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AM Herculis

{{Short description|Star in the constellation Hercules}}

{{about|the individual star|the type of cataclysmic variable star|Polar (cataclysmic variable)}}

{{Starbox begin

| name = AM Herculis

}}

{{Starbox image

| image = 250px

| caption = A visual band light curve for AM Herculis, from AAVSO data

}}

{{Starbox observe

| epoch = J2000.0

| constell = Hercules

| ra = {{RA|18|16|13.255}}

| dec = {{DEC|+49|52|04.76}}

| appmag_v = 12.30-15.7

}}

{{Starbox character

| class = pec + M4.5V

| variable = AM/XRM+E

}}

{{Starbox astrometry

| radial_v = -19.0

| prop_mo_ra = −45.957

| prop_mo_dec = +28.046

| dist_pc=

| dist_ly=

| parallax = 11.3953

| p_error = 0.0179

| parallax_footnote =

}}

{{Starbox orbit

| reference =

| period_unitless = 3.094 hours (variable)

| inclination = 50

| eccentricity = {{val|0.47|0.21}}

}}

{{Starbox detail

| component1 = White dwarf

| mass = 0.6 - 0.7

| radius =

| luminosity =

| temperature =

| component2 = Red dwarf

| mass2 = 0.26

| radius2 = 0.32

| luminosity2 =

| temperature2 =

}}

{{Starbox catalog

| names = AN 1923.0028, GSC 3533.01105, X 18149+498

}}

{{Starbox reference

| Simbad = AM+Her

| EPE =

}}

{{Starbox end}}

AM Herculis is a binary variable star located in the constellation Hercules. This star, along with the star AN Ursae Majoris, is the prototype for a category of cataclysmic variable stars called polars, or AM Her type stars.

History

AM Herculis was first cataloged in 1923 by Max Wolf and was listed at the time as Veränderlicher 28.1923, which is now AN 28.1923 in the General Catalogue of Variable Stars. It was observed to be an irregular variable star ranging from 12 to 14 in apparent magnitude. In 1976, the astronomer S. Tapia discovered that light from the star is both linearly and circularly polarized, showing that there was a strong magnetic field surrounding the system and revealing that the system was more complex than previously thought.

System

The AM Herculis binary system contains a white dwarf and a red dwarf. The white dwarf is accreting material directly from the red dwarf without an accretion disk. The white dwarf primary is highly magnetic and the infalling material is channelled towards the magnetic poles. The accretion rate is unstable, at times decreasing dramatically and reducing the brightness of the whole system. There are also periodic variations thought to be caused by the appearance and eclipse of the accreting regions during rotation of the white dwarf.

File:AM Her Light Curve.jpg

References

{{reflist|refs=

{{cite DR2|2123837555230207744}}

{{cite journal | journal=Astronomische Nachrichten | volume=220 | issue=15 | date=1923 | pages=255–256

| title=Mitteilungen über Veränderliche - Veränderlicher 28.1923 Herculis - M. Wolf - December 1923

| bibcode=1924AN....220..249H

| language=de | author=S. Seliwanow | doi=10.1002/asna.19232201505}}

{{ cite journal | author=Krzeminski, W. | author2=Serkowski, K. | name-list-style=amp | title=Extremely high circular polarization of AN Ursae Majoris | journal=The Astrophysical Journal Letters | volume=216 | pages=L45 | date=August 1977 | doi=10.1086/182506 | bibcode=1977ApJ...216L..45K| doi-access=free }}

{{ cite journal | author=Hessman, F.V. | author2=Gansicke, B.T. | author3=Mattei, J.A. | name-list-style=amp | title=The history and source of mass-transfer variations in AM Herculis | journal=Astronomy & Astrophysics | volume=361 | pages=952–958 | date=September 2000 | bibcode=2000A&A...361..952H}}

{{ cite journal | title=Discovery of a magnetic compact star in the AM Herculis/3U 1809+50 system | author=Tapia, S. | date=March 15, 1977 | journal=The Astrophysical Journal Letters | volume=212 | pages=L125–L129 | doi=10.1086/182390 | bibcode=1977ApJ...212L.125T}}

{{cite web | title=Query= AM Her

| url=http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=AM+Her

| publisher=Centre de Données astronomiques de Strasbourg

| work=General Catalogue of Variable Stars | access-date=2009-12-16}}

{{cite journal|doi=10.1093/mnras/stx3175|arxiv=1801.05815|title=Another look at AM Herculis – radio-astrometric campaign with the e-EVN at 6 cm|journal=Monthly Notices of the Royal Astronomical Society|volume=475|pages=1399–1409|year=2018|last1=Gawroński|first1=M. P.|last2=Goździewski|first2=K.|last3=Katarzyński|first3=K.|last4=Rycyk|first4=G.|issue=1|doi-access=free |bibcode=2018MNRAS.475.1399G|s2cid=54000035}}

{{cite journal|doi=10.1088/0004-637X/774/2/153|arxiv=1307.5135|title=Updated Photometry and Orbital Period Analysis for the Polar Am Herculis on the Upper Edge of the Period Gap|journal=The Astrophysical Journal|volume=774|issue=2|pages=153|year=2013|last1=Dai|first1=Zhibin|last2=Qian|first2=Shengbang|last3=Li|first3=Linjia|last4=Rycyk|first4=G.|bibcode=2013ApJ...774..153D|s2cid=118843221}}

{{cite web |title=Download Data |url=https://www.aavso.org/data-download |website=aavso.org |publisher=AAVSO |access-date=1 October 2021}}

{{cite journal|bibcode=1995A&AS..114..269D|title=Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue|journal=Astronomy and Astrophysics Supplement Series|volume=114|pages=269|last1=Duflot|first1=M.|last2=Figon|first2=P.|last3=Meyssonnier|first3=N.|year=1995}}

}}

Further reading

  • {{cite book|author=Coel Hellier|title=Cataclysmic Variable Stars - How and Why They Vary|url=https://books.google.com/books?id=5I-yLZ3oYxIC&pg=PR13|date=23 February 2001|publisher=Springer Science & Business Media|isbn=978-1-85233-211-2|pages=13–}}
  • {{cite book|author1=Cuno Hoffmeister|author2=Gerold Richter|author3=Wolfgang Wenzel|title=Variable stars|url=https://books.google.com/books?id=GpXvAAAAMAAJ|date=31 December 1985|publisher=Springer-Verlag|isbn=978-3-540-13403-9}}
  • {{cite journal|bibcode=1977S&T....53..351L|title=The Story of AM Herculis|journal=Sky and Telescope|volume=53|pages=351|last1=Liller|first1=W.|year=1977}}

External links

  • [https://web.archive.org/web/20070405152429/http://www.aavso.org/vstar/vsots/0601.shtml Variable Star Of The Month] by the American Association of Variable Star Observers

{{Stars of Hercules}}

{{DEFAULTSORT:AM Herculis}}

Category:Hercules (constellation)

Category:Polars (cataclysmic variable stars)

Herculis, AM

Category:M-type main-sequence stars