Helicity at Photospheric and Chromospheric Heights

In the solar atmosphere the twist parameter $\alpha$ has the same sign as magnetic helicity. It has been observed using photospheric vector magnetograms that negative/positive helicity is dominant in the northern/southern hemisphere of the Sun. Chromospheric features show dextral/sinistral dominance in the northern/southern hemisphere and sigmoids observed in X-rays also have a dominant sense of reverse-S/forward-S in the northern/southern hemisphere. It is of interest whether individual features have one-to-one correspondence in terms of helicity at different atmospheric heights. We use UBF \Halpha images from the Dunn Solar Telescope (DST) and other \Halpha data from Udaipur Solar Observatory and Big Bear Solar Observatory. Near-simultaneous vector magnetograms from the DST are used to establish one-to-one correspondence of helicity at photospheric and chromospheric heights. We plan to extend this investigation with more data including coronal intensities.Comment: 5 pages, 1 figure, 1 table To appear in "Magnetic Coupling between the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200

Stellar Coronal and Wind Models: Impact on Exoplanets

Surface magnetism is believed to be the main driver of coronal heating and stellar wind acceleration. Coronae are believed to be formed by plasma confined in closed magnetic coronal loops of the stars, with winds mainly originating in open magnetic field line regions. In this Chapter, we review some basic properties of stellar coronae and winds and present some existing models. In the last part of this Chapter, we discuss the effects of coronal winds on exoplanets.Comment: Chapter published in the "Handbook of Exoplanets", Editors in Chief: Juan Antonio Belmonte and Hans Deeg, Section Editor: Nuccio Lanza. Springer Reference Work

Effectiveness of Search for Unrelated Donor of Hematopoietic Stem Cells using Russian System Bone Marrow Donor Search: Experience of RM Gorbacheva Scientific Research Institute of Pediatric Hematology and Transplantation

Background & Aims. The key condition for allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the presence of HLA-compatible related or unrelated donor. If related donor is not found, further search is carried out in the Bone Marrow Donor Worldwide (BMDW) international data base, which is not effective enough (about 80–85 %), because of genotype specificity of Russian Federation residents. The recruitment procedure using BMDW takes a lot of time and is expensive. Therefore, there are good reasons to develop an alternative Russian data base, Bone Marrow Donor Search (BMDS), which includes data from Russian bone marrow donor registries and has a good potential. The aim is to evaluate the effectiveness of hematopoietic stem cell (HSC) donor search and transplant quality using the BMDS search system. Methods. 34 allo-HSCT recipients with malignancies and hematological diseases were enrolled in the study in RM Gorbacheva Scientific Research Institute of Pediatric Hematology and Transplantation from November, 2012, to March, 2016. A HLA-compatible donor was found for each patient in the BMDS (www.bmds.info), which includes data from 13 Russian registries of HSC donors. Results. 34 allo-HSCTs were performed from unrelated donors recruited using Russian registries: 1 in 2012; 3 in 2013; 5 in 2014; 21 in 2015; and 4 in the 1st quarter of 2016. The greatest effectiveness of the BMDS search was in 2015 (14 %, n = 17). In 30 cases (88.2 %) a complete 10/10 compatibility for 5 HLA-gene loci was observed; in 4 cases (11.8 %) there was an incomplete compatibility (9/10). AB0 compatibility was only in 7 cases (20.6 %). In 15 cases (44.1 %) bone marrow was used for transplant harvesting; in 19 cases (55.9 %) peripheral blood stem cells were harvested by means of cytapheresis. The CD34+ count in the transplant was 1.2–12.0 x 106 CD34+ cell/kg (median: 5.0 x 106 CD34+ cell/kg). Engraftment was observed in 79.4 % of cases (n = 27), graft failure in 17.7 % of cases (n = 6), and early posttransplant mortality in 2.9 % of cases (n = 1). Conclusion. There was an increasing efficiency of search for a HLA-compatible unrelated HSC donor using a Russian BMDS search system for Russian residents with a graft quality similar to the one found in the international BMDW database

Solar-type dynamo behaviour in fully convective stars without a tachocline

In solar-type stars (with radiative cores and convective envelopes), the magnetic field powers star spots, flares and other solar phenomena, as well as chromospheric and coronal emission at ultraviolet to X-ray wavelengths. The dynamo responsible for generating the field depends on the shearing of internal magnetic fields by differential rotation. The shearing has long been thought to take place in a boundary layer known as the tachocline between the radiative core and the convective envelope. Fully convective stars do not have a tachocline and their dynamo mechanism is expected to be very different, although its exact form and physical dependencies are not known. Here we report observations of four fully convective stars whose X-ray emission correlates with their rotation periods in the same way as in Sun-like stars. As the X-ray activity - rotation relationship is a well-established proxy for the behaviour of the magnetic dynamo, these results imply that fully convective stars also operate a solar-type dynamo. The lack of a tachocline in fully convective stars therefore suggests that this is not a critical ingredient in the solar dynamo and supports models in which the dynamo originates throughout the convection zone.Comment: 6 pages, 1 figure. Accepted for publication in Nature (28 July 2016). Author's version, including Method

Spectropolarimetry of stars across the H-R diagram

The growing sample of magnetic stars shows a remarkable diversity in the properties of their magnetic fields. The overall goal of current studies is to understand the origin, evolution, and structure of stellar magnetic fields in stars of different mass at different evolutionary stages. In this chapter we discuss recent measurements together with the underlying assumptions in the interpretation of data and the requirements, both observational and theoretical, for obtaining a realistic overview of the role of magnetic fields in various types of stars.Comment: 23 pages, 3 figures, chapter 7 of "Astronomical Polarisation from the Infrared to Gamma Rays", published in Astrophysics and Space Science Library 46

Magnetic twist and writhe of active regions - On the origin of deformed flux tubes

We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possible origin of this distortion is the nonlinear development of a kink-instability at the base of the convective zone; this would imply the formation of a non-planar flux tube which, while emerging across the photosphere, would show a rotation of its photospheric polarities as observed. A characteristic of the flux tubes deformed by this mechanism is that their magnetic twist and writhe should have the same sign. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the flux tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 35% of the 20 cases for which the sign of the twist can be unambiguously determined. Since at most only a fraction of the tilt evolution can be explained by this process, we discuss the role that other mechanisms may play in the inferred deformation. We find that 36% of the 22 cases may result from the action of the Coriolis force as the flux tube travels through the convection zone. Furthermore, because several bipoles overpass in their rotation the mean toroidal (East-West) direction or rotate away from it, we propose that a possible explanation for the deformation of all these flux tubes may lie in the interaction with large-scale vortical motions of the plasma in the convection zone, including also photospheric or shallow sub-photospheric large scale flows