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AZ Cygni

AZ Cygni seen by the CHARA array.
Observation data
Epoch J2000.0      Equinox J2000.0
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 mas[1]
Distance6,820+420
−380[10] ly
(2,090+130
−115[10] pc)
Absolute magnitude (MV)–5.32[11]
Details
Mass15[10] – 20±9[12] M☉
Radius911+57
−50[10] R☉
Luminosity109,800[10](94,800 – 249,400)[10] L☉
Surface gravity (log g)−0.5 – 0.0,[10] 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. Located 2,090 parsecs (6,800 ly) from Earth, it has been studied by the CHARA array in order to understand the surface variations of red supergiants.[10]

Observation history

[edit]
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±0.01 858+56
−49[a] 		UD
2011 3.93±0.01 883+57
−51[a] 		LDD
2014 3.81±0.01 856+56
−49[a] 		UD
2014 4.09±0.01 919+60
−53[a] 		LDD
2015 3.9±0.01 876+57
−50[a] 		UD
2015 4.11±0.01 924+59
−53[a] 		LDD
2016 3.99±0.01 897+57
−52[a] 		UD
2016 4.09±0.01 919+60
−53[a] 		LDD
Average (UD) 3.85±0.01 865+56
−50[a] 		UD
Average (LDD) 4.05±0.01 910+59
−52[a] 		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

[edit]

Luminosity

[edit]

The Gaia DR2 catalogue estimated AZ Cygni's absolute bolometric magnitude at −6.4839±0.6427, corresponding to a luminosity of approximately 30,870+13,790
−24,930 L☉.[20] 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][21]

A paper in 2019 calculated the luminosity of AZ Cygni using the Gaia distance and a bolometric magnitude of -7.58, which would result in a luminosity of around 84,700 L☉.[22] 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] According to a 2021 paper, the best fitting atmosphere models would correspond to luminosities of 249,443 L☉, 94,759 L☉ and 109,828 L☉.[10]

Radius

[edit]
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 2019 paper based on the Gaia-derived distance,[22] although it is potentially unreliable due to a high amount of astrometric noise.[13]

By using the angular diameter and Gaia parallax-derived distance in the 2019 Mid-infrared stellar Diameters and Fluxes compilation Catalogue (MDFC), a radius between 913 R☉ and 920 R☉ can be derived.[23] Another paper in 2019 estimated five different radii from observations between 2011 and 2016 based on the MDFC 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). The same paper also approximated AZ Cygni's radius based on model spectra, in which three values of 481 R☉, 642 R☉ and 600 R☉ were estimated with an average of 574±84 R☉.[12]

The radius of AZ Cygni was again estimated at 814+175
−124 R☉ based on its angular diameter and Gaia parallax in a 2021 study.[4] A separate paper in 2021 calculated a radius of 911+57
−50 R☉, an average value after using the star's angular diameter and Gaia parallaxes. Based on the best fitting atmosphere models, three different radii were calculated: 1,040 R☉, 641 R☉ and 700 R☉.[10]

Temperature and spectral type

[edit]

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.[24] 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] The RSG and Close Stars Catalog (2024) features an adopted mean spectral type of M3 for AZ Cygni based on previous spectral types.[25][26]

Mass

[edit]

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

[edit]

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

[edit]
  1. ^ a b c d e f g h i j Calculated assuming the given distance of 2,090+130
    −115     mentioned in Norris et al. (2021) and the estimated angular diameter.

    The average linear radius of 911+57
    −50     R☉ is the only one mentioned in the paper.[10]

See also

[edit]

References

[edit]
  1. ^ a b c d e f g h Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b c "AZ Cygni". International Variable Star Index. AAVSO. Retrieved 2023-01-23.
  3. ^ a b c d e Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  4. ^ a b c d e Norris, Ryan (27 February 2021). An Interferometric Imaging Survey of Red Supergiant Stars. The 20.5th Cambridge Workshop on Cool Stars. p. 263. Bibcode:2021csss.confE.263N. doi:10.5281/zenodo.4567641.
  5. ^ a b 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. arXiv:astro-ph/0311596. Bibcode:2004ApJS..151..387I. doi:10.1086/381752. S2CID 55537399.
  6. ^ a b Keenan, Philip C.; McNeil, Raymond C. (October 1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars". The Astrophysical Journal. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373. S2CID 123149047.
  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. arXiv:1602.03028. Bibcode:2016MNRAS.461.3296N. doi:10.1093/mnras/stw1453.
  8. ^ a b c d e Stassun K.G.; et al. (October 2019). "The revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467. S2CID 166227927.
  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. arXiv:1906.03879. Bibcode:2019MNRAS.487.4832C. doi:10.1093/mnras/stz1584.
  10. ^ a b c d e f g h i j k l m n o p q r s t u Norris, Ryan P.; Baron, Fabien R.; Monnier, John D.; Paladini, Claudia; Anderson, Matthew D.; Martinez, Arturo O.; Schaefer, Gail H.; Che, Xiao; Chiavassa, Andrea; Connelley, Michael S.; Farrington, Christopher D.; Gies, Douglas R.; Kiss, László L.; Lester, John B.; Montargès, Miguel; Neilson, Hilding R.; Majoinen, Olli; Pedretti, Ettore; Ridgway, Stephen T.; Roettenbacher, Rachael M.; Scott, Nicholas J.; Sturmann, Judit; Sturmann, Laszlo; Thureau, Nathalie; Vargas, Norman; Ten Brummelaar, Theo A. (29 June 2021). "Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg". The Astrophysical Journal. 919 (2): 124. arXiv:2106.15636. Bibcode:2021ApJ...919..124N. doi:10.3847/1538-4357/ac0c7e. S2CID 235683123.
  11. ^ Melnik, A. M.; Dambis, A. K. (2020). "Distance scale for high-luminosity stars in OB associations and in field with Gaia DR2. Spurious systematic motions". Astrophysics and Space Science. 365 (7): 112. arXiv:2006.14649. Bibcode:2020Ap&SS.365..112M. doi:10.1007/s10509-020-03827-0.
  12. ^ a b c d e f g h i j k l 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.
  13. ^ a b c d 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.
  14. ^ "V* AZ Cyg". Université de Strasbourg.
  15. ^ "ASAS-SN Variable Stars Database". ASAS-SN Variable Stars Database. ASAS-SN. Retrieved 6 January 2022.
  16. ^ Argelander, Friedrich Wilhelm August (1903). "Bonner Durchmusterung des nordlichen Himmels". Eds Marcus and Weber's Verlag. Bibcode:1903BD....C......0A.
  17. ^ Neugebauer, G.; Leighton, R. B. (1969). Two-micron sky survey. A preliminary catalogue. Bibcode:1969tmss.book.....N.
  18. ^ Cutri, R. M.; Skrutskie, M. F.; van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W.A.; Whealock, S.; Zacarias, N. (June 2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". Vizier Online Data Catalog. Bibcode:2003yCat.2246....0C.
  19. ^ Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (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.
  20. ^ "Long Period Variable stars (Gaia DR2)". VizieR.
  21. ^ Lindegren, L.; Klioner, S. A.; Hernández, J.; Bombrun, A.; Ramos-Lerate, M.; Steidelmüller, H.; Bastian, U.; Biermann, M.; de Torres, A.; Gerlach, E.; Geyer, R.; Hilger, T.; Hobbs, D.; Lammers, U.; McMillan, P. J. (May 2021). "Gaia Early Data Release 3: The astrometric solution". Astronomy & Astrophysics. 649: A2. arXiv:2012.03380. Bibcode:2021A&A...649A...2L. doi:10.1051/0004-6361/202039709. ISSN 0004-6361.
  22. ^ a b 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. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd. S2CID 148571616.
  23. ^ Cruzalèbes, P.; Petrov, R. G.; Robbe-Dubois, S.; Varga, J.; Burtscher, L.; Allouche, F.; Berio, P.; Hoffman, K. -H; Hron, J.; Jaffe, W.; Lagarde, S.; Lopez, B.; Matter, A.; Meilland, A.; Meisenheimer, K.; Millour, F.; Schertl, D. (1 October 2019). "A catalogue of stellar diameters and fluxes for mid-infrared interferometry". The Royal Astronomical Society. 490 (3): 3158–3176. arXiv:1910.00542. Bibcode:2019MNRAS.490.3158C. doi:10.1093/mnras/stz2803. ISSN 0035-8711. S2CID 203610229.
  24. ^ 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. Bibcode:2000A&AS..146..437S. doi:10.1051/aas:2000274.
  25. ^ Healy, Sarah; Horiuchi, Shunsaku; Molla, Marta Colomer; Milisavljevic, Dan; Tseng, Jeff; Bergin, Faith; Weil, Kathryn; Tanaka, Masaomi (2024-03-23). "Red Supergiant Candidates for Multimessenger Monitoring of the Next Galactic Supernova". Monthly Notices of the Royal Astronomical Society. 529 (4): 3630–3650. arXiv:2307.08785. Bibcode:2024MNRAS.529.3630H. doi:10.1093/mnras/stae738. ISSN 0035-8711.
  26. ^ "candidate_list/data/RSG_and_close_stars_catalog_4_11_24.csv at main · SNEWS2/candidate_list". GitHub. Retrieved 2024-08-05.
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