Stars and Their Main Properties  

Intrinsic Properties > s.a. astrophysics; gravitating bodies in general relativity; star formation and evolution; types of stars.
* Age: The oldest reliably dated stars (e.g., in globular cluster M92) are at least 12 × 109 years old.
* Lifetime: On the main sequence, it ranges from about 106–107 yr for type O stars, to more than 1011 yr for type M.
* Luminosity: The energy emitted per unit time by an astronomical object; To measure, for relatively nearby stars compare distance (independently measured) and apparent magnitude, for others read off from position on HR diagram as determined from spectral class and luminosity class; It ranges between about 106 LSun and about 10−3 LSun.
* Luminosity class: A roman numeral representing the type of star (supergiants I, bright stars II, giants III, subgiants IV, main sequence V).
* Mass: In general, it can be determined from gravitational effects on neighbors or on light (lensing); For spectroscopic and eclipsing binaries, it can be found from velocity and light curves; Ranges between about 60 MSun (stars with larger masses are pulsationally unstable, although a few are known), and about 0.1 MSun, 80 MJup or so (would-be smaller stars become brown dwarves instead); 2010, The most massive known star is R136a1 with 320 solar masses at birth.
* Rotation: It can be determined from the broadening of spectral lines (this gives a lower bound) or, for eclipsing binaries, velocity curves; In principle, information about rotation in the interior can be obtained from asteroseismology.
* Size: In general, it can be determined from occultation by the Moon (this works for about 10% of the stars), temperature and use of Stefan's law, and interferometry; For eclipsing binaries, light curves (Sp B or A); Ranges from about 10 RSun for class O to about 0.1 RSun for class M on the main sequence, but reaches almost 103 RSun for supergiants and 10−2 RSun for white dwarfs.
* Spectral class: A letter (O B A F G K M) and number (for finer subdivisions) combination that is determined from the lines in a star's spectrum (ionized He in class O, ..., strong H lines in class A, ... molecular lines in class M) or comparison of luminosity in different wavelength ranges, and represents the star's temperature.
* Temperature: Determined from spectral class; Ranges from about 40,000 K (class O) to about 3000 K (class M).
@ General references: Kaler 97 [spectral sequence], 01 [extreme stars]; Torres PASP-a1107 [interferometric techniques]; Croswell SA(11)jul [HR diagram, 100 years]; King 12 [short introduction]; Basu Phy(19)jun [interior, stellar opacity calculations and measurememts].
@ Mass: Figer Nat(05)ap [observation indicates M < 150 MSun]; Maíz et al ApJ(07)ap/06 [upper limit]; Yungelson et al A&A(08)-a0710, Yusof et al a1012-proc [supermassive]; news pt(17)dec [radii and masses from stellar light curves]; news cosmos(18)may [core mass functions and initial mass functions].
@ Temperature: Cenadelli et al AJP(12)may [use of Wien's law, and complications]; Petrovay JHA(20)-a2003 [history].
@ Age: Weiss & Schlattl ap/97/A&A [solar]; Kaler 01 [I; r pw(01)feb]; Chaboyer SA(01)may [solution of age problem]; news nat(13)jan [oldest known star]; Lebreton et al proc(14)-a1410, proc(14)-a1410 [accuracy and stellar models]; Dolgov a1410-conf [stars older than the universe, possible mechanism]; Catelan IAU(17)-a1709 [rev].
@ Size: O'Murchadha PRL(86); Castellani et al MNRAS(99)ap/98 [general-relativistic corrections for the Sun]; Gaudi et al ApJ(03)ap/02 [measurement by microlensing]; Mullan AJP(06)jan [simple argument using Coulomb's Law and proton de Broglie wavelength].
@ Rotation: Barnes IAU(08)-a0906 [gyrochronology]; news pw(11)may [correlation between rotation rate, mass and age]; Maeder & Meynet IAU(15)-a1408; Kissin & Thompson ApJ(15)-a1501 [giant post-main sequence stars]; Reinhold & Arlt A&A(15)-a1501 [solar vs antisolar differential rotation].

Position, Distribution, Velocity > s.a. solar system [stars in our neighborhood].
* Surveys: 1999, The Digital Palomar Sky Survey has so far collected information on 2 × 109 stars.
* Angular position: Hipparcos satellite achieves milliarcsec accuracy for astrometry of more than 105 stars [@ Watson Sci(97)feb].
* Distance ladder: For nearby stars (100s of pc), parallax; Out to 1000s of pc (clear spectrum), apparent magnitude and spectral class; For Cepheids, apparent magnitude and period; For novae, speed of shell and angular rate of expansion; For RR Lyrae stars, apparent magnitude; For supernovae, like novae and type Ia are standard candles; For pulsars, time delay at different wavelengths; > s.a. star clusters; galaxy distribution; interstellar matter.
* Angular size: Use stellar interferometers, down to about 0.003"; It works for 5–10% of the stars.
* Velocity: Radial velocity is measured from Doppler shift, transverse velocity from proper motion and precision astrometry.
* Hypervelocity stars: Stars leaving our galaxy with speeds of nearly 1000 km/s, providing strong evidence for the existence of a massive compact object at the galaxy's center; Calculations indicate that occasionally they could be moving at up to 100,000 km/s, or c/3; > s.a. cosmology; supernovae.
@ General references: Rowan-Robinson 85 [distance]; Lebreton IAU(07)-a0801 [rev, status].
@ Astrometry: Perryman PT(98)jun [Hipparcos mission]; Perryman 10; Turon et al ASS-a1202-conf [from Hipparcos to Gaia]; Malbet et al SPIE(12)-a1207 [NEAT proposal]; Perryman EPJH(12)-a1209 [history]; Høg a1408-conf [impact of ESA's astrometric satellites], a1408 [the next 50 years], a1408-proc [1960-1980]; Finch et al AJ(14)-a1408 [stars within 25 pc of the Sun]; Massari et al a1607-in [high-precision]; Astraatmadja & Bailer-Jones ApJ(16)-a1609 [parallax errors]; Høg a1804 [Hipparcos satellite]; > s.a. astronomy; Gaia Mission; milky way galaxy [the most distant stars]; tests of gravity theory.
@ Parallax: Hirshfeld 02; Riess et al ApJ(14)-a1401 [up to 5 kpc]; Bailer-Jones PASP(15)-a1507 [detailed tutorial].
@ Velocity: Dehnen ap/98-proc [distribution]; Brown et al ApJL(05)ap [largest velocity]; Steinmetz et al AP(06)ap [RAVE data release].
@ Hypervelocity stars: Guillochon & Loeb ApJ-a1411; Capuzzo-Dolcetta & Fragione a1507-MG14 [and supermassive black holes]; Brown PT(16)jun.
@ Nearby stars: Kürster et al A&AL(99)ap [Proxima]; Skuljan et al MNRAS(99)ap; Bovy et al ApJ(09)-a0905; Mamajek et al ApJL(15)-a1502 [closest past flyby of a star]; Pourbaix & Boffin A&A(16)-a1601 [alpha Centauri]; Heifetz & Tirion 17 [constellations].

More Specific Features > s.a. gravitating matter [metric, stability]; solar system [helioseismology]; {#Bayer [names]}.
* Asteroseismology: The study of oscillations and perturbations in stars; Useful for probing the internal structure of stars; For example, in addition to the Sun, oscillations have been discovered in HR1217 in Ap and α Centauri A [@ NS(90)jan13, 46].
* Magnetic field: Magnetic fields in stars are detected using the Zeeman effect and observing stellar spectra.
@ Asteroseismology: Kjeldsen & Bedding ap/00-proc, Aerts et al SP(08)-a0803 [status]; Christensen-Dalsgaard & Houdek ApSS(10)-a0911; Handler a1205-in; Lebreton proc(13)-a1312 [and stellar age determination]; Aerts PT(15)may, RMP(21) [rev].
@ Stellar spots: Heyrovský & Sasselov ApJ(00)ap/99 [microlensing].
@ Other features: Kallinger & Matthews ApJL(10)-a1001 [evidence for granulation]; Vink ApSS(11)-a1112 [stellar winds]; Schöoler & Hubrig a1501-ch [magnetic fields].

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