Luminosity temperature

One can therefore predict the expected scaling of the luminosity-temperature relation, a well observed quantity ... 

In the near infrared, many of the AFCRL sources exhibit strong CO and H2O absorption, which are indicative of the luminosity, temperature, and composition of the stars. Ice (3.1y) absorption is seen in the spectra of a few stars—generally those found near, or associated with, regions of active star formation. 

The luminometer index (ASTM D 1740) is a characteristic that is becoming less frequently used. It is determined using the standard lamp mentioned above, except that the lamp is equipped with thermocouples allowing measurement of temperatures corresponding to different flame heights, and a photo-electric cell to evaluate the luminosity. The jet fuel under test is compared to two pure hydrocarbons tetraline and iso-octane to which are attributed the indices 0 and 100, respectively. The values often observed in commercial products usually vary between 40 and 70 the official specification is around 45 for TRO. 

Methanol, a clean burning fuel relative to conventional industrial fuels other than natural gas, can be used advantageously in stationary turbines and boilers because of its low flame luminosity and combustion temperature. Low NO emissions and virtually no sulfur or particulate emissions have been observed (83). Methanol is also considered for dual fuel (methanol plus oil or natural gas) combustion power boilers (84) as well as to fuel gas turbines in combined methanol / electric power production plants using coal gasification (85) (see Power generation). 

When pressure-decay rates less than critical are employed, the gas-phase combustion zone is removed from the propellant surface and extinguished, but not the ignition from within the condensed phase. Therefore, the temperature of the surface material will be above the autoignition temperature, and steady-state combustion will eventually be initiated. This mechanism is consistent with the observation that the luminosity of the combustion zone can vanish without combustion having been completely terminated. 

A bluff-body stabilized flame of CH4/H2 in air (designated HMl by Dally et al. [22]) (a) time-averaged photograph of flame luminosity, (b) time-averaged streamlines from LES, (c) instantaneous visualization of OH "luminosity" from LES, and (d) instantaneous temperature field from LES. (b and d are adapted from Raman, V. and Pitch, H., Combust. Flame, 142,329,2005. With permission.)... 

Although the single bubble experiment in Fig. 14.10b and the aforementioned multi-bubble work of Didenko et al. does support the hypothesis that thermal conductivity is a defining parameter of SL emission intensity, an alternative explanation attributes the trend in multi-bubble systems to the gas solubility, rather than the thermal conductivity. If the SL data from Fig. 14.9 is re-plotted as a function of the gas solubility, as shown below in Fig. 14.11, a very good correlation is found. This explanation is supported by several studies by Okitsu et al. [42, 59]. They found sonochemical activity to obey the same trend for the rare gases as for thermal conductivity, SL luminosity and temperature, as described above. This is evident in Fig. 14.12, which shows the sonochemical reduction of Au(III) to colloidal gold as a function of sonication time for different gas atmospheres. 

Since most (if not all) low-metallicity objects that are currently observed in the halo are not in the AGB phase, material enriched in carbon and the s-process elements is assumed to have accreted from the companion AGB stars, which have already evolved to faint white dwarfs, to the surface of the surviving companion. This scenario is the same as that applied to classical CH stars [4], Unfortunately, long-term radial velocity monitoring has been obtained for only a limited number of objects a clear binarity signature has been established for six objects in our sample to date. However, there exists additional support for the mass-accretion scenario for the Ba-rich CEMP stars. Fig. lb shows [C/H] as a function of luminosity roughly estimated from the effective temperature... 

The age at which Li depletion occurs increases with decreasing mass (and Li-burning temperatures are never reached for M < 0.06 M0). As luminosity, L oc M2 for PMS stars, the luminosity at which complete Li depletion takes place is therefore a sensitive function of age between about 10 and 200 Myr [6]. This relationship depends little on ingredients of the PMS models such as the treatments of convection and interior radiative opacities because the stars are... 

Fig. 1. Luminosity evolution of tracks of 0.5 M0 starting at different central temperature, labelled in the figure. At the bottom we sketch the energy liberated per gram due to the deuterium fusion with protons. The tracks of logT > 6.0 start in the middle of D-burning.

Now that we have a simple model for the continuum spectrum of the stars based around the Planck curve, the temperature and the luminosity, we can make some observations and classifications of the stars. There are some constellations that dominate the night sky in both the northern and southern hemispheres and even a casual look should inspire wonder. Star hopping in the night sky should lead to the simplest observation not all stars have the same colour. A high-quality photograph of the constellation of Orion (see page 2 of the colour plate section) shows stars... 

The B/V intensity ratio is an excellent relative measure of magnitude and it is possible to derive a B/V magnitude and, using Equation 2.7, derive a calibration curve for the temperature of a star (Figure 2.4) so that the temperature of the star can be measured directly by telescopes. Now, with a measure of the luminosity of a star the radius can be determined, but there is a problem the luminosity of a star as measured on Earth depends on how far away the star is - the Inverse Square Law - so the distance to the star must also be known to understand the absolute luminosity of the star. 

Combining measurements of the temperature and the luminosity enables the diameter of the star to be estimated. Returning to the concept of magnitude, the... 

Herzprung and Russell independently analysed the spectral types, luminosities and temperatures to produce the Herzprung-Russell diagram. 

Big Bang nucleosynthesis produced only H and He atoms with a little Li, from which nuclei the first generation of stars must have formed. Large clouds of H and He when above the Jeans Mass condensed under the influence of gravitational attraction until they reached the temperatures and densities required for a protostar to form, as outlined. Nuclear fusion powers the luminosity of the star and also results in the formation of heavier atomic nuclei. 

The B-N object may be considered to be a zero-age main sequence star that evolves with increasing surface temperature and luminosity at optical wavelengths. The descent from the right-hand upper quarter of the HR diagram, along with what has been called the Hayashi track or birth lines, precedes the entrance onto the... 

The plot of luminosity versus temperature for all stars, resulting in the main sequence, red giants and white dwarfs. Stellar evolution leads to mass - dependent birth lines onto the main sequence... 

Consider the amount of radiation arriving on the surface of the Earth at a distance of 1 AU or 1.5 x 1011 m. The total flux of the Sun is distributed evenly over a sphere of radius at the distance of the planet, d. From the luminosity calculation of the Sun, F, the solar flux at the surface of Earth, FEarth, is F/47t(1.5 x 1011)2 = 1370 Wm-2 from the least-square law of radiation discussed in Example 2.4 (Equation 2.4). Substituting this into Equation 7.6 with the estimate of the albedo listed in Table 7.2 gives a surface temperature for Earth of 256 K. 

AU from the Sun, just outside the orbit of Mars, whereas the inner boundary is determined by the runaway-greenhouse effect as observed on Venus. If the surface temperature were too hot, above 373 K, this would vaporise all water on the surface of the planet. The inner boundary is around 0.85 AU so the habitable zone spans 0.85-1.7 AU for our Sun (Figure 7.7) but the current habitable zone spans 0.85 - 1.3 AU (t — 0) in Figure 7.7. The habitable zone was much larger when the Sun s luminosity was greater, and narrower when the luminosity was smaller. 

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