A galaxy that is much smaller than other members of the elliptical class; it is designated as dE. A subtype of dwarf ellipticals is called a dwarf spheroidal galaxy (dSph). The basic characteristics o
f the class are low surface brightness and smooth light distribution. They range in luminosity from that of the faintest dSph galaxies M_V ~ -9 to about -17. In the Local Group there are 19 known dEs. They are very common in galaxy clusters.
A small, low luminosity galaxy that is associated with a larger spiral galaxy and may make up part of a galactic halo. There are many of them in the Local Group, and often orbit around larger galaxies
such as the Milky Way and the Andromeda Galaxy. There are three main types of them: dwarf elliptical galaxy (dE), dwarf irregular galaxy (dI), and dwarf spiral galaxy (dSA).
An irregular galaxy that is much smaller than other irregulars. Dwarf irregulars are generally metal poor and have relatively high fractions of gas. They are thought to be similar to the earliest gala
xies that populated the Universe, and are therefore important to understand the overall evolution of galaxies.
An irregular galaxy that is much smaller than other irregulars. Dwarf irregulars are generally metal poor and have relatively high fractions of gas. They are thought to be similar to the earliest gala
xies that populated the Universe, and are therefore important to understand the overall evolution of galaxies.
A class of novae and cataclysmic variables that have multiple observed eruptions. Their prototype is U Geminorum star. Optically, dwarf nova eruptions have amplitudes of 2-6 mag in V, a duration of a
few to 20 days and a recurrence time-scale of weeks to years. Dwarf novae are thought to be semidetached binary stars consisting of a white dwarf primary accreting via Roche lobe overflow from a companion which is usually a late-type, generally main-sequence star. DN outbursts are usually attributed to the release of gravitational energy resulting from an instability in the accretion disk or by sudden mass transfers through the disk.
A class of novae and cataclysmic variables that have multiple observed eruptions. Their prototype is U Geminorum star. Optically, dwarf nova eruptions have amplitudes of 2-6 mag in V, a duration of a
few to 20 days and a recurrence time-scale of weeks to years. Dwarf novae are thought to be semidetached binary stars consisting of a white dwarf primary accreting via Roche lobe overflow from a companion which is usually a late-type, generally main-sequence star. DN outbursts are usually attributed to the release of gravitational energy resulting from an instability in the accretion disk or by sudden mass transfers through the disk.
A class of novae and cataclysmic variables that have multiple observed eruptions. Their prototype is U Geminorum star. Optically, dwarf nova eruptions have amplitudes of 2-6 mag in V, a duration of a
few to 20 days and a recurrence time-scale of weeks to years. Dwarf novae are thought to be semidetached binary stars consisting of a white dwarf primary accreting via Roche lobe overflow from a companion which is usually a late-type, generally main-sequence star. DN outbursts are usually attributed to the release of gravitational energy resulting from an instability in the accretion disk or by sudden mass transfers through the disk.