8,807 research outputs found

    Detection of Contact Binaries Using Sparse High Phase Angle Lightcurves

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    We show that candidate contact binary asteroids can be efficiently identified from sparsely sampled photometry taken at phase angles >60deg. At high phase angle, close/contact binary systems produce distinctive lightcurves that spend most of the time at maximum or minimum (typically >1mag apart) brightness with relatively fast transitions between the two. This means that a few (~5) sparse observations will suffice to measure the large range of variation and identify candidate contact binary systems. This finding can be used in the context of all-sky surveys to constrain the fraction of contact binary near-Earth objects. High phase angle lightcurve data can also reveal the absolute sense of the spin.Comment: 4 pages, 4 figures, 1 table. Accepted for publication in ApJ

    CCD photometry of 2060 Chiron, 1991 January

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    Observations of 2060 Chiron was performed on 7 to 8 Jan. 1991 with the Mt. Palomar 1.52 m telescope in the Gunn-R passband. On-chip field stars were used to perform differential reductions. The repeatability of the 5.9 hour light curve was excellent, both within a night and from night to night. No evidence for short-term secular variations similar to those seen last year by both Luu and Jewitt (1990) and Buratti and Dunbar (1991) is seen in the new light curve. Chiron's rotational light curve appears strikingly similar to that obtained a year earlier by Luu and Jewitt (1990), both in amplitude and shape. Both light curves show strongly correlated changes over a timescale of perhaps 15 minutes. These same features were marginally visible in the 1986 light curve. Such behavior is believed to be evidence that Chiron may be more aspherical than the 4 percent intensity variation might otherwise indicate, and favors a viewing geometry where the subearth latitude is rather low. Chiron was much fainter in 1985, when a partial light curve was obtained by Marcialis. Due to the lower sampling rate of these early data, no conclusions can be made regarding the high-frequency light curve structure back then. All three of these light curves differ significantly from that obtained by Buratti and Dunbar (1991), one week before the observations of Luu and Jewitt. The Chiron field was calibrated using Landolt standards on Ut 15 Mar. 1991. A mean R-magnitude of 15.6 + or - 0.1 was found. Variability of 2060 Chiron was demonstrated over timescales of minutes, hours, and years. An intense campaign was urged to monitor the photometric behavior of Chiron throughout the 1990s

    Chasing the second gamma-ray bright isolated neutron star: 3EG J1835+5918/RX J1836.2+5925

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    The EGRET telescope aboard NASAs Compton GRO has repeatedly detected 3EG J1835+5918, a bright and steady source of high-energy gamma-ray emission with no identification suggested until recently. The long absence of any likely counterpart for a bright gamma-ray source located 25 degrees off the Galactic plane initiated several attempts of deep observations at other wavelengths. We report on counterparts in X-rays on a basis of a 60 ksec ROSAT HRI image. In order to conclude on the plausibility of the X-ray counterparts, we reanalyzed data from EGRET at energies above 100 MeV and above 1 GeV, including data up to CGRO observation cycle 7. The gamma-ray source location represents the latest and probably the final positional assessment based on EGRET data. The X-ray counterparts were studied during follow-up optical identification campaigns, leaving only one object to be likely associated with the gamma-ray source 3EG J1835+5918. This object, RX J1836.2+5925, has the characteristics of an isolated neutron star and possibly of a radio-quiet pulsar.Comment: 5 pages, 3 figures. To appear in the Proceedings of the 270. WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan. 21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J. Truemper. Proceedings are available as MPE-Report 27

    The Gamma Ray Pulsar Population

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    We apply a likelihood analysis to pulsar detections, pulsar upper limits, and diffuse background measurements from the OSSE and EGRET instruments on the Compton Gamma Ray Observatory to constrain the luminosity law for gamma-ray pulsars and some properties of the gamma-ray pulsar population. We find that the dependence of luminosity on spin period and dipole magnetic field is much steeper at OSSE than at EGRET energies (50-200 keV and >100 MeV, respectively), suggesting that different emission mechanisms are responsible for low- and high-energy gamma-ray emission. Incorporating a spin-down model and assuming a pulsar spatial distribution, we estimate the fraction of the Galactic gamma-ray background due to unidentified pulsars and find that pulsars may be an important component of the OSSE diffuse flux, but are most likely not important at EGRET energies. Using measurements of the diffuse background flux from these instruments, we are able to place constraints on the braking index, initial spin period, and magnetic field of the Galactic pulsar population. We are also able to constrain the pulsar birthrate to be between 1/(25 yr) and 1/(500 yr). Our results are based on a large gamma-ray beam, but they do not scale in a simple way with beam size. With our assumed beam size, the implied gamma-ray efficiency for the EGRET detections is no more than 20%. We estimate that about 20 of the 169 unidentified EGRET sources are probably gamma-ray pulsars. We use our model to predict the pulsar population that will be seen by future gamma-ray instruments and estimate that GLAST will detect roughly 750 gamma-ray pulsars as steady sources, only 120 of which are currently known radio pulsars.Comment: 32 pages, including figures. submitted to Ap

    Polymorphisms in the circadian expressed genes PER3 and ARNTL2 are associated with diurnal preference and GNβ3 with sleep measures

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    Sleep and circadian rhythms are intrinsically linked, with several sleep traits, including sleep timing and duration, influenced by both sleep homeostasis and the circadian phase. Genetic variation in several circadian genes has been associated with diurnal preference (preference in timing of sleep), although there has been limited research on whether they are associated with other sleep measurements. We investigated whether these genetic variations were associated with diurnal preference (Morningness-Eveningness Questionnaire) and various sleep measures, including: the global Pittsburgh Sleep Quality index score; sleep duration; and sleep latency and sleep quality. We genotyped 10 polymorphisms in genes with circadian expression in participants from the G1219 sample (n = 966), a British longitudinal population sample of young adults. We conducted linear regressions using dominant, additive and recessive models of inheritance to test for associations between these polymorphisms and the sleep measures. We found a significant association between diurnal preference and a polymorphism in period homologue 3 (PER3) (P < 0.005, recessive model) and a novel nominally significant association between diurnal preference and a polymorphism in aryl hydrocarbon receptor nuclear translocator-like 2 (ARNTL2) (P < 0.05, additive model). We found that a polymorphism in guanine nucleotide binding protein beta 3 (GNβ3) was associated significantly with global sleep quality (P < 0.005, recessive model), and that a rare polymorphism in period homologue 2 (PER2) was associated significantly with both sleep duration and quality (P < 0.0005, recessive model). These findings suggest that genes with circadian expression may play a role in regulating both the circadian clock and sleep homeostasis, and highlight the importance of further studies aimed at dissecting the specific roles that circadian genes play in these two interrelated but unique behaviours
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