MOA-2009-BLG-387L
Encyclopedia
MOA-2009-BLG-387L is a red dwarf
in the Sagittarius
constellation that is host to the planet MOA-2009-BLG-387Lb
. The star is estimated to be nearly 20,000 light years away and approximately one fifth the mass of the Sun, although large confidence interval
s exist, reflecting the uncertainties in both the mass and distance. The star drew the attention of astronomers when it became the lens
of gravitational microlensing
event MOA-2009-BLG-387L, in which it eclipsed a background star and created distorted caustics
, an envelope of reflected or refracted light rays. Analysis of the caustic events and of follow-up observational data led to the planet's discovery, which was reported in February 2011.
collaboration (MOA) detected the star MOA-2009-BLG-387L eclipsing a background star in a microlensing event that was named MOA-2009-BLG-387. In a process called gravitational microlensing
, the star MOA-2009-BLG-387L became a lens
that created two distorted caustic
images. In the case of the microlensing event MOA-2009-BLG-387, these caustics produced a series of small "resonating" diffractions; such resonant-caustic events are valued because they tend to yield more information about an orbiting planet.
The first caustic event was detected by the South African Astronomical Observatory
(SAAO) on July 24, 2009. An alert was issued, which attracted many to cover the caustic event; as such, the end of the first caustic event was well-documented. The microlensing event's second caustic event was seven days later, an unusually long middle period for planetary microlensing events. An alert brought three different telescopes at SAAO and telescopes at ten different observatories to focus on the event.
Follow-up observations on the star MOA-2009-BLG-387L using the NACO imager at the Very Large Telescope
array successfully distinguished the star's mass. The collected data from VLT and from observations during the microlensing event was run through a series of models and analyzed. An orbiting planetary body larger than Jupiter (or of a similar size, given uncertainties) was discovered. The discovery of the planet was reported on February 21, 2011 in the journal Astronomy and Astrophysics
.
in the Sagittarius
constellation. It is estimated to be 5700 parsec
s (18,591 light years) away, although uncertainty has led the discovering team to place the confidence interval
s at ± 2200 parsecs (7,176 light years); in other words, although the distance of MOA-2009-BLG-387L from Earth is best placed at 5700 parsecs, astronomers can only be 90% certain that it is somewhere between 3,500 and 7,900 parsecs away. Likewise, although MOA-2009-BLG-387L's mass has been estimated at 0.19 times that of the Sun, the confidence intervals remain large , as uncertainty in the mass of the planet places its true mass between 0.07 and 0.49 times the mass of the Sun. This covers the entirety of the range of masses known in red dwarfs.
The ratio between planet MOA-2009-BLG-387Lb's mass to that of its host star has been found with accuracy. However, because the host star's characteristics are not as well-constrained, the planet's characteristics are not well-constrained either. The inability to constrain many of MOA-2009-BLG-387L's characteristics is a consequence of the fact that the star acted as the lens
in the microlensing event, which compromised the ability to collect most of the star's stellar parameters.
. However, because knowledge of the exact parameters of the planet are tied to the host star's parameters, and the host star's parameters are not well-constrained, uncertainty places MOA-2009-BLG-387Lb's mass between 1.0 and 6.7 times that of Jupiter. The planet is estimated to orbit its host star every 1970 days at a distance of 1.8 AU
, some 1.8 times the mean distance between Earth and the Sun. Uncertainty broadens the mean distance to between 1.1 and 2.7 AU.
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
in the Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
constellation that is host to the planet MOA-2009-BLG-387Lb
MOA-2009-BLG-387Lb
MOA-2009-BLG-387Lb is a planet in the orbit of the red dwarf MOA-2009-BLG-387L. Its discovery was announced on February 21, 2011, making it the eleventh planet discovered using gravitational microlensing. The planet is thought to be over twice the mass of Jupiter and to have an orbit 80 percent...
. The star is estimated to be nearly 20,000 light years away and approximately one fifth the mass of the Sun, although large confidence interval
Confidence interval
In statistics, a confidence interval is a particular kind of interval estimate of a population parameter and is used to indicate the reliability of an estimate. It is an observed interval , in principle different from sample to sample, that frequently includes the parameter of interest, if the...
s exist, reflecting the uncertainties in both the mass and distance. The star drew the attention of astronomers when it became the lens
Lens
-Optics:*Lens , an optical element which converges or diverges light**Lens , a part of the eye**Corrective lens for correction of human vision***Contact lens, placed on the cornea of the eye**Photographic lens, a lens designed for use on a camera...
of gravitational microlensing
Gravitational microlensing
Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects ranging from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit lots of light ...
event MOA-2009-BLG-387L, in which it eclipsed a background star and created distorted caustics
Caustic (optics)
In optics, a caustic or caustic network is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an...
, an envelope of reflected or refracted light rays. Analysis of the caustic events and of follow-up observational data led to the planet's discovery, which was reported in February 2011.
Observational history
On July 24, 2009, the Microlensing Observations in AstrophysicsMicrolensing Observations in Astrophysics
Microlensing Observations in Astrophysics is a collaborative project between researchers in New Zealand and Japan, led by Professor Yasushi Muraki of Nagoya University. They use microlensing to observe dark matter, extra-solar planets, and stellar atmospheres from the Southern Hemisphere...
collaboration (MOA) detected the star MOA-2009-BLG-387L eclipsing a background star in a microlensing event that was named MOA-2009-BLG-387. In a process called gravitational microlensing
Gravitational microlensing
Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects ranging from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit lots of light ...
, the star MOA-2009-BLG-387L became a lens
Lens
-Optics:*Lens , an optical element which converges or diverges light**Lens , a part of the eye**Corrective lens for correction of human vision***Contact lens, placed on the cornea of the eye**Photographic lens, a lens designed for use on a camera...
that created two distorted caustic
Caustic (optics)
In optics, a caustic or caustic network is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an...
images. In the case of the microlensing event MOA-2009-BLG-387, these caustics produced a series of small "resonating" diffractions; such resonant-caustic events are valued because they tend to yield more information about an orbiting planet.
The first caustic event was detected by the South African Astronomical Observatory
South African Astronomical Observatory
South African Astronomical Observatory is the national center for optical and infrared astronomy in South Africa. It was established in 1972. The observatory is run by the National Research Foundation of South Africa. The facility's function is to conduct research in astronomy and astrophysics...
(SAAO) on July 24, 2009. An alert was issued, which attracted many to cover the caustic event; as such, the end of the first caustic event was well-documented. The microlensing event's second caustic event was seven days later, an unusually long middle period for planetary microlensing events. An alert brought three different telescopes at SAAO and telescopes at ten different observatories to focus on the event.
Follow-up observations on the star MOA-2009-BLG-387L using the NACO imager at the Very Large Telescope
Very Large Telescope
The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
array successfully distinguished the star's mass. The collected data from VLT and from observations during the microlensing event was run through a series of models and analyzed. An orbiting planetary body larger than Jupiter (or of a similar size, given uncertainties) was discovered. The discovery of the planet was reported on February 21, 2011 in the journal Astronomy and Astrophysics
Astronomy and Astrophysics
* Astronomy and Astrophysics has a 2010 impact factor of 4.410.-See also:*The Astronomy and Astrophysics Review*Advanced Satellite for Cosmology and Astrophysics*Astronomy & Geophysics*Astronomical Journal*Astrophysical Journal...
.
Characteristics
MOA-2009-BLG-387L is an M-type red dwarfRed dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
in the Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
constellation. It is estimated to be 5700 parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s (18,591 light years) away, although uncertainty has led the discovering team to place the confidence interval
Confidence interval
In statistics, a confidence interval is a particular kind of interval estimate of a population parameter and is used to indicate the reliability of an estimate. It is an observed interval , in principle different from sample to sample, that frequently includes the parameter of interest, if the...
s at ± 2200 parsecs (7,176 light years); in other words, although the distance of MOA-2009-BLG-387L from Earth is best placed at 5700 parsecs, astronomers can only be 90% certain that it is somewhere between 3,500 and 7,900 parsecs away. Likewise, although MOA-2009-BLG-387L's mass has been estimated at 0.19 times that of the Sun, the confidence intervals remain large , as uncertainty in the mass of the planet places its true mass between 0.07 and 0.49 times the mass of the Sun. This covers the entirety of the range of masses known in red dwarfs.
The ratio between planet MOA-2009-BLG-387Lb's mass to that of its host star has been found with accuracy. However, because the host star's characteristics are not as well-constrained, the planet's characteristics are not well-constrained either. The inability to constrain many of MOA-2009-BLG-387L's characteristics is a consequence of the fact that the star acted as the lens
Lens
-Optics:*Lens , an optical element which converges or diverges light**Lens , a part of the eye**Corrective lens for correction of human vision***Contact lens, placed on the cornea of the eye**Photographic lens, a lens designed for use on a camera...
in the microlensing event, which compromised the ability to collect most of the star's stellar parameters.
Planetary system
MOA-2009-BLG-387Lb is the only known exoplanet in the orbit of host star MOA-2009-BLG-387L. The planet is estimated to be 2.6 times the mass of JupiterJupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
. However, because knowledge of the exact parameters of the planet are tied to the host star's parameters, and the host star's parameters are not well-constrained, uncertainty places MOA-2009-BLG-387Lb's mass between 1.0 and 6.7 times that of Jupiter. The planet is estimated to orbit its host star every 1970 days at a distance of 1.8 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
, some 1.8 times the mean distance between Earth and the Sun. Uncertainty broadens the mean distance to between 1.1 and 2.7 AU.