gjdonatiello
Pleiades (Messier 45)
Messier 45 - The Pleiades
Credit: Giuseppe Donatiello
RA 3h 47m Dec +24° 07′
The Pleiades or Seven Sisters (Messier 45 or M45), is an open star cluster containing some hot middle-aged B-type stars located in the constellation of Taurus. It is among the closest star clusters to Earth and is the most visible to the naked eye in the night sky, excluding the Hyades, Alpha Persei, Coma Berenices and Lambda Orionis groups.
The distance to the Pleiades can be used as an important first step in calibrating the cosmic distance ladder.
More recent results, using the Gaia satellite (September 2016), put it at 134 ±6 pc.
After decades of investigation, there are still those who believe that the cirrus clouds in the Pleiades are the remnants of their formation. How true is this?
With an estimated age of 130 ± 20 Myr (Barrado y Navascués et al. 2004), M45 is not as young as previously thought.
The most massive members are: Alcyone, Electra, Atlas, Maia, Merope, Taygeta, Pleione and Celeno. Some of them are Be stars, however less than 8 solar masses. It should be noted, however, that some are binary and multiple systems, so the real masses of the individual components could be lower [A&A 425, L45-L48 (2004)].
The group contains mainly A and F class stars, therefore between about 1 and 2.5 solar masses. Of course, there are red dwarfs and substellar objects such as numerous brown dwarfs. Considering the estimated age, all stars with masses greater than 8 times that of the Sun have already exploded as supernovae millions of years ago.
Some of the brightest stars are now in the process of evolving into red giants, and some have already done so, as evidenced by some massive white dwarfs.
If we had observed the Pleiades a few million years ago, we would have seen a nice mix of white stars and red giants, as in some younger OCs.
Regardless, M45 could not have remnants of the original cloud since they usually only last a few million years before being blown away by the radiation pressure exerted by the more massive stars.
Those clouds, which many believe to be remnants of the original hydrogen cloud, are therefore cirrus clouds belonging to the larger Taurus Molecular Cloud (TMC-1) that the cluster is now passing through. Cirrus clouds only scatter the light of nearby stars. That the cluster and the cloud are not related can be seen from their mutual, almost opposite, movements (Steven J. Gibson and Kenneth H. Nordsieck 2003 ApJ 589 362)
The Pleiades are moving towards the constellation of Orion and will resist for another 250 million years before they completely disintegrate under the effects of the tidal forces exerted by the Milky Way.
Pleiades (Messier 45)
Messier 45 - The Pleiades
Credit: Giuseppe Donatiello
RA 3h 47m Dec +24° 07′
The Pleiades or Seven Sisters (Messier 45 or M45), is an open star cluster containing some hot middle-aged B-type stars located in the constellation of Taurus. It is among the closest star clusters to Earth and is the most visible to the naked eye in the night sky, excluding the Hyades, Alpha Persei, Coma Berenices and Lambda Orionis groups.
The distance to the Pleiades can be used as an important first step in calibrating the cosmic distance ladder.
More recent results, using the Gaia satellite (September 2016), put it at 134 ±6 pc.
After decades of investigation, there are still those who believe that the cirrus clouds in the Pleiades are the remnants of their formation. How true is this?
With an estimated age of 130 ± 20 Myr (Barrado y Navascués et al. 2004), M45 is not as young as previously thought.
The most massive members are: Alcyone, Electra, Atlas, Maia, Merope, Taygeta, Pleione and Celeno. Some of them are Be stars, however less than 8 solar masses. It should be noted, however, that some are binary and multiple systems, so the real masses of the individual components could be lower [A&A 425, L45-L48 (2004)].
The group contains mainly A and F class stars, therefore between about 1 and 2.5 solar masses. Of course, there are red dwarfs and substellar objects such as numerous brown dwarfs. Considering the estimated age, all stars with masses greater than 8 times that of the Sun have already exploded as supernovae millions of years ago.
Some of the brightest stars are now in the process of evolving into red giants, and some have already done so, as evidenced by some massive white dwarfs.
If we had observed the Pleiades a few million years ago, we would have seen a nice mix of white stars and red giants, as in some younger OCs.
Regardless, M45 could not have remnants of the original cloud since they usually only last a few million years before being blown away by the radiation pressure exerted by the more massive stars.
Those clouds, which many believe to be remnants of the original hydrogen cloud, are therefore cirrus clouds belonging to the larger Taurus Molecular Cloud (TMC-1) that the cluster is now passing through. Cirrus clouds only scatter the light of nearby stars. That the cluster and the cloud are not related can be seen from their mutual, almost opposite, movements (Steven J. Gibson and Kenneth H. Nordsieck 2003 ApJ 589 362)
The Pleiades are moving towards the constellation of Orion and will resist for another 250 million years before they completely disintegrate under the effects of the tidal forces exerted by the Milky Way.