SU Cygni

{{Short description|Variable star system in the constellation Cygnus}}

{{Starbox image

| image = 250px

| caption = A light curve for SU Cygni, plotted from TESS data

}}

{{Starbox observe

| epoch = J2000

| constell = Cygnus

| ra = {{RA|19|44|48.734}}

| dec = {{DEC|29|15|52.90}}

| appmag_v = {{val|6.44|to|7.22}}

}}

{{Starbox character

| type =

| class = {{nowrap|F2Iab: + B8.0V + A0V:}}

| b-v =

| u-b =

| variable = δ Cep

}}

{{Starbox astrometry

| radial_v = −21.5{{±|2.4}}

| prop_mo_ra = 0.107

| prop_mo_dec = −3.247

| pm_footnote =

| parallax = 1.080

| p_error = 0.006

| parallax_footnote =

| dist_pc = {{val|926.3|5.0}}

| dist_ly = {{convert|926.3|±|5.0|pc|ly|disp=number}}

| dist_footnote =

| absmag_v =

}}

{{Starbox orbit

| reference =

| primary = SU Cyg A

| name = SU Cyg B

| period_unitless = {{val|549.077|0.013|u=days}}

| axis_unitless = {{val|2.827|0.009}}

| eccentricity = {{val|0.339|0.002}}

| inclination = {{val|81.28|0.27}}

| node = {{val|266.24|0.24}}

| periastron = {{val|2443765.94|0.63|ul=HJD|fmt=commas}}

| periarg = 223.18{{±|2.12}}

| k1 = 30.25{{±|0.05}}

| k2 = 28.59{{±|0.15}}

}}

{{Starbox orbit

| reference =

| primary = SU Cyg Ba

| name = SU Cyg Bb

| period_unitless = {{val|4.67529|(1)|u=days}}

| axis_unitless = ≥{{val|0.0287|0.0001}}

| eccentricity =

| inclination =

| node =

| periastron = {{val|2456977.994|0.003|ul=HJD|fmt=commas}}

| periarg =

| k1 = 66.89{{±|0.21}}

| k2 =

}}

{{Starbox detail

| source =

| component1 = Aa

| mass = {{val|4.859|0.058}}

| radius = {{val|31.9|6.0}}

| temperature = {{val|5956|to|6314|fmt=commas}}

| luminosity = 1,349

| gravity = 2.1–2.4

| metal_fe = −0.03{{±|0.04}}

| rotational_velocity =

| rotation =

| age_myr =

}}

{{Starbox detail|no_heading=y

| component1 = Ba

| mass = {{val|3.595|0.033}}

| component2 = Bb

| mass2 = {{val|1.546|0.009}}

}}

{{Starbox catalog

| names = {{odlist | V=SU Cyg | BD=+28°3460 | GC=27336 | HD=186688 | HIP=97150 | HR=7518 | PPM=109630 | SAO=87659 | WDS=J19448+2916Aa,Ab }}

}}

{{Starbox reference

| Simbad=SU+Cyg

}}

SU Cygni is a triple star system in the northern constellation of Cygnus, abbreviated SU Cyg. The primary component of the system is a classical Cepheid variable with a period of 3.84559 days. The changing luminosity of this star causes the system to vary in brightness from a peak apparent visual magnitude of 6.44 down to magnitude 7.22 over the course of its cycle. The distance to this system is approximately 3,000 light years based on parallax measurements, and is the most accurate distance among Cepheids. It is a member of the Turner 9 open cluster of stars.

The variable luminosity of this star was announced by G. Müller and G. Kempf in 1898. The following year, M. Luizet determined a period of 3.846 days. In 1906, the radial velocity of this star was found to be variable by J. D. Maddrill, with its cycle matching the luminosity period but trailing in phase by half a day. By 1916 it was classified as a Cepheid variable, with spectrographic studies showing that the spectral type varied over the course of each cycle. It ranged from a class of A6 near peak luminosity down to F7 at minimum.

A companion star, designated component B, was detected photometrically by B. F. Madore in 1977, with the colors suggesting a B-type main-sequence star with a class of B6–7V. This finding was supported by observations of J. D. Fernie in 1979, who determined a class of B6V. In 1984, M. Imbert measured an orbital period of 549.2 days for the pair, with an orbital eccentricity (ovalness) of 0.35. Ultraviolet observations with the IUE spacecraft in 1985 showed that the companion is a close binary system with a period of 4.7 days. The members of this pair have classes of B8 and A0. In 1998, the B-type companion was found to be a chemically peculiar HgMn star.

There is a candidate comoving companion star located at an angular separation of {{val|24|ul=arcsecond}} to the west of SU Cyg. It is an A-type main-sequence star with a class of A2V. This star does not appear to be gravitationally bound to SU Cyg.

References

{{reflist|refs=

{{Citation |last1=Gallenne |first1=A. |title=Multiplicity of Galactic Cepheids from long-baseline interferometry V. High-accuracy orbital parallax and mass of SU Cygni |date=2024-11-15 |arxiv=2411.06647 |last2=Evans |first2=N. R. |last3=Kervella |first3=P. |last4=Monnier |first4=J. D. |last5=Proffitt |first5=C. R. |last6=Schaefer |first6=G. H. |last7=Winston |first7=E. M. |last8=Kuraszkiewicz |first8=J. |last9=Mérand |first9=A.}}

{{citation | postscript=.

| title=MAST: Barbara A. Mikulski Archive for Space Telescopes

| url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html

| publisher=Space Telescope Science Institute

| access-date=6 January 2023 }}

{{citation

| display-authors=1 | last1=Samus | first1=N. N.

| last2=Kazarovets | first2=E. V. | last3=Durlevich | first3=O. V.

| last4=Kireeva | first4=N. N. | last5=Pastukhova | first5=E. N.

| title=General Catalogue of Variable Stars

| version=5.1 | journal=Astronomy Reports

| year=2017 | volume=61 | issue=1 | pages=80–88

| bibcode=2017ARep...61...80S | doi=10.1134/S1063772917010085

| s2cid=125853869 | postscript=. }}

{{citation

| title=Binary Cepheids: Separations and Mass Ratios in 5 M_⊙ Binaries

| first1=Nancy Remage | last1=Evans | first2=Howard E. | last2=Bond

| first3=Gail H. | last3=Schaefer | first4=Brian D. | last4=Mason

| first5=Margarita | last5=Karovska | first6=Evan | last6=Tingle

| display-authors=1 | journal=The Astronomical Journal

| volume=146 | issue=4 | id=93 | postscript=.

| date=October 2013 | page=93 | doi=10.1088/0004-6256/146/4/93

| arxiv=1307.7123 | bibcode=2013AJ....146...93E | s2cid=34133110 }}

{{citation | postscript=.

| title=Models for 60 double-lined binaries containing giants

| last1=Eggleton | first1=Peter P. | last2=Yakut | first2=Kadri

| journal=Monthly Notices of the Royal Astronomical Society

| volume=468 | issue=3 | pages=3533–3556

| date=July 2017 | doi=10.1093/mnras/stx598

| doi-access=free

| arxiv=1611.05041 | bibcode=2017MNRAS.468.3533E }}

{{citation | postscript=.

| title=Note on the variable radial velocity and the period of SU Cygni

| last=Maddrill | first=J. D.

| journal=Publications of the Astronomical Society of the Pacific

| volume=18 | pages=252–253 | date=August 1906

| issue=109

| doi=10.1086/121692 | bibcode=1906PASP...18..252M | s2cid=119576552

| doi-access=free

}}

{{citation | postscript=.

| title=The frequency of Cepheids with companions: a photoelectric approach

| last=Madore | first=B. F.

| journal=Monthly Notices of the Royal Astronomical Society

| volume=178 | pages=505–511 | date=March 1977

| issue=3

| doi=10.1093/mnras/178.3.505 | bibcode=1977MNRAS.178..505M | doi-access=free

}}

{{citation | postscript=.

| title=Zwei neue Veränderliche von kurzer Periode

| last1=Müller | first1=G. | last2=Kempf | first2=P.

| journal=Astronomische Nachrichten | language=De

| volume=146 | issue=3 | page=37 | date=March 1898

| doi=10.1002/asna.18981460303 | bibcode=1898AN....146...37M

| url=https://zenodo.org/record/1424765

}} Note: listed as BD. +28°3460.

{{citation | postscript=.

| title=Sur les deux nouvelles étoiles variables U Petit Renard et SU Cygne

| last=Luizet | first=Michel | language=Fr

| journal=Astronomische Nachrichten

| volume=149 | issue=18 | page=313 | date=May 1899

| doi=10.1002/asna.18991491804 | bibcode=1899AN....149..313L }}

{{citation | postscript=.

| title=Baade-Wesselink distances and the effect of metallicity in classical cepheids

| last=Groenewegen | first=M. A. T.

| journal=Astronomy and Astrophysics

| volume=488 | issue=1 | pages=25–35 | year=2008

| arxiv=0807.1269 | doi=10.1051/0004-6361:200809859

| bibcode=2008A&A...488...25G | s2cid=13871801 }}

{{citation | postscript=.

| title=The variations in spectral type of twenty Cepheid variables

| last=Shapley | first=H.

| journal=Astrophysical Journal

| volume=44 | pages=273 | year=1916

| bibcode=1916ApJ....44..273S | doi=10.1086/142295 | doi-access=free}}

{{citation | postscript=.

| title=Determination de rayons de cepheides. III. Vitesses radiales, orbite spectroscopique et dimension de SU Cyg

| last=Imbert | first=M. | language=Fr

| journal=Astronomy and Astrophysics Supplement Series

| volume=58 | pages=529–536 | date=December 1984

| bibcode=1984A&AS...58..529I }}

{{citation | postscript=.

| title=Ultraviolet Observations of the System Containing the Cepheid SU Cyg

| display-authors=1 | last1=Evans | first1=N. R.

| last2=Bohm-Vitense | first2=E. | last3=Bolton | first3=C. T.

| journal=Bulletin of the American Astronomical Society

| volume=17 | page=559 | date=March 1985

| bibcode=1985BAAS...17..559E }}

{{citation | postscript=.

| title=A HgMn companion to the Cepheid SU Cyg

| last1=Wahlgren | first1=G. M. | last2=Evans | first2=N. R.

| journal=Astronomy and Astrophysics

| volume=332 | pages=L33–L36 | date=April 1998

| bibcode=1998A&A...332L..33W }}

{{citation | postscript=.

| first=G. A. | last=Gontcharov

| title=Pulkovo Compilation of Radial Velocities for 35493 Hipparcos Stars

| journal=Astronomy Letters

| volume=32 | issue=11 | pages=759–771

| date=November 2006 | doi=10.1134/S1063773706110065

| arxiv=1606.08053 | bibcode=2006AstL...32..759G | s2cid=119231169 }}

{{citation | postscript=.

| title=Barium abundances in Cepheids | display-authors=1

| last1=Andrievsky | first1=S. M. | last2=Lépine | first2=J. R. D.

| last3=Korotin | first3=S. A. | last4=Luck | first4=R. E.

| last5=Kovtyukh | first5=V. V. | last6=MacIel | first6=W. J.

| journal=Monthly Notices of the Royal Astronomical Society

| volume=428 | issue=4 | pages=3252 | year=2013

| doi=10.1093/mnras/sts270 | doi-access=free

| bibcode=2013MNRAS.428.3252A | arxiv=1210.6211 }}

{{citation | postscript=.

| title=Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2. II. Resolved common proper motion pairs

| display-authors=1 | last1=Kervella | first1=Pierre

| last2=Gallenne | first2=Alexandre | last3=Evans | first3=Nancy Remage

| last4=Szabados | first4=Laszlo | last5=Arenou | first5=Frédéric

| last6=Mérand | first6=Antoine | last7=Nardetto | first7=Nicolas

| last8=Gieren | first8=Wolfgang | last9=Pietrzynski | first9=Grzegorz

| journal=Astronomy & Astrophysics

| volume=623 | id=A117 | pages=40

| date=March 2019 | doi=10.1051/0004-6361/201834211

| arxiv=1908.00545 | bibcode=2019A&A...623A.117K }}

}}

SU Cygni

References

Further reading