NML Cygni

{{Starbox begin

| name=NML Cygni

}}

{{Starbox image

| image=256px

| caption=NML Cygni, seen as the deep red star at the center, from the Sloan Digital Sky Survey DR9. Note the green circumstellar nebula surrounding the star.

}}

{{Starbox observe

| epoch=J2000.0

| equinox=J2000.0

| constell=Cygnus

| ra={{RA|20|46|25.54}}{{Cite simbad|title=NML Cyg|access_date=2024-04-30}}

| dec={{DEC|+40|06|59.5}}

| appmag_v=16.60 (variable){{Cite journal |last1=Johnson |first1=Harold L. |last2=Eugenio E. |first2=Mendoza V. |last3=Wisniewski |first3=Weislaw Z. |date=October 1965 |year=1965 |title=Observations of "Infrared Stars." |journal=The Astrophysical Journal |language=en |volume=142 |pages=1249 |bibcode=1965ApJ...142.1249J |doi=10.1086/148393 |issn=0004-637X}}

| pronounce=

}}

{{Starbox character

| type=OH/IR red hypergiant

| class=M4.5–M7.9 Ia–III

| b-v=+2.04

| appmag_1_passband=K

| appmag_1={{val|0.791|0.204}}

| appmag_4_passband=G

| appmag_4=11.148

| appmag_5_passband=J

| appmag_5={{val|4.877|0.037}}

| appmag_6_passband=H

| appmag_6={{val|2.389|0.2}}

| variable=Semiregular variable star{{cite journal|bibcode=2010A&A...523A..18D|arxiv=1008.1083|title=Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles. II. CO line survey of evolved stars: Derivation of mass-loss rate formulae|journal=Astronomy and Astrophysics|volume=523|pages=A18|last1=De Beck|first1=E.|last2=Decin|first2=L.|last3=De Koter|first3=A.|last4=Justtanont|first4=K.|last5=Verhoelst|first5=T.|last6=Kemper|first6=F.|last7=Menten|first7=K. M.|s2cid=16131273|year=2010|doi=10.1051/0004-6361/200913771}}

}}

{{Starbox astrometry

| radial_v=

| prop_mo_ra=−1.55

| prop_mo_dec=−4.59

| parallax=0.620

| p_error=0.047

| parallax_footnote=

| dist_pc={{val|1,610|130|110|fmt=commas}}

| dist_ly={{val|5,250|420|360|fmt=commas}}

}}

{{Starbox detail

| temperature=

| mass=25 (initial)

| radius=<{{val|{{Solar radius calculator|type=AD|7.8|1.61}}|195|229|fmt=commas}}{{efn|name=dust|Surrounding dusty region is very complex making the radius hard to determine.}}

| luminosity={{val|229,000|40000|41000|fmt=commas}},{{Cite journal|last1=Davies|first1=Ben|last2=Beasor|first2=Emma R.|s2cid=210714093|date=March 2020|title=The 'red supergiant problem': the upper luminosity boundary of Type II supernova progenitors|bibcode=2020MNRAS.493..468D|journal=MNRAS|language=en|volume=493|issue=1|pages=468–476|doi=10.1093/mnras/staa174|doi-access=free |arxiv=2001.06020 }} {{nowrap|{{val|270,000|50000|50000|fmt=commas}}}}

| age_myr=8

}}

{{Starbox catalog

| names = {{odlist | name=NML Cyg | V=V1489 Cyg | RAFGL=2650 | IRC=+40448 | 2MASS=J20462554+4006594 | AAVSO=2042+39 }}

}}

{{Starbox reference

| Simbad=NML+Cyg

}}

NML Cygni or V1489 Cygni (abbreviated to NML Cyg or V1489 Cyg) is a red hypergiant{{Cite journal |last1=Zhang |first1=B. |last2=Reid |first2=M. J. |last3=Menten |first3=K. M. |last4=Zheng |first4=X. W. |last5=Brunthaler |first5=A. |date=August 2012 |title=The distance and size of the red hypergiant NML Cygni from VLBA and VLA astrometry |journal=Astronomy & Astrophysics |volume=544 |pages=A42 |doi=10.1051/0004-6361/201219587 |issn=0004-6361|arxiv=1207.1850 |bibcode=2012A&A...544A..42Z }} or red supergiant (RSG) in the constellation Cygnus. It is possibly one of the largest known stars currently known, and is also possibly one of the most luminous and massive cool hypergiants, as well as one of the most luminous stars in the Milky Way.

The distance of NML Cygni from Earth is estimated to be around 1.6 kpc, about {{val|5,300|fmt=commas|ul=light-years}}.{{Cite book |last=Schuster |first=Michael Thomas |url=https://books.google.com/books?id=LrbvS-1punoC |title=Investigating the Circumstellar Environments of the Cool Hypergiants |date=2007 |publisher=University of Minnesota |isbn=978-0-549-32782-0}} It is a part of the Cygnus OB2 association, one of the closest massive associations to the Sun, spanning nearly 2° on the sky or ~{{val|30|u=pc}} in radius at the distance of {{val|1.74|0.2|u=kpc}}. Based on the estimated distance and a measurement of its angular diameter of {{val|7.8|0.64|u=milliarcseconds}}, NML Cygni's physical radius is of {{Solar radius calculator|type=AD|7.8|1.61|link=y|unit=y}}. If placed at the center of the Solar System, its surface would potentially extend past the orbit of Jupiter.

Observational history

File:V1489CygLightCurve.png for V1489 Cygni, plotted from data published by Strecker (1975){{cite journal |last1=Strecker |first1=D. W. |title=Variability of R CrB and NML Cyg at 3.5 μ|journal=The Astronomical Journal |date=June 1975 |volume=80 |issue=6 |pages=451–453 |doi=10.1086/111763 |bibcode=1975AJ.....80..451S |doi-access=free }}]]

NML Cygni was discovered in 1965 by American astronomers Neugebauer, Martz, and Leighton who described two extremely red luminous stars, their colour being consistent with a black body temperature of {{val|1,000|fmt=commas|u=K}}.{{cite journal | title = Observations of Extremely Cool Stars | last1 = Neugebauer | first1 = G. | last2 = Martz | first2 = D. E. | last3 = Leighton | first3 = R. B. | journal = Astrophysical Journal | volume = 142 | pages = 399–401 | date = July 1965| doi = 10.1086/148300 | bibcode = 1965ApJ...142..399N | url = https://authors.library.caltech.edu/74594/1/1965ApJ___142__399N.pdf }} The name NML comes from the names of these three discoverers.{{cite book|first=J. B.|last=Hearnshaw|title=The Measurement of Starlight: Two Centuries of Astronomical Photometry|chapter-url={{google books|id=Kp7G4IqK7woC|page=278|plainurl=yes}}|access-date=23 August 2012|date=2 May 1996|publisher=Cambridge University Press|isbn=978-0-521-40393-1|page=[https://archive.org/details/measurementofsta0000hear/page/278 278]|chapter=New infrared sources and their interpretation|url=https://archive.org/details/measurementofsta0000hear/page/278}} The second star was briefly referred to as NML Tauri{{Cite journal | last1 = Pesch | first1 = P. | doi = 10.1086/149015 | title = Objective-Prism Spectra of Some Very Red Stars | journal = The Astrophysical Journal | volume = 147 | pages = 381 | year = 1967 |bibcode = 1967ApJ...147..381P }} but is now known as IK Tauri,{{cite journal |last1=Kukarkin |first1=B. V. |last2=Efremov |first2=Yu. N. |last3=Frolov |first3=M. S. |last4=Medvedeva |first4=G. I. |last5=Kholopov |first5=P. N. |last6=Kurochkin |first6=N. E. |last7=Kukarkina |first7=N. P. |last8=Perova |first8=N. B. |last9=Fedorovich |first9=V. P. |display-authors=4 |date=8 November 1968 |title=Identification List of the New Variable Stars Nominated in 1968 |journal=Information Bulletin on Variable Stars |volume=311 |issue=1 |pages=1 |bibcode=1968IBVS..311....1K}} an M9 Mira variable. NML Cygni has since also been given the designation V1489 Cygni on account of the small semi-regular brightness variations,{{cite journal |last1=Kukarkin |first1=B. V. |last2=Kholopov |first2=P. N. |last3=Kukarkina |first3=N. P. |date=27 November 1975 |title=61st Name-List of Variable Stars |journal=Information Bulletin on Variable Stars |volume=1068 |issue=1 |pages=1 |bibcode=1975IBVS.1068....1K}} but is still most commonly referred to as NML Cygni. Its composition began to be revealed with the discovery of OH masers (1612 MHz) in 1968.{{cite journal | first1=R. J. | last1=Cohen | title=Narrow polarized components in the OH 1612-MHz maser emission from supergiant OH-IR sources | date=1 April 1987 | display-authors=4 | last2=Downs | first2=G. | last3=Emerson | first3=R. | last4=Grimm | first4=M. | last5=Gulkis | first5=S. | last6=Stevens | first6=G. | last7=Tarter | first7=J. | journal=Monthly Notices of the Royal Astronomical Society | volume=225 | issue=3 | pages=491–498 | doi=10.1093/mnras/225.3.491 | pmid=11540900 | bibcode = 1987MNRAS.225..491C | doi-access=free }} {{chem|link=water|H|2|O}}, {{chem|link=Silicon monoxide|Si|O}}, {{chem|link=Carbon monoxide|C|O}}, {{chem|link=Hydrogen cyanide|H|C|N}}, {{chem|link=Carbon monosulfide|C|S}}, {{chem|link=sulfur monoxide|S|O}}, {{chem|link=Sulfur dioxide|S|O|2}}, and {{chem|link=Hydrogen sulfide|H|2|S}} molecules have also been detected.{{cite book |last=Marvel |first=Kevin |url=https://books.google.com/books?id=wwx1Gj5wR5QC |title=The Circumstellar Environment of Evolved Stars As Revealed by Studies of Circumstellar Water Masers |date=19 December 1996 |publisher=Universal-Publishers |isbn=978-1-58112-061-5 |pages=182–212 |chapter=NML Cygni |access-date=23 August 2012 |chapter-url=https://books.google.com/books?id=wwx1Gj5wR5QC&pg=PR182}}

Physical characteristics

File:CygOB2 med.jpg light image of Cygnus OB2, the stellar association in which NML Cygni is located]]

NML Cygni is an extremely large and luminous cool supergiant with parameters similar to that of another notable but more extreme cool hypergiant star, VY Canis Majoris, and is also known as a heavily mass-losing OH/IR supergiant. It is also a semiregular variable star with a period of either 1,280 or 940 days. It occupies the upper-right hand corner of the Hertzsprung–Russell diagram although most of the properties of the star depend directly on its distance.

= Size, luminosity, and temperature =

File:NML Cygni compared to the Sun and Earth orbit.png

The bolometric luminosity (L_bol) for NML Cygni was originally calculated to be {{Solar luminosity|500,000}} at an assumed distance of {{val|2|ul=kpc}} and the radius was calculated to be {{convert|2600000000|km|solar radius|disp=out}} based on an {{val|8.6|ul=mas}} angular diameter and distance.{{cite journal|bibcode=2004ApJ...610..427Z|arxiv=astro-ph/0405044|title=Observations of Water Vapor Outflow from NML Cygnus|journal=The Astrophysical Journal|volume=610|issue=1|pages=427|last1=Zubko|first1=Viktor|last2=Li|first2=Di|last3=Lim|first3=Tanya|last4=Feuchtgruber|first4=Helmut|last5=Harwit|first5=Martin|s2cid=14352419|year=2004|doi=10.1086/421700}}{{cite journal|bibcode=1997ApJ...481..420M|title=Nonuniform Dust Outflow Observed around Infrared Object NML Cygni|journal=The Astrophysical Journal|volume=481|issue=1|pages=420|last1=Monnier|first1=J. D|last2=Bester|first2=M|last3=Danchi|first3=W. C|last4=Johnson|first4=M. A|last5=Lipman|first5=E. A|last6=Townes|first6=C. H|last7=Tuthill|first7=P. G|last8=Geballe|first8=T. R|last9=Nishimoto|first9=D|last10=Kervin|first10=P. W|s2cid=9503967|year=1997|doi=10.1086/304050|arxiv=astro-ph/9702103}} A 2006 study, similar to those conducted on VY Canis Majoris, suggests that NML Cygni is a normal red supergiant with consequently much lower luminosity and radius values.{{cite journal | last1 = Massey | first1 = Philip | last2 = Levesque | first2 = Emily M. | last3 = Plez | first3 = Bertrand | s2cid = 14314968 | title = Bringing VY Canis Majoris down to size: an improved determination of its effective temperature | journal = The Astrophysical Journal | volume = 646 | issue = 2 | pages = 1203–1208 | date = 1 August 2006 |arxiv=astro-ph/0604253 | doi = 10.1086/505025 | bibcode=2006ApJ...646.1203M}} More modern and accurate measurements give a distance around {{val|1.6|u=kpc}}, which gives a luminosity around {{solar luminosity|200,000}}. A radio angular diameter of 44 mas was given based on the distance, suggesting the optical angular diameter may be around 22 mas. This distance and a luminosity of {{solar luminosity|270,000}} were combined with assumptions of the effective temperature of the star, giving a radius of {{solar radius|1,640}} for a temperature of {{val|3,250|fmt=commas|u=K}} or possibly {{solar radius|2,770}} for a temperature of {{val|2,500|fmt=commas|u=K}}.{{efn|name=radius}} However, another paper gives a much lower radius of {{solar radius|1,183}} based on an assumed effective temperature of {{val|3,834|fmt=commas|u=K}} and a lower distance of {{val|1.22|u=kpc}}. There is a Gaia Data Release 2 parallax for NML Cygni of {{val|1.5259|0.5677|ul=mas}}, but the underlying measurements show a considerable level of noise and the parallax is considered unreliable.{{cite journal |bibcode=2019ApJ...875..114X |title=Comparison of Gaia DR2 Parallaxes of Stars with VLBI Astrometry |journal=The Astrophysical Journal |volume=875 |issue=2 |pages=114 |last1=Xu |first1=Shuangjing |last2=Zhang |first2=Bo |last3=Reid |first3=Mark J. |last4=Zheng |first4=Xingwu |last5=Wang |first5=Guangli |s2cid=119192180 |year=2019 |arxiv=1903.04105 |doi=10.3847/1538-4357/ab0e83 |doi-access=free }}

NML Cygni's uniform disk angular diameter was measured by the CHARM2 survey, leading to an apparent size of {{val|7.8|0.64|u=milliarcseconds}}. Assuming the distance measured by Zhang et al. (2012) ({{val|1610|130|110|u=parsecs}}), it leads to a physical radius of {{Solar radius calculator|type=AD|7.8|1.61|unit=y}}. If placed in the center of the Solar System, its photosphere would past the orbit of Jupiter. NML Cygni is covered by a complex dust shell, so the measured angular diameter likely contain some parts of this disk, and therefore its physical radius may be smaller.[https://vizier.cds.unistra.fr/viz-bin/VizieR?-6N&-out.form=H0&//*&-5N&%3C%22Label%22&catid%3D34310773&tabid%3D1&colid%3D4 Type of source (Bin, Cal, Com, Diam, UR)]

= Mass and mass loss =

NML Cygni lies close to the expected position that a {{solar mass|25}} star would evolve to after eight million years.

NML Cygni is evolved and a number of heavy elements and molecules have been detected in its atmosphere, particularly oxygen, hydroxyl, and water. It is surrounded by dusty material{{Cite journal | last1 = Schuster | first1 = M. T. | last2 = Marengo | first2 = M. | last3 = Hora | first3 = J. L. | last4 = Fazio | first4 = G. G. | last5 = Humphreys | first5 = R. M. | last6 = Gehrz | first6 = R. D. | last7 = Hinz | first7 = P. M. | last8 = Kenworthy | first8 = M. A. | last9 = Hoffmann | first9 = W. F. | s2cid = 17699562 | doi = 10.1088/0004-637X/699/2/1423 | title = Imaging the Cool Hypergiant NML Cygni's Dusty Circumstellar Envelope with Adaptive Optics | journal = The Astrophysical Journal | volume = 699 | issue = 2 | pages = 1423–1432 | year = 2009 |arxiv = 0904.4690 |bibcode = 2009ApJ...699.1423S }} and it exhibits a bean-shaped asymmetric nebula that is coincident with the distribution of its H₂O vapor masers.{{Cite journal |last1=Schuster |first1=Michael T. |last2=Humphreys |first2=Roberta M. |last3=Marengo |first3=Massimo |date=January 2006 |title=The Circumstellar Environments of NML Cygni and the Cool Hypergiants |journal=The Astronomical Journal |language=en |volume=131 |issue=1 |pages=603–611 |bibcode=2006AJ....131..603S |doi=10.1086/498395 |issn=0004-6256|arxiv=astro-ph/0510010 }}

NML Cygni has an estimated mass loss rate of 4.2 to {{val|4.8|e=-4|u={{solar mass}}}} per year, one of the highest known for any star. The annual parallax of NML Cygni is measured to be around 0.62 milliarcseconds. From the observations, it is estimated that NML Cygni has two discrete optically thick envelopes of dust and molecules. The optical depth of the inner shell is found to be 1.9, whereas that of the outer one is 0.33.{{cite journal | title=Proper Motions of Dust Shells Surrounding NML Cygni | first1 = W. C. | last1 = DanchiI | first2 = W. H. | display-authors = 4 | last2 = Green | first3 = D. D. S. | last3 = Hale | first4 = K. | last4 = McEleroy | first5 = J. D. | last5 = Monnier | first6 = P. G. | last6 = Tuthill | first7 = C. H. | last7 = Townes | journal=The Astrophysical Journal |date=July 2001 | doi=10.1086/322237 | volume=555 | issue = 1 | pages=405|bibcode = 2001ApJ...555..405D | doi-access = free }} These dust envelopes are formed due to the strong post-main-sequence wind, which has a velocity {{val|23|u=km/s}}.

Because of the star's position on the outskirts of the massive Cygnus OB2 association, the detectable effects of NML Cygni's radiation on the surrounding dust and gas are limited to the region away from the central hot stars of the association.

Notes

{{notelist|refs=

{{efn | name=radius | Applying the Stefan-Boltzmann Law with a nominal solar effective temperature of 5,772 K:

: $\sqrt{(5772/3250)^4 * 270,000} = 1638.96\ R\odot$

: $\sqrt{(5772/2500)^4 * 270,000} = 2769.84\ R\odot$ }}

}}

References

{{Reflist|30em|refs=

{{cite web |title=GCVS Query=V1489 Cyg |publisher=General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia |url=http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=V1489+Cyg |access-date=2018-09-21|website=Sternberg Astronomical Institute}}

{{Cite book |last=Lang |first=Kenneth R. |url=https://books.google.com/books?id=OvTjLcQ4MCQC&pg=PA41 |title=Astrophysical formulae |date=2006 |publisher=Springer |isbn=978-3-540-29692-8 |edition=3rd |series=Astronomy and astrophysics library |volume=1 |location=Berlin}}. The radius (R_*) is given by:

: $\begin{align} 2\cdot R_*$

& = \frac{(10^{-3}\cdot 1,610\cdot 7.8)\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\

& 2,701\cdot R_{\bigodot}

\end{align}

{{Cite journal | last1 = Monnier | first1 = J. D. | last2 = Millan-Gabet | first2 = R. | last3 = Tuthill | first3 = P. G. | last4 = Traub | first4 = W. A. | last5 = Carleton | first5 = N. P. | last6 = Coude Du Foresto | first6 = V. | last7 = Danchi | first7 = W. C. | last8 = Lacasse | first8 = M. G. | last9 = Morel | first9 = S. | last10 = Perrin | first10 = G. | last11 = Porro | first11 = I. L. | last12 = Schloerb | first12 = F. P. | last13 = Townes | first13 = C. H. | s2cid = 7851916 | title = High-Resolution Imaging of Dust Shells by Using Keck Aperture Masking and the IOTA Interferometer | doi = 10.1086/382218 | journal = The Astrophysical Journal | volume = 605 | issue = 1 | pages = 436–461 | year = 2004 |arxiv = astro-ph/0401363 |bibcode = 2004ApJ...605..436M }}

{{Cite journal |last1=Richichi |first1=A. |last2=Percheron |first2=I. |last3=Khristoforova |first3=M. |date=2005-02-01 |title=CHARM2: An updated Catalog of High Angular Resolution Measurements |journal=Astronomy & Astrophysics |language=en |volume=431 |issue=2 |pages=773–777 |doi=10.1051/0004-6361:20042039 |bibcode=2005A&A...431..773R |issn=0004-6361}} Data about NML Cygni is found [https://vizier.cds.unistra.fr/viz-bin/VizieR?-source=J/A+A/431/773&recno=3257 here] at VizieR.

{{cite journal|doi=10.3847/1538-3881/aab961|title=Searching for Cool Dust. II. Infrared Imaging of the OH/IR Supergiants, NML Cyg, VX SGR, S Per, and the Normal Red Supergiants RS per and T per|year=2018|last1=Gordon|first1=Michael S.|last2=Humphreys|first2=Roberta M.|last3=Jones|first3=Terry J.|last4=Shenoy|first4=Dinesh|last5=Gehrz|first5=Robert D.|last6=Helton|first6=L. Andrew|last7=Marengo|first7=Massimo|last8=Hinz|first8=Philip M.|last9=Hoffmann|first9=William F.|s2cid=73650032|journal=The Astronomical Journal|volume=155|issue=5|page=212|arxiv=1708.00018|bibcode=2018AJ....155..212G |doi-access=free }}|

}}

Category:M-type hypergiants

Category:M-type supergiants

Category:Cygnus (constellation)

Category:Semiregular variable stars

Category:Astronomical objects discovered in 1965

Cygni, V1489

J20462554+4006594

Category:Population I stars