Weighing the Galactic disk in sub-regions of the solar neighbourhood using Gaia DR2

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

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Chemical Abundances in Galactic Bulge Pn

Symposium - International Astronomical Union ◽

10.1017/s0074180900172559 ◽

1993 ◽

Vol 155 ◽

pp. 581-581 ◽

Cited By ~ 1

Author(s):

N.A. Walton ◽

M.J. Barlow ◽

R.E.S. Clegg

Keyword(s):

Galactic Disk ◽

Planetary Nebulae ◽

Solar Neighbourhood ◽

Galactic Bulge ◽

Low Resolution ◽

Chemical Abundances ◽

The Mean ◽

Optical Spectrophotometry ◽

High Metallicity

We present abundance determinations, in particular of carbon, and C/O ratios, for 11 Galactic bulge planetary nebulae (PN) based on our low resolution UV data from IUE observations and optical spectrophotometry from the Anglo-Australian Telescope. We compare the observed abundances with those predicted by dredge-up theory for the high metallicity Galactic bulge. The sample abundances are also contrasted with the abundances found for PN in the Galactic disk. The mean C/O ratio for the bulge PN is significantly lower than that found for Galactic disk PN. Further, we present an abundance analysis of the very metal-poor bulge PN M2-29. From an analysis of the differential extinction found from the observed ratios of the He ii 1640,4686Å lines, we find that the ultraviolet reddening law towards the bulge is steeper than in the solar neighbourhood.

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Not gone with the wind: Planet occurrence is independent of stellar galactocentric velocity

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2088 ◽

2019 ◽

Vol 489 (2) ◽

pp. 2505-2510 ◽

Cited By ~ 3

Author(s):

Moiya A S McTier ◽

David M Kipping

Keyword(s):

Solar Neighbourhood ◽

P Value ◽

Selection Function ◽

Strong Correlations ◽

Velocity Data ◽

Low Velocity ◽

Gone With The Wind ◽

Host Stars ◽

Radial Velocity Data ◽

Gaia Dr2

Abstract We demonstrate that planet occurrence does not depend on stellar galactocentric velocity in the Solar neighbourhood. Using Gaia DR2 astrometry and radial velocity data, we calculate 3D galactocentric velocities for 197 090 Kepler field stars, 1647 of which are confirmed planet hosts. When we compare the galactocentric velocities of planet hosts to those of the entire field star sample, we observe a statistically significant (KS p-value = 10−70) distinction, with planet hosts being apparently slower than field stars by ∼40 km s−1. We explore some potential explanations for this difference and conclude that it is not a consequence of the planet–metallicity relation or distinctions in the samples’ thin/thick disc membership, but rather an artefact of Kepler’s selection function. Non Kepler-host stars that have nearly identical distances, temperatures, surface gravities, and Kepler magnitudes to the confirmed planet hosts also have nearly identical velocity distributions. Using one of these identical non-host samples, we consider that the probability of a star with velocity vtot hosting a planet can be described by an exponential function proportional to $e^{(-v_{\mathrm{tot}}/v_0)}$. Using a Markov Chain Monte Carlo sampler, we determine that v0 >976 km s−1 to 99 per cent confidence, which implies that planets in the Solar neighbourhood are just as likely to form around high-velocity stars as they are around low-velocity stars. Our work highlights the subtle ways in which selection biases can create strong correlations without physical underpinnings.

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The UV and optical reddening law to the Galactic Bulge and CNO abundances in Bulge planetary nebulae

Symposium - International Astronomical Union ◽

10.1017/s0074180900123496 ◽

1993 ◽

Vol 153 ◽

pp. 337-338

Author(s):

N.A. Walton ◽

M.J. Barlow ◽

R.E.S. Clegg

Keyword(s):

Galactic Disk ◽

Planetary Nebulae ◽

Line Ratio ◽

Solar Neighbourhood ◽

Balmer Line ◽

Galactic Bulge ◽

The Mean ◽

Cno Abundances ◽

Halo Population ◽

Selective Extinction

An analysis of the differential ultraviolet extinction towards four bulge planetary nebulae, based on the observed line ratio of He II 1640/4686Å, shows that the ultraviolet reddening law towards the bulge is much steeper than in the solar neighbourhood. An analysis of the optical reddening law for 42 bulge PN, based upon observed Balmer line ratios and Hβ to radio free-free flux ratios, is presented. The optical reddening law towards the bulge is steeper than in the local ISM, and thus the ratio of total to selective extinction, Rv = 2.29 (± 0.50), is lower than the standard solar neighbourhood value of Rv = 3.10.We present abundance determinations, in particular C/H and C/O ratios, for 11 Galactic bulge PN, based on spectrophotometry in the UV from IUE and in the optical from the Anglo-Australian Telescope. The derived abundances are compared with values for PN in the Galactic disk. The mean C/O ratio for bulge PN is significantly lower than that found for Galactic disk PNs. Additionally we present an abundance analysis of the very metal-poor halo population PN M2-29, which is located in the bulge.

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The Geneva–Copenhagen Survey of the Solar Neighbourhood

Publications of the Astronomical Society of Australia ◽

10.1071/as04013 ◽

2004 ◽

Vol 21 (2) ◽

pp. 129-133 ◽

Cited By ~ 8

Author(s):

B. Nordström ◽

J. Andersen ◽

J. Holmberg ◽

B. R. Jørgensen ◽

M. Mayor ◽

...

Keyword(s):

Binary Stars ◽

Galactic Disk ◽

Classical Model ◽

Thin Disk ◽

Solar Neighbourhood ◽

Proper Motions ◽

Kinematic Data ◽

Model Predictions ◽

The Mean ◽

Metallicity Distribution

AbstractWe report on a new survey of metallicities, ages, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased all-sky sample of 16 682 nearby F- and G-dwarfs. Our ∼ 63 000 new, accurate radial velocities for nearly 13 500 of the stars, combined with Hipparcos parallaxes and Tycho-2 proper motions, complete the kinematic data for 14 139 stars and allow us to identify most of the binary stars in the sample. Isochrone ages have been determined whenever reliable results are possible, with particular attention to realistic error estimates.Among the basic properties of the Galactic disk that can be reinvestigated from our data are the metallicity distribution of G-dwarfs and the age–metallicity and age–velocity relations of the solar neighbourhood. We confirm the lack of metal-poor G-dwarfs relative to classical model predictions (the 'G-dwarf problem'), the near-constancy of the mean metallicity since the formation of the thin disk, and the appearance of the kinematic signature of the thick disk ∼ 10 Gyr ago.

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Determination of the local dark matter density using K-dwarfs from Gaia DR2

EPJ Web of Conferences ◽

10.1051/epjconf/202024004002 ◽

2020 ◽

Vol 240 ◽

pp. 04002

Author(s):

M. Dafa Wardana ◽

Hesti Wulandari ◽

Sulistiyowati ◽

Akbar H. Khatami

Keyword(s):

Dark Matter ◽

Galactic Disk ◽

Matter Density ◽

Solar Neighborhood ◽

Stellar Disk ◽

Vertical Position ◽

Dark Halo ◽

Detection Rates ◽

Dark Matter Density ◽

Gaia Dr2

Local dark matter density, ρdm, is one of the crucial astrophysical inputs for the estimation of detection rates in dark matter direct search experi- ments. Knowing the value also helps us to investigate the shape of the Galactic dark halo, which is of importance for indirect dark matter searches, as well as for various studies in astrophysics and cosmology. In this work, we performed kinematics study of stars in the solar neighborhood to determine the local dark matter density. As tracers we used 95,543 K-dwarfs from Gaia DR2 inside a heliocentric cylinder with a radius of 150 pc and height 200 pc above and below the Galactic mid plane. Their positions and motions were analyzed, assum- ing that the Galaxy is axisymmetric and the tracers are in dynamical equilib- rium. We applied Jeans and Poisson equations to relate the observed quantities, i.e. vertical position and velocity, with the local dark matter density. The tilt term in the Jeans equation is considered to be small and is therefore neglected. Galactic disk is modelled to consist of a single exponential stellar disk, a thin gas layer, and dark matter whose density is constant within the volume consid- ered. Marginalization for the free parameters was performed with Bayesian theorem using Markov Chain Monte Carlo (MCMC) method. We find that ρdm = 0.0116 ± 0.0012 MO/pc or ρdm = 0.439 ± 0.046 GeV/cm3, in agreement within the range of uncertainty with results of several previous studies.

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Chemical Evolution of the Galactic Disk and the Radial Metallicity Gradient

Symposium - International Astronomical Union ◽

10.1017/s0074180900008986 ◽

1976 ◽

Vol 72 ◽

pp. 207-208

Author(s):

M. Mayor

Keyword(s):

Chemical Evolution ◽

Galactic Disk ◽

Sodium Concentration ◽

Mean Value ◽

Heavy Elements ◽

Solar Neighbourhood ◽

Chemical Gradient ◽

The Galaxy ◽

The Mean ◽

Image Position

An analysis of the kinematical and photometric properties of about 600dF stars and 600 gG-gK stars permits the estimation of the radial chemical gradient in the Galaxy. The mean value in the solar neighbourhood obtained for all of these stars is: The values of [Fe/H] used for this estimation are deduced for the dF stars using uvby β photometric measurements and for the gG-gK stars from a list published by Hansen and Kjaergaard. An estimate of the chemical gradient using UBV photometry of dG stars in the solar neighbourhood gives a similar value. For all the samples studied (dF, dG or giants) the order of magnitude for the gradient is the same. However, for the youngest stars in these samples the metallicity gradient could be larger: Such a value may be affected by dynamical perturbations of the galactic disk.The values published by Hansen and Kjaergaard for the sodium concentration in giant star atmospheres also indicate a radial galactic gradient of the same order.If only the dF stars which are sufficiently evolved to allow an age estimate are considered, then a very distinct correlation is found between age and metallicity: An important fraction of the heavy elements actually present in the solar neighbourhood seems to have synthetized during the life of the galactic disk.The two derivatives and are not independent, but are connected by the chemical evolution of the galactic disk. Some elementary deductions show the coherency of these two estimates.The intrinsic dispersion of metallicities, at a given age and birthplace, is somewhat lower than the admitted values. It has not been possible to find any significant variation with age of this quantity from the present observational material. The simultaneous variation of σ2w and [Fe/H] as function of age is evidence for a z stratification in the mean abundance of the heavy elements. The ratio between the mean metallicity in the plane and at z = 500 pc is estimated to be about a factor of two.Finally it is shown that the interpretation of the kinematical diagrams for different groups of given metallicity is ambiguous. A relation as e vs [Fe/H] depends not only on the chemical and kinematical history of the Galaxy but is also strongly dependent on the observational errors of [Fe/H] and on criteria used to define the sample.A paper containing the above results has been submitted for publication in Astronomy and Astrophysics.

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Age and Metallicity Distributions among Galactic Disk Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900108472 ◽

1995 ◽

Vol 164 ◽

pp. 109-117

Author(s):

P.E. Nissen

Keyword(s):

Observational Studies ◽

Galactic Disk ◽

Open Clusters ◽

Recent Survey ◽

Solar Neighbourhood ◽

B Stars ◽

Nearby Stars

Observational studies of the relations between ages, metallicities and kinematics of disk stars in the solar neighbourhood are discussed with emphasis on the recent survey by Edvardsson et al. (1993), and galactic metallicity gradients inferred from these nearby stars are compared with gradients determined from distant B stars and open clusters.

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The Chemical Evolution of Magnesium Isotopic Abundances in the Solar Neighbourhood

Publications of the Astronomical Society of Australia ◽

10.1071/as03042 ◽

2003 ◽

Vol 20 (4) ◽

pp. 340-344 ◽

Cited By ~ 40

Author(s):

Y. Fenner ◽

B. K. Gibson ◽

H.-c. Lee ◽

A. I. Karakas ◽

J. C. Lattanzio ◽

...

Keyword(s):

Chemical Evolution ◽

Galactic Disk ◽

Asymptotic Giant Branch ◽

Solar Neighbourhood ◽

Asymptotic Giant Branch Stars ◽

Intermediate Mass ◽

Intermediate Mass Stars ◽

Isotopic Abundances ◽

First Time ◽

Giant Branch Stars

AbstractThe abundance of the neutron-rich magnesium isotopes observed in metal-poor stars is explained quantitatively with a chemical evolution model of the local Galaxy that considers — for the first time — the metallicity-dependent contribution from intermediate mass stars. Previous models that simulate the variation of Mg isotopic ratios with metallicity in the solar neighbourhood have attributed the production of 25Mg and 26Mg exclusively to hydrostatic burning in massive stars. These models match the data well for [Fe/H] > –1.0 but severely underestimate 25,26Mg/24Mg at lower metallicities. Earlier studies have noted that this discrepancy may indicate a significant role played by intermediate mass stars. Only recently have detailed calculations of intermediate mass stellar yields of 25Mg and 26Mg become available with which to test this hypothesis. In an extension of previous work, we present a model that successfully matches the Mg isotopic abundances in nearby Galactic disk stars through the incorporation of nucleosynthesis predictions of Mg isotopic production in asymptotic giant branch stars.

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Co-formation of the thin and thick discs revealed by APOGEE-DR16 and Gaia-DR2

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3966 ◽

2020 ◽

Author(s):

Leandro Beraldo e Silva ◽

Victor P Debattista ◽

David Nidever ◽

João A S Amarante ◽

Bethany Garver

Keyword(s):

Solar Neighbourhood ◽

Full Sample ◽

Thick Disc ◽

Thin Disc ◽

Vertical Scale ◽

Stellar Halo ◽

Sph Simulation ◽

Gaia Dr2 ◽

Cross Match ◽

Age Estimates

Abstract Since thin disc stars are younger than thick disc stars on average, the thin disc is predicted by some models to start forming after the thick disc had formed, around 10 Gyr ago. Accordingly, no significant old thin disc population should exist. Using 6-D coordinates from Gaia-DR2 and age estimates from Sanders & Das (2018), we select ∼24000 old stars (${\tau > 10{\, \rm{Gyr}}}$, with uncertainties $\lesssim 15\%$) within $2{\, \rm{kpc}}$ from the Sun (full sample). A cross-match with APOGEE-DR16 (∼1000 stars) reveals comparable fractions of old chemically defined thin/thick disc stars. We show that the full sample pericenter radius (rper) distribution has three peaks, one associated with the stellar halo and the other two having contributions from the thin/thick discs. Using a high-resolution N-body+SPH simulation, we demonstrate that one peak, at ${r_\rm{per}}\approx 7.1{\, \rm{kpc}}$, is produced by stars from both discs which were born in the inner Galaxy and migrated to the Solar Neighbourhood. In the Solar Neighbourhood, ∼1/2 (∼1/3) of the old thin (thick) disc stars are classified as migrators. Our results suggest that thin/thick discs are affected differently by radial migration inasmuch as they have different eccentricity distributions, regardless of vertical scale heights. We interpret the existence of a significant old thin disc population as evidence for an early co-formation of thin/thick discs, arguing that clump instabilities in the early disc offer a compelling explanation for the observed trends.

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