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AZ Cygni

{{Short description|Red supergiant star in the constellation Cygnus}}

{{starbox begin}}

{{Starbox image

| image=250px

| caption=A light curve for AZ Cygni, plotted from ASAS-SN data.

}}

{{starbox observe

| epoch = J2000.0

| ra = {{RA|20|57|59.4444}}

| dec = {{DEC|+46|28|00.583}}

| appmag_v = 7.8{{snd}}9.6

| constell= Cygnus

}}

{{Starbox character

| type = Red supergiant

| class = M3 Iab
(M2–4 Iab)

| appmag_1_passband=U

| appmag_1=13.91

| appmag_2_passband=B

| appmag_2={{val|10.897|0.065}}

| appmag_3_passband=G

| appmag_3={{val|6.190986|0.010832}}

| appmag_4_passband=T

| appmag_4={{val|4.618|0.018}}

| appmag_5_passband=J

| appmag_5={{val|2.765|0.234}}

| appmag_6_passband=H

| appmag_6={{val|1.744|0.164}}

| appmag_7_passband=K

| appmag_7=1.22–{{val|1.288|0.172}}

| b-v=+2.56

| j-k=+1.48

| variable=SRc

}}

{{Starbox astrometry

| radial_v={{val|-5.52|0.99}}

| prop_mo_ra={{val|-1.905|0.031}}

| prop_mo_dec={{val|-2.871|0.029}}

| parallax=0.4027

| p_error=0.027

| parallax_footnote =

| dist_pc = {{val|2,090|130|115|fmt=commas}}

| dist_ly = {{val|6,820|420|380|fmt=commas}}

| absmag_v = –5.32

}}

{{starbox detail

| mass = 15{{snd}}{{val|20|9}}

| radius = {{val|911|57|50}}

| luminosity = 109,800{{nowrap|(94,800{{snd}}249,400)}}

| temperature = {{val|3989|117|fmt=commas}} {{nowrap|(3,972{{snd}}4,000)}}

| gravity = −0.5{{snd}}0.0,

| metal_fe = 0.0

}}

{{starbox catalog

| names = AZ Cyg, BD+45 3349, TYC 3575-553-1, 2MASS J20575942+4628004, SAO 50296

}}

{{Starbox reference

| Simbad=V*+AZ+Cyg

}}

{{Starbox end}}

AZ Cygni (BD+45 3349) is a red supergiant (M3 Iab) 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.

Observation history

AZ Cygni was first observed in the observations used to produce the Bonner Durchmusterung catalogue, published by Friedrich Argelander in the mid 19th century. Thomas William Backhouse showed that BD+45°3349 (the 19th-century name for AZ Cygni) is a variable star, based on observations from 1894 to 1904. It was given the variable star designation AZ Cygni, in 1912. It has since been included in many star surveys and catalogues, including the Two-Micron Sky Survey, 2MASS, Tycho-2 Catalogue and Gaia (DR2 and DR3).

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) 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.

class="wikitable sortable"

|+ Parameters of AZ Cygni derived from CHARA array data

style="background:#efefef" width=300px | Year of observation

! style="background:#efefef" width=300px | Angular diameter (mas)

! style="background:#efefef" width=300px | Linear radius
({{solar radius}})

! style="background:#efefef width=300px | Estimation used

colspan="4" | Norris (2019)
2011

|{{val|3.93|0.01}}

|{{val|856|20|14}}

|LDD

2012

|{{val|4.26|0.02}}

|{{val|927|21|15}}

|LDD

2014

|{{val|4.09|0.01}}

|{{val|890|21|15}}

|LDD

2015

|{{val|4.11|0.01}}

|{{val|895|21|15}}

|LDD

2016

|{{val|4.09|0.01}}

|{{val|890|21|15}}

|LDD

colspan="4" | Norris (2021)
–

|3.74

|{{val|814|175|124}}

|?

colspan="4" | Norris et al. (2021)
2011

|{{val|3.82|0.01}}

|{{val|{{Solar radius calculator|type=AD|3.82|2.09}}|56|49}}{{efn|name=AD}}

|UD

2011

|{{val|3.93|0.01}}

|{{val|{{Solar radius calculator|type=AD|3.93|2.09}}|57|51}}{{efn|name=AD}}

|LDD

2014

|{{val|3.81|0.01}}

|{{val|{{Solar radius calculator|type=AD|3.81|2.09}}|56|49}}{{efn|name=AD}}

|UD

2014

|{{val|4.09|0.01}}

|{{val|{{Solar radius calculator|type=AD|4.09|2.09}}|60|53}}{{efn|name=AD}}

|LDD

2015

|{{val|3.9|0.01}}

|{{val|{{Solar radius calculator|type=AD|3.9|2.09}}|57|50}}{{efn|name=AD}}

|UD

2015

|{{val|4.11|0.01}}

|{{val|{{Solar radius calculator|type=AD|4.11|2.09}}|59|53}}{{efn|name=AD}}

|LDD

2016

|{{val|3.99|0.01}}

|{{val|{{Solar radius calculator|type=AD|3.99|2.09}}|57|52}}{{efn|name=AD}}

|UD

2016

|{{val|4.09|0.01}}

|{{val|{{Solar radius calculator|type=AD|4.09|2.09}}|60|53}}{{efn|name=AD}}

|LDD

style="background:#dfdfdf"

|Average (UD)

|{{val|3.85|0.01}}

|{{val|{{Solar radius calculator|type=AD|3.85|2.09}}|56|50}}{{efn|name=AD}}

|UD

style="background:#dfdfdf"

|Average (LDD)

|{{val|4.05|0.01}}

|{{val|{{Solar radius calculator|type=AD|4.05|2.09}}|59|52}}{{efn|name=AD}}

|LDD

class="wikitable sortable"

|+ Parameters of AZ Cygni derived from best fitting atmosphere models and model spectra

style="background:#efefef" width=200px | Model

! style="background:#efefef" width=200px | Teff (K)

! style="background:#efefef" width=300px | Surface gravity
(log g)

! style="background:#efefef" width=200px | Radius
({{solar radius}})

! style="background:#efefef" width=250px | Luminosity
({{solar luminosity}})

! style="background:#efefef" width=200px | Mass
({{solar mass}})

! style="background:#efefef" width=250px | Metallicity
[Fe/H] (dex)

! style="background:#efefef" width=200px | E(B – V)

colspan="8" | Norris (2019)
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

style="background:#dfdfdf"

|Average

|{{val|3,989|117|fmt=commas}}

|{{val|0.29|0.26}}

|{{val|574|84}}

|{{val|82,772|35,173|fmt=commas}}

|{{val|20|9}}

|{{val|0.0|0.0}}

|{{val|0.75|0.15}}

colspan="8" | Norris et al. (2021)
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=

The Gaia DR2 catalogue estimated AZ Cygni's absolute bolometric magnitude at {{val|-6.4839|0.6427}}, corresponding to a luminosity of approximately {{solar luminosity|{{val|30870|13790|24930|fmt=commas}}|link=y}}. 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'.{{Cite journal |last1=Lindegren |first1=L. |last2=Klioner |first2=S. A. |last3=Hernández |first3=J. |last4=Bombrun |first4=A. |last5=Ramos-Lerate |first5=M. |last6=Steidelmüller |first6=H. |last7=Bastian |first7=U. |last8=Biermann |first8=M. |last9=de Torres |first9=A. |last10=Gerlach |first10=E. |last11=Geyer |first11=R. |last12=Hilger |first12=T. |last13=Hobbs |first13=D. |last14=Lammers |first14=U. |last15=McMillan |first15=P. J. |date=May 2021 |title=Gaia Early Data Release 3: The astrometric solution |journal=Astronomy & Astrophysics |volume=649 |pages=A2 |doi=10.1051/0004-6361/202039709 |arxiv=2012.03380 |bibcode=2021A&A...649A...2L |issn=0004-6361}}

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 {{solar luminosity|84,700}}. Another paper in 2019 estimated three luminosity values of {{solar luminosity|53,206}}, {{solar luminosity|94,416}} and {{solar luminosity|110,495}} with an average of {{solar luminosity|{{val|82772|35173|fmt=commas}}}}. According to a 2021 paper, the best fitting atmosphere models would correspond to luminosities of {{solar luminosity|249,443}}, {{solar luminosity|94,759}} and {{solar luminosity|109,828}}.

=Radius=

File:CHARA_1497.jpgThe radius of AZ Cygni was first determined to be around {{solar radius|748}} in a 2019 paper based on the Gaia-derived distance, although it is potentially unreliable due to a high amount of astrometric noise.

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 {{solar radius|913}} and {{solar radius|920}} can be derived. Another paper in 2019 estimated five different radii from observations between 2011 and 2016 based on the MDFC angular diameter and Gaia parallax: {{solar radius|{{val|856|20|14}}}} (2011), {{solar radius|{{val|927|21|15}}}} (2012), {{solar radius|{{val|890|21|15}}}} (2014), {{solar radius|{{val|895|21|15}}}} (2015) and {{solar radius|{{val|890|21|15}}}} (2016). The same paper also approximated AZ Cygni's radius based on model spectra, in which three values of {{solar radius|481}}, {{solar radius|642}} and {{solar radius|600}} were estimated with an average of {{solar radius|{{val|574|84}}}}.

The radius of AZ Cygni was again estimated at {{solar radius|{{val|814|175|124}}}} based on its angular diameter and Gaia parallax in a 2021 study. A separate paper in 2021 calculated a radius of {{solar radius|{{val|911|57|50}}}}, 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: {{solar radius|1,040|fmt=commas}}, {{solar radius|641}} and {{solar radius|700}}.

=Temperature and spectral type=

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

A paper in 2004 estimated that the effective temperature of AZ Cygni is 3,200 K with a spectral type of M3 Iab. 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 {{val|3989|117|fmt=commas}} K. 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. The RSG and Close Stars Catalog (2024) features an adopted mean spectral type of M3 for AZ Cygni based on previous spectral types.{{Cite journal |last1=Healy |first1=Sarah |last2=Horiuchi |first2=Shunsaku |last3=Molla |first3=Marta Colomer |last4=Milisavljevic |first4=Dan |last5=Tseng |first5=Jeff |last6=Bergin |first6=Faith |last7=Weil |first7=Kathryn |last8=Tanaka |first8=Masaomi |date=2024-03-23 |title=Red Supergiant Candidates for Multimessenger Monitoring of the Next Galactic Supernova |journal=Monthly Notices of the Royal Astronomical Society |volume=529 |issue=4 |pages=3630–3650 |doi=10.1093/mnras/stae738 |doi-access=free |issn=0035-8711|arxiv=2307.08785 |bibcode=2024MNRAS.529.3630H }}{{Cite web |title=candidate_list/data/RSG_and_close_stars_catalog_4_11_24.csv at main · SNEWS2/candidate_list |url=https://github.com/SNEWS2/candidate_list/blob/main/data/RSG_and_close_stars_catalog_4_11_24.csv |access-date=2024-08-05 |website=GitHub |language=en}}

=Mass=

The mass of AZ Cygni was first determined based on the best fitting model spectra, which would correspond to three mass estimates: {{solar mass|15}}, {{solar mass|15}} and {{solar mass|30}} with an average of {{solar mass|{{val|20|9}}}}. A paper in 2021 estimated three mass estimates equal to {{solar mass|15}} based on the best fitting atmosphere models.

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.

Notes

{{notelist|refs=

{{efn|name=AD|Calculated assuming the given distance of {{val|2,090|130|115|fmt=commas}} mentioned in Norris et al. (2021) and the estimated angular diameter.
\delta = 206,265 ~ (d / D) ~ \mathrm{arcseconds} \Longrightarrow d = \frac{\delta * D}{206,265} \Longrightarrow R = \frac{d}{2}

The average linear radius of {{solar radius|{{val|911|57|50}}}} is the only one mentioned in the paper.}}

}}

See also

{{cmn|colwidth=35em|

}}

References

{{reflist|refs=

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{{Cite Gaia DR3|2163751614044043136}}

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{{Cite web|title=V* AZ Cyg|publisher=Université de Strasbourg|url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=V*+AZ+Cyg&submit=submit+id}}

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}}

{{Commons category}}

{{Stars of Cygnus}}

Category:M-type supergiants

Category:Cygnus (constellation)

Cygni, AZ

Category:TIC objects

J20575942+4628004

Category:Semiregular variable stars

Category:Durchmusterung objects