NGC 7142
Encyclopedia
NGC 7142 is an open cluster
about 6,200 light-year
s away in the constellation
Cepheus
.
NGC 7129
, which is a first indication that the cluster may be obscured by an interstellar cloud
. Many studies have demonstrated this to be true dating back to the earliest investigations of this cluster. A thorough study of the Cepheus region concluded "that no part of the field may be considered unobscured."
Other astronomers have noted that the reddening across the face of this cluster is likely to be uneven . The visibility of several background galaxies
in the NW corner of the cluster indicate that the obscuring medium may be lowest here.
Estimates of the amount of reddening range from 0.18 magnitude
s, to as high as 0.41 magnitudes.
(although age determinations for these two clusters varies wildly in the literature). This makes it one of the oldest open clusters currently known.
range from 12.5 to 14.5.
s.
.
Open cluster
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...
about 6,200 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away 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....
Cepheus
Cepheus (constellation)
Cepheus is a constellation in the northern sky. It is named after Cepheus, King of Aethiopia in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.-Stars:...
.
Observational Difficulties
NGC 7142 is located near the reflection nebulaReflection nebula
In Astronomy, reflection nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars. The energy from the nearby star, or stars, is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust...
NGC 7129
NGC 7129
NGC 7129 is a reflection nebula located 3,300 light years away in the constellation Cepheus. A young open cluster is responsible for illuminating the surrounding nebula. A recent survey indicates the cluster contains more than 130 stars less than 1 million years old...
, which is a first indication that the cluster may be obscured by an interstellar cloud
Interstellar cloud
Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium. Depending on the density, size and temperature of a given cloud, the hydrogen in it...
. Many studies have demonstrated this to be true dating back to the earliest investigations of this cluster. A thorough study of the Cepheus region concluded "that no part of the field may be considered unobscured."
Other astronomers have noted that the reddening across the face of this cluster is likely to be uneven . The visibility of several background galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
in the NW corner of the cluster indicate that the obscuring medium may be lowest here.
Estimates of the amount of reddening range from 0.18 magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
s, to as high as 0.41 magnitudes.
Age
Due to the uncertain amount of interstellar reddening, precise determination of age for this cluster has been especially difficult. Based on NGC 7142's Color-magnitude diagram, it is believed that this cluster is close in age to the old open clusters M 67 and NGC 188NGC 188
NGC 188 is an open cluster in the constellation Cepheus. It was discovered by John Herschel in 1825.Unlike most open clusters that drift apart after a few million years because of the gravitational interaction of our galaxy, NGC 188 lies far above the plane of the galaxy and is one of the most...
(although age determinations for these two clusters varies wildly in the literature). This makes it one of the oldest open clusters currently known.
Distance
The distance to this cluster has also been difficult to determine, again, owing to the absorption. Estimates for the Distance modulusDistance modulus
-Definition:The distance modulus \mu=m-M is the difference between the apparent magnitude m and the absolute magnitude M of an astronomical object...
range from 12.5 to 14.5.
Variable Stars
Due to the similarities between NGC 7142 and NGC 188 in both age and density, some astronomers have speculated that NGC 7142 should be home to a high number of a rare type of variable star known as W UMa since NGC 188 has a high number. Crinklaw & Talbert conducted a search for such stars in 1991, but their study only revealed one variable star. However, their investigation only spanned two days, which did not afford enough data points to determine the type of variable. Roughly two more nights of data were appended to the beginning of the Crinklaw & Talbert study but have still not given enough information to classify the variable star.Other Oddities
Although thought to be an old cluster, NGC 7142 contains a surprisingly high number of blue stars. This runs contrary to the standard model of cluster evolution which predicts that old clusters should be devoid of such stars since bluer stars are more massive and thus evolve and die off faster, which should prevent them from still being present. Such stars are said to be blue stragglerBlue straggler
Blue stragglers are main sequence stars in open or globular clusters that are more luminous and bluer than stars at the main sequence turn-off point for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3...
s.
Ongoing research
Due to the observational difficulties NGC 7142 presents, it has been an infrequent topic of research. Current known studies include only work being done at the University of KansasUniversity of Kansas
The University of Kansas is a public research university and the largest university in the state of Kansas. KU campuses are located in Lawrence, Wichita, Overland Park, and Kansas City, Kansas with the main campus being located in Lawrence on Mount Oread, the highest point in Lawrence. The...
.