classify the YSO evolutionary stage. ISOCAM mapping in the two filters LW2 (5-8.5 um) and LW3 (12-18 um) of a 19' x 16' field was combined with JHKs data from 2MASS, Ks data from Arnica/NOT, and L' data from SIRCA/NOT. Continuum emission at 1.3 mm (IRAM) and 3.6 cm (VLA) was mapped to study the cloud structure and the coldest/youngest sources. Deep narrow band imaging at the 2.12 um S(1) line of H2 from NOTCam/NOT was obtained to search for signs of bipolar outflows. Results. We have strong evidence for a stellar population of 31 Class II sources, 5 flat-spectrum sources, 5 Class I sources, and two Class 0 sources. Our method does not sample the Class III sources. The cloud is composed of two main dense clumps aligned along a ridge over ~ 0.5 pc plus a starless core coinciding with absorption features seen in the ISOCAM maps. We find two S-shaped bipolar collimated flows embedded in the NE clump, and propose the two driving sources to be a Class 0 candidate (MMS3) and a double Class I (MMS2). For the Class II population we find a best age of ~ 2 Myr and compatibility with recent Initial Mass Functions (IMFs) by comparing the observed Class II luminosity function (LF), which is complete to 0.08 L_sun, to various model LFs with different star formation scenarios and input IMFs.Comment: 18 pages, 16 figures, 3 online tables, accepted by A&

NSVS06507557; a low-mass double-lined eclipsing binary

In this paper we present the results of a detailed spectroscopic and photometric analysis of the V=13$^m$.4 low-mass eclipsing binary NSVS 06507557 with an orbital period of 0.515 d. We obtained a series of mid-resolution spectra covering nearly entire orbit of the system. In addition we obtained simultaneous VRI broadband photometry using a small aperture telescope. From these spectroscopic and photometric data we have derived the system's orbital parameters and determined the fundamental stellar parameters of the two components. Our results indicate that NSVS 06507557 consists of a K9 and an M3 pre-main-sequence stars with masses of 0.66$\pm$0.09 \Msun and 0.28$\pm$0.05 \Msun and radii of 0.60$\pm$0.03 and 0.44$\pm$0.02 \Rsun, located at a distance of 111$\pm$9 pc. The radius of the less massive secondary component is larger than that of the zero-age main-sequnce star having the same mass. While the radius of the primary component is in agreement with ZAMS the secondary component appers to be larger by about 35 % with respect to its ZAMS counterpart. Night-to-night intrinsic light variations up to 0$^m$.2 have been observed. In addition, the H$_{\alpha}$, H$_{\beta}$ lines and the forbidden line of [O{\sc i}] are seen in emission. The Li{\sc i} 6708 \AA absorption line is seen in most of the spectra. These features are taken to be the signs of the classic T Tauri stars' characteristics. The parameters we derived are consistent with an age of about 20 Myr according to the stellar evolutionary models. The spectroscopic and photometric results are in agreement with those obtained by theoretical predictions.Comment: 21 pages, 9 figures. Accepted by MNRA

Accretion properties of T Tauri stars in sigma Ori

Accretion disks around young stars evolve in time with time scales of few million years. We present here a study of the accretion properties of a sample of 35 stars in the ~3 million year old star-forming region sigma Ori. Of these, 31 are objects with evidence of disks, based on their IR excess emission. We use near-IR hydrogen recombination lines (Pa_gamma) to measure their mass accretion rate. We find that the accretion rates are significantly lower in sigma Ori than in younger regions, such as rho-Oph, consistently with viscous disk evolution. The He I 1.083 micron line is detected (either in absorption or in emission) in 72% of the stars with disks, providing evidence of accretion-powered activity also in very low accretors, where other accretion indicators dissapear.Comment: Astronomy and Astrophysics, accepte

Translation and cross-cultural adaptation of the protocol of orofacial myofunctional evaluation with scores for Italian Language

RESUMO O protocolo de avaliação miofuncional orofacial com escores (protocolo AMIOFE) é um instrumento validado para o diagnóstico de distúrbios miofuncionais orofaciais que pode ser utilizado por fonoaudiólogos em sua prática clínica. O presente estudo foi desenvolvido porque não há um instrumento validado para esta finalidade em língua Italiana. Objetivos: traduzir e realizar a adaptação transcultural do protocolo AMIOFE para a língua italiana e determinar os valores dos escores de normalidade em um grupo de jovens e adultos italianos. Métodos: o protocolo AMIOFE foi traduzido da língua inglesa para a italiana por três indivíduos bilíngues. A partir dessas traduções, uma versão de consenso foi preparada por um comitê de pesquisa (três fonoaudiólogos e um médico) e submetida a um comitê de juízes, composto por oito fonoaudiólogos italianos experientes na área. Os autores da versão original verificaram e aprovaram a versão italiana do protocolo. O instrumento foi testado por meio de avaliações de 40 sujeitos italianos jovens e adultos (faixa etária entre 18 e 56 anos de idade), realizadas por dois fonoaudiólogos. O ponto de corte, previamente descrito, foi usado para determinar as médias e desvios-padrão. Resultados: a etapa de tradução e a versão final da versão italiana do protocolo AMIOFE foram apresentadas, bem como as médias dos escores para os sujeitos com e sem distúrbio miofuncional orofacial. Conclusão: a versão italiana do protocolo AMIOFE foi desenvolvida, traduzida e adaptada transculturalmente. Valores de normalidade para sujeitos italianos jovens e adultos foram apresentados

The Coevality of Young Binary Systems

Multiple star systems are commonly assumed to form coevally; they thus provide the anchor for most calibrations of stellar evolutionary models. In this paper we study the binary population of the Taurus-Auriga association, using the component positions in an HR diagram in order to quantify the frequency and degree of coevality in young binary systems. After identifying and rejecting the systems that are known to be affected by systematic errors (due to further multiplicity or obscuration by circumstellar material), we find that the relative binary ages, |Delta log(tau)|, have an overall dispersion of sigma~0.40 dex. Random pairs of Taurus members are coeval only to within sigma~0.58 dex, indicating that Taurus binaries are indeed more coeval than the association as a whole. However, the distribution of |Delta log(tau)| suggests two populations, with ~2/3 of the sample appearing coeval to within the errors (sigma~0.16 dex) and the other ~1/3 distributed in an extended tail reaching |Delta log(tau)|~0.4-0.9 dex. To explain the finding of a multi-peaked distribution, we suggest that the tail of the differential age distribution includes unrecognized hierarchical multiples, stars seen in scattered light, or stars with disk contamination; additional followup is required to rule out or correct for these explanations. The relative coevality of binary systems does not depend significantly on the system mass, mass ratio, or separation. Indeed, any pair of Taurus members wider than ~10' (~0.7 pc) shows the full age spread of the association.Comment: 23 pages, 11 figures; accepted to Ap

Stellar Properties of Pre-Main Sequence Stars from High Resolution Near-IR Spectra

We present high resolution (R=50,000) spectra at 2.2 um of 16 young stars in the rho Ophiuchi dark cloud. Photospheric features are detected in the spectra of 11 of these sources, all Class II young stellar objects. In 10 of these sources, we measure effective temperatures, continuum veiling, and vsini rotation from the shapes and strengths of atomic photospheric lines by comparing to spectral synthesis models at 2.2 um. We measure surface gravities in 2 stars from the integrated line flux ratio of the 12CO line region at 2.3 um and the Na I line region at 2.2 um. Although the majority (8/10) of the Class II stars have similar effective temperatures (3530 K +/-100 K), they exhibit a large spread in bolometric luminosities (factor ~8), as derived from near-IR photometry. In the two stars where we have surface gravity measurements from spectroscopy, the photometrically derived luminosities are systematically higher than the spectroscopic luminosities. Our spectroscopic luminosities result in older ages on the H-R diagram than is suggested by photometry at J or K. Most of our sources show a substantially larger amount of continuum excess than stellar flux at 2.2 um. The derived veiling values at K appear correlated with mid-IR disk luminosity, and with Brackett gamma equivalent width, corrected for veiling. The derived vsini rotation is substantial (12-39 km s-1), but systematically less than the rotation measured in Class I.5 (flat) and Class I sources from other studies in Ophiuchus.Comment: Accepted for publication in the Astronomical Journal. 37 pages, 8 figure