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Coordinates: Sky map 07h 04m 04.85s, −03° 50′ 50.1″
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{{Short description|Star in the constellation Monoceros}}
Nominated for most mysterious star in the [[Milky Way]], '''V838 Monocerotis''' (abbreviated '''V838 Mon''') briefly became one of the brightest stars in our [[galaxy]]. Its outburst began around [[January 1]], [[2002]] and was discovered on [[January 6]], [[2002]]. It was initially thought to be a familiar type of classical [[nova]], but astronomers quickly realized that instead, V838 Mon may be a totally new addition to the astronomical zoo. Observations have indicated that V838 Mon is a binary system where one of the stars somehow transformed itself over a period of months from a small under-luminous star a little hotter than the [[Sun]], to a highly-luminous, cool supergiant star -- defying the conventional understanding of erupting stars and stellar life cycles. <!-- the star may have been a luminous supergiant originally, should be updated; binary companion itself is a very massive, hot star -->
{{Starbox begin}}
{{Starbox image
| image=[[Image:183213main image feature 877 ys full.jpg |250px]]
| caption=[[Hubble Space Telescope]] image of V838 Monocerotis and the surrounding nebula on September 9, 2006
| credit=[[NASA]]/[[ESA]]
}}
{{Starbox observe
| epoch=J2000.0
| constell=[[Monoceros (constellation)|Monoceros]]
| ra={{RA|07|04|04.822}}<ref name=mobeen2021/>
| dec={{DEC|−03|50|50.53}}<ref name=mobeen2021/>
| appmag_v=6.75 (2002), 15.6<ref name="Bond2003"/>
}}
{{Starbox character
| type = [[M-type star|M-type]] [[Red supergiant|supergiant]]<ref name=goranskij/>
| class = M7.5I -> M5.5I + B3V<ref name=goranskij/>
| variable = [[Luminous Red Nova|LRN]]<ref name=goranskij>{{cite journal |doi=10.1134/S1990341320030049 |title=Progenitor and Remnant of the Luminous Red Nova V838 Monocerotis |year=2020 |last1=Goranskij |first1=V. P. |last2=Barsukova |first2=E. A. |last3=Burenkov |first3=A. N. |last4=Valeev |first4=A. F. |last5=Zharova |first5=A. V. |last6=Kroll |first6=P. |last7=Metlova |first7=N. V. |last8=Shugarov |first8=S. Yu. |journal=Astrophysical Bulletin |volume=75 |issue=3 |pages=325–349 |bibcode=2020AstBu..75..325G |s2cid=221839336 }}</ref>
}}
{{Starbox astrometry
| radial_v = <!--Radial velocity (in km/sec)-->
| prop_mo_ra = {{val|-0.536|0.229}}<ref name=dr2>{{cite DR2|203107789548859766016}}</ref>
| prop_mo_dec = {{val|-0.078|0.174}}<ref name=dr2/>
| parallax = 0.163
| p_error = 0.016
| parallax_footnote = <ref name=reid2019/>
| dist_ly = 19,200
| dist_pc = {{val|5,900|400|fmt=commas}}<ref name=gisela>{{cite journal|arxiv=2004.01488|doi=10.1051/0004-6361/202037712|title=SiO maser astrometry of the red transient V838 Monocerotis|year=2020|last1=Ortiz-León|first1=Gisela N.|last2=Menten|first2=Karl M.|last3=Kamiński|first3=Tomasz|last4=Brunthaler|first4=Andreas|last5=Reid|first5=Mark J.|last6=Tylenda|first6=Romuald|journal=Astronomy & Astrophysics|volume=638|pages=A17|bibcode=2020A&A...638A..17O|s2cid=214794885}}</ref>
| absmag_v = <!--Absolute magnitude ([[UBV photometric system|Johnson-Cousins V system]])-->
| absmag_bol = <!--Absolute bolometric magnitude (accounts for emissions across all spectra of light)-->
}}
{{Starbox detail
| mass=5{{snd}}10<ref name="Tylenda2005b"/>
| temperature = 3,300<ref name=Kaminski2021/>
| radius = 464<ref name=Kaminski2021>{{Cite journal |arxiv=2106.07427 |last1=Kamiński |first1=Tomek |last2=Tylenda |first2=Romuald |last3=Kiljan |first3=Aleksandra |last4=Schmidt |first4=Mirek |last5=Lisiecki |first5=Krzysztof |last6=Melis |first6=Carl |last7=Frankowski |first7=Adam |last8=Joshi |first8=Vishal |last9=Menten |first9=Karl M. |title=V838 Monocerotis as seen by ALMA: A remnant of a binary merger in a triple system |journal=Astronomy & Astrophysics |year=2021 |volume=655 |pages=A32 |doi=10.1051/0004-6361/202141526 |bibcode=2021A&A...655A..32K |s2cid=235422695 }}</ref>
| luminosity = 23,000<ref name=Kaminski2021/>
| age_myr= 4<ref name="Munari2005"/>
}}
{{Starbox catalog |
names=[[Variable star designation|V838]]&nbsp;Mon, Nova&nbsp;Monocerotis&nbsp;2002, GSC&nbsp;04822-00039 }}
{{Starbox reference |
Simbad=V838+Mon }}
{{Starbox end}}


'''V838 Monocerotis''' ('''Nova Monocerotis 2002''') is a [[Cataclysmic variable star|cataclysmic]] [[binary star]] in the [[constellation]] [[Monoceros (constellation)|Monoceros]] about 19,000 [[light year]]s (6 [[parsec|kpc]]) from the [[Sun]]. The previously unremarked star was observed in early 2002 experiencing a major outburst, and was one of the [[List of largest known stars|largest known stars]] for a short period following the outburst.<ref name="Tylenda2005"/> Originally believed to be a typical [[nova]] eruption, it was then identified as the first of a new class of eruptive variables known as [[luminous red nova]]e. The reason for the outburst is still uncertain, but is thought to have been a merger of two stars within a triple system.
[[Image:V838_Mon_HST.jpg|thumb|V838 Monocerotis as imaged by the Hubble Space Telescope on [[December 17]], [[2002]]]]
In this spectacular image, one of a series recorded by the [[Hubble Space Telescope]], the dimmed V838 Mon is surrounded by an "expanding" [[nebula]]. But the nebula is actually a series of light echoes from formerly unseen shells of dust up to [[light-year]]s in diameter. Previously ejected, the intricate shells progressively reflect light as it reaches them from V838 Mon's outbursts. Astronomers anticipate that light echoes from farther out in the dust envelope will continue to be visible until about 2010. Some estimates now place V838 Mon about 20,000 light-years from planet [[Earth]].


The eruption occurred on one of two B3 [[main sequence]] stars in a close binary orbit. The erupting star appeared as an unusually cool supergiant and for a while engulfed its companion. By 2009 the [[temperature]] of the supergiant had increased (since 2005) to 3,270 K and its luminosity was 15,000 times solar ({{solar luminosity|link=y}}), but its radius had decreased to 380 times that of the Sun ({{solar radius|link=y}}), although the ejecta continues to expand.<ref name=tylenda>{{Cite journal | last1 = Tylenda | first1 = R. | last2 = Kamiński | first2 = T. | last3 = Schmidt | first3 = M. | last4 = Kurtev | first4 = R. | last5 = Tomov | first5 = T. | s2cid = 118649108 | title = High-resolution optical spectroscopy of V838 Monocerotis in 2009 | doi = 10.1051/0004-6361/201116858 | journal = Astronomy & Astrophysics | volume = 532 | pages = A138 | date = 2011 |arxiv = 1103.1763 |bibcode = 2011A&A...532A.138T }}</ref>
The shape of the light echo is far from spherical. For all points on the currently visible echo, the light has taken the same time to travel from V838 Mon to the dust and then to Earth. Thus the shape is of an extremely long [[ellipsoid]]; the illuminated part being almost [[parabolic]] with V838 Mon at its focus. The V838 Mon - dust - Earth path length is increasing at the speed of light, and the visible echo is simultaneously receding both from V838 Mon and from the Earth.


==Outburst==
The designation ''V838 Monocerotis'' means "838th [[variable star]] of [[Monoceros]] (the Unicorn)".
[[File:V838Mon2002LightCurve.png|thumb|left|The visual (blue points) and [[K band (infrared)|K band]] infrared (red points) light curves of the 2002 eruption of V838 Monocerotis, adapted from Starrfield ''et al.'', 2004<ref name="Starrfield">{{cite book|author1-link=Sumner Starrfield |last1=Starrfield |first1=S. |last2=Wagner |first2=R. M. |last3=Hauschildt |first3=P. H. |author4-link=Howard E. Bond|last4=Bond |first4=H. E. |last5=Evans |first5=A. |last6=Rushton |first6=M. T. |last7=Rushton |first7=M. T. |last8=Munari |first8=U. |last9=Henden |first9=A. |last10=Levay |first10=Z. G. |last11=Panagia |first11=N. |last12=Sparks |first12=W. B. |last13=Corradi |first13=R. L. M. |title=The 2002 Outburst of V838 Mon: As Cool As It Gets |date=July 2004 |url=https://www.researchgate.net/publication/241367516 |access-date=29 September 2021}}</ref>]]
[[File:V838 nova.jpg|thumb|left|Light echo of V838 Mon as imaged April 30, 2002]]
On January 6, 2002, an unknown star was seen to brighten in the constellation [[Monoceros (constellation)|Monoceros]], the Unicorn.<ref name=brown>{{cite journal|bibcode=2002IAUC.7785....1B|title=Peculiar variable in Monoceros|journal=IAU Circ|volume=7785|pages=1|last1=Brown|first1=N. J.|last2=Waagen|first2=E. O.|last3=Scovil|first3=C.|last4=Nelson|first4=P.|last5=Oksanen|first5=A.|last6=Solonen|first6=J.|last7=Price|first7=A.|date=2002}}</ref> Being a new variable star, it was designated V838 Monocerotis, the 838th variable star of Monoceros. The initial [[light curve]] resembled that of a [[nova]], an eruption that occurs when enough [[hydrogen]] gas accumulates on the surface of a [[white dwarf]] from its close [[binary star|binary]] companion. Therefore, the object was also designated Nova Monocerotis 2002. V838 Monocerotis reached a maximum [[visual magnitude]] of 6.75 on February 6, 2002, after which it started to dim rapidly, as expected. However, in early March, the star started to brighten again, particularly in [[infrared]] wavelengths. Yet another brightening in infrared occurred in early April. In 2003, the star returned to near its original brightness before the eruption (magnitude 15.6), but as a red [[supergiant]] rather than a blue [[main sequence|main-sequence]] star. The light curve produced by the eruption was unlike anything previously seen.<ref name="Bond2003">{{cite journal
| last = Bond
| first = Howard E.
|author2=Henden, Arne |author3=Levay, Zoltan G. |author4=Panagia, Nino |author5=Sparks, William B. |author6=Starrfield, Sumner |author7=Wagner, R. Mark |author8=Corradi, R. L. M. |author9= Munari, U.
| s2cid = 90973
| title = An energetic stellar outburst accompanied by circumstellar light echoes
| journal = Nature
| volume = 422
| issue = 6930
| pages = 405–408
| date = March 27, 2003
| bibcode = 2003Natur.422..405B
| doi = 10.1038/nature01508
| pmid = 12660776
|arxiv = astro-ph/0303513 }}</ref>
In 2009, the star was about {{solar luminosity|15,000}},<ref name=tylenda/> which, in the absence of [[Extinction (astronomy)|extinction]], would correspond to an [[apparent magnitude]] of 8.5.{{efn|The sun's [[absolute magnitude]] is 4.83, meaning that its apparent magnitude would be 4.83 at 10 parsecs, and V838 Mon was 15,000 times more luminous than the sun, assuming that it is {{val|6,500|fmt=commas|u=parsecs}} away, so the apparent magnitude of V838 Mon comes to 4.83 − 2.5×log(15000) + 5×log(6500/10) ≈ 8.5.}}

[[File:Monocerotis-en.svg|left|240px|thumb|Comparison between the size of V838 Monocerotis and the Inner Solar System.]]
The star brightened to about a million times solar [[luminosity]]<ref name="Soker2006">{{cite journal| author = Soker, N.
| author2 = Tylenda, R.
| title = Modelling V838 Monocerotis as a Mergeburst Object
| journal = The Nature of V838 Mon and Its Light Echo
| url = https://archive.org/details/arxiv-astro-ph0606371
| date = June 15, 2006
| volume = 363
| page = 280
| arxiv = astro-ph/0606371
| bibcode= 2007ASPC..363..280S
}}</ref> and an [[absolute magnitude]] of −9.8,<ref name=sparks/> ensuring that at the time of maximum, it was one of the [[List of most luminous stars|most luminous stars]] in the [[Milky Way]] galaxy. Its brightening was caused by a rapid expansion of its outer layers.

V838 Monocerotis was observed by use of the [[Palomar Testbed Interferometer]], which indicated a radius of {{val|1,570|400|fmt=commas|u={{solar radius}}}} (comparable to [[Jupiter]]'s orbital radius), confirming the earlier indirect calculations.<ref name="Lane2005">{{cite journal
| last1 = Lane | first1 = B. F.
| last2 = Retter | first2 = A.
| last3 = Thompson | first3 = R. R.
| last4 = Eisner | first4 = J. A.
| s2cid = 119473906
| title = Interferometric Observations of V838 Monocerotis
| journal = The Astrophysical Journal
| volume = 622
| issue = 2
| pages = L137–L140
| publisher = The American Astronomical Society
| date = April 2005
| arxiv = astro-ph/0502293
| doi = 10.1086/429619
| bibcode=2005ApJ...622L.137L
}}</ref> At the currently accepted distance of 6,100&nbsp;[[Parsec|pc]], the measured angular diameter in late 2004 (1.83&nbsp;[[Milliarcseconds|mas]]) corresponded to a radius of {{val|1,200|150|fmt=commas|u={{solar radius}}}}, but by 2014, it shrunk to {{val|750|200|u={{solar radius}}}}, around 70 solar radii larger than [[Antares]].<ref name=chesneau>{{cite journal|doi=10.1051/0004-6361/201424458|bibcode=2014A&A...569L...3C|arxiv=1407.5966|date=2014|title=V838 Monocerotis: the central star and its environment a decade after outburst
|author=Chesneau, Olivier
|author2=Millour, Florentin
|author3=De Marco, Orsola|author3-link=Orsola De Marco
|author4=Bright, S. N.
|author5=Spang, Alain
|author6=Banerjee, D. P. K.
|author7=Ashok, N. M.
|author8=Kaminski, T.
|author9=Wisniewski, John P.
|author10=Meilland, Anthony
|author11=Lagadec, Eric|s2cid=11558941|volume=569|journal=Astronomy|pages=L3
}}</ref> The expansion took only a couple of months, meaning that its speed was abnormal. Because the laws of [[thermodynamics]] dictate that expanding gases cool, the star became extremely cool and deep red. In fact, some astronomers argue that the [[stellar spectrum|spectrum]] of the star initially resembled that of [[stellar classification#Class L|L-type]] [[brown dwarf]]s. If that is the case, V838 Monocerotis was the first known L-type [[supergiant]].<ref name="Evans2003">{{cite journal
| last1 = Evans | first1 = A.
| last2 = Geballe | first2 = T. R.
| last3 = Rushton | first3 = M. T.
| last4 = Smalley | first4 = B.
| last5 = van Loon | first5 = J. Th.
| last6 = Eyres | first6 = S. P. S.
| last7 = Tyne | first7 = V. H.
| title = V838 Mon: an L supergiant?
| journal = Monthly Notices of the Royal Astronomical Society
| volume = 343
| issue = 3
| pages = 1054–1056
| publisher = Royal Astronomical Society
| date = August 2003
| bibcode = 2003MNRAS.343.1054E
| doi = 10.1046/j.1365-8711.2003.06755.x
| doi-access = free
}}</ref> Since then, it has shrunk and heated up and is now considered an [[Red supergiant|M-type supergiant]]. However, current estimates of the distance, and hence of the radius, are about 25% lower than assumed in those papers.<ref name=sparks/>

===Other possibly similar events===
There are a handful of outbursts resembling that of V838 Monocerotis. In 1988, a red star was detected erupting in the [[Andromeda Galaxy]]. The star, designated [[M31-RV]], reached the [[absolute magnitude|absolute bolometric magnitude]] of −9.95 at maximum (corresponding to a luminosity of {{solar luminosity|0.75 million}}) before dimming beyond detectability. A similar eruption, [[V4332 Sagittarii]], occurred in 1994 in the Milky Way.<ref name="Boschi2004">{{cite journal
| last = Boschi
| first = F.
|author2=Munari, U.
| s2cid = 18582562
| title = M 31-RV evolution and its alleged multi-outburst pattern
| journal = Astronomy & Astrophysics
| volume = 418
| issue = 3
| pages = 869–875
| date = May 2004
| arxiv = astro-ph/0402313
| doi = 10.1051/0004-6361:20035716
| bibcode=2004A&A...418..869B
}} M31-RV - 0402313</ref>

==Progenitor star==
[[File:V838_Milky_Way.jpg|thumb|250px|Location of V838 Monocerotis within the [[Milky Way]] galaxy.]]
Based on an incorrect interpretation of the [[light echo]] the eruption generated, the distance of the star was first estimated to be 1,900 to 2,900 light years. Combined with the apparent magnitude measured from pre-eruption photographs, it was thought to be an underluminous [[stellar classification#Class F|F-type]] dwarf, which posed a considerable enigma.<ref name="Tylenda2005">{{cite journal
| last = Tylenda
| first = R.
| s2cid = 3566688
| title = Evolution of V838 Monocerotis during and after the 2002 eruption
| journal = Astronomy and Astrophysics
| volume = 436
| issue = 3
| pages = 1009–1020
| date = June 4, 2005
| arxiv = astro-ph/0502060
| doi = 10.1051/0004-6361:20052800
| bibcode=2005A&A...436.1009T
}}</ref>

More accurate measurements gave a much larger distance, 20,000 light years (6&nbsp;kpc). It appears that the star was considerably more massive and luminous than the Sun. The star probably has a mass of from 5 to 10 times the mass of the Sun ({{solar mass|link=y}}).<ref name="Tylenda2005b">{{cite journal
| last1 = Tylenda | first1 = R.
| last2 = Soker | first2 = N.
| last3 = Szczerba | first3 = R.
| s2cid = 119363054
| title = On the progenitor of V838 Monocerotis
| journal = Astronomy and Astrophysics
| volume = 441
| issue = 3
| pages = 1099–1109
| date = October 2005
| url = http://adsabs.harvard.edu/cgi-bin/bib_query?astro-ph/0412183
| doi = 10.1051/0004-6361:20042485
| access-date = 10 August 2006
| bibcode=2005A&A...441.1099T | arxiv = astro-ph/0412183 }}</ref> It was apparently either a [[stellar classification#Class B|B1.5V]] star with a B3V companion, or an A0.5V with a B4V companion. In the latter case it would have had a [[luminosity]] around {{solar luminosity|550}} (being 0.43 times as luminous as its companion), and in the former case it would have been more luminous (about 1.9 times as luminous as its companion).<ref name="Tylenda2005b"/>{{efn|The reference does not explicitly give the luminosity in the first case.}} The star may have originally had a radius roughly {{solar radius|5}} and its temperature would have been that of a B-type star (more than 10,000K but less than 30,000K<ref name="Tylenda2005b"/>). Munari et al. (2005) suggested that the progenitor star was a very massive supergiant with an initial mass of about {{solar mass|65}},<ref name="Munari2005">{{cite journal
| last = Munari | first = U. | author2 = Munari, U. | author3 = Henden, A. | author4 = Vallenari, A.
| author5 = Bond, H. E. | author6 = Corradi, R. L. M. | author7 = Crause, L. | author8 = Desidera, S.
| author9 = Giro, E. | author10 = Marrese, P. M. | author11 = Ragaini, S. | author12 = Siviero, A.
| author13 = Sordo, R. | author14 = Starrfield, S. | author15 = Tomov, T. | author16 = Villanova, S.
| author17 = Zwitter, T. | author18 = Wagner, R. M.
| display-authors = 8
| title = On the distance, reddening and progenitor of V838 Mon
| journal = Astronomy and Astrophysics
| volume = 434
| issue = 3
| pages = 1107–1116
| date = May 2, 2005
| arxiv = astro-ph/0501604
| doi = 10.1051/0004-6361:20041751
| bibcode=2005A&A...434.1107M
| s2cid = 119330637 }}</ref> but this has been contested.<ref name="Tylenda2005b"/> There seems to be agreement that the star system is relatively young.
Munari et al. conclude that the system may be only about 4 million years old.

The spectrum of V838 Monocerotis reveals a companion, a hot blue [[stellar classification#Class B|B-type]] [[main sequence]] star probably not very different from the progenitor star.<ref name="Tylenda2005b"/> It is also possible that the progenitor was slightly less massive than the companion and only just entering the main sequence.<ref name="Tylenda2005"/>

Based on the photometric [[parallax]] of the companion, Munari et al. calculated a greater distance, 36,000 light years (10 kpc).<ref name="Munari2005"/>

==Light echo==
[[Image:V838 Mon.jpg|250px|left|thumb|Images showing the expansion of the light echo. Credit: [[NASA]]/[[ESA]].]]
[[File:Evolution of the light echo around V838 Monocerotis (Heic0617a).ogv|thumb|
The evolution of the [[light echo]] around V838 Monocerotis.<ref>{{Citation|title = The evolution of the light echo around V838 Monocerotis|url = http://www.spacetelescope.org/videos/heic0617a/|access-date = 2015-08-27|last = }}</ref>
]]
[[File:V838 Mon 1989-2006.gif|thumb|left|Animation of 11 images of light echo of V838 Mon]]
Rapidly brightening objects like novae and [[supernova]]e are known to produce a phenomenon known as [[light echo]]. The light that travels directly from the object arrives first. If there are clouds of [[interstellar medium|interstellar matter]] around the star, some light is reflected from the clouds. Because of the longer path, the reflected light arrives later, producing a vision of expanding rings of light around the erupted object. The rings appear to travel faster than the [[speed of light]], but in fact they do not.<ref name="Bond2003"/><ref>{{cite web|title=Many Epochs of V838 Mon|url=http://heritage.stsci.edu/2005/02/supplemental.html|publisher=The Hubble Heritage Project|access-date=3 October 2015}}</ref>

In the case of V838 Monocerotis, the light echo produced was unprecedented and is well documented in images taken by the [[Hubble Space Telescope]]. While the photos appear to depict an expanding spherical shell of debris, they are actually formed by the illumination of an ever-expanding [[ellipsoid]] with the progenitor star at one focus and the observer at the other. Hence, despite appearances, the structures in these photos are actually concave toward the viewer.

By March 2003 the size of the light echo in the sky was twice the [[angular diameter]] of Jupiter and was continuing to grow.<ref>{{cite web|title=Hubble Watches Light from Mysterious Erupting Star Reverberate Through Space|url=http://hubblesite.org/news_release/news/2003-10|website=Hubblesite|archive-url=https://web.archive.org/web/20171222041007/http://hubblesite.org/news_release/news/2003-10|archive-date=December 22, 2017|date=Mar 26, 2003|url-status=live}}</ref> Jupiter's angular diameter varies from 30 to 51 [[arcseconds]].

It is not yet clear if the surrounding nebulosity is associated with the star itself.<!-- The nebula is however related to the object, not somewhere between it and us.--> If that is the case, they may have been produced by the star in earlier eruptions which would rule out several models that are based on single catastrophic events.<ref name="Bond2003"/> However, there is strong evidence that the V838 Monocerotis system is very young and still embedded in the [[nebula]] from which it formed.<ref name="Soker2006"/>

The eruption initially emitted at shorter wavelengths (i.e. was bluer), which can be seen in the light echo: the outer border is bluish in the Hubble images.<ref name="Bond2003"/>

==Hypotheses==
[[File:V838 Monocerotis light echo (HST, November 2005 and September 2006).jpg|right|thumb|Two pictures taken in November 2005 and September 2006 showing the changes that occurred to the bright echo of V838 Mon.]]
This and other luminous red nova events are thought to be caused by the merger of two stars. In the case of V838 Monocerotis, it was the merger of two main sequence stars, or an {{Solar mass|8}} main sequence star and a {{Solar mass|0.3}} pre-main sequence star. The merger model explains the multiple peaks in the light curve observed during the outburst.<ref name="Soker2006"/> Based on further observations of stars similar to V838 Monocerotis, such as [[V1309 Scorpii]], astronomers have reached the conclusion that this is the most likely scenario.<ref name=mobeen2021/><ref name=woodward2021/>

Other explanations for the eruption of V838 Monocerotis have also been published.<ref>{{Cite news|title = The V838 Monocerotis Star Still Has Astronomers' Heads Exploding|url = https://www.nytimes.com/2014/09/03/science/space/the-v838-monocerotis-star-still-has-astronomers-heads-exploding.html|newspaper = The New York Times|date = 2014-09-03|access-date = 2015-08-30|issn = 0362-4331|first = Dennis|last = Overbye}}</ref>

===Atypical nova outburst===
The outburst of V838 Monocerotis may be a nova eruption after all, albeit a very unusual one. However, this is very unlikely considering that the system includes a B-type star, and stars of this type are young and massive. There has not been enough time for a possible white dwarf to cool and accrete enough material to cause the eruption.<ref name="Boschi2004"/>

===Thermal pulse of a dying star===
V838 Monocerotis may be a post-[[asymptotic giant branch]] star, on the verge of going [[supernova]]. The nebulosity illuminated by the light echo may actually be shells of dust surrounding the star, created by the star during previous similar outbursts. The brightening may have been a so-called [[helium flash]], where the core of a dying low-mass star suddenly ignites [[helium]] [[nuclear fusion|fusion]] disrupting, but not destroying, the star. Such an event is known to have occurred in [[Sakurai's Object]]. However, several pieces of evidence support the argument that the dust is interstellar rather than centered on V838 Monocerotis. A dying star that has lost its outer envelopes would be appropriately hot, but the evidence points to a young star instead.<ref name="Tylenda2005b"/>

===Thermonuclear event within a massive supergiant===
According to some evidence, V838 Monocerotis may be a very massive [[supergiant]]. Also in this case, the outburst may have been a helium flash. Very massive stars survive multiple such events; however, they experience heavy mass loss (about half of the original mass is lost while in the [[main sequence]]) before settling as extremely hot [[Wolf-Rayet star]]s. This theory may also explain the apparent dust shells around the star. V838 Monocerotis is located in the approximate direction of the [[galactic anticenter]] and off from the disk of the Milky Way. [[Stellar birth]] is less active in outer galactic regions, and it is not clear how such a massive star can form there. However, there are very young clusters like [[Ruprecht 44]] and the 4-million-year-old [[NGC 1893]] at a distance of about 7 and 6 [[kiloparsec]]s, respectively.<ref name="Munari2005"/>

===Planetary capture event===
Another possibility is that V838 Monocerotis may have swallowed its giant [[planet]]s. If one of the planets entered into the atmosphere of the star, the stellar atmosphere would have begun slowing down the planet. As the planet penetrated deeper into the atmosphere, friction would become stronger and kinetic energy would be released into the star more rapidly. The star's envelope would then warm up enough to trigger [[deuterium]] fusion, which would lead to rapid expansion. The later peaks may then have occurred when two other planets entered into the expanded envelope. The authors of this model calculate that every year about 0.4 planetary capture events occur in Sun-like stars in the Milky Way galaxy, whereas for massive stars like V838 Monocerotis the rate is approximately 0.5–2.5 events per year.<ref name="Retter2006">{{cite journal
| author = Retter, A.
| author2 = Zhang, B.
| author3 = Siess, L.
| author4 = Levinson, A.
| title = The planets capture model of V838 Monocerotis: conclusions for the penetration depth of the planet/s
| date = May 22, 2006
|bibcode = 2006MNRAS.370.1565C |doi = 10.1111/j.1365-2966.2006.10579.x
| journal = Monthly Notices of the Royal Astronomical Society
| volume = 370
| issue = 3
| pages = 1565–1572 | doi-access = free
|arxiv = astro-ph/0605552 }}</ref>

===Common envelope event===
See [[Common envelope#Observational manifestations|Common envelope]]


==See also==
==See also==
*[[M31 RV]]
* [[Stellar evolution]]

*[[V4332 Sagittarii|V4332 Sgr]]
==Notes==
{{Notelist}}

==References==
{{Reflist|30em|refs=

<ref name=sparks>{{Cite journal | last1 = Sparks | first1 = W. B. | last2 = Bond | first2 = H. E. | last3 = Cracraft | first3 = M. | last4 = Levay | first4 = Z. | last5 = Crause | first5 = L. A. | last6 = Dopita | first6 = M. A. | last7 = Henden | first7 = A. A. | last8 = Munari | first8 = U. | last9 = Panagia | first9 = N. | last10 = Starrfield | doi = 10.1088/0004-6256/135/2/605 | first10 = S. G. | last11 = Sugerman | first11 = B. E. | last12 = Wagner | first12 = R. M. | last13 = l. White | first13 = R. | s2cid = 13459320 | title = V838 Monocerotis: A Geometric Distance from Hubble Space Telescope Polarimetric Imaging of Its Light Echo | journal = The Astronomical Journal | volume = 135 | issue = 2 | pages = 605–617 | date = 2008 |arxiv = 0711.1495 |bibcode = 2008AJ....135..605S }}</ref>

<ref name="Lane2005">{{cite journal
| last1 = Lane | first1 = B. F.
| last2 = Retter | first2 = A.
| last3 = Thompson | first3 = R. R.
| last4 = Eisner | first4 = J. A.
| s2cid = 119473906
| title = Interferometric Observations of V838 Monocerotis
| journal = The Astrophysical Journal
| volume = 622
| issue = 2
| pages = L137–L140
| publisher = The American Astronomical Society
| date = April 2005
| arxiv = astro-ph/0502293
| doi = 10.1086/429619
| bibcode=2005ApJ...622L.137L
}}</ref>

<ref name=woodward2021>{{cite journal
| title=The Infrared Evolution of Dust in V838 Monocerotis
| last1=Woodward | first1=C. E. | last2=Evans | first2=A.
| last3=Banerjee | first3=D. P. K. | last4=Liimets | first4=T.
| last5=Djupvik | first5=A. A. | last6=Starrfield | first6=S.
| last7=Clayton | first7=G. C. | last8=Eyres | first8=S. P. S.
| last9=Gehrz | first9=R. D. | last10=Wagner | first10=R. M.
| display-authors=1 | journal=The Astronomical Journal
| volume=162 | issue=5 | id=183 | pages=9
| date=November 2021 | doi=10.3847/1538-3881/ac1f1e
| arxiv=2108.08149 | bibcode=2021AJ....162..183W | s2cid=237194996 | doi-access=free }}</ref>

<ref name=mobeen2021>{{cite journal
| title=The mid-infrared environment of the stellar merger remnant V838 Monocerotis
| display-authors=1 | last1=Zain Mobeen | first1=Muhammad
| last2=Kamiński, Tomasz | last3=Matter | first3=Alexis
| last4=Wittkowski | first4=Markus | last5=Paladini | first5=Claudia
| journal=Astronomy & Astrophysics | arxiv=2110.12758 | date=October 2021 | volume=655 | pages=A100 | doi=10.1051/0004-6361/202142297 | bibcode=2021A&A...655A.100M | s2cid=239768384 }}</ref>

<ref name=reid2019>{{cite journal| bibcode=2019ApJ...885..131R | title=Trigonometric Parallaxes of High-mass Star-forming Regions: Our View of the Milky Way | last1=Reid | first1=M. J. | last2=Menten | first2=K. M. | last3=Brunthaler | first3=A. | last4=Zheng | first4=X. W. | last5=Dame | first5=T. M. | last6=Xu | first6=Y. | last7=Li | first7=J. | last8=Sakai | first8=N. | last9=Wu | first9=Y. | last10=Immer | first10=K. | last11=Zhang | first11=B. | last12=Sanna | first12=A. | last13=Moscadelli | first13=L. | last14=Rygl | first14=K. L. J. | last15=Bartkiewicz | first15=A. | last16=Hu | first16=B. | last17=Quiroga-Nuñez | first17=L. H. | last18=Van Langevelde | first18=H. J. | journal=The Astrophysical Journal | year=2019 | volume=885 | issue=2 | page=131 | doi=10.3847/1538-4357/ab4a11 | arxiv=1910.03357 | s2cid=203904869 | doi-access=free }}</ref>

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<ref name="Loebman">{{Cite journal|last1=Loebman|first1=S. R.|last2=Wisniewski|first2=J. P.|last3=Schmidt|first3=S. J.|last4=Kowalski|first4=A. F.|last5=Barry|first5=R. K.|last6=Bjorkman|first6=K. S.|last7=Hammel|first7=H. B.|last8=Hawley|first8=S. L.|last9=Hebb|first9=L.|last10=Kasliwal|first10=M. M.|last11=Lynch|first11=D. K.|s2cid=35259252|date=January 2015|title=The Continued Optical to Mid-Infrared Evolution of V838 Monocerotis|journal=The Astronomical Journal|language=en|volume=149|issue=1|pages=17|doi=10.1088/0004-6256/149/1/17|arxiv=1409.2513|bibcode=2015AJ....149...17L|issn=0004-6256}}</ref>

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}}


== External links ==
==External links==
{{Commons category|V838 Monocerotis}}
*[http://www.spacetelescope.org/videos/html/heic0405a.html European Space Agency], Animated morphing video sequence between five individual Hubble images
* [http://www.aavso.org/vsots_v838mon AAVSO Variable Star of the Month, December 2002: V838 Mon]
*[http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/10/text/ Hubble Space Telescope press release]
* [http://hubblesite.org/explore_astronomy/hubbles_universe_unfiltered/12 Show 12: A Flash of Brilliance] Dr. Frank Summers tells about the Mysterious Erupting Star
*[http://www.space.com/scienceastronomy/light_echo_030326.html An article about V838 Monocerotis published at Space.com]
* [http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/10/ Hubble Watches Light from Mysterious Erupting Star Reverberate Through Space] — [[STScI]] press release STScI-2003-10 (26 March 2003; received on 10 August 2006)
* [http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/02/ Light Continues to Echo Three Years After Stellar Outburst] — [[STScI]] press release STScI-2005-02 (3 February 2005; received on 10 August 2006)
* [http://heritage.stsci.edu/2005/02/ The Hubble Heritage Project] — more information and images (received on 10 August 2006)
* [http://hubblesite.org/newscenter/archive/releases/2006/2006/50/ Hubble's Latest Views of Light Echo from Star V838 Monocerotis] — [[STScI]] press release STScI-2006-50 (Exposure dates: 17 November 2005 and 9 September 2006. Released 26 October 2006.)
* [http://www.spacetelescope.org/images/archive/freesearch/V838+Mon/viewall/1 V838 at ESA/Hubble]
* [http://antwrp.gsfc.nasa.gov/apod/ap021003.html NASA Astronomy Picture of the Day] for 3 October 2002. Photos taken by Lisa Crause using the [[South African Astronomical Observatory#1.0m Telescope|1 meter]] telescope at the [[South African Astronomical Observatory]]
* [http://www.constellation-guide.com/v838-monocerotis/ V838 Monocerotis at Constellation Guide]
* [https://www.nytimes.com/2014/09/03/science/space/the-v838-monocerotis-star-still-has-astronomers-heads-exploding.html V838 Monocerotis star still has astronomers heads exploding] ([[NYT]], 3 September 2014).
{{sky|07|04|04.85|-|03|50|50.1|20000}}
{{Stars of Monoceros}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Authority control}}


{{DEFAULTSORT:V838 Monocerotis}}
[[Category:Binary stars]]
[[Category:Monoceros constellation]]
[[Category:Spectroscopic binaries]]
[[Category:Supergiant stars]]
[[Category:Monoceros]]
[[Category:Variable stars]]
[[Category:L-type stars]]
[[Category:M-type supergiants]]
[[Category:Luminous red novae]]
[[Category:Objects with variable star designations|Monocerotis, V838]]
[[Category:Articles containing video clips]]
[[Category:B-type main-sequence stars]]

Latest revision as of 03:55, 13 November 2024

V838 Monocerotis

Hubble Space Telescope image of V838 Monocerotis and the surrounding nebula on September 9, 2006
Credit: NASA/ESA
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Monoceros
Right ascension 07h 04m 04.822s[1]
Declination −03° 50′ 50.53″[1]
Apparent magnitude (V) 6.75 (2002), 15.6[2]
Characteristics
Evolutionary stage M-type supergiant[3]
Spectral type M7.5I -> M5.5I + B3V[3]
Variable type LRN[3]
Astrometry
Proper motion (μ) RA: −0.536±0.229[4] mas/yr
Dec.: −0.078±0.174[4] mas/yr
Parallax (π)0.163 ± 0.016 mas[5]
Distance19,200 ly
(5,900±400[6] pc)
Details
Mass5 – 10[7] M☉
Radius464[8] R☉
Luminosity23,000[8] L☉
Temperature3,300[8] K
Age4[9] Myr
Other designations
V838 Mon, Nova Monocerotis 2002, GSC 04822-00039
Database references
SIMBADdata

V838 Monocerotis (Nova Monocerotis 2002) is a cataclysmic binary star in the constellation Monoceros about 19,000 light years (6 kpc) from the Sun. The previously unremarked star was observed in early 2002 experiencing a major outburst, and was one of the largest known stars for a short period following the outburst.[10] Originally believed to be a typical nova eruption, it was then identified as the first of a new class of eruptive variables known as luminous red novae. The reason for the outburst is still uncertain, but is thought to have been a merger of two stars within a triple system.

The eruption occurred on one of two B3 main sequence stars in a close binary orbit. The erupting star appeared as an unusually cool supergiant and for a while engulfed its companion. By 2009 the temperature of the supergiant had increased (since 2005) to 3,270 K and its luminosity was 15,000 times solar (L☉), but its radius had decreased to 380 times that of the Sun (R☉), although the ejecta continues to expand.[11]

Outburst

[edit]
The visual (blue points) and K band infrared (red points) light curves of the 2002 eruption of V838 Monocerotis, adapted from Starrfield et al., 2004[12]
Light echo of V838 Mon as imaged April 30, 2002

On January 6, 2002, an unknown star was seen to brighten in the constellation Monoceros, the Unicorn.[13] Being a new variable star, it was designated V838 Monocerotis, the 838th variable star of Monoceros. The initial light curve resembled that of a nova, an eruption that occurs when enough hydrogen gas accumulates on the surface of a white dwarf from its close binary companion. Therefore, the object was also designated Nova Monocerotis 2002. V838 Monocerotis reached a maximum visual magnitude of 6.75 on February 6, 2002, after which it started to dim rapidly, as expected. However, in early March, the star started to brighten again, particularly in infrared wavelengths. Yet another brightening in infrared occurred in early April. In 2003, the star returned to near its original brightness before the eruption (magnitude 15.6), but as a red supergiant rather than a blue main-sequence star. The light curve produced by the eruption was unlike anything previously seen.[2] In 2009, the star was about 15,000 L☉,[11] which, in the absence of extinction, would correspond to an apparent magnitude of 8.5.[a]

Comparison between the size of V838 Monocerotis and the Inner Solar System.

The star brightened to about a million times solar luminosity[14] and an absolute magnitude of −9.8,[15] ensuring that at the time of maximum, it was one of the most luminous stars in the Milky Way galaxy. Its brightening was caused by a rapid expansion of its outer layers.

V838 Monocerotis was observed by use of the Palomar Testbed Interferometer, which indicated a radius of 1,570±400 R☉ (comparable to Jupiter's orbital radius), confirming the earlier indirect calculations.[16] At the currently accepted distance of 6,100 pc, the measured angular diameter in late 2004 (1.83 mas) corresponded to a radius of 1,200±150 R☉, but by 2014, it shrunk to 750±200 R☉, around 70 solar radii larger than Antares.[17] The expansion took only a couple of months, meaning that its speed was abnormal. Because the laws of thermodynamics dictate that expanding gases cool, the star became extremely cool and deep red. In fact, some astronomers argue that the spectrum of the star initially resembled that of L-type brown dwarfs. If that is the case, V838 Monocerotis was the first known L-type supergiant.[18] Since then, it has shrunk and heated up and is now considered an M-type supergiant. However, current estimates of the distance, and hence of the radius, are about 25% lower than assumed in those papers.[15]

Other possibly similar events

[edit]

There are a handful of outbursts resembling that of V838 Monocerotis. In 1988, a red star was detected erupting in the Andromeda Galaxy. The star, designated M31-RV, reached the absolute bolometric magnitude of −9.95 at maximum (corresponding to a luminosity of 0.75 million L☉) before dimming beyond detectability. A similar eruption, V4332 Sagittarii, occurred in 1994 in the Milky Way.[19]

Progenitor star

[edit]
Location of V838 Monocerotis within the Milky Way galaxy.

Based on an incorrect interpretation of the light echo the eruption generated, the distance of the star was first estimated to be 1,900 to 2,900 light years. Combined with the apparent magnitude measured from pre-eruption photographs, it was thought to be an underluminous F-type dwarf, which posed a considerable enigma.[10]

More accurate measurements gave a much larger distance, 20,000 light years (6 kpc). It appears that the star was considerably more massive and luminous than the Sun. The star probably has a mass of from 5 to 10 times the mass of the Sun (M☉).[7] It was apparently either a B1.5V star with a B3V companion, or an A0.5V with a B4V companion. In the latter case it would have had a luminosity around 550 L☉ (being 0.43 times as luminous as its companion), and in the former case it would have been more luminous (about 1.9 times as luminous as its companion).[7][b] The star may have originally had a radius roughly 5 R☉ and its temperature would have been that of a B-type star (more than 10,000K but less than 30,000K[7]). Munari et al. (2005) suggested that the progenitor star was a very massive supergiant with an initial mass of about 65 M☉,[9] but this has been contested.[7] There seems to be agreement that the star system is relatively young. Munari et al. conclude that the system may be only about 4 million years old.

The spectrum of V838 Monocerotis reveals a companion, a hot blue B-type main sequence star probably not very different from the progenitor star.[7] It is also possible that the progenitor was slightly less massive than the companion and only just entering the main sequence.[10]

Based on the photometric parallax of the companion, Munari et al. calculated a greater distance, 36,000 light years (10 kpc).[9]

Light echo

[edit]
Images showing the expansion of the light echo. Credit: NASA/ESA.
The evolution of the light echo around V838 Monocerotis.[20]
Animation of 11 images of light echo of V838 Mon

Rapidly brightening objects like novae and supernovae are known to produce a phenomenon known as light echo. The light that travels directly from the object arrives first. If there are clouds of interstellar matter around the star, some light is reflected from the clouds. Because of the longer path, the reflected light arrives later, producing a vision of expanding rings of light around the erupted object. The rings appear to travel faster than the speed of light, but in fact they do not.[2][21]

In the case of V838 Monocerotis, the light echo produced was unprecedented and is well documented in images taken by the Hubble Space Telescope. While the photos appear to depict an expanding spherical shell of debris, they are actually formed by the illumination of an ever-expanding ellipsoid with the progenitor star at one focus and the observer at the other. Hence, despite appearances, the structures in these photos are actually concave toward the viewer.

By March 2003 the size of the light echo in the sky was twice the angular diameter of Jupiter and was continuing to grow.[22] Jupiter's angular diameter varies from 30 to 51 arcseconds.

It is not yet clear if the surrounding nebulosity is associated with the star itself. If that is the case, they may have been produced by the star in earlier eruptions which would rule out several models that are based on single catastrophic events.[2] However, there is strong evidence that the V838 Monocerotis system is very young and still embedded in the nebula from which it formed.[14]

The eruption initially emitted at shorter wavelengths (i.e. was bluer), which can be seen in the light echo: the outer border is bluish in the Hubble images.[2]

Hypotheses

[edit]
Two pictures taken in November 2005 and September 2006 showing the changes that occurred to the bright echo of V838 Mon.

This and other luminous red nova events are thought to be caused by the merger of two stars. In the case of V838 Monocerotis, it was the merger of two main sequence stars, or an 8 M☉ main sequence star and a 0.3 M☉ pre-main sequence star. The merger model explains the multiple peaks in the light curve observed during the outburst.[14] Based on further observations of stars similar to V838 Monocerotis, such as V1309 Scorpii, astronomers have reached the conclusion that this is the most likely scenario.[1][23]

Other explanations for the eruption of V838 Monocerotis have also been published.[24]

Atypical nova outburst

[edit]

The outburst of V838 Monocerotis may be a nova eruption after all, albeit a very unusual one. However, this is very unlikely considering that the system includes a B-type star, and stars of this type are young and massive. There has not been enough time for a possible white dwarf to cool and accrete enough material to cause the eruption.[19]

Thermal pulse of a dying star

[edit]

V838 Monocerotis may be a post-asymptotic giant branch star, on the verge of going supernova. The nebulosity illuminated by the light echo may actually be shells of dust surrounding the star, created by the star during previous similar outbursts. The brightening may have been a so-called helium flash, where the core of a dying low-mass star suddenly ignites helium fusion disrupting, but not destroying, the star. Such an event is known to have occurred in Sakurai's Object. However, several pieces of evidence support the argument that the dust is interstellar rather than centered on V838 Monocerotis. A dying star that has lost its outer envelopes would be appropriately hot, but the evidence points to a young star instead.[7]

Thermonuclear event within a massive supergiant

[edit]

According to some evidence, V838 Monocerotis may be a very massive supergiant. Also in this case, the outburst may have been a helium flash. Very massive stars survive multiple such events; however, they experience heavy mass loss (about half of the original mass is lost while in the main sequence) before settling as extremely hot Wolf-Rayet stars. This theory may also explain the apparent dust shells around the star. V838 Monocerotis is located in the approximate direction of the galactic anticenter and off from the disk of the Milky Way. Stellar birth is less active in outer galactic regions, and it is not clear how such a massive star can form there. However, there are very young clusters like Ruprecht 44 and the 4-million-year-old NGC 1893 at a distance of about 7 and 6 kiloparsecs, respectively.[9]

Planetary capture event

[edit]

Another possibility is that V838 Monocerotis may have swallowed its giant planets. If one of the planets entered into the atmosphere of the star, the stellar atmosphere would have begun slowing down the planet. As the planet penetrated deeper into the atmosphere, friction would become stronger and kinetic energy would be released into the star more rapidly. The star's envelope would then warm up enough to trigger deuterium fusion, which would lead to rapid expansion. The later peaks may then have occurred when two other planets entered into the expanded envelope. The authors of this model calculate that every year about 0.4 planetary capture events occur in Sun-like stars in the Milky Way galaxy, whereas for massive stars like V838 Monocerotis the rate is approximately 0.5–2.5 events per year.[25]

Common envelope event

[edit]

See Common envelope

See also

[edit]

Notes

[edit]
  1. ^ The sun's absolute magnitude is 4.83, meaning that its apparent magnitude would be 4.83 at 10 parsecs, and V838 Mon was 15,000 times more luminous than the sun, assuming that it is 6,500 parsecs away, so the apparent magnitude of V838 Mon comes to 4.83 − 2.5×log(15000) + 5×log(6500/10) ≈ 8.5.
  2. ^ The reference does not explicitly give the luminosity in the first case.

References

[edit]
  1. ^ a b c Zain Mobeen, Muhammad; et al. (October 2021). "The mid-infrared environment of the stellar merger remnant V838 Monocerotis". Astronomy & Astrophysics. 655: A100. arXiv:2110.12758. Bibcode:2021A&A...655A.100M. doi:10.1051/0004-6361/202142297. S2CID 239768384.
  2. ^ a b c d e Bond, Howard E.; Henden, Arne; Levay, Zoltan G.; Panagia, Nino; Sparks, William B.; Starrfield, Sumner; Wagner, R. Mark; Corradi, R. L. M.; Munari, U. (March 27, 2003). "An energetic stellar outburst accompanied by circumstellar light echoes". Nature. 422 (6930): 405–408. arXiv:astro-ph/0303513. Bibcode:2003Natur.422..405B. doi:10.1038/nature01508. PMID 12660776. S2CID 90973.
  3. ^ a b c Goranskij, V. P.; Barsukova, E. A.; Burenkov, A. N.; Valeev, A. F.; Zharova, A. V.; Kroll, P.; Metlova, N. V.; Shugarov, S. Yu. (2020). "Progenitor and Remnant of the Luminous Red Nova V838 Monocerotis". Astrophysical Bulletin. 75 (3): 325–349. Bibcode:2020AstBu..75..325G. doi:10.1134/S1990341320030049. S2CID 221839336.
  4. ^ a b Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. ^ Reid, M. J.; Menten, K. M.; Brunthaler, A.; Zheng, X. W.; Dame, T. M.; Xu, Y.; Li, J.; Sakai, N.; Wu, Y.; Immer, K.; Zhang, B.; Sanna, A.; Moscadelli, L.; Rygl, K. L. J.; Bartkiewicz, A.; Hu, B.; Quiroga-Nuñez, L. H.; Van Langevelde, H. J. (2019). "Trigonometric Parallaxes of High-mass Star-forming Regions: Our View of the Milky Way". The Astrophysical Journal. 885 (2): 131. arXiv:1910.03357. Bibcode:2019ApJ...885..131R. doi:10.3847/1538-4357/ab4a11. S2CID 203904869.
  6. ^ Ortiz-León, Gisela N.; Menten, Karl M.; Kamiński, Tomasz; Brunthaler, Andreas; Reid, Mark J.; Tylenda, Romuald (2020). "SiO maser astrometry of the red transient V838 Monocerotis". Astronomy & Astrophysics. 638: A17. arXiv:2004.01488. Bibcode:2020A&A...638A..17O. doi:10.1051/0004-6361/202037712. S2CID 214794885.
  7. ^ a b c d e f g Tylenda, R.; Soker, N.; Szczerba, R. (October 2005). "On the progenitor of V838 Monocerotis". Astronomy and Astrophysics. 441 (3): 1099–1109. arXiv:astro-ph/0412183. Bibcode:2005A&A...441.1099T. doi:10.1051/0004-6361:20042485. S2CID 119363054. Retrieved 10 August 2006.
  8. ^ a b c Kamiński, Tomek; Tylenda, Romuald; Kiljan, Aleksandra; Schmidt, Mirek; Lisiecki, Krzysztof; Melis, Carl; Frankowski, Adam; Joshi, Vishal; Menten, Karl M. (2021). "V838 Monocerotis as seen by ALMA: A remnant of a binary merger in a triple system". Astronomy & Astrophysics. 655: A32. arXiv:2106.07427. Bibcode:2021A&A...655A..32K. doi:10.1051/0004-6361/202141526. S2CID 235422695.
  9. ^ a b c d Munari, U.; Munari, U.; Henden, A.; Vallenari, A.; Bond, H. E.; Corradi, R. L. M.; Crause, L.; Desidera, S.; et al. (May 2, 2005). "On the distance, reddening and progenitor of V838 Mon". Astronomy and Astrophysics. 434 (3): 1107–1116. arXiv:astro-ph/0501604. Bibcode:2005A&A...434.1107M. doi:10.1051/0004-6361:20041751. S2CID 119330637.
  10. ^ a b c Tylenda, R. (June 4, 2005). "Evolution of V838 Monocerotis during and after the 2002 eruption". Astronomy and Astrophysics. 436 (3): 1009–1020. arXiv:astro-ph/0502060. Bibcode:2005A&A...436.1009T. doi:10.1051/0004-6361:20052800. S2CID 3566688.
  11. ^ a b Tylenda, R.; Kamiński, T.; Schmidt, M.; Kurtev, R.; Tomov, T. (2011). "High-resolution optical spectroscopy of V838 Monocerotis in 2009". Astronomy & Astrophysics. 532: A138. arXiv:1103.1763. Bibcode:2011A&A...532A.138T. doi:10.1051/0004-6361/201116858. S2CID 118649108.
  12. ^ Starrfield, S.; Wagner, R. M.; Hauschildt, P. H.; Bond, H. E.; Evans, A.; Rushton, M. T.; Rushton, M. T.; Munari, U.; Henden, A.; Levay, Z. G.; Panagia, N.; Sparks, W. B.; Corradi, R. L. M. (July 2004). The 2002 Outburst of V838 Mon: As Cool As It Gets. Retrieved 29 September 2021.
  13. ^ Brown, N. J.; Waagen, E. O.; Scovil, C.; Nelson, P.; Oksanen, A.; Solonen, J.; Price, A. (2002). "Peculiar variable in Monoceros". IAU Circ. 7785: 1. Bibcode:2002IAUC.7785....1B.
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