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!