WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William He... more WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable ‘mini’ integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366−959 nm at R ∼ 5000, or two shorter ranges at R ∼ 20 000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy’s origins by completing Gaia’s phase-space information, providing metallicities to its limiting magnitude for ∼3 million stars and detailed abundances for ∼1.5 million brighter field and open-cluster stars; (ii) survey ∼0.4 million Galactic-plane OBA stars, young stellar objects...
Ground-based and Airborne Instrumentation for Astronomy VIII, 2020
We present an update on the overall integration progress of the WEAVE next-generation spectroscop... more We present an update on the overall integration progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now scheduled for first light in early-2021, with almost all components now arrived at the observatory. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been implemented to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 mini integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000.
Final design and progress of WEAVE: the next generation wide-field spectroscopy facility for the William Herschel Telescope
SPIE Proceedings, 2016
We present the Final Design of the WEAVE next-generation spectroscopy facility for the William He... more We present the Final Design of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), together with a status update on the details of manufacturing, integration and the overall project schedule now that all the major fabrication contracts are in place. We also present a summary of the current planning behind the 5-year initial phase of survey operations. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000. The project is now in the manufacturing and integration phase with first light expected for early of 2018.
We present an integrated end-end simulation of the spectral images that will be obtained by the w... more We present an integrated end-end simulation of the spectral images that will be obtained by the weave spectrograph, which aims to include full modelling of all effects from the top of the atmosphere to the detector. These data are based in input spectra from a combination of library spectra and synthetic models, and will be used to provide inputs for an endend test of the full weave data pipeline and archive systems, prior to 1st light of the instrument.
Proceedings of the International Astronomical Union, 2013
We use observations of OGLE-III ab-type RRLyrae stars towards the Galactic centre (Soszyński et a... more We use observations of OGLE-III ab-type RRLyrae stars towards the Galactic centre (Soszyński et al. 2011, AcA 6,1) to study the metallicity and 3D spatial distribution of the old and metal-poor component of the Galactic bulge. Metallicities and distances to the RRLyrae stars are derived photometrically from Fourier-component analyses of their light curves, allowing the determination of distances accurate to ~7% from 0 to 40 kpc. The distance distribution of the RRLyrae stars peaks at 8.8 kpc, with the data indicating the presence of a bar-like structure inclined at ~30° to the line of sight. The dataset also exhibits a secondary concentration of stars beyond the Galactic centre at ~27 kpc. This is consistent with the distance to the Sagittarius (Sgr) dwarf galaxy, and can be attributed to the serendipitous alignment of the Sgr stream with the bulge. This dataset allows the Sgr stream to be traced in this part of the sky for the first time. The underlying metallicity distributions ar...
We present a proper-motion study on models of the dwarf spheroidal galaxy Sculptor, based on the ... more We present a proper-motion study on models of the dwarf spheroidal galaxy Sculptor, based on the predicted proper-motion accuracy of Gaia measurements. Gaia will measure proper motions of several hundreds of stars for a Sculptor-like system. Even with an uncertainty on the proper motion of order 1.5 times the size of an individual proper-motion value of ∼ 10 mas/century, we find that it is possible to recover Sculptor's systemic proper motion at its distance of 79 kpc.
ABSTRACT Two methods are given for determining distances to streams of high-velocityclouds in orb... more ABSTRACT Two methods are given for determining distances to streams of high-velocityclouds in orbit about the Galactic Centre. Both rely on the parallax generated by the offset of the Sun from the stream’s orbital plane. The distances to all points of the Magellanic Stream are found without use of the Magellanic Cloud distances.
We investigate the possibility that the recently discovered Hercules Milky Way satellite is in fa... more We investigate the possibility that the recently discovered Hercules Milky Way satellite is in fact a stellar stream in formation, thereby explaining its very elongated shape with an axis ratio of 3 to 1. Under the assumption that Hercules is a stellar stream and that its stars are flowing along the orbit of its progenitor, we find an orbit that would have recently brought the system close enough to the Milky Way to induce its disruption and transformation from a bound dwarf galaxy into a stellar stream. The application of simple analytical techniques to the tentative radial velocity gradient observed in the satellite provides tight constraints on the tangential velocity of the system (v t = -16 +6 -22 km s -1 in the Galactic Standard of Rest). Combined with its large receding velocity, the determined tangential velocity yields an orbit with a small pericentric distance (R peri = 6 +9 -2 kpc). Tidal disruption is therefore a valid scenario for explaining the extreme shape of Hercules. The increase in the mean flattening of dwarf galaxies as one considers fainter systems could therefore be the impact of a few of these satellites not being bound stellar systems dominated by dark matter but, in fact, stellar streams in formation, shedding their stars in the Milky Way's stellar halo.
We have obtained deep photometry in two 1 • × 1 • fields covering the close pair of dwarf spheroi... more We have obtained deep photometry in two 1 • × 1 • fields covering the close pair of dwarf spheroidal galaxies Leo IV and Leo V and part of the area in between. From the distribution of likely red giant branch (RGB) and horizontal-branch (HB) stars in the data set, we find that both Leo IV and Leo V are significantly larger than indicated by previous measurements based on shallower data. With a half-light radius of r h = 4. 6 ± 0. 8 (206 ± 36 pc) and r h = 2. 6 ± 0. 6 (133 ± 31 pc), respectively, both systems are now well within the physical size bracket of typical dwarf spheroidal Milky Way satellites. Both are also found to be significantly elongated with an ellipticity of 0.5, a characteristic shared by many of the fainter (M V > -8) Milky Way dwarf spheroidals. The large spatial extent of our survey allows us to search for extra-tidal features in the area between the two dwarf galaxies with unprecedented sensitivity. The spatial distribution of candidate RGB and HB stars in this region is found to be non-uniform at the ∼3σ level. Interestingly, this substructure is aligned along the direction connecting the two systems, indicative of a possible "bridge" of extra-tidal material. Fitting the stellar distribution with a linear Gaussian model yields a significance of 4σ for this overdensity, a most likely FWHM of ∼16 arcmin, and a central surface brightness of 32 mag arcsec -2 . We investigate different scenarios to explain the close proximity of Leo IV and Leo V, and the possible tidal bridge between them. Orbit calculations demonstrate that the two systems cannot share the exact same orbit, while a compromise orbit does not approach the Galactic center more than ∼160 kpc, rendering it unlikely that they are remnants of a single disrupted progenitor. A comparison with cosmological simulations shows that a chance collision between unrelated subhalos is negligibly small. Given their relative distance and velocity, Leo IV and Leo V could be a bound "tumbling pair," if their combined mass exceeds (8 ± 4) × 10 9 M . The scenario of an internally interacting pair that fell into the Milky Way together appears to be the most viable explanation for this close celestial companionship.
We present the first metallicity distribution functions of the old field populations in the Magel... more We present the first metallicity distribution functions of the old field populations in the Magellanic Clouds (MCs). Our metallicities are based on the Fourier decomposition of Type ab RR Lyrae light curves from the Optical Gravitational Lensing Experiment. On the metallicity scale of Zinn & West, we find a mean metallicity of [Fe/H] = −1.50 ± 0.24 dex based on 16,776 RR Lyrae stars in the Large Magellanic Cloud (LMC). For the Small Magellanic Cloud (SMC) we obtain −1.70 ± 0.27 dex based on 1831 RR Lyrae stars. These uncertainties represent the intrinsic spread in the population rather than the standard deviation of the mean. Our results are in good agreement with the few existing spectroscopic metallicity determinations for LMC RR Lyrae stars from the literature. For both the LMC and the SMC the metallicity spread exceeds 1 dex in [Fe/H]. The distribution of metallicities in both Clouds is very uniform, and no significant metallicity gradient is detectable. We also do not find any ...
Monthly Notices of the Royal Astronomical Society: Letters, 2009
We present a simple result in which the distance gradient along a stream can be used to derive th... more We present a simple result in which the distance gradient along a stream can be used to derive the transverse velocity (i.e. proper motion) along it, if the line-of-sight velocity is also known. We show its application to a mock orbit to illustrate its validity and usage. For less extended objects, such as globular clusters and satellite galaxies being tidally disrupted, the same result can be applied in its small-angle approximation. The procedure does not rely on energy or angular momentum conservation and hence does not require a Galactic model in order to deduce the local velocity vector of the stream.
Monthly Notices of the Royal Astronomical Society: Letters, 2010
We show that a string of H I clouds that form part of the high-velocity cloud complex known as GC... more We show that a string of H I clouds that form part of the high-velocity cloud complex known as GCN is a probable gaseous stream extending over more than 50 • in the Galactic halo. The radial velocity gradient along the stream is used to deduce transverse velocities as a function of distance, enabling a family of orbits to be computed. We find that a direction of motion towards the Galactic disc coupled with a mid-stream distance of ∼20 kpc provides a good match to the observed sky positions and radial velocities of the H I clouds comprising the stream. With an estimated mass of 10 5 M , its progenitor is likely to be a dwarf galaxy. However, no stellar counterpart has been found amongst the currently known Galactic dwarf spheroidal galaxies or stellar streams and the exact origin of the stream is therefore currently unknown.
Monthly Notices of the Royal Astronomical Society: Letters, 2007
We consider the possibility that the Galactic neutral hydrogen stream Complex A and the stellar O... more We consider the possibility that the Galactic neutral hydrogen stream Complex A and the stellar Orphan stream are related, and use this hypothesis to determine possible distances to Complex A and the Orphan stream, and line-of-sight velocities for the latter. The method presented uses our current knowledge of the projected positions of the streams, as well as line-of-sight velocities for Complex A, and we show that a solution exists in which the two streams share the same orbit. If Complex A and the Orphan stream are on this orbit, our calculations suggest the Orphan stream to be at an average distance of 9 kpc, with heliocentric radial velocities of approximately -95 km s -1 . Complex A would be ahead of the Orphan stream in the same wrap of the orbit, with an average distance of 4 kpc, which is consistent with the distance constraints determined through interstellar absorption line techniques.
Monthly Notices of the Royal Astronomical Society, 2008
A useful crude approximation for Abelian functions is developed and applied to orbits. The bound ... more A useful crude approximation for Abelian functions is developed and applied to orbits. The bound orbits in the power-law potentials Ar -α take the simple form ( /r) k = 1 + e cos (m φ), where k = 2 -α > 0 and and e are generalizations of the semi-latus-rectum and the eccentricity. m is given as a function of 'eccentricity'. For nearly circular orbits m is √ k, while the above orbit becomes exact at the energy of escape where e is 1 and m is k. Orbits in the logarithmic potential that gives rise to a constant circular velocity are derived via the limit α → 0. For such orbits, r 2 vibrates almost harmonically whatever the 'eccentricity'. Unbound orbits in power-law potentials are given in an appendix. The transformation of orbits in one potential to give orbits in a different potential is used to determine orbits in potentials that are positive powers of r. These transformations are extended to form a group which associates orbits in sets of six potentials, e.g. there are corresponding orbits in the potentials proportional to r, r -2/3 , r -3 , r -6 , r -4/3 and r 4 . A degeneracy reduces this to three, which are r -1 , r 2 and r -4 for the Keplerian case. A generalization of this group includes the isochrone with the Kepler set.
Monthly Notices of the Royal Astronomical Society, 2005
It is now established that several of the Local Group dwarf spheroidal galaxies (dSphs) have larg... more It is now established that several of the Local Group dwarf spheroidal galaxies (dSphs) have large mass-to-light ratios. We consider the possibility that the dark matter in the haloes of dSphs is composed of massive black holes with masses in the range 10 5 -10 7 M . We use direct N-body simulations to determine the long-term evolution of a two-component dSph composed of a pressure-supported stellar population within a black hole dominated halo. The black holes are initially distributed according to a Navarro-Frenk-White profile. For black hole masses between 10 5 and 10 6 M , the dark matter halo evolves towards a shallower inner profile in less than a Hubble time. This suggests that black holes in this mass range might provide an explanation for the origin of the dark matter cores inferred from observations of low surface brightness galaxy rotation curves. We compare the simulated evolution of the stellar population with observed data for the Draco dSph, and we find that dynamical heating generally leads to the rapid dispersal of the stellar population to large radii. The dependence of the heating rate on the black hole mass is determined, and an upper limit of 10 5 M is placed on the individual black holes comprising the dark matter halo of Draco, if its present stellar distribution is representative of the initial one. We also present a simple scaling argument, which demonstrates that the dynamical heating of an initially compact, although not selfgravitating, stellar distribution might produce a remnant distribution similar in extent to Draco after 10 Gyr, even for black hole masses somewhat in excess of 10 5 M .
Monthly Notices of the Royal Astronomical Society, 2008
We present a geometrodynamical method for determining distances to orbital streams of HI gas in t... more We present a geometrodynamical method for determining distances to orbital streams of HI gas in the Galaxy. The method makes use of our offset from the Galactic centre and assumes that the gas comprising the stream nearly follows a planar orbit about the Galactic centre. We apply this technique to the Magellanic Stream and determine the distances to all points along it; a consistency check shows that the angular momentum is approximately constant. Applying this technique to the Large Magellanic Cloud itself gives an independent distance which agrees within its accuracy of around 10%. Relaxing the demand for exact conservation of energy and angular momentum at all points along the stream allows for an increase in orbital period between the lagging end and the front end led by the Magellanic Clouds. Similar methods are applicable to other long streams of high-velocity clouds, provided they also nearly follow planar orbits; these would allow otherwise unknown distances to be determined.
WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William He... more WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable ‘mini’ integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366−959 nm at R ∼ 5000, or two shorter ranges at R ∼ 20 000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy’s origins by completing Gaia’s phase-space information, providing metallicities to its limiting magnitude for ∼3 million stars and detailed abundances for ∼1.5 million brighter field and open-cluster stars; (ii) survey ∼0.4 million Galactic-plane OBA stars, young stellar objects...
Ground-based and Airborne Instrumentation for Astronomy VIII, 2020
We present an update on the overall integration progress of the WEAVE next-generation spectroscop... more We present an update on the overall integration progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now scheduled for first light in early-2021, with almost all components now arrived at the observatory. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been implemented to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 mini integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000.
Final design and progress of WEAVE: the next generation wide-field spectroscopy facility for the William Herschel Telescope
SPIE Proceedings, 2016
We present the Final Design of the WEAVE next-generation spectroscopy facility for the William He... more We present the Final Design of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), together with a status update on the details of manufacturing, integration and the overall project schedule now that all the major fabrication contracts are in place. We also present a summary of the current planning behind the 5-year initial phase of survey operations. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000. The project is now in the manufacturing and integration phase with first light expected for early of 2018.
We present an integrated end-end simulation of the spectral images that will be obtained by the w... more We present an integrated end-end simulation of the spectral images that will be obtained by the weave spectrograph, which aims to include full modelling of all effects from the top of the atmosphere to the detector. These data are based in input spectra from a combination of library spectra and synthetic models, and will be used to provide inputs for an endend test of the full weave data pipeline and archive systems, prior to 1st light of the instrument.
Proceedings of the International Astronomical Union, 2013
We use observations of OGLE-III ab-type RRLyrae stars towards the Galactic centre (Soszyński et a... more We use observations of OGLE-III ab-type RRLyrae stars towards the Galactic centre (Soszyński et al. 2011, AcA 6,1) to study the metallicity and 3D spatial distribution of the old and metal-poor component of the Galactic bulge. Metallicities and distances to the RRLyrae stars are derived photometrically from Fourier-component analyses of their light curves, allowing the determination of distances accurate to ~7% from 0 to 40 kpc. The distance distribution of the RRLyrae stars peaks at 8.8 kpc, with the data indicating the presence of a bar-like structure inclined at ~30° to the line of sight. The dataset also exhibits a secondary concentration of stars beyond the Galactic centre at ~27 kpc. This is consistent with the distance to the Sagittarius (Sgr) dwarf galaxy, and can be attributed to the serendipitous alignment of the Sgr stream with the bulge. This dataset allows the Sgr stream to be traced in this part of the sky for the first time. The underlying metallicity distributions ar...
We present a proper-motion study on models of the dwarf spheroidal galaxy Sculptor, based on the ... more We present a proper-motion study on models of the dwarf spheroidal galaxy Sculptor, based on the predicted proper-motion accuracy of Gaia measurements. Gaia will measure proper motions of several hundreds of stars for a Sculptor-like system. Even with an uncertainty on the proper motion of order 1.5 times the size of an individual proper-motion value of ∼ 10 mas/century, we find that it is possible to recover Sculptor's systemic proper motion at its distance of 79 kpc.
ABSTRACT Two methods are given for determining distances to streams of high-velocityclouds in orb... more ABSTRACT Two methods are given for determining distances to streams of high-velocityclouds in orbit about the Galactic Centre. Both rely on the parallax generated by the offset of the Sun from the stream’s orbital plane. The distances to all points of the Magellanic Stream are found without use of the Magellanic Cloud distances.
We investigate the possibility that the recently discovered Hercules Milky Way satellite is in fa... more We investigate the possibility that the recently discovered Hercules Milky Way satellite is in fact a stellar stream in formation, thereby explaining its very elongated shape with an axis ratio of 3 to 1. Under the assumption that Hercules is a stellar stream and that its stars are flowing along the orbit of its progenitor, we find an orbit that would have recently brought the system close enough to the Milky Way to induce its disruption and transformation from a bound dwarf galaxy into a stellar stream. The application of simple analytical techniques to the tentative radial velocity gradient observed in the satellite provides tight constraints on the tangential velocity of the system (v t = -16 +6 -22 km s -1 in the Galactic Standard of Rest). Combined with its large receding velocity, the determined tangential velocity yields an orbit with a small pericentric distance (R peri = 6 +9 -2 kpc). Tidal disruption is therefore a valid scenario for explaining the extreme shape of Hercules. The increase in the mean flattening of dwarf galaxies as one considers fainter systems could therefore be the impact of a few of these satellites not being bound stellar systems dominated by dark matter but, in fact, stellar streams in formation, shedding their stars in the Milky Way's stellar halo.
We have obtained deep photometry in two 1 • × 1 • fields covering the close pair of dwarf spheroi... more We have obtained deep photometry in two 1 • × 1 • fields covering the close pair of dwarf spheroidal galaxies Leo IV and Leo V and part of the area in between. From the distribution of likely red giant branch (RGB) and horizontal-branch (HB) stars in the data set, we find that both Leo IV and Leo V are significantly larger than indicated by previous measurements based on shallower data. With a half-light radius of r h = 4. 6 ± 0. 8 (206 ± 36 pc) and r h = 2. 6 ± 0. 6 (133 ± 31 pc), respectively, both systems are now well within the physical size bracket of typical dwarf spheroidal Milky Way satellites. Both are also found to be significantly elongated with an ellipticity of 0.5, a characteristic shared by many of the fainter (M V > -8) Milky Way dwarf spheroidals. The large spatial extent of our survey allows us to search for extra-tidal features in the area between the two dwarf galaxies with unprecedented sensitivity. The spatial distribution of candidate RGB and HB stars in this region is found to be non-uniform at the ∼3σ level. Interestingly, this substructure is aligned along the direction connecting the two systems, indicative of a possible "bridge" of extra-tidal material. Fitting the stellar distribution with a linear Gaussian model yields a significance of 4σ for this overdensity, a most likely FWHM of ∼16 arcmin, and a central surface brightness of 32 mag arcsec -2 . We investigate different scenarios to explain the close proximity of Leo IV and Leo V, and the possible tidal bridge between them. Orbit calculations demonstrate that the two systems cannot share the exact same orbit, while a compromise orbit does not approach the Galactic center more than ∼160 kpc, rendering it unlikely that they are remnants of a single disrupted progenitor. A comparison with cosmological simulations shows that a chance collision between unrelated subhalos is negligibly small. Given their relative distance and velocity, Leo IV and Leo V could be a bound "tumbling pair," if their combined mass exceeds (8 ± 4) × 10 9 M . The scenario of an internally interacting pair that fell into the Milky Way together appears to be the most viable explanation for this close celestial companionship.
We present the first metallicity distribution functions of the old field populations in the Magel... more We present the first metallicity distribution functions of the old field populations in the Magellanic Clouds (MCs). Our metallicities are based on the Fourier decomposition of Type ab RR Lyrae light curves from the Optical Gravitational Lensing Experiment. On the metallicity scale of Zinn & West, we find a mean metallicity of [Fe/H] = −1.50 ± 0.24 dex based on 16,776 RR Lyrae stars in the Large Magellanic Cloud (LMC). For the Small Magellanic Cloud (SMC) we obtain −1.70 ± 0.27 dex based on 1831 RR Lyrae stars. These uncertainties represent the intrinsic spread in the population rather than the standard deviation of the mean. Our results are in good agreement with the few existing spectroscopic metallicity determinations for LMC RR Lyrae stars from the literature. For both the LMC and the SMC the metallicity spread exceeds 1 dex in [Fe/H]. The distribution of metallicities in both Clouds is very uniform, and no significant metallicity gradient is detectable. We also do not find any ...
Monthly Notices of the Royal Astronomical Society: Letters, 2009
We present a simple result in which the distance gradient along a stream can be used to derive th... more We present a simple result in which the distance gradient along a stream can be used to derive the transverse velocity (i.e. proper motion) along it, if the line-of-sight velocity is also known. We show its application to a mock orbit to illustrate its validity and usage. For less extended objects, such as globular clusters and satellite galaxies being tidally disrupted, the same result can be applied in its small-angle approximation. The procedure does not rely on energy or angular momentum conservation and hence does not require a Galactic model in order to deduce the local velocity vector of the stream.
Monthly Notices of the Royal Astronomical Society: Letters, 2010
We show that a string of H I clouds that form part of the high-velocity cloud complex known as GC... more We show that a string of H I clouds that form part of the high-velocity cloud complex known as GCN is a probable gaseous stream extending over more than 50 • in the Galactic halo. The radial velocity gradient along the stream is used to deduce transverse velocities as a function of distance, enabling a family of orbits to be computed. We find that a direction of motion towards the Galactic disc coupled with a mid-stream distance of ∼20 kpc provides a good match to the observed sky positions and radial velocities of the H I clouds comprising the stream. With an estimated mass of 10 5 M , its progenitor is likely to be a dwarf galaxy. However, no stellar counterpart has been found amongst the currently known Galactic dwarf spheroidal galaxies or stellar streams and the exact origin of the stream is therefore currently unknown.
Monthly Notices of the Royal Astronomical Society: Letters, 2007
We consider the possibility that the Galactic neutral hydrogen stream Complex A and the stellar O... more We consider the possibility that the Galactic neutral hydrogen stream Complex A and the stellar Orphan stream are related, and use this hypothesis to determine possible distances to Complex A and the Orphan stream, and line-of-sight velocities for the latter. The method presented uses our current knowledge of the projected positions of the streams, as well as line-of-sight velocities for Complex A, and we show that a solution exists in which the two streams share the same orbit. If Complex A and the Orphan stream are on this orbit, our calculations suggest the Orphan stream to be at an average distance of 9 kpc, with heliocentric radial velocities of approximately -95 km s -1 . Complex A would be ahead of the Orphan stream in the same wrap of the orbit, with an average distance of 4 kpc, which is consistent with the distance constraints determined through interstellar absorption line techniques.
Monthly Notices of the Royal Astronomical Society, 2008
A useful crude approximation for Abelian functions is developed and applied to orbits. The bound ... more A useful crude approximation for Abelian functions is developed and applied to orbits. The bound orbits in the power-law potentials Ar -α take the simple form ( /r) k = 1 + e cos (m φ), where k = 2 -α > 0 and and e are generalizations of the semi-latus-rectum and the eccentricity. m is given as a function of 'eccentricity'. For nearly circular orbits m is √ k, while the above orbit becomes exact at the energy of escape where e is 1 and m is k. Orbits in the logarithmic potential that gives rise to a constant circular velocity are derived via the limit α → 0. For such orbits, r 2 vibrates almost harmonically whatever the 'eccentricity'. Unbound orbits in power-law potentials are given in an appendix. The transformation of orbits in one potential to give orbits in a different potential is used to determine orbits in potentials that are positive powers of r. These transformations are extended to form a group which associates orbits in sets of six potentials, e.g. there are corresponding orbits in the potentials proportional to r, r -2/3 , r -3 , r -6 , r -4/3 and r 4 . A degeneracy reduces this to three, which are r -1 , r 2 and r -4 for the Keplerian case. A generalization of this group includes the isochrone with the Kepler set.
Monthly Notices of the Royal Astronomical Society, 2005
It is now established that several of the Local Group dwarf spheroidal galaxies (dSphs) have larg... more It is now established that several of the Local Group dwarf spheroidal galaxies (dSphs) have large mass-to-light ratios. We consider the possibility that the dark matter in the haloes of dSphs is composed of massive black holes with masses in the range 10 5 -10 7 M . We use direct N-body simulations to determine the long-term evolution of a two-component dSph composed of a pressure-supported stellar population within a black hole dominated halo. The black holes are initially distributed according to a Navarro-Frenk-White profile. For black hole masses between 10 5 and 10 6 M , the dark matter halo evolves towards a shallower inner profile in less than a Hubble time. This suggests that black holes in this mass range might provide an explanation for the origin of the dark matter cores inferred from observations of low surface brightness galaxy rotation curves. We compare the simulated evolution of the stellar population with observed data for the Draco dSph, and we find that dynamical heating generally leads to the rapid dispersal of the stellar population to large radii. The dependence of the heating rate on the black hole mass is determined, and an upper limit of 10 5 M is placed on the individual black holes comprising the dark matter halo of Draco, if its present stellar distribution is representative of the initial one. We also present a simple scaling argument, which demonstrates that the dynamical heating of an initially compact, although not selfgravitating, stellar distribution might produce a remnant distribution similar in extent to Draco after 10 Gyr, even for black hole masses somewhat in excess of 10 5 M .
Monthly Notices of the Royal Astronomical Society, 2008
We present a geometrodynamical method for determining distances to orbital streams of HI gas in t... more We present a geometrodynamical method for determining distances to orbital streams of HI gas in the Galaxy. The method makes use of our offset from the Galactic centre and assumes that the gas comprising the stream nearly follows a planar orbit about the Galactic centre. We apply this technique to the Magellanic Stream and determine the distances to all points along it; a consistency check shows that the angular momentum is approximately constant. Applying this technique to the Large Magellanic Cloud itself gives an independent distance which agrees within its accuracy of around 10%. Relaxing the demand for exact conservation of energy and angular momentum at all points along the stream allows for an increase in orbital period between the lagging end and the front end led by the Magellanic Clouds. Similar methods are applicable to other long streams of high-velocity clouds, provided they also nearly follow planar orbits; these would allow otherwise unknown distances to be determined.
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Papers by Shoko Jin