Reach for the Stars SciO Reference Sheet

Star Apparent Mgn(s).

Spectral Class Absolute Mgn(s).

Light Yrs. Right Ascension

Declination Surface Temperature

Solar/Stellar Masses

Altair (Aquila) 0.77 A7 V (White, Main Sequence

2.20 16.73 ± 0.05 19h 50m 46.99855s +08° 52′ 05.9563″ 6,900 – 8,500 K 1.79

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Capella (Auriga) 0.91 G1 III (Yellow, “Normal” Giant)

0.40 42.2 ± 0.5 05h 16m 41.3591s +45° 59′ 52.768″ 4,940 ± 50 K, 5,700 ± 100 K

2.69 ± 0.06A/2.56 ± 0.04B

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ET Arcturus (Boötes) –0.04 K1.5 III (Orange, “Normal”

Giant)–0.29 36.7 ± 0.3 14h 15m 39.7s +19° 10' 56" 4,290 ± 43 K 1.10 ± 0.06

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Sirius (Canis Major)

–1.46 A1 V (White, Main Sequence)

1. 33 8.60 ± 0.04 06h 45m 08.9173s −16° 42′ 58.017″ 9,940 K 2.02A/.978B

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Procyon (Canis Minor)

0.74 F5 IV–V (Yellow-White, Subgiant)

2.8 11.46 ± 0.05 07h 39m 18.11950s +05° 13′ 29.9552″ 6,530 ± 50 K 1.42 ± 0.04A/0.602 ± 0.015B

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Proxima Centauri (Centaurus)

1.33 G2 V (Yellow, Main Sequence)

4.38 – 5.71

4.366 ± 0.007 14h 29m 42.9487s −62° 40′ 46.141″ 3,042 ± 117 K 0.123 ± 0.006

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Mira (Cetus) 3.04 M7 IIIe (Red, “Normal” Giant)

–2.5 – +4.7 Approx. 300 02h 19m 20.79210s –02° 58′ 39.4956″ 2,918 – 3,192 K 1.18

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Deneb (Cygnus) 1.25 A2 Ia (White, Luminous Supergiant)

–7.00 Approx. 1400 20h 41m 25.9s +45° 16′ 49″ 8,525 K ~20

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Castor, Pollux (Gemini)

1.58, 1.14 A1 V (White, Mn. Sq.), K0 III (Orange, “Normal” Giant)

0.58, 1.08 49.8 ± 0.8, 33.78 ± 0.09

07h 34m 36s, 07h 45m 18.94987s

+31° 53' 18", +28° 01′ 34.3160″

10,286 K 2.76A/2.98B

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; 2.04 ± 0.3

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Gliese 581 (Libra) 10.56–10.58 M3 V (Red, Main Sequence) 11.6 20.3 ± 0.3 15h 19m 26.8250s −07° 43′ 20.209″ 4,666 ± 95 K 0.31

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Regulus (Leo) 1.38 B7 V (Blue-White, Main Sequence)

–0.52 77 ± 1 A: 10h 08m 22.3s +11° 58′ 02″ 12,460 ± 200 K 3.8

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Vega (Lyra) 0.03 A0 V (White, Main Sequence)

0.58 25.04 ± 0.07 18h 36m 56.33635s +38° 47′ 01.2802″ 9602 ± 180 K 2.135 ± 0.074

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Betelgeuse, Rigel (Orion)

0.42, 0.12 M2 Ia (Red, Luminous Supergiant), B8 Iae (Blue-

White, Luminous Supergiant)

–6.05, –7.84 ± 0.2

643 ± 146, 860 ± 80

05h 55m 10.3053s, 05h 14m 32.27210s

+07° 24′ 25.426″, −08° 12′ 05.8981″

3,500 K; 12,130 K ~18–19

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; 24 ± 3

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Algol (Perseus) 2.12 B8 V (Blue-White, Main Sequence)

–0.15 93 ± 2 03h 08m 10.1315s +40° 57′ 20.332″ 9,200/4,500/8,500 K 3.59/0.79/1.67

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Antares (Scorpius)

0.96 M1.5 Ib (Red, Less Luminous Supergiant)

–5.28 Approx. 550 16h 29m 24s –26° 25′ 55″ 3400 ± 200 K 12.4A/10B

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Aldebaran (Taurus)

0.75–0.95 K5 III (Orange, “Normal” Giant)

–0.63 65 ± 1 04h 35m 55.239s +16° 30′ 33.49″ 3,910 K 1.7

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Polaris (Ursa Minor)

1.97 F7 Ib (Yellow-White, Less Luminous Supergiant)

–3.63 ± 0.14

433 ± 6 02h 31m 49.09s +89° 15′ 50.8″ 7,200 K 7.54 ± 0.6

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Mizar, Alcor (Ursa Major)

2.23, 2.23 A2 V (White, Main Sequence), A2 V (White,

Main Sequence)

0.33, 0.33 82.8 ± 0.6, 82.8 ± 0.6

13h 23m 55.5s +54° 55′ 31” 9,600 K; 8,000 K 7.7

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Spica (Virgo) 1.04 B1 III-IV (Blue-White, “Normal” Giant)

–3.55 260 ± 20 13h 25m 11.5793s −11° 09′ 40.759″ 18,500 K 10.25 ± 0.68

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Spectral Class

Intrinsic Color Temperature (K)

Prominent Absorption/Spectral Lines

O Blue 41000 He+, O++, N++, Si++, He, H/Ionized He

B Blue 31000 He, H, O+, C+, N+, Si+/He, some H

A Blue-white 9500 H (strongest), Ca+, Mg+, Fe+/Strong H, some ionized metals

F White 7240 H(weaker), Ca+, ionized metals/H, ionized Ca, Fe

G Yellow-white 5920 H(weaker), Ca+, ionized & neutral metal/Neutral & ionized metals, esp.

Ca; strong G band

K Orange 5300 Ca+(strongest), neutral metals strong, H(weak)/Neutral metals, Na

M Red 3850 Strong neutral atoms, TiO/Strong titanium oxide, very strong sodium

Cepheid Variables – K-F supergiants, few tenths of mag. –2 mag., 70 days, important: length of pulsation related to absolute magnitude, longer period of variation, brighter star is. Divided into Classical, Type II, Anomalous, and

Dwarf Cepheids. (Red)

RR Lyrae Variables–Old A stars, vary by 1-2 mag. Last hour to day. Pulse in manner similar to Cepheids (blue).Long-Period Variables–Old M stars, vary by several mag. over 80-1000 days, a.k.a. Mira stars; Sun will become this.Irregular/Semiregular–Red supergiants vary in size/magnitude.

Variation of variables may caused by pulsation or eruption in star. Pulsating variables actually shrink/swell because of forces inside star. In Eruptive variables, there are flares/ejections from star, cause changes. Another variable: cataclysmic variable wherein an outburst stellar material into space causing intense brightness.

Winter Triangle – Betelgeuse, Procyon, SiriusSummer Triangle – Deneb, Vega, AltairWhite dwarfs no longer produce energy, takes a while for them to cool down. Because of small surface area, cooling down takes a long, long time.

Standard Candle–By comparing the known luminosity of latter to its observed brightness, the distance to the object can be computed using the inverse square law. Two problems: principal one’s calibration, how standard they are.

Population I Stars: Metal-rich, in young stars metallicity is highest, found in spiral arms.Population II Stars: Metal-poor, older stars, found in globular clusters, center of galaxy

Fuel of Stars – (H, He700000y) [C600y, O6mon, N*, Ne1y, Na*, Mg*, Si1day, S*, Ar*, Ca*, Ni*, Cr*, Cu*, Fe] {Sr*, Zr*}

Sun classified as yellow dwarf; G2 V star, main sequence

Will become Mira variable after 5 billion years.

Ia – Most Luminous SupergiantsIb – Less Luminous SupergiantsII –Luminous GiantsIII – Normal GiantsIV – SubgiantsV – Main Sq. +DwarfsVI – SubdwarfsVII – White Dwarfs0 hotter, 9 cooler

1⁄3,600o–1 arcsecond

1/60o–1 arcminute

1 parsec–3.262 ly–31 trillion km, ~19 trillion mi., 18,319,376,145,600 mi

1 AU–4.85×10−6 pc;149,597,870.7 kmLight Year –5,869,713,600,000 mi

Spectroscopic Parallax–Used for determining distance to stars. To apply method, one must measure apparent magnitude and know spectral type of star. Method limited to 10000 parsecs. d = 10^{(mv-Mv+5)/5}

Cephei Light Curve/Type Iδ Classical Cepheid

Mira Variable Light Curve

RV Tauri variables –Yellow supergiants, mostly G and K-class stars. Distinctive light curves show alternating deep-shallow minima with period equal to time between two successive deep minima. Typical values 20–100 days.

Flare Stars - Variable star capable of unpredictably brightening dramatically for a few minutes. Flare stars flare because of “magnetic reconnections”* in the atmosphere of the stars.

Hubble Sequence – Ellipticals (E0, E3, E5, E7, S0), Spirals (Sa, Sb, Sc), Barred Spirals (SBa, SBb, SBc)Spiral arms become “wider”, stretched out

W Virginis Cepheids –Intrinsically less luminous by 1.5-2 mag. than Type I Classical Cepheids, W Virginis Cepheids have typical periods of 12-30 days. As they older stars than Type I spectra characterized by having lower metallicities. Type II light curves show characteristic bump on decline side, have amplitude range of 0.3-1.2 mag.

Why Stars Pulsate1. If pressure outwards exceeds gravitational force inwards, outer layers of star expand outwards. 2. As star expands, gravitational force inwards diminish but outwards pressure drops at even greater rate.3. Eventually star would reach position which hydrostatic equilibrium occurs: gravity=pressure. However, outward moving layers have momentum so resist change in motion. Momentum carries layer past equilibrium position.4. As gravitational force acts on layer, slows down. Point reached where stops, now outward gas and radiation pressure’s weaker than inward-acting gravitational force. 5. Imbalanced forces causes star's outer layers collapse inwards. 6. As layers collapse gravity increases but pressure increases at greater rate.7. With pressure outwards exceeding inwards gravitational force collapsing layer slows down, eventually stops.

RR Lyrae Variables–Old population II giant stars mostly found globular clusters. Characterized by their short periods, about 1.5 hours a day + have brightness range of ~0.3–2 mag. Spectral classes range from A7– F5. RR Lyrae stars less massive than Cepheids, also follow own period-luminosity relationship, with mean absolute mag. of 0.6. Thus are useful in determining distances to globular clusters within which they commonly found to distance of ~200 kiloparsecs. Sub-types classified according to shape of light curves. RR Lyraes fit on Instability Strip on HR diagram.

Hydrogen Spectral Lines

Helium Spectral Lines

Science studying wave oscillations in Sun called helioseismology. Temperature, composition, motions deep in Sun influence oscillation periods, yield insights in conditions in solar interior.

Core of star is intense. Pressures are enormous, temperatures ≥15 million Kelvin. But these are kind of conditions needed for nuclear fusion. Once conditions are reached in core of a star, nuclear fusion converts H atoms to He atoms through multi-stage process.

Hydrostatic equilibrium–Gravity compression is balanced by pressure outward.Thermal equilibrium–If energy is flowing outward faster than it is being generated, then the interior is cooling; this lowers the gas pressure, and the star will shrink. But as the star shrinks, the density will increase and the release of gravitational energy will go into heating up the material.

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Reach for the Stars SciO Reference Sheet