Zach Hartman Outline What are they good for How do we classify them Optical Ultraviolet How weird can they get DSSNASA A Fistful of B Stars Why do we care about B stars H II Regions More common than O stars ID: 572144
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Slide1
The B Stars Trilogy
Zach HartmanSlide2
Outline
What are they good for?
How do we classify them?
OpticalUltravioletHow weird can they get?
DSS/NASASlide3
A Fistful of B StarsSlide4
Why do we care about B stars?
H II Regions
More common than O stars
First large scale classification surveys were of B stars
Morgan 1950sWinds
Hui Yang NASASlide5
B stars matter!
Used to determine distances and ages of nearby open
clusters
GarrisonThe spiral structure of the Milky WayRadiative atmospheres made them perfect candidates for testing models
HSTSlide6
What does “B stars” mean?
18 Solar Masses
50,000 K
7 Solar RadiiL = 20,000 Solar LuminositySlide7
For a few B stars more
Optical EditionSlide8
How do we classify them?
Originally defined by presence of neutral He.
Peaks at B2
This is not the case for all B stars.
Si III is also presentAlong with H and Mg IISlide9
Example of a B3V
Harvard WebsiteSlide10
Temperature Classification
Use several line ratios and other lines
Si IV 4089/ Si III 4552
DecreasesMg IIIncreasesBalmer line strength increases dramaticallySlide11
O9V to B3V
Lines we are looking at:
Balmer Lines:
H9, H8, H
ε, Hδ, H
γ
Si IV 4089 / Si III 4552
He I increases over course of early B-types.
Mg II 4481 increasesSlide12
B3V to A0V
Lines we are looking at:
Balmer Lines:
H9, H8, H
ε, Hδ, H
γ
Si IV 4089 / Si III 4552
He I decreases over course of late B-types.
Mg II 4481 increaseSlide13
Complications
The Stark Effect
Interaction between electrons and ions causes Zeeman-like splitting
Electrical analogue of Zeeman splittingDominant broadening mechanism for Balmer and He I lines With increasing luminosity, the He I lines narrow and become more shallow for early B stars.For mid B stars, He I lines narrow and deepen.
Means an evolved B star can be confused with early BSlide14
Stark effect in spectraSlide15
Rotation
Broadens the lines
Two solutions
Use equivalent widthsUse rapidly rotating standardsSlide16
Luminosity Classifications
Early Type
Balmer and He I become narrow and shallow
O II (4070, 4076 4348 4416) all increase
Silicon is betterNot affected by CNO
H
γ
O IISlide17
Luminosity Classifications
Late Types
Hard
O II weak
Can use N II 3995Balmer lines best choiceIterative processFit He I profilesSlide18
For a Few B Stars More
Ultraviolet EditionSlide19
Ultraviolet Observations
Space Instruments
Wanted to observe these stars at the peak of their Planck curves.
International Ultraviolet Explorer (IUE)Heck et al. 1984 published a catalog of stars in the UVSlide20
IUE Spectra of B Stars
UV is difficult because there are resonance lines from winds
C IV, Si IV, N V
To match MK classification use photospheric lines
Si II/III, C II/III, Al II/IIISlide21
Using IUE Spectra as T Classifier
Lines to Remember:
Si II 1264/Si III 1299
Si II 1265/Si III 1342C II 1334,1335/ C III 1175
Al II 1671 / Al III 1863
CIII
Si II Si III
Si IV
Si IISlide22
Using IUE Spectra as T Classifier
Lines to Remember:
Si II 1264/Si III 1299
Si II 1265/Si III 1342C II 1334,1335/ C III 1175Al II 1671 / Al III 1863
Si II
Si II Si IIISlide23
Using IUE Spectra as L Classifier
Early Type Lines:
Al III 1855
Fe III linesSi IIWhy not Si IV or C IV?Slide24
Using IUE Spectra as L Classifier
Late Type Lines:
Al III 1670
Fe III
Si II 1265O I 1656Slide25
The Weird, the Peculiar and the BrilliantSlide26
The WeirdSlide27
Be Stars
B stars with emission in the Balmer lines
Achernar
Also emission in Fe IIComes from a hot circumstellar gas diskFormation mechanism unknownNot Herbig Ae/Be Stars or supergiants
Pre-MS StarsSlide28
Be and B Shell Star Classification
Two goals of classifying Be and B Shell stars
Get the spectral type of the star
Get the emission spectra(Temperature class)(Luminosity class)(Emission class)Emission spectra can be variable
Star spectra is constantSlide29
Classifying Be Stars
Mild Be stars are easy
Little H
α or Hβ emissionFor others:
He I or Mg II 4481Use line ratiosFor extreme Be starsGood Luck!
Intense Balmer EmissionSlide30
Types of Be Stars – Lesh classes
- No H emission, some H lines filled in
- H
β
has narrow emission, is still absorption line
- H
β
in emission
- H
γ
has narrow emission
- Complete H emission spectrum
- Fe II lines at more prominent
- Extreme Be stars
Slide31
Be Star line profiles
Contain information about system
Dachs et al. 1986/1987
4 classesSymmetric double peakWine bottleAsymmetric
ShellSlide32
Be Star line profiles
Hanuschik et al. 1996
Symmetric (Class 1)
Anti-symmetric (Class 2)
Function of inclination and optical depthSlide33
B Shell Spectra
Shell Spectrum instead of emission
Disk becomes shell
Deep, narrow cores in BalmerFe II and Ti II absorption linesSlide34
B[e] stars
Goal same as for Be stars
Get underlying stars
Harder because photospheric line are hiddenShow forbidden lines in spectra[Fe II] and [O II]
Strong IR excessMultiple SituationsBroad category
Types of B[e] Stars:
B[e] supergiants (sgB[e])
Pre-MS B[e] (HAeB[e])
Pne B[e] (cPNB[e])
Symbiotic B[e] (SymB[e])
Unclassified B[e] (unclB[e])Slide35
Types of B[e] Stars
Supergiant
LMC, SMC
cPNB[e]B stars going into the PNe phase
HAeB[e]Same as Herbig AeBePlus forbidden linesSlide36
B[e] Stars
Symbiotic
Shows hot and cool components
Unclassified
The “shrug” classDoes not fit any criteriaSlide37
The PeculiarSlide38
He-strong Stars
Early B
Strong He lines
Abnormally strongσ Ori EStrong C II 4267Some are variable
B fieldsMost have strong B fieldsSlide39
He-weak Stars
Late B
H lines used
3 classesSi starsEnhanced Si IIPGa
Phosphorus-gallium starsSrTiStrontium-titanium starsSlide40
HgMn StarsSlide41
The BrilliantSlide42
B stars in Advanced States
High Galactic Latitude Normal B stars
Faint blue stars
5 possibilitiessdOBBlue H BranchYoung stars in HaloPop 1 stars ejected from disk
Old evolved starsSlide43
sdOB Stars
2 groups
Stars at extreme end of Horizontal branch
Post PNe stars at tip of White dwarf sequenceMajority appear to be in close binariesSome are known to pulsate as well
Mochejska, B.J., APODSlide44
Spectral Classification
Set by Drilling et al. 2003
Adds Helium class to T and L
T class set by line ratios
He I/He IISi III/ Si IIHe Class is function of He I, II and H
γ
line strengths
0 to 40
No He to no H
L is either VI, VII, VIII
Line widthsSlide45
Spectral Classification
Set by Drilling et al. 2003
Adds Helium class to T and L
T class set by line ratios
He I/He IISi III/ Si IIHe Class is function of He I, II and H
γ
line strengths
0 to 40
No He to no H
L is either VI, VII, VIII
Line widthsSlide46
BINARIES
!
!
!!!!!!
UberBlinkSlide47
sdB + dM Binaries
Close binaries
Have periods from hours to days
More massive companion evolved and overflowed its Roche lobeEnvelope disappeared somehowSlide48Slide49
Conclusions
B stars are very useful and need to be found
Spectral Classification depends on He, Si, and H lines in the Optical
Photospheric lines in the UV (Si, C, Al)Many interesting and weird objects are B stars