Interacting coronae of two T Tauri stars: first observational evidence for solar-like helmet streamers

Context {The young binary system V773 Tau A exhibits a persistent radio flaring activity that gradually increases from a level of a few mJy at apoastron to more than 100 mJy at periastron. Interbinary collisions between very large (> 15 R) magnetic structures anchored on the two rotating stars of the system have been proposed to be the origin of these periodic radio flares. Magnetic structures extended over tens of stellar radii, that can also account for the observed fast decay of the radio flares, seem to correspond to the typical solar semi-open quite extended magnetic configurations called helmet streamers.} Aims {We aim to find direct observational evidence for the postulated, solar-like, coronal topologies.} Methods {We performed seven-consecutive-day VLBI observations at 8.4 GHz using an array consisting of the VLBA and the 100-m Effelsberg telescope.} Results {Two distintive structures appear in the radio images here presented. They happen to be associated with the primary and secondary stars of the V773 Tau A system. In one image (Fig.2-B) the two features are extended up to 18 R each and are nearly parallel revealing the presence of two interacting helmet streamers. One image (Fig.2-E) taken a few hours after a flare monitored by the 100-m Effelsberg telescope shows one elongated fading structure substantially rotated with respect to those seen in the B run. The same decay scenario is seen in Fig.2-G for the helmet streamer associated with the other star.} Conclusions {This is the very first direct evidence revealing that even if the flare origin is magnetic reconnection due to interbinary collision, both stars independently emit in the radio range with structures of their own. These structures are helmet streamers, observed for the first time in stars other than the Sun.}Comment: 7 pages, 3 figures, A&A in pres

Analisis Unsur-unsur Stuktur Batin Beberapa Puisi Dalam Antologi Puisi “Jakarta-berlin”

TION In dieser Untersuchung wird die inneren Strukturelemente der einigen Poesien in der Antologinpoesie Jakarta-Berlin, bzw.“Die Steinerne Stadt” von Ernst Schur, “An Jakarta” von Ajip Rosidi, “Berlin” von Christian Morgenstern, und “Jakarta” von Arifin C Noer beschreiben. Inneren Strukturelemente der Poesien besteht aus Thema, Ton, Gefühl und Auftrag. Als die Theoretische Grundlage wird die Meinugen von Richards, die von Djojosuroto zitiert wird. Um diese Poesien zu analysieren werden sowohl deskriptive Methode als auch innerliche Ansätze angewendet. Als Schluβfolgerung dieser Untersuchung kann es gesagt werden, daβ: die Themen der vier Poesien, nähmlich: Die Steinerne Stadt von Ersnt Schur behandelt um ein Sozialsleben in Berlin; An Jakarta von Ajip Rosidi behandelt um ein Sozialsleben in Jakarta; Berlinvon Christian Morgenstern behandelt um eine Situation in Berlin am Tag und Nacht; Jakarta von Arifin C Noer behandelt um ein Leben in Jakarta, das individualistisch ist. Die Diskution über die Tone der vier Poesien kann es dargestellen, daβ: die Erste ist eine Klage gegen die Situation in Berlin, wo die Leuten einander hassen; die Zweite ist eine Klage gegen die Situation in Jakarta, wo die Leuten der Malaria versteckt hätten; die Dritte ist eine Klage gegen die Situation in Berlin am Tag, wo es einen Chaos passiert ist; die Vierte ist eine Satire gegen die Gesselschaft in Jakarta, wo die Leuten nicht mehr zueinander wertschäzen. Die Interprätation über das Gefühl der vier Poesien kann es dargestellen, daβ: die Erste beschreibt ein Leben, das unzufrieden in Berlin ist und eine Begrenzung hat; die Zweite beschreibt die Situation in Jakarta, die es den Hass und die Liebe gibt; die Dritte beschreibt die Liebe, die die Schonheit bei Nebel und bei Nacht in Berlin beton; die Vierte beschreibt den Mitleid für die verlassene Leiche und davon begräbt man nicht würdig. Die Interprätation über den Auftrag der vier Poesien kann es dargestellen, daβ: die Erste zeigt: Im Leben musst man die Liebe haben, weil die Liebe groβe Rolle in Leben hat; die Zweite zeigt: man musst die Wohnort hat, obwohl es nicht alles liebevoll ist; die Dritte zeigt: Im Leben musst man kämpfen, obwohl die Situation nicht mit unserem Leben versteht; die Vierte zeigt: Im Leben musst man nicht individualismus hat, sondern musst man miteinander respektieren. Die Schlüβwörter: Untersuchung, Interprätation, Sozialsleben

Monte-Carlo radiative transfer simulation of the circumstellar disk of the Herbig Ae star HD 144432

Studies of pre-transitional disks, with a gap region between the inner infrared-emitting region and the outer disk, are important to improving our understanding of disk evolution and planet formation. Previous infrared interferometric observations have shown hints of a gap region in the protoplanetary disk around the Herbig Ae star HD~144432. We study the dust distribution around this star with two-dimensional radiative transfer modeling. We compare the model predictions obtained via the Monte-Carlo radiative transfer code RADMC-3D with infrared interferometric observations and the {\SED} of HD~144432. The best-fit model that we found consists of an inner optically thin component at 0.21\enDash0.32~\AU and an optically thick outer disk at 1.4\enDash10~\AU. We also found an alternative model in which the inner sub-AU region consists of an optically thin and an optically thick component. Our modeling suggests an optically thin component exists in the inner sub-AU region, although an optically thick component may coexist in the same region. Our modeling also suggests a gap-like discontinuity in the disk of HD~144432.Comment: 18 pages, 12 figure

Spitzer-MIPS survey of the young stellar content in the Vela Molecular Cloud-D

A new, unbiased Spitzer-MIPS imaging survey (~1.8 square degs) of the young stellar content of the Vela Molecular Cloud-D is presented. The survey is complete down to 5mJy and 250mJy at 24micron (mu) and 70mu, respectively. 849 sources are detected at 24mu and 52 of them also have a 70mu counterpart. The VMR-D region is one that we have already partially mapped in dust and gas millimeter emission, and we discuss the correlation between the Spitzer compact sources and the mm contours. About half of the 24mu sources are located inside the region delimited by the 12CO(1-0) contours (corresponding to only one third of the full area mapped with MIPS) with a consequent density increase of about 100% of the 24mu sources [four times for 70mu ones] moving from outside to inside the CO contours. About 400 sources have a 2MASS counterpart. So we have constructed a Ks vs. Ks-[24] diagram and identified the protostellar population. We find an excess of Class I sources in VMR-D in comparison with other star forming regions. This result is reasonably biased by the sensitivity limits, or, alternatively, may reflect a very short lifetime (<=10^6yr) of the protostellar content in this cloud. The MIPS images have identified embedded cool objects in most of the previously identified starless cores; in addition, there are 6 very young, possibly Class 0 objects identified. Finally we report finding of the driving sources for a set of five out of six very compact protostellar jets previously discovered in near-infrared images.Comment: 29 pages, 14 figures. To appear in Ap.

Synchrotron emission from the T Tauri binary system V773 Tau A

The pre-main sequence binary system V773 Tau A shows remarkable flaring activity around periastron passage. Here, we present the observation of such a flare at a wavelength of 3 mm (90 GHz) performed with the Plateau de Bure Interferometer. We examine different possible causes for the energy losses responsible for the e-folding time of 2.3 hours of that flare. We exclude synchrotron, collisional, and inverse Compton losses because they are not consistent with observational constraints, and we propose that the fading of the emission is due to the leakage of electrons themselves at each reflection between the two mirror points of the magnetic structure partially trapping them. The magnetic structure compatible with both our leakage model and previous observations is that of a helmet streamer that, as in the solar case, can occur at the top of the X-ray-emitting, stellar-sized coronal loops of one of the stars. The streamer may extend up to 20 R and interact with the corona of the other star at periastron passage, causing recurring flares. The inferred magnetic field strength at the two mirror points of the helmet streamer is in the range 0.12 - 125 G, and the corresponding Lorentz factor, gamma, of the partially trapped electrons is in the range 20 < gamma < 632. We therefore rule out that the emission could be of gyro-synchrotron nature: the derived high Lorentz factor proves that the nature of the emission at 90 GHz from this pre-main binary system is synchrotron radiation. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).Comment: 8 pages, 5 figures, A&A in pres

The Spitzer-IRAC Point Source Catalog of the Vela-D Cloud

This paper presents the observations of the Cloud D in the Vela Molecular Ridge, obtained with the IRAC camera onboard the Spitzer Space Telescope at the wavelengths \lambda = 3.6, 4.5, 5.8, 8.0 {\mu}m. A photometric catalog of point sources, covering a field of approximately 1.2 square degrees, has been extracted and complemented with additional available observational data in the millimeter region. Previous observations of the same region, obtained with the Spitzer MIPS camera in the photometric bands at 24 {\mu}m and 70 {\mu}m, have also been reconsidered to allow an estimate of the spectral slope of the sources in a wider spectral range. A total of 170,299 point sources, detected at the 5-sigma sensitivity level in at least one of the IRAC bands, have been reported in the catalog. There were 8796 sources for which good quality photometry was obtained in all four IRAC bands. For this sample, a preliminary characterization of the young stellar population based on the determination of spectral slope is discussed; combining this with diagnostics in the color-magnitude and color-color diagrams, the relative population of young stellar objects in the different evolutionary classes has been estimated and a total of 637 candidate YSOs have been selected. The main differences in their relative abundances have been highlighted and a brief account for their spatial distribution is given. The star formation rate has been also estimated and compared with the values derived for other star forming regions. Finally, an analysis of the spatial distribution of the sources by means of the two-point correlation function shows that the younger population, constituted by the Class I and flat-spectrum sources, is significantly more clustered than the Class II and III sources.Comment: Accepted by Ap