Standard candles

Nk., NK.a66rcc. (Normalkerze) standard candle. d1, abbrev. (nicht Ibslich) not soluble, mn, abbrev. (nachmittags) afternoon, p.m. 

When it became possible to obtain the spectrum of one of these objects in 1937, it was obvious that they looked like nothing yet known. All supernovas discovered in subsequent years displayed a remarkable uniformity, both in intensity and in behaviour. This observation led Zwicky to suggest that they might be used as standard candles to calibrate distance across the cosmos. But then, in 1940, a supernova with a completely different spectrum was discovered. It soon became clear that there were at least two classes of supernova, distinguished by their spectral features. It was the presence or absence of the Balmer lines of hydrogen near the maximum of the light curve that provided this classification. 

The cosmological parameters and a can be determined from the Hubble diagram, provided that we have some well-calibrated cosmological standard candle that can be observed across a wide range of redshifts. This is precisely the approach adopted by Riess et al. (1998) and Perhnutter et al. (1999) when they used the type la supernovas. Pilar Ruiz-Lapuente at the University of Barcelona and Renald Pain at the University of Paris both made contributions to this exemplary cosmological programme. 

Astronomers use a variety of methods to determine the distance to objects in the universe. One of the most effective is the standard candle provided by Type la supemovae. These supemovae originate in a binary star system when a white dwarf star accretes matter from its companion. When the white dwarf reaches the Chandrasekhar limit of 1.4 solar masses, a thermonuclear runaway occurs that completely disrupts the star in a cataclysmic explosion that makes the supernova as bright as an entire galaxy. Because Type la supemovae occur in stars with similar masses and because the nuclear burning affects the entire star, they all have essentially the same intrinsic brightness and their apparent brightness observed from Earth can be used to derive the distance to the supernova. 

The standard candle, used by Mr. Waienr consumed one hundred and thirty grains per hour, and for this, to insure a greater regularity of flame, a No. 2 fish-tail, burning -4 feet per hour, was substituted, and found exactly equal to the candle. 

In the first of the following tables, the results are multiplied by one hundred and thirty, and divided by one hnndred and twenty, so as to reduce them to a standard candle of one hundred and twenty grams per hour, as dene by Mr. King... 

Candlepower is the luminous intensity in terms of a standard candle (a candle made of sperm wax, six to the pound, which bums 120grains of wax per hr). It is equal to 1.11 Hefner units Ref Hackh s (1944), 163... 

Briefly, astronomers have two basic methods for estimating distance scales for spiral galaxies that are independent of the observation of special standard candles such as supernovae. 

Cosmology with supernovae has developed over the second half of the last century. Their extreme luminosities always made them attractive candidates to measure large distances. Various methods were devised to use supernovae to measure cosmological parameters ranging from simple standard candle paradigms to physical explanations of the supernova explosions and subsequent derivation of distances. Essentially, supernovae have been used to determine luminosity distances, i.e. the comparison of the observed flux to the total emitted radiation. The trick is to find a reliable way to measure the absolute luminosity of the objects. 

Since no astronomical standard candle is known - all proposed objects have been shown to be essentially non-uniform in one way or another - we nowadays have to calculate and plot the distance modulus for the objects. The scatter around the linear expansion line is less than 0.2 magnitudes or 20% Tonry et al. 2003. Independent of our ignorance of the exact explosion mechanism or the radiation transport in the explosions this proves that SNe la can reliably be used as a distance indicator in the local universe. This situation is very much comparable to the Cepheid stars, where the period-luminosity relation is based on empirical data of objects in the Magellanic Clouds. 

The simplest method is to assume that all supernovae are identical. This is, of course, not true (see previous paper) but it turns out that the subclass of the Type la supernovae is indeed rather homogeneous. The first to plot a Hubble diagram of Type la Supernovae was Kowal Kowal 1968. There are essentially three quantities that can be derived from such a Hubble diagram in the nearby universe the slope of the expansion line, the scatter around the expansion line and the value of the local Hubble constant from the intercept at zero redshift (e.g. Tammann Leibundgut 1990 Leibundgut. Pinto 1992). The slope gives an indication of the local expansion and for a linear expansion in an isotropic universe it has a fixed value. The scatter around the expansion line provides a measure of the accuracy of the standard candle and the measurement errors. The intercept of the line, finally, together with an estimate of the... 

There are several fundamental tests that will need to be performed until we can be sure that the current paradigm will persist. It is very appealing to think we know all constituents of the universe by now, but further surprises may still be in store for us. The testing has to concentrate on the reliability of the individual measurements. The Type la supernovae have been criticised for the fact that they are based on a rather simple assumption, namely that the distances derived from them are accurate. Many publications oversimplify this picture by calling Type la supernovae standard candles. This is not only incorrect, also it is misleading and belittles the result. The tests done on supernovae are solid and the theoretical work is progressing steadily. 

By definition, photometers do not respond to radiation in the infrared or the ultraviolet (Fig. 4-4a). They are light meters in the sense that they mimic human vision that is, they respond to photons in the visible region, similar to the light meter on a camera. A candle is a unit of luminous intensity, originally based on a standard candle or lamp. The current international unit is called a candela (sometimes still referred to as a candle ), which was previously defined as the total light intensity of 1.67 mm2 of a blackbody radiator (one that radiates maximally) at the melting temperature of pure platinum (2042 K). In 1979 the candela was redefined as the luminous intensity of a monochromatic source with a frequency of 5.40 x 1014 cycles s-1 (A, of 555 nm) emitting 0.01840 Js-1 or 0.01840 W (1.464 mW steradian-1, where W is the abbreviation for watt and steradian... 

Crab Nebula. The Crab Nebula was hrst estabbshed as a TeV gamma-ray source by the Whipple telescope in 1989 [21] and for the moment being, is the best hrmly established TeV steady emitter in the northern sky. MAGIC will not use the Crab Nebula only as a standard candle but can also expect interesting physics from it as the detection of the Crab pulsar and the IC peak [22 23] once the 30 GeV energy threshold has been reached. 

Crab nebula. The Crab Nebula, first detected in the TeV regime by the Whipple experiment in 1989 (Weekes, 1989), is the standard candle of the... 

Light flux Measurement of light energy, expressed in lumens, a unit defined as the amount of light emitted from a standard candle light source into an area of standard square measurement the sides of which are equal in length to the distance of the light source from the centre of the square. 

Luminous intensity Amount of luminous flux emitted by a point source of light per solid angle, compared with a standard candle. 

Extension of the distance scale to, presumably more remote objects, hke galactic clusters, requires equally precarious assumptions. Like the brightest star in each galaxy, each cluster is assumed to harbour a dominant galaxy that shines as a standard candle. Finally the only criterion left to measure larger distances is Hubble s law and the redshift. 

Candle Power - The illuminating power of a standard candle employed as a unit for determining the illuminating quality of an illuminant. 

Fig.2 shows these distributions for two sources with equal fluxes above 1 GeV but different spectral indices -2 and -3, background is not included. It is important that spectral measuremens with CYGAM can be always made relative since the large field of view ensures an appropriate standard candle (Crab for example) any time. 

Candle (unit of luminous intensity) n. Candle power is a measure of intensity of a source of light as compared with a standard candle. 

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