4,562 research outputs found
Image Subtraction Reduction of Open Clusters M35 & NGC 2158 In The K2 Campaign-0 Super-Stamp
Observations were made of the open clusters M35 and NGC 2158 during the
initial K2 campaign (C0). Reducing these data to high-precision photometric
time-series is challenging due to the wide point spread function (PSF) and the
blending of stellar light in such dense regions. We developed an
image-subtraction-based K2 reduction pipeline that is applicable to both
crowded and sparse stellar fields. We applied our pipeline to the data-rich C0
K2 super-stamp, containing the two open clusters, as well as to the neighboring
postage stamps. In this paper, we present our image subtraction reduction
pipeline and demonstrate that this technique achieves ultra-high photometric
precision for sources in the C0 super-stamp. We extract the raw light curves of
3960 stars taken from the UCAC4 and EPIC catalogs and de-trend them for
systematic effects. We compare our photometric results with the prior
reductions published in the literature. For detrended, TFA-corrected sources in
the 12--12.25 magnitude range, we achieve a best 6.5 hour window
running rms of 35 ppm falling to 100 ppm for fainter stars in the 14--14.25 magnitude range. For stars with , our detrended and
6.5 hour binned light curves achieve the highest photometric precision.
Moreover, all our TFA-corrected sources have higher precision on all time
scales investigated. This work represents the first published image subtraction
analysis of a K2 super-stamp. This method will be particularly useful for
analyzing the Galactic bulge observations carried out during K2 campaign 9. The
raw light curves and the final results of our detrending processes are publicly
available at \url{http://k2.hatsurveys.org/archive/}.Comment: Accepted for publication in PASP. 14 pages, 5 figures, 2 tables.
Light curves available from http://k2.hatsurveys.org/archive
High Precision Photometry for K2 Campaign 1
The two reaction wheel K2 mission promises and has delivered new discoveries
in the stellar and exoplanet fields. However, due to the loss of accurate
pointing, it also brings new challenges for the data reduction processes. In
this paper, we describe a new reduction pipeline for extracting high precision
photometry from the K2 dataset, and present public light curves for the K2
Campaign 1 target pixel dataset. Key to our reduction is the derivation of
global astrometric solutions from the target stamps, from which accurate
centroids are passed on for high precision photometry extraction. We extract
target light curves for sources from a combined UCAC4 and EPIC catalogue --
this includes not only primary targets of the K2 campaign 1, but also any other
stars that happen to fall on the pixel stamps. We provide the raw light curves,
and the products of various detrending processes aimed at removing different
types of systematics. Our astrometric solutions achieve a median residual of ~
0.13". For bright stars, our best 6.5 hour precision for raw light curves is
~20 parts per million (ppm). For our detrended light curves, the best 6.5 hour
precisions achieved is ~15 ppm. We show that our detrended light curves have
fewer systematic effects (or trends, or red-noise) than light curves produced
by other groups from the same observations. Example light curves of transiting
planets and a Cepheid variable candidate, are also presented. We make all light
curves public, including the raw and de-trended photometry, at
http://k2.hatsurveys.org.Comment: submitted to MNRA
Low-density series expansions for directed percolation III. Some two-dimensional lattices
We use very efficient algorithms to calculate low-density series for bond and
site percolation on the directed triangular, honeycomb, kagom\'e, and
lattices. Analysis of the series yields accurate estimates of the critical
point and various critical exponents. The exponent estimates differ only
in the digit, thus providing strong numerical evidence for the
expected universality of the critical exponents for directed percolation
problems. In addition we also study the non-physical singularities of the
series.Comment: 20 pages, 8 figure
The exact evaluation of the corner-to-corner resistance of an M x N resistor network: Asymptotic expansion
We study the corner-to-corner resistance of an M x N resistor network with
resistors r and s in the two spatial directions, and obtain an asymptotic
expansion of its exact expression for large M and N. For M = N, r = s =1, our
result is
R_{NxN} = (4/pi) log N + 0.077318 + 0.266070/N^2 - 0.534779/N^4 + O(1/N^6).Comment: 12 pages, re-arranged section
Ogbu and the debate on educational achievement: an exploration of the links between education, migration, identity and belonging
This paper looks at some of the issues raised by Ogbuâs work in relation to the education of different minority ethnic groups. Ogbu poses questions such as the value attached to education,
its links to the future and its measurable outcomes in terms of âsuccessâ as experienced by black participants. The desire for better life chances leads families to consider migration to a new country or resettlement within the same country, thus making migration both a local and a global phenomenon. As an example, attention is drawn to the situation facing South Asian
children and their families in the UK. In terms of ethnicity and belonging, the wider question that is significant for many countries in the West after âNine-Elevenâ is the education of Muslim children. A consideration of this current situation throws Ogbuâs identification of âautonomous minorityâ into question. It is argued that a greater understanding of diverse needs has to be
accompanied by a concerted effort to confront racism and intolerance in schools and in society, thus enabling all communities to make a useful contribution and to avoid the âriskâ of failure and disenchantment
Stellar rotational periods in the planet hosting open cluster Praesepe
By using the dense coverage of the extrasolar planet survey project HATNet,
we Fourier analyze 381 high-probability members of the nearby open cluster
Praesepe (Beehive/M44/NGC 2632). In addition to the detection of 10 variables
(of \delta Scuti and other types), we identify 180 rotational variables
(including the two known planet hosts). This sample increases the number of
known rotational variables in this cluster for spectral classes earlier than M
by more than a factor of three. These stars closely follow a color/magnitude --
period relation from early F to late K stars. We approximate this relation by
polynomials for an easier reference to the rotational characteristics in
different colors. The total (peak-to-peak) amplitudes of the large majority
(94%) of these variables span the range of 0.005 to 0.04 mag. The periods cover
a range from 2.5 to 15 days. These data strongly confirm that Praesepe and the
Hyades have the same gyrochronological ages. Regarding the two planet hosts,
Pr0211 (the one with the shorter orbital period) has a rotational period that
is ~2 days shorter than the one expected from the main rotational pattern in
this cluster. This, together with other examples discussed in the paper, may
hint that star-planet interaction via tidal dissipation can be significant in
some cases in the rotational evolution of stars hosting Hot Jupiters.Comment: 17 pages, 13 figures, 5 tables; accepted for publication in MNRA
Post discharge medicines use review service for older patients: recruitment issues in a feasibility study
Background The community pharmacy medicines use review (MUR) service in England has been identified as a way of providing support with medication to recently discharged patients; however initial uptake of post-discharge MUR has been low. Objective To identify barriers to recruitment into a randomised controlled feasibility study of a hospital referral system to older patientsâ regular community pharmacists. Method Ward pharmacists at Southport District General Hospital identified patients aged over 65 to be approached by a researcher to assess eligibility and discuss involvement in the trial. Participants were randomised to referral for a post discharge MUR with their regular community pharmacist, or to standard discharge care. Reasons for patients not participating were collected. Results Over a 9-month period 337 potential participants were identified by ward pharmacists. Of these, 132 were eligible and 60 were recruited. Barriers to recruitment included competing priorities among ward pharmacists, and national restrictions placed on MURs e.g. housebound patients and those requiring carer support with medication. Lack of expected benefit resulted in a high proportion of patient refusals. Conclusion The current provisions for post discharge MURs exclude many older people from participation, including those possibly in greatest need. Unfamiliarity with the role of the pharmacist in transitional care may have affected patientsâ perceived âcost-benefitâ of taking part in this study
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