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Heliocentric Distances (heliocentric + distance)

Distribution by Scientific Domains

Physics and Astronomy	100%

Selected Abstracts

Cosmic-ray exposure age and heliocentric distance of the parent bodies of enstatite chondrites ALH 85119 and MAC 88136

METEORITICS & PLANETARY SCIENCE, Issue 6 2006
D. Nakashima
These two meteorites contain solar and cosmogenic noble gases. Based on the solar and cosmogenic noble gas compositions, we calculated heliocentric distances, parent body exposure ages, and space exposure ages of the two meteorites. The parent body exposure ages are longer than 6.7 Ma for ALH 85119 and longer than 8.7 Ma for MAC 88136. The space exposure ages are shorter than 2.2 Ma for ALH 85119 and shorter than 3.9 Ma for MAC 88136. The estimated heliocentric distances are more than 1.1 AU for ALH 85119 and 1.3 AU for MAC 88136. Derived heliocentric distances indicate the locations of parent bodies in the past when constituents of the meteorites were exposed to the Sun. From the mineralogy and chemistry of E chondrites, it is believed that E chondrites formed in regions within 1.4 AU from the Sun. The heliocentric distances of the two E chondrite parent bodies are not different from the formation regions of E chondrites. This may imply that heliocentric distances of E chondrites have been relatively constant from their formation stage to the stage of exposure to the solar wind. [source]

The distant activity of Short Period Comets,, II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
E. Mazzotta Epifani
ABSTRACT The activity of the Short Period Comets (SPCs) at large heliocentric distance (Rh > 3 au) occurs in a region of the Solar system where the water sublimation rate is low and so the sublimation of other volatiles, for example CO or CO2, could drive the presence of a coma. The detection of distant activity in a SPC can therefore give important hints on its composition. Moreover, a complete characterization of the distant SPCs degree of activity is crucial in order to give correct estimates of the nucleus size and to obtain more reliable size-distribution curves of cometary nuclei. The aim of this paper is to present the last results of a program of CCD imaging of distant SPCs, started in 2004 December and concluded with observing runs at the 3.5-m Telescopio Nazionale Galileo at La Palma, in 2005 April, and at the 2.2-m Centro Astronómico Hispano Alemán (CAHA) telescope in Spain, in 2005 May. During the Spring 2005 campaign, 12 SPCs have been targeted in the R band (eight numbered SPCs and four still unnumbered SPCs): 61P/Schajn,Schaldach, 71P/Clark, 98P/Takamizawa, 103P/Hartley 2, 117P/Helin,Roman,Alu 1, 118P/Shoemaker,Levy 4, 121P/Shoemaker,Holt 2, 136P/Mueller 3, P/2002 T5 (LINEAR), P/2003 S1 (NEAT), P/2003 S2 (NEAT), P/2004 DO29 (Spacewatch,LINEAR). The heliocentric distance of the targets was 3.05 ,Rh, 5.30 au. Several levels of activity were detected in the sample, from stellar appearance to well-developed coma and tail. In some cases, the occurrence of cometary activity could be enhanced only with deep visible imaging (e.g. with very long exposure time). For comets with stellar appearance, it was possible to derive a value or a range for the nucleus radius rnucleus (assuming a ,classical' albedo value of 0.04): 98P (rnucleus= 0.43 ± 0.10 km), 136P (rnucleus= 1.2 ± 0.2 km), P/2003 S2 (rnucleus= 0.81 to 1.55 km). For the active comets, we measured dust production levels in terms of Af, quantity, which was 9.9 , Af,, 671 cm. Ensemble properties of the whole sample of the long-term program (a total of 17 SPCs) have been analysed in terms of the relationship among distant activity and dynamical evolution of the targets (in particular, an inward ,jump' of the perihelion distance): we can conclude that, even if there is some theoretical indication that this could occur, the hypothesis of distant activity triggered by a rise in perihelion temperature cannot be univocally invoked for these comets. [source]

Displacement of the Sun from the Galactic plane

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
Y. C. Joshi
ABSTRACT We have carried out a comparative statistical study for the displacement of the Sun from the Galactic plane (z,) following three different methods. The study has been carried out using a sample of 537 young open clusters (YOCs) with log (Age) < 8.5, lying within a heliocentric distance of 4 kpc, and 2030 OB stars observed up to a distance of 1200 pc, all of which have distance information. We statistically separated the members of the Gould Belt before investigating the variation in the z, estimation with different upper cut-off limits in the heliocentric distance and distance perpendicular to the Galactic plane. We have found that z, varies in the range ,13,20 pc from the analysis of YOCs and in the range ,6,28 pc from the analysis of OB stars. A significant scatter in z,, because of different cut-off values, is noticed for the OB stars, although no such deviation is seen for the YOCs. We have also determined scaleheights of 56.9+3.8,3.4 and 61.4+2.7,2.4 pc for the distribution of YOCs and OB stars, respectively. [source]

Cosmic-ray exposure age and heliocentric distance of the parent bodies of enstatite chondrites ALH 85119 and MAC 88136

Photometry of cometary nuclei: rotation rates, colours and a comparison with Kuiper Belt Objects,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
C. Snodgrass
ABSTRACT We present time-series data on Jupiter Family Comets (JFCs) 17P/Holmes, 47P/Ashbrook-Jackson and 137P/Shoemaker-Levy 2. In addition we also present results from ,snap-shot' observations of comets 43P/Wolf-Harrington, 44P/Reinmuth 2, 103P/Hartley 2 and 104P/Kowal 2 taken during the same run. The comets were at heliocentric distances of between 3 and 7 au at this time. We present measurements of size and activity levels for the snap-shot targets. The time-series data allow us to constrain rotation periods and shapes, and thus bulk densities. We also measure colour indices (V,R) and (R,I) and reliable radii for these comets. We compare all of our findings to date with similar results for other comets and Kuiper Belt Objects (KBOs). We find that the rotational properties of nuclei and KBOs are very similar, that there is evidence for a cut-off in bulk densities at ,0.6 g cm,3 in both populations, and the colours of the two populations show similar correlations. For JFCs, there is no observational evidence for the optical colours being dependent on either position in the orbit or orbital parameters. [source]

The destruction of cometary grains and changes in the luminosity of comets

ASTRONOMISCHE NACHRICHTEN, Issue 8 2009
P. Gronkowski
Abstract One explanation of the sudden changes in the brightness of comets is proposed based on the author's earlier suggestions involving the fragmentation of cometary grains. Within the inner coma, a core-mantle model of the structure of grains is assumed. The proposed mechanism is a combination of electrostatic stress and thermodynamical fragmentation of the cometary grains water-ice mantle. It has been shown that the vapour pressure of volatile inclusions placed in the waterice mantle of grains can increase sufficiently to cause their fragmentation. It takes place before grains can completely sublime into the vacuum away. Numerical calculations have been carried out for a large range of values of probable physical characteristics of cometary material. The proposed approach yields increases in cometary brightness consistent with observations of typical cometary outbursts. It is concluded that this approach can provide an explanation of the sudden change in activity of comets for a wide range of heliocentric distances (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]