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]
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]
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+13,790 −24,930L☉.[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]
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☉.[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±35,173L☉.[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
The radius of AZ Cygni was first determined to be around 748 R☉ in a paper in 2019 based on the Gaia distance[22] 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.[23] 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 −14R☉ (2011), 927+21 −15R☉ (2012), 890+21 −15R☉ (2014), 895+21 −15R☉ (2015) and 890+21 −15R☉ (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±84R☉.[12]
The radius of AZ Cygni was estimated at 814+175 −124R☉ based on the angular diameter and Gaia parallax in a 2021 study.[4] In another paper in 2021, a radius of 911+57 −50R☉ 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.[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]
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±9M☉.[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 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
^
abcdefghijCalculated 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 −50R☉ is the only one mentioned in the paper.[10]
^
abcdefghijklmnopqrstuvNorris, 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.
S2CID235683123.
^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.