The flares of August 1972

Zirin, H.; Tanaka, K.

doi:10.1007/bf00152736

Cited by 249 publications

(65 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…These spectra are similar to red M dwarf flare spectra (Fuhrmeister et al 2008), and are understood as the result of the increase in electron density and heating of the chromosphere (Fuhrmeister et al 2010). The much longer duration of the emission lines is not surprising, and is consistent with solar flares (Zirin 1988) and the statistics of SDSS spectra of M dwarf flares (Kruse et al 2010;Hilton et al 2010). The flare luminosity for the first 100 minutes in units of 10 28 erg is 480, 13, and 3.5 in Hα, He i (6678 Å), and O i (7774 Å).…”

Section: Spectroscopy and Photometry Of The 2012 July 29 Flaressupporting

confidence: 62%

“…This interpretation could also be applied to the W1906+40 flare. Zirin & Tanaka (1973) noted broad (FWHM 12 Å) Hα emission from the kernels of a great solar flare; these are also responsible for the white light emission and show turbulent motions (Zirin 1988). Detailed modeling should be pursued, however, as very broad Hα emission wings are caused by Stark broadening in some Cram & Woods (1982) models along with the white light (Models 5 and 6), while Kowalski et al (2011Kowalski et al ( , 2012 found broad Hα absorption associated with a white light flare on YZ CMi reminiscent of an A star.…”

Section: Spectroscopy and Photometry Of The 2012 July 29 Flaresmentioning

confidence: 99%

See 1 more Smart Citation

KEPLERMONITORING OF AN L DWARF I. THE PHOTOMETRIC PERIOD AND WHITE LIGHT FLARES

Gizis

Burgasser

Berger

et al. 2013

ApJ

View full text Add to dashboard Cite

We report on the results of 15 months of monitoring the nearby field L1 dwarf WISEP J190648.47+401106.8 (W1906+40) with the Kepler mission. Supporting observations with the Karl G. Jansky Very Large Array and Gemini North Telescope reveal that the L dwarf is magnetically active, with quiescent radio and variable Hα emission. A preliminary trigonometric parallax shows that W1906+40 is at a distance of 16.35 +0.36 −0.34 pc, and all observations are consistent with W1906+40 being an old disk star just above the hydrogen-burning limit. The star shows photometric variability with a period of 8.9 hr and an amplitude of 1.5%, with a consistent phase throughout the year. We infer a radius of 0.92±0.07R J and sin i > 0.57 from the observed period, luminosity (10 −3.67±0.03 L ), effective temperature (2300 ± 75 K), and v sin i (11.2 ± 2.2 km s −1 ). The light curve may be modeled with a single large, high latitude dark spot. Unlike many L-type brown dwarfs, there is no evidence of other variations at the 2% level, either non-periodic or transient periodic, that mask the underlying rotation period. We suggest that the long-lived surface features may be due to starspots, but the possibility of cloud variations cannot be ruled out without further multi-wavelength observations. During the Gemini spectroscopy, we observed the most powerful flare ever seen on an L dwarf, with an estimated energy of ∼1.6 × 10 32 erg in white light emission. Using the Kepler data, we identify similar flares and estimate that white light flares with optical/ultraviolet energies of 10 31 erg or more occur on W1906+40 as often as 1-2 times per month.

show abstract

Section: Spectroscopy and Photometry Of The 2012 July 29 Flaressupporting

confidence: 62%

Section: Spectroscopy and Photometry Of The 2012 July 29 Flaresmentioning

confidence: 99%

KEPLERMONITORING OF AN L DWARF I. THE PHOTOMETRIC PERIOD AND WHITE LIGHT FLARES

Gizis

Burgasser

Berger

et al. 2013

ApJ

View full text Add to dashboard Cite

show abstract

“…The importance of magnetic shear has been stressed on many occasions (Zirin & Tanaka 1973;Hagyard et al 1984;Kurokawa 1987;Tanaka 1991;Kurokawa 1996;Ishii et al 1998). Some of these authors have focused on the twist of the rising flux tubes as the essential element in flare production.…”

Section: Introductionmentioning

confidence: 99%

A study of the causal relationship between the emergence of a twisted magnetic flux rope and a small Hαtwo-ribbon flare

Brooks

Kurokawa

Yoshimura

et al. 2003

A&A

View full text Add to dashboard Cite

Abstract. We present results from an analysis of a small two-ribbon flare which occurred above emerging flux in solar active region NOAA 8218 on 1998, May 13th and which was observed by the Swedish Vacuum Solar Telescope (SVST) on the island of La Palma, Spain. The relatively simple magnetic morphology and small size of the flare together with the high quality of the SVST observations allow us to examine the essential properties of flares in emerging flux regions in greater detail than before. In this paper we compare and contrast the flaring emerging flux region simultaneously with a non-flaring emerging flux region within the same field of view. Unusual magnetic footpoint motions are observed in the flaring region, coincident with the Hα kernels, which result in a high level of shearing of the magnetic neutral line between opposite polarities. The Hα images show dark filament structures which form an inverted S-like shape immediately prior to the flare and then separate after the energy release disrupts the magnetic field. We interpret the motions and structures as strong evidence for the emergence of a twisted magnetic flux rope which developed a sheared configuration with the overlying magnetic field. In contrast the companion region shows separating footpoints, with apparent arch-like filament connections in the Hα images, consistent with the expected appearance of emerging flux. The observations imply that the attachment of the inverted S-shaped structure may be an observational consequence of the magnetic reconnection or untwisting of the field which triggered the flare. We also find some evidence that the increase in magnetic flux is faster in the flaring region. Finally, we propose a simple schematic model of the emergence of a twisted magnetic flux rope and attached branch which can account for the observed footpoint motions and Hα structures of the flaring region. Such a model can, in principle, induce partial magnetic reconnection in the overlying coronal field and we found some evidence of coronal loop footpoint brightenings which support our conclusions. Our high resolution study supports the results of previous authors that even a small twisted structure in an emerging flux tube can be important for flare production.

show abstract

“…The importance of magnetic shear was first indicated from the orientation change of H loops during a very large flare (Zirin & Tanaka 1973). Hagyard et al (1984) first defined the magnetic shear Á , as the azimuth difference in the photospheric magnetic field between the observed transverse field and the potential magnetic field, which fits the boundary conditions imposed by the observed line-of-sight field.…”

Section: Magnetic Shear Anglementioning

confidence: 99%

Evolution of Magnetic Nonpotentiality in NOAA AR 10486

Dun

Kurokawa

Ishii

et al. 2007

ApJ

View full text Add to dashboard Cite

The active region NOAA 10486 was one of the most flare-productive regions during solar cycle 23. In this paper, we focus our analysis on the daily evolution of magnetic nonpotentiality for this region from 2003 October 26 to October 30. Daily averaged values of three nonpotential parameters: magnetic shear angle, line-of-sight current, and current helicity of the selected regions along the main neutral lines are calculated using the vector magnetograms obtained at Huairou Solar Observing Station. The magnetic flux evolution and proper motion of magnetic features are also studied in detail for the initial brightening regions of the two large X-class flares (X17 on October 28 and X10 on October 29). The main results are as follows. (1) Three parameters of the magnetic nonpotentiality in the photosphere obviously increased at the impulsively brightening flare sites from at least 1 day before the two large X-class flares, and most of the three parameters decreased after the flares around the main flare regions. (2) The increase of magnetic flux and complex proper motions of the magnetic knots were found to be simultaneously occurring at the non-potentiality developing sites along the main neutral lines. Such increases and motions of the magnetic flux can be explained by the model of emerging twisted flux ropes, and we conclude that the emergence of twisted magnetic flux ropes are a main reason for the development of nonpotentiality along the neutral line and for the production of strong X-class flares.

show abstract

The flares of August 1972

Cited by 249 publications

References 13 publications

KEPLERMONITORING OF AN L DWARF I. THE PHOTOMETRIC PERIOD AND WHITE LIGHT FLARES

KEPLERMONITORING OF AN L DWARF I. THE PHOTOMETRIC PERIOD AND WHITE LIGHT FLARES

A study of the causal relationship between the emergence of a twisted magnetic flux rope and a small Hαtwo-ribbon flare

Evolution of Magnetic Nonpotentiality in NOAA AR 10486

Contact Info

Product

Resources

About