endpoints of stellar evolution - physics & astronomy
TRANSCRIPT
Endpoints of Stellar Evolution Dicy Saylor ASTR 8000 Nov 19,
2014
Overview
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
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
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 , 4861 , and 6563
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.
“Pre-degenerate”
Blend of He II and C IV 4650 - 4690
Classified into three groups A, E, lgE.
PG1159 Stars
40 Eridani was the first WD star discovered. The primary has a hab zone similar to our Solar system.
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.
wikipedia.org
Chandra (x-ray) image of Sirius AB. This is one of the most massive WD known.
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
Overview
Novae Classical Novae and Cataclysmic Variables
Supernovae Type I and Type II
Background
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 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)
Evolution of Nova Cen 1991 spectrum
FeIIn type spectra evolve slowly Fe II permitted lines
Developed a nebular spectrum lower excitation lines
Entered auroral phase higher excitation
Pn Cne Ane
Optical spectrum of Nova Sgr 1991
Very fast He/N type Fade rapidly, or Enter coronal phase, or Enter nebular stage → “neon”
nebula
coronal [Fe X] λ6375 line
Faded rapidly
Always complications!
P Cygni profiles 5 days after discovery which later disappear
Evolved to resemble a luminous F supergiant
Dimmed then flared many times
Recurrent nova RS Ophiuchus in eruption on February 2006. It has been observed in eruption 6 times, making it a recurrant nova.
wikipedia.org
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.
Overview
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
Spectra of three cataclysmic variables
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)
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.
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
A near-infrared spectrum of V838 Mon, obtained in Oct 2002
Note the deep H2O molecular bands, and the strong lines of alkali metals.
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).
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
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.
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
Overview
Novae Classical Novae and Cataclysmic Variables
Supernovae Type I and Type II
Background
(neutron star remains) Accreting WD reaches
Chandrasekhar limit (destroys WD)
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 Si II λ6150 Ib He I λ5876 Ic weak/no He
Also see Fe II, Ca II, O I
Late time supernovae spectra
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
Type II
Hydrogen lines
Light curves for Type IIL and IIP
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
Overview of supernovae classification scheme
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.
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
Spitzer image of the Crab Nebula, a type II (or Ib/Ic) supernova remnant. Missing mass may be due to WR progenitor.
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
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.
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
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 WD reaches Chandrasekhar limit Type II 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
Thank you!
Overview
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
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
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 , 4861 , and 6563
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.
“Pre-degenerate”
Blend of He II and C IV 4650 - 4690
Classified into three groups A, E, lgE.
PG1159 Stars
40 Eridani was the first WD star discovered. The primary has a hab zone similar to our Solar system.
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.
wikipedia.org
Chandra (x-ray) image of Sirius AB. This is one of the most massive WD known.
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
Overview
Novae Classical Novae and Cataclysmic Variables
Supernovae Type I and Type II
Background
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 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)
Evolution of Nova Cen 1991 spectrum
FeIIn type spectra evolve slowly Fe II permitted lines
Developed a nebular spectrum lower excitation lines
Entered auroral phase higher excitation
Pn Cne Ane
Optical spectrum of Nova Sgr 1991
Very fast He/N type Fade rapidly, or Enter coronal phase, or Enter nebular stage → “neon”
nebula
coronal [Fe X] λ6375 line
Faded rapidly
Always complications!
P Cygni profiles 5 days after discovery which later disappear
Evolved to resemble a luminous F supergiant
Dimmed then flared many times
Recurrent nova RS Ophiuchus in eruption on February 2006. It has been observed in eruption 6 times, making it a recurrant nova.
wikipedia.org
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.
Overview
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
Spectra of three cataclysmic variables
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)
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.
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
A near-infrared spectrum of V838 Mon, obtained in Oct 2002
Note the deep H2O molecular bands, and the strong lines of alkali metals.
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).
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
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.
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
Overview
Novae Classical Novae and Cataclysmic Variables
Supernovae Type I and Type II
Background
(neutron star remains) Accreting WD reaches
Chandrasekhar limit (destroys WD)
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 Si II λ6150 Ib He I λ5876 Ic weak/no He
Also see Fe II, Ca II, O I
Late time supernovae spectra
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
Type II
Hydrogen lines
Light curves for Type IIL and IIP
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
Overview of supernovae classification scheme
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.
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
Spitzer image of the Crab Nebula, a type II (or Ib/Ic) supernova remnant. Missing mass may be due to WR progenitor.
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
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.
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
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 WD reaches Chandrasekhar limit Type II 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
Thank you!