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 | |
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.
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]
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]
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]
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]
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, 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 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 is a single star in the equatorial constellation of Cetus. It is readily visible in binoculars or a small telescope, but is considered too dim to be seen with the naked eye at an apparent visual magnitude of 6.76. The distance to this object is 160 light years based on parallax, and it is slowly drifting further away at the rate of about 1 km/s. It has been proposed as a member of the Beta Pictoris moving group or the Tucana-Horologium association of co-moving stars; there is some ambiguity as to its true membership.
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 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, 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.