Distance Indicator
Objects whose luminosities or diameters are known; used to find the distance to a star cluster or galaxy.
Distance Modulus ...
distance indicator: Object whose luminosity or diameter is known; used to find the distance to a star cluster or galaxy.
Primary Distance Indicator - A type of object, such a Cepheid variable, for which we know the size or brightness by observing them in the Milky Way ...
Physical distance indicators, used on progressively larger distance scales, include: ...
"Exotic" Distance Indicators
All of the above methods rely on a straightforward application of the inverse-square law or the angular diameter-distance relation.
This allows them to be used as "standard candles" and are thus important distance indicators for the extragalactic distance scale. Chandrasekhar limit The theoretical upper limit at which a stellar remnant can form a white dwarf.
gave the name "Cepheid variables" to the world (the set including Mekbuda in Gemini and even Polaris), regularly oscillating stars whose luminosities are proportional to their few-day periods and that provide us with the best distance indicators to ...
One very appealing attribute of Cepheid variables as a class of distance indicators is that the physics for the Cepheid period-luminosity relation is well understood.
Novae as distance indicators
Novae have some promise for use as standard candles. For instance, the distribution of their absolute magnitude is bimodal, with a main peak at magnitude -7.5, and a lesser one at -8.8.
There have been a number of difficulties associated with using Cepheids as distance indicators. Until recently, astronomers used photographic plates to measure the fluxes from stars.
In general, we use accurately determined distance indicators for small distance to calibrate distance indicators for greater distances. We have to use quite a few distance indicators because there is no single one that can measure all the distances.
Each new distance indicator, each new standard candle, requires calibration from objects whose distances depend upon other techniques.
Using Hubble's law as their distance indicator, these researchers are compiling a catalog of the positions and redshifts of all galaxies within about 250 Mpc of our Galaxy.
Planetary Nebulae - these are pretty hot and produce a lot of UV light, so they can be seen distinctly from other things in the galaxy; pretty reliable as distance indicators ...
In this way Cepheid variable stars can be used as one of the 'standard candles' in the Universe that act either as distance indicators themselves or can be used to calibrate (or set the zero point for) other distance indicators.
Astronomers then correct for the luminosity difference before using the supernova as a distance indicator. Consequently, SNIa are very precise distance indicators that can be observed over large distances.
With such rapid follow-up, Type Ia supernovae have become one of the primary distance indicators in astronomy, helping to tie down the Hubble constant and revealing that the Universe is, in fact, accelerating.
A general term for any astronomical object whose absolute magnitude can be inferred from its other observed characteristics, and which is therefore useful as a distance indicator.
star - (n.) ...
The Cepheid stars have taken on an even more important role since the Hubble Space Telescope Key Project on the extragalactic distance scale relies completely on them for the calibration of distance indicators to reach cosmologically large distances.
For example, the periods of Cepheids variables have been calibrated to reveal the absolute magnitudes, which can then be used to find distances. Thus astronomers say Capheids have been calibrated as distance indicators.
They have periods of less than one day, and all have roughly the same intrinsic brightness. The latter feature, along with their wide distribution throughout the galaxy, makes them another useful distance indicator.
which makes them almost 50 times more luminous than the Sun. They are Population II objects often (but not always) present in globular clusters. RR Lyrae stars are valid distance indicators out to more than 200 kpc.
RR Lyrae variables can still be employed as distance indicators because their absolute magnitudes tend to be alike. Short-period Cepheids belong to Population II, a class of older stars found in the core and in the halo of the Milky Way Galaxy.
The horizontal branch also contains the RR Lyrae variable stars, where the Cepheid instability strip crosses the horizontal branch. Like the Cepheid variables, RR Lyrae stars are also useful as distance indicators.
away from us with a velocity that is proportional to distance. The redshift of the light from these galaxies is therefore a measure of their distance. This distance measure, however, can only be calibrated against standard candle distance indicators.
 See also: Distance, Star, Galaxies, Galaxy, Light
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