We attempt to identify all microlensing parallax events for which the parallax fit improves Chi super(2) > 100 relative to a standard microlensing model. We outline a procedure to identify three ...types of discrete degeneracies (including a new one that we dub the "ecliptic degeneracy") and find many new degenerate solutions in 16 previously published and six unpublished events. Only four events have one unique solution, and the other 18 events have a total of 44 solutions. Our sample includes three previously identified black hole (BH) candidates. We consider the newly discovered degenerate solutions and determine the relative likelihood that each of these is a BH. We find that the lens of event MACHO-99-BLG-22 is a strong BH candidate (78%), event MACHO-96-BLG-5 is a marginal BH candidate (37%), and MACHO-98-BLG-6 is a weak BH candidate (2.2%). The lens of event OGLE-2003-BLG-84 may be a Jupiter-mass free-floating planet candidate based on a weak 3 s detection of finite-source effects. We find that event MACHO-179-A is a brown dwarf candidate within 6100 pc of the Sun, mostly due to its very small projected Einstein radius, r sub(E) = 0.23 c 0.05 AU. As expected, these microlensing parallax events are biased toward lenses that are heavier and closer than average. These events were examined for xallarap (or binary-source motion), which can mimic parallax. We find that 23% of these events are strongly affected by xallarap.
The Spatial Structure of an Accretion Disk Poindexter, Shawn; Morgan, Nicholas; Kochanek, Christopher S
The Astrophysical journal,
01/2008, Letnik:
673, Številka:
1
Journal Article
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Odprti dostop
Based on the microlensing variability of the two-image gravitational lens HE 1104-1805 observed between 0.4 and 8 mu m, we have measured the size and wavelength-dependent structure of the quasar ...accretion disk. Modeled as a power law in temperature, T proportional to R super(-8), we measure a B-band (0.13 mu m in the rest frame) half-light radius of R sub(mh.B) = 6.7 super(+) sub(-) super(6) sub(3) super(.) sub(.) super(2) sub(3) x 10 super(15) cm (68% confidence level) and a logarithmic slope of beta = 0.61 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(2) sub(1) super(1) sub(7) (68% confidence level) for our standard model with a logarithmic prior on the disk size. Both the scale and the slope are consistent with simple thin disk models where beta = unk and R sub(mh.B) = 5.9 x 10 super(15) cm for a Shakura-Sunyaev disk radiating at the Eddington limit with 10% efficiency. The observed fluxes favor a slightly shallower slope, beta = 0.55 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(0) sub(0) super(8) sub(2), and a significantly smaller size for beta = unk.
Using 11 years of OGLE V-band photometry of Q2237+0305, we measure the transverse velocity of the lens galaxy and the mean mass of its stars. We can do so because, for the first time, we fully ...include the random motions of the stars in the lens galaxy in the analysis of the light curves. In doing so, we are also able to correctly account for Earth's parallax motion and the rotation of the lens galaxy, further reducing systematic errors. We measure a lower limit on the transverse speed of the lens galaxy, v{sub t} > 338 km s{sup -1} (68% confidence) and find a preferred direction to the east. The mean stellar mass estimate, including a well-defined velocity prior, is 0.12 <= (M/M{sub sun}) <= 1.94 at 68% confidence, with a median of 0.52 M{sub sun}. We also show for the first time that analyzing subsets of a microlensing light curve, in this case the first and second halves of the OGLE V-band light curve, gives mutually consistent physical results.
Using a microlensing analysis of 11 years of OGLE V-band photometry of the four image gravitational lens Q2237+0305, we measure the inclination i of the accretion disk to be cos i > 0.66 at 68% ...confidence. Very edge on (cos i < 0.39) solutions are ruled out at 95% confidence. We measure the V-band radius of the accretion disk, defined by the radius where the temperature matches the monitoring band photon emission, to be R{sub V} = 5.8{sup +3.8}{sub -2.3} x 10{sup 15} cm assuming a simple thin disk model and including the uncertainties in its inclination. The projected radiating area of the disk remains too large to be consistent with the observed flux for a T {proportional_to} R {sup -3/4} thin disk temperature profile. There is no strong correlation between the direction of motion (peculiar velocity) of the lens galaxy and the orientation of the disk.
The Kilodegree Extremely Little Telescope (KELT) project is a survey for planetary transits of bright stars. It consists of a small‐aperture, wide‐field automated telescope located at Winer ...Observatory near Sonoita, Arizona. The telescope surveys a set of 26° × 26° fields that together cover about 25% of the northern sky, and targets stars in the range of
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mag, searching for transits by close‐in Jupiters. This paper describes the system hardware and software and discusses the quality of the observations. We show that KELT is able to achieve the necessary photometric precision to detect planetary transits around solar‐type main‐sequence stars.
We employ three-band Spitzer-MIPS observations to search for cold dust emission in three neutral hydrogen compact high-velocity clouds (CHVCs) in the vicinity of the Milky Way. Far-infrared emission ...correlated with Hi column density was previously reported in HVC Complex C, indicating that this object contains dust heated by the Galactic radiation field at its distance of ~10 kpc. Assuming published Spitzer, IRAS, and Planck, IR-H I correlations for Complex C, our Spitzer observations are of sufficient depth to directly detect 160 mu m dust emission in the CHVCs if it is present at the same level as in Complex C, but no emission is detected in any of the targets. For one of the targets (CHVC289) which has well-localized Hi clumps, we therefore conclude that it is fundamentally different from Complex C, with either a lower dust-to-gas ratio or a greater distance from the Galactic disk (and consequently cooler dust temperature). Firm conclusions cannot be drawn for the other two Spitzer-observed CHVCs since their small-scale H I structures are not sufficiently well known; nonetheless, no extended dust emission is apparent despite their relatively high H I column densities. The lack of dust emission in CHVC289 suggests that at least some compact high-velocity clouds objects may exhibit very low dust-to-gas ratios and/or greater Galactocentric distances than large HVC complexes.
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