Eta Corvi
Encyclopedia
Eta Corvi (Eta Crv, η Corvi, η Crv) is an F-type main sequence
star
, the sixth-brightest star in the constellation
of Corvus
. Two debris disks have been detected orbiting this star, one warm within a few AU and another out at ~150 AU.
in its atmosphere is only about 93% that of the Sun's. The projected rotational velocity
at the equator (v sin i) is a brisk 68 km/s.
The IRAS
satellite detected an excess of infrared
radiation from this star, beyond what would normally be expected for a stellar object of this class. Observations in the
submillimetre band
confirmed the presence of excess dust in orbit around the star having about 60% of the mass of the Moon
and a temperature of 80 K. The data indicated a debris disk
with an estimated maximum radius of 180 A.U.
from the star, or 180 times the separation of the Earth and the Sun. (Compare to the Kuiper belt
, which extends out to 55 A.U. from the Sun.)
Recent submillimeter observations confirm the presence of an outer flat, circumstellar disk of debris with an outer radius of 150 A.U. It is oriented at an inclination
to the line of sight from the Earth. Most of the inner 100 A.U. of the disk is relatively free of material, which suggests it was cleared away by a planetary system. In addition, infrared radiation which appears to be from an inner, hotter, debris disk within 3.5 AU of the star has been observed.
Since the Poynting-Robertson effect
would cause the dust in the outer disk to spiral in to the star within 20 million years, much younger than the age of the system, the observed presence of dust in the outer disk means that it must be constantly replenished. It is thought that this happens by the collisions of planetesimal
s orbiting at a distance of about 150 A.U., which are repeatedly broken down into smaller and smaller pieces, eventually becoming dust. The origin of the inner disk is not clear. It may have originated from planetesimals recently having moved from the outer regions of the system into the inner system, in a process similar to the Late Heavy Bombardment
in the history of the Solar System
, and subsequently being ground to dust by collisions.
Applied Physics Laboratory and his group analyzed the Spitzer
IRS 5 – 35 μm spectrum of the warm, ~360K
circumstellar dust and found that it showed clear evidence for warm, water- and carbon-rich dust at ~ 3 AU from the central star, in the system’s habitable zone
, uncoupled and in a separate reservoir from the system’s extended sub-mm dust ring at 150 ± 20 AU. Spectral features similar in kind and amplitude to those found for ultra-primitive, (i.e., formed very early in the lifetime of the Eta Corvi system) ~10 Myr
old cometary material were found (water ice & gas, olivine
s & pyroxene
s, amorphous carbon
and metal sulfides), in addition to emissions due to impact produced silica and high temperature/pressure carbonaceous
phases. The warm dust is very primitive, and definitely not from an asteroidal parent body. A large amount, at least 3 x 1019 kg, of 0.1 – 1000 µm warm dust is present, in a roughly collisional equilibrium
distribution with dn/da ~ a-3.5. This is the equivalent of a 160 km
radius large Centaur or medium sized Kuiper Belt
object of 1.0 g cm-3 density or a “comet
” of 260 km radius and 0.40 g cm-3 density. The warm dust mass is much larger than that of a solar system comet (1012 – 1015 kg), but is very similar to the mass of a Kuiper Belt
object (1019 – 1021 kg). The amount of water tied up in the observed material, ~1019 kg, is > 0.1% of the water in the Earth’s oceans, & the amount of carbon is also considerable, ~1018 kg.
The team found that the best model for what is going on is that some process (e.g., planetary migration
) is dynamically exciting the Eta Corvi-equivalent of our solar system's Kuiper Belt
(KB), causing frequent collisions amongst Kuiper Belt objects (KBOs) and producing the observed copious KB dust. As part of this process, one or more of the excited KBOs was scattered onto an orbit that sent it into the inner system, where it collided with a planetary-class body at ~3 AU, releasing a large amount of thermally unprocessed, primitive ice and carbon-rich dust. Their analysis suggests that the system is likely a good analogue for the Late Heavy Bombardment
(LHB) processes that occurred in the early Solar System at 0.6 – 0.8 Gyr
after the formation of the Calcium-aluminium-rich inclusions (mineral
s such as olivine
s that are among the first solid
s condensed from the cooling protoplanetary disk
) and is thus worthy of further detailed study in order to understand the nature of our LHB. It is also a good system to perform a search for a rocky planetary body at ~3 AU (the impactee), and for a giant planet at ~115 AU (the KB dynamical stirrer at ~ the 3:2 resonance of the KB dust at 150 AU).
, Eta Corvi is called 左轄, Pinyin
: Zuǒxiá, meaning Left Linchpin, because this star is marking itself and stand alone in Left Linchpin asterism, Chariot
mansion (see : Chinese constellation
). 左轄 (Zuǒxiá), westernized into Tso Hea, but the name Tso Hea was designated for β Corvi
(Kraz) by R.H. Allen.
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
, the sixth-brightest star in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Corvus
Corvus (constellation)
Corvus is a small constellation in the southern sky. Its name is Latin for raven or crow. It includes only 11 stars visible to the naked eye...
. Two debris disks have been detected orbiting this star, one warm within a few AU and another out at ~150 AU.
Properties
This star is about 40% more massive than the Sun but is only about 30% of the Sun's age. The concentration of ironIron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
in its atmosphere is only about 93% that of the Sun's. The projected rotational velocity
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....
at the equator (v sin i) is a brisk 68 km/s.
The IRAS
IRAS
The Infrared Astronomical Satellite was the first-ever space-based observatory to perform a survey of the entire sky at infrared wavelengths....
satellite detected an excess of infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation from this star, beyond what would normally be expected for a stellar object of this class. Observations in the
submillimetre band
Submillimetre astronomy
Submillimetre astronomy or submillimeter astronomy is the branch of observational astronomy that is conducted at submillimetre wavelengths of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a...
confirmed the presence of excess dust in orbit around the star having about 60% of the mass of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
and a temperature of 80 K. The data indicated a debris disk
Debris disk
A debris disk is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks have been found around both evolved and young stars, as well as at least one debris disk in orbit around a...
with an estimated maximum radius of 180 A.U.
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
from the star, or 180 times the separation of the Earth and the Sun. (Compare to the Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
, which extends out to 55 A.U. from the Sun.)
Recent submillimeter observations confirm the presence of an outer flat, circumstellar disk of debris with an outer radius of 150 A.U. It is oriented at an inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
to the line of sight from the Earth. Most of the inner 100 A.U. of the disk is relatively free of material, which suggests it was cleared away by a planetary system. In addition, infrared radiation which appears to be from an inner, hotter, debris disk within 3.5 AU of the star has been observed.
Since the Poynting-Robertson effect
Poynting-Robertson effect
The Poynting–Robertson effect, also known as Poynting–Robertson drag, named after John Henry Poynting and Howard Percy Robertson, is a process by which solar radiation causes a dust grain in the Solar System to slowly spiral into the sun...
would cause the dust in the outer disk to spiral in to the star within 20 million years, much younger than the age of the system, the observed presence of dust in the outer disk means that it must be constantly replenished. It is thought that this happens by the collisions of planetesimal
Planetesimal
Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger...
s orbiting at a distance of about 150 A.U., which are repeatedly broken down into smaller and smaller pieces, eventually becoming dust. The origin of the inner disk is not clear. It may have originated from planetesimals recently having moved from the outer regions of the system into the inner system, in a process similar to the Late Heavy Bombardment
Late Heavy Bombardment
The Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...
in the history of the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, and subsequently being ground to dust by collisions.
Water- and Organics-rich Habitable Zone Dust possibly from a Late Heavy Bombardment
In 2010-2011, Dr. Carey Lisse of the Johns Hopkins UniversityJohns Hopkins University
The Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university based in Baltimore, Maryland, United States...
Applied Physics Laboratory and his group analyzed the Spitzer
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
IRS 5 – 35 μm spectrum of the warm, ~360K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
circumstellar dust and found that it showed clear evidence for warm, water- and carbon-rich dust at ~ 3 AU from the central star, in the system’s habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...
, uncoupled and in a separate reservoir from the system’s extended sub-mm dust ring at 150 ± 20 AU. Spectral features similar in kind and amplitude to those found for ultra-primitive, (i.e., formed very early in the lifetime of the Eta Corvi system) ~10 Myr
Myr
The symbol myr was formerly used in English-language geology, and remains as the standard usage in astronomy, as a unit of one million years.It is an abbreviation for 'million years' and lower case is used in geology, while upper case is used in astronomy....
old cometary material were found (water ice & gas, olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
s & pyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
s, amorphous carbon
Amorphous carbon
Amorphous carbon or free, reactive carbon, is an allotrope of carbon that does not have any crystalline structure. As with all glassy materials, some short-range order can be observed...
and metal sulfides), in addition to emissions due to impact produced silica and high temperature/pressure carbonaceous
Carbonaceous
Carbonaceous is the defining attribute of a substance rich in carbon. Particularly, carbonaceous hydrocarbons are very unsaturated, high-molecular-weight hydrocarbons, having an elevated carbon:hydrogen ratio....
phases. The warm dust is very primitive, and definitely not from an asteroidal parent body. A large amount, at least 3 x 1019 kg, of 0.1 – 1000 µm warm dust is present, in a roughly collisional equilibrium
Thermodynamic equilibrium
In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, radiative equilibrium, and chemical equilibrium. The word equilibrium means a state of balance...
distribution with dn/da ~ a-3.5. This is the equivalent of a 160 km
KM
KM, Km, or km may stand for:*Kilometre *Kernel methods*Kettle Moraine High School*Khmer language *Kuomintang , a centre-right political party in the Republic of China on Taiwan...
radius large Centaur or medium sized Kuiper Belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
object of 1.0 g cm-3 density or a “comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
” of 260 km radius and 0.40 g cm-3 density. The warm dust mass is much larger than that of a solar system comet (1012 – 1015 kg), but is very similar to the mass of a Kuiper Belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
object (1019 – 1021 kg). The amount of water tied up in the observed material, ~1019 kg, is > 0.1% of the water in the Earth’s oceans, & the amount of carbon is also considerable, ~1018 kg.
The team found that the best model for what is going on is that some process (e.g., planetary migration
Planetary migration
Planetary migration occurs when a planet or other stellar satellite interacts with a disk of gas or planetesimals, resulting in the alteration of the satellite's orbital parameters, especially its semi-major axis...
) is dynamically exciting the Eta Corvi-equivalent of our solar system's Kuiper Belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
(KB), causing frequent collisions amongst Kuiper Belt objects (KBOs) and producing the observed copious KB dust. As part of this process, one or more of the excited KBOs was scattered onto an orbit that sent it into the inner system, where it collided with a planetary-class body at ~3 AU, releasing a large amount of thermally unprocessed, primitive ice and carbon-rich dust. Their analysis suggests that the system is likely a good analogue for the Late Heavy Bombardment
Late Heavy Bombardment
The Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...
(LHB) processes that occurred in the early Solar System at 0.6 – 0.8 Gyr
Byr
Byr was formerly used in English-language geology and astronomy as a unit of one billion years. The "B" is an abbreviation for "billion" , with "yr" simply an abbreviation for "year". Today, the term gigaannum is also used, but Gy or Gyr are still sometimes used in English-language works...
after the formation of the Calcium-aluminium-rich inclusions (mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
s such as olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
s that are among the first solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
s condensed from the cooling protoplanetary disk
Protoplanetary disk
A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...
) and is thus worthy of further detailed study in order to understand the nature of our LHB. It is also a good system to perform a search for a rocky planetary body at ~3 AU (the impactee), and for a giant planet at ~115 AU (the KB dynamical stirrer at ~ the 3:2 resonance of the KB dust at 150 AU).
Name
In Chinese astronomyChinese astronomy
Astronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...
, Eta Corvi is called 左轄, Pinyin
Pinyin
Pinyin is the official system to transcribe Chinese characters into the Roman alphabet in China, Malaysia, Singapore and Taiwan. It is also often used to teach Mandarin Chinese and spell Chinese names in foreign publications and used as an input method to enter Chinese characters into...
: Zuǒxiá, meaning Left Linchpin, because this star is marking itself and stand alone in Left Linchpin asterism, Chariot
Chariot (Chinese constellation)
The Chariot mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the southern mansions of the Vermilion Bird.-Asterisms:...
mansion (see : Chinese constellation
Chinese constellation
Chinese constellations are the way the ancient Chinese grouped the stars. They are very different from the modern IAU recognized constellations. This is because the IAU was based on Greco-Roman astronomy instead of Chinese astronomy....
). 左轄 (Zuǒxiá), westernized into Tso Hea, but the name Tso Hea was designated for β Corvi
Beta Corvi
Beta Corvi is the second brightest star in the constellation of Corvus. It also has the name Kraz....
(Kraz) by R.H. Allen.