Studying chromospheric activity of contact binaries is an important way of revealing the magnetic activity processes of these systems. An efficient but somewhat neglected method for that is to follow the changes of the H$α$ line profiles via optical spectroscopy. Our goal was to perform a comprehensive analysis based on the optical spectral signs of chromospheric activity on the largest sample of contact binaries to date. We collected echelle spectra on 12 bright contact binaries and derived new radial velocity curves from our observations. For quantifying the apparent chromospheric activity levels of the systems, we subtracted self-constructed synthetic spectra from the observed ones and measured the equivalent widths of the residual H$α$-profiles at each observed epoch. Our well-sampled data set allowed us to study the short-term variations of chromospheric activity levels as well as to search for correlations between them and some basic physical parameters of the systems. Fitting the radial velocity curves, we re-determined the mass ratios and systemic velocities of all observed objects. We found that chromospheric activity levels of the studied systems show various changes during the orbital revolution: we see either flat, or one-peaked, or two-peaked distributions of equivalent width vs. the orbital phase. The first case means that the activity level is probably constant, while the latter two cases suggest the presence of one or two active longitudes at the stellar surfaces. Our correlation diagrams show that mean chromospheric activity levels may be in connection with orbital periods, B$-$V color indices, inverse Rossby numbers, and temperature differences of the components. At the same time, no clear trend is visible with respect to mass ratios, inclinations and fill-out factors of the systems. A- and W-type contact binaries in our sample show similar distributions.
Chromospheric flare ribbons observed in H-alpha appear well-organized when first examined: ribbons impulsively brighten, morphologically evolve, and exponentially decay back to pre-flare levels. Upon closer inspection of H-alpha flares, there is often a significant number of compact areas brightening in concert with the flare eruption but are spatially separated from the evolving flare ribbon. One class of these brightenings is known as sequential chromospheric brightenings (SCBs). SCBs are often observed in the intimidate vicinity of erupting flares and are associated with coronal mass ejecti…
{Chromospheric evaporation is a key process in solar flares that has extensively been investigated using the spectroscopic observations. However, direct soft X-ray (SXR) imaging of the process is rare, especially in remote brightenings associated with the primary flares that have recently attracted dramatic attention.} {We intend to find the evidence for chromospheric evaporation and figure out the cause of the process in sympathetic coronal bright points (CBPs), i.e., remote brightenings induced by the primary CBP.} {We utilise the high-cadence and high-resolution SXR observations of CBPs fro…
We investigate the chromospheric counterpart of small-scale coronal loops constituting a coronal bright point (CBP) and its response to a photospheric magnetic-flux increase accompanied by co-temporal CBP heating. We used co-observations from the AIA and HMI/SDO, together with data from the Fast Imaging Solar Spectrograph taken in the Halpha and Ca II 8542 lines. We used a new multi-layer spectral inversion technique to derive the temporal variations of the temperature of the Halpha loops (HLs). We find that the counterpart of the CBP, as seen at chromospheric temperatures, is composed of a bu…
In this investigation oscillation periods in Mg II k line intensity, brightness temperature, and Doppler velocity obtained above Magnetic Bright Points (MBPs) are investigated. For that purpose, data from the Interface Region Imaging Spectrometer (IRIS) observing the higher chromosphere and transition region (TR) were analysed together with imaging and magnetogram data obtained by Solar Dynamics Observatory (SDO). The MBPs were identified in combining Si IV 1403 A Slit Jaw Images (SJIs) with the magnetogram information from the Heliospheric and Magnetic Imager (HMI). A time-slice analysis foll…
We report detection of oscillations in brightness temperature, size, and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with high temporal resolution (i.e., 2-sec cadence) with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, $90 \pm 22$ s, $110 \pm 12$ s and $66 \pm 23$ s, respectively. We find anti-correlatio…
We present multi-wavelength observations of a prominence eruption originating from a quadrupolar field configuration, in which the prominence was embedded in a side-arcade. Within the two-day period prior to its eruption on 2012 October 22, the prominence was perturbed three times by chromospheric fibrils underneath, which rose upward, became brightened, and merged into the prominence, resulting in horizontal flows along the prominence axis, suggesting that the fluxes carried by the fibrils were incorporated into the magnetic field of the prominence. These perturbations caused the prominence t…
The Interface Region Imaging Spectrograph (IRIS) reveals small-scale rapid brightenings in the form of bright grains all over coronal holes and the quiet sun. These bright grains are seen with the IRIS 1330 Å, 1400 Å and 2796 Å slit-jaw filters. We combine coordinated observations with IRIS and from the ground with the Swedish 1-m Solar Telescope (SST) which allows us to have chromospheric (Ca II 8542 Å, Ca II H 3968 Å, Hα, and Mg II k 2796 Å), and transition region (C II 1334 Å, Si IV 1402) spectral imaging, and single-wavelength Stokes maps in Fe I 6302 Åat high spatial (0.33"), temporal and…
Using the observations recorded by Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO), the Interface Region Imaging Spectrograph (IRIS) and the Extreme-ultraviolet Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) both on-board Hinode, we present the evidence of chromospheric evaporation in a coronal loop after the occurrence of two active region transient brightenings (ARTBs) at the two footpoints. The chromospheric evaporation started nearly simultaneously in all the three hot channels of AIA such as 131~Å, 94~Å and 335~Å, which was observed to be temperature…
We present a method of chromospheric flux simulation for 13 late-type main-sequence stars. These Sun-like stars have well-determined cyclic flux variations similar to 11 yr solar activity cycle. Our flux prediction is based on chromospheric HK emission time series measurements from Mount Wilson Observatory and comparable solar data. We show that solar three - component modeling explains well the stellar observations. We find that the 10 - 20% of K - stars disc surfaces are occupied by bright active regions.
We investigate the upper chromosphere and the transition region of the sunspot umbra using the radio brightness temperature at 34 GHz (corresponding to 8.8-mm observations) as observed by the Nobeyama Radioheliograph (NoRH). Radio free-free emission in the longer millimeter range is generated around the transition region, and its brightness temperature yields the region's temperature and density distribution. We use the NoRH data at 34 GHz by applying the Steer-CLEAN image synthesis. These data and the analysis method enable us to investigate the chromospheric structures in the longer millimet…
With the ever increasing influx of high resolution images of the solar surface obtained at a multitude of wavelengths, various processes occurring at small spatial scales have become a greater focus of our attention. Complex small-scale magnetic fields have been reported that appear to have enough stored to heat the chromosphere. While significant progress has been made in understanding small-scale phenomena, many specifics remain elusive. We present here a detailed study of a single event of disappearance of a magnetic dipole and associated chromospheric activity. Based on New Solar Telescope…
The Atmospheric Response to Large Electron Beam Fluxes in Solar Flares III: Comprehensive Modeling of the Brightest Observed Near-Ultraviolet Continuum Source in an X9 Solar Flare
Context: Except for the Ca II resonance lines, fibrils are ubiquitously present in most high-resolution observations of chromospheric lines. Aims: We show that fibrils are also a prevailing feature in Ca II K, provided the spatial-resolution is sufficiently high. Methods: We present high spatial resolution observations of an active region in the Ca I} K line from the Swedish Solar Telescope. Through a comparison between photospheric intensity and magnetic field data, we study the connection between bright chromospheric fibrils and photospheric structures. Additionally, using Fourier analysis w…
Photometric and Spectroscopic study of Ten Low Mass Ratio Contact Binary Systems: Orbital Stability, O'Connell Effect and Infra-red Calcium Line Filling
We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS. These 50 stars were selected from the solar-type superflare stars that we had discovered from the Kepler data. More than half (34 stars) of these 50 target superflare stars show no evidence of binarity, and we estimated stellar parameters of these 34 stars in our previous study (Notsu et al. 2015, hereafter called Paper I). According to our previous studies using Kepler data, superflare stars show quasi-periodic brightness variations whose amplitude (0.1-10\%) is much larger than that of the solar b…
We present Kepler light curves and optical spectroscopy of twenty X-ray bright stars located in the Kepler field of view. The stars, spectral type FK, show evidence for rapid rotation including chromospheric activity 100 times or more above the Sun at maximum and flaring behavior in their light curves. Eighteen of our objects appear to be (sub)giants and may belong to the class of FK Com variables, that is evolved rapidly spinning single stars with no excretion disk and high levels of chromospheric activity. Such stars are rare and are likely the result of W UMa binary mergers, a process belie…
We present the first high-resolution, simultaneous observations of the solar chromosphere in the optical and millimeter wavelength ranges, obtained with ALMA and the IBIS instrument at the Dunn Solar Telescope. In this paper we concentrate on the comparison between the brightness temperature observed in ALMA Band 3 (3 mm; 100 GHz) and the core width of the H$α$ 656.3 nm line, previously identified as a possible diagnostic of the chromospheric temperature. We find that in the area of plage, network and fibrils covered by our FOV the two diagnostics are well correlated, with similar spatial stru…
The Sun and stars with low magnetic activity levels, become photometrically brighter when their activity increases. Magnetically more active stars display the opposite behaviour and get fainter when their activity increases. We reproduce the observed photometric trends in stellar variations with a model that treats stars as hypothetical Suns with coverage by magnetic features different from that of the Sun. The presented model attributes the variability of stellar spectra to the imbalance between the contributions from different components of the solar atmosphere, such as dark starspots and br…
We present analysis of medium resolution optical spectra and long term V band photometry of four cool stars, BD+13 5000, BD+11 3024, TYC 3557-919-1 and TYC 5163-1764-1. Our spectroscopic analysis reveals that the stars are giant or sub-giant from K0 or K1 spectral type, and all of them exhibit emission features in their Ca ii H& K lines. These features appear to be modulated with the rotation of the stars. Except BD+11 3024, we observe that the radial velocities of the target stars are not stable, which suggests that each of them might be a member of a binary system. Global analysis of photome…
We analyse sunspot oscillations using Interface Region Imaging Spectrograph (IRIS) slit-jaw and spectral data and narrow-band chromospheric images from the New Solar Telescope (NST) for the main sunspot in NOAA AR 11836. We report that the difference between the shock arrival times as measured the Mg II k 2796.35Å and Si IV 1393.76Å line formation levels changes during the observed period and peak-to-peak delays may range from 40~s to zero. The intensity of chromospheric shocks also displays a long term (about 20~min) variations. NST's high spatial resolution \ha\ data allowed us to conclude t…
Short-lived (100s or less), sub-arcsec to a couple of arcsec size features of enhanced brightenings in the narrowband images at the $\mathrm{H_{2V}}$ and $\mathrm{K_{2V}}$ positions of the Ca II H and K lines in the quiet Sun are known as bright grains. With simultaneous observations of a quiet Sun internetwork region in the Fe I 6173 Å, Ca II 8542 {AA}, and Ca II K lines acquired by the CRisp Imaging Spectro-Polarimeter and the CHROMospheric Imaging Spectrometer instruments on the Swedish 1-m Solar Telescope, we performed multi-line non-local thermodynamic equilibrium inversions using the STo…
We performed photometric and spectroscopic investigations of NSVS 5029961 for the first time. The new BV(RI)$_c$-band light curves were obtained with the 1.0-m telescope at Weihai Observatory of Shandong University. Applying the Wilson-Devinney program, we found that NSVS 5029961 is an A-subtype shallow contact binary with extremely low mass ratio (q = 0.1515, f = 19.1\%). Six spectra have been obtained by LAMOST, and many chromospheric activity emission line indicators were detected in the spectra, revealing that the target exhibits strong chromospheric activity. We calculated the absolute pa…
We present the high precession photometric studies in V band and spectroscopic studies centered around H-alpha line for two extreme mass-ratio short period contact binaries ASAS J082243+1927.0 (V1) and ASAS J085710+1856.8 (V2). The variables in study are in the direction of open cluster Praesepe. From the light curve analysis V1 was found to be a low mass-ratio over-contact binary of A-type, with a mass ratio q 0.121 and fill-out factor f 72%, and V2 was found to be a low mass contact binary of W-type, with a mass-ratio q 1.29 and fill-out factor f 11% (marginal contact). The study of H-alpha …
The structure and energy balance of the solar chromosphere remain poorly known. We have used the imaging spectrometer IBIS at the Dunn Solar Telescope to obtain fast-cadence, multi-wavelength profile sampling of Halpha and Ca II 854.2 nm over a sizable two-dimensional field of view encompassing quiet-Sun network. We provide a first inventory of how the quiet chromosphere appears in these two lines by comparing basic profile measurements in the form of image displays, temporal-average displays, time slices, and pixel-by-pixel correlations. We find that the two lines can be markedly dissimilar i…
We examine the thermal free-free millimetre fluxes expected from non-dusty and non-pulsating K through mid-M giant stars based on our limited understanding of their inhomogeneous chromospheres. We present a semi-analytic model that provides estimates of the radio fluxes for the mm wavelengths (e.g., CARMA, ALMA, JVLA Q-band) based on knowledge of the effective temperatures, angular diameters and chromospheric Mg II h & k emission fluxes. At 250 GHz, the chromospheric optical depths are expected to be significantly less than unity, which means that fluxes across the mm and sub-mm range will hav…
The strong chromospheric absorption lines Ca H & K are tightly connected to stellar surface magnetic fields. Only for the Sun, spectral activity indices can be related to evolving magnetic features on the solar disk. The Solar Disk-Integrated (SDI) telescope feeds the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) of the Large Binocular Telescope (LBT) at Mt. Graham International Observatory (MGIO), Arizona, U.S.A. We present high-resolution, high-fidelity spectra that were recorded on 184 & 82 days in 2018 & 2019 and derive the Ca H & K emission ratio, i.e., the S-index. In…
We gathered high resolution spectra for an ensemble of 55 bright active and inactive stars using the ARC 3.5 m Telescope Echelle Spectrograph at Apache Point Observatory ($R\approx$31,500). We measured spectroscopic effective temperatures, surface gravities and metallicities for most stars in the sample with SME and MOOG. Our stellar property results are consistent with the photometric effective temperatures from the Gaia DR2 pipeline. We also measured their chromospheric $S$ and $\log R^\prime_\mathrm{HK}$ indices to classify the stars as active or inactive and study the connection between ch…
We investigate magnetic activity properties of 21 stars via medium resolution optical spectra and long-term photometry. Applying synthetic spectrum fitting method, we find that all targets are cool giant or sub-giant stars possessing overall [M/H] abundances between $0$ and $-0.5$. We find that six of these targets exhibit only linear trend in mean brightness while eight of them clearly shows cyclic mean brightness variation. Remaining seven target appear to exhibit cyclic mean brightness variation but this can not be confirmed due to the long time scales of the predicted cycle compared to the…
We study the connection between the chromospheric and photospheric behaviour of the active late-type star FK Comae. We use spot temperature modelling, light curve inversion based on narrow- and wide-band photometric measurements, Halpha observations from 1997-2010, and Doppler maps from 2004-2010 to compare the behaviour of chromospheric and photospheric features. Investigating low-resolution Halpha spectra we find that the changes in the chromosphere seem to happen mainly on a time scale longer than a few hours, but shorter variations were also observed. According to the Halpha measurements p…
Using a time series of high-resolution spectra and high-quality multi-colour photometry, we reconstruct surface maps of the primary component of the RS CVn type rapidly rotating eclipsing binary, SV Cam (F9V + K4V). We measure a mass ratio, q, of 0.641(2) using our highest quality spectra and obtain surface brightness maps of the primary component, which exhibit predominantly high-latitude spots located between 60-70-degree latitudes with a mean filling factor of about 35%. This is also indicated by the R-band light curve inversion, subjected to rigourous numerical tests. The spectral subtract…
Extremely Low Mass Ratio Contact Binaries. II. The First Photometric and Spectroscopic Investigations of Six Systems with Orbital Periods Longer than 0.5 days
We analyze data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the observed solar active region and discover the appearance of very distinctive small-scale and short-lived dark features in Ca II H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading. In time series of magnetogra…
Several late-type stars present activity cycles similar to that of the Sun. However, these cycles have been mostly studied in F to K stars. Due to their small intrinsic brightness, M dwarfs are not usually the targets of long-term observational studies of stellar activity, and their long-term variability is generally not known. In this work, we study the long-term activity of two M dwarf stars: Gl 229 A (M1/2) and Gl 752 A (M2.5). We employ medium resolution echelle spectra obtained at the 2.15 m telescope at the Argentinian observatory CASLEO between the years 2000 and 2010 and photometric ob…
Recent observations of sunspot light-bridges have shed new light on the fact that they are often associated with significant chromospheric activity. In particular chromospheric jets (Shimizu et al. 2009) persisting over a period of days have been identifies, sometimes associated with large downflows at the photospheric level (Louis et al. 2009). One possible explanation for this activity is reconnection low in the atmosphere. Light-bridges have also been associated with a constant brightness enhancement in the 1600 angstroms passband of TRACE, and the heating of 1 MK loops. Using data from EIS…
Multi band photometry and light curve analysis for two newly recognized contact binary systems, TYC 6995-813-1 and NSVS 13602901 are presented. Both were found to be of extreme low mass ratios 0.11 and 0.17, respectively. The secondary components of both systems show evidence of considerable evolution with elevated densities as well as both luminosity and radii well above their main sequence counterparts. Even in the absence of significant spot activity at least one of the systems, TYC 6995-813-1, shows features of magnetic and chromospheric activity. TYC 6995-813-1 is also determined to be a …
At radio wavelengths, solar-type stars emit thermal free-free and gyroresonance, gyrosynchrotron, and impulsive coherent emission. Thermal free-free emission originates at layers where the optical depth is close to unit, while high brightness temperature, variable emission, can be due to flares via gyrosynchrotron emission. We observed the alpha Cen system with the Australian Telescope Compact Array at 2 GHz for three days and 17 GHz for one day. Both stars have been detected at 17 GHz, while only an upper limit has been obtained at low frequency despite the longer integration time. The bright…
We present photometric analysis of three bright red nova progenitor contact binary systems: ASAS J082151-0612.6, TYC 7281-269-1 and TYC 7275-1968-1. The primary components in all three systems are solar-type low mass stars with radii somewhat larger than their Zero Age Main Sequence counterparts. The secondaries, as in most contact binary systems, have radii and luminosities well above their main sequence counterparts. All three have extreme low mass ratios ranging from 0.075 to 0.097 and two have high degrees of contact, in excess of 75%. All three have mass ratios and separations below the t…
The observations of post eruption arcades (PEAs) in X-rays and EUV reveal strong localised brightenings at the loop top regions. The origin of these brightenings and their dynamics is not well understood to date. Here, we study the dynamics of PEAs using one-dimensional hydrodynamic modelling with the focus on the the understanding of the formation of localised brightening.Our findings suggest that these brightenings are the result of collisions between the counter-streaming chromospheric evaporation from both the foot points. We further perform forward modelling of the emission observed in si…
We performed new photometric observations for two contact binaries (i.e., CRTS J025408.1+265957 and CRTS J012111.1+272933), which were observed by the 1.0-m telescope at Xingjiang Astronomical Observatory. From our light curves and several survey data, we derived several sets of photometric solutions. We found that CRTS J025408.1+265957 and CRTS J012111.1+272933 were Aand W-type W UMa, respectively. The results imply that the spot migrates or disappears in two contact binaries, which were identified by chromospheric activity emissions (e.g. Hα emission) from LAMOST spectra. From the O-C curves…
ZZ PsA is a neglected bright southern contact binary system with maximum V magnitude of 9.26. We present the first multi-band photometric analysis and find the system to be in deep contact (>95%) with an extremely low mass ratio of 0.078. The primary has a mass of 1.213 M? in keeping with its reported spectral class of F6. In order to determine if ZZ PsA is a merger candidate we outline the current status regarding the instability mass ratio and develop new relationship linking the mass of the primary to the instability mass ratio of the system and the degree of contact. We find that ZZ PsA al…
The NaD1 line in the solar spectrum is sometimes attributed to the solar chromosphere. We study its formation in quiet-Sun network and internetwork. We first present high-resolution profile-resolved images taken in this line with the imaging spectrometer IBIS at the Dunn Solar Telescope and compare these to simultaneous chromospheric images taken in Ca 8542 and Halpha. We then model NaD1 formation by performing 3D NLTE profile synthesis for a snapshot from a 3D radiation-magnetohydrodynamics simulation. We find that most NaD1 brightness is not chromospheric but samples the magnetic concentrati…
Radio and optical observations of the evolution of flare-associated phenomena have shown an initial and rapid burst at 0.4 THz only followed subsequently by a localized chromospheric heating producing an Hα brightening with later heating of the whole active region. A major instability occurred several minutes later producing one impulsive burst at microwaves only, associated with an M2.0 GOES X-ray flare that exhibited the main Hα brightening at the same site as the first flash. The possible association between long-enduring time profiles at soft X-rays, microwaves, Hα and sub-THz wavelengths …
We report observations of white-light ejecta in the low corona, for two X-class flares on the 2013 May 13, using data from the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory. At least two distinct kinds of sources appeared (chromospheric and coronal), in the early and later phases of flare development, in addition to the white-light footpoint sources commonly observed in the lower atmosphere. The gradual emissions have a clear identification with the classical loop-prominence system, but are brighter than expected and possibly seen here in the continuum rather than li…
The solar analogs of M67 let us glimpse the probable behavior of the Sun on time scales surpassing the duration of human civilization. M67 can serve as a solar proxy because its stars share a similar age and composition with the Sun. Previous surveys of M67 observed that 15% of its Sun-like stars exhibited chromospheric activity levels below solar minimum, which suggest that these stars might be in activity-minimum states analogous to the Maunder Minimum. The activity diagnostic used, the HK index (relative intensities of the Ca II H&K lines integrated over 1 Ang. bandpasses), was measured fro…
The chromospheric H-alpha spectral line is a strong line in the spectrum of the Sun and other stars. In the stellar regime, this spectral line is already used as a powerful tracer of stellar activity. For the Sun, other tracers (i.e, CaII K) are typically used to monitor solar activity. We used observations of full-disk H-alpha filtergrams of the Chromospheric Telescope (ChroTel) to extract the imaging H-alpha excess and deficit, which are related to bright features (plage regions) and dark absorption features (filaments and sunspots), respectively. The aim of this study is to introduce the im…
M stars are ideal targets to search for Earth-like planets. However, they usually have high levels of magnetic activity, which could affect their habitability and make difficult the detection of exoplanets orbiting around them. Unfortunately, long-term variability of dM stars has not been extensively studied, due to their low intrinsic brightness. For this reason, in 1999 we started the HKalpha project, which systematically observes the spectra of a large number of stars, in particular dM stars, at the Complejo Astronomico El Leoncito (CASLEO). In this work, we study the long-term activity of …
New instruments sensitive to chromospheric radiation at X-ray, UV, Visible, IR, and sub-mm wavelengths have become available that significantly enhance our ability to understand the bi-directional flow of energy through the chromosphere. We describe the calibration, co-alignment, initial results, and public release of a new data set combining a large number of these instruments to obtain multi-wavelength photospheric, chromospheric, and coronal observations capable of improving our understanding of the connectivity between the photosphere and the corona via transient brightenings and wave sign…
A small-scale flare SOL2012-09-21T02:19 (B2) occurred in a spotless active region that we observed at a ground-based telescope equipped with a spectrograph. During the flare, we registered an increase in absorption in the He I 10830 Å line by 25%, while other chromospheric and coronal spectral lines demonstrated increase in brightness at the same location. This phenomenon called negative flare had rarely been observed at the Sun before. In this paper, we describe the morphology of this flare and investigate its dynamics based on our spectral observations and space imaging data. The H$α$ and He…
We have carried out the first comprehensive investigation of enhanced line emission from molecular hydrogen, H$_{2}$ at 1333.79 Å, observed at flare ribbons in SOL2014-04-18T13:03. The cool H$_{2}$ emission is known to be fluorescently excited by Si IV 1402.77 Å UV radiation and provides a unique view of the temperature minimum region (TMR). Strong H$_{2}$ emission was observed when the Si IV 1402.77 Å emission was bright during the flare impulsive phase and gradual decay phase, but it dimmed during the GOES peak. H$_{2}$ line broadening showed non-thermal speeds in the range 7-18 $\rm{km~s}^{…
Aims: We investigate the temporal evolution of magnetic flux emergence in the quiet Sun atmosphere close to disk center. Methods: We combine high-resolution SoHO/MDI magnetograms with TRACE observations taken in the 1216 Å channel in order to analyze the temporal evolution of an emerging small-scale magnetic loop and its traces in the chromosphere. Results: At first place, we find signatures of flux emergence very close to the edge of a supergranular network boundary located at disk center. The new emerging flux appears first in the MDI magnetograms in form of an asymmetric bipolar element, i.…
In this study, we present the preliminary light curve analysis of the contact binary SW Lac, using B, V light curves of the system spanning 2 years (2009 - 2010). During the spot modeling process, we used the information coming from the Doppler maps of the system, which was performed using the high resolution and phase dependent spectra obtained at the 2.1 m Otto Struve Telescope of the McDonald Observatory, in 2009. The results showed that the spot modeling from the light curve analysis are in accordance with the Doppler maps, while the non-circular spot modeling technique is needed in order …
