31 Cygni

{{short description|Triple star system in the constellation Cygnus}}

{{about|ο^1/2 Cygni|other star systems with this Bayer designation|Omicron Cygni{{!}}ο Cygni}}

{{Starbox begin

| name = 31 Cygni

}}

{{Starbox image

| image=

{{Location mark

|image=Cygnus constellation map.svg|alt=|float=center|width=280

|label=|position=right

|mark=Red circle.svg|mark_width=8|mark_link=31 Cyg

|x=436|y=283

}}

|caption=Location of 31 Cygni (circled)

}}

{{Starbox observe 2s

| epoch = J2000.0

| constell = Cygnus

| component1 = 31 Cygni A

| ra1 = {{RA|20|13|37.908}}

| dec1 = {{DEC|+46|44|28.76}}

| appmag_v1 = 3.73 - 3.89

| component2 = HD 192579

| ra2 = {{RA|20|13|39.199}}

| dec2 = {{DEC|+46|42|42.70}}

| appmag_v2 = 6.99

}}

{{Starbox character

| component1 = 31 Cygni A

| class = K3Ib + B2IV-V

| appmag_1_passband =

| appmag_1 =

| r-i =

| v-r =

| b-v =

| u-b =

| variable = Algol

| component2 = HD 192579

| class2 = B5V

| type2 = main sequence

}}

{{Starbox astrometry

| component1 = 31 Cygni A

| radial_v = {{val|-7.41|0.08}}

| prop_mo_ra = 1.744

| prop_mo_dec = 3.390

| parallax = 2.9167

| p_error = 0.1327

| parallax_footnote =

| absmag_v =

| component2 = HD 192579

| prop_mo_ra2 = 3.906

| prop_mo_dec2 = 1.978

| parallax2 = 2.9160

| p_error2 = 0.0336

| parallax_footnote2 =

| absmag_v2 =

}}

{{Starbox orbit

| reference =

| primary = 31 Cygni Aa

| name = 31 Cygni Ab

| period_unitless = {{val|3784.3|ul=days|fmt=commas}}

| eccentricity = {{val|0.2084|0.0031}}

| periastron = {{val|2,452,345|9|fmt=commas}}

| periarg = {{val|204.5|1.0}}

| k1 = {{val|13.94|0.04}}

| k2 = 18.0

}}

{{Starbox detail

| source =

| component1 = K supergiant

| mass = 6.73

| radius = 127

| temperature = {{val|4,043|170|fmt=commas}}

| luminosity = 2,512 - 2,559{{cite journal |arxiv=1905.03744 |bibcode=2019AJ....158...20M |doi=10.3847/1538-3881/ab1cbd |title=A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2 |year=2019 |last1=Messineo |first1=M. |last2=Brown |first2=A. G. A. |journal=The Astronomical Journal |volume=158 |issue=1 |page=20 |s2cid=148571616 |doi-access=free }}

| component2 = B dwarf

| mass2 = 5.22

| radius2 = {{val|5.2|0.5}}

| temperature2 = {{val|16,500|+1000|-2000|fmt=commas}}

| age_myr2 = 39.8

}}

{{Starbox detail|no_heading=y

| component1 = HD 192579

| mass =4.1

| temperature = 13,949

| luminosity = 373

| radius = 3.3

| metal_fe = +0.68

| gravity = 4.04

| age_myr =

}}

{{Starbox catalog

| names = ο¹ Cyg, ο² Cyg, 31 Cyg, ADS 13554, WDS J20136+4644

| component2 = 31 Cygni A (HD 192577)

| names2 = V695 Cyg, HD 192577, BD+46°2882, HIP 99675, HR 7735, SAO 49337

| component3 = HD 192579

| names3 = HD 192579, BD+46°2883, HIP 99676, SAO 49338

}}

{{Starbox reference

|Simbad=31+Cygni

|Simbad2=31+cygni+B|sn2=HD 192579

}}

{{Starbox end}}

File:Albireo 20150919.jpg towards top left. (north is to the left)]]

31 Cygni, also known as ο¹ Cygni, Omicron¹ Cygni, ο² Cygni or V695 Cygni, is a ternary star system about 750 light years away in the constellation Cygnus.

The Bayer designation ο (omicron) has been variously applied to two or three of the stars 30, 31, and 32 Cygni. 31 Cygni has been designated, variously, as ο¹ or ο² Cygni — therefore for clarity, it is preferred to use the Flamsteed designation 31 Cygni.

31 Cygni consists of a visible pair of stars {{val|109|ul="}} apart as of 2016, and the brighter of the two is also a spectroscopic binary. 31 Cygni A is also designated HD 192577 and HR 7735, while its 7th-magnitude visual companion is designated HD 192579. Some multiple star catalogues designate a 13th-magnitude star {{val|36|u="}} from 31 Cygni A as 31 Cygni B, and HD 192579 as 31 Cygni C. The 13th-magnitude star is likely to be an unrelated background object.

The spectroscopic pair are an orange supergiant of spectral type K3Ib and a blue-white star likely to be evolving off the main sequence with a spectral type of B2IV-V. The visible companion is a 7th-magnitude B5 main sequence star.

File:V695CygLightCurve.png light curve for the 1982 eclipse of V695 Cygni, adapted from Stencel et al. (1984)]]

31 Cygni A is an Algol-type eclipsing binary and ranges between magnitudes 3.73 and 3.89 over a period of ten years. The eclipsing system has been studied in attempts to determine an accurate direct mass for a red supergiant. The value {{solar mass|6.73}} is believed to be accurate to about 2%, but there are some discrepancies in the orbital fit.

30 Cygni is another naked eye star a tenth of a degree away, forming a bright triple.

32 Cygni is about a degree away to the north, also a detached eclipsing binary system. It comprises a large cool evolved star and a small hot main sequence or subgiant companion.

{{clear left}}