357 research outputs found
Exoplanet Transit Parallax
The timing and duration of exoplanet transits has a dependency on observer
position due to parallax. In the case of an Earth-bound observer with a 2 AU
baseline the dependency is typically small and slightly beyond the limits of
current timing precision capabilities. However, it can become an important
systematic effect in high-precision repeated transit measurements for long
period systems due to its relationship to secular perspective acceleration
phenomena. In this short paper we evaluate the magnitude and characteristics of
transit parallax in the case of exoplanets using simplified geometric examples.
We also discuss further implications of the effect, including its possible
exploitation to provide immediate confirmation of planetary transits and/or
unique constraints on orbital parameters and orientations.Comment: 12 Pages, 3 Figures, Accepted for publication in Ap
New surveys of UBV photometry and absolute proper motions at intermediate latitude
A photometric and proper motion survey has been obtained in 2 directions at
intermediate latitude: (, ;
,) and
(, ; ,
). The survey covers 7.13 and 20.84 square
degrees, respectively. The limiting magnitude is about 18.5 in V for both
directions. We have derived the density laws for stars (M 3.5) as a
function of distance from the galactic plane. The density laws for stars follow
a sum of two exponentials with scale heights of 240 pc (thin disk) and 790 pc
(thick disk), respectively. The local density of thick disk is found to be
6.13 % relative to the thin disk. The kinematical distribution of stars
has been probed to distances up to 3.5 kpc above the galactic plane. New
estimates of the parameters of velocity ellipsoid have been derived for the
thick disk of the Galaxy. A comparison of our data sets with the Besan\c con
model star count predictions has been performed, giving a good agreement in the
magnitude range V = 13 to 18.Comment: 13 pages, 8 PS figures, To appear in A&
The ALADIN Interactive Sky Atlas
The Aladin interactive sky atlas, developed at CDS, is a service providing
simultaneous access to digitized images of the sky, astronomical catalogues,
and databases.
The driving motivation is to facilitate direct, visual comparison of
observational data at any wavelength with images of the optical sky, and with
reference catalogues.
The set of available sky images consists of the STScI Digitized Sky Surveys,
completed with high resolution images of crowded regions scanned at the MAMA
facility in Paris.
A Java WWW interface to the system is available at:
http://aladin.u-strasbg.fr/Comment: 8 pages, 3 Postscript figures; to be published in A&
Models of Veritcal Disturbances in the Interstellar Medium
This paper describes some interesting properties of waves in, and
oscillations of, the interstellar medium in the direction normal to the plane
of the Galaxy. Our purpose is to examine possible reasons for four observed
phenomena: the falling sky in the northern hemisphere; the apparent presence of
clouds in absorption spectra when a sightline is occupied primarily only by
warm intercloud gas; the peculiar structuring of spiral arms involving clumps,
spurs, and feathering; and the existence of an abundance of high stage ions far
off the plane of the Galaxy.
We explored the reaction of the interstellar medium - in the vertical
direction only - to large imposed disturbances (initial displacements,
expansive velocities, and compressions), and to the introduction of small
amplitude waves via oscillation of the midplane. Our findings included: 1) the
anticipated growth in amplitude of high frequency waves with height; 2) the
four lowest normal modes for the oscillation of the atmosphere as a whole, as
functions of the height of the outer boundary; 3) the time for material to
`bounce' from one unusually dense state to the next as a function of height;
and 4) the tendency for the disk to develop a hot outer halo, either after the
passage of a single shock from a large event, or in response to a continuous
stream of small amplitude waves.Comment: This paper contains 31 pages of text and 23 figures. This paper was
submitted to The Astrophysical Journal on 6/6/2000. It was revised and
resubmitted on 9/29/200
A Multicolor Survey of Absolute Proper Motions : Galactic Structure and Kinematics in the Direction of Galactic Center at Intermediate Latitude
We have derived a new photographic photometry and proper motions for 20000
stars with completeness to V = 18 in the direction of galactic center at the
intermediate latitude (l = 3 deg,b = 47 deg; alpha(1950)=15h 18m, delta(1950) =
+02deg 16') for a 15.5 sq deg field. The combination of four glass copies of
the Palomar Observatory Sky Survey (i.e. POSS 1402 E&O and POSS 1429 E&O) has
been used as a first epoch for proper motion determination. The random error of
the proper motions is approximately 0.''3/cen to V=17. The photometric accuracy
ranges between 0.07 to 0.10 in the V, B and U bands. We stress the importance
of the magnitude and color effects in astrometric surveys of field stars. Using
color-magnitude diagrams of a few cluster member stars, a new distance of
6.9+-0.5 kpc is derived for M5 and 20.3+-0.8 kpc for Pal 5 globular clusters.
This is in good agreement with other determinations. We have analyzed the
components of U+W and V galactic space motions resulting from the accurate
proper motions survey. No dependence with z distance is found in the asymmetric
drift of the thick disk population. New estimates of the parameters of the
velocity ellipsoid have been derived for the thin disk, thick disk and halo
populations of the Galaxy.Comment: PS file, 15 pages, 13 figures (available on request), paper accepted
for publication in Astron. & Astrophy
Extracting galactic structure parameters from multivariated density estimation
Multivariate statistical analysis, including includes cluster analysis (unsupervised classification), discriminant analysis (supervised classification) and principle component analysis (dimensionlity reduction method), and nonparameter density estimation have been successfully used to search for meaningful associations in the 5-dimensional space of observables between observed points and the sets of simulated points generated from a synthetic approach of galaxy modelling. These methodologies can be applied as the new tools to obtain information about hidden structure otherwise unrecognizable, and place important constraints on the space distribution of various stellar populations in the Milky Way. In this paper, we concentrate on illustrating how to use nonparameter density estimation to substitute for the true densities in both of the simulating sample and real sample in the five-dimensional space. In order to fit model predicted densities to reality, we derive a set of equations which include n lines (where n is the total number of observed points) and m (where m: the numbers of predefined groups) unknown parameters. A least-square estimation will allow us to determine the density law of different groups and components in the Galaxy. The output from our software, which can be used in many research fields, will also give out the systematic error between the model and the observation by a Bayes rule
Patterns in the Outer Parts of Galactic Disks
This paper describes test particle simulations of the response of the outer
parts of Galactic disks to barring and spiral structure. Simulations are
conducted for cold Mestel disks and warm quasi-exponential disks with
completely flat rotation curves, subjected to pure quadrupoles and logarithmic
spirals. Even though the starting velocity distributions are smooth, the
end-points of the bar simulations show bimodality and multi-peaked structures
at locations near the outer Lindblad resonance (OLR), although spirality can
make this smoother. The growth of a bar may cause the disk isophotes to become
boxy at the OLR, as stars accummulate particularly along the minor axis. The
growth of a bar is also accompanied by substantial heating of the disk stars
near the OLR. For the growth of a bar, the radial
velocity dispersion is typically quadrupled for initially cold disks (initial
\sigmau \kms), and typically doubled for disks with final \sigmau
\kms. Simulations performed of the growth and dissolution of bars
give very similar results, demonstrating that the heat once given to disk stars
is very difficult to remove.Comment: 14 pages, 19 figure
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