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

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

Afferent Neural Branching at Human Acupuncture Points: Do Needles Stimulate or Inhibit?

Background: Acupuncture has previously been considered to be stimulatory to the nervous system; however, the specific mechanism for this remains unknown, with the few published studies of acupuncture-point histology showing reduced numbers of nerves and neural receptors at acupuncture-point sites. Objective: This study was undertaken to visualize the neuroanatomic features of acupuncture points in humans. Materials and Methods: Light microscopy was performed on silver-stained sections of a human cadaver at P 6, and confocal microscopy was performed on PgP9.5 and P2X3 immunostained sections of 2 points (GB 20 and SP 6) from a live human volunteer. Results: At each point, but not at control sites, a single nerve bundle extending to the dermal–epidermal junction was identified where it branched into two parts, with each branch running perpendicularly, parallel to the dermal–epidermal junction. Conclusions: Acupuncture may incise afferent unmyelinated axonal branch points, disrupting both neural transmission to the spinal cord and crosstalk along meridians, while simultaneously stimulating larger, myelinated afferents, thus explaining both the immediate and long-lasting effects of acupuncture

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.

Evidence of an asymmetrical Keplerian disk in the Br{\gamma} and He I emission lines around the Be star HD 110432

Context. HD 110432 was classified as a "\gamma Cas X-ray analog" since it has similar peculiar X-ray and optical characteristics, i.e. a hard-thermal X-ray variable emission and an optical spectrum affected by an extensive disk. Lopes de Oliveira et al. (2007) suggest that it might be a Be star harboring an accreting white dwarf or that the X-rays may come from an interaction between the surface of the star and its disk. Aims. To investigate the disk around this Be star we used the VLTI/AMBER instrument, which combines high spectral (R=12000) and high spatial (\theta min =4 mas) resolutions. Methods. We constrain the geometry and kinematics of its circumstellar disk from the highest spatial resolution ever achieved on this star. Results. We obtain a disk extension in the Br{\gamma} line of 10.2 D\ast and 7.8 D\ast in the He I line at 2.05 \mu m assuming a Gaussian disk model. The disk is clearly following a Keplerian rotation. We obtained an inclination angle of 55\degree, and the star is a nearly critical rotator with Vrot /Vc =1.00$\pm$0.2. This inclination is greater than the value found for \gamma Cas (about 42\degree, Stee et al. 2012), and is consistent with the inference from optical Fe II emission profiles by Smith & Balona (2006) that the inclination should be more than the \gamma Cas value. In the near-IR continuum, the disk of HD 110432 is 3 times larger than \gamma Cas's disk. We have no direct evidence of a companion around HD 110432, but it seems that we have a clear signature for disk inhomogeneities as detected for {\zeta} Tau. This asymmetrical disk detection may be interpreted within the one-armed oscillation viscous disk framework. Another finding is that the disk size in the near-IR is similar to other Be stars with different spectral types and thus may be independent of the stellar parameters, as found for classical Be stars.Comment: 9 page

Searching for coronal radio emission from protostars using Very-Long-Baseline Interferometry

In order to directly study the role of magnetic fields in the immediate vicinity of protostars, we use Very-Long-Baseline Interferometry (VLBI), aiming at the detection of non-thermal centimetric radio emission. This is technically the only possibility to study coronal emission at sub-AU resolution. We performed VLBI observations of the four nearby protostars HL Tau, LDN 1551 IRS5, EC 95, and YLW 15 in order to look for compact non-thermal centimetric radio emission. For maximum sensitivity, we used the High Sensitivity Array (HSA) where possible, involving the Very Long Baseline Array (VLBA), the phased Very Large Array (VLA), as well as the Arecibo, Green Bank, and Effelsberg radio telescopes. While all four protostars were detected in VLA-only data, only one source (YLW 15 VLA 2) was detected in the VLBI data. The possibility of non-detections due to free-free absorption, possibly depending on source geometry, is considered. For YLW 15 VLA 2, the prospects for an accurate orbit determination appear to be good.Comment: 8 pages, 4 figures, accepted for publication in A&

The inner circumstellar disk of the UX Ori star V1026 Sco

The UX Ori type variables (named after the prototype of their class) are intermediate-mass pre-main sequence objects. One of the most likely causes of their variability is the obscuration of the central star by orbiting dust clouds. We investigate the structure of the circumstellar environment of the UX~Ori star V1026 Sco (HD 142666) and test whether the disk inclination is large enough to explain the UX Ori variability. We observed the object in the low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument and derived H- and K-band visibilities and closure phases. We modeled our AMBER observations, published Keck Interferometer observations, archival MIDI/VLTI visibilities, and the spectral energy distribution using geometric and temperature-gradient models. Employing a geometric inclined-ring disk model, we find a ring radius of 0.15 +- 0.06 AU in the H band and 0.18 +- 0.06 AU in the K band. The best-fit temperature-gradient model consists of a star and two concentric, ring-shaped disks. The inner disk has a temperature of 1257^{+133}_{-53} K at the inner rim and extends from 0.19 +- 0.01 AU to 0.23 +- 0.02 AU. The outer disk begins at 1.35^{+0.19}_{-0.20} AU and has an inner temperature of 334^{+35}_{-17} K. The derived inclination of 48.6^{+2.9}_{-3.6}deg approximately agrees with the inclination derived with the geometric model (49 +- 5deg in the K band and 50 +- 11deg in the H band). The position angle of the fitted geometric and temperature-gradient models are 163 +- 9deg (K band; 179 +- 17deg in the H band) and 169.3^{+4.2}_{-6.7}deg, respectively. The narrow width of the inner ring-shaped model disk and the disk gap might be an indication for a puffed-up inner rim shadowing outer parts of the disk. The intermediate inclination of ~50deg is consistent with models of UX Ori objects where dust clouds in the inclined disk obscure the central star

Fully Ir(iii) tetrazolate soft salts: the road to white-emitting ion pairs

The first examples of anionic Ir(iii) bis-tetrazolate complexes and their combination with a cationic Ir(iii)tetrazole derivative forming "fully tetrazolate" Ir(iii) based soft salts as O2-sensitive white emitters are described herein