Cooling Corona

Despite the observational identification of a possible site of dust formation, however, the dust-driven wind could not be applied to stars without dust envelope, as noted in Sect.II. Then, a more interesting possibility is a turbulence-driven wind,in which the high turbulent pressure of the transition layer(or cool corona) pushes the gas out of star,just as the high thermal pressure in corona does in solar-type stars. In fact, if the turbulent zone is extended to about 10 stellar radii, the local escape velocity there may already be small enough to be comparable with the observed flow velocities. Thus, the Maxwellian tail of the turbulent motion in the quasi-static molecular formation zone can directly lead to stellar mass-loss in all... 

Abstract. Coronal abundances have been a subject of debate in the last years due to the availability of high-quality X-ray spectra of many cool stars. Coronal abundance determinations have generally been compared to solar photospheric abundances from this a number of general properties have been inferred, such as the presence of a coronal metal depletion with an inverse First Ionization Potential dependence, with a functional form dependent on the activity level. We report a detailed analysis of the coronal abundance of 4 stars with various levels of activity and with accurately known photospheric abundances. The coronal abundance is determined using a line flux analysis and a full determination of the differential emission measure. We show that, when coronal abundances are compared with real photospheric values for the individual stars, the resulting pattern can be very different some active stars with apparent Metal Abundance Deficiency in the corona have coronal abundances that are actually consistent with their photospheric counterparts. 

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. 

As to the origin of mass-loss in cool luminous stars, several possibilities have been proposed, but none of them could provide satisfactory answer yet. As noted in Sect.I, the cool wind should originate not in the stellar surface but in outer layer at least several stellar radii above the stellar surface. We already know such a case in the thermally-driven wind from the hot corona of the Sun. However, the difficulty to apply the theory of thermally-driven wind to cool luminous stars has already been recognized at an early time( e.g., Weymann, 1963). More recent discovery of nonexistence of hot transition region( and hence of corona) in these stars by IUE obser-vations(Linsky,Haisch,1979) finally disclosed that the origin of mass-loss in cool luminous stars may be radically different from that in solar type stars. 

The phenomenon of cooling flows , described for luminous clusters, also applies to other systems with gaseous atmospheres. In particular, galaxy groups, the poorer cousins of rich clusters, (e.g., Helsdon et al. 2001) and individual early type galaxies with their luminous, X-ray coronae (Forman, Jones Tucker 1985) also frequently have short gas cooling times at their centers (Thomas et al. 1986). 

Figure 80 Types of treater for applying corona discharge (a) for non-conductive substrates, with an earthed base roll covered with a dielectric (b) for material of all types, with a bare, earthed base roll and the dielectric on the discharge electrode The main components are (1) Multi-fin electrode (2) Electrode tube in ceramic or quartz (3) Earthed base roll covered with dielectric (4) Bare, earthed base roll (5) Housing for the electrode assembly, enabling the extraction of ozone and cooling of the electrode (6) Path of material being treated...

An example of an alternative use of FT technology in the UV/VIS is our work on the X2Z" B2Z+ emission spectrum of jet-cooled CN [21], These experiments were made possible by the development of the corona-excited supersonic expansion source by Engelking [20]. The Engelking source creates radicals in a continuous discharge, followed by immediate cooling in the expansion. A high number density of rotationally and translationally cold radicals in excited electronic and vibrational states is produced. As a result, excited vibronic states of reactive species can be studied with a minimum of rotational congestion. 

A electrooptic polymer crosslinked film was formed by spin-coating a 25 wt% of the Step 12 product in cyclopentanone onto an ITO covered glass slide. The solution was filtered through a 0.2 pm nylon filter, spin-coated at 500 rpm for 6 seconds and 1000 rpm for 30 seconds, and then soft baked at 50°C overnight under vacuum to give a 3.2 pm thick film. The film was corona poled with a needle at 20 kVand heated to 220°C for 5 minutes for crosslinking. The film was then cooled to ambient temperature under the applied field to give an electro-optic film with an raa of 36 pm/V at 1.31 pm. 

Figure 9 Photomicrograph of spectacularly well-developed corona around relict garnet from Llano Uplift, Texas. The coronas permit identification of the original rim position of the garnet (assuming isovolu-metric replacement), which in turn allows quantification of the amount of garnet that was resorbed during cooling (source Carlson and Schwarze, 1997).

Jan M. Q. and Karim A. (1995) Coronas and high-P veins in metagabbros of the Kohistan island arc, northern Pakistan evidence for crustal thickening during cooling. J. Metamorph. Geol. 13(3), 357-366. 

Ozone (approximately 1 ml.) was prepared by corona discharge in a laboratory ozonizer and condensed in the receiver tube, R. Tube R was then attached to the apparatus, Ti, which was cooled in liquid nitrogen. The system was evacuated, and ozone was distilled successively into Ti, T2, and the U-tube section of the apparatus. A, with the system open to the pump. The multiple distillation ensured removal of oxygen. Results indicate that oxygen is easily removed from liquid ozone and that a single distillation through a re-entrant trap is sufficient. 

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