CR Boötis
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CR Boötis is an interacting binary system in the northern
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...
of
Boötes Boötes ( ) is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere. The name comes from la, Boōtēs, which comes from grc-gre, Βοώτης, Boṓtēs ...
, abbreviated CR Boo. It is one of the best-known
AM Canum Venaticorum star An AM Canum Venaticorum star (AM CVn 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 st ...
s. The system varies widely in brightness, ranging in apparent visual magnitude from 13.6 down to 17.5. The distance to this system is approximately 1,150 
light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
s from the Sun, based on
parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...
measurements. The variable luminosity of this object was discovered in 1983 by M. A. Wood and associates, with a light curve that is very similar to that of
AM Canum Venaticorum 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 wh ...
. It was found to have an ultraviolet excess by the Palomar-Green survey and assigned the identifier PG 1346+082 in 1986. The system varies in both its photometric and spectroscopic properties, with a photometric
quasi-period Quasiperiodicity is the property of a system that displays irregular periodicity. Periodic behavior is defined as recurring at regular intervals, such as "every 24 hours". Quasiperiodic behavior is a pattern of recurrence with a component of unpred ...
of 4–5 days. The optical spectrum displays only
lines Line most often refers to: * Line (geometry), object with zero thickness and curvature that stretches to infinity * Telephone line, a single-user circuit on a telephone communication system Line, lines, The Line, or LINE may also refer to: Arts ...
of helium. Rapid flickering suggests this is a close binary system undergoing mass transfer, while emission by neutral helium indicates there is a thick
accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other fo ...
orbiting a
compact object In astronomy, the term compact star (or compact object) refers collectively to white dwarfs, neutron stars, and black holes. It would grow to include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects ha ...
. The lack of X-ray emission means this accreting object is a white dwarf, rather than something more massive. The lack of hydrogen in the spectrum demonstrates that the
donor star In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, wi ...
is a helium white dwarf with a lower mass than the primary. The pair have a brief orbital period of with a mass ratio of 0.101. The orbital plane is inclined at an angle of about 30° to the line of sight from the Earth. This system displays two different states. The first is a lower state of quiescence that displays regular superoutbursts similar to
ER Ursae Majoris ER Ursae Majoris is a variable star in the northern circumpolar constellation of Ursa Major, abbreviated ER UMa. It is a prototype system for a subclass of SU Ursae Majoris dwarf novae. The system ranges in brightness from a peak appare ...
on a roughly 46 day cycle. The second state is brighter with frequent outbursts. The system becomes bluer during superoutbursts, with a higher temperature.


References


Further reading

* * * * * * * * * {{DEFAULTSORT:CR Bootis AM CVn stars White dwarfs Binary stars Boötes Boötis, CR