A New Look at T Tauri Star Forbidden Lines: MHD Driven Winds from the Inner Disk

Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. We report the first high-resolution ($\Delta v\sim$6\kms) analysis of [S II] $\lambda$4068, [O I] $\lambda$5577, and [O I] $\lambda$6300 lines from a sample of 48 T Tauri stars. Following Simon et al. (2016), we decompose them into three kinematic components: a high-velocity component (HVC) associated with jets, and a low-velocity narrow (LVC-NC) and broad (LVC-BC) components. We confirm previous findings that many LVCs are blueshifted by more than 1.5 kms$^{-1}$ thus most likely trace a slow disk wind. We further show that the profiles of individual components are similar in the three lines. We find that most LVC-BC and NC line ratios are explained by thermally excited gas with temperatures between 5,000$-$10,000 K and electron densities $\sim10^{7}-10^{8}$ cm$^{-3}$. The HVC ratios are better reproduced by shock models with a pre-shock H number density of $\sim10^{6}-10^{7}$ cm$^{-3}$. Using these physical properties, we estimate $\dot{M}_{\rm wind}/\dot{M}_{\rm acc}$ for the LVC and $\dot{M}_{\rm jet}/\dot{M}_{\rm acc}$ for the HVC. In agreement with previous work, the mass carried out in jets is modest compared to the accretion rate. With the likely assumption that the NC wind height is larger than the BC, the LVC-BC $\dot{M}_{\rm wind}/\dot{M}_{\rm acc}$ is found to be higher than the LVC-NC. These results suggest that most of the mass loss occurs close to the central star, within a few au, through an MHD driven wind. Depending on the wind height, MHD winds might play a major role in the evolution of the disk mass.Comment: 45 pages, 23 figures, and 7 tables, accepted by Ap

The Vector Analyzing Power in Elastic Electron-Proton Scattering

We compute the vector analyzing power (VAP) for the elastic scattering of transversely polarized electrons from protons at low energies using an effective theory of electrons, protons, and photons. We study all contributions through second order in $E/M$, where $E$ and $M$ are the electron energy and nucleon mass, respectively. The leading order VAP arises from the imaginary part of the interference of one- and two-photon exchange amplitudes. Sub-leading contributions are generated by the nucleon magnetic moment and charge radius as well as recoil corrections to the leading-order amplitude. Working to ${\cal O}(E/M)^2$, we obtain a prediction for $A_n$ that is free of unknown parameters and that agrees with the recent measurement of the VAP in backward angle $ep$ scattering.Comment: 24 pages, 11 figures. Typos fixe

X-ray to NIR emission from AA Tauri during the dim state - Occultation of the inner disk and gas-to-dust ratio of the absorber

AA Tau is a well-studied, nearby classical T Tauri star, which is viewed almost edge-on. A warp in its inner disk periodically eclipses the central star, causing a clear modulation of its optical light curve. The system underwent a major dimming event beginning in 2011 caused by an extra absorber, which is most likely associated with additional disk material in the line of sight toward the central source. We present new XMM-Newton X-ray, Hubble Space Telescope FUV, and ground based optical and near-infrared data of the system obtained in 2013 during the long-lasting dim phase. The line width decrease of the fluorescent H$_2$ disk emission shows that the extra absorber is located at $r>1\,$au. Comparison of X-ray absorption ($N_H$) with dust extinction ($A_V$), as derived from measurements obtained one inner disk orbit (eight days) after the X-ray measurement, indicates that the gas-to-dust ratio as probed by the $N_H$ to $A_V$ ratio of the extra absorber is compatible with the ISM ratio. Combining both results suggests that the extra absorber, i.e., material at $r>1\,$au, has no significant gas excess in contrast to the elevated gas-to-dust ratio previously derived for material in the inner region ($\lesssim0.1\,$au).Comment: 16 pages, 12 figures, accepted by A&

Warm gas towards young stellar objects in Corona Australis - Herschel/PACS observations from the DIGIT key programme

The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an intermediate-mass young star. We study the effects on the warm gas and dust in a group of low-mass young stellar objects from the irradiation by the young luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented. The distribution of CO, OH, H2O, [C II], [O I], and continuum emission is investigated. We have developed a deconvolution algorithm which we use to deconvolve the maps, separating the point-source emission from the extended emission. We also construct rotational diagrams of the molecular species. By deconvolution of the Herschel data, we find large-scale (several thousand AU) dust continuum and spectral line emission not associated with the point sources. Similar rotational temperatures are found for the warm CO ($282\pm4$ K), hot CO ($890\pm84$ K), OH ($79\pm4$ K), and H2O ($197\pm7$ K) emission, respectively, in the point sources and the extended emission. The rotational temperatures are also similar to what is found in other more isolated cores. The extended dust continuum emission is found in two ridges similar in extent and temperature to molecular mm emission, indicative of external heating from the Herbig Be star R CrA. Our results show that a nearby luminous star does not increase the molecular excitation temperatures in the warm gas around a young stellar object (YSO). However, the emission from photodissociation products of H2O, such as OH and O, is enhanced in the warm gas associated with these protostars and their surroundings compared to similar objects not suffering from external irradiation.Comment: 37 pages, accepted for publication in A&

The CP-violating asymmetry in \eta\to\pi^+ \pi^- e^+e^-

We study the CP-violating asymmetry {\cal A}_{\rm CP}, which arises, in \eta\to\pi^+\pi^- e^+e^-, from the angular correlation of the e^+ e^- and \pi^+\pi^- planes due to the interference between the magnetic and electric decay amplitudes. With the phenomenologically determined magnetic amplitude and branching ratio as input, the asymmetry, induced by the electric bremsstrahlung amplitude through the CP-violating decay \eta\to\pi^+\pi^-, and by an unconventional tensor type operator, has been estimated respectively. The upper bound of {\cal A}_{\rm CP} from the former is about 10^{-3}, and the asymmetry from the latter might be up to O(10^{-2}). One can therefore expect that this CP asymmetry would be an interesting CP-violating observable for the future precise measurements in the \eta factories.Comment: LaTeX, 6 pages. One reference corrected, and some new references adde

Testing particle trapping in transition disks with ALMA

We present new Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations at 336GHz of two transition disks, SR21 and HD135344B. In combination with previous ALMA observations from Cycle 0 at 689GHz, we compare the visibility profiles at the two frequencies and calculate the spectral index ($\alpha_{\rm{mm}}$). The observations of SR21 show a clear shift in the visibility nulls, indicating radial variations of the inner edge of the cavity at the two wavelengths. Notable radial variations of the spectral index are also detected for SR21 with values of $\alpha_{\rm{mm}}{\sim}3.8-4.2$ in the inner region ($r<35$ AU) and $\alpha_{\rm{mm}}{\sim}2.6-3.0$ outside. An axisymmetric ring (which we call the ring model) or a ring with the addition of an azimuthal Gaussian profile, for mimicking a vortex structure (which we call the vortex model), is assumed for fitting the disk morphology. For SR21, the ring model better fits the emission at 336GHz, conversely the vortex model better fits the 689GHz emission. For HD135344B, neither a significant shift in the null of the visibilities nor radial variations of $\alpha_{\rm{mm}}$ are detected. Furthermore, for HD135344B, the vortex model fits both frequencies better than the ring model. However, the azimuthal extent of the vortex increases with wavelength, contrary to model predictions for particle trapping by anticyclonic vortices. For both disks, the azimuthal variations of $\alpha_{\rm{mm}}$ remain uncertain to confirm azimuthal trapping. The comparison of the current data with a generic model of dust evolution that includes planet-disk interaction suggests that particles in the outer disk of SR21 have grown to millimetre sizes and have accumulated in a radial pressure bump, whereas with the current resolution there is not clear evidence of radial trapping in HD135344B, although it cannot be excluded either.Comment: Minor changes after language edition. Accepted for publication in A&A (abstract slightly shortened for arXiv

A Deep Chandra X-ray Spectrum of the Accreting Young Star TW Hydrae

We present X-ray spectral analysis of the accreting young star TW Hydrae from a 489 ks observation using the Chandra High Energy Transmission Grating. The spectrum provides a rich set of diagnostics for electron temperature T_e, electron density N_e, hydrogen column density N_H, relative elemental abundances and velocities and reveals its source in 3 distinct regions of the stellar atmosphere: the stellar corona, the accretion shock, and a very large extended volume of warm postshock plasma. The presence of Mg XII, Si XIII, and Si XIV emission lines in the spectrum requires coronal structures at ~10 MK. Lower temperature lines (e.g., from O VIII, Ne IX, and Mg XI) formed at 2.5 MK appear more consistent with emission from an accretion shock. He-like Ne IX line ratio diagnostics indicate that T_e = 2.50 +/- 0.25 MK and N_e = 3.0 +/- 0.2 x 10^(12) cm^(-3) in the shock. These values agree well with standard magnetic accretion models. However, the Chandra observations significantly diverge from current model predictions for the postshock plasma. This gas is expected to cool radiatively, producing O VII as it flows into an increasingly dense stellar atmosphere. Surprisingly, O VII indicates N_e = 5.7 ^(+4.4}_(-1.2) x 10^(11) cm^(-3), five times lower than N_e in the accretion shock itself, and ~7 times lower than the model prediction. We estimate that the postshock region producing O VII has roughly 300 times larger volume, and 30 times more emitting mass than the shock itself. Apparently, the shocked plasma heats the surrounding stellar atmosphere to soft X-ray emitting temperatures and supplies this material to nearby large magnetic structures -- which may be closed magnetic loops or open magnetic field leading to mass outflow. (Abridged)Comment: 13 pages (emulateapj style), 10 figures, ApJ, in pres

D vs d: CP Violation in Beta Decay and Electric Dipole Moments

The T-odd correlation coefficient D in nuclear beta decay probes CP violation in many theories beyond the Standard Model. We provide an analysis for how large D can be in light of constraints from electric dipole moment (EDM) searches. We argue that the neutron EDM d_n currently provides the strongest constraint on D, which is 10 - 10^3 times stronger than current direct limits on D (depending on the model). In particular, contributions to D in leptoquark models (previously regarded as "EDM safe") are more constrained than previously thought. Bounds on D can be weakened only by fine-tuned cancellations or if theoretical uncertainties are larger than estimated in d_n. We also study implications for D from mercury and deuteron EDMs.Comment: 17 pages, 6 figure

Increasing melanism along a latitudinal gradient in a widespread amphibian: local adaptation, ontogenic or environmental plasticity?

<p>Abstract</p> <p>Background</p> <p>The thermal benefits of melanism in ectothermic animals are widely recognized, but relatively little is known about population differentiation in the degree of melanism along thermal gradients, and the relative contributions of genetic <it>vs. </it>environmental components into the level of melanism expressed. We investigated variation in the degree of melanism in the common frog (<it>Rana temporaria</it>; an active heliotherm thermoregulator) by comparing the degree of melanism (i) among twelve populations spanning over 1500 km long latitudinal gradient across the Scandinavian Peninsula and (ii) between two populations from latitudinal extremes subjected to larval temperature treatments in a common garden experiment.</p> <p>Results</p> <p>We found that the degree of melanism increased steeply in the wild as a function of latitude. Comparison of the degree of population differentiation in melanism (<it>P_ST</it>) and neutral marker loci (<it>F_ST</it>) revealed that the <it>P_ST</it> ><it>F_ST</it>, indicating that the differences cannot be explained by random genetic drift alone. However, the latitudinal trend observed in the wild was not present in the common garden data, suggesting that the cline in nature is not attributable to direct genetic differences.</p> <p>Conclusions</p> <p>As straightforward local adaptation can be ruled out, the observed trend is likely to result from environment-driven phenotypic plasticity or ontogenetic plasticity coupled with population differences in age structure. In general, our results provide an example how phenotypic plasticity or even plain ontogeny can drive latitudinal clines and result in patterns perfectly matching the genetic differences expected under adaptive hypotheses.</p