scholarly journals The Flare and Warp of the Young Stellar Disk Traced with LAMOST DR5 OB-type Stars

2021 ◽  
Vol 922 (1) ◽  
pp. 80
Author(s):  
Yang Yu ◽  
Hai-Feng Wang ◽  
Wen-Yuan Cui ◽  
Lin-Lin Li ◽  
Chao Liu ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Scale Height ◽  
Stellar Disk ◽  
Spatial Density ◽  
Galactocentric Distance ◽  
Secular Evolution ◽  
The North ◽  
Red Giant ◽  
Almost All ◽  
North And South

Abstract We present an analysis of the spatial density structure for the outer disk from 8–14 kpc with the LAMOST DR5 13,534 OB-type stars and observe similar flaring on the north and south sides of the disk, implying that the flaring structure is symmetrical about the Galactic plane, for which the scale height at different Galactocentric distances is from 0.14 to 0.5 kpc. By using the average slope to characterize the flaring strength, we find that the thickness of the OB stellar disk is similar but that flaring is slightly stronger compared to the thin disk as traced by red giant branch stars, possibly implying that secular evolution is not the main contributor to the flaring but rather perturbation scenarios such as interactions with passing dwarf galaxies could be possible. When comparing the scale height of the OB stellar disk on the north and south sides with the gas disk, the former one is slightly thicker than the latter one by ≈33 and 9 pc, meaning that one could tentatively use young OB-type stars to trace the gas properties. Meanwhile, we determine that the radial scale length of the young OB stellar disk is 1.17 ± 0.05 kpc, which is shorter than that of the gas disk, confirming that the gas disk is more extended than the stellar disk. What is more, by considering the midplane displacements (Z 0) in our density model we find that almost all values of Z 0 are within 100 pc, with an increasing trend as Galactocentric distance increases.

scholarly journals The kinematics of the white dwarf population from the SDSS DR12

2017 ◽  
Vol 12 (S330) ◽  
pp. 201-202
Author(s):  
B. Anguiano ◽  
A. Rebassa-Mansergas ◽  
E. García-Berro ◽  
S. Torres ◽  
K. Freeman ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Galactic Plane ◽  
Three Dimensional ◽  
Radial Distance ◽  
Space Velocity ◽  
Galactic Disc ◽  
Present Sample ◽  
Secular Evolution ◽  
The North

AbstractWe use the Sloan Digital Sky Survey Data Release 12, which is the largest available white dwarf catalog to date, to study the evolution of the kinematical properties of the population of white dwarfs in the Galactic disc. We derive masses, ages, photometric distances and radial velocities for all white dwarfs with hydrogen-rich atmospheres. For those stars for which proper motions from the USNO-B1 catalog are available the true three-dimensional components of the stellar space velocity are obtained. This subset of the original sample comprises 20,247 objects, making it the largest sample of white dwarfs with measured three-dimensional velocities. Furthermore, the volume probed by our sample is large, allowing us to obtain relevant kinematical information. In particular, our sample extends from a Galactocentric radial distance RG = 7.8 kpc to 9.3 kpc, and vertical distances from the Galactic plane ranging from Z = −0.5 kpc to 0.5 kpc. We examine the mean components of the stellar three-dimensional velocities, as well as their dispersions with respect to the Galactocentric and vertical distances. We confirm the existence of a mean Galactocentric radial velocity gradient, ∂〈VR〉/∂RG = −3 ± 5 km s−1 kpc−1. We also confirm North-South differences in 〈Vz〉. Specifically, we find that white dwarfs with Z > 0 (in the North Galactic hemisphere) have 〈Vz〉 < 0, while the reverse is true for white dwarfs with Z < 0. The age-velocity dispersion relation derived from the present sample indicates that the Galactic population of white dwarfs may have experienced an additional source of heating, which adds to the secular evolution of the Galactic disc.

Potential Distribution of Fall Armyworm in Africa and Beyond, Considering Climate Change and Irrigation Patterns

2021 ◽  
Author(s):  
Bipana Paudel Timilsena ◽  
Saliou Niassy ◽  
Emily Kimathi ◽  
Elfatih. M. Abdel-Rahman ◽  
Irmgard Seidl-Adams ◽  
...  
Keyword(s):  
Central Africa ◽  
Fall Armyworm ◽  
Large Area ◽  
Western Africa ◽  
The North ◽  
Management Interventions ◽  
Population Establishment ◽  
Almost All ◽  
North And South ◽  
Irrigation Patterns

Abstract The fall armyworm, Spodoptera frugiperda (FAW), first invaded Africa in 2016 and has since become established in many areas across the continent where it poses a serious threat to food and nutrition security. We re-parameterized the existing CLIMEX model to assess the FAW global invasion threat, emphasizing the risk of transient and permanent population establishment in Africa under current and predicted future climates, considering irrigation patterns. FAW can establish itself in almost all countries in eastern and central Africa and a large part of western Africa under the current climate. Climatic barriers, such as heat and dry stresses, may limit the spread of FAW to North and South Africa. Future predictions suggest that FAW invasive range will retract from both northern and southern regions towards the equator. However, a large area in eastern and central Africa is predicted to have an optimal climate for FAW persistence. These areas will serve as FAW ‘hotspots’ from where it may migrate to the north and south during winter seasons and then pose an economic threat. Our projections can be used to identify countries at risk for permanent and transient FAW-population establishment and inform timely integrated pest management interventions under present and future climate in Africa.

scholarly journals Gaia kinematics reveal a complex lopsided and twisted Galactic disc warp

2019 ◽  
Vol 627 ◽  
pp. A150 ◽  
Author(s):  
M. Romero-Gómez ◽  
C. Mateu ◽  
L. Aguilar ◽  
F. Figueras ◽  
A. Castro-Ginard
Keyword(s):  
Spatial Data ◽  
Large Scale ◽  
Galactic Plane ◽  
Proper Motions ◽  
Galactocentric Distance ◽  
Bending Mode ◽  
Data Release ◽  
Kinematic Models ◽  
Red Giant ◽  
Galactic Warp

Context. There are few warp kinematic models of the Galaxy able to characterise both structure and kinematics, since these require high accuracy at large distances. These models are necessary to shed light on the lopsidedness of the warp and the twisting of the line-of-nodes of the stellar warp already seen in gas and dust. Aims. We use the vertical information coming from the Gaia Data Release 2 astrometric data up to G = 20 mag to characterise the structure of the Galactic warp, the related vertical motions, and the dependency of Galactic warp on age. Methods. We analyse two populations up to Galactocentric distances of 16 kpc: a young bright sample mainly formed by OB stars and an older one of red giant branch (RGB) stars. We use two methods (the pole count maps of great circle bands and Galactic longitude – proper motion in latitude lines) based on the Gaia observables, together with 2D projections of the positions and proper motions in the Galactic plane. Results. This work confirms the age dependency of the Galactic warp, both in position and kinematics, the height of the Galactic warp being of the order of 0.2 kpc for the OB sample and 1.0 kpc for the RGB at a Galactocentric distance of 14 kpc. Both methods find that the onset radius of the warp is 12 ∼ 13 kpc for the OB sample and 10 ∼ 11 kpc for the RGB. From the RGB sample, we find from Galactocentric distances larger than 10 kpc that the line-of-nodes twists away from the Sun-anticentre line towards Galactic azimuths ≈180−200° increasing with radius, though possibly influenced by extinction. Also, the RGB sample reveals a slightly lopsided stellar warp with ≈250 pc difference between the up and down sides. The line of maximum of proper motions in latitude is systematically offset from the line-of-nodes estimated from the spatial data, which our warp models predict as a kinematic signature of lopsidedness. We also show a prominent wave-like pattern of a bending mode different in the OB and RGB samples. Both positions and kinematics also reveal substructures that might not be related to the large-scale Galactic warp or to the bending mode. Conclusions. Gaia Data Release 2 data reveals a high degree of complexity in terms of both position and velocity that triggers the need for complex kinematic models flexible enough to combine both wave-like patterns and an S-shaped lopsided warp.

scholarly journals Determinate pigeon pea [Cajanus cajan (L) Millsp] genotypes on the north and south coasts of Puerto Rico

1969 ◽  
Vol 72 (4) ◽  
pp. 545-556
Author(s):  
Abad Morales ◽  
Brunilda Luciano ◽  
Francisco H. Ortiz ◽  
Nabor Mendoza
Keyword(s):  
Cajanus Cajan ◽  
Seed Weight ◽  
Pigeon Pea ◽  
Date Seed ◽  
The North ◽  
Agricultural Experiment ◽  
Almost All ◽  
North And South ◽  
Number Of Seeds ◽  
Better Than

Seven experiments were established at the Juana Díaz and Isabela agricultural experiment substations to evaluate the performance of determinate pigeon pea [Cajanus cajan (L.) Millsp] genotypes. Significant differences were found for yield, height, flowering date, seed weight and number of seeds per pod in almost all the experiments. Many genotypes performed better than the commercial cultivar 2B-Bushy used as check.

Kinematics of the Milky Way Thick disk in solar neighborhood

2021 ◽  
Author(s):  
K. Vieira ◽  
V. Korchagin ◽  
A. Lutsenko
Keyword(s):  
Milky Way ◽  
Galactic Plane ◽  
Thick Disk ◽  
Solar Neighborhood ◽  
Stellar Disk ◽  
The Sun ◽  
Complete Sample ◽  
Two Component ◽  
Thick Disks ◽  
Red Giant

Using GAIA EDR3 catalog, we present the detailed analysis of the two-component Milky Way stellar disk in the solar neighborhood. To determine the kinematical properties of the thin and of the Thick disks, we select the complete sample of about 278,000 evolved red giant branch (RGB) stars distributed in the cylinder of 1 kpc radius and 0.5 kpc height centered at the Sun. We measured the following mean velocities and dispersions for the thin and the Thick disks, respectively: [Formula: see text][Formula: see text]km s[Formula: see text] with [Formula: see text][Formula: see text]km s[Formula: see text], and [Formula: see text][Formula: see text]km s[Formula: see text] with [Formula: see text][Formula: see text]km s[Formula: see text]. Errors in mean velocities and dispersions are all less than 1[Formula: see text]km s[Formula: see text]. Same values were computed on much smaller subsamples of our Gaia data with RAVE DR5 [Fe/H] values, from which a metallicity selection was added. Results are basically the same. We find that up to 500 pc height above/below the galactic plane, Thick disk stars comprise about half the stars of the disk. We also find evidence of a substructure in [Formula: see text] versus [Formula: see text] in the thick disk population mostly that would give support to the accretion scenario for the formation of the thick disk.

scholarly journals Studies of 0-F5 stars at the Galactic poles

1985 ◽  
Vol 106 ◽  
pp. 163-164
Author(s):  
R. W. Hilditch ◽  
A.D. Mcfadzean ◽  
Graham Hill ◽  
J. V. Barnes
Keyword(s):  
Chemical Evolution ◽  
Galactic Plane ◽  
Early Type ◽  
Population Groups ◽  
The North ◽  
The Galaxy ◽  
Early Type Stars ◽  
Velocity Dispersions ◽  
North And South ◽  
Kinematic Properties

We report progress on a spectroscopic and photometric programme devoted to the study of the dynamics of O-F5 stars within 15° of the North and South Galactic Poles. The aims of the programme are to test dynamical and chemical evolution models of the Galaxy by establishing velocity dispersions as a function of z-distance for stars of different population groups. We are also able to investigate the interstellar reddening at the poles and the kinematic properties of apparently normal early-type stars found more than 1 kpc from the galactic plane.

scholarly journals Mean Chemical Abundance of the F Stars as a Function of Distance from the Galactic Plane

1977 ◽  
Vol 4 (2) ◽  
pp. 51-52
Author(s):  
A. Blaauw
Keyword(s):  
Galactic Plane ◽  
Photometric System ◽  
Chemical Abundance ◽  
The North ◽  
Polar Caps ◽  
Metal Abundance ◽  
The Mean ◽  
F Stars ◽  
North And South ◽  
European Regional

At the Tbilisi European Regional Meeting 1975, I reported on results of uvby, Hß photometry of F-type stars in the north and south galactic polar caps (Blaauw and Garmany, 1976), based on stars in the McCormick proper motion fields between latitudes 60° and the poles. A relation was shown to exist between the quantity Am. as determined in this photometric system, and the distance, z, from the galactic plane; Δm1. being a measure of the metal abundance in these stars. The spectral range we deal with is defined by b-y = 0.25 to 0.40, corresponding with F0 to G2. It was found that, from the solar neighbourhood near z = 0, to z = 700 pc, the mean relative metal abundance M/H decreases by a factor of about one third.

scholarly journals Morphology of various strains of the trypanosome causing disease in man in Nyasaland.—The mzimba strain

1913 ◽  
Vol 87 (592) ◽  
pp. 26-35 ◽  
Keyword(s):  
Central Africa ◽  
Medical Officer ◽  
Sleeping Sickness ◽  
Separate Species ◽  
North East ◽  
The North ◽  
Western Shore ◽  
Trade Route ◽  
Almost All ◽  
North And South

Up to the present time it has usually been considered that almost all the cases of Human trypanosome disease in man in Nyasaland have been confined to a small area. This, the so-called Sleeping-Sickness District, has been described in a former paper, but it may be repeated here that it is the part of the “fly-country” lying along the western shore of Lake Nyasa, between S. lat. 13° 20' and 13° 50', and extending some twenty miles inland. Through the centre of this area a road runs from Domira Bay on the Lake into North-East Rhodesia. This road, until lately, was a principal highway between the coast and Central Africa. Dr. Aylmer May, the Principal Medical Officer of North-East Rhodesia, who lately visited Kasu, informed the Commission that it was along this trade-route that all the North-East Rhodesian, cases of Human trypanosome disease have occurred. It is said that some 25,000 native porters passed along this road every year, and as they entered a Glossina palpalis area at the Congo end of their journey, it seemed at first natural to suspect that the disease was true Sleeping Sickness, and had spread from west to east along this trade-route. This suspicion was shown to be groundless by the discovery that the parasite causing the disease in North-East Rhodesia and Nyasaland is not Trypanosoma gambiense , but a distinct and separate species giving rise to a totally different disease. The question then arose as to whether this was an imported or indigenous disease. It has, therefore, been one of the objects of this Commission to determine whether the trypanosome causing Human trypanosome disease in Nyasaland is restricted to the game and “fly” of the Proclaimed Area, or if it extends to the north and south along the “fly-belt.” If it is found to extend over all the “fly-area” in Nyasaland, then the disease is probably native to the soil and not an importation from Tanganyika or the Congo. But it will be well at this point to lay down definitely the various opinions or theories at issue. These are three in number.

scholarly journals Potential distribution of fall armyworm in Africa and beyond, considering climate change and irrigation patterns

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Bipana Paudel Timilsena ◽  
Saliou Niassy ◽  
Emily Kimathi ◽  
Elfatih M. Abdel-Rahman ◽  
Irmgard Seidl-Adams ◽  
...  
Keyword(s):  
Central Africa ◽  
Fall Armyworm ◽  
Large Area ◽  
Western Africa ◽  
The North ◽  
Management Interventions ◽  
Population Establishment ◽  
Almost All ◽  
North And South ◽  
Irrigation Patterns

AbstractThe fall armyworm, Spodoptera frugiperda (FAW), first invaded Africa in 2016 and has since become established in many areas across the continent where it poses a serious threat to food and nutrition security. We re-parameterized the existing CLIMEX model to assess the FAW global invasion threat, emphasizing the risk of transient and permanent population establishment in Africa under current and projected future climates, considering irrigation patterns. FAW can establish itself in almost all countries in eastern and central Africa and a large part of western Africa under the current climate. Climatic barriers, such as heat and dry stresses, may limit the spread of FAW to North and South Africa. Future projections suggest that FAW invasive range will retract from both northern and southern regions towards the equator. However, a large area in eastern and central Africa is projected to have an optimal climate for FAW persistence. These areas will serve as FAW ‘hotspots’ from where it may migrate to the north and south during favorable seasons and then pose an economic threat. Our projections can be used to identify countries at risk for permanent and transient FAW-population establishment and inform timely integrated pest management interventions under present and future climate in Africa.

The Orientation of Middle American Sites

1945 ◽  
Vol 11 (2) ◽  
pp. 118-118 ◽  
Author(s):  
Kenneth Macoowan
Keyword(s):  
American Culture ◽  
General Pattern ◽  
Common Axis ◽  
The North ◽  
The Individual ◽  
Almost All ◽  
South Axis ◽  
The City ◽  
North And South ◽  
Of Greece

One of the first aspects of Middle American culture which strikes an amateur as interesting and possibly significant is the ordered arrangement of the buildings in almost all sites. Like those of Egypt—and unlike those of Greece and Rome —the sites seem to have been planned on a large pattern. The individual buildings are arranged according to a scheme which gives them space and which orients them on a common axis. They are not dropped in helter-skelter, crowded cheek-by-jowl, and set at odd angles to one another. Further, the city plans of Middle America seemollow fhe another and larger pattern. This is the pattern of the north and south axis of each site and each building. This orientation almost invariably follows one of three schemes. I t is sometimes true north, sometimes about 7 degrees east of north, sometimes about 17 degrees east of north, but practically never west of north. There are some sites which have no general pattern, and therefore no orientation.

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