564 research outputs found
Astrometry and photometry with HST-WFC3. I. Geometric distortion corrections of F225W, F275W, F336W bands of the UVIS-channel
An accurate geometric distortion solution for the Hubble Space Telescope
UVIS-channel of Wide Field Camera 3 is the first step towards its use for high
precision astrometry. In this work we present an average correction that
enables a relative astrometric accuracy of ~1 mas (in each axis for well
exposed stars) in three broad-band ultraviolet filters (F225W, F275W, and
F336W). More data and a better understanding of the instrument are required to
constrain the solution to a higher level of accuracy.Comment: 20 pages, 7 figures (3 in low resolution), 3 tables. Accepted for
publication in PASP on October 16 200
A PSF-based approach to Kepler/K2 data. I. Variability within the K2 Campaign 0 star clusters M 35 and NGC 2158
Kepler and K2 data analysis reported in the literature is mostly based on
aperture photometry. Because of Kepler's large, undersampled pixels and the
presence of nearby sources, aperture photometry is not always the ideal way to
obtain high-precision photometry and, because of this, the data set has not
been fully exploited so far. We present a new method that builds on our
experience with undersampled HST images. The method involves a point-spread
function (PSF) neighbour-subtraction and was specifically developed to exploit
the huge potential offered by the K2 "super-stamps" covering the core of dense
star clusters. Our test-bed targets were the NGC 2158 and M 35 regions observed
during the K2 Campaign 0. We present our PSF modeling and demonstrate that, by
using a high-angular-resolution input star list from the Asiago Schmidt
telescope as the basis for PSF neighbour subtraction, we are able to reach
magnitudes as faint as Kp~24 with a photometric precision of 10% over 6.5
hours, even in the densest regions. At the bright end, our photometric
precision reaches ~30 parts-per-million. Our method leads to a considerable
level of improvement at the faint magnitudes (Kp>15.5) with respect to the
classical aperture photometry. This improvement is more significant in crowded
regions. We also extracted raw light curves of ~60,000 stars and detrended them
for systematic effects induced by spacecraft motion and other artifacts that
harms K2 photometric precision. We present a list of 2133 variables.Comment: 27 pages (included appendix), 2 tables, 25 figures (5 in low
resolution). Accepted for publication in MNRAS on November 05, 2015. Online
materials will be available on the Journal website soo
Ground-based CCD astrometry with wide field imagers. IV. An improved Geometric Distortion Correction for the Blue prime-focus Camera at the LBT
High precision astrometry requires an accurate geometric distortion solution.
In this work, we present an average correction for the Blue Camera of the Large
Binocular Telescope which enables a relative astrometric precision of ~15 mas
for the B_Bessel and V_Bessel broad-band filters. The result of this effort is
used in two companion papers: the first to measure the absolute proper motion
of the open cluster M67 with respect to the background galaxies; the second to
decontaminate the color-magnitude diagram of M67 from field objects, enabling
the study of the end of its white dwarf cooling sequence. Many other
applications might find this distortion correction useful.Comment: 13 pages, 11 figures, 4 tables. accepted for publication on Astronomy
and Astrophysic
Search for giant planets in M67 IV: survey results
We present the results of a seven-year-long radial velocity survey of a
sample of 88 main-sequence and evolved stars to reveal signatures of
Jupiter-mass planets in the solar-age and solar-metallicity open cluster M67.
We aim at studying the frequency of giant planets in this cluster with respect
to the field stars. In addition, our sample is also ideal to perform a
long-term study to compare the chemical composition of stars with and without
giant planets in detail. We analyzed precise radial velocity (RV) measurements
obtained with five different instruments. We conducted Monte Carlo simulations
to estimate the occurrence rate of giant planets in our radial velocity survey.
All the planets previously announced in this RV campaign with their properties
are summarized here: 3 hot Jupiters around the main-sequence stars YBP1194,
YBP1514, and YBP401, and 1 giant planet around the evolved star S364. Two
additional planet candidates around the stars YBP778 and S978 are also analyzed
in the present work. We discuss stars that exhibit large RV variability or
trends individually. For 2 additional stars, long-term trends are compatible
with new binary candidates or substellar objects, which increases the total
number of binary candidates detected in our campaign to 14. Based on the
Doppler-detected planets discovered in this survey, we find an occurrence of
giant planets of ~18.0%(+12.0/-8.0%) in the selected period-mass range. This
frequency is slightly higher but consistent within the errors with the estimate
for the field stars, which leads to the general conclusion that open cluster
and field statistics agree. However, we find that the rate of hot Jupiters in
the cluster (~5.7%(+5.5/-3.0%)) is substantially higher than in the field.Comment: Accepted by A&
A Gaia DR2 view of white dwarfs in the Hyades
We have exploited the very precise parallaxes, proper motions, and photometry of Gaia Data Release 2 to study white dwarf members of the Hyades star cluster. Gaia photometry and parallaxes for the eight DA white dwarfs confirmed members have been then used to compute absolute magnitudes and colours. These were compared to three independent sets of white dwarf evolutionary tracks, to derive cooling times and white dwarf (final) masses. All sets of models provide the same mass values, with only small differences in the cooling ages. The precision in the derived masses and cooling ages is typically 1-3 per cent. Our derived masses are generally consistent with spectroscopic estimates from the literature, whilst cooling ages are generally larger. The recent estimate of the cluster age from the Gaia Data Release 2 main-sequence turn offcolour-magnitude diagram (790 Myr) has been employed to derive progenitor (initial) masses. We find a slope of the initial-final mass relation for the Hyades white dwarfs (masses between ~0.67 and ~0.84 M⊙) steeper than that derived for the same mass range from global estimates - averaged over the whole spectrum of white dwarf masses - irrespectively of the cooling models adopted. However, when considering the error in this age estimate (-100+160Myr), a definitive conclusion on this issue cannot be reached yet. The lower limit of 690 Myr (closer to the classical Hyades age of 600-650 Myr) would provide a slope of the initial-final mass relation closer to the global determinations. We also find hints of an intrinsic spread of the cluster initial-final mass relation for the cluster. © 2018 The Author(s)
The M4 Core Project with HST - IV. Internal Kinematics from Accurate Radial Velocities of 2771 Cluster Members
We present a detailed study of the internal kinematics of the Galactic
Globular Cluster M 4 (NGC 6121), by deriving the radial velocities from 7250
spectra for 2771 stars distributed from the upper part of the Red Giant Branch
down to the Main Sequence. We describe new approaches to determine the
wavelength solution from day-time calibrations and to determine the radial
velocity drifts that can occur between calibration and science observations
when observing with the GIRAFFE spectrograph at VLT. Two techniques to
determine the radial velocity are compared, after a qualitative description of
their advantages with respect to other commonly used algorithm, and a new
approach to remove the sky contribution from the spectra obtained with
fibre-fed spectrograph and further improve the radial velocity precision is
presented. The average radial velocity of the cluster is km s with an average dispersion of km
s. Using the same dataset and the same statistical approach of previous
analyses, 20 additional binary candidates are found, for a total of 87
candidates. A new determination of the internal radial velocity dispersion as a
function of cluster distance is presented, resulting in a dispersion of
km s within 2 from the center of cluster and steadily
decreasing outward. We statistically confirm the small amplitude of the cluster
rotation, as suggested in the past by several authors. This new analysis
represents a significant improvement with respect to previous results in
literature and provides a fundamental observational input for the modeling of
the cluster dynamics.Comment: 17 pages, 17 figures. Accepted for publication in MNRAS on September
15, 201
Ground-Based CCD Astrometry with Wide Field Imagers. I. [Observations just a few years apart allow decontamination of field objects from members in two Globular clusters.]
This paper is the first of a series of papers in which we will apply the
methods we have developed for high-precision astrometry (and photometry) with
the Hubble Space Telescope to the case of wide-field ground-based images. In
particular, we adapt the software originally developed for WFPC2 to
ground-based, wide field images from the WFI at the ESO 2.2m telescope. In this
paper, we describe in details the new software, we characterize the WFI
geometric distortion, discuss the adopted local transformation approach for
proper-motion measurements, and apply the new technique to two-epoch archive
data of the two closest Galactic globular clusters: NGC 6121 (M4) and NGC 6397.
The results of this exercise are more than encouraging. We find that we can
achieve a precision of ~7 mas (in each coordinate) in a single exposure for a
well-exposed star, which allows a very good cluster-field separation in both
M4, and NGC 6397, with a temporal baseline of only 2.8, and 3.1 years,
respectively.Comment: 1 pages, 17 figures, 1 table. Accepted for publication in A&A, on
April 15 2006. For high resolution version:
http://www.eso.org/~lbedin/WFI_method/ms.ps.g
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