Astronomy

Strong orange line in wood fire spectrum?

Strong orange line in wood fire spectrum?


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I just built a DIY spectroscope using a CD and after making some tests, I noticed a really strong emission line located in the orange-yellowish zone of the fire spectrum (specifically, burning wood).

I think that the strong line could be actually sodium, but wouldn't that mean that wood contains a lot of sodium in order to see such a strong emission line?


Graphene-based materials represent a useful tool for the realization of novel neural interfaces. Several studies have demonstrated the biocompatibility of graphene-based supports, but the biological interactions between graphene and neurons still pose open questions. In this work, the influence of graphene films with different characteristics on the growth and maturation of primary cortical neurons is investigated. Graphene films are grown by chemical vapor deposition progressively lowering the temperature range from 1070 to 650 °C to change the lattice structure and corresponding electrical conductivity. Two graphene-based films with different electrical properties are selected and used as substrate for growing primary cortical neurons: i) highly crystalline and conductive (grown at 1070 °C) and ii) highly disordered and 140-times less conductive (grown at 790 °C). Electron and fluorescence microscopy imaging reveal an excellent neuronal viability and the development of a mature, structured, and excitable network onto both substrates, regardless of their microstructure and electrical conductivity. The results underline that high electrical conductivity by itself is not fundamental for graphene-based neuronal interfaces, while other physico–chemical characteristics, including the atomic structure, should be also considered in the design of functional, bio-friendly templates. This finding widens the spectrum of carbon-based materials suitable for neuroscience applications.

In the last years, the combined advancements in biomaterial science and neurotechnology led to a big leap in neural tissue engineering research. In this scenario, innovative materials can be designed to engineer advanced biological interfaces that can adapt to the central nervous system and interact with it. [ 1, 2 ] To build an original platform for potential applications in neurobiology, it is pivotal to ascertain if and how a new material interferes with neuronal activity and/or can be manipulated to regulate it. Graphene, a representative 2D material characterized by sp 2 -hybridized carbon atoms in a honeycomb arrangement, [ 3-5 ] yields gapless semi-metal characteristics [ 6, 7 ] with high carrier mobility [ 4, 6, 8 ] and thermal conductivity. [ 9 ] The distinctive properties of graphene have motivated its experimental applications in a variety of fields, including electronics, energy storage, composites [ 10-22 ] and biomedicine. [ 2, 23-27 ] Graphene-based materials can be engineered into advanced biological interfaces that can adapt to the central nervous system and interact with neurons, thanks to a host of tunable properties (e.g., mechanical, electrical, chemical, and frictional). To build an innovative platform for potential treatments of neurodegenerative diseases, it is pivotal to exclude any unwanted biological effects and ascertain if and how graphene-based materials can affect neuronal activity and/or be manipulated to regulate it. Recently, graphene-based materials, such as graphene oxide and functionalized graphene, have been used as 2D/3D templates for in vitro and in vivo neuroscientific applications, enabling stimulation of neural growth and regeneration, as well as modulating neuronal firing properties. [ 28-30 ] Despite a few studies in primary neurons and astrocytes, [ 31-35 ] the physio-chemical nature of the interactions between cultured cells and carbon-based surfaces is not fully understood. It has been shown that chemically modified graphene featuring high wettability fosters biocompatibility and increases the adhesion of biomolecules, [ 28, 30, 36, 37 ] displaying its potential incorporation in biological systems. Graphene-based materials were reported to affect electron transfer of biomolecules [ 38, 39 ] and couple electrically with neural stem cells. [ 40 ] Moreover, graphene appeared to influence neuronal excitability by restricting the mobility of K + ions near the graphene surface deposited onto electrically insulating substrates. [ 29 ] Nevertheless, there is a need to further investigate the capability of graphene-based supports to promote the neuronal activity from a morphological and physiological point of view, taking into consideration the distinct electrical, chemical, and structural properties of graphene.

Nowadays, the production of graphene by chemical vapor deposition (CVD) affords high standards in terms of materials quality, scale and cost, which suit the requirements of different applications and indicate the way toward a sustainable mass production. [ 41-43 ] CVD provides a favorable flexibility in the design of the graphene films’ properties, which can be aptly tuned by adjusting the process parameters. Polycrystalline graphene films with a wide range of grain size and electrical conductivity can be produced. Single-crystal graphene with a large grain size and monolayer amorphous carbon with infinitesimal grain size sit at the respective ends of the range, being electrically conductive and insulating, respectively. In the latter case, a form of “insulating amorphous graphene” (i.e., a freestanding, continuous and stable monolayer of sp 2 -bonded carbon atoms with amorphous structure) has been recently reported. [ 44 ] In between the two extremes, the use of ethanol as carbon precursor in CVD offers a suitable control on the grain size and electrical conductivity. [ 45-47 ]

Here, we studied the interaction of primary neurons with graphene-films with different structure and electrical conductivity grown by ethanol-based CVD at various temperatures (spanning from 650 to 1070 °C). While the temperatures >1000 °C led to the formation of polycrystalline graphene with large grain size [ 48-50 ] and sheet resistance values below 1 kΩ □ −1 , [ 51, 52 ] lowering the growth temperature reduced the grain size, with a corresponding increase of grain boundaries, structural disorder and electrical resistance (up to 70 kΩ □ −1 ). Neurons grown on both high and low conductivity graphene films supported on poly(ethylene terephthalate) (PET) substrates formed a highly structured and mature network, with no clear alteration of their physiological activity. Intriguingly, the neuronal network architecture tended to improve onto low-conductivity graphene as compared to pristine graphene, suggesting that an insulating astrocyte-like environment (induced by nanocrystalline or sp 3 carbon regions) might decrease the degree of neuronal cell clumping and favor neuron spreading, without affecting the cells’ physiological activity. The observation that electrical conductivity by itself is not the crucial property to foster the activity of neuronal networks highlights a key point to be considered for the design of future graphene-based implants.


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Python scripts used to perform significant calculations, and to reproduce all figures, are available from https://github.com/robertdstein/at2019dsg, and at https://doi.org/10.5281/zenodo.4308124.

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BOOK III. OBSERVATION

10. INSTRUMENTS OF PRECISION&mdashSTATE OF THE SOLAR SYSTEM.

Having now traced the progress of physical astronomy up to the time when very striking proofs of the universality of the law of gravitation convinced the most sceptical, it must still be borne in mind that, while gravitation is certainly the principal force governing the motions of the heavenly bodies, there may yet be a resisting medium in space, and there may be electric and magnetic forces to deal with. There may, further, be cases where the effects of luminous radiative repulsion become apparent, and also Crookes&rsquo vacuum-effects described as &ldquoradiant matter.&rdquo Nor is it quite certain that Laplace&rsquos proofs of the instantaneous propagation of gravity are final.

And in the future, as in the past, Tycho Brahe&rsquos dictum must be maintained, that all theory shall be preceded by accurate observations. It is the pride of astronomers that their science stands above all others in the accuracy of the facts observed, as well as in the rigid logic of the mathematics used for interpreting these facts.

It is interesting to trace historically the invention of those instruments of precision which have led to this result, and, without entering on the details required in a practical handbook, to note the guiding principles of construction in different ages.

It is very probable that the Chaldeans may have made spheres, like the armillary sphere, for representing the poles of the heavens and with rings to show the ecliptic and zodiac, as well as the equinoctial and solstitial colures but we have no record. We only know that the tower of Belus, on an eminence, was their observatory. We have, however, distinct records of two such spheres used by the Chinese about 2500 B.C. Gnomons, or some kind of sundial, were used by the Egyptians and others and many of the ancient nations measured the obliquity of the ecliptic by the shadows of a vertical column in summer and winter. The natural horizon was the only instrument of precision used by those who determined star positions by the directions of their risings and settings while in those days the clepsydra, or waterclock, was the best instrument for comparing their times of rising and setting.

About 300 B.C. an observatory fitted with circular instruments for star positions was set up at Alexandria, the then centre of civilisation. We know almost nothing about the instruments used by Hipparchus in preparing his star catalogues and his lunar and solar tables but the invention of the astrolabe is attributed to him. [1]

In more modern times Nuremberg became a centre of astronomical culture. Waltherus, of that town, made really accurate observations of star altitudes, and of the distances between stars and in 1484 A.D. he used a kind of clock. Tycho Brahe tried these, but discarded them as being inaccurate.

Tycho Brahe (1546-1601 A.D.) made great improvements in armillary spheres, quadrants, sextants, and large celestial globes. With these he measured the positions of stars, or the distance of a comet from several known stars. He has left us full descriptions of them, illustrated by excellent engravings. Previous to his time such instruments were made of wood. Tycho always used metal. He paid the greatest attention to the stability of mounting, to the orientation of his instruments, to the graduation of the arcs by the then new method of transversals, and to the aperture sight used upon his pointer. There were no telescopes in his day, and no pendulum clocks. He recognised the fact that there must be instrumental errors. He made these as small as was possible, measured their amount, and corrected his observations. His table of refractions enabled him to abolish the error due to our atmosphere so far as it could affect naked-eye observations. The azimuth circle of Tycho&rsquos largest quadrant had a diameter of nine feet, and the quadrant a radius of six feet. He introduced the mural quadrant for meridian observations. [2]

ANCIENT CHINESE INSTRUMENTS,
Including quadrant, celestial globe, and two armillae, in the Observatory at Peking. Photographed in Peking by the author in 1875, and stolen by the Germans when the Embassies were relieved by the allies in 1900.

The French Jesuits at Peking, in the seventeenth century, helped the Chinese in their astronomy. In 1875 the writer saw and photographed, on that part of the wall of Peking used by the Mandarins as an observatory, the six instruments handsomely designed by Father Verbiest, copied from the instruments of Tycho Brahe, and embellished with Chinese dragons and emblems cast on the supports. He also saw there two old instruments (which he was told were Arabic) of date 1279, by Ko Show-King, astronomer to Koblai Khan, the grandson of Chenghis Khan. One of these last is nearly identical with the armillae of Tycho and the other with his &ldquoarmillae æquatoriæ maximæ,&rdquo with which he observed the comet of 1585, besides fixed stars and planets. [3]

The discovery by Galileo of the isochronism of the pendulum, followed by Huyghens&rsquos adaptation of that principle to clocks, has been one of the greatest aids to accurate observation. About the same time an equally beneficial step was the employment of the telescope as a pointer not the Galilean with concave eye-piece, but with a magnifying glass to examine the focal image, at which also a fixed mark could be placed. Kepler was the first to suggest this. Gascoigne was the first to use it. Huyghens used a metal strip of variable width in the focus, as a micrometer to cover a planetary disc, and so to measure the width covered by the planet. The Marquis Malvasia, in 1662, described the network of fine silver threads at right angles, which he used in the focus, much as we do now.

In the hands of such a skilful man as Tycho Brahe, the old open sights, even without clocks, served their purpose sufficiently well to enable Kepler to discover the true theory of the solar system. But telescopic sights and clocks were required for proving some of Newton&rsquos theories of planetary perturbations. Picard&rsquos observations at Paris from 1667 onwards seem to embody the first use of the telescope as a pointer. He was also the first to introduce the use of Huyghens&rsquos clocks for observing the right ascension of stars. Olaus Romer was born at Copenhagen in 1644. In 1675, by careful study of the times of eclipses of Jupiter&rsquos satellites, he discovered that light took time to traverse space. Its velocity is 186,000 miles per second. In 1681 he took up his duties as astronomer at Copenhagen, and built the first transit circle on a window-sill of his house. The iron axis was five feet long and one and a-half inches thick, and the telescope was fixed near one end with a counterpoise. The telescope-tube was a double cone, to prevent flexure. Three horizontal and three vertical wires were used in the focus. These were illuminated by a speculum, near the object-glass, reflecting the light from a lantern placed over the axis, the upper part of the telescope-tube being partly cut away to admit the light. A divided circle, with pointer and reading microscope, was provided for reading the declination. He realised the superiority of a circle with graduations over a much larger quadrant. The collimation error was found by reversing the instrument and using a terrestrial mark, the azimuth error by star observations. The time was expressed in fractions of a second. He also constructed a telescope with equatoreal mounting, to follow a star by one axial motion. In 1728 his instruments and observation records were destroyed by fire.

Hevelius had introduced the vernier and tangent screw in his measurement of arc graduations. His observatory and records were burnt to the ground in 1679. Though an old man, he started afresh, and left behind him a catalogue of 1,500 stars.

Flamsteed began his duties at Greenwich Observatory, as first Astronomer Royal, in 1676, with very poor instruments. In 1683 he put up a mural arc of 140°, and in 1689 a better one, seventy-nine inches radius. He conducted his measurements with great skill, and introduced new methods to attain accuracy, using certain stars for determining the errors of his instruments and he always reduced his observations to a form in which they could be readily used. He introduced new methods for determining the position of the equinox and the right ascension of a fundamental star. He produced a catalogue of 2,935 stars. He supplied Sir Isaac Newton with results of observation required in his theoretical calculations. He died in 1719.

Halley succeeded Flamsteed to find that the whole place had been gutted by the latter&rsquos executors. In 1721 he got a transit instrument, and in 1726 a mural quadrant by Graham. His successor in 1742, Bradley, replaced this by a fine brass quadrant, eight feet radius, by Bird and Bradley&rsquos zenith sector was purchased for the observatory. An instrument like this, specially designed for zenith stars, is capable of greater rigidity than a more universal instrument and there is no trouble with refraction in the zenith. For these reasons Bradley had set up this instrument at Kew, to attempt the proof of the earth&rsquos motion by observing the annual parallax of stars. He certainly found an annual variation of zenith distance, but not at the times of year required by the parallax. This led him to the discovery of the &ldquoaberration&rdquo of light and of nutation. Bradley has been described as the founder of the modern system of accurate observation. He died in 1762, leaving behind him thirteen folio volumes of valuable but unreduced observations. Those relating to the stars were reduced by Bessel and published in 1818, at Königsberg, in his well-known standard work, Fundamenta Astronomiae. In it are results showing the laws of refraction, with tables of its amount, the maximum value of aberration, and other constants.

Bradley was succeeded by Bliss, and he by Maskelyne (1765), who carried on excellent work, and laid the foundations of the Nautical Almanac (1767). Just before his death he induced the Government to replace Bird&rsquos quadrant by a fine new mural circle, six feet in diameter, by Troughton, the divisions being read off by microscopes fixed on piers opposite to the divided circle. In this instrument the micrometer screw, with a divided circle for turning it, was applied for bringing the micrometer wire actually in line with a division on the circle&mdasha plan which is still always adopted.

Pond succeeded Maskelyne in 1811, and was the first to use this instrument. From now onwards the places of stars were referred to the pole, not to the zenith the zero being obtained from measures on circumpolar stars. Standard stars were used for giving the clock error. In 1816 a new transit instrument, by Troughton, was added, and from this date the Greenwich star places have maintained the very highest accuracy.

George Biddell Airy, Seventh Astronomer Royal, [4] commenced his Greenwich labours in 1835. His first and greatest reformation in the work of the observatory was one he had already established at Cambridge, and is now universally adopted. He held that an observation is not completed until it has been reduced to a useful form and in the case of the sun, moon, and planets these results were, in every case, compared with the tables, and the tabular error printed.

Airy was firmly impressed with the object for which Charles II. had wisely founded the observatory in connection with navigation, and for observations of the moon. Whenever a meridian transit of the moon could be observed this was done. But, even so, there are periods in the month when the moon is too near the sun for a transit to be well observed. Also weather interferes with many meridian observations. To render the lunar observations more continuous, Airy employed Troughton&rsquos successor, James Simms, in conjunction with the engineers, Ransome and May, to construct an altazimuth with three-foot circles, and a five-foot telescope, in 1847. The result was that the number of lunar observations was immediately increased threefold, many of them being in a part of the moon&rsquos orbit which had previously been bare of observations. From that date the Greenwich lunar observations have been a model and a standard for the whole world.

Airy also undertook to superintend the reduction of all Greenwich lunar observations from 1750 to 1830. The value of this laborious work, which was completed in 1848, cannot be over-estimated.

The demands of astronomy, especially in regard to small minor planets, required a transit instrument and mural circle with a more powerful telescope. Airy combined the functions of both, and employed the same constructors as before to make a transit-circle with a telescope of eleven and a-half feet focus and a circle of six-feet diameter, the object-glass being eight inches in diameter.

Airy, like Bradley, was impressed with the advantage of employing stars in the zenith for determining the fundamental constants of astronomy. He devised a reflex zenith tube, in which the zenith point was determined by reflection from a surface of mercury. The design was so simple, and seemed so perfect, that great expectations were entertained. But unaccountable variations comparable with those of the transit circle appeared, and the instrument was put out of use until 1903, when the present Astronomer Royal noticed that the irregularities could be allowed for, being due to that remarkable variation in the position of the earth&rsquos axis included in circles of about six yards diameter at the north and south poles, discovered at the end of the nineteenth century. The instrument is now being used for investigating these variations and in the year 1907 as many as 1,545 observations of stars were made with the reflex zenith tube.

In connection with zenith telescopes it must be stated that Respighi, at the Capitol Observatory at Rome, made use of a deep well with a level mercury surface at the bottom and a telescope at the top pointing downwards, which the writer saw in 1871. The reflection of the micrometer wires and of a star very near the zenith (but not quite in the zenith) can be observed together. His mercury trough was a circular plane surface with a shallow edge to retain the mercury. The surface quickly came to rest after disturbance by street traffic.

Sir W. M. H. Christie, Eighth Astronomer Royal, took up his duties in that capacity in 1881. Besides a larger altazimuth that he erected in 1898, he has widened the field of operations at Greenwich by the extensive use of photography and the establishment of large equatoreals. From the point of view of instruments of precision, one of the most important new features is the astrographic equatoreal, set up in 1892 and used for the Greenwich section of the great astrographic chart just completed. Photography has come to be of use, not only for depicting the sun and moon, comets and nebulae, but also to obtain accurate relative positions of neighbouring stars to pick up objects that are invisible in any telescope and, most of all perhaps, in fixing the positions of faint satellites. Thus Saturn&rsquos distant satellite, Phoebe, and the sixth and seventh satellites of Jupiter, have been followed regularly in their courses at Greenwich ever since their discovery with the thirty-inch reflector (erected in 1897) and while doing so Mr. Melotte made, in 1908, the splendid discovery on some of the photographic plates of an eighth satellite of Jupiter, at an enormous distance from the planet. From observations in the early part of 1908, over a limited arc of its orbit, before Jupiter approached the sun, Mr. Cowell computed a retrograde orbit and calculated the future positions of this satellite, which enabled Mr. Melotte to find it again in the autumn&mdasha great triumph both of calculation and of photographic observation. This satellite has never been seen, and has been photographed only at Greenwich, Heidelberg, and the Lick Observatory.

Greenwich Observatory has been here selected for tracing the progress of accurate measurement. But there is one instrument of great value, the heliometer, which is not used at Greenwich. This serves the purpose of a double image micrometer, and is made by dividing the object-glass of a telescope along a diameter. Each half is mounted so as to slide a distance of several inches each way on an arc whose centre is the focus. The amount of the movement can be accurately read. Thus two fields of view overlap, and the adjustment is made to bring an image of one star over that of another star, and then to do the same by a displacement in the opposite direction. The total movement of the half-object glass is double the distance between the star images in the focal plane. Such an instrument has long been established at Oxford, and German astronomers have made great use of it. But in the hands of Sir David Gill (late His Majesty&rsquos Astronomer at the Cape of Good Hope), and especially in his great researches on Solar and on Stellar parallax, it has been recognised as an instrument of the very highest accuracy, measuring the distance between stars correctly to less than a tenth of a second of arc.

The superiority of the heliometer over all other devices (except photography) for measuring small angles has been specially brought into prominence by Sir David Gill&rsquos researches on the distance of the sun&mdashi.e., the scale of the solar system. A measurement of the distance of any planet fixes the scale, and, as Venus approaches the earth most nearly of all the planets, it used to be supposed that a Transit of Venus offered the best opportunity for such measurement, especially as it was thought that, as Venus entered on the solar disc, the sweep of light round the dark disc of Venus would enable a very precise observation to be made. The Transit of Venus in 1874, in which the present writer assisted, overthrew this delusion.

In 1877 Sir David Gill used Lord Crawford&rsquos heliometer at the Island of Ascension to measure the parallax of Mars in opposition, and found the sun&rsquos distance 93,080,000 miles. He considered that, while the superiority of the heliometer had been proved, the results would be still better with the points of light shown by minor planets rather than with the disc of Mars.

In 1888-9, at the Cape, he observed the minor planets Iris, Victoria, and Sappho, and secured the co-operation of four other heliometers. His final result was 92,870,000 miles, the parallax being 8",802 (Cape Obs., Vol. VI.).

So delicate were these measures that Gill detected a minute periodic error of theory of twenty-seven days, owing to a periodically erroneous position of the centre of gravity of the earth and moon to which the position of the observer was referred. This led him to correct the mass of the moon, and to fix its ratio to the earth&rsquos mass = 0.012240.

Another method of getting the distance from the sun is to measure the velocity of the earth&rsquos orbital motion, giving the circumference traversed in a year, and so the radius of the orbit. This has been done by comparing observation and experiment. The aberration of light is an angle 20&rdquo 48, giving the ratio of the earth&rsquos velocity to the velocity of light. The velocity of light is 186,000 miles a second whence the distance to the sun is 92,780,000 miles. There seems, however, to be some uncertainty about the true value of the aberration, any determination of which is subject to irregularities due to the &ldquoseasonal errors.&rdquo The velocity of light was experimentally found, in 1862, by Fizeau and Foucault, each using an independent method. These methods have been developed, and new values found, by Cornu, Michaelson, Newcomb, and the present writer.

Quite lately Halm, at the Cape of Good Hope, measured spectroscopically the velocity of the earth to and from a star by observations taken six months apart. Thence he obtained an accurate value of the sun&rsquos distance. [5]

But the remarkably erratic minor planet, Eros, discovered by Witte in 1898, approaches the earth within 15,000,000 miles at rare intervals, and, with the aid of photography, will certainly give us the best result. A large number of observatories combined to observe the opposition of 1900. Their results are not yet completely reduced, but the best value deduced so far for the parallax [6] is 8".807 ± 0".0028. [7]

[1] In 1480 Martin Behaim, of Nuremberg, produced his astrolabe for measuring the latitude, by observation of the sun, at sea. It consisted of a graduated metal circle, suspended by a ring which was passed over the thumb, and hung vertically. A pointer was fixed to a pin at the centre. This arm, called the alhidada, worked round the graduated circle, and was pointed to the sun. The altitude of the sun was thus determined, and, by help of solar tables, the latitude could be found from observations made at apparent noon.

[3] See Dreyer&rsquos article on these instruments in Copernicus, Vol. I. They were stolen by the Germans after the relief of the Embassies, in 1900. The best description of these instruments is probably that contained in an interesting volume, which may be seen in the library of the R. A. S., entitled Chinese Researches, by Alexander Wyllie (Shanghai, 1897).

[4] Sir George Airy was very jealous of this honourable title. He rightly held that there is only one Astronomer Royal at a time, as there is only one Mikado, one Dalai Lama. He said that His Majesty&rsquos Astronomer at the Cape of Good Hope, His Majesty&rsquos Astronomer for Scotland, and His Majesty&rsquos Astronomer for Ireland are not called Astronomers Royal.

[5] Annals of the Cape Observatory, vol. x., part 3.

[6] The parallax of the sun is the angle subtended by the earth&rsquos radius at the sun&rsquos distance.

[7] A. R. Hinks, R.A.S. Monthly Notices, June, 1909.

11. HISTORY OF THE TELESCOPE

Accounts of wonderful optical experiments by Roger Bacon (who died in 1292), and in the sixteenth century by Digges, Baptista Porta, and Antonio de Dominis (Grant, Hist. Ph. Ast.), have led some to suppose that they invented the telescope. The writer considers that it is more likely that these notes refer to a kind of camera obscura, in which a lens throws an inverted image of a landscape on the wall.

The first telescopes were made in Holland, the originator being either Henry Lipperhey, [1] Zacharias Jansen, or James Metius, and the date 1608 or earlier.

In 1609 Galileo, being in Venice, heard of the invention, went home and worked out the theory, and made a similar telescope. These telescopes were all made with a convex object-glass and a concave eye-lens, and this type is spoken of as the Galilean telescope. Its defects are that it has no real focus where cross-wires can be placed, and that the field of view is very small. Kepler suggested the convex eye-lens in 1611, and Scheiner claimed to have used one in 1617. But it was Huyghens who really introduced them. In the seventeenth century telescopes were made of great length, going up to 300 feet. Huyghens also invented the compound eye-piece that bears his name, made of two convex lenses to diminish spherical aberration.

But the defects of colour remained, although their cause was unknown until Newton carried out his experiments on dispersion and the solar spectrum. To overcome the spherical aberration James Gregory, [2] of Aberdeen and Edinburgh, in 1663, in his Optica Promota, proposed a reflecting speculum of parabolic form. But it was Newton, about 1666, who first made a reflecting telescope and he did it with the object of avoiding colour dispersion.

Some time elapsed before reflectors were much used. Pound and Bradley used one presented to the Royal Society by Hadley in 1723. Hawksbee, Bradley, and Molyneaux made some. But James Short, of Edinburgh, made many excellent Gregorian reflectors from 1732 till his death in 1768.

Newton&rsquos trouble with refractors, chromatic aberration, remained insurmountable until John Dollond (born 1706, died 1761), after many experiments, found out how to make an achromatic lens out of two lenses&mdashone of crown glass, the other of flint glass&mdashto destroy the colour, in a way originally suggested by Euler. He soon acquired a great reputation for his telescopes of moderate size but there was a difficulty in making flint-glass lenses of large size. The first actual inventor and constructor of an achromatic telescope was Chester Moor Hall, who was not in trade, and did not patent it. Towards the close of the eighteenth century a Swiss named Guinand at last succeeded in producing larger flint-glass discs free from striae. Frauenhofer, of Munich, took him up in 1805, and soon produced, among others, Struve&rsquos Dorpat refractor of 9.9 inches diameter and 13.5 feet focal length, and another, of 12 inches diameter and 18 feet focal length, for Lamont, of Munich.

In the nineteenth century gigantic reflectors have been made. Lassel&rsquos 2-foot reflector, made by himself, did much good work, and discovered four new satellites. But Lord Rosse&rsquos 6-foot reflector, 54 feet focal length, constructed in 1845, is still the largest ever made. The imperfections of our atmosphere are against the use of such large apertures, unless it be on high mountains. During the last half century excellent specula have been made of silvered glass, and Dr. Common&rsquos 5-foot speculum (removed, since his death, to Harvard) has done excellent work. Then there are the 5-foot Yerkes reflector at Chicago, and the 4-foot by Grubb at Melbourne.

Passing now from these large reflectors to refractors, further improvements have been made in the manufacture of glass by Chance, of Birmingham, Feil and Mantois, of Paris, and Schott, of Jena while specialists in grinding lenses, like Alvan Clark, of the U.S.A., and others, have produced many large refractors.

Cooke, of York, made an object-glass, 25-inch diameter, for Newall, of Gateshead, which has done splendid work at Cambridge. We have the Washington 26-inch by Clark, the Vienna 27-inch by Grubb, the Nice 29½-inch by Gautier, the Pulkowa 30-inch by Clark. Then there was the sensation of Clark&rsquos 36-inch for the Lick Observatory in California, and finally his tour de force, the Yerkes 40-inch refractor, for Chicago.

At Greenwich there is the 28-inch photographic refractor, and the Thompson equatoreal by Grubb, carrying both the 26-inch photographic refractor and the 30-inch reflector. At the Cape of Good Hope we find Mr. Frank McClean&rsquos 24-inch refractor, with an object-glass prism for spectroscopic work.

It would be out of place to describe here the practical adjuncts of a modern equatoreal&mdashthe adjustments for pointing it, the clock for driving it, the position-micrometer and various eye-pieces, the photographic and spectroscopic attachments, the revolving domes, observing seats, and rising floors and different forms of mounting, the siderostats and coelostats, and other convenient adjuncts, besides the registering chronograph and numerous facilities for aiding observation. On each of these a chapter might be written but the most important part of the whole outfit is the man behind the telescope, and it is with him that a history is more especially concerned.

SPECTROSCOPE.

Since the invention of the telescope no discovery has given so great an impetus to astronomical physics as the spectroscope and in giving us information about the systems of stars and their proper motions it rivals the telescope.

Frauenhofer, at the beginning of the nineteenth century, while applying Dollond&rsquos discovery to make large achromatic telescopes, studied the dispersion of light by a prism. Admitting the light of the sun through a narrow slit in a window-shutter, an inverted image of the slit can be thrown, by a lens of suitable focal length, on the wall opposite. If a wedge or prism of glass be interposed, the image is deflected to one side but, as Newton had shown, the images formed by the different colours of which white light is composed are deflected to different extents&mdashthe violet most, the red least. The number of colours forming images is so numerous as to form a continuous spectrum on the wall with all the colours&mdashred, orange, yellow, green, blue, indigo, and violet. But Frauenhofer found with a narrow slit, well focussed by the lens, that some colours were missing in the white light of the sun, and these were shown by dark lines across the spectrum. These are the Frauenhofer lines, some of which he named by the letters of the alphabet. The D line is a very marked one in the yellow. These dark lines in the solar spectrum had already been observed by Wollaston. [3]

On examining artificial lights it was found that incandescent solids and liquids (including the carbon glowing in a white gas flame) give continuous spectra gases, except under enormous pressure, give bright lines. If sodium or common salt be thrown on the colourless flame of a spirit lamp, it gives it a yellow colour, and its spectrum is a bright yellow line agreeing in position with line D of the solar spectrum.

In 1832 Sir David Brewster found some of the solar black lines increased in strength towards sunset, and attributed them to absorption in the earth&rsquos atmosphere. He suggested that the others were due to absorption in the sun&rsquos atmosphere. Thereupon Professor J. D. Forbes pointed out that during a nearly total eclipse the lines ought to be strengthened in the same way as that part of the sun&rsquos light, coming from its edge, passes through a great distance in the sun&rsquos atmosphere. He tried this with the annular eclipse of 1836, with a negative result which has never been accounted for, and which seemed to condemn Brewster&rsquos view.

In 1859 Kirchoff, on repeating Frauenhofer&rsquos experiment, found that, if a spirit lamp with salt in the flame were placed in the path of the light, the black D line is intensified. He also found that, if he used a limelight instead of the sunlight and passed it through the flame with salt, the spectrum showed the D line black or the vapour of sodium absorbs the same light that it radiates. This proved to him the existence of sodium in the sun&rsquos atmosphere. [4] Iron, calcium, and other elements were soon detected in the same way.

Extensive laboratory researches (still incomplete) have been carried out to catalogue (according to their wave-length on the undulatory theory of light) all the lines of each chemical element, under all conditions of temperature and pressure. At the same time, all the lines have been catalogued in the light of the sun and the brighter of the stars.

Another method of obtaining spectra had long been known, by transmission through, or reflection from, a grating of equidistant lines ruled upon glass or metal. H. A. Rowland developed the art of constructing these gratings, which requires great technical skill, and for this astronomers owe him a debt of gratitude.

In 1842 Doppler [5] proved that the colour of a luminous body, like the pitch or note of a sounding body, must be changed by velocity of approach or recession. Everyone has noticed on a railway that, on meeting a locomotive whistling, the note is lowered after the engine has passed. The pitch of a sound or the colour of a light depends on the number of waves striking the ear or eye in a second. This number is increased by approach and lowered by recession.

Thus, by comparing the spectrum of a star alongside a spectrum of hydrogen, we may see all the lines, and be sure that there is hydrogen in the star yet the lines in the star-spectrum may be all slightly displaced to one side of the lines of the comparison spectrum. If towards the violet end, it means mutual approach of the star and earth if to the red end, it means recession. The displacement of lines does not tell us whether the motion is in the star, the earth, or both. The displacement of the lines being measured, we can calculate the rate of approach or recession in miles per second.

In 1868 Huggins [6] succeeded in thus measuring the velocities of stars in the direction of the line of sight.

In 1873 Vogel [7] compared the spectra of the sun&rsquos East (approaching) limb and West (receding) limb, and the displacement of lines endorsed the theory. This last observation was suggested by Zöllner.

[1] In the Encyclopaedia Britannica, article &ldquoTelescope,&rdquo and in Grant&rsquos Physical Astronomy, good reasons are given for awarding the honour to Lipperhey.

[2] Will the indulgent reader excuse an anecdote which may encourage some workers who may have found their mathematics defective through want of use? James Gregory&rsquos nephew David had a heap of MS. notes by Newton. These descended to a Miss Gregory, of Edinburgh, who handed them to the present writer, when an undergraduate at Cambridge, to examine. After perusal, he lent them to his kindest of friends, J. C. Adams (the discoverer of Neptune), for his opinion. Adams&rsquos final verdict was: &ldquoI fear they are of no value. It is pretty evident that, when he wrote these notes, Newton&rsquos mathematics were a little rusty.&rdquo

[4] The experiment had been made before by one who did not understand its meaning. But Sir George G. Stokes had already given verbally the true explanation of Frauenhofer lines.

[5] Abh. d. Kön. Böhm. d. Wiss., Bd. ii., 1841-42, p. 467. See also Fizeau in the Ann. de Chem. et de Phys., 1870, p. 211.


Strong orange line in wood fire spectrum? - Astronomy

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Images

Figure 1

(a) Schematic demonstration of the donor-acceptor system. (b) Schematic illustration of the simplified model of a three-level system.

Figure 2

The typical range of the coupling potential Δ in a FRET process as a function of intermolecular distances ξ in log-log scale. The horizontal line in the middle is the value of Γ = 10 − 4 . We assume Γ h = 10 − 9 .

Figure 3

(a) Rate of energy transfer vs donor-acceptor separation ξ in log-log scale. The solid navy line (top): the resonance case ( Ω = R * = ω 1 − ω 2 ). The dotted navy line below it: 0.2 % off the resonance. The overly high Rabi frequency case ( Ω = 2 R * ) coincides with the rates at low Rabi frequencies Ω ω 1 − ω 2 < 0.2 , which are marked by the slanted orange line. For other parameter regimes, the results lie between the navy and the orange lines. The dotted black line overlapping with the orange is the weak laser limit (assume Ω ≳ Γ ). δ 1 = 0 , R * = 0.1 , Γ = 10 − 4 . (b) Quantum yield vs distance ξ in log-log scale at the same condition as (a). The efficiency is almost identical to the rate κ up to a factor of Γ when κ ≪ 1 . (c) Quantum yield vs Rabi frequency at fixed distance. The characteristic Rabi frequencies are set to R * = 0.01 (the navy line on the left) and R * = 0.02 (the orange line on the right). Here δ 1 = 0 , Δ = 5 × 10 − 4 , and Γ = 10 − 4 .

Figure 4

The dynamics of the excitations on the acceptor state with the time multiplied by laser frequency ν . (a) In-resonance Ω = R * . (b) Off-resonance Ω = R * ( 1 % ± 3 % ) . The color code is given as follows (from top to bottom), the blue lines: Δ = 4 Γ , the orange lines: Δ = 2 Γ , the green lines: Δ = Γ , and the red lines: Δ = 0.5 Γ . For (a) and (b), Γ = 10 − 4 , Γ h = 10 − 9 , and ω 1 − ω 2 = 0.1 .

Figure 5

(a) Schematic demonstration the energy level splitting due to the dynamic Stark effect. (b) Population on state “a” (navy, top) and “b” (orange, bottom) vs Rabi frequency Ω . δ 1 = 0 , R * = 0.01 . The peak value of excitation of around 0.2 can be inferred from the constant term in Eq. (20). (c) Quantum coherence vs bias of Rabi frequency from the R * in logarithmic scale. The off-diagonal element of the density matrix corresponding to the coherence between the excitation on the donor and the excitation on the acceptor. For all, Δ = 2 × 10 − 4 , Γ = 10 − 4 .

Figure 6

Population on state “a” (navy, top) and “b” (orange, bottom) vs detuning δ 1 . Solid lines: Ω = R * = 0.1 . Dotted lines: Ω = 0.1 , R * = 0.11 . The peak value of excitation of around 0.2 can be inferred from the constant term in Eq. (20). Here Δ = 5 × 10 − 4 , Γ = 10 − 4 .


2 Instrumentation and Cloud Data Analysis

2.1 LACROS

The Leipzig Aerosol and Cloud Remote Observation System (LACROS, 51.3°N, 12.4°E) [Wandinger et al., 2012 ] of the Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany, was established in 2011. Cornerstones of LACROS are the multiwavelength Raman/polarization lidar MARTHA (Multiwavelength Atmospheric Raman Lidar for Temperature, Humidity, and Aerosol Profiling) which is part of EARLINET (European Aerosol Research Lidar Network) [Mattis et al., 2004 , 2008 , 2010 Wandinger et al., 2004 Schmidt et al., 2013 ], the wind Doppler lidar WILI [Engelmann et al., 2008 Bühl et al., 2012 ], the 35 GHz cloud radar MIRA35 [Bühl et al., 2013 ], and the microwave radiometer HATPRO (Humidity And Temperature Profiler) [Rose et al., 2005 ].

MARTHA is a powerful Raman lidar and was upgraded to perform dual-FOV Raman lidar measurements for the retrieval of cloud microphysical properties in 2008 [Schmidt et al., 2013 ]. A Nd:YAG laser emits radiation pulses at the wavelengths of 355, 532, and 1064nm with pulse energies of 0.3, 0.6, and 0.5J, respectively, and a repetition rate of 30Hz. The receiver of MARTHA consists of a 0.8 m diameter telescope and a beam separation unit with 12 detection channels. Particle backscatter coefficients at 355, 532, and 1064nm and extinction coefficients at 355 and 532nm can be determined from these lidar observations [Ansmann et al., 1990 , 1992 Ansmann and Müller, 2005 ]. By applying the method of inversion with regularization with constraints [Müller et al., 1999 Wandinger et al., 2002 Ansmann and Müller, 2005 ] to the set of spectrally resolved particle backscatter and extinction coefficients, microphysical properties of the aerosol particles in terms of volume and surface concentration, effective radius, and APNC (covering accumulation and coarse-mode particles with diameters of 0.1–10 μm) can be derived.

The novel dual-FOV Raman lidar technique makes use of two receiver FOVs. Raman scattered light with a wavelength of 607nm is detected with a conventional, circular FOV and an annular, outer FOV encompassing the inner, circular FOV. The measurement geometry is illustrated in Figure 1. In the case of lidar measurements in clouds, multiply scattered light is detected due to the pronounced forward scattering peak of the phase function of cloud droplets. The width of the forward scattering peak correlates unambiguously with the size of the scattering droplets. As the forward scattering angles determine the ratio between the signals of the inner and outer FOV, the ratio of the signals from the inner and outer FOV contains information about cloud droplet size up to 50 g/m 2 .

The new aspect introduced here is the detection of light which is forward scattered by cloud droplets and Raman backscattered by nitrogen molecules. As illustrated in Figure 2, the key point of the technique is that Raman backscattering from nitrogen molecules is nearly isotropic for scattering angles close to 180° so that the angular distribution of the incoming light depends on the forward scattering by droplets only. In strong contrast, the conventional multiple-scattering lidar technique is based on the measurement of elastically backscattered laser light [Bissonnette and Hutt, 1995 Bissonnette et al., 2002 Bissonnette, 2005 ]. Forward scattering and backscattering by cloud droplets influence the angular distribution of the incoming light but both scattering processes depend on drop size in a different way (see Figure 2, green and blue curves). This prohibits a clear straightforward determination of the drop size characteristics.

To be capable of performing dual-FOV cloud measurements in an extended altitude range from 1.3 to 6 km height, the receiver of MARTHA is set up in the way that the measurement geometry can be easily optimized regarding the contrast of the multiple-scattering effects in the two channels by exchanging the field stop [Schmidt et al., 2013 ]. FOV pairs of 0.28 and 0.78 mrad (for clouds above about 4 km height), of 0.5 and 2.0 mrad (for clouds from about 2.7 to 4 km height), and of 0.78 and 3.8 mrad (for clouds with base <2.7 km) are used [Schmidt et al., 2013 ]. Due to the small Raman scattering cross section, the dual-FOV Raman lidar measurements are restricted to nighttime hours.

The Doppler wind lidar WILI operates at a wavelength of 2022nm and emits laser pulses of 450ns (140m) length and 1.5mJ pulse energy with a pulse repetition rate of 750Hz [Engelmann et al., 2008 Bühl et al., 2012 ]. Vertical and temporal resolutions are 75 m and 2 s, respectively. The uncertainty in the determination of the vertical-wind component is of the order of 10 cm/s. WILI observations were mainly used in our study to separate regions with upward and downward motions. To remotely sense the same volume with WILI and MARTHA, both systems were located within a distance of less than 10m, and both lidars were pointing exactly to the zenith.

The cloud radar is used here only for drizzle detection and cloud top identification to corroborate the lidar observations in cases with optically dense clouds. The HATPRO microwave radiometer allows us to estimate LWP [Rose et al., 2005 ] which can be compared with the column-integrated liquid water content (LWC) obtained from the dual-FOV Raman lidar observations (as explained in the next section). The uncertainty in the HATPRO LWP is about 15–30 g/m 2 [Westwater et al., 2001 Crewell and Löhnert, 2003 Gaussiat et al., 2007 Ebell et al., 2011 ]. For a distinct reduction of the relative error to about 10%, the LWPs from HATPRO were calibrated to 0g/m 2 in cloud-free regions indicated by lidar or ceilometer before or after the passage of layered clouds [Gaussiat et al., 2007 ].

2.2 Retrieval of Cloud Microphysical Parameters

The novel dual-FOV Raman lidar technique permits the derivation of profiles of the cloud droplet effective radius re (3V/A with droplet volume concentration V and surface area concentration A) and cloud droplet (single-scattering) extinction coefficient α [Malinka and Zege, 2007 Schmidt et al., 2013 ]. The effective radius is the third moment (LWC) over the second moment (α). LWC is given by 2/3ρre(z)α(z) with water density ρ. No assumptions about cloud properties (e.g., adiabatic profile of LWC or certain cloud droplet size distribution) have to be made in our dual-FOV lidar approach. The measured width (in terms of scattering angle) of the light-scattering defraction peak is unambiguously related to the effective droplet radius re. The range of observable effective radii is about 1.5–30 μm [Schmidt et al., 2013 ], in agreement with simulation studies of Veselovskii et al. [ 2006 ]. The uncertainties in the derived quantities (as shown as error bars in section 3) are obtained by input variation of the measured signals in both FOVs, comparison of the results when different height resolutions are applied in the computations, and by considering uncertainties in the retrieved cloud base and cloud top heights [Schmidt et al., 2013 ]. The resulting uncertainties in the presented cloud properties are mostly of the order of 10% to 30%.

Miles et al. [ 2000 ] set up a database from various in situ measurements of droplet size distributions of low-level stratus clouds. The fit of a modified gamma distribution to the size distributions obtained from measurements in continental air masses yielded ν = 8.7 ± 6.3 and thus a mean value of l of 0.74 within a range from 0.42 to 0.83.

Similar to equation 4, an alternative approach can be obtained by starting from with the volume mean radius rv[Martin et al., 1994 ] so that equation 4 is then given as a function of k instead of l. For continental air masses, Lu and Seinfeld [ 2006 ] compiled a list of k-values for stratiform clouds based on a literature review. The k range of 0.75±0.15 well represents the values found for continental air masses. In the following, we use 0.75 for l in equation 4 and assume an uncertainty in l of 20% in the computation of the uncertainty in N after equation 4.

2.3 Retrieval of Cloud Base Height

The detection of the cloud base height with lidar is often masked by a strong increase of the backscatter coefficient by a factor of >5 below cloud base due to the rapid growth of aerosol particles by water uptake. In the case of the dual-FOV Raman lidar, the outer–FOV signals (multiple-scattering channels) can be used to identify the true cloud base (at which relative humidity reaches the 100% level). Significant multiple-scattering occurs only if the aerosol particles become activated. Even large aerosol particles after water uptake are not able to produce a significant multiple scattering signal. This potential to unambiguously detect cloud base height is illustrated in Figure 3. The simulations of the Raman signals shown in Figure 3 are based on the model of Malinka and Zege [ 2003 ]. In all simulations, the Raman signal from the outer FOV strongly increases at cloud base. The slope of the increase differs with the measurement geometry and cloud properties. Water–uptake by aerosol particles is considered in the simulations and, as shown, does not affect the precise cloud base detection.


Utility Flag Color Code

So what does this rainbow of marking flags in your yard mean?

  • Red flags – Red is the most common flag. It signifies electric utilities, such as cables and power lines. These mark the power lines that connect to a neighbor’s power grid. Marking these junctions helps avoid a neighborhood-wide power outage.
  • White flags – White flags mean excavation. Often you’ll see these set out for a city excavation project. The extent of the white flagged area will give you a sense of how big a project you’re in for.
  • Pink flags – These are used as temporary survey markings. As surveyors measure, they mark their work with pink flags. Measure twice, cut once, and use plenty of pink flags. Pink is also used to mark mysteries. If a utility can’t be identified, a worker will pink flag it.
  • Yellow flags – Just like yellow caution tape, you want to stand back from yellow flags. These mark gaseous materials, petroleum, steam and other stuff that’s nasty when it gets loose, possibly causing soil contamination or explosions.
  • Orange flags – Remember land lines? These get orange flags, as do other communication systems, such as signal or alarm lines, or TV cables. Don’t enrage your neighbor by cutting through that cable just before the big game.
  • Blue flags – Blue means water, irrigation or slurry. Usually this is drinking water. Damage this line and you could flood your home or find yourself without drinking water for a few days.
  • Purple flags – Purple also marks water, but the kind you don’t want to drink: recycled water from waste water. But it’s good for landscape irrigation.
  • Green flags – Green flags mean drain lines and sewers. Cutting this line could release poisonous gasses and flood the neighborhood.

Utility Flag Marking Cheatsheet

Having trouble memorizing what each color flag is used for? Use our flag color cheatsheet.

Flag ColorUse
RedElectrical utilities like power lines
WhiteExcavation
PinkTemporary survey markings
YellowGas lines like petroleum, steam
OrangeCommunication lines
BlueWater lines
PurpleUndrinkable water lines
GreenSewer lines


Analysis of radio astronomy bands using CALLISTO spectrometer at Malaysia-UKM station

The e-CALLISTO system is a worldwide network that aims to observe solar radio emission for astronomical science. CALLISTO instruments have been deployed worldwide in various locations that together can provide continuous observation of the solar radio spectrum for 24 h per day year-round. Malaysia-UKM is a strategic equatorial location and can observe the Sun 12 h per day. This paper gives an overview of the spectrum allocation for radio astronomy, which falls in the specified operating frequency band of the CALLISTO spectrometer. The radio astronomy bands are analyzed at the Malaysia-UKM station according to the International Telecommunication Union recommendations. Some observational results are also presented in this paper.

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4. Discussion and Summary

Here, we have used HST and XMM-Newton observational constraints to derive a model of the equatorial obscurer. We have shown that the equatorial obscurer, which modifies the SED to produce the emission-line holiday, is itself a significant source of line emission, solving several long-standing problems in emission-line physics. The model predicts that lines should have a core formed in the classical BLR and strong broad wings, a profile consistent with the line deconvolution presented in Kriss et al. (2019), and that much of the UV He ii and X-ray Fe Kα can originate in the equatorial obscurer. Finally, we found that the obscurer has a modest optical depth to electron scattering and so adds reflection and scattering to the physics of the line-continuum transfer function and emission-line profiles. This is a unified model of the disk wind in which the remarkable responses of the emission lines in NGC 5548are explained and the properties of the unobservable part of the wind are derived.

Figure 5 shows a cartoon of our derived geometry. This figure is consistent with Figure 1 of D19b, however, here we also consider the emission from the wind. The very bright area, the base of the wind, indicates this emission from the equatorial obscurer. Variations in this part of the wind produce the emission-line holiday (D19b).

Figure 5. Cartoon of the disk wind in NGC 5548 (not to scale). The disk wind (blue) surrounds the central black hole and extends to the LOS to HST in the upper-right corner. The BLR is shown as the orange cloud around the disk. The green cloud at the upper right shows the absorbing cloud discussed in D19a. The bright region in the lower part of the wind indicates that the wind is a major contributor to the very broad components of the observed emission lines.

This model is also consistent with the Sim et al. (2010) Monte Carlo radiative transfer predictions of the X-ray spectra of a line-driven AGN disk wind. They argued that a disk wind can easily produce a significant strong, broad Fe Kα component which has a complex line profile. Based on their simulations, the wind's effects on reflecting or reprocessing radiation is at least as important as the wind's effects on the absorption signatures. Their model was later followed by Tatum et al. (2012), in which a Compton-thick disk wind is responsible for all moderately broad Fe K emission components observed in a sample of AGNs. Their disk wind is not located in the LOS to the source and still affects the observed X-ray spectrum.

The electron scattering optical depth could be larger than estimated here, τe

0.1. Our derived parameters are highly approximate suggestions of the properties of the equatorial obscurer. We choose the smallest Lyman continuum optical depth (and H 0 column density) obscurer that is consistent with D19b. Other solutions with similar atomic column density but greater thickness are possible. They would have larger ionized column density and electron scattering optical depth. The Thomson optical depths reported in Figure 3 are normal to the slab. A ray passing into the slab at an angle θ will see an optical depth of τ0/cos θ. For isotropic illumination the mean optical depth is larger than the normal.

A region with a significant electron scattering optical depth and warm temperature, T ≈ 5 × 10 4 K, would solve several outstanding problems, which we summarize next.

It could be a part of the Compton reflector and so constitutes a translucent mirror in the inner regions. Scattering off warm gas will help producing smooth line profiles (Arav et al. 1998), a long-standing mystery in the geometry of the BLR. Gas with these properties also produces bremsstrahlung emission with a temperature similar to that deduced by Antonucci & Barvainis (1988) and so could provide the location of the non-disk emission. The obscurer modeled here is not a significant source of bremsstrahlung emission, however.

A model with an electron scattering optical depth ≥0.5 could provide an obscuration required for explaining the velocity-delay maps of Horne et al. (2020). They show that the emission from the far side of the BLR is much fainter than expected with isotropic emission from the central source and no obscuration. If the base of the wind is transparent we will observe both the near and far sides of the BLR. This indicates that there must be an obscuring cloud between the BLR and the source, acting like a mirror.

D19b proposed that the disk wind can be transparent or translucent. This hypothesis is compatible with Figure 4 of Giustini & Proga (2019), in which NGC 5548 is on the border of having a line-driven disk wind or a failed wind. This means that small changes in the disk luminosity/mass-loss rate will affect the state of the wind. The reason is that decreasing the disk luminosity leads to a reduction in the mass flux density of the wind, making it over-ionized (Proga & Kallman 2004). A transparent wind has little effect on the SED and no spectral holidays occur, while holidays occur when the wind is translucent. In this state, the equatorial obscurer absorbs a great deal of the XUV/X-ray part of the SED which must be reemitted in other spectral regions.

In this paper, we introduced a new approach to derive the wind's properties. This will have important implications for future studies of AGN outflows and feedback. We used observations to discover the behavior of a part of the wind the can never be directly observed. Our models of the wind will be expanded to better approximate the hydrodynamics of the wind. Deriving these "next generation" hydrodynamical/microphysical models and comparing them with the observations will be the subject of our future study.

Support for HST program number GO-13330 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We thank NSF (1816537, 1910687), NASA (17-ATP17-0141, 19-ATP19-0188), and STScI (HST-AR-15018, HST-AR-14556). M.C. acknowledges support from NASA through STScI grant HST-AR-14556.001-A and NASA grant 19-ATP19-0188, and also support from National Science Foundation through grant AST-1910687. M.D. and G.F. and F.G. acknowledge support from the NSF (AST-1816537), NASA (ATP 17-0141), and STScI (HST-AR-13914, HST-AR-15018), and the Huffaker Scholarship. M.M. is supported by the Netherlands Organization for Scientific Research (NWO) through the Innovational Research Incentives Scheme Vidi grant 639.042.525. J.M.G. gratefully acknowledges support from NASA under the ADAP award 80NSSC17K0126. M.V. gratefully acknowledges support from the Independent Research Fund Denmark via grant number DFF 8021-00130.


Watch the video: Fishing Knots: Albright Knot - How to Tie Braid to Mono or Braid to Fluorocarbon (November 2022).