Statistical properties of solar granulation derived from the SOUP instrument on Spacelab 2

Title, A. M.; Tarbell, T. D.; Topka, K.; Ferguson, S. H.; Shine, R. A.; Team, Soup

doi:10.1086/167026

Cited by 306 publications

(226 citation statements)

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“…There is no significant difference in the granular lifetimes during the first and second halves of the time-series. Our findings are in good agreement with the original work of Bahng & Schwarzschild (1961) and match accurately the findings of Title et al (1989). G-band bright points show two types of behavior: either they remain stationary as at the supergranular boundary at the western periphery of the FOV or they stream away from the satellite sunspot towards the main spot.…”

Section: Decorrelation Timessupporting

confidence: 92%

Horizontal flow fields observed in Hinode G-band images

Verma

Denker

2012

A&A

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Context. Emergence of magnetic flux plays an important role in the initiation of flares. However, the role of submerging magnetic flux in prompting flares is more ambiguous, not the least because of the scarcity of observations. Aims. The flare-prolific active region NOAA 10930 offered both a developing δ-spot and a decaying satellite sunspot of opposite polarity. The objective of this study is to characterize the photometric decay of the satellite sunspot as well as the evolution of photospheric and chromospheric horizontal proper motions in its surroundings. Methods. We apply the local correlation tracking technique to a 16-h time-series of Hinode G-band and Ca ii H images and study the horizontal proper motions in the vicinity of the satellite sunspot on 2006 December 7. Decorrelation times were computed to measure the lifetime of solar features in intensity and flow maps. Results. We observed shear flows in the dominant umbral cores of the satellite sunspot. These flows vanished once the penumbra had disappeared. This slow penumbral decay had an average rate of 152 Mm 2 day −1 over an 11-h period. Typical lifetimes of intensity features derived from an autocorrelation analysis are 3-5 min for granulation, 25-35 min for G-band bright points, and up to 200−235 min for penumbrae, umbrae, and pores. Long-lived intensity features (i.e., the dominant umbral cores) are not related to long-lived flow features in the northern part of the sunspot, where flux removal, slowly decaying penumbrae, and persistent horizontal flows of up to 1 km s −1 contribute to the erosion of the sunspot. Finally, the restructuring of magnetic field topology was responsible for a homologous M2.0 flare, which shared many characteristics with an X6.5 flare on the previous day. Conclusions. Notwithstanding the prominent role of δ-spots in flaring, we conclude based on the decomposition of the satellite sunspot, the evolution of the surrounding flow fields, and the timing of the M2.0 flare that the vanishing magnetic flux in the decaying satellite sunspot played an instrumental role in triggering the homologous M2.0 flare and the eruption of a small Hα filament. The strong magnetic field gradients of the neighboring δ-spot merely provided the vehicle for the strongest flare emission about 10 min after the onset of the flare.

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Section: Decorrelation Timessupporting

confidence: 92%

Horizontal flow fields observed in Hinode G-band images

Verma

Denker

2012

A&A

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“…Thus the reduction of the HF intensity a b oscillations may indicate direct magnetic damping of the oscillations. We note that reduced convective motion in the presence of magnetic fields is commonly observed (e.g., Title et al, 1989) …”

Section: Magnetic Suppression Of Oscillatory Powermentioning

confidence: 67%

Space – Time Distribution of G-band and Ca ii H-line Intensity Oscillations in Hinode/SOT – FG Observations

Lawrence

Cadavid

2009

Sol Phys

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Abstract.We study the space-time distributions of intensity fluctuations in 2 -3 hour sequences of multispectral, high-resolution, high-cadence, broad-band filtergram images of the Sun made by the SOT-FG system aboard the Hinode spacecraft. In the frequency range 5.5 < f < 8.0 mHz both G-band and Ca II H-line oscillations are suppressed in the presence of magnetic fields, but the suppression disappears for f > 10 mHz.By looking at G-band frequencies above 10 mHz we find that the oscillatory power, both at these frequencies and at lower frequencies too, lies in a mesh pattern with cell scale 2 -3 Mm, clearly larger than normal granulation, and with correlation times on the order of hours. The mesh pattern lies in the dark lanes between stable cells found in time-integrated G-band intensity images. It also underlies part of the bright pattern in time-integrated H-line emission. This discovery may reflect dynamical constraints on the sizes of rising granular convection cells together with the turbulence created in strong intercellular downflows.2

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“…Schrijver & Zwann 2000;Kjeldsen et al 2005). Granulation corresponds to a small convective pattern with a lifetime shorter than 25 min, and a diameter smaller than 2 Mm (Title et al 1989;Del Moro 2004). On much larger scales, we can find supergranulation.…”

Section: Introductionmentioning

confidence: 92%

Planetary detection limits taking into account stellar noise

Dumusque

Udry

Lovis

et al. 2010

A&A

284

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Context. Stellar noise produced by oscillations, granulation phenomena (granulation, mesogranulation, and supergranulation), and activity affects radial velocity measurements. The signature of the corresponding effect in radial velocity is small, around the meterper-second, but already too large for the detection of Earth-mass planets in habitable zones. Aims. We address the important role played by observational strategies in averaging out the radial velocity signature of stellar noise. We also derive the planetary mass detection limits expected in the presence of stellar noise. Methods. We start with HARPS asteroseismology measurements for four stars (β Hyi, α Cen A, μ Ara, and τ Ceti) available in the ESO archive and very precise measurements of α Cen B. This sample covers different spectral types from G2 to K1 and different evolutionary stages, from subgiant to dwarf stars. Since data span between 5 and 8 days, only stellar noise sources with timescales shorter than this time span will be extracted from these observations. Therefore, we are able to study oscillation modes and granulation phenomena without being significantly affected by activity noise present on longer timescales. For those five stars, we generate synthetic radial velocity measurements after fitting the corresponding models of stellar noise in Fourier space. These measurements allow us to study the radial velocity variation due to stellar noise for different observational strategies as well as the corresponding planetary mass detection limits. Results. Applying three measurements per night of 10 min exposure each, 2 h apart, seems to most efficiently average out the stellar noise considered. For quiet K1V stars such as α Cen B, this strategy allows us to detect planets of about three times the mass of Earth with an orbital period of 200 days, corresponding to the habitable zone of the star. Moreover, our simulations suggest that planets smaller than typically 5 M ⊕ can be detected with HARPS over a wide range of separations around most non-active solar-type dwarfs. Since activity is not yet included in our simulation, these detection limits correspond to a case, which exists, where the host star has few magnetic features and stellar noise is dominated by oscillation modes and granulation phenomena. For our star sample, a trend between spectral type and surface gravity and the level of radial velocity variation is also identified by our simulations.

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Statistical properties of solar granulation derived from the SOUP instrument on Spacelab 2

Cited by 306 publications

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Horizontal flow fields observed in Hinode G-band images

Horizontal flow fields observed in Hinode G-band images

Space – Time Distribution of G-band and Ca ii H-line Intensity Oscillations in Hinode/SOT – FG Observations

Planetary detection limits taking into account stellar noise

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