<i>Astrophysical Quantities</i>
            . C. W. Allen. Athlone Press, London, 1955 (distributed in the United States by John de Graff, Inc., New York 10). xi + 263 pp. $10.

Aller, L. H.

doi:10.1126/science.123.3200.735.a

Cited by 211 publications

(258 citation statements)

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“…Stauffer 1996) that this cluster has similar age as the Hyades (∼ 600 Myr). A conservative estimate lies between 400 Myr, the value reported by Allen (1973), and 900 Myr, as reported by Vandenberg & Bridges (1984). Following Hambly et al (1995) we will assume extinction and reddening to be zero in front of Praesepe.…”

Section: Discussionmentioning

confidence: 98%

A Brown Dwarf Candidate in the Praesepe Open Cluster

Magazzù¹,

Реболо²,

Osorio³

et al. 1998

The Astrophysical Journal

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We present optical and infrared observations of RPr 1, a faint (I = 21.01) and very red object (I − K = 4.57) discovered in a deep CCD survey, covering an area of 800 square arcmin of the Praesepe open cluster. A low resolution spectrum shows that RPr 1 is a very late object, the latest object in Praesepe for which a spectrum has been taken to date. Our estimates give a mass between 0.063 and 0.084 M ⊙ , and indicate that RPr 1 may turn out to be the first brown dwarf in this cluster.

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Section: Discussionmentioning

confidence: 98%

A Brown Dwarf Candidate in the Praesepe Open Cluster

Magazzù¹,

Реболо²,

Osorio³

et al. 1998

The Astrophysical Journal

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“…The combined emissivity of the the Si VIII lines peaks at 2.3 × 10 −26 erg cm 6 s −1 according to CHIANTI (Landi et al 1999) assuming the Mazzotta et al (1998) ionization equilibrium and Allen (1973) silicon abundance, with excitation rates from Bhatia & Mason (1980). Departure from ionization equilibrium cannot greatly enhance this emissivity, because the Mazzotta et al calculations show a fairly large fraction of silicon in this ion near its peak abundance.…”

Section: Uv Emission From the X-ray Emitting Gasmentioning

confidence: 99%

A Detailed Analysis of a Cygnus Loop Shock-Cloud Interaction

Danforth¹,

Blair²,

Raymond³

2001

The Astronomical Journal

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The XA region of the Cygnus Loop is a complex zone of radiative and nonradiative shocks interacting with interstellar clouds. We combine five far ultraviolet spectral observations from the Hopkins Ultraviolet Telescope (HUT), a grid of 24 IUE spectra and a high-resolution longslit Halpha spectrum to study the spatial emission line variations across the region. These spectral data are placed in context using ground-based, optical emission line images of the region and a far-UV image obtained by the Ultraviolet Imaging Telescope (UIT). The presence of high-ionization ions (OVI, NV, CIV) indicates a shock velocity near 170 km/s while other diagnostics indicate v_shock=140 km/s. It is likely that a large range of shock velocities may exist at a spatial scale smaller than we are able to resolve. By comparing CIV 1550, CIII 977 and CIII] 1909, we explore resonance scattering across the region. We find that a significant column depth is present at all positions, including those not near bright optical/UV filaments. Analysis of the OVI doublet ratio suggests an average optical depth of about unity in that ion while flux measurements of [SiVIII] 1443 suggest a hot component in the region at just below 10^6K. Given the brightness of the OVI emission and the age of the interaction, we rule out the mixing layer interpretation of the UV emission. Furthermore, we formulate a picture of the XA region as the encounter of the blast wave with a finger of dense gas protruding inward from the pre-SN cavity.Comment: 21 pages, 9 figures, accepted by the Astronomical Journal, July 2001 Full resolution figures available at http://fuse.pha.jhu.edu/~danforth/xa

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“…where p is the albedo, and the object diameter is D (assuming a spherical asteroid). The constant 17.9 was derived by assuming that the apparent magnitude of the Sun in the r ′ band is -26.95, obtained from V ⊙ = -26.75 and (B − V ) ⊙ = 0.65 (Allen 1973) with the aid of photometric transformations from Fukugita et al (1996). This constant in an equivalent expression for the IAU-recommended (see e.g.…”

Section: 2mentioning

confidence: 99%

Solar System Objects Observed in the Sloan Digital Sky Survey Commissioning Data

Ivezić¹,

Tabachnik²,

Rafikov³

et al. 2001

The Astronomical Journal

433

384

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We discuss measurements of the properties of ∼10,000 asteroids detected in 500 deg 2 of sky in the Sloan Digital Sky Survey (SDSS) commissioning data. The moving objects are detected in the magnitude range 14 < r * < 21.5, with a baseline of ∼5 minutes, resulting in typical velocity errors of ∼3%. Extensive tests show that the sample is at least 98% complete, with the contamination rate of less than 3%.We find that the size distribution of asteroids resembles a broken power-law, independent of the heliocentric distance: D −2.3 for 0.4 km ∼ < D ∼ < 5 km, and D −4 for 5 km ∼ < D ∼ < 40 km. As a consequence of this break, the number of 1 Based on observations obtained with the Sloan Digital Sky Survey.-3asteroids with r * < 21.5 is ten times smaller than predicted by extrapolating the power-law relation observed for brighter asteroids (r * ∼ < 18). The observed counts imply that there are about 530,000 objects with D > 1 km in the asteroid belt, or about four times less than previous estimates. We predict that by its completion SDSS will obtain about 100,000 near simultaneous five-band measurements for a subset drawn from 280,000 asteroids brighter than r * < 21.5 at opposition. Only about a third of these asteroids have been previously observed, and usually in just one band.The distribution of main belt asteroids in the 4-dimensional SDSS color space is bimodal, and the two groups can be associated with S (rocky) and C (carbonaceous) asteroids. A strong bimodality is also seen in the heliocentric distribution of asteroids and suggests the existence of two distinct belts: the inner rocky belt, about 1 AU wide (FWHM) and centered at R ∼2.8 AU, and the outer carbonaceous belt, about 0.5 AU wide and centered at R ∼3.2 AU. The median color of each class becomes bluer by about 0.03 mag AU −1 as the heliocentric distance increases. The observed number ratio of S and C asteroids in a sample with r * < 21.5 is 1.5:1, while in a sample limited by absolute magnitude it changes from 4:1 at 2 AU, to 1:3 at 3.5 AU. In a size-limited sample with D > 1 km, the number ratio of S and C asteroids in the entire main belt is 1:2.3.The colors of Hungarias, Mars crossers, and near-Earth objects, selected by their velocity vectors, are more similar to the C-type than to S-type asteroids, suggesting that they originate in the outer belt. In about 100 deg 2 of sky along the Celestial Equator observed twice two days apart, we find one plausible Kuiper Belt Object (KBO) candidate, in agreement with the expected KBO surface density. The colors of the KBO candidate are significantly redder than the asteroid colors, in agreement with colors of known KBOs. We explore the possibility that SDSS data can be used to search for very red, previously uncatalogued asteroids observed by 2MASS, by extracting objects without SDSS counterparts. We do not find evidence for a significant population of such objects; their contribution is no more than 10% of the asteroid population.

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Astrophysical Quantities . C. W. Allen. Athlone Press, London, 1955 (distributed in the United States by John de Graff, Inc., New York 10). xi + 263 pp. $10.

Cited by 211 publications

References 0 publications

A Brown Dwarf Candidate in the Praesepe Open Cluster

A Brown Dwarf Candidate in the Praesepe Open Cluster

A Detailed Analysis of a Cygnus Loop Shock-Cloud Interaction

Solar System Objects Observed in the Sloan Digital Sky Survey Commissioning Data

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