AM Canum Venaticorum

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AM Canum Venaticorum
Observation data
Epoch J2000.0        Equinox J2000.0 (ICRS)
Constellation Canes Venatici
Right ascension 12h 34m 54.60s [1]
Declination +37° 37′ 44.1″ [1]
Apparent magnitude  (V)+14.02 (13.7–14.2) [2]
Characteristics
Spectral type DBp [3]
U−B color index −1.01 [4]
B−V color index −0.23 [4]
Variable type AM CVn [5]
Astrometry
Proper motion (μ)RA: 30.935 [6]   mas/yr
Dec.: 12.420 [6]   mas/yr
Parallax (π)3.3512 ± 0.0452 [6]   mas
Distance 970 ± 10  ly
(298 ± 4  pc)
Absolute magnitude  (MV)4.90+0.37
−0.45 [2]
Orbit [5]
Period (P)1,028.7322±0.0003 s (17:08.732±0.018 min)
Inclination (i)43±2°
Details
WD
Mass 0.6 [7]   M☉
Radius 0.0137 [7]   R☉
Temperature 100,000 [7]   K
donor
Mass 0.1 [7]   M☉
Other designations
EGGR 91, HZ 29, GSC  03018-02523, PG 1232+379, WD 1232+37, AAVSO  1229+38.
Database references
SIMBAD data

AM Canum Venaticorum (AM CVn) is a hydrogen-deficient cataclysmic variable binary star in the constellation of Canes Venatici. It is the type star of its class of variables, the AM Canum Venaticorum stars. The system consists of a white dwarf gaining matter via an accretion disk from a semi-degenerate or white dwarf companion.

Contents

Observations

Photoelectric V light curve for AM Canum Venaticorum over a 330-minute period Amcvn lightcurve.png
Photoelectric V light curve for AM Canum Venaticorum over a 330-minute period

During 1939–40, a survey for faint white dwarfs was carried out using an 18-inch (46 cm) Schmidt telescope at Palomar observatory. Part of the survey was made around the north galactic pole in order to exclude stars of stellar classifications O, B, and A, as these higher mass, shorter-lived stars tend to be concentrated along the plane of the Milky Way where new star formation occurs. Out of the stars observed, a list of faint blue stars was constructed by Milton L. Humason and Fritz Zwicky in 1947, [8] with their blue hue suggesting a relatively high effective temperature. The 29th star on their list, HZ 29, was found to have the most peculiar spectrum out of the set. It displayed an absence of hydrogen lines, but broad, diffuse lines of neutral (non-ionized) helium. [9] This was interpreted as a hydrogen-deficient white dwarf. In 1962, this star was observed with a photoelectric detector and was found to vary in magnitude over a period of 18 minutes. The light curve of the variation displayed a double sinusoid pattern. [10] Later, a flickering behavior was observed, which suggested a mass transfer. [2]

Distance

The distance of AM CVn has been difficult to determine. It is too faint to have a measured Hipparcos parallax, too distant to have a reliable precise parallax determined by other means, and too rare to have its parameters known by comparison with other objects.

Calibration against other cataclysmic variables yields a distance of 143  pc . [11] Other estimates of its distance, by comparison to models of its accretion disk, give 288±50 pc and 420±80 pc. One ground-based measurement of its absolute parallax gave a distance of 235 pc. Derivation of a relative parallax, by comparison to the estimated parallaxes of three comparison stars, using the Hubble Space Telescope Fine Guidance Sensor gives a very large distance of 606+135
−93 pc. [2]

Gaia Data Release 2 gives a parallax of 3.3512±0.0452  mas , leading to a distance of 295±4 pc. [12] This value gives the system a lower luminosity and accretion rate, closer to what would be expected by accretion disk models. [13]

Description

The model developed to explain the observations was that AM Canum Venaticorum is a binary system consisting of a pair of white dwarfs in a close orbit. The primary is a more massive white dwarf composed of carbon/oxygen, whereas the secondary is a less massive white dwarf made of helium, with no hydrogen but traces of heavier elements. [2] At the unexpectedly large distance found by the HST, the secondary would be a semi-degenerate object such as subdwarf B star. [2]

Gravitational wave radiation is causing a loss of angular momentum in the orbit, leading to the transfer of helium from the secondary to the primary as the two draw closer. [14] This transfer is occurring because the secondary is overflowing its Roche lobe—a tear drop shaped lobe created by the gravitational interaction between the two stars. [2]

The mass transfer rate between the two stars is estimated as about 7×10−9 solar masses per year, which is creating an accretion disk around the companion white dwarf. [5] The energy output from the mass flow onto this accretion disk is actually the primary contributor to the visual luminosity of this system; outshining both of the stellar components. The temperature of this disk is about 30,000 K. [5]

High speed photometry of the system shows multiple periods of variation in the luminosity. The main period of 1,028.73 seconds (17m 8.73s) is the orbital period of the pair. [14] A secondary period of 1,051 seconds (17m 31s) is believed to be caused by a superhump—an elevated outburst in the signal that occurs with a period slightly longer than the orbital period. The superhump may be the result of an elongation of the accretion disk in combination with precession. The elliptical disk precesses about the white dwarf over a time interval much longer than the orbital period, causing a slight change in the orientation of the disk over each orbit. [15]

Flares

Normally AM CVn only exhibits magnitude variations of 0.05. However, AM CVn star systems such as this are nova-like objects that are known to randomly generate intense flares in luminosity. AM Canum Venaticorum displayed just such flaring behavior twice during the period 1985–1987, with these flares showing rapid fluctuations in luminosity. A 1986 flare caused an increase in magnitude of up to Δm = 1.07±0.03 and lasted for 212 seconds. The amount of energy released during this event is estimated as 2.7×1036  erg. [16] These flashes are caused by the brief thermonuclear fusion of helium being accumulated along an outer shell by the primary. [17]

Related Research Articles

Cor Caroli Star in constellation Canes Venatici

The Cor Caroli system is a binary star designated Alpha Canum Venaticorum or α Canum Venaticorum. The International Astronomical Union uses the name "Cor Caroli" specifically for the brighter star of the binary. Alpha Canum Venaticorum is the brightest point of light in the northern constellation of Canes Venatici.

Beta Canum Venaticorum Star in constellation Canes Venatici

Beta Canum Venaticorum, also named Chara, is a G-type main-sequence star in the northern constellation of Canes Venatici. At an apparent visual magnitude of 4.26, it is the second-brightest star in the constellation. Based upon an annual parallax shift of 118.49 mas, this star is 27.53 light-years distant from the Sun.

La Superba Variable star in the contellation Canes Venatici

La Superba is a strikingly red giant star in the constellation Canes Venatici. It is a carbon star and semiregular variable.

24 Canum Venaticorum is a single star in the northern constellation of Canes Venatici, located 277 light years away from the Sun. This object is visible to the naked eye as a faint white-hued star with an apparent visual magnitude of +4.68. It is moving closer to the Earth with a heliocentric radial velocity of −18 km/s.

20 Canum Venaticorum is a single variable star in the northern constellation of Canes Venatici, located 238 light years from the Sun. This object has the variable star designation AO Canum Venaticorum; 20 Canum Venaticorum is the Flamsteed designation. It is visible to the naked eye as a faint, white-hued star with a baseline apparent visual magnitude of +4.72. The star is moving further from the Earth with a heliocentric radial velocity of +9 km/s. Eggen (1971) listed this star as a member of the Hyades Stream.

5 Canum Venaticorum is a probable binary star system in the northern constellation of Canes Venatici, located about 375 light years from the Sun. It is visible to the naked eye as a faint, yellow-hued star with an apparent visual magnitude of +4.77. The system is moving closer to the Earth with a heliocentric radial velocity of −14 km/s.

6 Canum Venaticorum is a single star in the northern constellation Canes Venatici, located 246 light years from the Sun. It is visible to the naked eye as a faint yellow-hued star with an apparent visual magnitude of +5.01. The star is moving closer to the Earth with a heliocentric radial velocity of −4.2 km/s.

21 Canum Venaticorum is a single variable star in the northern constellation of Canes Venatici, located 277 light years away from the Sun. This object has the variable star designation BK Canum Venaticorum; 21 Canum Venaticorum is the Flamsteed designation. It is visible to the naked eye as a faint white-hued star with a baseline apparent visual magnitude of +5.14.

HD 17925 is a variable star in the equatorial constellation of Eridanus. It has the Gould designation 32 G. Eridani and the variable star designation EP Eri. The star has a yellow-orange hue and is dimly visible to the naked eye in good seeing conditions with an apparent visual magnitude that varies from 6.03 down to 6.08. It is located nearby at a distance of 34 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +18 km/s. It is a likely member of the Local Association of nearby, co-moving stars. The spectrum shows a strong abundance of lithium, indicating that it is young star. This likely makes its point of origin the nearby Scorpio–Centaurus Complex.

HD 15115 Star in the constellation Cetus

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An AM Canum Venaticorum star, is a rare type of cataclysmic variable star named after their type star, AM Canum Venaticorum. In these hot blue binary variables, a white dwarf accretes hydrogen-poor matter from a compact companion star.

IQ Aurigae Single, variable star in the constellation Auriga

IQ Aurigae is a single, variable star in the northern constellation of Auriga. It is visible to the naked eye as a dim, white-hued star with an apparent visual magnitude that fluctuates around 5.38. The star is located at a distance of about 470 light-years from the Sun based on parallax and is drifting further away with a radial velocity of +28.6 km/s.

V538 Aurigae is a single star in the northern constellation of Auriga. With an apparent visual magnitude of 6.23, this star requires good dark sky conditions to view with the naked eye. It is located at a distance of 40.0 light-years (12.3 pc) from Sun based on parallax. The star is drifting further away with a radial velocity of 0.9 km/s. It is a member of the Local Association, and is most likely a thin disk star.

HR 4072 is a binary star system in the northern circumpolar constellation of Ursa Major. It has the variable star designation ET Ursae Majoris, abbreviated ET Uma, while HR 4072 is the system's designation from the Bright Star Catalogue. It has a white hue and is faintly visible to the naked eye with an apparent visual magnitude that fluctuates around 4.94. The system is located at a distance of approximately 339 light years from the Sun based on parallax measurements. The radial velocity measurement is poorly constrained, but it appears to be drifting closer to the Sun at the rate of around −3 km/s.

50 Persei is a star in the constellation Perseus. Its apparent magnitude is 5.52, which is bright enough to be seen with the naked eye. Located around 21.00 parsecs (68.5 ly) distant, it is a White main-sequence star of spectral type F7V, a star that is currently fusing its core hydrogen. In 1998 the star was named a candidate Gamma Doradus variable with a period of 3.05 days, which would means it displays variations in luminosity due to non-radial pulsations in the photosphere. Subsequently, it was classified as a RS Canum Venaticorum and BY Draconis variable by an automated program.

HIP 57274 is a star in the northern circumpolar constellation of Ursa Major with a system of three planets. It is invisible to the naked eye, having an apparent visual magnitude of 8.96. The distance to this system is 84.4 light years based on stellar parallax, and it is drifting further away with a radial velocity of +30 km/s. The star has a relatively high rate of proper motion, traversing the celestial sphere at the rate of 0.382 arcsecond/year.

10 Canum Venaticorum is the Flamsteed designation for an ordinary star in the northern constellation of Canes Venatici. It has an apparent visual magnitude of 5.95, which, according to the Bortle scale, can be seen with the naked eye from suburban locations. Based upon an annual parallax shift of 0.0569 arcseconds, this system is 57.3 light-years from Sun. It is drifting further away with a radial velocity of +80 km/s.

Nu Horologii Star in the constellation Horologium

Nu Horologii, Latinized from ν Horologii, is the Bayer designation for a single star in the southern constellation of Horologium. It was catalogued by the Dutch explorer Frederick de Houtman in 1603. With an apparent visual magnitude of 5.3, this star can be seen with the naked eye from the southern hemisphere. Based upon parallax measurements made by the Gaia space observatory, Nu Horologii lies at a distance of 169±1 light-years from Earth. It is drifting closer to the Sun with a radial velocity of +31 km/s.

SU Ursae Majoris, or SU UMa, is a close binary star in the northern circumpolar constellation of Ursa Major. It is a periodic cataclysmic variable that varies in magnitude from a peak of 10.8 down to a base of 14.96. The distance to this system, as determined from its annual parallax shift of 4.53 mas, is 719 light-years. It is moving further from the Earth with a heliocentric radial velocity of +27 km/s.

RS Canum Venaticorum is a binary star system in the northern constellation of Canes Venatici. It serves as the prototype to the class of RS Canum Venaticorum variables. The peak apparent visual magnitude of this system is below the level needed to observe it with the naked eye. It is located at a distance of approximately 443 light years from the Sun based on parallax, but is drifting closer with a net radial velocity of −14 km/s. Olin J. Eggen (1991) included this system as a member of the IC 2391 supercluster, but it was later excluded.

References

  1. 1 2 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C. S2CID   115529446.
  2. 1 2 3 4 5 6 7 Roelofs, G. H. A.; et al. (September 2007), "Hubble Space Telescope Parallaxes of AM CVn Stars and Astrophysical Consequences", The Astrophysical Journal, 666 (2): 1174–1188, arXiv: 0705.3855 , Bibcode:2007ApJ...666.1174R, doi:10.1086/520491, S2CID   18785732
  3. ↑ Van Altena, W. F.; Lee, J. T.; Hoffleit, E. D. (1995). "The general catalogue of trigonometric [stellar] parallaxes". New Haven. Bibcode:1995gcts.book.....V.
  4. 1 2 Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data: 0. Bibcode:1986EgUBV........0M.
  5. 1 2 3 4 Roelofs, G. H. A.; et al. (September 2006), "Kinematics of the ultracompact helium accretor AM Canum Venaticorum", Monthly Notices of the Royal Astronomical Society , 371 (3): 1231–1242, arXiv: astro-ph/0606327 , Bibcode:2006MNRAS.371.1231R, doi:10.1111/j.1365-2966.2006.10718.x, S2CID   15295671
  6. 1 2 3 Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics . 616. A1. arXiv: 1804.09365 . Bibcode: 2018A&A...616A...1G . doi: 10.1051/0004-6361/201833051 . Gaia DR2 record for this source at VizieR.
  7. 1 2 3 4 Kusterer, D. -J; Nagel, T.; Hartmann, S.; Werner, K.; Feldmeier, A. (2014). "Monte Carlo radiation transfer in CV disk winds: Application to the AM CVn prototype". Astronomy and Astrophysics. 561: A14. Bibcode:2014A&A...561A..14K. doi: 10.1051/0004-6361/201321438 .
  8. ↑ Humason, M. L.; Zwicky, F. (January 1947), "A Search for Faint Blue Stars", Astrophysical Journal, 105: 85, Bibcode:1947ApJ...105...85H, doi:10.1086/144884
  9. ↑ Greenstein, Jesse L.; Matthews, Mildred S. (July 1957), "Studies of the White Dwarfs. I. Broad Features in White Dwarf Spectra", Astrophysical Journal, 126: 14, Bibcode:1957ApJ...126...14G, doi:10.1086/146364
  10. ↑ Smak, J. (February 1967), "18-min. Light-Variations of HZ 29", Information Bulletin on Variable Stars, 182: 1, Bibcode:1967IBVS..182....1S
  11. ↑ Ak, T.; Bilir, S.; Ak, S.; Eker, Z. (2008). "Spatial distribution and galactic model parameters of cataclysmic variables". New Astronomy. 13 (3): 133–143. arXiv: 0708.1053 . Bibcode:2008NewA...13..133A. doi:10.1016/j.newast.2007.08.003. S2CID   17804687.
  12. ↑ Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Mantelet, G.; Andrae, R. (2018). "VizieR Online Data Catalog: Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)". VizieR On-line Data Catalog. Bibcode:2018yCat.1347....0B.
  13. ↑ G. Ramsay; et al. (2018). "The physical properties of AM CVn stars: new insights from Gaia DR2". Astronomy & Astrophysics. 620: A141. arXiv: 1810.06548 . Bibcode:2018A&A...620A.141R. doi:10.1051/0004-6361/201834261. S2CID   76652045.
  14. 1 2 Nelemans, G.; Steeghs, D.; Groot, P. J. (September 2001), "Spectroscopic evidence for the binary nature of AM CVn", Monthly Notices of the Royal Astronomical Society, 326 (2): 621–627, arXiv: astro-ph/0104220 , Bibcode:2001MNRAS.326..621N, doi:10.1046/j.1365-8711.2001.04614.x, S2CID   19290217
  15. ↑ Pearson, K. J. (July 2007), "Are superhumps good measures of the mass ratio for AM CVn systems?", Monthly Notices of the Royal Astronomical Society, 379 (1): 183–189, arXiv: 0705.0141 , Bibcode:2007MNRAS.379..183P, doi:10.1111/j.1365-2966.2007.11932.x, S2CID   2685807
  16. ↑ Marar, T. M. K.; et al. (January 1988), "Flares on AM Canum Venaticorum", Astronomy and Astrophysics, 189 (1–2): 119–123, Bibcode:1988A&A...189..119M
  17. ↑ Bildsten, Lars; Shen, Ken J.; Weinberg, Nevin N.; Nelemans, Gijs (June 2007), "Faint Thermonuclear Supernovae from AM Canum Venaticorum Binaries", The Astrophysical Journal, 662 (2): L95–L98, arXiv: astro-ph/0703578 , Bibcode:2007ApJ...662L..95B, doi:10.1086/519489, S2CID   119369896

Coordinates: Jupiter and moon.png 12h 34m 54.58s, +37° 37′ 43.4″

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