We present a homogeneous analysis of line and continuum emission from simultaneous high-cadence spectra and photometry covering near-ultraviolet and optical wavelengths for 20?M dwarf flares. These data were obtained to study the white-light continuum components at bluer and redder wavelengths than the Balmer jump. Our goals were to break the degeneracy between emission mechanisms that have been fit to broadband colors of flares and to provide constraints for radiative-hydrodynamic (RHD) flare models that seek to reproduce the white-light flare emission. The main results from the analysis are the following: (1) the detection of Balmer continuum (in emission) that is present during all flares and with a wide range of relative contributions to the continuum flux at bluer wavelengths than the Balmer jump; (2) a blue continuum at flare maximum that is linearly decreasing with wavelength from ? = 4000-4800 ?, indicative of hot, blackbody emission with typical temperatures of T BB ~ 9000-14, 000?K; (3) a redder continuum apparent at wavelengths longer than H? (? 4900 ?) which becomes relatively more important to the energy budget during the late gradual phase. The hot blackbody component and redder continuum component have been detected in previous studies of flares. However, we have found that although the hot blackbody emission component is relatively well-represented by a featureless, single-temperature Planck function, this component includes absorption features and has a continuum shape strikingly similar to the spectrum of an A-type star as directly observed in our flare spectra. New model constraints are presented for the time evolution among the hydrogen Balmer lines and between Ca II K and the blackbody continuum emission. We calculate Balmer jump flux ratios and compare to the solar-type flare heating predictions from RHD models. The model ratios are too large and the blue-optical (? = 4000-4800 ?) slopes are too red in both the impulsive and gradual decay phases of all 20 flares. This discrepancy implies that further work is needed to understand the heating at high column mass during dMe flares.

TIME-RESOLVED PROPERTIES AND GLOBAL TRENDS IN dMe FLARES FROM SIMULTANEOUS PHOTOMETRY AND SPECTRA*

We present a homogeneous survey of line and continuum emission from near-ultraviolet (NUV) to optical wavelengths during twenty M dwarf flares with simultaneous, high cadence photometry and spectra. These data were obtained to study the white-light continuum components at bluer and redder wavelengths than the Balmer jump. Our goals were to break the degeneracy between emission mechanisms that have been fit to broadband colors of flares and to provide constraints for radiative-hydrodynamic (RHD) flare models that seek to reproduce the white-light flare emission. The main results from the continuum analysis are the following: 1) the detection of Balmer continuum (in emission) that is present during all flares and with a wide range of relative contributions to the continuum flux at bluer wavelengths than the Balmer jump; 2) a blue continuum at flare maximum that is linearly decreasing with wavelength from \lambda = 4000-4800A, matched by the spectral shape of hot, blackbody emission with typical temperatures of T_{BB}~9000-14,000 K; 3) a redder continuum apparent at wavelengths longer than H\beta\ (\lambda > 4900A) which becomes relatively more important to the energy budget during the late gradual phase. We calculate Balmer jump flux ratios and compare to RHD model spectra. The model ratios are too large and the blue-optical (\lambda = 4000-4800A) slopes are too red in both the impulsive and gradual decay phases of all twenty flares. This discrepancy implies that further work is needed to understand the heating at high column mass during dMe flares. (Abridged)

Time-Resolved Properties and Global Trends in dMe Flares from Simultaneous Photometry and Spectra

Quasi-periodic pulsations (or QPPs) are periodic intensity variations in the flare emission that occur across all wavelength bands. In this article, we review the observational and modelling achievements since the previous review on this topic by Nakariakov and Melnikov (Space Sci. Rev.149, 119, 2009). In recent years, it has become clear that QPPs are an inherent feature of solar flares because almost all flares exhibit QPPs. Moreover, it is now firmly established that QPPs often show multiple periods. We also review possible mechanisms for generating QPPs. Up to now, it has not been possible to conclusively identify the triggering mechanism or cause of QPPs. The lack of this identification currently hampers possible seismological inferences of flare plasma parameters. QPPs in stellar flares have been detected for a long time, and the high-quality data of the Kepler mission allows studying the QPP more systematically. However, it has not been conclusively shown whether the timescales of stellar QPPs are different or the same as those in solar flares.

Quasi-periodic Pulsations in Solar and Stellar Flares: An Overview of Recent Results (Invited Review)

On UT 2009 January 16, we observed a white light megaflare on the dM4.5e star YZ CMi as part of a long-term spectroscopic flare-monitoring campaign to constrain the spectral shape of optical flare continuum emission. Simultaneous U-band photometric and 3350-9260 A spectroscopic observations were obtained during 1.3 hr of the flare decay. The event persisted for more than 7 hr and at flare peak, the U-band flux was almost 6 mag brighter than in the quiescent state. The properties of this flare mark it as one of the most energetic and longest-lasting white light flares ever to be observed on an isolated low-mass star. We present the U-band flare energetics and a flare continuum analysis. For the first time, we show convincingly with spectra that the shape of the blue continuum from 3350 A to 4800 A can be represented as a sum of two components: a Balmer continuum as predicted by the Allred et al. radiative hydrodynamic flare models and a T{approx} 10,000 K blackbody emission component as suggested by many previous studies of the broadband colors and spectral distributions of flares. The areal coverage of the Balmer continuum and blackbody emission regions vary during the flare decay, withmore » the Balmer continuum emitting region always being significantly ({approx}3-16 times) larger. These data will provide critical constraints for understanding the physics underlying the mysterious blue continuum radiation in stellar flares.« less

https://iopscience.iop.org/article/10.1088/2041-8205/714/1/L98/pdf

A White Light Megaflare on the dM4.5e Star YZ CMi

The phenomenon of quasi-periodic pulsations (QPPs) in solar and stellar flares has been known for over 50 years and significant progress has been made in this research area. It has become clear that QPPs are not rare—they are found in many flares and, therefore, robust flare models should reproduce their properties in a natural way. At least fifteen mechanisms/models have been developed to explain QPPs in solar flares, which mainly assume the presence of magnetohydrodynamic (MHD) oscillations in coronal structures (magnetic loops and current sheets) or quasi-periodic regimes of magnetic reconnection. We review the most important and interesting results on flare QPPs, with an emphasis on the results of recent years, and we present the predicted and prominent observational signatures of each of the fifteen mechanisms. However, it is not yet possible to draw an unambiguous conclusion as to the correct underlying QPP mechanism because of the qualitative, rather than quantitative, nature of most of the models and also due to insufficient observational information on the physical properties of the flare region, in particular the spatial structure of the QPP source. We also review QPPs in stellar flares, where progress is largely based on solar-stellar analogies, suggesting similarities in the physical processes in flare regions on the Sun and magnetoactive stars. The presence of QPPs with similar properties in solar and stellar flares is, in itself, a strong additional argument in favor of the likelihood of solar-stellar analogies. Hence, advancing our understanding of QPPs in solar flares provides an important additional channel of information about stellar flares. However, further work in both theory/simulations and in observations is needed.

Quasi-Periodic Pulsations in Solar and Stellar Flares: A Review of Underpinning Physical Mechanisms and Their Predicted Observational Signatures

Many-site multichannel simultaneous observations of the flare star EV Lac revealed high-frequency brightness os- cillations superimposed on the mean flare light curve. Oscilla- tions occur at the earliest stage of a flare and are visible during the high state. Coherent oscillations of 26 and 13 sec were seen during three flare events. The pulsed fractions were 2.5% in the B band and 10-15% in the U band. This oscillatory phenomenon can be used to improve our understanding of the flare process.

http://aa.springer.de/papers/0364002/2300641.pdf

Detection of high-frequency optical oscillations on the flare star EV Lacertae

Magnetic activity in stars on the giant branches: Twenty years of observations

A slitless UBVR spectrograph has been built for use on small telescopes. Test observations on the Zeiss-600 telescope at the Terskol peak demonstrated that the spectrograph is an efficient instrument for studying high-speed processes in variable stars with a high temporal resolution. The spectrograph resolving power R ≈ 100 in the vicinity of λ = 480 nm and the error in the determination of the wavelength is approximately 3 nm. The spectrograph provides a moderate signal-to-noise ratio for stars up to 16m. It permits one to measure equivalent widths of unblended lines down to 0.1 nm. The developed special software based on the theory of quantum statistics makes it possible to detect relative variations in the spectrum of approximately 10−5–10−6 of the bolometric flux of the star. Observations with the spectrograph made it possible to detect variations of emissions in Balmer lines and Ca II H, K lines in the EV Lac flare star in the subsecond range. The spectroscopic monitoring permits one to study stellar flares with small amplitude, to carry out a comprehensive colorimetric analysis of flare plasma, and to determine temperatures and sizes of flares in the light intensity maximum. Observations of the transit of the HAT-P-1 B exoplanet demonstrate that the chromospheric activity power of the parent star does not vary during the transit. The slitless spectrograph with a low resolving capacity opens new prospects in studying active processes occurring on stars’ surfaces.

Slitless spectrograph for small telescopes: First results

Results of cooperative observations of the flare star EV Lac in September 1993 are presented. One of the about 30 optical flares detected was powerful enough to permit a quantitative analysis of its intrinsic radiation with the colour-colour technique. Sinusoidal brightness variations due to spottedness of the stellar surface was found to have an amplitude Δ V = 0.m0.24. Behaviour of the K band stellar brightness during strong and weak U band flares are considered. The upper limits of very fast optical brightness variations were estimated during both a moderate flare and quiet state of the star. No decametric bursts were observed during the campaign that could be certainly attributed to flare activity.

Coordinated observations of the red dwarf flare star EV Lac in 1998

We present the results of fast spectrophotometry for two flares on EV Lac with a time resolution of 8 s and a spectroscopic resolution R ∼ 100. The observations were performed in May and August 2010 with a slitless spectrograph on the Zeiss-600 telescope at Peak Terskol. We have estimated the UBVR magnitudes from spectrograms through a mathematical convolution of the spectra with the filter transmission curves. The UBV R amplitudes of the August 10, 2010 flare are $2\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 83$, $1\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 94$, $0\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 82$, and $0\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 28$, respectively. The UBV R amplitudes of the May 30, 2010 flare are $0\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 65$, $0\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 25$, $0\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 15$, and $0\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m} 10$, respectively. A detailed colorimetric analysis has allowed important parameters of the flares on EV Lac to be estimated: the temperatures at maximum light and their sizes. The color-color (U − B)−(B − V ) diagrams confirm that both flares at maximum light radiate as a blackbody. The temperatures at maximum light was 13 400 ± 500 K for the August flare and 5700 ± 100 K for the May flare. During the May flare, an additional hydrogen emission appeared in the Balmer Hα, Hβ, Hγ, Hδ, Hɛ, Hζ lines and the Balmer continuum (3647 A) in the spectrum of EV Lac. The excess of emission in the Balmer lines was approximately from two to thirty percent. Based on our colorimetric analysis, we have estimated the linear sizes of the flares at maximum light. The size of the May 30, 2010 flare is approximately 7% of the stellar radius. The size of the August 10, 2010 flare is 3.9% of the stellar radius.

Fast spectrophotometry of the flare star EV lacertae

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

B. E. Zhilyaev

Author Tools

Chat about Author