137 research outputs found
Evolution of the Velocity Ellipsoids in the Thin Disk of the Galaxy and the Radial Migration of Stars
Data from the revised Geneva--Copenhagen catalog are used to study the
influence of radial migration of stars on the age dependences of parameters of
the velocity ellipsoids for nearby stars in the thin disk of the Galaxy,
assuming that the mean radii of the stellar orbits remain constant. It is
demonstrated that precisely the radial migration of stars, together with the
negative metallicity gradient in the thin disk,are responsible for the observed
negative correlation between the metallicities and angular momenta of nearby
stars, while the angular momenta of stars that were born at the same
Galactocentric distances do not depend on either age or metallicity. (abridged)Comment: Astronomy Reports, Vol. 86 No. 9, P.1117-1126 (2009
The OSACA Database and a Kinematic Analysis of Stars in the Solar Neighborhood
We transformed radial velocities compiled from more than 1400 published
sources, including the Geneva--Copenhagen survey of the solar neighborhood
(CORAVEL-CfA), into a uniform system based on the radial velocities of 854
standard stars in our list. This enabled us to calculate the average weighted
radial velocities for more than 25~000 HIPPARCOS stars located in the local
Galactic spiral arm (Orion arm) with a median error of +-1 km/s. We use these
radial velocities together with the stars' coordinates, parallaxes, and proper
motions to determine their Galactic coordinates and space velocities. These
quantities, along with other parameters of the stars, are available from the
continuously updated Orion Spiral Arm CAtalogue (OSACA) and the associated
database. We perform a kinematic analysis of the stars by applying an
Ogorodnikov-Milne model to the OSACA data. The kinematics of the nearest single
and multiple main-sequence stars differ substantially. We used distant
(r\approx 0.2 kpc) stars of mixed spectral composition to estimate the angular
velocity of the Galactic rotation -25.7+-1.2 km/s/kpc, and the vertex
deviation,l=13+-2 degrees, and detect a negative K effect. This negative K
effect is most conspicuous in the motion of A0-A5 giants, and is equal to
K=-13.1+-2.0 km/s/kpc.Comment: 16 pages, 8 figure
Kinematics of Tycho-2 Red Giant Clump Stars
Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95 633
red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort
constants have been found: A = 15.9+-0.2 km/s/kpc and B = -12.0+-0.2 km/s/kpc.
Using 3632 RGC stars with known proper motions, radial velocities, and
photometric distances, we show that, apart from the star centroid velocity
components relative to the Sun, only the model parameters that describe the
stellar motions in the XY plane differ significantly from zero. We have studied
the contraction (a negative K-effect) of the system of RGC stars as a function
of their heliocentric distance and elevation above the Galactic plane. For a
sample of distant (500--1000 pc) RGC stars located near the Galactic plane
(|Z|<200 pc) with an average distance of d=0.7 kpc, the contraction velocity is
shown to be Kd= -3.5+-0.9 km/s; a noticeable vertex deviation, lxy = 9.1+-0.5
degrees, is also observed for them. For stars located well above the Galactic
plane (|Z|>=200 pc), these effects are less pronounced, Kd = -1.7+-0.5 km/s and
lxy = 4.9+-0.6 degrees. Using RGC stars, we have found a rotation around the
Galactic X axis directed toward the Galactic center with an angular velocity of
-2.5+-0.3 km/s/kpc, which we associate with the warp of the Galactic
stellar-gaseous disk.Comment: 23 pages, 7 figures, 4 table
Kinematic Control of the Inertiality of the System of Tycho-2 and UCAC2 Stellar Proper Motions
Based on the Ogorodnikov-Milne model, we analyze the proper motions of
Tycho-2 and UCAC2 stars. We have established that the model component that
describes the rotation of all stars under consideration around the Galactic y
axis differs significantly from zero at various magnitudes. We interpret this
rotation found using the most distant stars as a residual rotation of the
ICRS/Tycho-2 system relative to the inertial reference frame. For the most
distant ( pc) Tycho-2 and UCAC2 stars, the mean rotation around
the Galactic y axis has been found to be mas yr.
The proper motions of UCAC2 stars with magnitudes in the range are
shown to be distorted appreciably by the magnitude equation in
, which has the strongest effect for northern-sky stars
with a coefficient of mas yr mag. We have detected
no significant effect of the magnitude equation in the proper motions of UCAC2
stars brighter than .Comment: 15 pages, 6 figure
Galactic Rotation Parameters from Data on Open Star Clusters
Currently available data on the field of velocities Vr, Vl, Vb for open star
clusters are used to perform a kinematic analysis of various samples that
differ by heliocentric distance, age, and membership in individual structures
(the Orion, Carina--Sagittarius, and Perseus arms). Based on 375 clusters
located within 5 kpc of the Sun with ages up to 1 Gyr, we have determined the
Galactic rotation parameters
Wo =-26.0+-0.3 km/s/kpc,
W'o = 4.18+-0.17 km/s/kpc^2,
W''o=-0.45+-0.06 km/s/kpc^3, the system contraction parameter K = -2.4+-0.1
km/s/kpc, and the parameters of the kinematic center Ro =7.4+-0.3 kpc and lo =
0+-1 degrees. The Galactocentric distance Ro in the model used has been found
to depend significantly on the sample age. Thus, for example, it is 9.5+-0.7
kpc and 5.6+-0.3 kpc for the samples of young (50 Myr)
clusters, respectively. Our study of the kinematics of young open star clusters
in various spiral arms has shown that the kinematic parameters are similar to
the parameters obtained from the entire sample for the Carina-Sagittarius and
Perseus arms and differ significantly from them for the Orion arm. The
contraction effect is shown to be typical of star clusters with various ages.
It is most pronounced for clusters with a mean age of 100 Myr, with the
contraction velocity being Kr = -4.3+-1.0 km/s.Comment: 14 pages, 4 figures, 2 table
Relationship between the Velocity Ellipsoids of Galactic-Disk Stars and their Ages and Metallicities
The dependences of the velocity ellipsoids of F-G stars of the thin disk of
the Galaxy on their ages and metallicities are analyzed based on the new
version of the Geneva-Copenhagen Catalog. The age dependences of the major,
middle, and minor axes of the ellipsoids, and also of the dispersion of the
total residual veltocity, obey power laws with indices 0.25,0.29,0.32, and 0.27
(with uncertainties \pm 0.02). Due to the presence of thick-disk objects, the
analogous indices for all nearby stars are about a factor of 1.5 larger.
Attempts to explain such values are usually based on modeling relaxation
processes in the Galactic disk. With increasing age, the velocity ellipsoid
increases in size and becomes appreciably more spherical, turns toward the
direction of the Galactic center, and loses angular momentum. The shape of the
velocity ellipsoid remains far from equilibrium. With increasing metallicity,
the velocity ellipsoid for stars of mixed age increases in size, displays a
weak tendency to become more spherical, and turns toward the direction of the
Galactic center (with these changes occurring substantially more rapidly in the
transition through the metallicity [Fe/H]= -0.25). Thus, the ellipsoid changes
similarly to the way it does with age; however, with decreasing metallicity,
the rotational velocity about the Galactic center monotonically increases,
rather than decreases(!). Moreover, the power-law indices for the age
dependences of the axes depend on the metallicity, and display a maximum near
[Fe/H]=-0.1. The age dependences of all the velocity-ellipsoid parameters for
stars with equal metallicity are roughly the same. It is proposed that the
appearance of a metallicity dependence of the velocity ellipsoids for thin-disk
stars is most likely due to the radial migration of stars.Comment: 15 pages, 6 figures, accepted 2009, Astronomy Reports, Vol. 53 No. 9,
P.785-80
Kinematic Control of the Inertiality of ICRS Catalogs
We perform a kinematic analysis of the Hipparcos and TRC proper motions of
stars by using a linear Ogorodnikov-Milne model. All of the distant (r more
than 0.2 kpc) stars of the Hipparcos catalog have been found to rotate around
the Galactic y axis with an angular velocity of -0.36 +/- 0.09 mas/year. One of
the causes of this rotation may be an uncertainty in the lunisolar precession
constant adopted when constructing the ICRS. In this case? the correction to
the IAU (1976) lunisolar precession constant in longitude is shown to be -3.26
+/- 0.10 mas/yr. Based on the TRC catalog, we have determined the main Oort
constants: A = 14.9 +/- 1.0 and B = -10.8 +/- 0.3 km/s/kpc. The component of
the model that describes the rotation of all TRC stars around the Galactic y
axis is nonzero for all magnitudes, My= -0.86 +/- 0.11 mas/yr.Comment: 10 pages, 4 figures, 2 table
Kinematic Peculiarities of Gould Belt Stars
We analyzed the space velocities of Gould Belt stars younger than 125 Myr
located at heliocentric distances <650 pc. We determined the rotation and
expansion parameters of the Gould Belt by assuming the existence of a single
kinematic center whose direction was found to be the following:
and pc. The linear velocities reach their
maximum at a distance of pc from the center and are -6 km s
for the rotation (whose direction coincides with the Galactic rotation) and +4
km s for the expansion. The stellar rotation model used here is shown to
give a more faithful description of the observed velocity field than the linear
model based on the Oort constants and . We present evidence that the
young clusters Pic, Tuc/HorA, and TWA belong to the Gould Belt
structure.Comment: 17 pages, 5 figure
The Oort Constants Measured from Proper Motions
The Oort constants describe the local variations of the stellar streaming
field. Classically, they are determined from stellar proper motions. We discuss
problems arising in this procedure. A large, hitherto overlooked, source of
systematic error arises from longitudinal variations of the mean stellar
parallax. Together with the solar reflex motion, these variations create
contributions to the longitudinal proper motions mu_l*(l) that are
indistinguishable from the Oort Constants at the 20% level. Fortunately, we can
correct for this "mode mixing" using the latitudinal proper motions mu_b(l). We
use ~10^6 stars from the ACT/Tycho-2 catalogs with proper motion errors of ~ 3
mas/yr. We find significant deviations from expectations based on a smooth
axisymmetric equilibrium disk, in particular non-zero C for old red giant
stars. We also find variations of the Oort constants with the asymmetric drift
of the sub-sample. These correlations are different in nature than those
expected for an axisymmetric Galaxy. The most reliable tracers for the ``true''
Oort constants are red giants, which are old enough to be in equilibrium and
distant enough to be unaffected by possible local anomalies. For these stars we
find, A ~ 16, B ~- 17, A - B ~ 33, and C ~- 10 km/s/kpc with internal errors of
about 1-2 and external error of perhaps the same order. These values are
consistent with our knowledge of the Milky Way (flat rotation curve and Omega=A
- B ~ 28 +/- 2). Based on observations made with the ESA Hipparcos astrometry
satellite. (Abridged)Comment: Submitted to Ap
Type I interferon autoantibodies are associated with systemic immune alterations in patients with COVID-19
Neutralizing autoantibodies against type I interferons (IFNs) have been found in some patients with critical coronavirus disease 2019 (COVID-19), the disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the prevalence of these antibodies, their longitudinal dynamics across the disease severity scale, and their functional effects on circulating leukocytes remain unknown. Here, in 284 patients with COVID-19, we found type I IFN–specific autoantibodies in peripheral blood samples from 19% of patients with critical disease and 6% of patients with severe disease. We found no type I IFN autoantibodies in individuals with moderate disease. Longitudinal profiling of over 600,000 peripheral blood mononuclear cells using multiplexed single-cell epitope and transcriptome sequencing from 54 patients with COVID-19 and 26 non–COVID-19 controls revealed a lack of type I IFN–stimulated gene (ISG-I) responses in myeloid cells from patients with critical disease. This was especially evident in dendritic cell populations isolated from patients with critical disease producing type I IFN–specific autoantibodies. Moreover, we found elevated expression of the inhibitory receptor leukocyte-associated immunoglobulin-like receptor 1 (LAIR1) on the surface of monocytes isolated from patients with critical disease early in the disease course. LAIR1 expression is inversely correlated with ISG-I expression response in patients with COVID-19 but is not expressed in healthy controls. The deficient ISG-I response observed in patients with critical COVID-19 with and without type I IFN–specific autoantibodies supports a unifying model for disease pathogenesis involving ISG-I suppression through convergent mechanisms
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