View source for Abell 39

{{Short description|Nebula in the constellation Hercules}}
{{Dablink|Note that Abell 39 can also refer to [[ACO 39]], the 39th member of the [[Abell catalogue]] of around 4,000 [[galaxy cluster]]s.}}
{{Use dmy dates|date=January 2020}}
{{Planetary nebula
| image = Abell 39.jpg
| caption= Credit: [Adam Block/Mount Lemmon SkyCenter/University of Arizona]
| name = Abell 039
| type = 
planetary
| epoch = [[J2000]]
| ra = {{RA|16|27|33.720}}<ref name="simbad">{{citation|last1 = SIMBAD|title = Results for PN A66 39|authorlink = SIMBAD|date = 3 September 2023|publisher = SIMBAD, Centre de Données Astronomiques de Strasbourg|url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=PN+A66+39}}</ref>
| dec = {{DEC|+27|54|33.47}}<ref name="simbad" />
| dist_ly = 3800<ref name="simbad" />
| appmag_v = Integrated: 13.7;<ref name="Darling2008">{{citation|last1 = Darling|first1 = David|authorlink = David Darling (astronomer)|journal = [[Internet Encyclopedia of Science]]|title = Abell 39|date = 2008|url = http://www.daviddarling.info/encyclopedia/A/Abell_39.html|access-date = 6 September 2008|archive-date = 28 November 2017|archive-url = https://web.archive.org/web/20171128084900/http://www.daviddarling.info/encyclopedia/A/Abell_39.html| url-status = dead}}</ref><ref name=Abell1966>{{cite journal|last1 = Abell|first1 = George O.|authorlink1 = George Ogden Abell|title = Properties of Some Old Planetary Nebulae|journal=[[Astrophysical Journal]]|date = April 1966|volume = 144|pages = 259|bibcode = 1966ApJ...144..259A|doi = 10.1086/148602}}</ref> Central Star: 15.5 ± 0.2<ref name="Jacobyetal2001">{{cite journal|last1 = Jacoby|first1 = George. H.|last2 = Ferland|first2 = Gary. J.|last3 = Korista|first3 = Kirk T.|journal = [[The Astrophysical Journal]]|volume = 560|issue = 1|pages = 272–286|title = The Planetary Nebula A39: An Observational Benchmark for Numerical Modeling of Photoionized Plasmas|date = 10 October 2001|doi = 10.1086/322489|bibcode = 2001ApJ...560..272J|url = http://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1104&context=physastron_facpub|doi-access = free}}</ref>
| size_v = 155.1{{pprime}} × 154.5{{pprime}}<ref name="Jacobyetal2001" />
| constellation  = [[Hercules (constellation)|Hercules]]
| radius_ly = 1.4
| absmag_v = 
| notes = Almost perfectly spherical<ref name="Darling2008" />
| names = PN&nbsp;A66&nbsp;39,<ref name="simbad" /> PN&nbsp;ARO&nbsp;180,<ref name="simbad" /> PK&nbsp;047+42&nbsp;1<ref name="simbad" />
}}

'''Abell 39''' ('''PN A66 39''') is a low [[surface brightness]]<ref name="Jacobyetal2001" /> [[planetary nebula]] in the constellation of [[Hercules (constellation)|Hercules]]. It is the 39th entry in [[George Ogden Abell|George Abell's]] 1966 [[Abell Catalog of Planetary Nebulae]] (and 27th in his 1955 catalog) of 86 old planetary nebulae which either Abell or [[Albert George Wilson]] discovered before August 1955 as part of the [[National Geographic Society - Palomar Observatory Sky Survey]].<ref name=Abell1966 /><ref name="Abell1955">{{cite journal|last1 = Abell|first1 = George O.|authorlink = George Ogden Abell|title = Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey|journal=[[Publications of the Astronomical Society of the Pacific]]|date = 1955|volume = 67|issue = 397|pages = 258|bibcode = 1955PASP...67..258A|doi = 10.1086/126815|doi-access = free}}</ref> It is estimated to be about 3,800 [[light-year]]s from earth and thus 2,600 light-years above the [[Galactic plane]].<ref name="simbad" /> It is almost perfectly spherical and also one of the largest known spheres with a radius of about 1.4 light-years.<ref name="Jacobyetal2001" /><ref name="Darling2008" /><ref name="simbad" />

== Central star==
Its central star is slightly west of center by about 2{{pprime}} or 0.1 light-years.<ref name="Darling2008" /> This offset does not appear to be due to interaction with the [[interstellar medium]], but instead, it is hypothesized that a small asymmetric mass ejection has accelerated the central star.<ref name="Jacobyetal2001" /> The mass of the central star is estimated to be about {{Solar mass|0.61|link=y}} with the material in the planetary nebula comprising an additional {{Solar mass|0.6|link=y}}.<ref name="Jacobyetal2001" />

This planetary nebula has a nearly uniform [[spherical]] shell. However, the eastern limb of the nebula is 50% more luminous than the western limb. Additionally, irregularities in the surface brightness are seen across the face of the shell. The source of the east–west asymmetry is not known but it could be related to the offset of the central star.<ref name="Jacobyetal2001" />

The central star is classified as a [[subdwarf O star]] with surface temperature of 8900 K.<ref name=GreensteinMinkowski1964>{{cite journal|last1=Greenstein|first1=Jesse L.|last2=Minkowski|first2=Rudolph|title=The Central Stars of Planetary Nebulae of Low Surface Brightness.|journal=The Astrophysical Journal|date=1964|volume=140|issue=1|pages=1601–1603|doi=10.1086/148064|bibcode=1964ApJ...140.1601G|doi-access=free}}</ref><ref name="simbad" />

== Structure and composition==
The bright rim of the planetary nebula has an average thickness of about 10.1{{pprime}}, or an absolute size of about 0.19 light-years. There is a faint halo that extends about 18{{pprime}} beyond the bright rim giving a complete diameter of around 190{{pprime}} under the assumption that this emission is uniform around the planetary nebula.<ref name="Jacobyetal2001" /><ref name="simbad" />

This planetary nebula has been expanding for an estimated 11,000 years, based on an assumed expansion velocity between 32 and 37 [[km/s]] and a 0.4 parsec radius.<ref name="Jacobyetal2001" /><ref name="simbad" />

Background [[galaxy|galaxies]] are visible near the nebula, and some can be seen through it.<ref name="Jacobyetal2001" />

[[Oxygen]] is only about half as abundant in the nebula as it is in our own [[sun]].<ref name="Darling2008" />

== References ==
{{reflist}}

== External links ==
{{commons category}}
*[http://www.noao.edu/image_gallery/html/im0636.html George Jacoby et al. created a spectacular image of Abell 39 in 1997.] {{Webarchive|url=https://web.archive.org/web/20081204064301/http://www.noao.edu/image_gallery/html/im0636.html |date=4 December 2008 }}
* {{Cite APOD
 | title = Abell 39
 | date = 28 July 2005
 }}

{{Hercules (constellation)|state=collapsed}}

{{DEFAULTSORT:Abell 39}}
[[Category:Planetary nebulae]]
[[Category:Hercules (constellation)]]
[[Category:Abell planetary nebulae|39]]