The Experts below are selected from a list of 18324 Experts worldwide ranked by ideXlab platform
Stephen R Kane - One of the best experts on this subject based on the ideXlab platform.
-
detection of rotation in a binary microlens planet photometry of macho 97 blg 41
The Astrophysical Journal, 2000Co-Authors: M D Albrow, J A R Caldwell, Magdalena Dominik, B. Scott Gaudi, Jennene Greenhill, K. Hill, Andrew Gould, J. P. Beaulieu, Stephen R KaneAbstract:We analyze PLANET collaboration data for MACHO 97-BLG-41, the only microlensing event observed to date in which the source transits two disjoint caustics. The PLANET data, consisting of 46 V -band and 325 I-band observations from —ve southern observatories, span a period from the initial alert until the end of the event. Our data are incompatible with a static binary lens, but are well —tted by a rotating binary lens of mass ratio q \ 0.34 and angular separation d B 0.5 (in units of the Einstein Ring Radius), in which the binary separation changes in size by dd \( 0.070 ^ 0.009 and in orientation by duRing the 35.17 days between the separate caustic transits. We use this measurement, dh \ 5i.61^ 0i.36 combined with other observational constraints, to derive the —rst kinematic estimate of the mass, dis- tance, and period of a binary microlens. The relative probability distributions for these parameters peak at a total lens mass M D 0.3 (M-dwarf binary system), lens distance kpc, and binary period M _ D L D 5.5 P D 1.5 yr. The robustness of our model is demonstrated by its striking agreement with MACHO/ GMAN data that cover several sharp features in the light curve not probed by the PLANET obser- vations, and which did not enter our modeling procedure in any way. Available data sets thus indicate that the light curve of MACHO 97-BLG-41 can be modeled as a source crossing two caustics of a physi- cally realistic rotating binary. Thus, contrary to a recent suggestion, the additional eUects of a postulated planetary companion to the binary lens are not required. Subject headings: binaries: generalgravitational lensingplanetary systems
-
limb darkening of a k giant in the galactic bulge planet photometry of macho 97 blg 28
The Astrophysical Journal, 1999Co-Authors: M D Albrow, J A R Caldwell, Stephen R Kane, K. Hill, J. P. Beaulieu, M Dominik, J GreenhillAbstract:We present the PLANET photometric data set10 for the binary-lens microlensing event MACHO 97- BLG-28, consisting of 696 I- and V -band measurements, and analyze it to determine the radial surface brightness pro—le of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed an isolated cusp of the central caustic of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3¨30 minute) and continuous monitoRing from PLANET sites in Chile, South Africa, and Australia. This is the —rst time that such a cusp crossing has been observed. Analysis of the PLANET data set has produced a measure- ment of the square-root limb-darkening coefficients of the source star in the I and V bands; the resulting stellar pro—les are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the —rst derived from microlensing. They are also among the —rst found for normal giants by any technique and the —rst for any star as distant as the Galactic bulge. Modeling of our light curve for MACHO 97-BLG-28 indicates that the lensing binary has a mass ratio q \ 0.23 and an (instantaneous) separation in units of the angular Einstein Ring Radius of d \ 0.69. For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer (i.e., in the Galactic disk), the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is k \ 19.4 ^ 2.6 km s~1 kpc~1, consistent with a disk or bulge lens. If the nonlensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself. Subject headings: binaries: visualgravitational lensingstars: fundamental parameters ¨ stars: late-type
-
limb darkening of a k giant in the galactic bulge planet photometry of macho 97 blg 28
arXiv: Astrophysics, 1998Co-Authors: M D Albrow, J A R Caldwell, Stephen R Kane, K. Hill, J. P. Beaulieu, M Dominik, J Greenhill, R Martin, J Menzies, R M NaberAbstract:We present the PLANET photometric dataset for the binary-lens microlensing event MACHO 97-BLG-28 consisting of 696 I and V-band measurements, and analyze it to determine the radial surface brightness profile of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed the central isolated cusp of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3 - 30 minute) and continuous monitoRing from PLANET sites in Chile, South Africa, and Australia. Our modeling of these data has produced stellar profiles for the source star in the I and V bands that are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the first derived from microlensing, among the first for normal giants by any technique, and the first for any star as distant as the Galactic bulge. Modeling indicates that the lensing binary has a mass ratio q = 0.23 and an (instantaneous) separation in units of the angular Einstein Ring Radius of d = 0.69 . For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer, the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is mu = 19.4 +/- 2.6 km/s /kpc, consistent with a disk or bulge lens. If the non-lensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself.
M D Albrow - One of the best experts on this subject based on the ideXlab platform.
-
microlensing constraints on the frequency of jupiter mass companions analysis of 5 years of planet photometry
The Astrophysical Journal, 2002Co-Authors: M D Albrow, J A R Caldwell, B. Scott Gaudi, J. P. Beaulieu, D L Depoy, M Dominik, A Gould, J GreenhillAbstract:We analyze 5 years of PLANET photometry of microlensing events toward the Galactic bulge to search for the short-duration deviations from single-lens light curves that are indicative of the presence of planetary companions to the primary microlenses. Using strict event-selection criteria, we construct a well-defined sample of 43 intensively monitored events. We search for planetary perturbations in these events over a densely sampled region of parameter space spanning two decades in mass ratio and projected separation, but find no viable planetary candidates. By combining the detection efficiencies of the events, we find that, at 95% confidence, less than 25% of our primary lenses have companions with mass ratio q = 10-2 and separations in the lensing zone, [0.6-1.6]θE, where θE is the Einstein Ring Radius. Using a model of the mass, velocity, and spatial distribution of bulge lenses, we infer that the majority of our lenses are likely M dwarfs in the Galactic bulge. We conclude that less than 33% of M dwarfs in the Galactic bulge have companions with mass mp = MJ between 1.5 and 4 AU, and less than 45% have companions with mp = 3MJ between 1 and 7 AU, the first significant limits on planetary companions to M dwarfs. We consider the effects of the finite size of the source stars and changing our detection criterion, but find that these do not alter our conclusions substantially.
-
detection of rotation in a binary microlens planet photometry of macho 97 blg 41
The Astrophysical Journal, 2000Co-Authors: M D Albrow, J A R Caldwell, Magdalena Dominik, B. Scott Gaudi, Jennene Greenhill, K. Hill, Andrew Gould, J. P. Beaulieu, Stephen R KaneAbstract:We analyze PLANET collaboration data for MACHO 97-BLG-41, the only microlensing event observed to date in which the source transits two disjoint caustics. The PLANET data, consisting of 46 V -band and 325 I-band observations from —ve southern observatories, span a period from the initial alert until the end of the event. Our data are incompatible with a static binary lens, but are well —tted by a rotating binary lens of mass ratio q \ 0.34 and angular separation d B 0.5 (in units of the Einstein Ring Radius), in which the binary separation changes in size by dd \( 0.070 ^ 0.009 and in orientation by duRing the 35.17 days between the separate caustic transits. We use this measurement, dh \ 5i.61^ 0i.36 combined with other observational constraints, to derive the —rst kinematic estimate of the mass, dis- tance, and period of a binary microlens. The relative probability distributions for these parameters peak at a total lens mass M D 0.3 (M-dwarf binary system), lens distance kpc, and binary period M _ D L D 5.5 P D 1.5 yr. The robustness of our model is demonstrated by its striking agreement with MACHO/ GMAN data that cover several sharp features in the light curve not probed by the PLANET obser- vations, and which did not enter our modeling procedure in any way. Available data sets thus indicate that the light curve of MACHO 97-BLG-41 can be modeled as a source crossing two caustics of a physi- cally realistic rotating binary. Thus, contrary to a recent suggestion, the additional eUects of a postulated planetary companion to the binary lens are not required. Subject headings: binaries: generalgravitational lensingplanetary systems
-
limb darkening of a k giant in the galactic bulge planet photometry of macho 97 blg 28
The Astrophysical Journal, 1999Co-Authors: M D Albrow, J A R Caldwell, Stephen R Kane, K. Hill, J. P. Beaulieu, M Dominik, J GreenhillAbstract:We present the PLANET photometric data set10 for the binary-lens microlensing event MACHO 97- BLG-28, consisting of 696 I- and V -band measurements, and analyze it to determine the radial surface brightness pro—le of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed an isolated cusp of the central caustic of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3¨30 minute) and continuous monitoRing from PLANET sites in Chile, South Africa, and Australia. This is the —rst time that such a cusp crossing has been observed. Analysis of the PLANET data set has produced a measure- ment of the square-root limb-darkening coefficients of the source star in the I and V bands; the resulting stellar pro—les are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the —rst derived from microlensing. They are also among the —rst found for normal giants by any technique and the —rst for any star as distant as the Galactic bulge. Modeling of our light curve for MACHO 97-BLG-28 indicates that the lensing binary has a mass ratio q \ 0.23 and an (instantaneous) separation in units of the angular Einstein Ring Radius of d \ 0.69. For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer (i.e., in the Galactic disk), the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is k \ 19.4 ^ 2.6 km s~1 kpc~1, consistent with a disk or bulge lens. If the nonlensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself. Subject headings: binaries: visualgravitational lensingstars: fundamental parameters ¨ stars: late-type
-
limb darkening of a k giant in the galactic bulge planet photometry of macho 97 blg 28
arXiv: Astrophysics, 1998Co-Authors: M D Albrow, J A R Caldwell, Stephen R Kane, K. Hill, J. P. Beaulieu, M Dominik, J Greenhill, R Martin, J Menzies, R M NaberAbstract:We present the PLANET photometric dataset for the binary-lens microlensing event MACHO 97-BLG-28 consisting of 696 I and V-band measurements, and analyze it to determine the radial surface brightness profile of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed the central isolated cusp of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3 - 30 minute) and continuous monitoRing from PLANET sites in Chile, South Africa, and Australia. Our modeling of these data has produced stellar profiles for the source star in the I and V bands that are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the first derived from microlensing, among the first for normal giants by any technique, and the first for any star as distant as the Galactic bulge. Modeling indicates that the lensing binary has a mass ratio q = 0.23 and an (instantaneous) separation in units of the angular Einstein Ring Radius of d = 0.69 . For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer, the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is mu = 19.4 +/- 2.6 km/s /kpc, consistent with a disk or bulge lens. If the non-lensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself.
J. P. Beaulieu - One of the best experts on this subject based on the ideXlab platform.
-
microlensing constraints on the frequency of jupiter mass companions analysis of 5 years of planet photometry
The Astrophysical Journal, 2002Co-Authors: M D Albrow, J A R Caldwell, B. Scott Gaudi, J. P. Beaulieu, D L Depoy, M Dominik, A Gould, J GreenhillAbstract:We analyze 5 years of PLANET photometry of microlensing events toward the Galactic bulge to search for the short-duration deviations from single-lens light curves that are indicative of the presence of planetary companions to the primary microlenses. Using strict event-selection criteria, we construct a well-defined sample of 43 intensively monitored events. We search for planetary perturbations in these events over a densely sampled region of parameter space spanning two decades in mass ratio and projected separation, but find no viable planetary candidates. By combining the detection efficiencies of the events, we find that, at 95% confidence, less than 25% of our primary lenses have companions with mass ratio q = 10-2 and separations in the lensing zone, [0.6-1.6]θE, where θE is the Einstein Ring Radius. Using a model of the mass, velocity, and spatial distribution of bulge lenses, we infer that the majority of our lenses are likely M dwarfs in the Galactic bulge. We conclude that less than 33% of M dwarfs in the Galactic bulge have companions with mass mp = MJ between 1.5 and 4 AU, and less than 45% have companions with mp = 3MJ between 1 and 7 AU, the first significant limits on planetary companions to M dwarfs. We consider the effects of the finite size of the source stars and changing our detection criterion, but find that these do not alter our conclusions substantially.
-
detection of rotation in a binary microlens planet photometry of macho 97 blg 41
The Astrophysical Journal, 2000Co-Authors: M D Albrow, J A R Caldwell, Magdalena Dominik, B. Scott Gaudi, Jennene Greenhill, K. Hill, Andrew Gould, J. P. Beaulieu, Stephen R KaneAbstract:We analyze PLANET collaboration data for MACHO 97-BLG-41, the only microlensing event observed to date in which the source transits two disjoint caustics. The PLANET data, consisting of 46 V -band and 325 I-band observations from —ve southern observatories, span a period from the initial alert until the end of the event. Our data are incompatible with a static binary lens, but are well —tted by a rotating binary lens of mass ratio q \ 0.34 and angular separation d B 0.5 (in units of the Einstein Ring Radius), in which the binary separation changes in size by dd \( 0.070 ^ 0.009 and in orientation by duRing the 35.17 days between the separate caustic transits. We use this measurement, dh \ 5i.61^ 0i.36 combined with other observational constraints, to derive the —rst kinematic estimate of the mass, dis- tance, and period of a binary microlens. The relative probability distributions for these parameters peak at a total lens mass M D 0.3 (M-dwarf binary system), lens distance kpc, and binary period M _ D L D 5.5 P D 1.5 yr. The robustness of our model is demonstrated by its striking agreement with MACHO/ GMAN data that cover several sharp features in the light curve not probed by the PLANET obser- vations, and which did not enter our modeling procedure in any way. Available data sets thus indicate that the light curve of MACHO 97-BLG-41 can be modeled as a source crossing two caustics of a physi- cally realistic rotating binary. Thus, contrary to a recent suggestion, the additional eUects of a postulated planetary companion to the binary lens are not required. Subject headings: binaries: generalgravitational lensingplanetary systems
-
limb darkening of a k giant in the galactic bulge planet photometry of macho 97 blg 28
The Astrophysical Journal, 1999Co-Authors: M D Albrow, J A R Caldwell, Stephen R Kane, K. Hill, J. P. Beaulieu, M Dominik, J GreenhillAbstract:We present the PLANET photometric data set10 for the binary-lens microlensing event MACHO 97- BLG-28, consisting of 696 I- and V -band measurements, and analyze it to determine the radial surface brightness pro—le of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed an isolated cusp of the central caustic of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3¨30 minute) and continuous monitoRing from PLANET sites in Chile, South Africa, and Australia. This is the —rst time that such a cusp crossing has been observed. Analysis of the PLANET data set has produced a measure- ment of the square-root limb-darkening coefficients of the source star in the I and V bands; the resulting stellar pro—les are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the —rst derived from microlensing. They are also among the —rst found for normal giants by any technique and the —rst for any star as distant as the Galactic bulge. Modeling of our light curve for MACHO 97-BLG-28 indicates that the lensing binary has a mass ratio q \ 0.23 and an (instantaneous) separation in units of the angular Einstein Ring Radius of d \ 0.69. For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer (i.e., in the Galactic disk), the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is k \ 19.4 ^ 2.6 km s~1 kpc~1, consistent with a disk or bulge lens. If the nonlensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself. Subject headings: binaries: visualgravitational lensingstars: fundamental parameters ¨ stars: late-type
-
limb darkening of a k giant in the galactic bulge planet photometry of macho 97 blg 28
arXiv: Astrophysics, 1998Co-Authors: M D Albrow, J A R Caldwell, Stephen R Kane, K. Hill, J. P. Beaulieu, M Dominik, J Greenhill, R Martin, J Menzies, R M NaberAbstract:We present the PLANET photometric dataset for the binary-lens microlensing event MACHO 97-BLG-28 consisting of 696 I and V-band measurements, and analyze it to determine the radial surface brightness profile of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed the central isolated cusp of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3 - 30 minute) and continuous monitoRing from PLANET sites in Chile, South Africa, and Australia. Our modeling of these data has produced stellar profiles for the source star in the I and V bands that are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the first derived from microlensing, among the first for normal giants by any technique, and the first for any star as distant as the Galactic bulge. Modeling indicates that the lensing binary has a mass ratio q = 0.23 and an (instantaneous) separation in units of the angular Einstein Ring Radius of d = 0.69 . For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer, the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is mu = 19.4 +/- 2.6 km/s /kpc, consistent with a disk or bulge lens. If the non-lensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself.
M Dominik - One of the best experts on this subject based on the ideXlab platform.
-
microlensing constraints on the frequency of jupiter mass companions analysis of 5 years of planet photometry
The Astrophysical Journal, 2002Co-Authors: M D Albrow, J A R Caldwell, B. Scott Gaudi, J. P. Beaulieu, D L Depoy, M Dominik, A Gould, J GreenhillAbstract:We analyze 5 years of PLANET photometry of microlensing events toward the Galactic bulge to search for the short-duration deviations from single-lens light curves that are indicative of the presence of planetary companions to the primary microlenses. Using strict event-selection criteria, we construct a well-defined sample of 43 intensively monitored events. We search for planetary perturbations in these events over a densely sampled region of parameter space spanning two decades in mass ratio and projected separation, but find no viable planetary candidates. By combining the detection efficiencies of the events, we find that, at 95% confidence, less than 25% of our primary lenses have companions with mass ratio q = 10-2 and separations in the lensing zone, [0.6-1.6]θE, where θE is the Einstein Ring Radius. Using a model of the mass, velocity, and spatial distribution of bulge lenses, we infer that the majority of our lenses are likely M dwarfs in the Galactic bulge. We conclude that less than 33% of M dwarfs in the Galactic bulge have companions with mass mp = MJ between 1.5 and 4 AU, and less than 45% have companions with mp = 3MJ between 1 and 7 AU, the first significant limits on planetary companions to M dwarfs. We consider the effects of the finite size of the source stars and changing our detection criterion, but find that these do not alter our conclusions substantially.
-
limb darkening of a k giant in the galactic bulge planet photometry of macho 97 blg 28
The Astrophysical Journal, 1999Co-Authors: M D Albrow, J A R Caldwell, Stephen R Kane, K. Hill, J. P. Beaulieu, M Dominik, J GreenhillAbstract:We present the PLANET photometric data set10 for the binary-lens microlensing event MACHO 97- BLG-28, consisting of 696 I- and V -band measurements, and analyze it to determine the radial surface brightness pro—le of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed an isolated cusp of the central caustic of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3¨30 minute) and continuous monitoRing from PLANET sites in Chile, South Africa, and Australia. This is the —rst time that such a cusp crossing has been observed. Analysis of the PLANET data set has produced a measure- ment of the square-root limb-darkening coefficients of the source star in the I and V bands; the resulting stellar pro—les are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the —rst derived from microlensing. They are also among the —rst found for normal giants by any technique and the —rst for any star as distant as the Galactic bulge. Modeling of our light curve for MACHO 97-BLG-28 indicates that the lensing binary has a mass ratio q \ 0.23 and an (instantaneous) separation in units of the angular Einstein Ring Radius of d \ 0.69. For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer (i.e., in the Galactic disk), the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is k \ 19.4 ^ 2.6 km s~1 kpc~1, consistent with a disk or bulge lens. If the nonlensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself. Subject headings: binaries: visualgravitational lensingstars: fundamental parameters ¨ stars: late-type
-
limb darkening of a k giant in the galactic bulge planet photometry of macho 97 blg 28
arXiv: Astrophysics, 1998Co-Authors: M D Albrow, J A R Caldwell, Stephen R Kane, K. Hill, J. P. Beaulieu, M Dominik, J Greenhill, R Martin, J Menzies, R M NaberAbstract:We present the PLANET photometric dataset for the binary-lens microlensing event MACHO 97-BLG-28 consisting of 696 I and V-band measurements, and analyze it to determine the radial surface brightness profile of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed the central isolated cusp of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3 - 30 minute) and continuous monitoRing from PLANET sites in Chile, South Africa, and Australia. Our modeling of these data has produced stellar profiles for the source star in the I and V bands that are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the first derived from microlensing, among the first for normal giants by any technique, and the first for any star as distant as the Galactic bulge. Modeling indicates that the lensing binary has a mass ratio q = 0.23 and an (instantaneous) separation in units of the angular Einstein Ring Radius of d = 0.69 . For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer, the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is mu = 19.4 +/- 2.6 km/s /kpc, consistent with a disk or bulge lens. If the non-lensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself.
Yasuhide Fukumoto - One of the best experts on this subject based on the ideXlab platform.
-
A generalized vortex Ring model
Journal of Fluid Mechanics, 2009Co-Authors: F. Kaplanski, Sergei Sazhin, Yasuhide Fukumoto, Steven Begg, Morgan HeikalAbstract:A conventional laminar vortex Ring model is generalized by assuming that the time dependence of the vortex Ring thickness l is given by the relation l = a t b , where a is a positive number and 1/4 ≤ b ≤ 1/2. In the case in which a = √2v, where v is the laminar kinematic viscosity, and b = 1/2, the predictions of the generalized model are identical with the predictions of the conventional laminar model. In the case of b = 1/4 some of its predictions are similar to the turbulent vortex Ring models, assuming that the time-dependent effective turbulent viscosity v. is equal to ll'. This generalization is performed both in the case of a fixed vortex Ring Radius R 0 and increasing vortex Ring Radius. In the latter case, the so-called second Saffman's formula is modified. In the case of fixed R 0 , the predicted vorticity distribution for short times shows a close agreement with a Gaussian form for all b and compares favourably with available experimental data. The time evolution of the location of the region of maximal vorticity and the region in which the velocity of the fluid in the frame of reference moving with the vortex Ring centroid is equal to zero is analysed. It is noted that the locations of both regions depend upon b, the latter region being always further away from the vortex axis than the first one. It is shown that the axial velocities of the fluid in the first region are always greater than the axial velocities in the second region. Both velocities depend strongly upon b. Although the radial component of velocity in both of these regions is equal to zero, the location of both of these regions changes with time. This leads to the introduction of an effective radial velocity component; the latter case depends upon b. The predictions of the model are compared with the results of experimental measurements of vortex Ring parameters reported in the literature.
-
curvature instability of a vortex Ring
Journal of Fluid Mechanics, 2005Co-Authors: Yasuhide Fukumoto, Yuji HattoriAbstract:A global stability analysis of Kelvin's vortex Ring to three-dimensional disturbances of infinitesimal amplitude is made. The basic state is a steady asymptotic solution of the Euler equations, in powers of the ratio ∈ of the core Radius to the Ring Radius, for an axisymmetric vortex Ring with vorticity proportional to the distance from the symmetric axis. The effect of Ring curvature appears at first order, in the form of a dipole field, and a local straining field, which is a quadrupole field, follows at second order. The eigenvalue problem of the Euler equations, retaining the terms to first order, is solved in closed form, in terms of the Bessel and the modified Bessel functions. We show that the dipole field causes a parametric resonance instability between a pair of Kelvin waves whose azimuthal wavenumbers are separated by 1. The most unstable mode occurs in the short-wavelength limit, under the constraint that the radial and the azimuthal wavenumbers are of the same magnitude, and the limiting value of maximum growth rate coincides with the value 165/256∈ obtained by Hattori & Fukumoto (Phys. Fluids, vol. 15, 2003, p. 3151) by means of the geometric optics method. The instability mechanism is traced to stretching of disturbance vorticity in the toroidal direction. In the absence of viscosity, the dipole effect outweighs the straining field effect of O(∈ 2 ) known as the Moore-Saffman-Tsai-Widnall instability. The viscosity acts to damp the former preferentially and these effects compete with each other.
-
motion and expansion of a viscous vortex Ring part 1 a higher order asymptotic formula for the velocity
Journal of Fluid Mechanics, 2000Co-Authors: Yasuhide Fukumoto, H K MoffattAbstract:A large-Reynolds-number asymptotic solution of the Navier-Stokes equations is sought for the motion of an axisymmetric vortex Ring of small cross-section embedded in a viscous incompressible fluid. In order to take account of the influence of elliptical deformation of the core due to the self-induced strain, the method of matched asymptotic expansions is extended to a higher order in a small parameter e =(ν/Γ ) 1/2 , where v is the kinematic viscosity of fluid and Γ is the circulation. Alternatively, e is regarded as a measure of the ratio of the core Radius to the Ring Radius, and our scheme is applicable also to the steady inviscid dynamics. We establish a general formula for the translation speed of the Ring valid up to third order in e. This is a natural extension of Fraenkel-Saffman's first-order formula, and reduces, if specialized to a particular distribution of vorticity in an inviscid fluid, to Dyson's third-order formula
-
motion and expansion of a viscous vortex Ring part 1 a higher order asymptotic formula for the velocity
Journal of Fluid Mechanics, 2000Co-Authors: Yasuhide Fukumoto, H K MoffattAbstract:A large-Reynolds-number asymptotic solution of the Navier{Stokes equations is sought for the motion of an axisymmetric vortex Ring of small cross-section embedded in a viscous incompressible fluid. In order to take account of the influence of elliptical deformation of the core due to the self-induced strain, the method of matched asymptotic expansions is extended to a higher order in a small parameter =( = ) 1=2 , where is the kinematic viscosity of fluid and is the circulation. Alternatively, is regarded as a measure of the ratio of the core Radius to the Ring Radius, and our scheme is applicable also to the steady inviscid dynamics. We establish a general formula for the translation speed of the Ring valid up to third order in . This is a natural extension of Fraenkel{Saman’s rst-order formula, and reduces, if specialized to a particular distribution of vorticity in an inviscid fluid, to Dyson’s third-order formula. Moreover, it is demonstrated, for a Ring starting from an innitely thin circular loop of Radius R0, that viscosity acts, at third order, to expand the circles of stagnation points of radii Rs(t) and ~ Rs(t) relative to the laboratory frame and a comoving frame respectively, and that of peak vorticity of Radius Rp(t) as Rs R0 +[ 2 log(4R0= p t )+1 :4743424]t=R0, ~ Rs R0 +2 :5902739t=R0, and Rp R0 +4 :5902739t=R0. The growth of the radial centroid of vorticity, linear in time, is also deduced. The results are compatible with the experimental results of Sallet & Widmayer (1974) and Weigand & Gharib (1997). The procedure of pursuing the higher-order asymptotics provides a clear picture of the dynamics of a curved vortex tube; a vortex Ring may be locally regarded as a line of dipoles along the core centreline, with their axes in the propagating direction, subjected to the self-induced flow eld. The strength of the dipole depends not only on the curvature but also on the location of the core centre, and therefore should be specied at the initial instant. This specication removes an indeterminacy of the rst-order theory. We derive a new asymptotic development of the Biot-Savart law for an arbitrary distribution of vorticity, which makes the non-local induction velocity from the dipoles calculable at third order.
-
motion and expansion of a viscous vortex Ring part 1 a higher order asymptotic formula for the velocity
Journal of Fluid Mechanics, 2000Co-Authors: Yasuhide Fukumoto, H K MoffattAbstract:A large-Reynolds-number asymptotic solution of the Navier–Stokes equations is sought for the motion of an axisymmetric vortex Ring of small cross-section embedded in a viscous incompressible fluid. In order to take account of the influence of elliptical deformation of the core due to the self-induced strain, the method of matched of matched asymptotic expansions is extended to a higher order in a small parameter e = (v/Γ)1/2, where v is the kinematic viscosity of fluid and Γ is the circulation. Alternatively, e is regarded as a measure of the ratio of the core Radius to the Ring Radius, and our scheme is applicable also to the steady inviscid dynamics.We establish a general formula for the translation speed of the Ring valid up to third order in e. This is a natural extension of Fraenkel–Saffman's first-order formula, and reduces, if specialized to a particular distribution of vorticity in an inviscid fluid, to Dyson's third-order formula. Moreover, it is demonstrated, for a Ring starting from an infinitely thin circular loop of Radius R0, that viscosity acts, at third order, to expand the circles of stagnation points of radii Rs(t) and R˜s(t) relative to the laboratory frame and a comoving frame respectively, and that of peak vorticity of Radius R˜p(t) as Rs ≈ R0 + [2 log(4R0/√vt) + 1.4743424] vt/R0, R˜s ≈ R0 + 2.5902739 vt/R0, and Rp ≈ R0 + 4.5902739 vt/R0. The growth of the radial centroid of vorticity, linear in time, is also deduced. The results are compatible with the experimental results of Sallet & Widmayer (1974) and Weigand & Gharib (1997).The procedure of pursuing the higher-order asymptotics provides a clear picture of the dynamics of a curved vortex tube; a vortex Ring may be locally regarded as a line of dipoles along the core centreline, with their axes in the propagating direction, subjected to the self-induced flow field. The strength of the dipole depends not only on the curvature but also on the location of the core centre, and therefore should be specified at the initial instant. This specification removes an indeterminacy of the first-order theory. We derive a new asymptotic development of the Biot-Savart law for an arbitrary distribution of vorticity, which makes the non-local induction velocity from the dipoles calculable at third order.
