View source for NGC 6781

{{Short description|Planetary nebula in the constellation Aquila}}
{{Infobox nebula
 | name          = {{PAGENAME}}
 | image         = NGC-6781.jpg
 | caption       = NGC 6781 from the [[La Silla Observatory]]
 | credit        = <!-- Per MOS:CREDITS, credits are discouraged -->
 | type          = Planetary
 | type2         = <!-- can be wikilinked -->
 | epoch         = [[J2000]]
 | subtype       = 
 | class         = 
 | ra            = {{RA|19|18|28.085}}<ref name=Kerber_et_al_2003/>
 | dec           = {{DEC|+06|32|19.29}}<ref name=Kerber_et_al_2003/>
 | dist_ly       = {{cvt|460|pc|ly|disp=output number only}}
 | dist_pc       = 460<ref name=Otsuka_et_al_2017/>
 | dist_z        = 
 | appmag_v      = 11.4<ref name=O'Meara2007/>
 | appdia        = <!-- dd°mm'ss".mas -->
 | size_v        = {{nowrap|1′.9 × 1′.8}}<ref name=O'Meara2007/>
 | constellation = [[Aquila (constellation)|Aquila]]
 | radius_ly     = {{cvt|0.135|pc|ly|disp=output number only|lk=off}}<ref name=Otsuka_et_al_2017/>
 | radius_pc     = 
 | dimensions    = 
 | absmag_v      = 
 | notes         = 
 | names         = {{odlist | NGC=6781 | IRAS=19160+0626 }}<ref name="simbad"/>
}}

'''NGC 6781''', also known as the '''Snowglobe Nebula''',<ref name="interstellarum">{{cite book|last1=Stoyan|first1=Ronald|last2=Schurig|first2=Stephan|title=interstellarum Deep Sky Atlas|publisher=Cambridge University Press; Oculum-Verlag GmbH|publication-place=Erlangen|date=2014|isbn=978-1-107-50338-0|oclc=920437579|url=http://www.deep-sky-atlas.com/}}</ref> is a [[planetary nebula]] located in the [[celestial equator|equatorial]] [[constellation]] of [[Aquila (constellation)|Aquila]], about 2.5° east-northeast of the 5th [[visual magnitude|magnitude]] star [[19 Aquilae]].<ref name=O'Meara2007/> It was discovered July 30, 1788 by the Anglo-German astronomer [[William Herschel]].<ref name=Seligman/> The nebula lies at a distance of {{cvt|460|pc|ly|disp=out|abbr=off}} from the [[Sun]].<ref name=Otsuka_et_al_2017/> It has a visual magnitude of 11.4 and spans an [[angular size]] of {{nowrap|1.9 × 1.8 [[arcminute]]s}}.<ref name=O'Meara2007/>

The bipolar dust shell of this nebula is believed to be barrel-shaped and is being viewed from nearly pole-on.<ref name=Phillips_et_al_2011/> It has an outer [[angular radius]] of {{val|61|ul=arcsecond}}; equivalent to a physical radius of {{cvt|0.135|pc|ly|order=flip|lk=off}}. The total mass of gas ejected as the central star passed through its last [[asymptotic giant branch]] (AGB) [[thermal pulse]] event is {{val|0.41|ul=solar mass}}, while the estimated dust mass is {{val|1.53|u=solar mass}}.<ref name=Otsuka_et_al_2017/>

The magnitude 16.88 central star of the planetary nebula is a [[white dwarf]] with a [[spectral type]] of DAO. It has an [[M-type star|M-type]] co-moving companion at a projected separation of under {{val|5000|ul=AU|fmt=commas}}.<ref name=González-Santamaría_et_al_2021/> The white dwarf progenitor star had an estimated initial mass of {{val|2.5|ul=solar mass|p=~}}. It left the AGB and entered the cooling stage around 9,400&nbsp;years ago.<ref name=Otsuka_et_al_2017/>

==References==
{{reflist|refs=

<ref name="simbad">{{cite simbad
  | title=NGC 6781
  | access-date=2007-04-18 }}</ref>

<ref name=Seligman>{{cite web
 | first=Courtney | last=Seligman
 | title=NGC Objects: NGC 6750 - 6799
 | work=Celestial Atlas
 | url=https://cseligman.com/text/atlas/ngc67a.htm
 | access-date=2021-01-07 }}</ref>

<ref name=O'Meara2007>{{cite book
 | title=Herschel 400 Observing Guide
 | first=Steve | last=O'Meara | date=2007
 | isbn=9780521858939 | page=249
 | publisher=Cambridge University Press
 | url=https://books.google.com/books?id=Nyh9fAC_tpIC&pg=PA249 }}</ref>

<ref name=Phillips_et_al_2011>{{cite journal
 | title=Optical and mid-infrared observations of the planetary nebula NGC 6781
 | display-authors=1 | last1=Phillips | first1=J. P.
 | last2=Ramos-Larios | first2=Gerardo | last3=Guerrero | first3=Martín A.
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=415 | issue=1 | pages=513–524
 | date=July 2011 | doi=10.1111/j.1365-2966.2011.18722.x
 | doi-access=free | arxiv=1106.3706 | bibcode=2011MNRAS.415..513P | s2cid=119269567 }}</ref>

<ref name=Otsuka_et_al_2017>{{cite journal
 | title=The Herschel Planetary Nebula Survey (HerPlaNS): A Comprehensive Dusty Photoionization Model of NGC6781
 | last1=Otsuka | first1=Masaaki | last2=Ueta | first2=Toshiya
 | last3=van Hoof | first3=Peter A. M. | last4=Sahai | first4=Raghvendra
 | last5=Aleman | first5=Isabel | last6=Zijlstra | first6=Albert A.
 | last7=Chu | first7=You-Hua | last8=Villaver | first8=Eva
 | last9=Leal-Ferreira | first9=Marcelo L. | last10=Kastner | first10=Joel
 | last11=Szczerba | first11=Ryszard | last12=Exter | first12=Katrina M.
 | display-authors=1 | journal=The Astrophysical Journal Supplement Series
 | volume=231 | issue=2 | id=22 | pages=29
 | date=August 2017 | doi=10.3847/1538-4365/aa8175
 | pmid=28966408 | pmc=5619666 | arxiv=1707.06565 | bibcode=2017ApJS..231...22O | doi-access=free }}</ref>

<ref name=González-Santamaría_et_al_2021>{{cite journal
 | title=Planetary nebulae in Gaia EDR3: Central star identification, properties, and binarity
 | last1=González-Santamaría | first1=I. | last2=Manteiga | first2=M.
 | last3=Manchado | first3=A. | last4=Ulla | first4=A.
 | last5=Dafonte | first5=C. | last6=López Varela | first6=P.
 | display-authors=1 | journal=Astronomy & Astrophysics
 | volume=656 | pages=A51 | year=2021
 | doi=10.1051/0004-6361/202141916 | arxiv=2109.12114
 | bibcode=2021A&A...656A..51G | s2cid=237940344 }}</ref>

<ref name=Kerber_et_al_2003>{{cite journal
 | title=Galactic Planetary Nebulae and their central stars. I. An accurate and homogeneous set of coordinates
 | last1=Kerber | first1=F. | last2=Mignani | first2=R. P.
 | last3=Guglielmetti | first3=F. | last4=Wicenec | first4=A.
 | display-authors=1 | journal=Astronomy and Astrophysics
 | volume=408 | issue=3 | pages=1029–1035 | date=September 2003
 | doi=10.1051/0004-6361:20031046 | doi-access=free
 | bibcode=2003A&A...408.1029K }}</ref>

}}

==External links==
*{{commonscat-inline}}
*{{WikiSky}}

{{Ngc70}}
{{Aquila (constellation)}}
{{Sky|19|18|28|+|06|32|19.3|1}}

{{DEFAULTSORT:NGC 6781}}
[[Category:Planetary nebulae]]
[[Category:NGC objects|6781]]
[[Category:Aquila (constellation)]]