V1794 Cygni

{{Short description|FK Comae Berenices variable in the constellation Cygnus}}

{{Starbox observe

| epoch = J2000.0

| constell = Cygnus

| ra = {{RA|20|53|53.652}}

| dec = {{DEC|+44|23|11.08}}

| appmag_v = 7.23

}}

{{Starbox character

| type = Hertzsprung gap

| class = G7III-IVne

| b-v = 0.785{{±|0.015}}

| u-b =

| variable = FK Com

}}

{{Starbox astrometry

| radial_v = −30.76{{±|0.33}}

| prop_mo_ra = 26.451

| prop_mo_dec = −0.877

| pm_footnote =

| parallax = 8.8912

| p_error = 0.0147

| parallax_footnote =

| absmag_v = 2.21

}}

{{Starbox detail

| mass = 1.65

| radius = 6.1

| luminosity = 12.9

| gravity =

| temperature = 5,180{{±|92}}

| metal_fe =

| rotation = {{val|3.32|u=days}}

| rotational_velocity = 84.3{{±|4.5}}

| age_gyr = 2.014

}}

{{Starbox catalog

| names = {{odlist | V=V1794 Cyg | BD=+43°3759 | GC=29168 | HD=199178 | HIP=103144 | SAO=50198 }}

}}

{{Starbox reference

| Simbad = HD+199178

}}

V1794 Cygni is a single variable star in the northern constellation Cygnus. It has the identifier HD 199178 from the Henry Draper Catalogue; V1794 Cygni is its variable star designation. With an apparent visual magnitude of 7.24, it's too dim to be visible with the naked eye but can be seen with binoculars. V1794 is located at a distance of {{Convert|367|ly|pc|lk=on}} based on parallax measurements, but is drifting closer to the Sun with a radial velocity of −31 km/s. It lies superimposed over a region of faint nebulosity to the west of the North American Nebula.

File:V1794CygLightCurve.png light curve for V1794 Cygni, adapted from Strassmeier et al. (1999)]]

Spectrographs of HD 199178 taken in 1926 showed unusually diffuse lines for a star of its type. In 1981, a broad, variable emission of Hydrogen alpha was noted, and the star showed a photometric variability with a period a few days. It showed extreme rotational broadening of the absorption lines but no variation in radial velocity. The existence of a class of single, cool, rapidly rotating giant stars such as FK Com and HD 199178 presented a puzzle for astronomers. The star showed a variable polarization with a period of four days, suggesting chromospheric activity with an asymmetric distribution of star spots and faculae, modulated by rotation. Photometric measurements established a rotation period of 3.337 days by 1983.

V1794 Cygni was classified as a Herbig Ae/Be star in 1999 in a catalog of UX Orionis stars. However, this proved incorrect because of the star's its fast rotation compared to other giants and it is now classified as a FK Comae Berenices variable. The stellar classification of V1794 Cygni is G7III-IVne, matching an evolved subgiant/giant star with emission lines (e) plus "nebulous" lines (n) due to rapid rotation. It is currently crossing the Hertzsprung gap, which indicates it has ceased core hydrogen burning.

This star has 165% of the mass and 6.1 times the radius of the Sun, but, with an age of around 2 billion years is younger than the latter. It is spinning with a projected rotational velocity of 84 km/s. V1794 Cygni is radiating 13 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 5,180 K, which gives it a yellow hue. For a giant star it has an exceptionally high X-ray emission, which suggests there is a high surface density of active regions.

References

{{reflist|refs=

{{cite simbad

| title=HD 199178 | access-date=2022-02-04 | postscript=. | mode=cs2 }}

{{cite journal

| last1=Anderson | first1=E. | last2=Francis | first2=Ch.

| title=XHIP: An extended hipparcos compilation

| journal=Astronomy Letters

| volume=38 | issue=5 | pages=331 | year=2012

| bibcode=2012AstL...38..331A | arxiv=1108.4971

| doi=10.1134/S1063773712050015 | s2cid=119257644 }}

{{cite journal

| title=Abundances in the Local Region. I. G and K Giants

| last1=Luck | first1=R. Earle

| journal=Astronomical Journal

| volume=150 | issue=3 | at=88 | year=2015

| bibcode=2015AJ....150...88L | doi=10.1088/0004-6256/150/3/88

| arxiv=1507.01466 | s2cid=118505114 }}

{{cite journal

| title=Starspots

| last=Strassmeier | first=Klaus G.

| journal=The Astronomy and Astrophysics Review

| volume=17 | issue=3 | pages=251–308 | date=September 2009

| doi=10.1007/s00159-009-0020-6 | bibcode=2009A&ARv..17..251S | doi-access=free }}

{{cite journal

| title=A spectroscopic survey of the youngest field stars in the solar neighborhood . II. The optically faint sample

| last1=Frasca | first1=A. | last2=Guillout | first2=P.

| last3=Klutsch | first3=A. | last4=Ferrero | first4=R. Freire

| last5=Marilli | first5=E. | last6=Biazzo | first6=K.

| last7=Gandolfi | first7=D. | last8=Montes | first8=D.

| display-authors=1 | journal=Astronomy and Astrophysics

| volume=612 | pages=A96 | date=May 1, 2018

| bibcode=2018A&A...612A..96F | arxiv=1801.00671

| s2cid=119537437 | issn=0004-6361

| doi=10.1051/0004-6361/201732028 }}

{{cite journal

| title=Optical spectroscopy of HD 199178 : velocity and activity

| last=Huenemoerder | first=D. P.

| journal=Astronomical Journal

| volume=92 | pages=673–677 | date=September 1986

| doi=10.1086/114201 | bibcode=1986AJ.....92..673H | doi-access=free }}

{{cite journal

| title=General Catalogue of Variable Stars

| 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.

| version=5.1 | journal=Astronomy Reports

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

| doi=10.1134/S1063772917010085 | bibcode=2017ARep...61...80S | s2cid=255195566 }}

{{cite journal

| title=Starspot photometry with robotic telescopes. U BV (RI)C and by light curves of 47 active stars in 1996/97

| display-authors=1 | last1=Strassmeier | first1=K. G.

| last2=Serkowitsch | first2=E. | last3=Granzer | first3=Th.

| journal=Astronomy and Astrophysics Supplement Series

| date=November 1999 |volume=140 |pages=29–53

| doi=10.1051/aas:1999116 | bibcode=1999A&AS..140...29S | doi-access=free }}

{{Cite journal

| last1=Herbst | first1=W. | last2=Shevchenko | first2=V. S.

| title=A Photometric Catalog of Herbig AE/BE Stars and Discussion of the Nature and Cause of the Variations of UX Orionis Stars

| journal=The Astronomical Journal

| volume=118 | issue=2 | pages=1043–1060 | date=1999-08-01

| doi=10.1086/300966 | issn=0004-6256

| bibcode=1999AJ....118.1043H | s2cid=118185834 | doi-access=free }}

{{Cite journal

| title=The solar neighbourhood age-metallicity relation - Does it exist?

| display-authors=1 | last1=Feltzing | first1=S.

| last2=Holmberg | first2=J. | last3=Hurley | first3=J. R.

| journal=Astronomy and Astrophysics

| volume=377 | issue=3 | pages=911–924 | date=2001-10-01

| doi=10.1051/0004-6361:20011119 | doi-access=free

| arxiv=astro-ph/0108191 | s2cid=4811000

| bibcode=2001A&A...377..911F | issn=0004-6361 }}

{{cite journal

| title=Photographic studies of nebulae. IV.

| last=Duncan | first=J. C.

| journal=Astrophysical Journal

| volume=63 | pages=122–126 | date=March 1926

| doi=10.1086/142956 | bibcode=1926ApJ....63..122D | doi-access=free }}

{{cite journal

| title=The FK COM stars

| last1=Bopp | first1=B. W. | last2=Stencel | first2=R. E.

| journal=Astrophysical Journal

| volume=247 | pages=L131–L134 | date=August 1981

| doi=10.1086/183606 | bibcode=1981ApJ...247L.131B }}

{{cite web

| title=V1794 Cyg

| url=https://www.aavso.org/vsx/index.php?view=detail.top&oid=12714

| website=The International Variable Star Index

| publisher=AAVSO | access-date=29 December 2021 }}

{{cite journal

| title=Polarimetric observations of HD 199178- an FK COM type star.

| last1=Piirola | first1=V. | last2=Vilhu | first2=O.

| journal=Astronomy and Astrophysics

| volume=110 | pages=351–354 | date=June 1982

| bibcode=1982A&A...110..351P }}

{{cite journal

| title=Five-colour (UBVRI) photopolarimetry of FK Comae and HD 199178.

| display-authors=1 | last1=Huovelin | first1=J.

| last2=Vilhu | first2=O. | last3=Piirola | first3=V.

| last4=Efimov | first4=Iu. S. | last5=Shakhovskoi | first5=N. M.

| journal=Astronomy and Astrophysics

| volume=176 | pages=83–92 | date=April 1987

| bibcode=1987A&A...176...83H }}

{{cite journal

| title=Observations of active chromosphere stars

| display-authors=1 | last1=Bopp | first1=B. W.

| last2=Africano | first2=J. L. | last3=Stencel | first3=R. E.

| last4=Noah | first4=P. V. | last5=Klimke | first5=A.

| journal=Astrophysical Journal

| volume=275 | pages=691–703 | date=December 1983

| doi=10.1086/161566 | bibcode=1983ApJ...275..691B }}

{{cite journal

| title=The corona of HD 199178 (V 1794 Cygni)

| last=Gondoin | first=P.

| journal=Astronomy and Astrophysics

| volume=413 | pages=1095–1104 | date=January 2004

| issue=3 | doi=10.1051/0004-6361:20031575 | bibcode=2004A&A...413.1095G | doi-access=free }}

}}

V1794 Cygni

References

Further reading