4,273 research outputs found

    Image Subtraction Reduction of Open Clusters M35 & NGC 2158 In The K2 Campaign-0 Super-Stamp

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    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 Kp\rm K_{p} 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 Kp \rm K_{p} magnitude range. For stars with Kp>14\rm K_{p}> 14, 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

    Ogbu and the debate on educational achievement: an exploration of the links between education, migration, identity and belonging

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    This paper looks at some of the issues raised by Ogbu’s 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 ‘success’ 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 ‘Nine-Eleven’ is the education of Muslim children. A consideration of this current situation throws Ogbu’s identification of ‘autonomous minority’ 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 ‘risk’ of failure and disenchantment

    Low-density series expansions for directed percolation III. Some two-dimensional lattices

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    We use very efficient algorithms to calculate low-density series for bond and site percolation on the directed triangular, honeycomb, kagom\'e, and (4.82)(4.8^2) lattices. Analysis of the series yields accurate estimates of the critical point pcp_c and various critical exponents. The exponent estimates differ only in the 5th5^{th} 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

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    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

    Stellar rotational periods in the planet hosting open cluster Praesepe

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    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

    HAT-P-49b: A 1.7 M_J Planet Transiting a Bright 1.5 M_S F-Star

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    We report the discovery of the transiting extrasolar planet HAT-P-49b. The planet transits the bright (V = 10.3) slightly evolved F-star HD 340099 with a mass of 1.54M_S and a radius of 1.83 R_S. HAT-P-49b is orbiting one of the 25 brightest stars to host a transiting planet which makes this a favorable candidate for detailed follow-up. This system is an especially strong target for Rossiter- McLaughlin follow-up due to the fast rotation of the host star, 16 km/s. The planetary companion has a period of 2.6915 d, mass of 1.73 M_J and radius of 1.41 R_J. The planetary characteristics are consistent with that of a classical hot Jupiter but we note that this is the fourth most massive star to host a transiting planet with both M_p and R_p well determined.Comment: Accepted to the Astronomical Journa

    HAT-P-55b: A Hot Jupiter Transiting a Sun-like Star

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    We report the discovery of a new transiting extrasolar planet, HAT-P-55b. The planet orbits a V = 13.207 +/- 0.039 sun-like star with a mass of 1.013 +/- 0.037 solar masses, a radius of 1.011 +/- 0.036 solar radii and a metallicity of -0.03 +/- 0.08. The planet itself is a typical hot Jupiter with a period of 3.5852467 +/- 0.0000064 days, a mass of 0.582 +/- 0.056 Jupiter masses and a radius of 1.182 +/- 0.055 Jupiter radii. This discovery adds to the increasing sample of transiting planets with measured bulk densities, which is needed to put constraints on models of planetary structure and formation theories.Comment: 7 pages, 4 figures, accepted for publication in PAS

    HAT-P-57b: A Short-Period Giant Planet Transiting A Bright Rapidly Rotating A8V Star Confirmed Via Doppler Tomography

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    We present the discovery of HAT-P-57b, a P = 2.4653 day transiting planet around a V = 10.465 +- 0.029 mag, Teff = 7500 +- 250 K main sequence A8V star with a projected rotation velocity of v sin i = 102.1 +- 1.3 km s^-1. We measure the radius of the planet to be R = 1.413 +- 0.054 R_J and, based on RV observations, place a 95% confidence upper limit on its mass of M < 1.85 M_J . Based on theoretical stellar evolution models, the host star has a mass and radius of 1.47 +- 0.12 M_sun, and 1.500 +- 0.050 R_sun, respectively. Spectroscopic observations made with Keck-I/HIRES during a partial transit event show the Doppler shadow of HAT-P-57b moving across the average spectral line profile of HAT-P- 57, confirming the object as a planetary system. We use these observations, together with analytic formulae that we derive for the line profile distortions, to determine the projected angle between the spin axis of HAT-P-57 and the orbital axis of HAT-P-57b. The data permit two possible solutions, with -16.7 deg < lambda < 3.3 deg or 27.6 deg < lambda < 57.4 deg at 95% confidence, and with relative probabilities for the two modes of 26% and 74%, respectively. Adaptive optics imaging with MMT/Clio2 reveals an object located 2.7" from HAT-P-57 consisting of two point sources separated in turn from each other by 0.22". The H and L -band magnitudes of the companion stars are consistent with their being physically associated with HAT-P-57, in which case they are stars of mass 0.61 +- 0.10 M_sun and 0.53 +- 0.08 M_sun. HAT-P-57 is the most rapidly rotating star, and only the fourth main sequence A star, known to host a transiting planet.Comment: 18 pages, 14 figures, 5 tables, accepted for publication in A
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