Search

We have searched for stellar activity cycles in late low mass M dwarfs (M0--M6) located in the TESS north and south continuous viewing zones using data from sectors 1--61 (Cycle 1 to part way through Cycle 5). We utilise TESS-SPOC data which initially had a cadence of 30 min but reducing to 10 min in Cycles 3. In addition, we require each star to be observed in at least 6 sectors in each North/South Cycle: 1,950 low mass stars meet these criteria. Strong evidence was seen in 245 stars for a very stable photometric variation which we assume to be a signature of the stars rotation period. We did a similar study for Solar-like stars and found that 194 out of 1432 stars had a very stable modulation. We then searched for evidence of a variation in the rotational amplitude. We found 26 low mass stars showed evidence of variability in their photometric amplitude and only one Solar-like star. Some show a monotonic trend over 3--4 yrs whilst other show shorter term variations. We determine the predicted cycle durations of these stars using the relationship found by Irving (2023} using an estimate of the stars Rossby number. Finally we find a marginally statistically significant correlation between the range in the rotational amplitude modulation and the rotation period., Comment: Accepted by A&A. 8 pages plus 3 pages of figures in an Appendix

Shock waves are excited by coronal mass ejections (CMEs) and large-scale extreme-ultraviolet (EUV) wave fronts and can result in low-frequency radio emission under certain coronal conditions. In this work, we investigate a moving source of low-frequency radio emission as a CME and an associated EUV wave front move along a channel of a lower density, magnetic field, and Alfv\'en speed in the solar corona. Observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, the Nan\c{c}ay Radio Heliograph (NRH), and the Irish Low Frequency Array(I-LOFAR) were analysed. Differential emission measure maps were generated to determine densities and Alfv\'en maps, and the kinematics of the EUV wave front was tracked using CorPITA. The radio sources' positions and velocity were calculated from NRH images and I-LOFAR dynamic spectra. The EUV wave expanded radially with a uniform velocity of $\sim$ 500 km s$^{-1}$. However, the radio source was observed to be deflected and appeared to move along a channel of a lower Alfv\'en speed, abruptly slowing from 1700 km s$^{-1}$ to 250 km s$^{-1}$ as it entered a quiet-Sun region. A shock wave with an apparent radial velocity of > 420 km s$^{-1}$ was determined from the drift rate of the associated Type II radio burst. The apparent motion of the radio source may have resulted from a wave front moving along a coronal wave guide or by different points along the wave front emitting at locations with favourable conditions for shock formation., Comment: 6 pages, 3 figures

New instrumental and telescopes covering the optical and ultra-violet spectral regions have revealed a range of small-scale dynamic features, many which may be related. For example, the range of spicule-like features hints towards a spectrum of features and not just two types; however, direct observational evidence in terms of tracking spicules across multiple wavelengths are needed in order to provide further insight into the dynamics of the Sun's outer atmosphere. This paper uses H $\alpha$ data obtained with the CRisp Imaging SpectroPolarimeter instrument on the Swedish 1-m Solar Telescope, and in the transition region using the Interface Region Imaging Spectrograph with the SJI 1400 {\AA} channel plus spectral data via the Si IV 1394 {\AA} line to track spicules termed Rapid Blue-shifted Excursions (RBEs). The RBEs as seen in the H $\alpha$ blue-wing images presented here can be sub-divided into two categories; a single or multi-threaded feature. Based on the H $\alpha$ spectra, the features can be divided into events showing broadening and line core absorption, events showing broadening and line core emission, events with a pure blue shifted H $\alpha$ profile without any absorption in the red wing, broadened line profile with the absorption in the blue stronger compared to the red wing. From the RBE-like events which have a Si IV 1394 {\AA} line profile, 78% of them show a Si IV line flux increase. Most of these features show a second broadened Si IV component which is slightly blue-shifted., Comment: 13 pages, 11 figures

This report shows the design and the performance of a large area Silicon Photomultiplier (SiPM) module developed detection of fluorescent light emitted from a 10 cm scale volume. The module was optimized for the planned ACME III electron electric dipole moment (eEDM) search, which will be a powerful probe for the existence of physics beyond the Standard Model of particle physics. The ACME experiment searched for the eEDM with the world's highest sensitivity using cold ThO polar molecules (ACME II). In ACME III, SiPMs will be used for detection of fluorescent photons (the fundamental signal of the experiment) instead of PMTs, which were used in the previous measurement. We have developed an optimized SiPM module, based on a 16-channel SiPM array. Key operational parameters are characterized, including gain and noise. The SiPM dark count rate, background light sensitivity, and optical crosstalk are found to all be well suppressed and more than sufficient for the ACME III application., Comment: 10 pages, 6 figures, proceedings for NDIP20

We show signatures of spicules termed Rapid Blue-shifted Excursions (RBEs) in the Si iv 1394 {\AA} emission line using a semi-automated detection approach. We use the H{\alpha} filtergrams obtained by the CRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope and co-aligned Interface Region Imaging Spectrograph data using the SJI 1400 {\AA} channel to study the Spatio-temporal signature of the RBEs in the transition region. The detection of RBEs is carried out using an oriented coronal loop tracing algorithm on H{\alpha} Dopplergrams at 35 km s^-1. We find that the number of detected features is significantly impacted by the time-varying contrast values of the detection images, which are caused by the changes in the atmospheric seeing conditions. We detect 407 events with lifetime greater than 32 sec. This number is further reduced to 168 RBEs based on the H{\alpha} profile and the proximity of RBEs to the large scale flow. Of these 168 RBEs, 89 of them display a clear Spatio-temporal signature in the SJI 1400 {\AA} channel, indicating that a total of ~53% are observed to have co-spatial signatures between the chromosphere and the transition region.

Solar radio emission at low frequencies (<1 GHz) can provide valuable information on processes driving flares and coronal mass ejections (CMEs). Radio emission has been detected from active M dwarf stars, suggestive of much higher levels of activity than previously thought. Observations of active M dwarfs at low frequencies can provide information on the emission mechanism for high energy flares and possible stellar CMEs. Here, we conducted two observations with the Australian Square Kilometre Pathfinder Telescope (ASKAP) totalling 26 hours and scheduled to overlap with the Transiting Exoplanet Survey Satellite (TESS) Sector 36 field, utilising the wide fields of view of both telescopes to search for multiple M dwarfs. We detected variable radio emission in Stokes I centered at 888 MHz from four known active M dwarfs. Two of these sources were also detected with Stokes V circular polarisation. When examining the detected radio emission characteristics, we were not able distinguish between the models for either electron cyclotron maser or gyrosynchrotron emission. These detections add to the growing number of M dwarfs observed with variable low frequency emission., Comment: 10 pages, 6 figures, 3 tables

Using the ULTRASPEC instrument mounted on the 2.4-m Thai National Telescope, we observed two large flares, each with a total energy close to 10^34 erg with sub-second cadence. A combination of a wavelet analysis, a Fourier transform plus an empirical mode decomposition, reveals quasi-period pulsations (QPP) which exhibit an apparent doubling of the oscillation period. Both events showed oscillations of a few minutes over a interval of several minutes, and despite the availability of sub-second cadence, there was no evidence of sub-minute oscillations. The doubling of the QPP periods and shorter lifetime of shorter-period QPP modes strongly favour resonant dynamics of magnetohydrodynamic waves in a coronal loop. We estimate loop lengths to be 0.2-0.7 R*, in agreement with a typical length of solar coronal loops. These observations presents rare and compelling evidence for the presence of compact plasma loops in a stellar corona.

The last decade has seen unprecedented effort in dark matter model building at all mass scales coupled with the design of numerous new detection strategies. Transformative advances in quantum technologies have led to a plethora of new high-precision quantum sensors and dark matter detection strategies for ultralight ($<10\,$eV) bosonic dark matter that can be described by an oscillating classical, largely coherent field. This white paper focuses on searches for wavelike scalar and vector dark matter candidates., Comment: Snowmass 2021 White Paper

Observations made using TESS revealed a sample of low mass stars which show a periodic modulation on a period $<0.2$~d. Surprisingly many of these Ultra Fast Rotating (UFR) stars showed no evidence of flare activity which would be expected from such rapidly rotating stars. We present results from a spectroscopic survey of UFRs using the Nordic Optical Telescope to search for radial velocity variations which could reveal evidence for binarity. Our sample of 29 sources have a photometric period between 0.1-0.2d, cover spectral classes of M0-4V, and show no evidence for flares. We detect only one source with clear radial velocity shifts, with another two having Gaia RUWE values which suggests they are binaries. Further observations reveal the former star possibly contains a brown dwarf companion with a mass of M$_2$>58 M$_{\rm Jup}$ and probability P(M$_2$<90 M$_{\rm Jup}$) = 50\%. There is no evidence for the companion in our spectra, strengthening the case for a brown dwarf companion. We also examine the folded TESS light curves of all our targets, finding at least two are eclipsing binaries and one which has been contaminated by a spatially nearby $\delta$ Sct star. We estimate that around 1/4 of our targets may have been contaminated by short period variable stars. However, the majority of our targets are consistent with being single, low mass stars whose variability is due to starspots. We outline the possible reasons why they are not flare active despite being such rapid rotators., Comment: Accepted MNRAS main journal

We investigate high resolution spectroscopic and imaging observations from the CRisp Imaging SpectroPolarimeter (CRISP) instrument to study the dynamics of chromospheric spicule type events. It is widely accepted that chromospheric fine structures are waveguides for several types of magnetohydrodynamic (MHD) oscillations, which can transport energy from the lower to upper layers of the Sun. We provide a statistical study of 30 high frequency waves associated with spicule type events. These high frequency oscillations have two components of transverse motions: the plane of sky (POS) motion and the line of sight (LOS) motion. We focus on single isolated spicules and track the POS using time distance analysis and in the LOS direction using Doppler information. We use moment analysis to find the relation between the two motions. The composition of these two motions suggests that the wave has a helical structure. The oscillations do not have phase differences between points along the structure. This may be the result of the oscillation being a standing mode, or that propagation is mostly in the perpendicular direction. There is evidence of fast magnetoacoustic wave fronts propagating across these structures. To conclude, we hypothesize that the compression and rarefaction of passing magnetoacoustic waves may influence the appearance of spicule type events, not only by contributing to moving them in and out of the wing of the spectral line but also through the creation of density enhancements and an increase in opacity in the Halpha line., Comment: 24 pages, 18 Figures

We report on the properties of coronal loop foot-point heating with observations at the highest resolution, from the CRisp Imaging Spectro-Polarimeter (CRISP) located at the Swedish 1-m Solar Telescope (SST) and co-aligned NASA Solar Dynamics Observatory (SDO) observations, of Type II spicules in the chromosphere and their signatures in the EUV corona. Here, we address one important issue, as to why there is not always a one-to-one correspondence, between Type II spicules and hot coronal plasma signatures, i.e. beyond TR temperatures. We do not detect any difference in their spectral properties in a quiet Sun region compared to a region dominated by coronal loops. On the other hand, the number density close to the foot-points in the active region is found to be an order of magnitude higher than in the quiet Sun case. A differential emission measure analysis reveals a peak at $\sim 5 \times 10^5$ K on the order of 10$^{22}$~cm$^{-5}$~K$^{-1}$. Using this result as a constraint, we conduct numerical simulations and show that with an energy input of $1.25 \times 10^{24}$ erg (corresponding to $\sim$10 RBEs contributing to the burst) we manage to reproduce the observation very closely. However, simulation runs with lower thermal energy input do not reproduce the synthetic AIA $171 {\AA}$ signatures, indicating that there is a critical number of spicules required in order to account for the AIA $171{\AA}$ signatures in the simulation. Furthermore, the higher energy ($1.25 \times 10^{24}$ ergs) simulations reproduce catastrophic cooling with a cycle duration of $\sim$5 hours, matching a periodicity we observe in the EUV observations.

Modern radio interferometers such as the LOw Frequency ARray (LOFAR) are capable of producing data at hundreds of gigabits to terabits per second. This high data rate makes the analysis of radio data cumbersome and computationally expensive. While high performance computing facilities exist for large national and international facilities, that may not be the case for instruments operated by a single institution or a small consortium. Data rates for next generation radio telescopes are set to eclipse those currently in operation, hence local processing of data will become all the more important. Here, we introduce the REAL-time Transient Acquisition backend (REALTA), a computing backend at the Irish LOFAR station (I-LOFAR) which facilitates the recording of data in near real-time and post-processing. We also present first searches and scientific results of a number of radio phenomena observed by I-LOFAR and REALTA, including pulsars, fast radio bursts (FRBs), rotating radio transients (RRATs), the search for extraterrestrial intelligence (SETI), Jupiter, and the Sun., Comment: 12 pages, 10 figures, accepted for publication in Astronomical instrumentation section of Astronomy & Astrophysics 24/08/2021

We have performed a search for flares and Quasi-Periodic Pulsations (QPPs) from low mass M dwarf stars using TESS 2 min cadence data. We find seven stars which show evidence of QPPs. Using Fourier and Empirical Mode Decomposition techniques, we confirm the presence of 11 QPPs in these seven stars with a period between 10.2 and 71.9 min, including an oscillation with strong drift in the period and a double-mode oscillation. The fraction of flares we examined which showed QPPs (7 percent) is higher than other studies of stellar flares, but is very similar to the fraction of Solar C-class flares. Based on the stellar parameters taken from the TESS Input Catalog, we determine the lengths and magnetic field strengths of the flare coronal loops using the period of the QPPs and various assumptions about the origin of the QPPs. We also use a scaling relationship based on flares from Solar and Solar-type stars and the observed energy, plus the duration of the flares, finding that the different approaches predict loop lengths which are consistent to a factor of $\sim$2. We also discuss the flare frequency of the seven stars determining whether this could result in ozone depletion or abiogenesis. Three of our stars have a sufficiently high rate of energetic flares which are likely to cause abiogenesis. However, two of them are also in the range where ozone depletion is likely to occur. We speculate on the implications for surface life on these stars and the effects of the loop lengths and QPPs on potential exoplanets in the habitable zone., Comment: Accepted for publication in Solar Physics

The Variables and Slow Transients Survey (VAST) on the Australian Square Kilometre Array Pathfinder (ASKAP) is designed to detect highly variable and transient radio sources on timescales from 5 seconds to $\sim 5$ years. In this paper, we present the survey description, observation strategy and initial results from the VAST Phase I Pilot Survey. This pilot survey consists of $\sim 162$ hours of observations conducted at a central frequency of 888~MHz between 2019 August and 2020 August, with a typical rms sensitivity of 0.24~mJy~beam$^{-1}$ and angular resolution of $12-20$ arcseconds. There are 113 fields, \red{each of which was observed for 12 minutes integration time}, with between 5 and 13 repeats, with cadences between 1 day and 8 months. The total area of the pilot survey footprint is 5\,131 square degrees, covering six distinct regions of the sky. An initial search of two of these regions, totalling 1\,646 square degrees, revealed 28 highly variable and/or transient sources. Seven of these are known pulsars, including the millisecond pulsar J2039--5617. Another seven are stars, four of which have no previously reported radio detection (SCR~J0533--4257, LEHPM~2-783, UCAC3~89--412162 and 2MASS J22414436--6119311). Of the remaining 14 sources, two are active galactic nuclei, six are associated with galaxies and the other six have no multiwavelength counterparts and are yet to be identified.

Numerous studies have analysed inferred power-law distributions between frequency and energy of impulsive events in the outer solar atmosphere in an attempt to understand the predominant energy supply mechanism in the corona. Here, we apply a burst detection algorithm to high-resolution imaging data obtained by the Interface Region Imaging Spectrograph to further investigate the derived power-law index, $\gamma$, of bright impulsive events in the transition region. Applying the algorithm with a constant minimum event lifetime (of either $60$ s or $110$ s) indicated that the target under investigation, such as Plage and Sunspot, has an influence on the observed power-law index. For regions dominated by sunspots, we always find $\gamma <2$; however, for datasets where the target is a plage region, we often find that $\gamma >2$ in the energy range [$\sim10^{23}$, $\sim10^{26}$] erg. Applying the algorithm with a minimum event lifetime of three timesteps indicated that cadence was another important factor, with the highest cadence datasets returning $\gamma >2$ values. The estimated total radiative power obtained for the observed energy distributions is typically 10-25 % of what would be required to sustain the corona indicating that impulsive events in this energy range are not sufficient to solve coronal heating. If we were to extend the power-law distribution down to an energy of $10^{21}$ erg, and assume parity between radiative energy release and the deposition of thermal energy, then such bursts could provide 25-50 % of the required energy to account for the coronal heating problem.

In our previous study of low mass stars using TESS, we found a handful which show a periodic modulation on a period <1 d but also displayed no flaring activity. Here we present the results of a systematic search for Ultra Fast Rotators (UFRs) in the southern ecliptic hemisphere which were observed in 2 min cadence with TESS. Using data from Gaia DR2, we obtain a sample of over 13,000 stars close to the lower main sequence. Of these, we identify 609 stars which lie on the lower main sequence and have a periodic modulation <1 d. The fraction of stars which show flares appears to drop significantly at periods <0.2 d. If the periods are a signature of the rotation rate, this would be a surprise, since faster rotators would be expected to have a stronger magnetic field and, therefore, produce more flares. We explore possible reasons for our finding: the flare inactive stars are members of binaries, in which case the stars rotation rate could have increased as the binary orbital separation reduced due to angular momentum loss over time, or that enhanced emission occurs at blue wavelengths beyond the pass band of TESS. Follow-up spectroscopy and flare monitoring at blue/ultraviolet wavelengths of these flare inactive stars are required to resolve this question., Comment: Accepted for publication in MNRAS

The resonance lines of \ion{Si}{4} formed at $\lambda$1394 and 1403 {\AA} are the most critical for the diagnostics of the solar transition region in the observations of the Interface Region Imaging Spectrograph (IRIS). Studying the intensity ratios of these lines (1394{\AA}/1403{\AA}), which under optically thin condition is predicted to be two, helps us to diagnose the optical thickness of the plasma being observed. Here we study the evolution of the distribution of intensity ratios in 31 IRIS rasters recorded for four days during the emergence of an active region. We found that during the early phase of the development, the majority of the pixels show intensity ratios smaller than two. However, as the active region evolves, more and more pixels show the ratios closer to two. Besides, there are a substantial number of pixels with ratio values larger than 2. At the evolved stage of the active region, the pixels with ratios smaller than two were located on the periphery, whereas those with values larger than 2 were in the core. However, for quiet Sun regions, the obtained intensity ratios were close to two irrespective of the location on the disk. Our findings suggest that the \ion{Si}{4} lines observed in active regions are affected by the opacity during the early phase of the flux emergence. The results obtained here could have important implications for the modelling of the solar atmosphere, including the initial stage of the emergence of an active region as well as quiet Sun., Comment: 22 pages, 17 figs, in press, ApJ

We observe plasma flows in cool loops using the Slit-Jaw Imager (SJI) onboard the Interface Region Imaging Spectrometer (IRIS). Huang et al. (2015) observed unusually broadened Si IV 1403 angstrom line profiles at the footpoints of such loops that were attributed to signatures of explosive events (EEs). We have chosen one such uni-directional flowing cool loop system observed by IRIS where one of the footpoints is associated with significantly broadened Si IV line profiles. The line profile broadening indirectly indicates the occurrence of numerous EEs below the transition region (TR), while it directly infers a large velocity enhancement /perturbation further causing the plasma flows in the observed loop system. The observed features are implemented in a model atmosphere in which a low-lying bi-polar magnetic field system is perturbed in the chromosphere by a velocity pulse with a maximum amplitude of 200 km/s. The data-driven 2-D numerical simulation shows that the plasma motions evolve in a similar manner as observed by IRIS in the form of flowing plasma filling the skeleton of a cool loop system. We compare the spatio-temporal evolution of the cool loop system in the framework of our model with the observations, and conclude that their formation is mostly associated with the velocity response of the transient energy release above their footpoints in the chromosphere/TR. Our observations and modeling results suggest that the velocity responses most likely associated to the EEs could be one of the main candidates for the dynamics and energetics of the flowing cool loop systems in the lower solar atmosphere., Comment: In Press; The Astrophysical Journal; 14 Pages; 9 Figures

Superflares on solar-type stars has been a rapidly developing field ever since the launch of $\it Kepler$. 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 $\it TESS$ of the whole southern hemisphere (sectors 1 - 13). We derive rotational periods for all stars in our sample from rotational modulations present in the lightcurve as a result of large starspot(s) on the surface. We identify 1980 stellar flares from 209 solar-type stars with energies in the range of $10^{31} - 10^{36}$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 lightcurves spanning one year, as a result, we examine the stellar variability of these stars in more detail., Comment: Accepted for publication in MNRAS. 16 pages, 11 figures and one online table available in the published version

We present a detailed analysis of a confined filament eruption and jet associated with a C1.5 class solar flare. Multi-wavelength observations from GONG and SDO reveal the filament forming over several days following the emergence and then partial cancellation of a minority polarity spot within a decaying bipolar active region. The emergence is also associated with the formation of a 3D null point separatrix that surrounds the minority polarity. The filament eruption occurs concurrent with brightenings adjacent to and below the filament, suggestive of breakout and flare reconnection, respectively. The erupting filament material becomes partially transferred into a strong outflow jet (~ 60 km/s) along coronal loops, becoming guided back towards the surface. Utilising high resolution H$\alpha$ observations from SST/CRISP, we construct velocity maps of the outflows demonstrating their highly structured but broadly helical nature. We contrast the observations with a 3D MHD simulation of a breakout jet in a closed-field background and find close qualitative agreement. We conclude that the suggested model provides an intuitive mechanism for transferring twist/helicity in confined filament eruptions, thus validating the applicability of the breakout model not only to jets and coronal mass ejections but also to confined eruptions and flares., Comment: Accepted for publication in ApJ. 21 pages, 14 figures and 6 animations which will be avaliable in the published version

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 utilise TESS photometric 2-min cadence of 167 low mass stars from Sectors 1 - 3 to investigate the relationship between starspots and stellar flares. From our sample, 90 percent show clear rotational modulation likely due to the presence of a large, dominant starspot and we use this to determine a rotational period for each star. Additionally, each low mass star shows one or more flares in its lightcurve and using Gaia DR2 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 $6.0\times 10^{29}$ - $2.4\times 10^{35}$~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., Comment: 10 pages, 9 figures, 2 tables, accepted for publication in MNRAS

Experimental searches for the electron electric dipole moment, $d_e$, probe new physics beyond the Standard Model. Recently, the ACME Collaboration set a new limit of $|d_e| <1.1\times 10^{-29}$ $e\cdot \textrm{cm}$ [Nature $\textbf{562}$, 355 (2018)], constraining time reversal symmetry (T) violating physics in the 3-100 TeV energy scale. ACME extracts $d_e$ from the measurement of electron spin precession due to the thorium monoxide (ThO) molecule's internal electric field. This recent ACME II measurement achieved an order of magnitude increased sensitivity over ACME I by reducing both statistical and systematic uncertainties in the measurement of the electric dipole precession frequency. The ACME II statistical uncertainty was a factor of 1.7 above the ideal shot-noise limit. We have since traced this excess noise to timing imperfections. When the experimental imperfections are eliminated, we show that shot noise limit is attained by acquiring noise-free data in the same configuration as ACME II., Comment: 7 pages, 4 figures

Empirical correlations between stellar parameters such as rotation or radius and magnetic activity diagnostics require estimates of the effective temperatures and the stellar radii. The aim of this study is to propose simple methods that can be applied to large samples of stars in order to derive estimates of the stellar parameters. Good empirical correlations between Red/Infra-Red colours (e.g. (R-I)$_C$) and effective temperatures have been well established for a long time (e.g. Veeder 1974, Bessell 1979, Leggett 1992). The more recent (R-I)$_C$ colour-$T_{eff}$ correlation using the data of Mann et al. (2015: hereafter M15) and Boyajian et al. (2012: hereafter B12) shows that this colour can be applied as a temperature estimate for large samples of stars. We find that the mean scatter in $T_{eff}$ relative to the (R-I)$_C$-$T_{eff}$ relationship of B12 and M15 data is only $\pm 3\sigma =$44.6~K for K dwarfs and $\pm 3\sigma =$39.4~K for M dwarfs. These figures are small and show that the (R-I)$_C$ colour can be used as a first guess effective temperature estimator for K and M dwarfs. We derive effective temperatures for about 1910 K and M dwarfs using the calibration of (R-I)$_C$ colour-$T_{eff}$ from B12 and M15 data. We also compiled $T_{eff}$ and metallicity measurements available in the literature using the VizieR database. We determine $T_{eff}$ for 441 stars with previously unknown effective temperatures. We also identified 21 new spectroscopic binaries and 1 triple system from our high resolution spectra., Comment: Accepted by the Astronomical Journal

Using multiwavelength imaging observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) on 03 May 2012, we present a novel physical scenario for the formation of a temporary X-point in the solar corona, where plasma dynamics is forced externally by a moving prominence. Natural diffusion was not predominant, however, a prominence driven inflow occurred firstly, forming a thin current sheet and thereafter enabling a forced magnetic reconnection at a considerably high rate. Observations in relation to the numerical model reveal that forced reconnection may rapidly and efficiently occur at higher rates in the solar corona. This physical process may also heat the corona locally even without establishing a significant and self-consistent diffusion region. Using a parametric numerical study, we demonstrate that the implementation of the external driver increases the rate of the reconnection even when the resistivity required for creating normal diffusion region decreases at the X-point. We conjecture that the appropriate external forcing can bring the oppositely directed field lines into the temporarily created diffusion region firstly via the plasma inflows as seen in the observations. The reconnection and related plasma outflows may occur thereafter at considerably larger rates., Comment: 14 Pages; 07 Figures; The Astrophysical Journal (in press)

We present an analysis of K2 short cadence data of 34 M dwarfs which have spectral types in the range M0 - L1. Of these stars, 31 showed flares with a duration between $\sim$10-90 min. Using distances obtained from Gaia DR2 parallaxes, we determined the energy of the flares to be in the range $\sim1.2\times10^{29}-6\times10^{34}$ erg. In agreement with previous studies we find rapidly rotating stars tend to show more flares, with evidence for a decline in activity in stars with rotation periods longer than $\sim$10 days. The rotational modulation seen in M dwarf stars is widely considered to result from a starspot which rotates in and out of view. Flux minimum is therefore the rotation phase where we view the main starspot close to the stellar disk center. Surprisingly, having determined the rotational phase of each flare in our study we find none show any preference for rotational phase. We outline three scenarios which could account for this unexpected finding. The relationship between rotation phase and flare rate will be explored further using data from wide surveys such as NGTS and TESS., Comment: Accepted main Journal MNRAS

Random noise plays a beneficial role in cognitive processing and produces measurable improvement in simulations and biological agents' task performance. Stochastic facilitation, the phenomenon of additive noise improving signal transmission in complex systems, has been shown to occur in a variety of neural contexts. However, neuroscience analyses to date have not fully explored the colours that neural noise could be. The literature shows a 1/f pink noise power spectrum distribution at many levels, but many less rigourous studies assume white noise, with little justification of why that assumption is made. In this work, we briefly review the colours of noise and their useful applications in other fields. If we consider that noise is not so black and white, we could more colourfully regularize artificial neural networks and re-investigate some surprising results about how the brain benefits from noise., Comment: 4-page paper submitted to 2018 Conference on Cognitive Computational Neuroscience

Using the data obtained from XMM-Newton, we show the gradual evolution of two periodicities of ~4500 s and ~2200 s in the decay phase of the flare observed in a solar analog EK Dra. The longer period evolves firstly for first 14 ks, while the shorter period evolves for next 10 ks in the decay phase. We find that these two periodicities are associated with the magnetoacoustic waves triggered in the flaring region. The flaring loop system shows cooling and thus it is subjected to the change in the scale height and the acoustic cut-off period. This serves to filter the longer period magnetoacoustic waves and enables the propagation of the shorter period waves in the later phase of the flare. We provide the first clues of the dynamic behaviour of EK Dra's corona which affects the propagation of waves and causes their filtering., Comment: 14 Pages; 04 Figures; 01 Table; Comment: Remarks are welcome from Solar and Stellar Physics Community

We study the thermal structure and energetics of the point-like EUV brightenings within a system of fan loops observed in the active region \textsl{AR~11520}. These brightenings were simultaneously observed on 2012 July 11 by the HIgh-resolution Coronal (Hi-C) imager and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We identified 27 brightenings by automatically determining intensity enhancements in both Hi-C and AIA ~193~{\AA} light curves. The energetics of these brightenings were studied by using the Differential Emission Measure (DEM) diagnostics. The DEM weighted temperatures of these transients are in the range $\log{T} (K) = 6.2 - 6.6$ with radiative energies ${\approx}10^{24-25}$~ergs and densities ${\approx}$ a few times $10^{9}$~cm$^{-3}$. To the best of our knowledge, these are the smallest brightenings in EUV ever detected. We used these results to determine the mechanism of energy loss in these brightenings. Our analysis reveals that the dominant mechanism of energy loss for all the identified brightenings is conduction rather than radiation., Comment: 17 pages, 8 Figures, 3 tables, accepted for publication in Astronomy and Astrophysics

We use spectropolarimetric observations of the Ca II 8542~\AA\ line, taken from the Swedish 1-m Solar Telescope (SST), in an attempt to recover dynamic activity in a micro-flaring region near a sunspot via inversions. These inversions show localized mean temperature enhancements of $\sim$1000~K in the chromosphere and upper photosphere, along with co-spatial bi-directional Doppler shifting of 5 - 10 km s$^{-1}$. This heating also extends along a nearby chromospheric fibril, co-spatial to 10 - 15 km s$^{-1}$ down-flows. Strong magnetic flux cancellation is also apparent in one of the footpoints, concentrated in the chromosphere. This event more closely resembles that of an Ellerman Bomb (EB), though placed slightly higher in the atmosphere than is typically observed., Comment: 9 pages, 9 figures, accepted in ApJ. Movies are stored here: https://star.pst.qub.ac.uk/webdav/public/areid/Microflare/

We use observations of quiet Sun (QS) regions in the H$\alpha$ 6563 \AA, Ca~{\sc ii} 8542 \AA\, and Fe~{\sc i} 6302 \AA\ lines. We observe brightenings in the wings of the H$\alpha$ and Ca~{\sc ii} combined with observations of the interacting magnetic concentrations observed in the Stokes signals of Fe~{\sc i}. These brightenings are similar to Ellerman bombs (EBs), i.e. impulsive bursts in the wings of the Balmer lines which leave the line cores unaffected. Such enhancements suggest that these events have similar formation mechanisms to the classical EBs found in active regions, with the reduced intensity enhancements found in the QS regions due to a weaker feeding magnetic flux. The observations also show that the quiet Sun Ellerman bombs (QSEBs) are formed at a higher height in the upper photosphere than the photospheric continuum level. Using simulations, we investigate the formation mechanism associated with the events and suggest that these events are driven by the interaction of magnetic field-lines in the upper photospheric regions. The results of the simulation are in agreement with observations when comparing the light-curves, and in most cases we found that the peak in the Ca~{\sc ii} 8542 \AA\ wing occurred before the peak in H$\alpha$ wing. Moreover, in some cases, the line profiles observed in Ca~{\sc ii} are asymmetrical with a raised core profile. The source of heating in these events is shown by the MURaM simulations and is suggested to occur 430 km above the photosphere., Comment: 14 pages, 11 figures, 1 table (Published on 2018/6/1)

Recent observations from the Interface Region Imaging Spectrograph (IRIS) appear to show impulsive brightenings in high temperature lines, which when combined with simultaneous ground based observations in H$\alpha$, appear co-spatial to Ellerman Bombs (EBs). We use the RADYN 1-dimensional radiative transfer code in an attempt to try and reproduce the observed line profiles and simulate the atmospheric conditions of these events. Combined with the MULTI/RH line synthesis codes, we compute the H$\alpha$, Ca II 8542~\AA, and Mg II h \& k lines for these simulated events and compare them to previous observations. Our findings hint that the presence of superheated regions in the photosphere ($>$10,000 K) is not a plausible explanation for the production of EB signatures. While we are able to recreate EB-like line profiles in H$\alpha$, Ca II 8542~\AA, and Mg II h \& k, we cannot achieve agreement with all of these simultaneously., Comment: Accepted into ApJL. 4 Figures, 1 Table

We present the results of a series of short radio observations of six ultracool dwarfs made using the upgraded VLA in S (2--4GHz) and C (4--7GHz) bands. LSR J1835+3259 exhibits a 100 percent right-hand circularly polarised burst which shows intense narrowband features with a fast negative frequency drift of about $-30$ MHz $\textrm{s}^{-1}$. They are superimposed on a fainter broadband emission feature with a total duration of about 20 minutes, bandwidth of about 1 GHz, centred at about 3.5 GHz, and a slow positive frequency drift of about 1 MHz $\textrm{s}^{-1}$. This makes it the first such event detected below 4 GHz and the first one exhibiting both positive and negative frequency drifts. Polarised radio emission is also seen in 2MASS J00361617+1821104 and NLTT 33370, while LP 349-25 and TVLM 513-46546 have unpolarised emission and BRI B0021-0214 was not detected. We can reproduce the main characteristics of the burst from LSR J1835+3259 using a model describing the magnetic field of the dwarf as a tilted dipole. We also analyse the origins of the quiescent radio emission and estimate the required parameters of the magnetic field and energetic electrons. Although our results are non-unique, we find a set of models which agree well with the observations., Comment: 16 pages, 9 figures, 5 tables

Transition-region explosive events (EEs) are characterized by non-Gaussian line profiles with enhanced wings at Doppler velocities of 50-150 km/s. They are believed to be the signature of solar phenomena that are one of the main contributors to coronal heating. The aim of this study is to investigate the link of EEs to dynamic phenomena in the transition region and chromosphere in an active region. We analyze observations simultaneously taken by the Interface Region Imaging Spectrograph (IRIS) in the Si IV 1394\AA\ line and the slit-jaw (SJ) 1400\AA\ images, and the Swedish 1-m Solar Telescope (SST) in the H$\alpha$ line. In total 24 events were found. They are associated with small-scale loop brightenings in SJ 1400\AA\ images. Only four events show a counterpart in the H$\alpha$-35 km/s and H$\alpha$+35 km/s images. Two of them represent brightenings in the conjunction region of several loops that are also related to a bright region (granular lane) in the H$\alpha$-35km/s and H$\alpha$+35 km/s images. Sixteen are general loop brightenings that do not show any discernible response in the H$\alpha$ images. Six EEs appear as propagating loop brightenings, from which two are associated with dark jet-like features clearly seen in the H$\alpha$-35 km/s images. We found that chromospheric events with jet-like appearance seen in the wings of the H$\alpha$ line can trigger EEs in the transition region and in this case the IRIS Si IV 1394\AA\ line profiles are seeded with absorption components resulting from Fe II and Ni II. Our study indicates that EEs occurring in active regions have mostly upper-chromosphere/transition-region origin. We suggest that magnetic reconnection resulting from the braidings of small-scale transition region loops is one of the possible mechanisms of energy release that are responsible for the EEs reported in this paper., Comment: 10 pages, 6 figs, accepted by MNRAS

Burst-like events with signatures in the UV are often observed co-spatial to strong line-of-sight photospheric magnetic fields. Several authors, for example, have noted the spatial relationship between Ellerman bombs (EBs) and Moving Magnetic Features (MMFs), regions of flux which disconnect from a sunspot or pore before propagating away in the moat flow and often displaying evidence of cancellation. In this article, data collected by the Solar Dynamics Observatory's Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly are analysed in an attempt to understand the potential links between such cancellation and UV burst formation. Two MMFs from AR 11579, three bi-poles from AR 11765, and six bi-poles (four of which were co-spatial to IRIS bursts) in AR 11850 were identified for analysis. All of these cancellation features were found to have lifetimes of the order hours and cancellation rates of the order 10^14-10^15 Mx s^-1. H-alpha line wing data from the Dunn Solar Telescope's Interferometric BIdimensional Spectrometer were also available for AR 11579 facilitating a discussion of links between MMFs and EBs. Using an algebraic model of photospheric magnetic reconnection, the measured cancellation rates are then used to ascertain estimates of certain quantities (such as up-flow speeds, jet extents, and potential energy releases) which compared reasonably to the properties of EBs reported within the literature. Our results suggest that cancellation rates of the order measured here are capable of supplying enough energy to drive certain UV bursts (including EBs), however, they are not a guaranteeing condition for burst formation., Comment: 13 pages, 6 figures, 2 tables in Monthly Notices of the Royal Astronomical Society 2016

Experimental searches for the electron electric dipole moment (EDM) probe new physics beyond the Standard Model. The current best EDM limit was set by the ACME Collaboration [Science \textbf{343}, 269 (2014)], constraining time reversal symmetry ($T$) violating physics at the TeV energy scale. ACME used optical pumping to prepare a coherent superposition of ThO $H^3\Delta_1$ states that have aligned electron spins. Spin precession due to the molecule's internal electric field was measured to extract the EDM. We report here on an improved method for preparing this spin-aligned state of the electron by using STIRAP. We demonstrate a transfer efficiency of $75\pm5\%$, representing a significant gain in signal for a next generation EDM experiment. We discuss the particularities of implementing STIRAP in systems such as ours, where molecular ensembles with large phase-space distributions are transfered via weak molecular transitions with limited laser power and limited optical access.

Ellerman Bombs (EBs) are often found co-spatial with bipolar photospheric magnetic fields. We use H$\alpha$ imaging spectroscopy along with Fe I 6302.5 \AA\ spectro-polarimetry from the Swedish 1-m Solar Telescope (SST), combined with data from the Solar Dynamic Observatory (SDO) to study EBs and the evolution of the local magnetic fields at EB locations. The EBs are found via an EB detection and tracking algorithm. We find, using NICOLE inversions of the spectro-polarimetric data, that on average (3.43 $\pm$ 0.49) x 10$^{24}$ ergs of stored magnetic energy disappears from the bipolar region during the EBs burning. The inversions also show flux cancellation rates of 10$^{14}$ - 10$^{15}$ Mx s$^{-1}$, and temperature enhancements of 200 K at the detection footpoints. We investigate near-simultaneous flaring of EBs due to co-temporal flux emergence from a sunspot, which shows a decrease in transverse velocity when interacting with an existing, stationary area of opposite polarity magnetic flux and the EBs are formed. We also show that these EBs can get fueled further by additional, faster moving, negative magnetic flux regions., Comment: 5 Figures, 1 Movie, Accepted in ApJ

Chromospheric observations taken at high cadence and high spatial resolution show a range of spicule like features, including Type I, Type II (as well as RBEs and RREs) and those which seem to appear within a few seconds, which if interpreted as flows would imply mass flow velocities in excess of 1000 km/s. This article seeks to quantify and study rapidly appearing spicular type events. We also compare the MOMFBD and speckle reconstruction techniques in order to understand if such spicules are more favourably observed using a particular technique. We use spectral imaging observations taken with the CRISP on the Swedish 1 m Solar Telescope. Data was sampled at multiple positions within the Halpha line profile for both an ondisk and limb location. The data is host to numerous rapidly appearing features which are observed at different locations within the Halpha line profile. The feature's durations vary between 10 and 20 s and lengths around 3500 km. Sometimes, a time delay in their appearance between the blue and red wings of 3 and 5 s is evident, whereas sometimes they are near simultaneous. In some instances features are observed to fade and then re emerge at the same location several tens of seconds later. We provide the first statistical analysis of these spicules and suggest that these observations can be interpreted as the LOS movement of highly dynamic spicules moving in and out of the narrow 60 mA transmission filter used to observe in different parts of the Halpha line profile. The LOS velocity component of the observed fast chromospheric features, manifested as Doppler shifts, are responsible for their appearance in the red and blue wings of Halpha line. Additional work involving data at other wavelengths is required to investigate the nature of their possible wavelike activity., Comment: 15 pages, 13 figs

Ubiquitous small-scale vortices have recently been found in the lower atmosphere of the quiet Sun in state-of-the-art solar observations and in numerical simulations. We investigate the characteristics and temporal evolution of a granular-scale vortex and its associated upflows through the photosphere and chromosphere of a quiet Sun internetwork region. We analyzed high spatial and temporal resolution ground- and spaced-based observations of a quiet Sun region. The observations consist of high-cadence time series of wideband and narrowband images of both H-alpha 6563 A and Ca II 8542 A lines obtained with the CRisp Imaging SpectroPolarimeter (CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well as ultraviolet imaging and spectral data simultaneously obtained by the Interface Region Imaging Spectrograph (IRIS). A small-scale vortex is observed for the first time simultaneously in H-alpha, Ca II 8542 A, and Mg II k lines. During the evolution of the vortex, H-alpha narrowband images at -0.77 A and Ca II 8542 A narrowband images at -0.5 A, and their corresponding Doppler Signal maps, clearly show consecutive high-speed upflow events in the vortex region. These high-speed upflows with a size of 0.5-1 Mm appear in the shape of spiral arms and exhibit two distinctive apparent motions in the plane of sky for a few minutes: (1) a swirling motion with an average speed of 13 km/s and (2) an expanding motion at a rate of 4-6 km/s. Furthermore, the spectral analysis of Mg II k and Mg II subordinate lines in the vortex region indicates an upward velocity of up to about 8 km/s along with a higher temperature compared to the nearby quiet Sun chromosphere. The consecutive small-scale vortex events can heat the upper chromosphere by driving continuous high-speed upflows through the lower atmosphere., Comment: 9 pages, 7 figures, accepted for publication in A&A

Upflows at the edges of active regions (ARs) are studied by spatially and temporally combining multi-instrument observations obtained with EIS/Hinode, AIA and HMI/SDO and IBIS/NSO, to derive their plasma parameters. This information is used for benchmarking data-driven modelling of the upflows (Galsgaard et al., 2015). The studied AR upflow displays blueshifted emission of 5-20 km/s in Fe XII and Fe XIII and its average electron density is 1.8x10^9 cm^3 at 1 MK. The time variation of the density shows no significant change (in a 3sigma error). The plasma density along a single loop drops by 50% over a distance of 20000 km. We find a second velocity component in the blue wing of the Fe XII and Fe XIII lines at 105 km/s. This component is persistent during the whole observing period of 3.5 hours with variations of only 15 km/s. We also study the evolution of the photospheric magnetic field and find that magnetic flux diffusion is responsible for the formation of the upflow region. High cadence Halpha observations of the chromosphere at the footpoints of the upflow region show no significant jet-like (spicule/rapid blue excursion) activity to account for several hours/days of plasma upflow. Using an image enhancement technique, we show that the coronal structures seen in the AIA 193A channel is comparable to the EIS Fe XII images, while images in the AIA 171A channel reveals additional loops that are a result of contribution from cooler emission to this channel. Our results suggest that at chromospheric heights there are no signatures that support the possible contribution of spicules to AR upflows. We suggest that magnetic flux diffusion is responsible for the formation of the coronal upflows. The existence of two velocity components possibly indicate the presence of two different flows which are produced by two different physical mechanisms, e.g. magnetic reconnection and pressure-driven., Comment: Accepted for publication in A&A. Data driven modelling using observations from this paper is presented in Galsgaard et al. 2015 (also accepted for publication in A&A and on arxiv)

Aurorae are detected from all the magnetized planets in our Solar System, including Earth. They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kilohertz and megahertz frequencies produced by the precipitating electrons, as well as continuum and line emission in the infrared, optical, ultraviolet and X-ray parts of the spectrum, associated with the collisional excitation and heating of the hydrogen-dominated atmosphere. Here we report simultaneous radio and optical spectroscopic observations of an object at the end of the stellar main sequence, located right at the boundary between stars and brown dwarfs, from which we have detected radio and optical auroral emissions both powered by magnetospheric currents. Whereas the magnetic activity of stars like our Sun is powered by processes that occur in their lower atmospheres, these aurorae are powered by processes originating much further out in the magnetosphere of the dwarf star that couple energy into the lower atmosphere. The dissipated power is at least four orders of magnitude larger than what is produced in the Jovian magnetosphere, revealing aurorae to be a potentially ubiquitous signature of large-scale magnetospheres that can scale to luminosities far greater than those observed in our Solar System. These magnetospheric current systems may also play a part in powering some of the weather phenomena reported on brown dwarfs., Comment: Accepted for publication in the 30 July 2015 issue of Nature. 27 pages, 2 figures, 2 extended data figures

We report on I band photometric observations of 21 stars with spectral types between M8 and L4 made using the Isaac Newton Telescope. The total amount of time for observations which had a cadence of <2.3 mins was 58.5 hrs, with additional data with lower cadence. We test for photometric variability using the Kruskal-Wallis H-test and find that 4 sources (2MASS J10224821+5825453, 2MASS J07464256+2000321, 2MASS J16262034+3925190 and 2MASS J12464678+4027150) were found to be significantly variable at least on one epoch. Three of these sources are reported as photometrically variable for the first time. If we include sources which were deemed marginally variable, the number of variable sources is 6 (29 percent). No flares were detected from any source. The percentage of sources which we found were variable is similar to previous studies. We summarise the mechanisms which have been put forward to explain the light curves of brown dwarfs., Comment: Accepted MNRAS 6 pages

The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere - a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases., Comment: 73 pages, 21 figures ; Space Science Reviews (accepted December 10th, 2015); accepted version