We fit the data for the binary lens microlensing event MACHO 98-SMC-1 from five different microlensing collaborations and find two distinct solutions characterized by binary separation d and mass ...ratio q: (d,q)=(0.54,0.50) and (d,q)=(3.65,0.36), where d is in units of the Einstein radius. However, the relative proper motion of the lens is very similar in the two solutions, 1.30 km s-1 kpc-1 and 1.48 km s-1 kpc-1, thus confirming that the lens is in the Small Magellanic Cloud. The close binary can be either rotating or approximately static but the wide binary must be rotating at close to its maximum allowed rate to be consistent with all the data. We measure limb-darkening coefficients for five bands ranging from I to V. As expected, these progressively decrease with rising wavelength. This is the first measurement of limb darkening for a metal-poor A star. (c) 2000 The American Astronomical Society.
The two rings of (50000) Quaoar Pereira, C. L.; Sicardy, B.; Morgado, B. E. ...
Astronomy and astrophysics (Berlin),
05/2023, Letnik:
673
Journal Article
Recenzirano
Odprti dostop
Context.
Quaoar is a classical trans-Neptunian object (TNO) with an area-equivalent diameter of 1100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations ...observed between 2018 and 2021, an inhomogeneous ring (Q1R, i.e., Quaoar’s first ring) has been detected around this body.
Aims.
A new stellar occultation by Quaoar was observed on August 9, 2022, with the aim of improving Quaoar’s shape models and the physical parameters of Q1R, while searching for additional material around the body.
Methods.
The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements).
Results.
Quaoar’s elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of 579.5 ± 4.0 km, apparent oblateness of 0.12 ± 0.01, and area-equivalent radius of 543 ± 2 km. Quaoar’s limb orientation is consistent with Q1R and Weywot orbiting in Quaoar’s equatorial plane. The orbital radius of Q1R is refined to a value of 4057 ± 6 km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of ∼5 km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of 2520 ± 20 km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10 km and a normal optical depth of ∼0.004. Just as Q1R, it also lies outside Quaoar’s classical Roche limit.
We present a measurement of the systemic proper motion of the Large Magellanic Cloud (LMC) from astrometry with the High Resolution Camera (HRC) of the Advanced Camera for Surveys (ACS) on the Hubble ...Space Telescope (HST). We observed LMC fields centered on 21 background QSOs that were discovered from their optical variability in the MACHO database. The QSOs are distributed homogeneously behind the central few degrees of the LMC. With two epochs of HRC data and a 62 yr baseline, we determine the proper motion of the LMC to better than 5% accuracy: k sub(W) = -2.03 c 0.08 mas yr super(-1), and k sub(N) = 0.44 c 0.05 mas yr super(-1). This is the most accurate proper-motion measurement for any Milky Way satellite thus far. When combined with H I data from the Magellanic Stream, this should provide new constraints on both the mass distribution of the Galactic halo and models of the Stream.
Early Optical Brightening in GRB 071010B Wang, J. H; Schwamb, M. E; Huang, K. Y ...
The Astrophysical journal,
05/2008, Letnik:
679, Številka:
1
Journal Article
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We report the detection of early (60-230 s) optical emission of the gamma-ray burst afterglow of GRB 071010B. No significant correlation with the prompt Y-ray emission was found. Our high time ...resolution data combining with other measurements within 2 days after the burst indicate that GRB 071010B is composed of a weak early brightening ( alpha similar to 0.6), probably caused by the peak frequency passing through the optical wavelengths, followed by a decay ( alpha similar to -0.51), attributed to continuous energy injection by patchy Jets.
In general, patients with malignant tumours of the skull base have a poor prognosis. Treatment may have a disfiguring physical and disabling mental effect on patients. To evaluate the effect of ...treatment on physical and mental quality of life in patients with skull base malignancy, we conducted a cross-sectional patient survey of 18 patients treated for such tumours, using the University of Washington (version 4) quality of life questionnaire and the hospital anxiety and depression scale. The total quality of life score (median value) was 980 (550-1125). Patients with anterior skull base malignancy scored lower than those with lateral skull base malignancy (p=0.003). In general, the worst individual domain scores were: mood (64 per cent); activity (69 per cent); and, specifically for patients with anterior skull base malignancy, taste (54 per cent, p=0.004) and anxiety (60 per cent, p=0.034). One-third of skull base cancer patients were at risk of suffering from mental distress and psychiatric morbidity (indicated as a score of more than seven on the hospital anxiety and depression scale).
We present a catalog of 450 relatively high signal-to-noise ratio microlensing events observed by the MACHO collaboration between 1993 and 1999. The events are distributed throughout our fields, and ...as expected, they show a clear concentration toward the Galactic center. No optical depth is given for this sample, since no blending efficiency calculation has been performed and we find evidence for substantial blending. In a companion paper we give optical depths for the subsample of events on clump giant source stars, where blending is a less significant effect. Several events with sources that may belong to the Sagittarius dwarf galaxy are identified. For these events even relatively low dispersion spectra could suffice to classify these events as either consistent with Sagittarius membership or as non-Sagittarius sources. Several unusual events, such as microlensing of periodic variable source stars, binary lens events, and an event showing extended source effects, are identified. We also identify a number of contaminating background events as cataclysmic variable stars.
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