scholarly journals From birth associations to field stars: mapping the small-scale orbit distribution in the Galactic disc

2020 ◽  
Vol 495 (4) ◽  
pp. 4098-4112 ◽  
Author(s):  
Johanna Coronado ◽  
Hans-Walter Rix ◽  
Wilma H Trick ◽  
Kareem El-Badry ◽  
Jan Rybizki ◽  
...  
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Space Distribution ◽  
Small Scale ◽  
Galactic Disc ◽  
Main Sequence Stars ◽  
Orbital Phase ◽  
Angle Space ◽  
Order Of Magnitude ◽  
Gaia Dr2

ABSTRACT Stars born at the same time in the same place should have formed from gas of the same element composition. But most stars subsequently disperse from their birth siblings, in orbit and orbital phase, becoming ‘field stars’. Here, we explore and provide direct observational evidence for this process in the Milky Way disc, by quantifying the probability that orbit-similarity among stars implies indistinguishable metallicity. We define the orbit similarity among stars through their distance in action-angle space, Δ(J, θ), and their abundance similarity simply by Δ[Fe/H]. Analysing a sample of main-sequence stars from Gaia DR2 and LAMOST, we find an excess of pairs with the same metallicity (Δ[Fe/H] < 0.1) that extends to remarkably large separations in Δ(J, θ) that correspond to nearly 1 kpc distances. We assess the significance of this effect through a mock sample, drawn from a smooth and phase-mixed orbit distribution. Through grouping such star pairs into associations with a friend-of-friends algorithm linked by Δ(J,θ), we find 100s of mono-abundance groups with ≥3 (to ≳20) members; these groups – some clusters, some spread across the sky – are over an order-of-magnitude more abundant than expected for a smooth phase-space distribution, suggesting that we are witnessing the ‘dissolution’ of stellar birth associations into the field.

scholarly journals The GALAH survey and Gaia DR2: Linking ridges, arches, and vertical waves in the kinematics of the Milky Way

2019 ◽  
Vol 489 (4) ◽  
pp. 4962-4979 ◽  
Author(s):  
Shourya Khanna ◽  
Sanjib Sharma ◽  
Thor Tepper-Garcia ◽  
Joss Bland-Hawthorn ◽  
Michael Hayden ◽  
...  
Keyword(s):  
Large Scale ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Elemental Abundance ◽  
Space Distribution ◽  
Orbital Energy ◽  
Small Scale ◽  
Constant Energy ◽  
Third Dimension ◽  
Gaia Dr2

ABSTRACT Gaia DR2 has revealed new small-scale and large-scale patterns in the phase-space distribution of stars in the Milky Way. In cylindrical Galactic coordinates $(R,\phi ,z)$, ridge-like structures can be seen in the $(R,V_\phi)$ plane and asymmetric arch-like structures in the $(V_R,V_\phi)$ plane. We show that the ridges are also clearly present when the third dimension of the $(R,V_\phi)$ plane is represented by $\langle z \rangle$, $\langle V_z \rangle$, $\langle V_R \rangle$, $\langle$[Fe/H]$\rangle$, and $\langle [\alpha /{\rm Fe}]\rangle$. The maps suggest that stars along the ridges lie preferentially close to the Galactic mid-plane ($|z|\lt 0.2$ kpc), and have metallicity and $\alpha$ elemental abundance similar to that of the Sun. We show that phase mixing of disrupting spiral arms can generate both the ridges and the arches. It also generates discrete groupings in orbital energy – the ridges and arches are simply surfaces of constant energy. We identify eight distinct ridges in the Gaia DR2 data: six of them have constant energy while two have constant angular momentum. Given that the signature is strongest for stars close to the plane, the presence of ridges in $\langle z \rangle$ and $\langle V_z \rangle$ suggests a coupling between planar and vertical directions. We demonstrate, using N-body simulations that such coupling can be generated both in isolated discs and in discs perturbed by an orbiting satellite like the Sagittarius dwarf galaxy.

scholarly journals Which stars can see Earth as a transiting exoplanet?

2020 ◽  
Vol 499 (1) ◽  
pp. L111-L115
Author(s):  
L Kaltenegger ◽  
J Pepper
Keyword(s):  
Main Sequence ◽  
Line Of Sight ◽  
Main Sequence Stars ◽  
Target List ◽  
Distant Observer ◽  
Spectroscopic Observations ◽  
Transiting Planets ◽  
Vantage Points ◽  
Life On Earth ◽  
Gaia Dr2

ABSTRACT Transit observations have found the majority of exoplanets to date. Also spectroscopic observations of transits and eclipses are the most commonly used tool to characterize exoplanet atmospheres and will be used in the search for life. However, an exoplanet’s orbit must be aligned with our line of sight to observe a transit. Here, we ask, from which stellar vantage points would a distant observer be able to search for life on Earth in the same way? We use the TESS Input Catalog and data from Gaia DR2 to identify the closest stars that could see Earth as a transiting exoplanet: We identify 1004 main-sequence stars within 100 parsecs, of which 508 guarantee a minimum 10-h long observation of Earth’s transit. Our star list consists of about 77 percent M-type, 12 percent K-type, 6 percent G-type, 4 percent F-type stars, and 1 percent A-type stars close to the ecliptic. SETI searches like the Breakthrough Listen Initiative are already focusing on this part of the sky. Our catalogue now provides a target list for this search. As part of the extended mission, NASA’s TESS will also search for transiting planets in the ecliptic to find planets that could already have found life on our transiting Earth .

scholarly journals A comparison of the density gradients of main sequence stars obtained by two different methods in different galactic latitudes

1970 ◽  
Vol 38 ◽  
pp. 232-235
Author(s):  
W. Becker ◽  
R. Fenkart
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Absolute Magnitude ◽  
Galactic Centre ◽  
Density Gradients ◽  
The Sun ◽  
Main Sequence Stars

The Basel Observatory program of the determination of disc- and halo-density gradients for different intervals of absolute magnitude comprises in addition to Milky Way fields several directions, all pointing to Selected Areas near a plane perpendicular to the galactic equator and passing through the sun and the galactic centre. It was started with SA 51 (Becker, 1965) and continued with Sa 57, 54 and 141 (Fenkart, 1967, 1968, 1969).

scholarly journals Mapping the Galactic disc with the LAMOST and Gaia red clump sample: II. 3D asymmetrical kinematics of mono-age populations in the disc between 6–14  kpc

2019 ◽  
Vol 491 (2) ◽  
pp. 2104-2118 ◽  
Author(s):  
H-F Wang ◽  
M López-Corredoira ◽  
Y Huang ◽  
J L Carlin ◽  
B-Q Chen ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Disc ◽  
Giant Stars ◽  
Bending Mode ◽  
Red Clump ◽  
Minor Mergers ◽  
Gaia Dr2 ◽  
South Asymmetry ◽  
Spiral Arm ◽  
Fast Rotating

ABSTRACT We perform analysis of the 3D kinematics of Milky Way disc stars in mono-age populations. We focus on stars between Galactocentric distances of R = 6 and 14  kpc, selected from the combined LAMOST Data Release 4 (DR4) red clump giant stars and Gaia DR2 proper motion catalogue. We confirm the 3D asymmetrical motions of recent works and provide time tagging of the Galactic outer disc asymmetrical motions near the anticentre direction out to Galactocentric distances of 14 kpc. Radial Galactocentric motions reach values up to 10 km s−1, depending on the age of the population, and present a north–south asymmetry in the region corresponding to density and velocity substructures that were sensitive to the perturbations in the early 6  Gyr. After that time, the disc stars in this asymmetrical structure have become kinematically hotter, and are thus not sensitive to perturbations, and we find the structure is a relatively younger population. With quantitative analysis, we find stars both above and below the plane at R ≳ 9 kpc that exhibit bending mode motions of which the sensitive duration is around 8  Gyr. We speculate that the in-plane asymmetries might not be mainly caused by a fast rotating bar, intrinsically elliptical outer disc, secular expansion of the disc, or streams. Spiral arm dynamics, out-of-equilibrium models, minor mergers or others are important contributors. Vertical motions might be dominated by bending and breathing modes induced by complicated inner or external perturbers. It is likely that many of these mechanisms are coupled together.

scholarly journals HALO7D I. The Line-of-sight Velocities of Distant Main-sequence Stars in the Milky Way Halo

2019 ◽  
Vol 876 (2) ◽  
pp. 124 ◽  
Author(s):  
Emily C. Cunningham ◽  
Alis J. Deason ◽  
Constance M. Rockosi ◽  
Puragra Guhathakurta ◽  
Zachary G. Jennings ◽  
...  
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Line Of Sight ◽  
Main Sequence Stars ◽  
Milky Way Halo

scholarly journals The extended main-sequence turn-off of the Milky Way open cluster Collinder 347

2019 ◽  
Vol 490 (2) ◽  
pp. 2414-2420 ◽  
Author(s):  
Andrés E Piatti ◽  
Charles Bonatto
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Open Cluster ◽  
Age Difference ◽  
Proper Motions ◽  
Gaussian Distributions ◽  
Young Object ◽  
Magnitude Diagram ◽  
Chemical Content ◽  
Gaia Dr2

ABSTRACT We made use of the Gaia DR2 archive to comprehensively study the Milky Way open cluster Collinder 347, known until now as a very young object of solar metal content. However, the G versus GBP − GRP colour–magnitude diagram (CMD) of bonafide probable cluster members, selected on the basis of individual stellar proper motions, their spatial distribution, and placement in the CMD, reveals the existence of a Hyades-like age open cluster (log(t /yr) = 8.8) of moderately metal-poor chemical content ([Fe/H]  = −0.4 dex), with a present-day mass of 3.3 × 103 M⊙. The cluster exhibits an extended main-sequence turn-off (eMSTO) of nearly 500 Myr, while that computed assuming Gaussian distributions from photometric errors, stellar binarity, rotation, and metallicity spread yields an eMSTO of ∼340 Myr. Such an age difference points to the existence within the cluster of stellar populations with different ages.

scholarly journals The Rotation of Low-Mass Pre-Main-Sequence Stars

2004 ◽  
Vol 215 ◽  
pp. 113-122 ◽  
Author(s):  
Robert D. Mathieu
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Rotation Period ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Rotation Periods ◽  
Order Of Magnitude ◽  
Critical Velocities

Major photometric monitoring campaigns of star-forming regions in the past decade have provided rich rotation period distributions of pre-main-sequence stars. The rotation periods span more than an order of magnitude in period, with most falling between 1 and 10 days. Thus the broad rotation period distributions found in 100 Myr clusters are already established by an age of 1 Myr. The most rapidly rotating stars are within a factor of 2-3 of their critical velocities; if angular momentum is conserved as they evolve to the ZAMS, these stars may come to exceed their critical velocities. Extensive efforts have been made to find connections between stellar rotation and the presence of protostellar disks; at best only a weak correlation has been found in the largest samples. Magnetic disk-locking is a theoretically attractive mechanism for angular momentum evolution of young stars, but the links between theoretical predictions and observational evidence remain ambiguous. Detailed observational and theoretical studies of the magnetospheric environments will provide better insight into the processes of pre-main-sequence stellar angular momentum evolution.

scholarly journals Dynamo and Fossil Magnetic Field in Young Stars

1993 ◽  
Vol 157 ◽  
pp. 171-175
Author(s):  
A.E. Dudorov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Main Sequence ◽  
Young Stars ◽  
Small Scale ◽  
Scaling Relations ◽  
Main Sequence Stars ◽  
Nonlinear Stabilization ◽  
Turbulent Dynamo ◽  
Solar Type

The theory of fossil magnetic fields shows that new born stars may have internal magnetic fields of more than 1 million gauss. Convection inside young solar type stars will tangle any strong fossil magnetic field. The small scale magnetic field rises to the surface and determines the young stars activity attenuating with their age. When a fossil field is diminished a turbulent dynamo may begin to work in the condition of nonlinear stabilization. The scaling relations for the turbulent αω dynamo show that the strength of the generated “fossil” magnetic field inside the main sequence stars is stabilized on the level one tenth — 10 millions gauss, depending on the mass of the stars.

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