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77-456: Wolf–Rayet (WR) can mean: Wolf–Rayet star , a type of evolved, massive star Wolf–Rayet galaxy , which contains large numbers of Wolf–Rayet stars Wolf–Rayet nebula , which surrounds a Wolf–Rayet star Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Wolf–Rayet . If an internal link led you here, you may wish to change

154-406: A planetary nebula formed by a post- AGB star. The nebulosity presents a variety of forms and classification has been difficult. Many were originally catalogued as planetary nebulae and sometimes only a careful multi-wavelength study can distinguish a planetary nebula around a low mass post-AGB star from a similarly shaped nebula around a more massive core helium-burning star. A Wolf–Rayet galaxy

231-1080: A Wolf–Rayet star. This is caused by the same physical mechanism: rapid expansion of dense gases around an extremely hot central source. The separation of Wolf–Rayet stars from spectral class O stars of a similar temperature depends on the existence of strong emission lines of ionised helium, nitrogen, carbon, and oxygen, but there are a number of stars with intermediate or confusing spectral features. For example, high-luminosity O stars can develop helium and nitrogen in their spectra with some emission lines, while some WR stars have hydrogen lines, weak emission, and even absorption components. These stars have been given spectral types such as O3If /WN6 and are referred to as slash stars. Class O supergiants can develop emission lines of helium and nitrogen, or emission components to some absorption lines. These are indicated by spectral peculiarity suffix codes specific to this type of star: These codes may also be combined with more general spectral type qualifiers such as p or a. Common combinations include OIafpe and OIf , and Ofpe. In

308-468: A companion rather than inherent mass loss due to a stellar wind. This process is relatively insensitive to the metallicity or rotation of the individual stars and is expected to produce a consistent set of WR stars across all the local group galaxies. As a result, the fraction of WR stars produced through the binary channel, and therefore the number of WR stars observed to be in binaries, should be higher in low metallicity environments. Calculations suggest that

385-687: A cooperation was realized in the Variable Star Section of the British Astronomical Association and the American Association of Variable Star Observers (AAVSO). Pickering had a good relationship with the AAVSO and received a gold paper knife with precious stones. In 1882, Pickering developed a method to photograph the spectra of multiple stars simultaneously by putting a large prism in front of

462-493: A letter to Mrs. Draper "...pray recollect that if I can in any way advise or aid you, I shall be doing but little to repay Dr. Draper for a friendship which I shall always value, but which can never be replaced." Mrs. Draper urgently responded and soon dropped off her husband's work to Pickering. Pickering concluded that Draper's use of photography in astronomy was very promising compared to the traditional method of observation and recording using one's eye through instruments. In 1884,

539-635: A numeric suffix in order of discovery. This applies to all discoveries since the 2006 annex, although some of these have already been named under the previous nomenclature; thus WR 42e is now numbered WR 42-1. Wolf–Rayet stars are a normal stage in the evolution of very massive stars, in which strong, broad emission lines of helium and nitrogen ("WN" sequence), carbon ("WC" sequence), and oxygen ("WO" sequence) are visible. Due to their strong emission lines they can be identified in nearby galaxies. About 600 Wolf–Rayets have been catalogued in our own Milky Way Galaxy . This number has changed dramatically during

616-404: A numerical sequence from WR 1 to WR 158 in order of right ascension. Compiled in 2001, the seventh catalogue and its annex used the same numbering scheme and inserted new stars into the sequence using lower case letter suffixes, for example WR 102ka for one of the numerous WR stars discovered in the galactic centre. Modern high volume identification surveys use their own numbering schemes for

693-442: A paper on such observations was published with the author "the late Henry Draper . " After receiving criticism from Dr. William Huggins , a friend of Dr. Draper, Pickering began to hire more assistants to strengthen Draper's findings. This consequently also strengthened and contributed to Harvard Computers. In 1882 he started his appeals for international variable star observations. This was met with opposition, but eventually such

770-473: A rapidly expanding helium-rich ejecta similar to an extreme Wolf–Rayet wind. The WR spectral features only last a matter of hours, the high ionisation features fading by maximum to leave only weak neutral hydrogen and helium emission, before being replaced with a traditional supernova spectrum. It has been proposed to label these spectral types with an "X", for example XWN5(h). Similarly, classical novae develop spectra consisting of broad emission bands similar to

847-742: A stellar classification system based on an alphabetic system for spectral classes that was first known as the Harvard Stellar Classification and became the basis for the Henry Draper Catalog . In 1896, Pickering published observations of previously unknown lines in the spectra of the star ζ-Puppis . These lines became known as the Pickering series (or the Pickering–Fowler series) and Pickering attributed them to hydrogen in 1897. Alfred Fowler gave

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924-495: A tendency to higher atmospheric hydrogen fractions. SMC WR stars almost universally show some hydrogen and even absorption lines even at the earliest spectral types, due to weaker winds not entirely masking the photosphere. The maximum mass of a main-sequence star that can evolve through a red supergiant phase and back to a WNL star is calculated to be around 20  M ☉ in the Milky Way, 32  M ☉ in

1001-452: Is a type of starburst galaxy where a sufficient number of WR stars exist that their characteristic emission line spectra become visible in the overall spectrum of the galaxy. Specifically a broad emission feature due to the 468.6 nm He   ii and nearby spectral lines is the defining characteristic of a Wolf–Rayet galaxy. The relatively short lifetime of WR stars means that the starbursts in such galaxies must have occurred within

1078-449: Is associated with a negative connotation, he was known during the time to give women more equal treatment than most. Doing so paved the way for many more women to become interested and involved in astronomy. Pickering's work with using glass plates to photograph the sky was the start of major technological advances for astronomical photography. Although glass plates are no longer used, his work led to modern uses of charged coupled devices in

1155-414: Is not universally accepted. The type WN1 was proposed for stars with neither N   IV nor N   V lines, to accommodate Brey 1 and Brey 66 which appeared to be intermediate between WN2 and WN2.5. The relative line strengths and widths for each WN sub-class were later quantified, and the ratio between the 541.1 nm He   II and 587.5 nm, He   I lines was introduced as

1232-578: The Harvard John A. Paulson School of Engineering and Applied Sciences ), where he received his Bachelor of Science (BS) degree in 1865. Immediately upon graduating from Harvard he was hired as an instructor of mathematics there, and a year later he moved to the Massachusetts Institute of Technology to be an assistant professor of physics. In 1868, he was made Thayer Professor of Physics, succeeding William Barton Rogers . During

1309-555: The Henry Draper catalogue . These stars and others were referred to as Wolf–Rayet stars from their initial discovery but specific naming conventions for them would not be created until 1962 in the "fourth" catalogue of galactic Wolf–Rayet stars. The first three catalogues were not specifically lists of Wolf–Rayet stars and they used only existing nomenclature. The fourth catalogue of Wolf-Rayet stars numbered them sequentially in order of right ascension . The fifth catalogue used

1386-510: The M101 Group , over a thousand potential WR stars have been detected, from magnitude 21 to 25, and astronomers hope to eventually catalog over ten thousand. These stars are expected to be particularly common in the Wolf–Rayet galaxies named after them and in starburst galaxies . Their characteristic emission lines are formed in the extended and dense high-velocity wind region enveloping

1463-614: The Small Magellanic Cloud SMC WR numbers are used, usually referred to as AB numbers, for example AB7 . There are only twelve known WR stars in the SMC, a very low number thought to be due to the low metallicity of that galaxy In 2012, an IAU working group expanded the numbering system from the Catalogue of Galactic Wolf–Rayet stars so that additional discoveries are given the closest existing WR number plus

1540-580: The Sun while on the main sequence, but have now ceased fusion and shed their atmospheres to reveal a bare carbon-oxygen core. All Wolf–Rayet stars are highly luminous objects due to their high temperatures—thousands of times the bolometric luminosity of the Sun ( L ☉ ) for the CSPNe, hundreds of thousands  L ☉ for the population I WR stars, to over a million  L ☉ for

1617-676: The 10 years he was there, he created the first physics lab in America that was designed for students to publish their own findings and research. Pickering named this lab the Rogers Laboratory of Physics and pronounced himself Director of the Laboratory. He resigned as Thayer Professor of Physics in 1877, and was succeeded by Charles R. Cross . Later, Pickering served as director of Harvard College Observatory (HCO) from 1877 to his death in 1919, where he made great leaps forward in

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1694-495: The 1970s, it was recognised that there was a continuum of spectra from pure absorption class O to unambiguous WR types, and it was unclear whether some intermediate stars should be given a spectral type such as O8Iafpe or WN8-a. The slash notation was proposed to deal with these situations, and the star Sk−67°22 was assigned the spectral type O3If /WN6-A. The criteria for distinguishing OIf , OIf /WN, and WN stars have been refined for consistency. Slash star classifications are used when

1771-407: The 19th century, the nature of these stars was uncertain until towards the end of the 20th century. Before the 1960s, even the classification of WR stars was highly uncertain, and their nature and evolution was essentially unknown. The very similar appearance of the central stars of planetary nebulae (CSPNe) and the much more luminous classical WR stars contributed to the uncertainty. By about 1960,

1848-678: The H β line has a P Cygni profile; this is an absorption line in O supergiants and an emission line in WN stars. Criteria for the following slash star spectral types are given, using the nitrogen emission lines at 463.4–464.1 nm, 405.8 nm, and 460.3–462.0 nm, together with a standard star for each type: Another set of slash star spectral types is in use for Ofpe/WN stars. These stars have O supergiant spectra plus nitrogen and helium emission, and P Cygni profiles. Alternatively they can be considered to be WN stars with unusually low ionisation levels and hydrogen. The slash notation for these stars

1925-545: The LMC, and over 50  M ☉ in the SMC. The more evolved WNE and WC stages are only reached by stars with an initial mass over 25  M ☉ at near-solar metallicity, over 60  M ☉ in the LMC. Normal single star evolution is not expected to produce any WNE or WC stars at SMC metallicity. Mass loss is influenced by a star's rotation rate, especially strongly at low metallicity. Fast rotation contributes to mixing of core fusion products through

2002-712: The Large Magellanic Cloud have spectra that contain both WN3 and O3V features, but do not appear to be binaries. Many of the WR stars in the Small Magellanic Cloud also have very early WN spectra plus high excitation absorption features. It has been suggested that these could be a missing link leading to classical WN stars or the result of tidal stripping by a low-mass companion. The first three Wolf–Rayet stars to be identified, coincidentally all with hot O-class companions, had already been numbered in

2079-492: The Large Magellanic Cloud" prefixed by BAT-99 , for example BAT-99 105 . Many of these stars are also referred to by their third catalogue number, for example Brey 77 . As of 2018, 154 WR stars are catalogued in the LMC, mostly WN but including about twenty-three WCs as well as three of the extremely rare WO class. Many of these stars are often referred to by their RMC (Radcliffe observatory Magellanic Cloud) numbers, frequently abbreviated to just R, for example R136a1 . In

2156-511: The Milky Way showing higher metallicities closer to the centre, and M31 showing higher metallicity in the disk than in the halo. Thus the SMC is seen to have few WR stars compared to its stellar formation rate and no WC stars at all (one star has a WO spectral type), the Milky Way has roughly equal numbers of WN and WC stars and a large total number of WR stars, and the other main galaxies have somewhat fewer WR stars and more WN than WC types. LMC, and especially SMC, Wolf–Rayets have weaker emission and

2233-410: The N   IV lines at 347.9–348.4 nm and 405.8 nm, and the N   V lines at 460.3 nm, 461.9 nm, and 493.3–494.4 nm. These lines are well separated from areas of strong and variable He emission and the line strengths are well correlated with temperature. Stars with spectra intermediate between WN and Ofpe have been classified as WN10 and WN11 although this nomenclature

2310-630: The O   V (and O   III ) blend at 557.2–559.8 nm. The sequence was extended to include WC10 and WC11, and the subclass criteria were quantified based primarily on the relative strengths of carbon lines to rely on ionisation factors even if there were abundance variations between carbon and oxygen. For WO-type stars the main lines used are C   IV at 580.1 nm, O   IV at 340.0 nm, O   V (and O   III ) blend at 557.2–559.8 nm, O   VI at 381.1–383.4 nm, O   VII at 567.0 nm, and O   VIII at 606.8 nm. The sequence

2387-557: The Pickering series had demonstrated the need for "a re-examination of problems that seemed already to have been solved within classical theories" and provided important confirmation for his atomic theory. Pickering is credited for making the Harvard College Observatory known and respected around the world, and it continues today to be a well-respected observatory and program. The Harvard College Observatory

Wolf–Rayet - Misplaced Pages Continue

2464-494: The WN stars without hydrogen. Despite the similar spectra, they are much more massive, much larger, and some of the most luminous stars known. They have been detected as early as WN5h in the Magellanic Clouds. The nitrogen seen in the spectrum of WNh stars is still the product of CNO cycle fusion in the core, but it appears at the surface of the most massive stars due to rotational and convectional mixing while still in

2541-648: The WNh stars—although not exceptionally bright visually since most of their radiation output is in the ultraviolet . The naked-eye star systems γ Velorum and θ Muscae both contain Wolf-Rayet stars, and one of the most massive known stars , R136a1 in 30 Doradus , is also a Wolf–Rayet star. In 1867, using the 40 cm Foucault telescope at the Paris Observatory , astronomers Charles Wolf and Georges Rayet discovered three stars in

2618-672: The WO classification was adopted for them. The OVI stars were subsequently classified as [WO] stars, consistent with the population I WR stars. The understanding that certain late, and sometimes not-so-late, WN stars with hydrogen lines in their spectra are at a different stage of evolution from hydrogen-free WR stars has led to the introduction of the term WNh to distinguish these stars generally from other WN stars. They were previously referred to as WNL stars, although there are late-type WN stars without hydrogen as well as WR stars with hydrogen as early as WN5. Wolf–Rayet stars were named on

2695-674: The basis of the strong broad emission lines in their spectra, identified with helium , nitrogen , carbon , silicon , and oxygen , but with hydrogen lines usually weak or absent. Initially simply referred to as class W or W-type stars, the classification was then split into stars with dominant lines of ionised nitrogen (N   III , N   IV , and N   V ) and those with dominant lines of ionised carbon (C   III and C   IV ) and sometimes oxygen (O   III – O   VI ), referred to as WN and WC respectively. The two classes WN and WC were further split into temperature sequences WN5–WN8 and WC6–WC8 based on

2772-446: The binary fraction of WR stars observed in the SMC should be as high as 98%, although less than half are actually observed to have a massive companion. The binary fraction in the Milky Way is around 20%, in line with theoretical calculations. A significant proportion of WR stars are surrounded by nebulosity associated directly with the star, not just the normal background nebulosity associated with any massive star forming region, and not

2849-537: The case of the famous binary WR 104 ; however this process occurs on single ones too. A few – roughly 10% – of the central stars of planetary nebulae , despite their much lower masses – typically ~0.6 M ☉ – are also observationally of the WR-type; i.e. they show emission line spectra with broad lines from helium, carbon and oxygen. Denoted [WR], they are much older objects descended from evolved low-mass stars and are closely related to white dwarfs , rather than to

2926-475: The central stars of planetary nebulae are qualified by surrounding them with square brackets (e.g. [WC4]). They are almost all of the WC sequence with the known [WO] stars representing the hot extension of the carbon sequence. There are also a small number of [WN] and [WC/WN] types, only discovered quite recently. Their formation mechanism is as yet unclear. Temperatures of the planetary nebula central stars tend to

3003-449: The chemical element having just been discovered in 1868. Pickering noted similarities between Wolf–Rayet spectra and nebular spectra, and this similarity led to the conclusion that some or all Wolf–Rayet stars were the central stars of planetary nebulae . By 1929, the width of the emission bands was being attributed to Doppler broadening , and hence the gas surrounding these stars must be moving with velocities of 300–2400 km/s along

3080-426: The constellation Cygnus (HD 191765, HD 192103 and HD 192641, now designated as WR 134 , WR 135 , and WR 137 respectively) that displayed broad emission bands on an otherwise continuous spectrum. Most stars only display absorption lines or bands in their spectra, as a result of overlying elements absorbing light energy at specific frequencies, so these were clearly unusual objects. The nature of

3157-409: The cooler ones as late, consistent with other spectral types. WNE and WCE refer to early type spectra while WNL and WCL refer to late type spectra, with the dividing line approximately at sub-class six or seven. There is no such thing as a late WO-type star. There is a strong tendency for WNE stars to be hydrogen-poor while the spectra of WNL stars frequently include hydrogen lines. Spectral types for

Wolf–Rayet - Misplaced Pages Continue

3234-400: The core hydrogen burning phase, rather than after the outer envelope is lost during core helium fusion. Some Wolf–Rayet stars of the carbon sequence ("WC"), especially those belonging to the latest types, are noticeable due to their production of dust . Usually this takes place on those belonging to binary systems as a product of the collision of the stellar winds forming the pair, as is

3311-442: The core. A subset of the population I WR stars show hydrogen lines in their spectra and are known as WNh stars; they are young extremely massive stars still fusing hydrogen at the core, with helium and nitrogen exposed at the surface by strong mixing and radiation-driven mass loss. A separate group of stars with WR spectra are the central stars of planetary nebulae (CSPNe), post- asymptotic giant branch stars that were similar to

3388-417: The distinction between CSPNe and massive luminous classical WR stars was more clear. Studies showed that they were small dense stars surrounded by extensive circumstellar material, but not yet clear whether the material was expelled from the star or contracting onto it. The unusual abundances of nitrogen, carbon, and oxygen, as well as the lack of hydrogen, were recognised, but the reasons remained obscure. It

3465-473: The emission bands in the spectra of a Wolf–Rayet star remained a mystery for several decades. E.C. Pickering theorized that the lines were caused by an unusual state of hydrogen , and it was found that this "Pickering series" of lines followed a pattern similar to the Balmer series when half-integer quantum numbers were substituted. It was later shown that these lines resulted from the presence of helium ,

3542-477: The evolution of massive stars and also the properties of Wolf–Rayet stars. Higher levels of mass loss cause stars to lose their outer layers before an iron core develops and collapses, so that the more massive red supergiants evolve back to hotter temperatures before exploding as a supernova, and the most massive stars never become red supergiants. In the Wolf–Rayet stage, higher mass loss leads to stronger depletion of

3619-401: The extremes when compared to population I WR stars, so [WC2] and [WC3] are common and the sequence has been extended to [WC12]. The [WC11] and [WC12] types have distinctive spectra with narrow emission lines and no He   II and C   IV lines. Certain supernovae observed before their peak brightness show WR spectra. This is due to the nature of the supernova at this point:

3696-550: The first spectroscopic binary stars. He wrote Elements of Physical Manipulations (2 vol., 1873–76). Pickering was born at 43 Bowdoin Street in Boston, Massachusetts, on July 19, 1846, to a distinguished, cultivated family consisting of his brother, William Henry Pickering , father, Edward Pickering, and his mother, Charlotte Hammond. Edward's brother, William, was a graduate of MIT and professor of physics and astronomy. Edward

3773-421: The gathering of stellar spectra through the use of photography. Shortly after the death of college doctor and amateur astronomer Henry Draper , an opportunity presented itself for Pickering. Draper's death left the incompletion of his work studying astronomy using photography. Draper had no children to carry on and finish his legacy, so his wife, Mary Anna Draper , planned on finishing his work. Pickering wrote

3850-596: The large numbers of new discoveries. A 2006 Annex was added to the seventh catalog. In 2011, an online Galactic Wolf Rayet Catalogue was set up, hosted by the University of Sheffield . As of 2023, it includes 669 stars. Wolf–Rayet stars in external galaxies are numbered using different schemes. In the Large Magellanic Cloud , the most widespread and complete nomenclature for WR stars is from "The Fourth Catalogue of Population I Wolf–Rayet stars in

3927-523: The last few million years, and must have lasted less than a million years or else the WR emission would be swamped by large numbers of other luminous stars. Theories about how WR stars form, develop, and die have been slow to form compared to the explanation of less extreme stellar evolution . They are rare, distant, and often obscured, and even into the 21st century many aspects of their lives are unclear. Although Wolf–Rayet stars have been clearly identified as an unusual and distinctive class of stars since

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4004-814: The last few years as the result of photometric and spectroscopic surveys in the near-infrared dedicated to discovering this kind of object in the Galactic plane . It is expected that there are fewer than 1,000 WR stars in the rest of the Local Group galaxies, with around 166 known in the Magellanic Clouds , 206 in the Triangulum Galaxy , and 154 in the Andromeda Galaxy . Outside the local group, whole galaxy surveys have found thousands more WR stars and candidates. For example, in

4081-516: The layers outside the convective core, lower hydrogen surface abundances and more rapid stripping of helium to produce a WC spectrum. These trends can be observed in the various galaxies of the local group, where metallicity varies from near-solar levels in the Milky Way, somewhat lower in M31, lower still in the Large Magellanic Cloud, and much lower in the Small Magellanic Cloud. Strong metallicity variations are seen across individual galaxies, with M33 and

4158-556: The line of sight. The conclusion was that a Wolf–Rayet star is continually ejecting gas into space, producing an expanding envelope of nebulous gas. The force ejecting the gas at the high velocities observed is radiation pressure . It was well known that many stars with Wolf–Rayet type spectra were the central stars of planetary nebulae, but also that many were not associated with an obvious planetary nebula or any visible nebulosity at all. In addition to helium, Carlyle Smith Beals identified emission lines of carbon, oxygen and nitrogen in

4235-544: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Wolf–Rayet&oldid=551253151 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Wolf%E2%80%93Rayet star Classic (or population I ) Wolf–Rayet stars are evolved , massive stars that have completely lost their outer hydrogen and are fusing helium or heavier elements in

4312-457: The main spectral classification: The classification of Wolf–Rayet spectra is complicated by the frequent association of the stars with dense nebulosity, dust clouds, or binary companions. A suffix of "+OB" is used to indicate the presence of absorption lines in the spectrum likely to be associated with a more normal companion star, or "+abs" for absorption lines with an unknown origin. The hotter WR spectral sub-classes are described as early and

4389-425: The period-luminosity relationship for Cepheids , published by Pickering, would prove the foundation for the modern understanding of cosmological distances. Pickering's treatment of women, during his time, was considered better than most. It is true that they were underpaid compared to their male counterparts and were not given credit nearly as often, but his willingness to include them in the world of astronomy paved

4466-446: The photographic plate. Using this method, Pickering and his team captured images of over 220,000 stars. This immense amount of photographic research has provided scientists for decades with a seemingly endless library containing the history of every visible star's movements. It is said that this research weighs 120 tons due to the size of photographic plates . He also, along with Williamina Fleming and Annie Jump Cannon , designed

4543-593: The position of director of the University Observatory continuing an odd 42-year tradition of HCO Directors dying in office. After his death, Solon Bailey served as interim director. Pickering's friends and colleges would remember him for his great ability, originality, initiative, and warm-heartedness. Pickering would be remembered by the world for his contribution to astronomical photography, advancement of astronomical discoveries, and his progressive view of women. Although today his treatment of women

4620-562: The primary indicator of the ionisation level and hence of the spectral sub-class. The need for WN1 disappeared and both Brey 1 and Brey 66 are now classified as WN3b. The somewhat obscure WN2.5 and WN4.5 classes were dropped. The WC spectral sequence was expanded to include WC4–WC11, although some older papers have also used WC1–WC3. The primary emission lines used to distinguish the WC sub-types are C   II 426.7 nm, C   III at 569.6 nm, C   III/IV 465.0 nm, C   IV at 580.1–581.2 nm, and

4697-424: The relative strengths of the 541.1 nm He   II and 587.5 nm He   I lines. Wolf–Rayet emission lines frequently have a broadened absorption wing ( P Cygni profile ) suggesting circumstellar material. A WO sequence has also been separated from the WC sequence for even hotter stars where emission of ionised oxygen dominates that of ionised carbon, although the actual proportions of those elements in

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4774-446: The rest of the star, enhancing surface abundances of heavy elements, and driving mass loss. Rotation causes stars to remain on the main sequence longer than non-rotating stars, evolve more quickly away from the red supergiant phase, or even evolve directly from the main sequence to hotter temperatures for very high masses, high metallicity or very rapid rotation. Stellar mass loss produces a loss of angular momentum and this quickly brakes

4851-504: The rotation of massive stars. Very massive stars at near-solar metallicity should be braked almost to a standstill while still on the main sequence, while at SMC metallicity they can continue to rotate rapidly even at the highest observed masses. Rapid rotation of massive stars may account for the unexpected properties and numbers of SMC WR stars, for example their relatively high temperatures and luminosities. Massive stars in binary systems can develop into Wolf–Rayet stars due to stripping by

4928-488: The same attribution to similar lines that he observed in a hydrogen-helium mixture in 1912. Analysis by Niels Bohr included in his 'trilogy' on atomic structure argued that the spectral lines arose from ionized helium , He , and not from hydrogen. Fowler was initially-skeptical but was ultimately convinced that Bohr was correct, and by 1915 " spectroscopists had transferred [the Pickering series] definitively [from hydrogen] to helium." Bohr's theoretical work on

5005-466: The same numbers prefixed with MR after the author of the fourth catalogue, plus an additional sequence of numbers prefixed with LS for new discoveries. Neither of these numbering schemes remains in common use. The sixth Catalogue of Galactic Wolf–Rayet stars was the first to actually bear that name, as well as to describe the previous five catalogues by that name. It also introduced the WR numbers widely used ever since for galactic WR stars. These are again

5082-585: The spectra of Wolf–Rayet stars. In 1938, the International Astronomical Union classified the spectra of Wolf–Rayet stars into types WN and WC, depending on whether the spectrum was dominated by lines of nitrogen or carbon-oxygen respectively. In 1969, several CSPNe with strong oxygen   VI (O   VI ) emissions lines were grouped under a new "O   VI sequence", or just OVI type. Similar stars not associated with planetary nebulae were described shortly after and

5159-429: The stars are likely to be comparable. WC and WO spectra are formally distinguished based on the presence or absence of C   III emission. WC spectra also generally lack the O   VI lines that are strong in WO spectra. The WN spectral sequence was expanded to include WN2–WN9, and the definitions refined based on the relative strengths of the N   III lines at 463.4–464.1 nm and 531.4 nm,

5236-412: The very hot stellar photosphere , which produces a flood of UV radiation that causes fluorescence in the line-forming wind region. This ejection process uncovers in succession, first the nitrogen-rich products of CNO cycle burning of hydrogen (WN stars), and later the carbon-rich layer due to He burning (WC and WO-type stars). It can be seen that the WNh stars are completely different objects from

5313-475: The very young, very massive population I stars that comprise the bulk of the WR class. These are now generally excluded from the class denoted as Wolf–Rayet stars, or referred to as Wolf–Rayet-type stars. The numbers and properties of Wolf–Rayet stars vary with the chemical composition of their progenitor stars. A primary driver of this difference is the rate of mass loss at different levels of metallicity. Higher metallicity leads to high mass loss, which affects

5390-460: The way for many great female scientists and leaders. This added to the observatory's funding through fellowships and the procurement of women including alumnus and professors aiding in the creation of Harvard Computers. Pickering was the fourth and longest-running director of HCO, serving for 42 years. On February 3, 1919, Pickering unexpectedly died from pneumonia and heart complications after being ill for around ten days. He died while holding

5467-594: Was becoming a premiere observatory in the world and with it came the demand for more assistants. These assistants were critical for taking notes, running calculations and performing analytics. College educated women from around the country offered to work for the Harvard Observatory unpaid to gain experience or until proving their value to be paid. During this time, Pickering recruited over 80 women to work for him, including Annie Jump Cannon , Henrietta Swan Leavitt , Antonia Maury , and Florence Cushman . It

5544-624: Was busy trying to devise useful applications to win the war. The Pickering Polaris Attachment was a device used to determine the range of guns. In 1874, Pickering married Lizzie Wadsworth Sparks, whose father was formerly the President of Harvard . Mrs. Pickering died in 1906, and Edward died in 1919. Pickering was educated at Boston Latin School , and then studied at the Lawrence Scientific School at Harvard (now known as

5621-710: Was controversial and an alternative was to extend the WR nitrogen sequence to WN10 and WN11 Other authors preferred to use the WNha notation, for example WN9ha for WR 108 . A recent recommendation is to use an O spectral type such as O8Iaf if the 447.1 nm He   i line is in absorption and a WR class of WN9h or WN9ha if the line has a P Cygni profile. However, the Ofpe/WN slash notation as well as WN10 and WN11 classifications continue to be widely used. A third group of stars with spectra containing features of both O class stars and WR stars has been identified. Nine stars in

5698-459: Was expanded to include WO5 and quantified based the relative strengths of the O   VI /C   IV and O   VI /O   V lines. A later scheme, designed for consistency across classical WR stars and CSPNe, returned to the WO1 to WO4 sequence and adjusted the divisions. Detailed modern studies of Wolf–Rayet stars can identify additional spectral features, indicated by suffixes to

5775-493: Was interested in the stars as a boy and constructed his own telescope by the age of 12. Pickering enjoyed his work at the observatory, but he also enjoyed mountain climbing and bicycling in earlier days and later he was an interested spectator of football games. He was co-founder and first president of the Appalachian Mountain Club . He was also a lover of classic music . During the first world war he

5852-402: Was recognised that WR stars were very young and very rare, but it was still open to debate whether they were evolving towards or away from the main sequence. Edward Charles Pickering Edward Charles Pickering (July 19, 1846 – February 3, 1919) was an American astronomer and physicist and the older brother of William Henry Pickering . Along with Carl Vogel , Pickering discovered

5929-500: Was very unusual for such an accomplished scientist to work with this many women, but it has been said that he "became so exasperated with his male assistant's inefficiency, that even his maid could do a better job of copying and computing". These women, the Harvard Computers (also described as "Pickering's Harem" by the male scientific community at the time), made several important discoveries at HCO. Leavitt's discovery of

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