1,285 research outputs found

    A Possible Detection of Occultation by a Proto-planetary Clump in GM Cephei

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    GM Cep in the young (~ 4 Myr) open cluster Trumpler 37 has been known to be an abrupt variable and to have a circumstellar disk with very active accretion. Our monitoring observations in 2009–2011 revealed the star to show sporadic ?are events, each with brightening of . 0.5 mag lasting for days. These brightening events, associated with a color change toward the blue, should originate from an increased accretion activity. Moreover, the star also underwent a brightness drop of ~ 1 mag lasting for about a month, during which the star became bluer when fainter. Such brightness drops seem to have a recurrence time scale of a year, as evidenced in our data and the photometric behavior of GM Cep over a century. Between consecutive drops, the star brightened gradually by about 1 mag and became blue at peak luminosity. We propose that the drop is caused by obscuration of the central star by an orbiting dust concentration. The UX Orionis type of activity in GM Cep therefore exemplifies the disk inhomogeneity process in transition between grain coagulation and planetesimal formation in a young circumstellar disk

    Interferometric Studies of Interstellar Calcium Lines

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    Interferometric, photoelectric scans of the interstellar calcium K-lines in the spectra of 65 stars are presented. The scans were obtained with a PEPSIOS spectrometer having a passband with a full half-intensity width of 1.0 kms(-1) or 0.013A. The fivefold improvement in resolution over that used by Adams reveals numerous line components which correspond very well to those of the interstellar sodium lines, apart from frequent differences in relative intensities

    Foraging in a patchy environment: prey-encounter rate and residence time distributions

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    Small bluegill sunfish, Lepomis macrochirus, foraging among patches in the laboratory did not search systematically within a patch; their intercapture intervals did not differ from a model of random prey encounter within a patch. Patch-residence time, number of prey eaten, and giving-up time (time between last prey capture and leaving the patch) were measured for bluegills foraging in two different three-patch 'environments' (a constant environment, in which each patch began with the same number of prey and a variable environment, in which two patches began with low prey density and one patch with high prey density). When compared with three decision rules a forager may use to determine when to leave a patch, the data most closely agreed with predictions from a 'constant residence time' rule. Bluegills responded to changes in the distribution of prey among patches, but not by using different decision rules. There was qualitative, but not quantitative, agreement with a model of random residence times. The total number of prey eaten by a bluegill during a foraging bout was similar to the number predicted from a model of random search and random residence times

    Voicing our concerns: Attempts at Decentring German Theatre and Performance Studies

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    The field of German Theatre and Performance Studies shows a lack of engagement with colonial history and questions of race. Its overwhelming whiteness manifests itself in a persistent ignorance of a decades-long tradition of works produced by women of colour, feminists, and Black, Indigenous and People of Colour (BIPOC) researchers and activists who have actively worked on decentring the discipline from a German-speaking context. This article, a critical conversation between four German theatre scholars, sets out to clarify what it means to decentre GTPS from a Western-centric focus and proposes some methodological solutions to achieve this goal. Through reflecting on our own educational experiences and the sharing of anecdotes from the classroom, we conclude that decentring means more than adding to the reading list, rather it entails a visceral, continuous unlearning of racist attitudes and methodologies and requires a careful positioning of teachers, students and researchers alike

    Photometry of the Chromospherically Active Binary HD 197010

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    For the past several years we have been conducting a study of the spectroscopic and photometric characteristics of a sample X-ray emitting stars from the Einstein Observatory Medium Sensitivity Survey identified as probable binary systems by Fleming (1988) and Fleming, et al.(1989). One of these stars, HD 197010 ( = 1E2038.3-0046 = SAO 144692 = BD -1degree 4025) was discovered to be a short period eclipsing binary by Robb, et al.(1990). The ephemeris he presented was based on observations in 1989 and 1990, but only the 1990 observations included points at eclipse minimum. We report here on first results of almost a year of observations at Gettysburg College Observatory and the National Undergraduate Research Observatory, permitting a new determination of the photometric ephemeris of HD 197010

    Improved OCT Human Corneal segmentation Using Bayesian Residual Transform

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    The inherent poor signal to noise ratio of Optical Coherent Tomography(OCT) is considered as a main limitation of OCT segmentation,particularly because images are sampled quickly, at high resolutions,and in-vivo. Furthermore, speckle noise is generated bythe reflections of the OCT LASER limits the ability of automaticallysegmenting OCT images. This paper presents a novel method toautomatically segment human corneal OCT images. The proposedmethod uses Bayesian Residual Transform (BRT) to build a noiserobust external force map, that guides active contours model to thecorneal data in OCT images. Experimental results show that theproposed method outperforms the classical as well as the state-ofthe-art methods

    SAO 23229: A New Double-Lined Spectroscopic Eclipsing Binary

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    The discovery of eclipses of the bright star SAO 23229 (HD 14384; V=6.9; Spectral Type F5 V) by Indiana observer Dan Kaiser was described in a recent article in Sky and Telescope magazine (MacRobert, 1990). Photoelectric observations by H. Landis and D. Williams, reproduced in that article, show eclipses of 0.55 mag depth and period of 2.111 days. No secondary eclipses are reported, leaving open the question of whether the system contains a very dim secondary or whether it consists of two identical stars with an actual period of 4.2 days. We report here observations that favor the latter interpretation. [excerpt
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