Stars:variables

But such behaviour is not really restricted to the Luminous Blue Variables. Humphreys (1987) described a cool star ("variable A") that shows the same behaviour, and so does the cool hypergiant HR 8752 (Piters et al., 1987) here an episodical mass ejection started around 1968 the star obtained a later spectral type the expelled gas remained detectable till 1980-1982. It would make sense to include such variables in the sample and to speak just of Very Luminous Variables, hence adding the word "Very" and deleting "Bright". 

The numbers of vertices and edges in a pair of dual polyhedrafP and fP satisfy the relationships v =/, e = e,f = v, in which the starred variables refer to the dual polyhedron P Thus, in the case of the trigonal bipyramid (fP)/trigonal prism (IP ) dual pair depicted above, = f= 6, e = e = 9, J = v = 5. 

As the system approaches a stationary state the starred variables approach their values of the stationary state. For the Selkov model the stationary state of the linear equivalent system is... 

This book presents a unified treatment of the chemistry of the elements. At present 112 elements are known, though not all occur in nature of the 92 elements from hydrogen to uranium all except technetium and promethium are found on earth and technetium has been detected in some stars. To these elements a further 20 have been added by artificial nuclear syntheses in the laboratory. Why are there only 90 elements in nature Why do they have their observed abundances and why do their individual isotopes occur with the particular relative abundances observed Indeed, we must also ask to what extent these isotopic abundances commonly vary in nature, thus causing variability in atomic weights and possibly jeopardizing the classical means of determining chemical composition and structure by chemical analysis. 

Henrietta Leavitt, Harvard College Observatory, 1912, established the relation period-luminosity of Cepheid variable stars. Being a woman i.e. confined to the tedious and ridiculously paid work of examining photographic plates for the benefit of an all-male establishment, she would not be awarded credit for her milestone discovery... 

Guttman, A., Cooke, N., and Star, C. M., Capillary electrophoresis separation of oligosaccharides. I. Effect of operational variables, Electrophoresis, 15,1518, 1994. 

The salient feature of the experimental results is the observation of a pronounced minimum in the Q(Q)/Q3 vs. z plot. It occurs at the same position, where the static structure factor in its Kratky representation exhibits its maximum. Furthermore, the reduced line width scales with the scaling variable z in the same way that the static structure factor does. Thus, the occurrence of the minimum is directly related to peculiarities of the star architecture. 

Note that, again, three different types of variables were combined chain length, component ratio, and absolute component level. Thus, a "standard" constrained mixture design was not appropriate. In this case a full factorial, central composite design was used, with a total of 20 data points. The star points were... 

In 2000, Krishnamurthy et al. have presented the 2/,3/-HMBC experiment (Figure 20), that affords for the first time the means of unequivocally differentiating between 2/ch from 3Jch correlations.59 Their approach is based on a further derivative of the constant-time variable delay introduced in the IMPEACH-MBC experiment. The user-definable /-scaling factor of the CIGAR-HMBC is used in the new experiment, the 2J,3J-HMBC experiment, to differentiate between 2/CH from 3Jch correlations. This new pulse sequence element has been given the acronym STAR (Selectively Tailored Accordion F1 Refocused) operator. 

Figure 20 Timing diagram of the suggested 2y,3y-HMBC experiment, including a LPJF3 for efficient 1JCH suppression. The sequence is virtually identical to the CIGAR-HMBC pulse sequence. The STAR operator is also a constant-time variable element. In this fashion, scalable F, modulation can be specifically introduced for 2JCH cross-peaks into the spectrum independently of the digitization employed in the second frequency domain.

In Franchini et al. (2004) we introduced four Lick/IDS index-index diagrams, i.e. NaD vs Ca4227, NaD vs Mg2, NaD vs Mgb, and NaD vs CaMg, to identify SSA and a-enhanced stars irrespectively of their Teg, log g and [Fe/H]. By applying this method to the 84 normal (i.e. excluding binaries and variable) stars from the S4N web site with [Fe/H] determined by AP04, it results that 8 stars are... 

The comparison of coronal and photospheric abundances in cool stars is a very important tool in the interpretation of the physics of the corona. Active stars show a very different pattern to that followed by low activity stars such as the Sun, being the First Ionization Potential (FIP) the main variable used to classify the elements. The overall solar corona shows the so-called FIP effect the elements with low FIP (<10 eV, like Ca, N, Mg, Fe or Si), are enhanced by a factor of 4, while elements with higher FIP (S, C, O, N, Ar, Ne) remain at photospheric levels. The physics that yields to this pattern is still a subject of debate. In the case of the active stars (see [2] for a review), the initial results seemed to point towards an opposite trend, the so called Inverse FIP effect , or the MAD effect (for Metal Abundance Depletion). In this case, the elements with low FIP have a substantial depletion when compared to the solar photosphere, while elements with high FIP have same levels (the ratio of Ne and Fe lines of similar temperature of formation in an X-ray spectrum shows very clearly this effect). However, most of the results reported to date lack from their respective photospheric counterparts, raising doubts on how real is the MAD effect. 

Having at hand the complete set of C,N,0 abundances, it is possible to test whether the observed pattern is due to CNO-cycle alone. From the large sample in literature (see right panel in Fig. 3) we know that since the sum C+N increases as C decreases, either the ON-cycle is involved (raising the N abundance) or there is a variable amount of N. On the other hand, over about 2 dex of spread in N, the sum C+N+O is almost constant, signature of the action of complete CNO-cycle (left panel of Fig. 4). Again, the source has to be found outside the observed stars. 

Four multiperiodic [3 Cephei and eleven SPB stars were found in the SMC. There are also two monoperiodic short-period variables that are good candidates for / Cephei stars in this galaxy. 

Many multiperiodic variables with periods in the range between 0.25 and 1.5 d were found. They can be identified with the known emission-line objects (Be stars), so that their light variations are of A Eri-type. 

Variable stars are so called because the luminosity of the star varies intrinsically and is not due to the passage of an eclipsing star. One such class of stars is the... 

The emission of light from Cepheid stars has a characteristic light curve seen in Figure 4.14 for a Cepheid in the constellation of Perseus. The sawtooth pattern is characteristic of the class and enables the period of variation to be determined. The observation, however, that the luminosity and period are related has powerful consequences. The Cepheid variables fall into two classes type I classical Cepheids have periods of 5-10 days and type II have periods of 12-20 days. The two types of Cepheids initially caused problems when determining the luminosity-period relation but the relation has now been determined. Type I Cepheids follow the expression... 

A type II Cepheid variable is observed in the elliptical galaxy M49 in the Virgo cluster of galaxies with a period of 30 days. Calculate the absolute magnitude of this star. If the total flux on the Earth from the star is 4.2 x 10 22 W m-2, estimate the distance to the Virgo cluster. 

Cepheid variable Stars that have a periodic variation in their luminosity with a direct relation between the luminosity and the period. These stars are important distance markers. 

---