scholarly journals Astrometric Plate Reduction with Orthogonal Functions and Milliarcseconds Accuracy in Deep Proper Motion Surveys

1995 ◽  
Vol 166 ◽  
pp. 368-368
Author(s):  
Devendra Ojha ◽  
Olivier Bienaymé
Keyword(s):  
Galactic Plane ◽  
Structural Parameters ◽  
Thin Disk ◽  
Scale Height ◽  
Thick Disk ◽  
Sample Survey ◽  
Time Base ◽  
List Type ◽  
Proper Motions ◽  
Velocity Dispersions

We have been doing a sample survey in UBV photometry and proper motions as part of an investigation of galactic structure and evolution. The 3 fields in the direction of galactic anticentre (l = 167°, b = 47°), centre (l = 3°, b = 47°) and antirotation (l = 278°, b = 47°) have been surveyed. The high astrometric quality of the MAMA machine (CAI, Paris) gives access to micronic accuracy (leading to < 2 mas per year) on proper motions with a 35 years time base. The kinematical distribution of F and G–type stars have been probed to distances up to 2.5 kpc above the galactic plane. We have derived the constrain on the structural parameters of the thin and thick disk components of the Galaxy (Ojha et al. 1994abc): • The scale lengths of the thin and thick disks are found to be 2.6±0.1 and 3.3±0.5 kpc, respectively. The density laws for stars with 3.5≤MV≤5 as a function of distance above the plane follow a single exponential with scale height of ∼ 260 pc (thin disk) and a second exponential with scale height of ∼ 800 pc (thick disk) with a local normalization of 5–6% of the disk.• The thin disk population was found with (〈 U+W〉, 〈V〉) = (1±4, −14±2) km/s and velocity dispersions (σU+W, σV) = (35±2, 30±1) km/s. The thick disk population was found to have a rotational velocity of Vrot = 177 km/s and velocity dispersions (σU, σV, σW) = (67,51,42) km/s. No dependence with r and z distances was found in the asymmetric drift measurements of the thick disk population.

scholarly journals The Scatter of Metallicities of Stars in the Solar Neighbourhood

1996 ◽  
Vol 169 ◽  
pp. 431-432 ◽  
Author(s):  
B. Fuchs ◽  
C. Dettbarn ◽  
R. Wielen
Keyword(s):  
Main Sequence ◽  
Thin Disk ◽  
Thick Disk ◽  
Solar Neighbourhood ◽  
Data Sets ◽  
Main Sequence Stars ◽  
The Third ◽  
Nearby Stars ◽  
Velocity Dispersions

It is well known that the velocity dispersions of the stars in the solar neighbourhood increase with their ages (Wielen 1977). In Fig.1 we show |W| weighted velocity dispersions (cf. Wielen 1977) of the stars in the Third Catalog of Nearby Stars (Gliese and Jahreiß 1994). Open symbols indicate main sequence stars and crosses indicate McCormick stars, a kinematically unbiased subset of the CNS3, respectively, whereas the filled symbols are the Edvardsson et al. (1993) data. Stars older than 14 Gyr are not shown because they are probably thick disk stars (Freeman 1991). We have assumed a maximum age of the old thin disk stars of 12 Gyr as suggested by the Edvardsson et al. data. As can be seen from Fig.1 both data sets fit ideally together. The solid line indicates a σ ∝ τ1/2 law.

scholarly journals Impacts of Radial Mixing on the Galactic Thick and Thin Disks

2017 ◽  
Vol 13 (S334) ◽  
pp. 132-135
Author(s):  
Daisuke Kawata
Keyword(s):  
Thin Disk ◽  
Scale Height ◽  
Thick Disk ◽  
The Other ◽  
Galactic Disks ◽  
Spiral Arms ◽  
Other Hand ◽  
Initial Scale ◽  
Thin Disks ◽  
Metallicity Distribution

AbstractUsing N-body simulations of the Galactic disks, we qualitatively study how the metallicity distributions of the thick and thin disk stars are modified by radial mixing induced by the bar and spiral arms. We show that radial mixing drives a positive vertical metallicity gradient in the mono-age disk population whose initial scale-height is constant and initial radial metallicity gradient is tight and negative. On the other hand, if the initial disk is flaring, with scale-height increasing with galactocentric radius, radial mixing leads to a negative vertical metallicity gradient, which is consistent with the current observed trend. We also discuss impacts of radial mixing on the metallicity distribution of the thick disk stars. By matching the metallicity distribution of N-body models to the SDSS/APOGEE data, we argue that the progenitor of the Milky Way’s thick disk should not have a steep negative metallicity gradient.

scholarly journals Structure and Kinematical Properties of the Galaxy at Intermediate Galactic Latitudes

1998 ◽  
Vol 179 ◽  
pp. 221-222
Author(s):  
D. K. Ojha ◽  
O. Bienaymé ◽  
A. C. Robin
Keyword(s):  
Vertical Structure ◽  
Local Density ◽  
Thick Disk ◽  
Sample Survey ◽  
Galactic Centre ◽  
Proper Motions ◽  
Perfect Agreement ◽  
The Galaxy ◽  
Centre Region ◽  
Disk Component

We have carried out a sample survey in UBVR photometry and proper motions in various directions in the Galaxy. Three fields in the direction of galactic anticentre, centre, and antirotation have been surveyed. Using our new data together with wide-area surveys in other fields available to date, we discuss the radial and vertical structure of the Galaxy. Our results confirm that the thick disk population is distinct from other populations based on their kinematical and spatial distribution. The most probable value of scale height for the thick disk component is determined to be hz≃760±50 pc and a local density of ≃7.4+2.5−1.5% relative to the thin disk. The ratio of the number of thick disk stars in our galactic centre region to that in anticentre region yield hR≃3±1 kpc for the scale length of thick disk. These values are in perfect agreement with the recent determination given by Robin et al. (1996).

scholarly journals Vertical abundances variation in the galaxy: The case of PN

1997 ◽  
Vol 180 ◽  
pp. 406-406
Author(s):  
F. Cuisinier ◽  
J. Köppen
Keyword(s):  
Vertical Structure ◽  
Velocity Dispersion ◽  
Thin Disk ◽  
Scale Height ◽  
Young Stars ◽  
Low Velocity ◽  
The Galaxy ◽  
Different Populations ◽  
Velocity Dispersions

The vertical structure of the Galaxy is stratified in different populations. Gas and young stars have a low velocity dispersion (about 10 km/s) and thus are confined in a very thin disk (100 pc of scale height). Old stars have larger velocity dispersions, and are thus encountered up to a few kpc.

scholarly journals Exploration of Galactic Structures beyond the Sun toward the anti-center of the Milky Way

2013 ◽  
Vol 9 (S298) ◽  
pp. 450-450
Author(s):  
Yan Xu ◽  
Heidi Newberg
Keyword(s):  
Milky Way ◽  
Galactic Plane ◽  
Wave Structure ◽  
Thin Disk ◽  
Thick Disk ◽  
The Sun ◽  
The South ◽  
The North ◽  
Metallicity Distribution ◽  
Kinematic Distribution

AbstractWe map the stellar distribution on Hess diagram in the Anti-Center roughly in the boxes 130<l<230, −30<b<−10 and 10<b<30. There are ‘extra components’ associated with the anti-center structures of figure 1 of Newberg et al. (2002). The turnoff point of the structure in the North sky is at 16m.5 and the turnoff point in the South is at 17m.5. In our work, these structures can be found in all of the longitude in our box that can't be explained by standard thin or thick disk models. The distance of the North structure is about 2 kpc (we call it the North near structure) and the galactic height is about 0.7 kpc, the distance of the South structure is about 4 – 6 kpc (we call it the South middle structure). The Vgsr distribution of stars selected along the North near structure has a kinematic distribution similar to that of thick disk stars. But the metallicities of these stars are quite similar to the metallicity distribution of thin disk stars. We try to explain these structures with wave structure of the Galactic plane.

scholarly journals Kinematics of Disk Stars in the Solar Neighbourhood

1998 ◽  
Vol 11 (1) ◽  
pp. 574-574
Author(s):  
A.E. Gómez ◽  
S. Grenier ◽  
S. Udry ◽  
M. Haywood ◽  
V. Sabas ◽  
...  
Keyword(s):  
Dispersion Relation ◽  
Radial Velocity ◽  
Velocity Dispersion ◽  
Tangential Velocity ◽  
Thin Disk ◽  
The Other ◽  
Proper Motions ◽  
Velocity Data ◽  
Kinematic Data ◽  
Radial Velocity Data

Using Hipparcos parallaxes and proper motions together with radial velocity data and individual ages estimated from isochones, the velocity ellipsoid has been determined as a function of age. On the basis of the available kinematic data two different samples were considered: a first one (7789 stars) for which only tangential velocities were calculated and a second one containing 3104 stars with available U, V and W velocity components and total velocities ≤ 65 km.s-1. The main conclusions are: -Mixing is not complete at about 0.8-1 Gyr. -The shape of the velocity ellipsoid changes with time getting rounder from σu/σv/σ-w = 1/0.63/0.42 ± 0.04 at about 1 Gyr to1/0.7/0.62 ±0.04 at 4-5 Gyr. -The age-velocity-dispersion relation (from the sample with kinematical selection) rises to a maximum, thereafter remaining roughly constant; there is no dynamically significant evolution of the disk after about 4-5 Gyr. -Among the stars with solar metallicities and log(age) > 9.8 two groups are identified: one has typical thin disk characteristics, the other is older than 10 Gyr and lags the LSR at about 40 km.s-1 . -The variation of the tangential velocity with age(without selection on the tangential velocity) shows a discontinuity at about 10 Gyr, which may be attributed to stars typically of the thick disk populations for ages > 10 Gyr.

Design and Evaluation of the Key Units in a Rapeseed Direct Seeder Integrated with Plowing-Rotating Combined Tillage

2021 ◽  
Vol 37 (6) ◽  
pp. 1005-1014
Author(s):  
Guoliang Wei ◽  
Qingsong Zhang ◽  
Biao Wang ◽  
QingXi Liao
Keyword(s):  
Field Experiments ◽  
Optimal Parameter ◽  
Structural Parameters ◽  
List Type ◽  
Oil Crops ◽  
Orthogonal Experiments ◽  
Heavy Soil ◽  
Tillage Depth ◽  
Working Parameters ◽  
Orthogonal Field

HighlightsThe seeder combined the plowing and rotating tillage to overcome the heavy soil and a large amount of straws.The plow could lift and turn the soil and straw before rotary tillage.The optimal working parameters of the seeder were obtained by orthogonal field experiments.Abstract. Rapeseed, one of the most important oil crops in China, is mainly planted in the mid-lower reaches of the Yangtze River. However, limited by the special long-term rice-rapeseed rotation, rotary tillage is applied in most of the planted areas apply instead of plow tillage, leading to a shallow arable layer. On the other hand, maintaining a high-quality seedbed for rapeseed becomes a challenge because a large amount of straw remains buried in the soil. As a solution, a rapeseed direct seeder that combines plow tillage and rotary tillage was designed. The structure of the plowing unit, whose key components were a lifting-turning plow and symmetrical plow, was analyzed based on the forming principle of the plow. Furthermore, a mechanical soil throwing model of the rotary tillage blade was built to determine the structural parameters. Then, the interaction between the rotary tillage unit and the lift-turning plow was analyzed. Finally, the performance and optimal parameters were evaluated by orthogonal field experiments. The seedbed after the operations indicated that the seeder could achieve the function of turning the soil and straw first and then rotating the soil with good passability, mixing the straw and the soil, flattening the surface of the seed bed, and stabilizing the tillage depth. Orthogonal experiments showed that the optimal working parameters of the seeder were as follows: the tillage depth was 180 mm, the equipment forward speed was 2.1 km/h, and the speed of the rotary tillage blade was 250 r/min. Under the optimal parameter combination, the power consumption of the seeder, the thickness of the tillage layer, the crop residue burial efficiency, the soil breakage efficiency, and the flatness of the seed bed surface were 30.48 kW, 231 mm, 90.88%, 93.26%, and 21.15 mm, respectively. The working performance of the seeder could meet the tillage requirements of rapeseed planting. Keywords: Direct seeder, Evaluation, Plow, Plowing-rotating combined tillage, Rapeseed.

scholarly journals Phylogeny of the Milky Way’s inner disk and bulge populations: Implications for gas accretion, (the lack of) inside-out thick disk formation, and quenching

2018 ◽  
Vol 618 ◽  
pp. A78 ◽  
Author(s):  
Misha Haywood ◽  
Paola Di Matteo ◽  
Matthew Lehnert ◽  
Owain Snaith ◽  
Francesca Fragkoudi ◽  
...  
Keyword(s):  
Star Formation ◽  
Accretion Rate ◽  
Large Fraction ◽  
Formation Rate ◽  
Thin Disk ◽  
Thick Disk ◽  
Star Formation History ◽  
Two Phase ◽  
Disk Formation ◽  
Gas Accretion

We show that the bulge and the disk of the Milky Way (MW) at R ≲ 7 kpc are well described by a unique chemical evolution and a two-phase star formation history (SFH). We argue that the populations within this inner disk, not the entire disk, are the same, and that the outer Lindblad resonance (OLR) of the bar plays a key role in explaining this uniformity. In our model of a two-phase SFH, the metallicity, [α/Fe] and [α/H] distributions, and age-metallicity relation are all compatible with the observations of both the inner disk and bulge. The dip at [Fe/H] ∼ 0 dex seen in the metallicity distributions of the bulge and inner disk reflects the quenching episode in the SFH of the inner MW at age ∼8 Gyr, and the common evolution of the bulge and inner disk stars. Our results for the inner region of the MW, R ≲ 7 kpc, are consistent with a rapid build-up of a large fraction of its total baryonic mass within a few billion years. We show that at z ≤ 1.5, when the MW was starting to quench, transitioning between the end of the α-enhanced thick disk formation to the start of the thin disk, and yet was still gas rich, the gas accretion rate could not have been significant. The [α/Fe] abundance ratio before and after this quenching phase would be different, which is not observed. The decrease in the accretion rate and gas fraction at z ≤ 2 was necessary to stabilize the disk allowing the transition from thick to thin disks, and for beginning the secular phase of the MW’s evolution. This possibly permitted a stellar bar to develop which we hypothesize is responsible for quenching the star formation. The present analysis suggests that MW history, and in particular at the transition from the thick to the thin disk – the epoch of the quenching – must have been driven by a decrease of the star formation efficiency. We argue that the decline in the intensity of gas accretion, the formation of the bar, and the quenching of the star formation rate (SFR) at the same epoch may be causally connected thus explaining their temporal coincidence. Assuming that about 20% of the gas reservoir in which metals are diluted is molecular, we show that our model is well positioned on the Schmidt-Kennicutt relation at all times.

scholarly journals Maser, infrared and optical emission for late-type stars in the Galactic plane

2017 ◽  
Vol 13 (S336) ◽  
pp. 184-186
Author(s):  
L. H. Quiroga-Nuñez ◽  
H. J. van Langevelde ◽  
L. O. Sjouwerman ◽  
Y. M. Pihlström ◽  
M. J. Reid ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Population Distribution ◽  
Massive Stars ◽  
Optical Emission ◽  
Proper Motions ◽  
Late Type ◽  
Intrinsic Properties ◽  
Radio Observations ◽  
Evolved Stars

AbstractRadio astrometric campaigns using VLBI have provided distances and proper motions for masers associated with young massive stars (BeSSeL survey). The ongoing BAaDE project plans to obtain astrometric information of SiO maser stars located in the inner Galaxy. These stars are associated with evolved, mass-losing stars. By overlapping optical (Gaia), infrared (2MASS, MSX and WISE) and radio (BAaDE) sources, we expect to obtain important clues on the intrinsic properties and population distribution of late-type stars. Moreover, a comparison of the Galactic parameters obtained with Gaia and VLBI can be done using radio observations on different targets: young massive stars (BeSSeL) and evolved stars (BAaDE).

Chemo-dynamical signatures in simulated Milky Way-like galaxies

2017 ◽  
Vol 12 (S330) ◽  
pp. 263-264
Author(s):  
Alessandro Spagna ◽  
Anna Curir ◽  
Marco Giammaria ◽  
Mario G. Lattanzi ◽  
Giuseppe Murante ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Plane ◽  
Dynamical Evolution ◽  
Thin Disk ◽  
Disk Galaxy ◽  
Radial Gradient ◽  
Heating Mechanism ◽  
Disk Evolution ◽  
Inside Out

AbstractWe have investigated the chemo-dynamical evolution of a Milky Way-like disk galaxy, AqC4, produced by a cosmological simulation integrating a sub-resolution ISM model. We evidence a global inside-out and upside-down disk evolution, that is consistent with a scenario where the “thin disk” stars are formed from the accreted gas close to the galactic plane, while the older “thick disk” stars are originated in situ at higher heights. Also, the bar appears the most effective heating mechanism in the inner disk. Finally, no significant metallicity-rotation correlation has been observed, in spite of the presence of a negative [Fe/H] radial gradient.

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