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A Gandorfer - One of the best experts on this subject based on the ideXlab platform.
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Brightness Distribution and evolution of sunspot umbral dots
arXiv: Astrophysics, 2008Co-Authors: T L Riethmueller, S K Solanki, V Zakharov, A GandorferAbstract:We present a 106-minute TiO (705.7nm) time series of high spatial and temporal resolution that contains thousands of umbral dots (UDs) in a mature sunspot in the active region NOAA 10667 at $\mu$=0.95. The data were acquired with the 1-m Swedish Solar Telescope on La Palma. With the help of a multilevel tracking (MLT) algorithm the sizes, Brightnesses, and trajectories of 12836 umbral dots were found and analyzed. The MLT allows UDs with very low contrast to be reliably identified. Inside the umbra we determine a UD filling factor of 11%. The histogram of UD lifetimes is monotonic, i.e. a UD does not have a typical lifetime. Three quarters of the UDs lived for less than 150s and showed no or little motion. The histogram of the UD diameters exhibits a maximum at 225km, i.e. most of the UDs are spatially resolved. UDs display a typical horizontal velocity of 420m/s and a typical peak intensity of 51% of the mean intensity of the quiet photosphere, making them on average 20% brighter than the local umbral background. Almost all mobile UDs (large birth-death distance) were born close to the umbra-penumbra boundary, move towards the umbral center, and are brighter than average. Notably bright and mobile UDs were also observed along a prominent UD chain, both ends of which are located at the umbra-penumbra boundary. Their motion started primarily at either of the ends of the chain, continued along the chain, and ended near the chain's center. We observed the splitting and merging of UDs and the temporal succession of both. For the first time the evolution of Brightness, size, and horizontal speed of a typical UD could be determined in a statistically significant way. Considerable differences between the evolution of central and peripheral UDs are found, which point to a difference in origin.
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Brightness Distribution and evolution of sunspot umbral dots
Astronomy and Astrophysics, 2008Co-Authors: T L Riethmuller, S K Solanki, V Zakharov, A GandorferAbstract:Context. Umbral Dots (UDs) are thought to be manifestations of magnetoconvection in sunspot umbrae. Recent advances in their theoretical description point to the need for a thorough study of their properties and evolution based on data with the highest currently achievable resolution. Aims. Our UD analysis aims to provide parameters such as lifetimes, diameters, horizontal velocities, and peak intensities, as well as the evolution of selected parameters. Methods. We present a 106-min TiO (705.7 nm) time series of high spatial and temporal resolution that contains thousands of UDs in the umbra of a mature sunspot in the active region NOAA 10667 at μ = 0.95. The data were acquired with the 1-m Swedish Solar Telescope (SST) on La Palma. With the help of a multilevel tracking (MLT) algorithm the sizes, Brightnesses, and trajectories of 12 836 umbral dots were found and extensively analyzed. The MLT allows UDs with very low contrast to be reliably identified. Results. Inside the umbra we determine a UD filling factor of 11%. The histogram of UD lifetimes is monotonic, i.e. a UD does not have a typical lifetime. Three quarters of the UDs lived for less than 150 s and showed no or little motion. The histogram of the UD diameters exhibits a maximum at 225 km, i.e. most of the UDs are spatially resolved. UDs display a typical horizontal velocity of 420 m s -1 and a typical peak intensity of 51% of the mean intensity of the quiet photosphere, making them on average 20% brighter than the local umbral background. Almost all mobile UDs (large birth-death distance) were born close to the umbra-penumbra boundary, move towards the umbral center, and are brighter than average. Notably bright and mobile UDs were also observed along a prominent UD chain, both ends of which are located at the umbra-penumbra boundary. Their motion started primarily at either of the ends of the chain, continued along the chain, and ended near the chain's center. We observed the splitting and merging of UDs and the temporal succession of both. For the first time the evolution of Brightness, size, and horizontal speed of a typical UD could be determined in a statistically significant way. Considerable differences between the evolution of central and peripheral UDs are found, which point to a difference in origin.
Simon P Driver - One of the best experts on this subject based on the ideXlab platform.
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the millennium galaxy catalogue the space density and surface Brightness Distribution s of galaxies
Monthly Notices of the Royal Astronomical Society, 2005Co-Authors: Simon P Driver, Jesper Liske, N J G Cross, R De Propris, P D AllenAbstract:We recover the joint and individual space density and surface-Brightness Distribution(s) of galaxies from the Millennium Galaxy Catalogue (MGC). The MGC is a local survey spanning 30.9 deg 2 and probing approximately 1-2 mag arcsec -2 deeper than either the Two-Degree Field Galaxy Redshift Survey (2dFGRS) or the Sloan Digital Sky Survey (SDSS). The MGC contains 10095 galaxies to B MGC < 20 mag with 96 per cent spectroscopic completeness. For each galaxy we derive individual K-corrections and seeing-corrected sizes. We implement a joint luminosity-surface-Brightness step-wise maximum-likelihood method to recover the bivariate Brightness Distribution (BBD) inclusive of most selection effects. Integrating the BBD over surface Brightness we recover the following Schechter function parameters: Φ* = (0.0177 ± 0.0015)h 3 Mpc -3 , M* BMGC - 5 log h = (-19.60 ± 0.04) mag and a = -1.13 ± 0.02. Compared to the 2dFGRS we find a consistent M* value but a slightly flatter faint-end slope and a higher normalization, resulting in a final luminosity density j bJ = (1.99 ± 0.17) x 10 8 h L ○. Mpc -3 - marginally higher than, but consistent with, the earlier 2dFGRS, ESP, and SDSS z = 0.1 results. The MGC is inconsistent with the SDSS z = 0.0 result (+3σ) if one adopts the derived SDSS evolution. The MGC surface-Brightness Distribution is a well-bounded Gaussian at the M* point with Φ* = (3.5 ± 0.1) x 10 -2 h 3 Mpc -3 , μ e * = (21.90 ± 0.01) mag arcsec -2 and σ InRe = 0.35 ± 0.01. The characteristic surface Brightness for luminous systems is invariant to M BMGC -5 log h -19 mag faintwards of which it moves to lower surface Brightness. The surface-Brightness Distribution also broadens (σ lnRe 0.5 - 0.7) towards lower luminosities. The luminosity dependence of σ lnRe provides a new constraint for both the theoretical development and numerical simulations, which typically predict a mass-independent σ ln Re 0.56 ± 0.04. Higher resolution (FWHM « 1 arcsec) and deeper (μ lim » 26 mag arcsec -2 in the B-band) observations of the local Universe are now essential to probe to lower luminosity and lower surface-Brightness levels.
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The Millennium Galaxy Catalogue: the space density and surface Brightness Distribution(s) of galaxies
Monthly Notices of the Royal Astronomical Society, 2005Co-Authors: Simon P Driver, Jesper Liske, R De Propris, Nicholas Cross, P D AllenAbstract:We recover the joint and individual space density and surface Brightness Distribution(s) of galaxies from the Millennium Galaxy Catalogue. The MGC is a local survey spanning 30.9 sq deg and probing approximately one--two mag/sq arcsec deeper than either the Two-Degree Field Galaxy Redshift Survey (2dFGRS) or the Sloan Digital Sky Survey (SDSS). The MGC contains 10,095 galaxies to B_mgc 26 mag/sq arcsec in the B-band) observations of the local universe are now essential to probe to lower luminosity and lower surface Brightness levels. [abridged]
P D Allen - One of the best experts on this subject based on the ideXlab platform.
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the millennium galaxy catalogue the space density and surface Brightness Distribution s of galaxies
Monthly Notices of the Royal Astronomical Society, 2005Co-Authors: Simon P Driver, Jesper Liske, N J G Cross, R De Propris, P D AllenAbstract:We recover the joint and individual space density and surface-Brightness Distribution(s) of galaxies from the Millennium Galaxy Catalogue (MGC). The MGC is a local survey spanning 30.9 deg 2 and probing approximately 1-2 mag arcsec -2 deeper than either the Two-Degree Field Galaxy Redshift Survey (2dFGRS) or the Sloan Digital Sky Survey (SDSS). The MGC contains 10095 galaxies to B MGC < 20 mag with 96 per cent spectroscopic completeness. For each galaxy we derive individual K-corrections and seeing-corrected sizes. We implement a joint luminosity-surface-Brightness step-wise maximum-likelihood method to recover the bivariate Brightness Distribution (BBD) inclusive of most selection effects. Integrating the BBD over surface Brightness we recover the following Schechter function parameters: Φ* = (0.0177 ± 0.0015)h 3 Mpc -3 , M* BMGC - 5 log h = (-19.60 ± 0.04) mag and a = -1.13 ± 0.02. Compared to the 2dFGRS we find a consistent M* value but a slightly flatter faint-end slope and a higher normalization, resulting in a final luminosity density j bJ = (1.99 ± 0.17) x 10 8 h L ○. Mpc -3 - marginally higher than, but consistent with, the earlier 2dFGRS, ESP, and SDSS z = 0.1 results. The MGC is inconsistent with the SDSS z = 0.0 result (+3σ) if one adopts the derived SDSS evolution. The MGC surface-Brightness Distribution is a well-bounded Gaussian at the M* point with Φ* = (3.5 ± 0.1) x 10 -2 h 3 Mpc -3 , μ e * = (21.90 ± 0.01) mag arcsec -2 and σ InRe = 0.35 ± 0.01. The characteristic surface Brightness for luminous systems is invariant to M BMGC -5 log h -19 mag faintwards of which it moves to lower surface Brightness. The surface-Brightness Distribution also broadens (σ lnRe 0.5 - 0.7) towards lower luminosities. The luminosity dependence of σ lnRe provides a new constraint for both the theoretical development and numerical simulations, which typically predict a mass-independent σ ln Re 0.56 ± 0.04. Higher resolution (FWHM « 1 arcsec) and deeper (μ lim » 26 mag arcsec -2 in the B-band) observations of the local Universe are now essential to probe to lower luminosity and lower surface-Brightness levels.
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The Millennium Galaxy Catalogue: the space density and surface Brightness Distribution(s) of galaxies
Monthly Notices of the Royal Astronomical Society, 2005Co-Authors: Simon P Driver, Jesper Liske, R De Propris, Nicholas Cross, P D AllenAbstract:We recover the joint and individual space density and surface Brightness Distribution(s) of galaxies from the Millennium Galaxy Catalogue. The MGC is a local survey spanning 30.9 sq deg and probing approximately one--two mag/sq arcsec deeper than either the Two-Degree Field Galaxy Redshift Survey (2dFGRS) or the Sloan Digital Sky Survey (SDSS). The MGC contains 10,095 galaxies to B_mgc 26 mag/sq arcsec in the B-band) observations of the local universe are now essential to probe to lower luminosity and lower surface Brightness levels. [abridged]
W. J. G. De Blok - One of the best experts on this subject based on the ideXlab platform.
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The bimodal spiral galaxy surface Brightness Distribution
Monthly Notices of the Royal Astronomical Society, 2000Co-Authors: Eric F. Bell, W. J. G. De BlokAbstract:We have assessed the significance of Tully and Verheijen’s bimodal Ursa Major Cluster spiral galaxy near-infrared surface Brightness Distribution, focusing on whether this bimodality is simply an artefact of small number statistics. A Kolmogorov–Smirnov style of significance test shows that the total Distribution is fairly represented by a single-peaked Distribution, but that their isolated galaxy subsample (with no significant neighbours within a projected distance of ∼80 kpc) is bimodal at the 96 per cent level. We have also investigated the assumptions underlying the isolated galaxy surface Brightness Distribution, finding that the (often large) inclination corrections used in the construction of this Distribution reduce the significance of the bimodality. We conclude that the Ursa Major Cluster data set is insufficient to establish the presence of a bimodal near-infrared surface Brightness Distribution: an independent sample of ∼100 isolated, low-inclination galaxies is required to establish bimodality at the 99 per cent level.
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the bimodal spiral galaxy surface Brightness Distribution
arXiv: Astrophysics, 1999Co-Authors: Eric F. Bell, W. J. G. De BlokAbstract:We have assessed the significance of Tully and Verheijen's (1997) bimodal Ursa Major Cluster spiral galaxy near-infrared surface Brightness Distribution, focussing on whether this bimodality is simply an artifact of small number statistics. A Kolmogorov-Smirnov style of significance test shows that the total Distribution is fairly represented by a single-peaked Distribution, but that their isolated galaxy subsample (with no significant neighbours within a projected distance of around 80 kpc) is bimodal at the 96 per cent level. We have also investigated the assumptions underlying the isolated galaxy surface Brightness Distribution, finding that the (often large) inclination corrections used in the construction of this Distribution reduce the significance of the bimodality. We conclude that the Ursa Major Cluster dataset is insufficient to establish the presence of a bimodal near-infrared surface Brightness Distribution: an independent sample of around 100 isolated, low inclination galaxies is required to establish bimodality at the 99 per cent level.
T L Riethmuller - One of the best experts on this subject based on the ideXlab platform.
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Brightness Distribution and evolution of sunspot umbral dots
Astronomy and Astrophysics, 2008Co-Authors: T L Riethmuller, S K Solanki, V Zakharov, A GandorferAbstract:Context. Umbral Dots (UDs) are thought to be manifestations of magnetoconvection in sunspot umbrae. Recent advances in their theoretical description point to the need for a thorough study of their properties and evolution based on data with the highest currently achievable resolution. Aims. Our UD analysis aims to provide parameters such as lifetimes, diameters, horizontal velocities, and peak intensities, as well as the evolution of selected parameters. Methods. We present a 106-min TiO (705.7 nm) time series of high spatial and temporal resolution that contains thousands of UDs in the umbra of a mature sunspot in the active region NOAA 10667 at μ = 0.95. The data were acquired with the 1-m Swedish Solar Telescope (SST) on La Palma. With the help of a multilevel tracking (MLT) algorithm the sizes, Brightnesses, and trajectories of 12 836 umbral dots were found and extensively analyzed. The MLT allows UDs with very low contrast to be reliably identified. Results. Inside the umbra we determine a UD filling factor of 11%. The histogram of UD lifetimes is monotonic, i.e. a UD does not have a typical lifetime. Three quarters of the UDs lived for less than 150 s and showed no or little motion. The histogram of the UD diameters exhibits a maximum at 225 km, i.e. most of the UDs are spatially resolved. UDs display a typical horizontal velocity of 420 m s -1 and a typical peak intensity of 51% of the mean intensity of the quiet photosphere, making them on average 20% brighter than the local umbral background. Almost all mobile UDs (large birth-death distance) were born close to the umbra-penumbra boundary, move towards the umbral center, and are brighter than average. Notably bright and mobile UDs were also observed along a prominent UD chain, both ends of which are located at the umbra-penumbra boundary. Their motion started primarily at either of the ends of the chain, continued along the chain, and ended near the chain's center. We observed the splitting and merging of UDs and the temporal succession of both. For the first time the evolution of Brightness, size, and horizontal speed of a typical UD could be determined in a statistically significant way. Considerable differences between the evolution of central and peripheral UDs are found, which point to a difference in origin.