4,566 research outputs found
Vertical velocities from proper motions of red clump giants
We derive the vertical velocities of disk stars in the range of
Galactocentric radii of R=5-16 kpc within 2 kpc in height from the Galactic
plane. This kinematic information is connected to dynamical aspects in the
formation and evolution of the Milky Way, such as the passage of satellites and
vertical resonance and determines whether the warp is a long-lived or a
transient feature.
We used the proper motions of the PPMXL survey, correcting of systematic
errors with the reference of quasars. From the color-magnitude diagram K versus
(J-K) we selected the standard candles corresponding to red clump giants and
used the information of their proper motions to build a map of the vertical
motions of our Galaxy. We derived the kinematics of the warp both analytically
and through a particle simulation to fit these data. Complementarily, we also
carried out the same analysis with red clump giants spectroscopically selected
with APOGEE data, and we predict the improvements in accuracy that will be
reached with future Gaia data.
A simple model of warp with the height of the disk z_w(R,phi)=gamma (R-R_sun)
sin(phi-phi_w) fits the vertical motions if d(gamma)/dt/gamma=-34+/-17
Gyr^{-1}; the contribution to d(gamma)/dt comes from the southern warp and is
negligible in the north. The vertical motion in the warp apparently indicates
that the main S-shaped structure of the warp is a long-lived feature, whereas
the perturbation that produces an irregularity in the southern part is most
likely a transient phenomenon. With the use of the Gaia end-of-mission products
together with spectroscopically classified red clump giants, the precision in
vertical motions can be increased by an order of magnitude at least.Comment: Accepted for publication in A&A. arXiv admin note: text overlap with
arXiv:1402.355
Inversion of stellar statistics equation for the Galactic Bulge
A method based on Lucy (1974, AJ 79, 745) iterative algorithm is developed to
invert the equation of stellar statistics for the Galactic bulge and is then
applied to the K-band star counts from the Two-Micron Galactic Survey in a
number of off-plane regions (10 deg.>|b|>2 deg., |l|<15 deg.).
The top end of the K-band luminosity function is derived and the morphology
of the stellar density function is fitted to triaxial ellipsoids, assuming a
non-variable luminosity function within the bulge. The results, which have
already been outlined by Lopez-Corredoira et al.(1997, MNRAS 292, L15), are
shown in this paper with a full explanation of the steps of the inversion: the
luminosity function shows a sharp decrease brighter than M_K=-8.0 mag when
compared with the disc population; the bulge fits triaxial ellipsoids with the
major axis in the Galactic plane at an angle with the line of sight to the
Galactic centre of 12 deg. in the first quadrant; the axial ratios are
1:0.54:0.33, and the distance of the Sun from the centre of the triaxial
ellipsoid is 7860 pc. The major-minor axial ratio of the ellipsoids is found
not to be constant. However, the interpretation of this is controversial. An
eccentricity of the true density-ellipsoid gradient and a population gradient
are two possible explanations.
The best fit for the stellar density, for 1300 pc<t<3000 pc, are calculated
for both cases, assuming an ellipsoidal distribution with constant axial
ratios, and when K_z is allowed to vary. From these, the total number of bulge
stars is ~ 3 10^{10} or ~ 4 10^{10}, respectively.Comment: 19 pages, 23 figures, accepted in MNRA
Detection of the old stellar component of the major Galactic bar
We present near-IR colour--magnitude diagrams and star counts for a number of
regions along the Galactic plane. It is shown that along the l=27 b=0 line of
sight there is a feature at 5.7 +-0.7kpc with a density of stars at least a
factor two and probably more than a factor five times that of the disc at the
same position. This feature forms a distinct clump on an H vs. J-H diagram and
is seen at all longitudes from the bulge to about l=28, but at no longitude
greater than this. The distance to the feature at l=20 is about 0.5kpc further
than at l=27 and by l=10 it has merged with, or has become, the bulge. Given
that at l=27 and l=21 there is also a clustering of very young stars, the only
component that can reasonably explain what is seen is a bar with half length of
around 4kpc and a position angle of about 43+-7.Comment: 5 pages, 5 figures accepted as a letter in MNRA
Disk stars in the Milky Way detected beyond 25 kpc from its center
CONTEXT. The maximum size of the Galactic stellar disk is not yet known. Some
studies have suggested an abrupt drop-off of the stellar density of the disk at
Galactocentric distances kpc, which means that in practice no
disk stars or only very few of them should be found beyond this limit. However,
stars in the Milky Way plane are detected at larger distances. In addition to
the halo component, star counts have placed the end of the disk beyond 20 kpc,
although this has not been spectroscopically confirmed so far.
AIMS. Here, we aim to spectroscopically confirm the presence of the disk
stars up to much larger distances.
METHODS. With data from the LAMOST and SDSS-APOGEE spectroscopic surveys, we
statistically derived the maximum distance at which the metallicity
distribution of stars in the Galactic plane is distinct from that of the halo
populations.
RESULTS. Our analysis reveals the presence of disk stars at R>26 kpc (99.7%
C.L.) and even at R>31 kpc (95.4% C.L.).Comment: 4 pages, accepted to be published in A&A-Letter
Stellar density distribution in the NIR on the Galactic plane at longitudes 15-27 deg. Clues for the Galactic bar ?
12 pages, 15 figures, accepted by A&AGarzon et al. (1997), Lopez-Corredoira et al. (1999) and Hammersley et al. (2000)have identified in TMGS and DENIS data a large excess of stars at l=27 deg andb=0 deg which might correspond to an in-plane bar. We compared near infraredCAIN star counts and simulations from the Besancon Model of Galaxy on 15 fieldsbetween 15 deg and 45 deg in longitude and -2 deg and 2 deg in latitude.Comparisons confirm the existence of an overdensity at longitudes lower than 27deg which is inhomogeneous and decreases very steeply off the Galactic plane.The observed excess in the star distribution over the predicted density is evenhigher than 100%. Its distance from the sun is estimated to be lower than 6kpc. If this overdensity corresponds to the stellar population of the bar, weestimate its half-length to 3.9 +/ -0.4 kpc and its angle from the Sun-centerdirection to 45 +/- 9 degrees
Temperature dependent asymmetry of the nonlocal spin-injection resistance: evidence for spin non-conserving interface scattering
We report nonlocal spin injection and detection experiments on mesoscopic
Co-Al2O3-Cu spin valves. We have observed a temperature dependent asymmetry in
the nonlocal resistance between parallel and antiparallel configurations of the
magnetic injector and detector. This strongly supports the existence of a
nonequilibrium resistance that depends on the relative orientation of the
detector magnetization and the nonequilibrium magnetization in the normal metal
providing evidence for increasing interface spin scattering with temperature.Comment: 5 pages, 4 figures, accepted for publication in PRL, minor
corrections (affiliation, acknowledgements, typo
An excess of very bright stars in the inner bulge
From an analysis of the stars remaining in central regions of the Galaxy
after subtracting those belonging to the disc and the bulge, we deduce that the
inner bulge must have an extra young population with respect the rest of the
bulge. It is shown that there is a higher ratio of very bright stars in the
central bulge than than there is in the outer bulge. This is interpreted as
being an additional young component due to the presence of star formation
regions near the Galactic Centre which is absent in the outer bulge.Comment: 6 pages, 12 figures, accepted to be published in MNRA
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