查看完整版本: Did you know:Planetary nebula

Did you know:Planetary nebula

<h1 class="firstHeading">Planetary nebula</h1><div id="bodyContent"><h3 id="siteSub"><div id="jump-to-nav"><a href="http://en.wikipedia.org/wiki/Planetary_nebula#searchInput"></a></div><!--Element not supported - Type: 8 Name: #comment--></h3><div class="thumb tright"><div class="thumbinner" style="WIDTH: 222px;"><a class="internal" title="NGC 6543, the Cat's Eye Nebula" href="http://en.wikipedia.org/wiki/Image:NGC6543.jpg"><img class="thumbimage" height="240" alt="NGC 6543, the Cat's Eye Nebula" src="http://upload.wikimedia.org/wikipedia/commons/thumb/5/5a/NGC6543.jpg/220px-NGC6543.jpg" width="220" longdesc="/wiki/Image:NGC6543.jpg"/></a>
                                <div class="thumbcaption"><div class="magnify" style="FLOAT: right;"><a class="internal" title="Enlarge" href="http://en.wikipedia.org/wiki/Image:NGC6543.jpg"><img height="11" alt="" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" width="15"/></a></div>NGC 6543, the <a title="Cat's Eye Nebula" href="http://en.wikipedia.org/wiki/Cat's_Eye_Nebula">Cat's Eye Nebula</a></div></div></div><p>A <b>planetary nebula</b> is an <a title="Astronomy" href="http://en.wikipedia.org/wiki/Astronomy">astronomical</a>
                        <a title="Astronomical object" href="http://en.wikipedia.org/wiki/Astronomical_object">object</a> consisting of a glowing shell of <a title="Gas" href="http://en.wikipedia.org/wiki/Gas">gas</a> and <a title="Plasma (physics)" href="http://en.wikipedia.org/wiki/Plasma_(physics)">plasma</a> formed by certain types of <a title="Star" href="http://en.wikipedia.org/wiki/Star">stars</a> at the end of their lives. They are in fact unrelated to <a title="Planet" href="http://en.wikipedia.org/wiki/Planet">planets</a>; the name originates from a supposed similarity in appearance to <a title="Gas giant" href="http://en.wikipedia.org/wiki/Gas_giant">giant planets</a>. They are a short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years. About 1,500 are known to exist in the <a title="Milky Way Galaxy" href="http://en.wikipedia.org/wiki/Milky_Way_Galaxy">Milky Way Galaxy</a>.</p><p>Planetary nebulae are important objects in astronomy because they play a crucial role in the <a title="Chemistry" href="http://en.wikipedia.org/wiki/Chemistry">chemical</a>
                        <a title="Evolution of the galaxy" href="http://en.wikipedia.org/wiki/Evolution_of_the_galaxy">evolution of the galaxy</a>, returning material to the <a title="Interstellar medium" href="http://en.wikipedia.org/wiki/Interstellar_medium">interstellar medium</a> which has been enriched in <a title="Heavy element" href="http://en.wikipedia.org/wiki/Heavy_element">heavy elements</a> and other products of <a title="Nucleosynthesis" href="http://en.wikipedia.org/wiki/Nucleosynthesis">nucleosynthesis</a> (such as carbon, nitrogen, oxygen and calcium). In other galaxies, planetary nebulae may be the only objects observable enough to yield useful information about chemical abundances.</p><p>In recent years, <a title="Hubble Space Telescope" href="http://en.wikipedia.org/wiki/Hubble_Space_Telescope">Hubble Space Telescope</a> images have revealed many planetary nebulae to have extremely complex and varied morphologies. About a fifth are roughly <a title="Sphere" href="http://en.wikipedia.org/wiki/Sphere">spherical</a>, but the majority are not spherically symmetric. The mechanisms which produce such a wide variety of shapes and features are not yet well understood, but <a title="Binary star" href="http://en.wikipedia.org/wiki/Binary_star">binary central stars</a>, <a title="Stellar wind" href="http://en.wikipedia.org/wiki/Stellar_wind">stellar winds</a> and <a title="Magnetic field" href="http://en.wikipedia.org/wiki/Magnetic_field">magnetic fields</a> may all play a role.</p></div>

<p>Stingray Nebula</p><p>&nbsp;</p><p>The <b>Stingray nebula</b> (Hen-1357) is the youngest known <a title="Planetary nebula" href="http://en.wikipedia.org/wiki/Planetary_nebula">planetary nebula</a> (PN). (<a title="Stingray Nebula" href="http://en.wikipedia.org/wiki/Stingray_Nebula#CITEREFGry2002">Gry 2002</a>) The Stingray is located in the direction of the southern constellation <a title="Ara (constellation)" href="http://en.wikipedia.org/wiki/Ara_(constellation)">Ara</a> (the Altar).</p><p>&nbsp;</p><h2>&nbsp;<span class="mw-headline">History</span></h2><p><a title="Karl Gordon Henize" href="http://en.wikipedia.org/wiki/Karl_Gordon_Henize">Karl Gordon Henize</a> classified it as an A or B type <a title="H-alpha" href="http://en.wikipedia.org/wiki/H-alpha">Hα</a> emission line star in 1950. In 1971, it was observed to be a post <a title="Asymptotic giant branch" href="http://en.wikipedia.org/wiki/Asymptotic_giant_branch">asymptotic giant branch</a> (AGB) B1 <a title="Supergiant" href="http://en.wikipedia.org/wiki/Supergiant">supergiant</a>. It was discovered to have become a PN in 1989 by the IUE (Parthasarathy et al 1993).<sup class="reference" id="_ref-Parthasarathy2000_3"><a title="" href="http://en.wikipedia.org/wiki/Stingray_Nebula#_note-Parthasarathy2000">[2]</a></sup> (<a title="Stingray Nebula" href="http://en.wikipedia.org/wiki/Stingray_Nebula#CITEREFGry2002">Gry 2002</a>) Parthasarathy et al. conclude that it became a PN subsequent to 1975. (<a title="Stingray Nebula" href="http://en.wikipedia.org/wiki/Stingray_Nebula#CITEREFParthasarathy2000">Parthasarathy 2000</a>)</p><p><a id="Central_star" name="Central_star"></a></p><h2>&nbsp;<span class="mw-headline">Central star</span></h2><p>In 1995 its central star (CS) was observed to be rapidly transforming into a DA <a title="White dwarf" href="http://en.wikipedia.org/wiki/White_dwarf">white dwarf</a>, having faded by a factor of 3 between 1987 and 1995. The central star has a companion star with a 0″.3 angular separation. The CS is estimated to have a mass of 0.6 <a title="Solar mass" href="http://en.wikipedia.org/wiki/Solar_mass">M_☉</a> while the nebula itself is estimated to have a mass of 0.015 M_☉. Its luminosity is estimated to be 3000 <a title="Solar luminosity" href="http://en.wikipedia.org/wiki/Solar_luminosity">L_☉</a>. (<a title="Stingray Nebula" href="http://en.wikipedia.org/wiki/Stingray_Nebula#CITEREFParthasarathy2000">Parthasarathy 2000</a>)</p><p>&nbsp;</p>[attach]5984[/attach]<br/>