Messier 67 | |
---|---|
Observation data (J2000.0 epoch) | |
Right ascension | 08h 51.3m |
Declination | +11° 49′ |
Distance | ~2.61–2.93 kly (800–900 pc [1] [2] [3] [4] ) |
Apparent magnitude (V) | 6.1 |
Apparent dimensions (V) | 30.0′ |
Physical characteristics | |
Radius | 10 ly [ citation needed ] |
Estimated age | 3.2 to 5 billion years |
Other designations | NGC 2682, Cr 204 |
Associations | |
Constellation | Cancer |
Messier 67 (also known as M67 or NGC 2682) and sometimes called the King Cobra Cluster or the Golden Eye Cluster [5] is an open cluster in the southern, equatorial half of Cancer. It was discovered by Johann Gottfried Koehler in 1779. Estimates of its age range between 3.2 and 5 billion years. Distance estimates are likewise varied, but typically are 800–900 parsecs (2,600–2,900 ly). [1] [2] [3] [4] Estimates of 855, 840, and 815 pc were established via binary star modelling and infrared color-magnitude diagram fitting. [2] [3] [4]
M67 is not the oldest known open cluster, several Milky Way clusters are known to be older, yet farther than M67. It is a paradigm study object in stellar evolution: [6]
M67 is one of the most-studied open clusters, yet estimates of its physical parameters such as age, mass, and number of stars of a given type, vary substantially. Richer et al. estimate its age to be 4 billion years, its mass to be 1080 solar masses (M☉), and number its white dwarfs at 150. [7] Hurley et al. estimate its current mass to be 1,400 M☉ and its initial mass to be approximately 10 times as great. [8]
It has more than 100 stars similar to the Sun, and numerous red giants. The total star count has been estimated at well over 500. [9] The ages and prevalence of Sun-like stars had led some astronomers to theorize it as the possible parent cluster of the Sun. [10] However, computer simulations disagree on whether the outer Solar System would have survived an ejection from M67, [11] [12] and the cluster itself would probably not have survived such an ejection event. [13]
The cluster contains no main sequence stars bluer (hotter) than spectral type F, other than perhaps some of the blue stragglers, since the brighter stars of that age have already left the main sequence. In fact, when the stars of the cluster are plotted on the Hertzsprung-Russell diagram, there is a distinct "turn-off" representing the stars which have terminated hydrogen fusion in the core and are destined to become red giants. As a cluster ages, the turn-off moves progressively down the main sequence to cooler stars.
It appears that M67 has a bias toward heavier stars. One cause of this is mass segregation, the process by which lighter stars gain speed at the expense of more massive stars during close encounters, which moves them to greater average distance from the center of the cluster or allows escape altogether. [14]
A March 2016 joint AIP/JHU study by Barnes et al. on rotational periods of 20 Sun-like stars, measured by the effects of moving starspots on light curves, suggests that these approximately 4 billion-year old stars spin in about 26 days – like the Sun, which has a period at the equator of 25.38 days. [15] Measurements were carried out as part of the extended K2 mission of Kepler space telescope. This reinforces the applicability of many key properties of the sun to stars of the same size and age, a fundamental principle of modern solar and stellar physics. [16] The authors abbreviate this as the "solar-stellar connection". [16]
A radial velocity survey of M67 has found exoplanets around five stars in the cluster: YBP 1194, YBP 1514, YBP 401, Sand 978, and Sand 1429. [17] [18] [19] [20] A sixth star, Sand 364, was also thought to have a planet, but a follow-up study did not find evidence for it and concluded that the radial velocity variations have a non-planetary origin, likely stellar variability. [21]
Scutum is a small constellation. Its name is Latin for shield, and it was originally named Scutum Sobiescianum by Johannes Hevelius in 1684. Located just south of the celestial equator, its four brightest stars form a narrow diamond shape. It is one of the 88 IAU designated constellations defined in 1922.
The Butterfly Cluster is an open cluster of stars in the southern constellation of Scorpius. Its name derives from the resemblance of its shape to a butterfly.
The Wild Duck Cluster is an open cluster of stars in the constellation Scutum. It was discovered by Gottfried Kirch in 1681. Charles Messier included it in his catalogue of diffuse objects in 1764. Its popular name derives from the brighter stars forming a triangle which could resemble a flying flock of ducks. The cluster is located just to the east of the Scutum Star Cloud midpoint.
Xi Boötis, Latinised from ξ Boötis, is a binary star system located at a distance of 22 light-years away from Earth. It is the nearest visible star in the constellation Boötes. The brighter, primary component of the pair has a visual magnitude of 4.70, making it visible to the naked eye.
Messier 19 or M19 is a globular cluster in the constellation Ophiuchus. It was discovered by Charles Messier on June 5, 1764 and added to his catalogue of comet-like objects that same year. It was resolved into individual stars by William Herschel in 1784. His son, John Herschel, described it as "a superb cluster resolvable into countless stars". The cluster is located 4.5° WSW of Theta Ophiuchi and is just visible as a fuzzy point of light using 50 mm (2.0 in) binoculars. Using a telescope with a 25.4 cm (10.0 in) aperture, the cluster shows an oval appearance with a 3′ × 4′ core and a 5′ × 7′ halo.
Messier 21 or M21, also designated NGC 6531 or Webb's Cross, is an open cluster of stars located to the north-east of Sagittarius in the night sky, close to the Messier objects M20 to M25. It was discovered and catalogued by Charles Messier on June 5, 1764. This cluster is relatively young and tightly packed. A few blue giant stars have been identified in the cluster, but Messier 21 is composed mainly of small dim stars. With a magnitude of 6.5, M21 is not visible to the naked eye; however, with the smallest binoculars it can be easily spotted on a dark night. The cluster is positioned near the Trifid nebula, but is not associated with that nebulosity. It forms part of the Sagittarius OB1 association.
Messier 23, also known as NGC 6494, is an open cluster of stars in the northwest of the southern constellation of Sagittarius. It was discovered by Charles Messier in 1764. It can be found in good conditions with binoculars or a modestly sized telescope. It is in front of "an extensive gas and dust network", which there may be no inter-association. It is within 5° the sun's position so can be occulted by the moon.
Messier 26, also known as NGC 6694, is an open cluster of stars in the southern constellation of Scutum. It was discovered by Charles Messier in 1764. This 8th magnitude cluster is a challenge to find in ideal skies with typical binoculars, where it can be, with any modern minimum 3-inch (76 mm) aperture device. It is south-southwest of the open cluster Messier 11 and is 14′ across. About 25 stars are visible in a telescope with a 150–200 mm (6–8 in) aperture.
Messier 18 or M18, also designated NGC 6613 and sometimes known as the Black Swan Cluster, is an open cluster of stars in the constellation Sagittarius. It was discovered by Charles Messier in 1764 and included in his list of comet-like objects. From the perspective of Earth, M18 is situated between the Omega Nebula (M17) and the Small Sagittarius Star Cloud (M24).
Messier 37 is the brightest and richest open cluster in the constellation Auriga. It was discovered by the Italian astronomer Giovanni Battista Hodierna before 1654. M37 was missed by French astronomer Guillaume Le Gentil when he rediscovered M36 and M38 in 1749. French astronomer Charles Messier independently rediscovered M37 in September 1764 but all three of these clusters were recorded by Hodierna. It is classified as Trumpler type I,1,r or I,2,r.
Solar-type stars, solar analogs, and solar twins are stars that are particularly similar to the Sun. The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type. Observations of these stars are important for understanding better the properties of the Sun in relation to other stars and the habitability of planets.
58 Eridani is a main-sequence star in the constellation Eridanus. It is a solar analogue, having similar physical properties to the Sun. The star has a relatively high proper motion across the sky, and it is located 43 light years distant. It is a probable member of the IC 2391 moving group of stars that share a common motion through space.
The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster of stars in the northern constellation of Perseus. To the naked eye, the cluster consists of several blue-hued spectral type B stars. The most luminous member is the ~2nd magnitude white-yellow supergiant Mirfak, also known as Alpha Persei. Bright members also include Delta, Sigma, Psi, 29, 30, 34, and 48 Persei. The Hipparcos satellite and infrared color-magnitude diagram fitting have been used to establish a distance to the cluster of ~560 light-years (172 pc). The distance established via the independent analyses agree, thereby making the cluster an important rung on the cosmic distance ladder. As seen from the Earth, the extinction of the cluster due to interstellar dust is around 0.30.
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.
IC 4651 is an open cluster of stars located about 2,900 light years distant in the constellation Ara. It was first catalogued by John Louis Emil Dreyer in his 1895 version of the Index Catalogue. This is an intermediate age cluster that is 1.2 ± 0.2 billion years old. Compared to the Sun, the members of this cluster have a higher abundance of the chemical elements other than hydrogen and helium. The combined mass of the active stars in this cluster is about 630 times the mass of the Sun.
29 Persei is a single star in the northern constellation of Perseus, located approximately 640 light years away from the Sun based on parallax. It is visible to the naked eye as faint, blue-white hued star with an apparent visual magnitude of 5.16. This object is a member of the Alpha Persei Cluster.
139 Tauri is a single, blue-white hued star in the zodiac constellation of Taurus. It is faintly visible to the naked eye with an apparent visual magnitude of 4.81. The distance to this star, as determined from an annual parallax shift of 2.10±0.19 mas, is roughly 1,600 light years. Because this star is located near the ecliptic, it is subject to occultations by the Moon. One such event was observed April 28, 1990.
33 Pegasi is the Flamsteed designation for a visual binary star in the northern constellation of Pegasus. It has an apparent visual magnitude of 6.2, placing it near the limit of naked eye visibility. Measurements show an annual parallax shift of 0.0298125″, which is equivalent to a distance of 109 ly (33 pc) from the Sun. It is drifting further away with a radial velocity of 24 km/s.
YBP 1194 is a G-type main-sequence star, class G5V, in the open cluster Messier 67, about 2,890 light-years from the Sun in the constellation Cancer. It is a solar twin, having the near exact same temperature and mass as the Sun. YBP 1194 has a slightly higher metallicity than the Sun, and may be slightly younger at an age of 3.5-4.8 billion years. In January 2014, this star was announced to have an exoplanet. It is packed in a small cluster, Messier 67, with a radius of 10 light-years, with over 500 other stars. For comparison, the Sun has 9 star systems within 10 light-years and 94 star systems within 20 light-years.
HD 165185 is the Henry Draper Catalogue designation for a star in the southern zodiac constellation of Sagittarius. It has an apparent visual magnitude of 5.94, which indicates it is a sixth magnitude star that is faintly visible to the naked eye. Parallax measurements give an estimated distance of 55.8 light years from the Sun. It is drifting further away with a heliocentric radial velocity of +15.4 km/s.