Stars
and Their Main Properties| Stars
and Their Main Properties |
Position, Distance, Distribution > s.a. astronomical
objects [clusters]; tests of general relativity [astrometry].
* Numbers: 1999, The
Digital Palomar Sky Survey has so far collected info on 2 
109 stars.
* Angular position: Hipparcos
satellite achieves milliarcsec accuracy for astrometry of 105 stars
[@ Watson Sci(97)feb].
* Distance ladder:
| Stars: | nearby ( 100
pc): clear spectrum ( 1000
pc)cepheids: novae: RR Lyrae: supernovae: pulsars: |
parallax apparent magnitude and spectral class. apparent magnitude and period. speed of shell and angular rate of expansion apparent magnitude. like novae; type I are standard candles. time delay at different wavelengths. |
| Clusters: | nearby ( 10–100 pc):distant ( 100 pc):globular: |
extended parallax, convergent point method. apparent magnitude and color index. variables in them. |
| Nebulae: | dark: | diagram of star count vs apparent magnitude |
| Galaxies: | nearby: distant: |
variables in them. Hubble's law. |
* Angular size: Use
stellar interferometers, down to about 0.003";
Works for 5–10% of the stars.
@ References: Rowan-Robinson 85 [distance]; Perryman PT(98)jun
[Hipparcos
astrometry mission]; Hirshfeld 01 [parallax]; Lebreton a0801 [rev,
status]; > s.a. solar system [stars in our neighborhood].
Other Overall Properties > s.a. astrophysics [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; 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, determined from gravitational effects on neighbors; For spectroscopic
and eclipsing binaries, 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).
* Rotation: Can be determine
from the broadening of spectral lines (gives a lower bound) or, for eclipsing
binaries, velocity curves; In principle, info about rotation in the interior
can be obtained from astroseismology.
* Size: In general,
can be determined from occultation by the Moon (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).
* Velocity: Radial velocity
is measured from Doppler shift.
@ Mass: Figer Nat(05)ap [observation
indicates M < 150 MSun];
Yungelson et al a0710-A&A [supermassive].
@ Age: Weiss & Schlattl ap/97/A&A
[solar]; Kaler 01 [I; r pw(01)feb];
Chaboyer SA(01)may [solution
of age problem].
@ Size: O'Murchadha PRL(86); Castellani et al MNRAS(99)ap/98 [gr
corrections for Sun]; Gaudi et al ApJ(03)ap/02 [measurement
by microlensing]; Mullan AJP(06)
[simple argument using Coulomb's Law and proton de Broglie wavelength].
@ Velocity: Dehnen ap/98-in
[distribution]; Kürster et al A&AL(99)ap [Proxima];
Skuljan et al MNRAS(99)ap [solar
neighborhood]; Brown et al ApJL(05)ap [largest
velocity]; Steinmetz et al AP(06)ap [RAVE
data release].
More Specific Features > s.a. gravitating
matter [metric, stability]; solar system [helioseismology];
{#Bayer [names]}.
* Astroseismology: 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 
Centauri
A [@ NS(90)jan13, 46].
@ Astroseismology: Kjeldsen & Bedding ap/00-in,
Aerts et al a0803-SP
[status].
@ Stellar spots: Heyrovsky & Sasselov ApJ(00)ap/99 [microlensing].
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Send feedback and suggestions to: bombelli<at>olemiss.edu – Modified
22 jul 2008