A synthetic view on structure and evolution   of the Milky Way

Robin, A. C.; Reylé, C.; Derriére, S.; Picaud, S.

doi:10.1051/0004-6361:20040968

Cited by 134 publications

(145 citation statements)

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“…In the first box, which are located around the HB magnitude level (21 < r Sloan [mag] < 22), we found that about 8% of Galactic stars survive our proper motion selection, while 25% are in the second box, located at a fainter magnitude level (22 < r Sloan [mag] < 23). We note that similar fractions are expected from a Galactic simulation taken from the Besançon stellar population synthesis models (Robin et al 2003(Robin et al , 2004 after applying the same PM-selection criteria described above. The same simulation allows us to estimate the residual fraction of Galactic stars expected at the same levels of magnitude as above, but for the Galactic blue plume in the colour range −0.5 < B Bessel − r Sloan [mag] < 1.8.…”

Section: Proper Motion Selectionsupporting

confidence: 67%

A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members

Fabrizio

Raimondo

Brocato

et al. 2014

A&A

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Context. Discovered in the last decade as overdensities of resolved stars, the ultra-faint dwarfs (UFDs) are among the least luminous, most dark-matter dominated, and most metal-poor galaxies known today. They appear as sparse, loose objects with high mass-to-light ratios. Hercules is the prototype of the UFD galaxies. To date, there are still no firm constraints on its total luminosity due to the difficulty of disentangling Hercules bona-fide stars from the severe Galactic field contamination. Aims. To better constrain Hercules properties, we aim at removing foreground and background contaminants in the galaxy field using the proper motions of the Milky Way stars and the colour-colour diagram. Methods. We have obtained images of Hercules in the r Sloan , B Bessel and U spec bands with the Large Binocular Telescope (LBT) and LBC-BIN mode capabilities. The r Sloan new dataset combined with data from the LBT archive span a time baseline of about 5 yr, allowing us to measure proper motions of stars in the Hercules direction for the first time. The U spec data along with existing LBT photometry allowed us to use colour-colour diagram to further remove the field contamination.Results. Thanks to a highly-accurate procedure to derive the r Sloan -filter geometric distortion solution for the LBC-red, we were able to measure stellar relative proper motions to a precision of better than 5 mas yr −1 down to r Sloan 22 mag and disentangle a significant fraction (>90%) of Milky Way contaminants. We ended up with a sample of 528 sources distributed over a large portion of the galaxy body (∼0.12 deg 2 ). Of these sources, 171 turned out to be background galaxies and additional foreground stars from the analysis of the U spec − B Bessel vs. B Bessel − r Sloan colour-colour diagram. This leaves us with a sample of 357 likely members of the Hercules UFD. We compared the cleaned colour-magnitude diagram (CMD) with evolutionary models and synthetic CMDs, confirming the presence in Hercules of an old population (t = 12 ± 2 Gyr) with wide spread metallicity (−3.3 < [Fe/H] < −1.8). Conclusions. Our procedure to estimate star proper motions proved to be a very effective way to identify likely members for stellar systems as far as 130 kpc. The present selection, based on both proper motions and colour-colour diagram, provides a robust identification of Hercules members and a new target list for more spectroscopic investigations.

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Section: Proper Motion Selectionsupporting

confidence: 67%

A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members

Fabrizio

Raimondo

Brocato

et al. 2014

A&A

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“…A statistical conversion from relative to absolute parallax and proper motions -based on the Besançon Galaxy model (Robin et al 2003(Robin et al , 2004) -is applied to derive final estimates of absolute proper motions and trigonometric parallaxes (see Ducourant et al 2007, for a detailed description).…”

Section: Trigonometric Parallax and Proper Motion Determinationmentioning

confidence: 99%

The TW Hydrae association: trigonometric parallaxes and kinematic analysis

Ducourant

Teixeira

Galli

et al. 2014

A&A

101

135

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Context. The nearby TW Hydrae association (TWA) is currently a benchmark for the study of the formation and evolution of young low-mass stars, circumstellar disks, and the imaging detection of planetary companions. For these studies, it is crucial to evaluate the distance to group members in order to access their physical properties. Membership of several stars is strongly debated and age estimates vary from one author to another with doubts about coevality. Aims. We revisit the kinematic properties of the TWA in light of new trigonometric parallaxes and proper motions to derive the dynamical age of the association and physical parameters of kinematic members. Methods. Using observations performed with the New Technology Telescope (NTT) from ESO we measured trigonometric parallaxes and proper motions for 13 stars in TWA. Results. With the convergent point method we identify a co-moving group with 31 TWA stars. We deduce kinematic distances for seven members of the moving group that lack trigonometric parallaxes. A traceback strategy is applied to the stellar space motions of a selection of 16 of the co-moving objects with accurate and reliable data yielding a dynamical age for the association of t 7.5 ± 0.7 Myr. Using our new parallaxes and photometry available in the literature we derive stellar ages and masses from theoretical evolutionary models. Conclusions. With new parallax and proper motion measurements from this work and current astrometric catalogs we provide an improved and accurate database for TWA stars to be used in kinematical analysis. We conclude that the dynamical age obtained via traceback strategy is consistent with previous age estimates for the TWA, and is also compatible with the average ages derived in the present paper from evolutionary models for pre-main-sequence stars.

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“…The Besançon Galaxy model (Robin et al 2004) was used to generate a sample of bright giants and supergiants (M V < 0) in the region 0 ≤ l ≤ 180 and −20 ≤ b ≤ 20 of our Galaxy (where l and b are the galactic coordinates). The reddening was added separately using the extinction model from Drimmel et al (2003).…”

Section: Number Of Supergiant Stars With Detectable Photocentric Motionmentioning

confidence: 99%

Radiative hydrodynamic simulations of red supergiant stars

Chiavassa

Pasquato

Jorissen

et al. 2011

A&A

115

106

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Context. It has been shown that convection in red supergiant stars (RSG) gives rise to large granules that cause surface inhomogeneities and shock waves in the photosphere. The resulting motion of the photocentre (on time scales ranging from months to years) could possibly have adverse effects on the parallax determination with Gaia. Aims. We explore the impact of the granulation on the photocentric and photometric variability. We quantify these effects in order to better characterise the error that could possibly alter the parallax. Methods. We use 3D radiative-hydrodynamics (RHD) simulations of convection with CO5BOLD and the post-processing radiative transfer code Optim3D to compute intensity maps and spectra in the Gaia G band [325-1030 nm]. Results. We provide astrometric and photometric predictions from 3D simulations of RSGs that are used to evaluate the possible degradation of the astrometric parameters of evolved stars derived by Gaia. We show in particular from RHD simulations that a supergiant like Betelgeuse exhibits a photocentric noise characterised by a standard deviation of the order of 0.1 AU. The number of bright giant and supergiant stars whose Gaia parallaxes will be altered by the photocentric noise ranges from a few tens to several thousands, depending on the poorly known relation between the size of the convective cells and the atmospheric pressure scale height of supergiants, and to a lower extent, on the adopted prescription for galactic extinction. In the worst situation, the degradation of the astrometric fit caused by this photocentric noise will be noticeable up to about 5 kpc for the brightest supergiants. Moreover, parallaxes of Betelgeuse-like supergiants are affected by an error of the order of a few percents. We also show that the photocentric noise, as predicted by the 3D simulation, does account for a substantial part of the supplementary "cosmic noise" that affects Hipparcos measurements of Betelgeuse and Antares.

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A synthetic view on structure and evolution of the Milky Way

Cited by 134 publications

References 0 publications

A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members

A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members

The TW Hydrae association: trigonometric parallaxes and kinematic analysis

Radiative hydrodynamic simulations of red supergiant stars

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