Direct Determination of the Spiral Pattern Rotation Speed of the Galaxy

The determination of the birth radius of the Sun is important to understand the evolution and consequent disruption of the Sun's birth cluster in the Galaxy. Motivated by this fact, we study the motion of the Sun in the Milky Way during the last 4.6 Gyr in order to find its birth radius. We carried out orbit integrations backward in time using an analytical model of the Galaxy which includes the contribution of spiral arms and a central bar. We took into account the uncertainty in the parameters of the Milky Way potential as well as the uncertainty in the present day position and velocity of the Sun. We find that in general the Sun has not migrated from its birth place to its current position in the Galaxy (R ). However, significant radial migration of the Sun is possible when: 1) The 2 : 1 Outer Lindblad resonance of the bar is separated from the corrotation resonance of spiral arms by a distance ∼ 1 kpc. 2) When these two resonances are at the same Galactocentric position and further than the solar radius. In both cases the migration of the Sun is from outer regions of the Galactic disk to R , placing the Sun's birth radius at around 11 kpc. We find that in general it is unlikely that the Sun has migrated significantly from the inner regions of the Galactic disk to R .

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“…Dias & Lépine 2005), while others argue that the value is Ωsp = 20 km s −1 kpc −1 (e.g. Martos et al 2004).…”

Section: Spiral Arm Parametersmentioning

confidence: 99%

Radial migration of the Sun in the Milky Way: a statistical study

Martínez-Barbosa

Brown

Zwart

2014

Monthly Notices of the Royal Astronomical Society

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“…Our group has been devoted to this field in the past few years, obtaining results, which includes the determination of the velocity of spiral pattern based on the integration of the orbits of known clusters and, consequently, the location of the co-rotation radius close to the solar radius (Dias & Lépine 2005). The open clusters have also provided constraints on the understanding of the step-like abrupt decrease in metallicity at 1 kpc from the Sun (Lépine et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Proper motions of the optically visible open clusters based on the UCAC4 catalog

Dias

Monteiro

Caetano

et al. 2014

A&A

177

207

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We present a catalog of mean proper motions and membership probabilities of individual stars for optically visible open clusters, which have been determined using data from the UCAC4 catalog in a homogeneous way. The mean proper motion of the cluster and the membership probabilities of the stars in the region of each cluster were determined by applying the statistical method in a modified fashion. In this study, we applied a global optimization procedure to fit the observed distribution of proper motions with two overlapping normal bivariate frequency functions, which also take the individual proper motion errors into account. For 724 clusters, this is the first determination of proper motion, and for the whole sample, we present results with a much larger number of identified astrometric member stars. Furthermore, it was possible to estimate the mean radial velocity of 364 clusters (102 unpublished so far) with the stellar membership using published radial velocity catalogs. These results provide an increase of 30% and 19% in the sample of open clusters with a determined mean absolute proper motion and mean radial velocity, respectively.

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“…Only very young clusters tend to cluster close to the spiral arms, where they recently formed (Dias & Lépine 2005). High resolution spectra allow us to measure the abundance of light elements and in particular lithium, which is an invaluable probe of the mixing mechanisms in stellar envelopes.…”

Section: Introductionmentioning

confidence: 99%

Abundances and physical parameters for stars in the open clusters NGC 5822 and IC 4756

Pace¹,

Danziger

Carraro³

et al. 2010

A&A

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Context. Classical chemical analyses may be affected by systematic errors that would cause observed abundance differences between dwarfs and giants. For some elements, however, the abundance difference could be real. Aims. We address the issue by observing 2 solar-type dwarfs in NGC 5822 and 3 in IC 4756, and comparing their composition with that of 3 giants in either of the aforementioned clusters. We determine iron abundance and stellar parameters of the dwarf stars, and the abundances of calcium, sodium, nickel, titanium, aluminium, chromium, silicon, and oxygen for both the giants and dwarfs. For the dwarfs, we also estimate the rotation velocities, and and lithium abundances. We improve the cluster parameter estimates (distance, age, and reddening) by comparing existing photometry with new isochrones. Methods. We acquired UVES high-resolution, of high signal-to-noise ratio (S /N) spectra. The width of the cross correlation profiles was used to measure rotation velocities. For abundance determinations, the standard equivalent width analysis was performed differentially with respect to the Sun. For lithium and oxygen, we derived abundances by comparing synthetic spectra with observed line features. Results. We find an iron abundance for dwarf stars equal to solar to within the margins of error for IC 4756, and slightly above for NGC 5822 ([Fe/H] = 0.01 and 0.05 dex respectively). The 3 stars in NGC 4756 have lithium abundances between Log N(Li) ≈ 2.6 and 2.8 dex, the two stars in NGC 5822 have Log N(Li) ≈ 2.8 and 2.5, respectively. Conclusions. For sodium, silicon, and titanium, we show that abundances of giants are significantly higher than those of the dwarfs of the same cluster (about 0.15, 0.15, and 0.35 dex). Other elements may also undergo enhancement, but all within 0.1 dex. Indications of much stronger enhancements can be found using literature data. But artifacts of the analysis may be partly responsible for this.

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Direct Determination of the Spiral Pattern Rotation Speed of the Galaxy

Cited by 159 publications

References 33 publications

Radial migration of the Sun in the Milky Way: a statistical study

Radial migration of the Sun in the Milky Way: a statistical study

Proper motions of the optically visible open clusters based on the UCAC4 catalog

Abundances and physical parameters for stars in the open clusters NGC 5822 and IC 4756

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