663,508 research outputs found
Millisecond Pulsar Velocities
We present improved timing parameters for 13 millisecond pulsars (MSPs)
including 9 new proper motion measurements. These new proper motions bring to
23 the number of MSPs with measured transverse velocities. In light of these
new results we present and compare the kinematic properties of MSPs with those
of ordinary pulsars. The mean transverse velocity of MSPs was found to be
85+/-13 km/s; a value consistent with most models for the origin and evolution
of MSPs and approximately a factor of four lower than that of ordinary pulsars.
We also find that, in contrast to young ordinary pulsars, the vast majority of
which are moving away from the Galactic plane, almost half of the MSPs are
moving towards the plane. This near isotropy would be expected of a population
that has reached dynamic equilibrium. Accurate measurements of MSP velocities
have allowed us to correct their measured spin-down rates for Doppler
acceleration effects, and thereby derive their intrinsic magnetic field
strengths and characteristic ages. We find that close to half of our sample of
MSPs have a characteristic age comparable to or greater than the age of the
Galaxy.Comment: 10 pages LaTeX including 2 LaTeX tables and 3 postscript figures;
submitted to MNRA
Reconstruction with velocities
Reconstruction is becoming a crucial procedure of galaxy clustering analysis for future spectroscopic redshift surveys to obtain subper cent level measurement of the baryon acoustic oscillation scale. Most reconstruction algorithms rely on an estimation of the displacement field from the observed galaxy distribution. However, the displacement reconstruction degrades near the survey boundary due to incomplete data and the boundary effects extend to ∼100 Mpc/h within the interior of the survey volume. We study the possibility of using radial velocities measured from the cosmic microwave background observation through the kinematic Sunyaev-Zeldovich effect to improve performance near the boundary. We find that the boundary effect can be reduced to ∼30 − 40 Mpc/h with the velocity information from Simons Observatory. This is especially helpful for dense low redshift surveys where the volume is relatively small and a large fraction of total volume is affected by the boundary
Deriving High-Precision Radial Velocities
This chapter describes briefly the key aspects behind the derivation of
precise radial velocities. I start by defining radial velocity precision in the
context of astrophysics in general and exoplanet searches in particular. Next I
discuss the different basic elements that constitute a spectrograph, and how
these elements and overall technical choices impact on the derived radial
velocity precision. Then I go on to discuss the different wavelength
calibration and radial velocity calculation techniques, and how these are
intimately related to the spectrograph's properties. I conclude by presenting
some interesting examples of planets detected through radial velocity, and some
of the new-generation instruments that will push the precision limit further.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Precision radial velocities with CSHELL
Radial velocity identification of extrasolar planets has historically been
dominated by optical surveys. Interest in expanding exoplanet searches to M
dwarfs and young stars, however, has motivated a push to improve the precision
of near infrared radial velocity techniques. We present our methodology for
achieving 58 m/s precision in the K band on the M0 dwarf GJ 281 using the
CSHELL spectrograph at the 3-meter NASA IRTF. We also demonstrate our ability
to recover the known 4 Mjup exoplanet Gl 86 b and discuss the implications for
success in detecting planets around 1-3 Myr old T Tauri stars.Comment: 31 pages, 3 figures, 2 tables, accepted for publication in Ap
Peculiar Velocities of Galaxy Clusters
We investigate the peculiar velocities predicted for galaxy clusters by
theories in the cold dark matter family. A widely used hypothesis identifies
rich clusters with high peaks of a suitably smoothed version of the linear
density fluctuation field. Their peculiar velocities are then obtained by
extrapolating the similarly smoothed linear peculiar velocities at the
positions of these peaks. We test these ideas using large high resolution
N-body simulations carried out within the Virgo supercomputing consortium. We
find that at early times the barycentre of the material which ends up in a rich
cluster is generally very close to a high peak of the initial density field.
Furthermore the mean peculiar velocity of this material agrees well with the
linear value at the peak. The late-time growth of peculiar velocities is,
however, systematically underestimated by linear theory. At the time clusters
are identified we find their rms peculiar velocity to be about 40% larger than
predicted. Nonlinear effects are particularly important in superclusters. These
systematics must be borne in mind when using cluster peculiar velocities to
estimate the parameter combination .Comment: 8 pages, 4 figures; submitted to MNRA
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