Astronomy:AZ Cygni

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Short description: Red supergiant star in the constellation Cygnus
AZ Cygni
Cygnus constellation map.svg
Red circle.svg
Location of AZ Cygni (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cygnus
Right ascension  20h 57m 59.4444s[1]
Declination +46° 28′ 00.583″[1]
Apparent magnitude (V) 7.8 – 9.6[2]
Characteristics
Evolutionary stage Red supergiant
Spectral type M3 Iab[3][4][5]
(M2–4 Iab)[6][7]
Apparent magnitude (U) 13.91[3]
Apparent magnitude (B) 10.897±0.065[8]
Apparent magnitude (G) 6.190986±0.010832[1]
Apparent magnitude (T) 4.618±0.018[8]
Apparent magnitude (J) 2.765±0.234[8]
Apparent magnitude (H) 1.744±0.164[8]
Apparent magnitude (K) 1.22[9]–1.288±0.172[8]
B−V color index +2.56[3]
J−K color index +1.48[2]
Variable type SRc[2]
Astrometry
Radial velocity (Rv)−5.52±0.99[1] km/s
Proper motion (μ) RA: −1.905±0.031[1] mas/yr
Dec.: −2.871±0.029[1] mas/yr
Parallax (π)0.4027 ± 0.027[1] mas
Distance6,820+420
−380[10] ly
(2,090+130
−115[10] pc)
Absolute magnitude (MV)−6.4839±0.6427[11]
Details
Mass15[10] – 20±9[12] M☉
Radius814+175
−124[4] – 911+57
−50[10] R☉
Luminosity109,828[10](94,759 – 249,443)[10] L☉
Surface gravity (log g)−0.5 – 0.0,[10] 0.29±0.26[12] cgs
Temperature3,989±117[12] (3,972 – 4,000)[10] K
Metallicity [Fe/H]0.0[10][12][13] dex
Other designations
AZ Cyg, BD+45 3349, TYC 3575-553-1, 2MASS J20575942+4628004, SAO 50296[14]
Database references
SIMBADdata

AZ Cygni (BD+45 3349) is a large red supergiant (M3 Iab)[3] in the constellation of Cygnus. It is located 2,090 pc (6,800 ly) from Earth.[10] It has been studied by the CHARA array in order to understand the surface variations of red supergiants.[10]

Observation history

A light curve for AZ Cygni, plotted from ASAS-SN data[15]

AZ Cygni was first observed in the Bonner Durchmusterung catalogue, published by Friedrich Argelander in 1903.[16] It has since then been included in many star surveys and catalogues, including the Two-Micron Sky Survey,[17] 2MASS,[18] Tycho-2 Catalogue[19] and Gaia (DR2[13] and DR3[1]).

From 2011 to 2016, it was observed using the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular Resolution Astronomy Array (CHARA array)[10][12][4] to investigate the evolution of surface features on red supergiants. These observations were used to derive the fundamental stellar parameters of the star, reconstruct images of the star and test models of 3D radiative hydrodynamics in red supergiants.

Parameters of AZ Cygni derived from CHARA array data[12][4][10]
Year of observation Angular diameter (mas) Linear radius
(R☉)
 Estimation used
Norris (2019)[12]
2011 3.93±0.01 856+20
−14 		LDD
2012 4.26±0.02 927+21
−15 		LDD
2014 4.09±0.01 890+21
−15 		LDD
2015 4.11±0.01 895+21
−15 		LDD
2016 4.09±0.01 890+21
−15 		LDD
Norris (2021)[4]
– 3.74 814+175
−124 		?
Norris et al. (2021)[10]
2011 3.82±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] UD
2011 3.93±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] LDD
2014 3.81±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] UD
2014 4.09±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] LDD
2015 3.9±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] UD
2015 4.11±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] LDD
2016 3.99±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] UD
2016 4.09±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] LDD
Average (UD) 3.85±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] UD
Average (LDD) 4.05±0.01 Error in {{val}}: parameter 1 is not a valid number.[lower-alpha 1] LDD
Parameters of AZ Cygni derived from best fitting atmosphere models and model spectra[10][12]
Model Teff (K) Surface gravity
(log g)
 Radius
(R☉)
 Luminosity
(L☉)
 Mass
(M☉)
 Metallicity
[Fe/H] (dex) 		E(B – V)
Norris (2019)[12]
MARCS 4,000 0.5 481 53,206 15 0.0 0.76
PHOENIX 4,100 0.0 642 94,614 15 0.0 0.59
SATLAS 3,867 0.36 600 110,495 30 0.0 0.89
Average 3,989±117 0.29±0.26 574±84 82,772±35,173 20±9 0.0±0.0 0.75±0.15
Norris et al. (2021)[10]
MARCS 4,000 -0.5 1,040 249,443 15 0.0 0.56
PHOENIX 4,000 0.0 641 94,759 15 0.0 0.55
SATLAS 3,972 -0.07 700 109,828 15 0.0 0.54

Physical parameters

Luminosity

In Gaia DR2 AZ Cygni's absolute bolometric magnitude was estimated at −6.4839±0.6427, which correspond to a luminosity of approximately 30,870+24,930
−13,790 L☉.[11] Although the distance is potentially unreliable due to a very high amount of astrometric noise, rated at a significance of 47.4, anything above a rating of 2 is 'probably significant'.[13]

The luminosity of AZ Cygni was calculated in a paper in 2019 derived from the Gaia distance with a bolometric magnitude of -7.58 which would correspond to a luminosity of around 84,700 L☉.[20] Another paper in 2019 estimated three luminosity values of 53,206 L☉, 94,416 L☉ and 110,495 L☉ with an average of 82,772±35,173 L☉.[12] In a paper in 2021, the best fitting atmosphere models would correspond to luminosities of 249,443 L☉, 94,759 L☉ and 109,828 L☉.[10]

Radius

One of six telesopes in the CHARA array, used to derive AZ Cygni's angular diameter.

The radius of AZ Cygni was first determined to be around 748 R☉ in a paper in 2019 based on the Gaia distance[20] although it is likely unreliable due to a very high amount of astrometric noise.[13] Using the angular diameter and Gaia parallax derived distance in the Mid-infrared stellar Diameters and Fluxes compilation Catalogue (MDFC), also from 2019, a radius of between 913 R☉ and 920 R☉ can be derived.[21] Another paper in 2019 estimated 5 different radii from observations lasting from 2011 to 2016 based on the angular diameter and Gaia parallax: 856+20
−14 R☉ (2011), 927+21
−15 R☉ (2012), 890+21
−15 R☉ (2014), 895+21
−15 R☉ (2015) and 890+21
−15 R☉ (2016). In the same paper the radius was estimated based on the model spectra where three radii of 481 R☉, 642 R☉ and 600 R☉ were estimated with an average of 574±84 R☉.[12]

The radius of AZ Cygni was estimated at 814+175
−124 R☉ based on the angular diameter and Gaia parallax in a 2021 study.[4] In another paper in 2021, a radius of 911+57
−50 R☉ was calculated. This was an average using the angular diameter and Gaia parallaxes. Three different radii were calculated based on the best fitting atmosphere models: 1,040 R☉, 641 R☉ and 700 R☉.[10]

Temperature and spectral type

In a 1989 paper it was estimated that AZ Cygni would have spectral types of between M2Iab and M4Iab.[6] A study in 2000 estimated that the spectral type of AZ Cygni is M3.1Iab.[22] The spectral type of AZ Cygni was estimated at M3 Iab in a 2002 paper.[3]

A paper in 2004 estimated that the effective temperature of AZ Cygni is 3,200 K with a spectral type of M3 Iab.[5] AZ Cygni had 3 different effective temperature estimates in a paper in 2019 derived from model spectra: 4,000 K, 4,100 K and 3,867 K with an average of 3,989±117 K.[12] In another study in 2021 AZ Cygni would have three effective temperature estimates based on the best fitting atmosphere models: 4,000 K, 4,000 K and 3,972 K and also mentions that it is an M2–4.5 Iab star.[10]

Mass

The mass of AZ Cygni was first determined based on the best fitting model spectra, which would correspond to three mass estimates: 15 M☉, 15 M☉ and 30 M☉ with an average of 20±9 M☉.[12] A paper in 2021 estimated three mass estimates equal to 15 M☉ based on the best fitting atmosphere models.[10]

Surface features

AZ Cygni seen by the CHARA array.

AZ Cygni has a complex surface, with large and small features that vary over different timescales. Patterns of large convection cells, varying over periods of more than a year, are combined with smaller hot granules of rising gas that vary over shorter timescales. The size of the larger surface features is in line with models of 3D radiative hydrodynamics in red supergiants.[10]

Notes

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Calculated assuming the given distance of 2,090+130
    −115     mentioned in Norris et al. (2021) and the estimated angular diameter.
    [math]\displaystyle{ \delta = 206,265 ~ (d / D) ~ \mathrm{arcseconds} \Longrightarrow d = \frac{\delta * D}{206,265} \Longrightarrow R = \frac{d}{2} }[/math]
    The average linear radius of 911+57
    −50     R☉ is the only one mentioned in the paper.[10]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 "AZ Cygni". AAVSO. https://www.aavso.org/vsx/index.php?view=detail.top&oid=10999. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system.". Collection of Electronic Catalogues. Bibcode: 2002yCat.2237....0D. https://ui.adsabs.harvard.edu/abs/2002yCat.2237....0D/abstract. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Norris, Ryan (27 February 2021). "An Interferometric Imaging Survey of Red Supergiant Stars". The 20.5th Cambridge Workshop on Cool Stars. p. 263. doi:10.5281/zenodo.4567641. Bibcode: 2021csss.confE.263N. 
  5. ↑ 5.0 5.1 Ivanov, Valentin D.; Rieke, Marcia J.; Engelbracht, Charles W.; Alonso-Herrero, Almudena; Rieke, George H.; Luhman, Kefin L. (2004). "A Medium-Resolution Near-Infrared Spectral Library of Late-Type Stars. I.". The Astrophysical Journal 151 (2): 387–397. doi:10.1086/381752. Bibcode: 2004ApJS..151..387I. 
  6. ↑ 6.0 6.1 Keenan, Philip C.; McNeil, Raymond C. (October 1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars". The Astrophysical Journal 71: 245. doi:10.1086/191373. Bibcode: 1989ApJS...71..245K. https://ui.adsabs.harvard.edu/abs/1989ApJS...71..245K/abstract. 
  7. ↑ Nakamura, Ko; Horiuchi, Shunsaku; Tanaka, Masaomi; Hayama, Kazuhiro; Takiwaki, Tomoya; Kotake, Kei (9 February 2016). "Multimessenger signals of long-term core-collapse supernova simulations: synergetic observation strategies". The Royal Astronomical Society 461 (3): 3296–3313. doi:10.1093/mnras/stw1453. Bibcode: 2016MNRAS.461.3296N. 
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Stassun K.G. (October 2019). "The revised TESS Input Catalog and Candidate Target List". The Astronomical Journal 158 (4): 138. doi:10.3847/1538-3881/ab3467. Bibcode: 2019AJ....158..138S. 
  9. ↑ Chatys, Filip W.; Bedding, Timothy R.; Murphy, Simon J.; Kiss, László L.; Dobie, Dougal; Grindlay, Jonathan E. (10 June 2019). "The period-luminosity relation of red supergiants with Gaia DR2". The Royal Astronomical Society 487 (4): 4832–4846. doi:10.1093/mnras/stz1584. Bibcode: 2019MNRAS.487.4832C. https://ui.adsabs.harvard.edu/abs/2019MNRAS.487.4832C/abstract. 
  10. ↑ 10.00 10.01 10.02 10.03 10.04 10.05 10.06 10.07 10.08 10.09 10.10 10.11 10.12 10.13 10.14 10.15 10.16 10.17 10.18 10.19 10.20 10.21 Norris, Ryan P.; Baron, Fabien R.; Monnier, John D.; Paladini, Claudia; Anderson, Matthew D.; Martinez, Arturo O.; Schaefer, Gail H.; Che, Xiao et al. (29 June 2021). "Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg". The Astrophysical Journal 919 (2): 124. doi:10.3847/1538-4357/ac0c7e. Bibcode: 2021ApJ...919..124N. 
  11. ↑ 11.0 11.1 "Long Period Variable stars (Gaia DR2)". VizieR. https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=I/345/lpv. 
  12. ↑ 12.00 12.01 12.02 12.03 12.04 12.05 12.06 12.07 12.08 12.09 12.10 12.11 12.12 Norris, Ryan Patrick (13 December 2019). Seeing stars like never before: A long-term interferometric imaging survey of red supergiants. Physics and Astronomy Dissertations (Thesis). Georgia State University. Bibcode:2019PhDT........63N. doi:10.57709/15009706 Check |doi= value (help).
  13. ↑ 13.0 13.1 13.2 13.3 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  14. ↑ "V* AZ Cyg". Université de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-id?Ident=V*+AZ+Cyg&submit=submit+id. 
  15. ↑ "ASAS-SN Variable Stars Database". ASAS-SN. https://asas-sn.osu.edu/variables/lookup. 
  16. ↑ Argelander, Friedrich Wilhelm August (1903). "Bonner Durchmusterung des nordlichen Himmels.". Eds Marcus and Weber's Verlag. Bibcode: 1903BD....C......0A. https://ui.adsabs.harvard.edu/abs/1903BD....C......0A/abstract. 
  17. ↑ Neugebauer, G.; Leighton, R. B. (1969). Two-micron sky survey. A preliminary catalogue. Bibcode: 1969tmss.book.....N. https://ui.adsabs.harvard.edu/abs/1969tmss.book.....N/abstract. 
  18. ↑ Cutri, R. M.; Skrutskie, M. F.; van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T. et al. (June 2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". Vizier Online Data Catalog. Bibcode: 2003yCat.2246....0C. https://ui.adsabs.harvard.edu/abs/2003yCat.2246....0C/abstract. 
  19. ↑ Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P. et al. (3 January 2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355 (500): L27–L30. Bibcode: 2000A&A...355L..27H. https://ui.adsabs.harvard.edu/abs/2000A%26A...355L..27H/abstract. 
  20. ↑ 20.0 20.1 Messineo, M.; Brown, A. G. A (13 May 2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal 158 (1): 20. doi:10.3847/1538-3881/ab1cbd. Bibcode: 2019AJ....158...20M. 
  21. ↑ Cruzalèbes, P.; Petrov, R. G.; Robbe-Dubois, S.; Varga, J.; Burtscher, L.; Allouche, F.; Berio, P.; Hoffman, K. -H et al. (1 October 2019). "A catalogue of stellar diameters and fluxes for mid-infrared interferometry". The Royal Astronomical Society 490 (3): 3158–3176. doi:10.1093/mnras/stz2803. ISSN 0035-8711. Bibcode: 2019MNRAS.490.3158C. https://ui.adsabs.harvard.edu/abs/2019MNRAS.490.3158C/abstract. 
  22. ↑ Speck, A. K.; Barlow, M. J.; Sylvester, R. J.; Hofmeister, A. M. (15 November 2000). "Dust features in the 10-mu m infrared spectra of oxygen-rich evolved stars". Astronomy and Astrophysics 146 (3): 437–464. doi:10.1051/aas:2000274. Bibcode: 2000A&AS..146..437S. 



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