Could the Magnetic Star HD 135348 Possess a Rigidly Rotating Magnetosphere?

We report the detection and characterization of a new magnetospheric star, HD 135348, based on photometric and spectropolarimetric observations. The TESS light curve of this star exhibited variations consistent with stars known to possess rigidly rotating magnetospheres (RRMs), so we obtained spectropolarimetric observations using the Robert Stobie Spectrograph (RSS) on the South African Large Telescope (SALT) at four different rotational phases. From these observations, we calculated the longitudinal magnetic field of the star 〈B z 〉, as well as the Alfvén and Kepler radii, and deduced that this star contains a centrifugal magnetosphere. However, an archival spectrum does not exhibit the characteristic “double-horned” emission profile for Hα and the Brackett series that has been observed in many other RRM stars. This could be due to the insufficient rotational phase coverage of the available set of observations, as the spectra of these stars significantly vary with the star’s rotation. Our analysis underscores the use of TESS in photometrically identifying magnetic star candidates for spectropolarimetric follow-up using ground-based instruments. We are evaluating the implementation of a machine-learning classifier to search for more examples of RRM stars in TESS data.

Dzhanibekov effect in a physics classroom

The purpose of this publication is to present a novel approach to the demonstration of the Dzhanibekov effect. The main idea of our version is to use a lightweight spinning top of a spherical external form but distinct principal moments of inertia floating in the upward flow of air. As a result, the Dzhanibekov effect can be easily demonstrated anywhere on Earth: in any classroom, or even in the ‘home-lab’. The proposed demonstration allows one to observe the periodical flipping motion of the asymmetrical top with the clearly seen quasi-stable rotational phase. It may also become the base for various theoretical and experimental research projects for students.

The auroral radio emission of the magnetic B-type star ρ OphC

ABSTRACT The non-thermal radio emission of main-sequence early-type stars is a signature of stellar magnetism. We present multiwavelength (1.6–16.7 GHz) ATCA measurements of the early-type magnetic star ρ OphC, which is a flat-spectrum non-thermal radio source. The ρ OphC radio emission is partially circularly polarized with a steep spectral dependence: the fraction of polarized emission is about $60{{\ \rm per\ cent}}$ at the lowest frequency sub-band (1.6 GHz) while is undetected at 16.7 GHz. This is clear evidence of coherent Auroral Radio Emission (ARE) from the ρ OphC magnetosphere. Interestingly, the detection of the ρ OphC’s ARE is not related to a peculiar rotational phase. This is a consequence of the stellar geometry, which makes the strongly anisotropic radiation beam of the amplified radiation always pointed towards Earth. The circular polarization sign evidences mainly amplification of the ordinary mode of the electromagnetic wave, consistent with a maser amplification occurring within dense regions. This is indirect evidence of the plasma evaporation from the polar caps, a phenomenon responsible for the thermal X-ray aurorae. ρ OphC is not the first early-type magnetic star showing the O-mode dominated ARE but is the first star with the ARE always on view.

Superflares and variability in solar-type stars with TESS in the Southern hemisphere

ABSTRACT Superflares on solar-type stars have been a rapidly developing field ever since the launch of Kepler. Over the years, there have been several studies investigating the statistics of these explosive events. In this study, we present a statistical analysis of stellar flares on solar-type stars made using photometric data in 2-min cadence from Transiting Exoplanet Survey Satellite of the whole Southern hemisphere (sectors 1–13). We derive rotational periods for all the stars in our sample from rotational modulations present in the light curve as a result of large star-spot(s) on the surface. We identify 1980 stellar flares from 209 solar-type stars with energies in the range of 1031–1036 erg (using the solar flare classification, this corresponds to X1–X100 000) and conduct an analysis into their properties. We investigate the rotational phase of the flares and find no preference for any phase, suggesting the flares are randomly distributed. As a benchmark, we use GOES data of solar flares to detail the close relationship between solar flares and sunspots. In addition, we also calculate approximate spot areas for each of our stars and compare this to flare number, rotational phase, and flare energy. Additionally, two of our stars were observed in the continuous viewing zone with light-curves spanning 1 yr; as a result we examine the stellar variability of these stars in more detail.

Rotational Evolution of Western Anatolia since the Miocene and Its Implications on the Subduction Dynamics of Eurasia-Africa Collision

<p>The African-European convergent tectonic setting has resulted in a complex deformation history with several large-scale tectonic features in western Anatolia, where is dominated by a crustal-scale extension since the late Eocene. The Menderes metamorphic core complex, the İzmir-Balıkesir Transfer Zone, and the North Anatolian Fault Zone are some of these main tectonic features. To understand their spatio-temporal relationships we employ paleomagnetic, geochronologic and kinematic studies in the northernmost part of the western Anatolia, where these structures interacting with each other. </p><p>Our results show that western Anatolia has experienced at least two separate rotational phases since the Miocene. The first rotational phase is clockwise and related volcanism is dated as 21–16 Ma. The second rotational phase is counterclockwise and related volcanic rocks are dated as 14–12 Ma. According to collected kinematic data, pervasive transcurrent tectonism was dominated during the first phase, while the second one was dominated by extensional (and/or transtensional) tectonism. Here, the mode of extension switched from distributed diffuse deformation to discrete local deformation, possibly due to tearing and retreating of the northward subducting African oceanic slab below the western  Anatolian crust. This interrelated process also led to the localization of the İzmir-Balıkesir Transfer Zone with the decoupling of strike-slip faults, and to the episodic exhumation of the Menderes metamorphic core complex. This study is supported by a Tübitak Project, Grant Number of 117R011.</p>

Finite-Gap CMV Matrices: Periodic Coordinates and a Magic Formula

We prove a bijective unitary correspondence between (1) the isospectral torus of almost-periodic, absolutely continuous CMV matrices having fixed finite-gap spectrum ${\textsf{E}}$ and (2) special periodic block-CMV matrices satisfying a Magic Formula. This latter class arises as ${\textsf{E}}$-dependent operator Möbius transforms of certain generating CMV matrices that are periodic up to a rotational phase; for this reason we call them “MCMV.” Such matrices are related to a choice of orthogonal rational functions on the unit circle, and their correspondence to the isospectral torus follows from a functional model in analog to that of GMP matrices. As a corollary of our construction we resolve a conjecture of Simon; namely, that Caratheodory functions associated to such CMV matrices arise as quadratic irrationalities.

Probing the origin of stellar flares on M dwarfs using TESS data sectors 1–3

ABSTRACT Detailed studies of the Sun have shown that sunspots and solar flares are closely correlated. Photometric data from Kepler/K2 has allowed similar studies to be carried out on other stars. Here, we utilize Transiting Exoplanet Survey Satellite (TESS) photometric 2-min cadence of 167 low-mass stars from Sectors 1 to 3 to investigate the relationship between star-spots and stellar flares. From our sample, 90 per cent show clear rotational modulation likely due to the presence of a large, dominant star-spot and we use this to determine a rotational period for each star. Additionally, each low-mass star shows one or more flares in its light curve and using Gaia Data Release 2 parallaxes and SkyMapper magnitudes we can estimate the energy of the flares in the TESS band-pass. Overall, we have 1834 flares from the 167 low-mass stars with energies from 6.0 × 1029 to 2.4 × 1035 erg. We find none of the stars in our sample show any preference for rotational phase, suggesting the lack of a correlation between the large, dominant star-spot, and flare number. We discuss this finding in greater detail and present further scenarios to account for the origin of flares on these low-mass stars.