Movatterモバイル変換
[0]ホーム
4 AQL (4 Aquilae). Shiftingconstellationboundaries, not to mention "new" (now several hundred years old)constellations, can play havoc withstarnames. The most westerlyFlamsteed star inAquila, the Eagle, is fifth magnitude(5.02) 4 Aquilae. Whatever happened to 1, 2, and 3 Aquilae? Theyare to be found in the modern constellation ofScutum (invented by Hevelius in 1684), the Shield, justoff the Eagle's southwestern edge, which was ignored by Flamsteed. The trio later becameAlpha,Delta, andEpsilonScuti. At a healthy distance of 465 light years (give or take15), 4 Aql nicely stands out in its own right not just as a classB (B9)dwarf, but also as a"B-emission" ("Be") star that is surrounded by a radiating disk. Classic examples areGamma CassiopiaeandZeta Tauri. Four Aql's disk seemsto be set more or less on edge, making it into a "shell star" (asthe light from the star must shine through the disk, which acts asa sort-of "shell"). Though set into theMilkyWay, there is no evidence for any dimming byinterstellar dust. With atemperature of 10,970 Kelvin (needed to account for]spectra.html#emspectrum">ultraviolet light), 4 Aquilaeradiates at a rate of 242 times that of theSun, which with temperature gives a stellarradius of 4.3 times solar. As is the case for all Be stars, 4Aquilae is a fast rotator, spinning with an equatorial speed of atleast 265 kilometers per second (with a large uncertainty), whichgives it a rotation period of under 0.8 days (the link between thedisk and rotation not entirely clear). The theory of stellarstructure and evolution yields a mass of 3.4 times that of the Sun,and shows the star to be nearing the end of its dwarf lifetime ofsome 270 million years. It will eventually slough off its outerlayers and die as awhitedwarf with a mass of about three-fourths that of the Sun. TheFlamsteed numbers then spread across the constellation toward theeast, ending in71 Aquilae, 6 and 9 Aquilae renamed asBeta and Eta Scuti. (Thanks to MortonWagman in his "Lost Stars").
Written byJim Kaler 9/20/13. Return toSTARS.
[8]ページ先頭