Endpoints of Stellar Evolution Dicy Saylor ASTR 8000 Nov 19, 2014
Overview White Dwarfs PNNe, White Dwarfs, and PG1159, oh my! Novae Classical Novae and Cataclysmic Variables Supernovae Type I and Type II
Background Intermediate mass stars evolving away from AGB, ejecting shells of gas Initially PNNe/Post-AGB then rapidly evolve into WD Abell 39 noao.edu
Background Degenerate matter remnant of an intermediate mass star Cool over time Sirius AB nasa.gov
History Do not fit the normal MK system (faint, but A type) Intrinsically faint Difficult to obtain decent spectra Williamina Fleming was one of the first astronomers to note the strange characteristics of white dwarfs. wikipedia.org
Nomenclature D indicates degenerate A, B, C, O, Z, Q indicate the main features Additional features noted with P, H, X, E,?, V, d, (CI), (CII), (OI), (OII)
WD DA show only H lines; no He I or metals. Note the broad Balmer lines at 4342 Å, 4861 Å, and 6563 Å
WD DZ show strong Ca II H & K lines in addition to other metals, e.g. Mg I λ3835 and Fe I λ3730. WD DQ show strong molecular C bands. Both are He-rich.
PG1159 Stars Pre-degenerate Spectra lack H and He I Blend of He II and C IV 4650Å - 4690Å Classified into three groups A, E, lge.
wikipedia.org The primary component has a metallicity about 65% of the solar metallicity, thus providing a probably sufficient heavy element abundance for the formation of terrestrial planets. However, no planet orbiting a member of 40 Eridani is known so far. The habitable zone of 40 Eridani A, where a planet could exist with liquid water, is near 0.68 AU. At this distance a planet would complete a revolution in 223 Earth days and 40 Eridani A would appear nearly 20% wider than the Sun does on Earth. An observer on a planet in the 40 Eridani A system would see the B/C pair as unusually bright (magnitudes -8 and -6) white and reddish-orange stars in the night sky. This is not bright enough to diminish the darkness at night, though they would be visible in daylight It is extremely unlikely that habitable planets exist around the B star because planets circling 40 Eridani B would probably have been destroyed or sterilized by its evolution into a white dwarf. As for 40 Eridani C, it is prone to flares, which cause large momentary increases in the emission of X-rays as well as visible light. This would be lethal to Earth-type life on planets near the flare star. 40 Eridani was the first WD star discovered. The primary has a hab zone similar to our Solar system.
With a mass nearly equal to the Sun's, Sirius B is one of the more massive white dwarfs known (0.98 solar masses); it is almost double the 0.5 0.6 solar-mass average. Yet that same mass is packed into a volume roughly equal to the Earth's. The current surface temperature is 25,200 K. However, because there is no internal heat source, Sirius B will steadily cool as the remaining heat is radiated into space over a period of more than two billion years. nasa.gov Chandra (x-ray) image of Sirius AB. This is one of the most massive WD known.
Overview White Dwarfs PNNe, White Dwarfs, and PG1159, oh my! Novae Classical Novae and Cataclysmic Variables Supernovae Type I and Type II
Background MS star with accreting WD companion Runaway thermonuclear reaction ejects outer layers characteristic emission lines nasa.gov
Background WD is NOT destroyed in the process This type of nova event is recurrent on a timescale of 1,000s of years Nova Eridani 2009 wikipedia.org.
History Payne-Gaposchkin first described nova spectral evolution in 1957, but did not attempt to develop a classification system Williams et al. (1991) proposed the Tololo Nova Spectral Classification System wikipedia.org
Nomenclature Tololo focuses on classifying post-outburst evolution P, N, A, C phases defined for 3400-7500 Å spectral region. Subclass defined by strongest non-balmer line a, he, he+, n, o, ne, fe, c, na, ca, s Fe II vs He/N type nova (defined during P phase)
FeIIn type spectra evolve slowly Fe II permitted lines Developed a nebular spectrum lower excitation lines Entered auroral phase higher excitation Pn Cne Ane Evolution of Nova Cen 1991 spectrum
Very fast He/N type Fade rapidly, or Enter coronal phase, or Enter nebular stage neon nebula Developed coronal phase characterized by appearance of the coronal [Fe X] λ6375 line Faded rapidly Optical spectrum of Nova Sgr 1991
Always complications! P Cygni profiles 5 days after discovery which later disappear Evolved to resemble a luminous F supergiant Dimmed then flared many times Blue-violet non-flux calibrated spectrum of Nova Cas 1995
RS Ophiuchi (RS Oph) is a recurrent nova system approximately 5,000 light-years away in the constellation Ophiuchus. In its quiet phase it has an apparent magnitude of about 12.5. It erupted in 1898, 1933, 1958, 1967, 1985, and 2006 and reached about magnitude 5 on average. The recurrent nova is produced by a white dwarf star and a red giant circling about each other in a close orbit. wikipedia.org Recurrent nova RS Ophiuchus in eruption on February 2006. It has been observed in eruption 6 times, making it a recurrant nova.
Overview White Dwarfs PNNe, White Dwarfs, and PG1159, oh my! Novae Classical Novae and Cataclysmic Variables Supernovae Type I and Type II
Background Classical novae are a type of cataclysmic variable 1. Recurrent 2. Dwarf 3. Nova-like variables 4. Helium CVs 5. Polar wikipedia.org
Background Recurrent are classical novae that have been observed to have more than one outburst Dwarf novae show emission lines in quiescence and absorption in outbursts (instabilities in accretion disk?)
Background Nova-like are (probably) classical variables that haven t been been observed in outburst Helium CV are classical nova with He rich material being transferred Polar variables have strong magnetic fields that funnel material on to a hot spot
Recurrent nova T CrB at quiescence U Gem-type dwarf nova SS Cyg also at quiescence (shows Balmer emission) SU UMa-type dwarf nova EF Peg caught during a superoutburst (shows Balmer absorption) Spectra of three cataclysmic variables
V838 Monocerotis (V838 Mon) is a red variable star in the constellation Monoceros about 20,000 light years (6 kpc) from the Sun. The previously unknown star was observed in early 2002 experiencing a major outburst, and was possibly one of the largest known stars for a short period following the outburst. Originally believed to be a typical nova eruption, it was then realized to be something completely different. The reason for the outburst is still uncertain, but several conjectures have been put forward, including an eruption related to stellar death processes and a merger of a binary star or planets. wikipedia.org V838 Mon and its light echo as imaged by the Hubble Space Telescope on December 17, 2002. The exact mechanism that produced the outburst is unknown.
Note the deep H2O molecular bands, and the strong lines of alkali metals. A near-infrared spectrum of V838 Mon, obtained in Oct 2002
KIC 9406652 is a remarkable variable star in the Kepler field of view that shows both very rapid oscillations and long term outbursts in its light curve. We present an analysis of the light curve over quarters 1 15 and new spectroscopy that indicates that the object is a cataclysmic variable with an orbital period of 6.108 hr. However, an even stronger signal appears in the light curve periodogram for a shorter period of 5.753 hr, and we argue that this corresponds to the modulation of flux from the hot spot region in a tilted, precessing disk surrounding the white dwarf star. We present a preliminary orbital solution from radial velocity measurements of features from the accretion disk and the photosphere of the companion. We use a Doppler tomography algorithm to reconstruct the disk and companion spectra, and we also consider how these components contribute to the object s spectral energy distribution from ultraviolet to infrared wavelengths. This target offers us a remarkable opportunity to investigate disk processes during the high mass transfer stage of evolution in cataclysmic variables. Gies et al., 2013 Unusual variable star in KIC 9406652 observed by Kepler in Q1-15. The light curve shows features of outbursts, binary orbital period, as well as a titled, precessing disk (hot spot).
Blue spectral features Balmer and He I absorption+emission Similar to B-star spectrum Too broad to be stellar photosphere Weak Ca II λ3933 and DIB at 4428Å Little extinction along LOS Red spectral features Balmer and He I emission+absorption Hα absorption missing Telluric absorption Blue and red spectra of KIC 9406642 show similarities to CV RW Sextantis. Absorption wings originate in disk. Emission cores form in the cool face of the MS star facing the WD companion.
Overview White Dwarfs PNNe, White Dwarfs, and PG1159, oh my! Novae Classical Novae and Cataclysmic Variables Supernovae Type I and Type II
Background Two types I no Hydrogen lines II Hydrogen lines Two formation scenarios Core collapse of a massive star (neutron star remains) Accreting WD reaches Chandrasekhar limit (destroys WD) SN remnant N 63A in the LMC wikipedia.org
Background SN II spiral galaxies or irregulars with star forming regions near spiral arms or H II regions association with massive star death SN Ia occur in all galaxy types no association with spiral arms when seen in spirals WD explosion SN Ib, Ic also occur in spirals or H II regions massive star death lack of H indicates a WR or LBV progenitor (high mass loss rate)
Type I No Hydrogen lines Absorption features Ia Ib Ic Si II λ6150 He I λ5876 weak/no He Also see Fe II, Ca II, O I
Ia complex of forbidden Fe and Co emission lines Ib and Ic dominated by emission from lighter elements C I, O I, Ca II, Mg I λ4562 Difficult to distinguish Ib and Ic as He I λ5876 fades and blends with Na I D Late time supernovae spectra
Type II Hydrogen lines Broad P Cygni profiles ejection velocities 10,000 km s-1
SN IIL single maximum steep, linear decline less steep after ~100d SN IIP Plateau shortly after maximum due to recombination of H that was ionized in initial outburst Short, steep decline Ends with shallow, linear decline SN I show rapid, uniform linear decline as result of radioactive decay of 56-Ni 56-Co 56-Fe Light curves for Type IIL and IIP
Overview of supernovae classification scheme
Supernova 1604, also known as Kepler's Supernova, Kepler's Nova or Kepler's Star, was a supernova of Type Ia that occurred in the Milky Way, in the constellation Ophiuchus. Appearing in 1604, it is the most recent supernova to have been unquestionably observed by the naked eye in our own galaxy, occurring no farther than 6 kiloparsecs or about 20,000 light-years from Earth. Visible to the naked eye, Kepler's Star was brighter at its peak than any other star in the night sky, and brighter than all the planets other than Venus, with an apparent magnitude of 2.5. It was visible during the day for over three weeks. wikipedia.org Composite image of type Ia supernova remnant SN 1604 (HST/NASA/ESA). This is most recent SN even in the MW and could be seen during the day.
A significant problem in studies of the Crab Nebula is that the combined mass of the nebula and the pulsar add up to considerably less than the predicted mass of the progenitor star, and the question of where the 'missing mass' is, remains unresolved. Estimates of the mass of the nebula are made by measuring the total amount of light emitted, and calculating the mass required, given the measured temperature and density of the nebula. Estimates range from about 1 5 solar masses, with 2 3 solar masses being the generally accepted value. The neutron star mass is estimated to be between 1.4 and 2 solar masses.the predominant theory to account for the missing mass of the Crab is that a substantial proportion of the mass of the progenitor was carried away before the supernova explosion in a fast stellar wind, a phenomenon commonly seen in Wolf-Rayet stars. However, this would have created a shell around the nebula. Although attempts have been made at several wavelengths to observe a shell, none has yet been found. wikipedia.org Spitzer image of the Crab Nebula, a type II (or Ib/Ic) supernova remnant. Missing mass may be due to WR progenitor.
SN 1993J was discovered on 28 March 1993 by F. Garcia in Spain. At the time, it was considered the second brightest type II supernova observed in the twentieth century behind SN 1987A. The spectral characteristics of the supernova changed over time. Initially, it looked more like a type II supernova with strong hydrogen spectral line emission, but later the hydrogen lines faded and strong helium spectral lines appeared, making the supernova look more like a type Ib. Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovae, but did resemble the variations observed in type Ib supernovae. Hence, the supernova has been classified as a type IIb, an intermediate class between type II and type Ib. wikipedia.org SN 1993J is a supernova of type IIb in M81. SN 1993J is an example of a type II that evolves to look like a type Ib.
Summary White Dwarfs PNNe degenerate, nebula still visible PG 1159 pre-degenerate Novae Classical Novae runaway t nuclear explosion Cataclysmic Variables general class of novae
Summary Cont d Supernovae Type I Type II WD reaches Chandrasekhar limit death of a high mass star
References Gies, D.R., Guo, Z., Howell, S.B., et al. 2013, ApJ, 775, 64 Stellar Spectral Classification Richard O. Gray & Christopher J. Corbally nasa.gov & wikipedia.org
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