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M Giants M Giants

M Giants - PowerPoint Presentation

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M Giants - PPT Presentation

Gray and Corbally Chapter 8 Karen Garcia Georgia State University Outline Basic characteristics Spectral f eatures Mira variables Carbon stars ID: 295166

gray stars spectra corbally stars gray corbally spectra luminosity spectral bands carbon giants molecular temperature stellar sequence variables cycle oxides cool dissociation

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Slide1

M Giants

Gray and Corbally Chapter 8

Karen Garcia

Georgia State UniversitySlide2

Outline

Basic characteristics

Spectral

f

eatures

Mira variablesCarbon starsS type starsM MS S SC CSymbiotic stars Slide3

Basic Characteristics

T

eff

: 2200 – 3800K

Mass: 0.3 – 8M

☉Radii 20–100 R☉

Beta

Pegasi

Radius : 95R

Mass: 2.1 M

☉Slide4

Molecular Bands

Characteristic spectra in cool stars are caused by molecular bandsIn cooler stars more molecules form and surviveSlide5

Spectral Classification- Temperature

Dominant feature Titanium Oxide (TiO)Ca I λ4226 after M5Vanadium Oxide (VO) at M7Metallic lines decline – molecular features remove the background continuumSlide6

Gray and

Corbally pg 297Slide7

Spectral Classification-Luminosity

Luminosity indicator Ca I λ4226 line Negative luminosity effect – strength varies inversely with stellar brightnessSlide8

Gray and

Corbally pg 299Slide9

NIR Spectra

Temperature

TiO

and VO bands

Increase with decreasing temperature

LuminosityCaH and Na Dnegative luminosity effectSlide10

Gray and

Corbally

pg

300Slide11

Gray and

Corbally

pg

302Slide12

Mira Variables

Unstable interiors and atmospheres

Variation in temperature and luminosity (irregular, semi-regular, or fairly-regular)

Long period variables: 80-1000 days

Amplitude in luminosity ranges of 2.5-10 magnitudes

Spectra change throughout their light cycle, and from cycle to cycleSlide13

Mira Variables - Spectra

Similar to M giant spectra

Difference lies in the presence of H and Fe II

H and Fe II are visible during pulsation periodsSlide14

Gray and

Corbally

pg

305Slide15

Carbon Stars

Temperature and luminosities correspond to G, K, and M giants

Difference between M giants lies in the large overabundances of carbon relative to oxygen

Spectra is dominated by molecular bands due to molecules including CH, CN, C

2Slide16

CR Stars

Gray and

Corbally

pg 311Slide17

CN Stars

Gray and

Corbally

pg

315Slide18

CJ Stars

Gray and

Corbally

pg

318Slide19

CH Stars

Gray and

Corbally

pg

321Slide20

S type stars

Long period variables

Zirconium Oxide (

ZrO

)

Cover the same range of temperatures of M giantsMetallic oxides VO, YO, and LaOBridge between M giants and carbon starsSlide21

Gray and

Corbally

Pg

326Slide22

M MS S SC C sequence

M MS S strengthening of

ZrO

bands at expense of

TiO

bandsS SC C fading of ZrO bands, strengthening of Na I D lines, and the appearance of C2 and other carbon moleculesSlide23

Physical Basis of Sequence

Increase in C/O ratio

Two physical effects

Change in mean opacity in the cool atmosphere

As C/O increases, decrease in H

2O reduces mean opacityMolecular dissociation effectMetallic oxides with dissociation energies below 7eV experience dissociationAs C/O approaches unity metallic oxides dissociateSlide24

Stellar evolution M Giants

Alpha capture of

13

C nuclei can yield neutrons during helium shell burning which can lead to the production of many heavy elements via the s process (zirconium, technetium barium)

Convective currents in envelope dredge nuclear-processed, carbon-rich material from the helium burning shell region to the surfaceSlide25

Thermal pulses cause the episodic formation of deep convective currents that are able to dredge the carbon-rich, s process-rich material up to the surface

Successive dredge ups increase the C/O

ratio in the atmosphere of the star as well as the abundance of s process elements moving the star through the spectral type sequence

Stellar evolution M GiantsSlide26

Symbotic Stars

Symbiotic Stars

Interacting Binaries

UV – white

d

warf spectraOptical - cool giant spectraDistinguished from normal stars – strong Hydrogen emission lines, He II, [O III], Slide27

Gray and

Corbally

Pg

332Slide28

References

References

Gray, Richard, and Christopher

Corbally

.

Stellar Spectral Classification. New Jersey: Princeton University Press, 2009Kaler, James. Stars and their Spectra: An Introduction to the Spectral Sequence. New York: Cambridge University Press, 2011