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AMERICAVOTES!

Adric Riedel ASTR8600 2008 02 05

• 12% of nearby stars are K stars (68% are M stars)• K stars are the brightest dwarfs visible to the

unaided eye• Most of the red color of Pop II stars is K giants• All K star temperatures range between roughly

5180K and 3850K• Marked by the first appearance of TiO lines• Spectra no longer approximate blackbody• Not well studied (even the Kaler book has a lot of

filler)• K dwarfs could have tidally unlocked planets in their

habitable zones

Commonality of K stars3

TitleK star propertiesK star featuresDescriptions

Luminosity classesExamples:Class VII

Class IClass IIIClass V

S and C starsWorks Cited

• Luminosity range is smaller for K stars: -9.2 (RW Ceph, K0Ia-0) to 8.46 (HIP 20302, K9V)

• Luminosity Class VII (White Dwarfs) first appears in K stars (15.43 (GJ 223.2, DZ9) may actually be in the M star range.)

• Subdwarfs are still distinct in luminosity from Main Sequence stars in the K region.

Commonality of K stars4





• Not all luminosity classes or subtypes are equally meaningful.

• Keenan, 1985:

Spectral Features of K stars5





• “The letter K represents spectra of the later second type, or intermediate between the second and third types. The letter K may be briefly described as representing the spectra in which the bands K and H, the band G, and the line 4227.0 are the most conspicuous features, and in which the end of the shorter wave length is faint, and the distribution of light is not uniform with different parts of the spectrum. The hydrogen lines in this class are fainter than numerous solar lines”

• 'Second' and 'Third' are remnants of an earlier system

• 4227.0Å is CaI

The Henry Draper Catalog (1901)6





MKK System (1943)7

4030-4034 (Mn I) 4300 (G Band) K04290 (G band) 4300 (G Band) K0,K2,K3,K54226 (CaI) 4325 (Fe I) K2,K3,K54383 (Fe I) 4406 (Continuum) K54102 (H I) 4096 (Continuum) K0Luminosity indicators:4063 (Fe I) 4077 (Sr II) K0,K2,K3,K54071 (Fe I) 4077 (Sr II) K0,K2,K34045 (Fe I) 4077 (Sr II) K34144 (Fe I) 4077 (Sr II) K04260 (Fe I) 4215 (CN break) K3,K54325 (Fe I) 4340 (H I) K3Intensity of continuous spectrum across 4215 (K0,K2)





• “The G-band continues to increase in strength until the early K-type stars (about K2) and then begins to fade. The Ca I 4227 line grows gradually in strength until the early K stars, and then becomes dramatically stronger by mid-K... The temperature type may be estimated with precision, even in metal-weak stars by using the ratio of the Cr I 4254 line with the two neighboring Fe I lines at 4250 and 4260... Notice that the Cr I line (which arises from a low-lying level) becomes stronger in ratio with the two flanking Fe I lines, being clearly stronger than both by K5.

• In the K-type dwarfs, the spectral type may be estimated from the ratio of Ca I 4227 to Fe I 4383, in the sense that Ca I/Fe I grows toward later types. By M0, bands due to TiO become visible in the spectrum, and these strengthen quite dramatically toward later types; by M4.5 they dominate the spectrum.”Richard Gray's Spectral Atlas8





• Classified between 6000A and 9000A, instead of 3800A-4900A

• Boundary between K and M set based on continuum slope between 7700A and 8100A

• Ten types defined, like Cannon (1901), but unlike the MKK system (0,2,3,5) or the revised MK system (added K7 halftype)

Beaulieu et al. (2008, in prep)9





• G band breaks up in cooler subtypes• Ca I 4227 Å increases in strength with cooler subtypes• Ca II H and K lines weaken with cooler subtypes• Ba II visible in giant and supergiant atmospheres

(Boeshaar, private communication)... but also more prominent in Barium stars regardless of type.

• If you look in any atlas of spectral types, you will find the feature at 4077 Å marked as an ultimate line of Sr II, and used as an important criterion in estimating luminosity of the stars. Actually, however, this line is blended with rather strong lines of Y I, La II, Dy II and Fe I ( 4078). The iron line is not sensitive to luminosity, while abundance of the heavy elements is an important factor in determining the strength of the other contributors. (Keenan, 1984)







Keenan-McNeil Spectral Atlas





• Heavily studied in the blue part of the spectrum• the 'G' band visible in K stars and hotter (where

visible)• Inversions in the Calcium K bands• The 'CN' break at 4215A is stronger for supergiants

(though this depends on abundances of Carbon and Nitrogen)

• Color-magnitude diagrams (also useful for multiplicity)

Weeding out luminosity classes12

Keenan-McNeil Spectral Atlas





• epsilon Pegasi: K2 Ib

• (Alberio A: K3 II)

• (Pollux: K0 III & planet)

• Aldebaran: K5 III

• Arcturus: K1 III

• Alpha Centauri B: K1 V

• epsilon Eridani: K2 V & planet

• 61 Cygni A&B K5 V & K7 V

• GJ 223.2: DZ9 (VII)

Our Famous K Star Contenders13





GJ 223.2: DZ 9 white dwarf14

SSS plates assembled with Aladin Skyview


Luminosity classesExamples:

•Class VII•Class I

•Class III•Class V

•S and C starsWorks Cited

GJ 223.2: DZ 9 white dwarf15





epsilon Pegasi: K2 Ib supergiant16

http://www.seds.org/messier/Pics/More/m15cnoao.jpg






• Second brightest star in Pegasus, after Alpha Andromeda (!) (http://www.astro.uiuc.edu/~kaler/sow/enif.html)

• 150 Rsun, 10 Msun, 6700 Lsun, variable with erratic behavior

epsilon Pegasi: K2 Ib supergiant17





Aldebaran: K5 III giant18

http://www.df9cy.de/image_astro/moon_aldebaran.jpg






• Giant star, has changed to helium fusion

• 40 Rsun, 350 Lsun, variable star

• 13th brightest star in the sky

Aldebaran: K5 III giant19





Epsilon Eridani: K2 V dwarf20

NASA, ESA, and G. Bacon (STScI)






• Nearby young dwarf K star

• 0.85 Msun, 0.84 Rsun, 0.27 Lsun. ~600 Myr old (http://www.solstation.com/stars/eps-erid.htm)

epsilon Eridani: K2 V dwarf21





Alpha Centauri B: K0 V dwarf22

RECONS






• 21st brightest star in the sky

• ~17” away from the third brightest star in the sky

• ~6 Gyr old

• Only 1.338 parsecs away

• 0.92 Msun, 0.51 Lsun

SUN 14 39 35.1 -60 50 14.0 3.724 284.8 3 b GJ0559B V 1.34 K0 V CNS91 RECONS ALPHA CEN B, I dare you!

Alpha Centauri B: K0 V dwarf23





61 Cygni A&B: K5 V & K7 V24

Lowell Observatory, 1916 & 1951 photos(Possibly assembled by Guy K. McArthur)

Via solstation.com






61 Cygni AB (K5V, K7V)25

0.15 and 0.09 Solar Luminosities; 0.6 and 0.5 solar masses

Highest proper motion stars known in the 1800s

First stars with a known parallax (2/3 arcsec, by Bessel)Title

K star propertiesK star featuresDescriptions




• The Morgan & Keenan C,N, and S types extend into K as well, both as giants and dwarfs (Green, P. 1996, IAU symposium)

• S stars are thought to be halfway between main-sequence stars and C class Carbon Stars, with extra Yttrium and Zirconium in their upper atmospheres.

• C dwarfs are mass transfer recipients, and are fairly common

Various unusual oddballs: C and S stars26





• Note the extreme VO and ZrO absorption bands that reduce the 'continuum' to spikes.

S stars27





• C2 bands, CN bands, and apparently presence of C13 isotopes

C stars28





Works Cited30

Green, P.J. 1996, IAU #177 invited talk Keenan, P.C. 1985, Calibration of Fundamental

Stellar Quantities, 111, 121 Keenan, P.C. 1984, The MK Process and Stellar

Classification, 29 Turnshek, et al. “An Atlas of Digital Spectra of Cool

Stars” 1985 Star parameters from James Kaler's “Stars”:

http://www.astro.uiuc.edu/~kaler/sow/sowlist.html Politician images courtesy of Google Images





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