Number Densities of Stars of Different Types in the Solar Vicinity
Eric Mamajek
What fraction of the stars in the solar neighborhood of are of given spectral class?
A good starting point is Chapter 19 of Cox's (2000) "Allen's
Astrophysical Quantities" (AIP Press: Springer, New York). However I
wanted to be able to answer this question by stellar type. I decided
to check the latest census of nearby stars from Todd Henry's
RECONS survey, and I'd
like to acknowledge the hard work of his team which has been helping
fill in the census of nearby objects from all angles (fast-moving
stars, slow-moving stars, "blue" stars, "red" stars, etc.). T. Henry
has made several plots describing the nearby 10 pc sample
here. I also refer back
to calculations done by
Kroupa et
al. (1993).
The overall number density of
stars in the solar neighborhood
is approximately
0.0984±0.0068 star/pc^3 (i.e. ~0.10
stars per cubic parsec), including white dwarfs, but
not
including brown dwarfs, neutron stars, or black holes. Approximately
~0.092 star/pc^3 of this number density is just M dwarfs, with the remaining ~0.026 due to all
other types of stars. Hence, M dwarfs represent approximately ~78% of
all stars (depending on how it is calculated, this number seems to
consistently come up in the 70-80% range).
Star Type
# Density (pc^-3)
Fraction of stars
Reference
Comments
O stars
4.4e-8(±2.0e-8)[#1]
~5e-7
(1 in ~2,000,000)
EEM
#1: cross-referenced GOSS (Sota+2014) catalog w/van Leeuwen(2007) & Gaia DR1 TGAS.
N=5 O-type stars w/ plx> 3.33 mas (d<300pc): zeta Oph, delta Ori, zeta Ori, 15 Mon, HD 37737. Parallaxes very poor beyond that for most stars.
B stars
3.2e-5(±4.7e-6) [#1]
3.9e-4
(1 in 2600)
EEM
#1: calc from HIP2 (B-type, Mv < 2, plx/e(plx)>8, d<70pc, N=46)
A stars
4.9e-4(±6.6e-5) [#1]
6.0e-3
(1 in 170)
EEM
#1: calc from HIP2 (A-type, Mv<4, plx/e(plx)>8, d<30pc, N=55)
G stars
(all lum class)
0.0048(±0.0011) [#1]
0.00332(±0.00044)[#2]
0.059
(1 in 17)
#1: calc from RECONS (10pc, N=20, likely complete)
#2: EEM SIMBAD plx>62.5 (d<16pc) (N=57), vetted for binarity, best SpTs, junk parallaxes.
G dwarfs
0.0033(±0.0004) [#1]
0.0038(±0.0010) [#2]
0.0037(±0.0013) [#3]
0.041
(1 in 25)
EEM
#1: calc from Mamajek+08 (16pc, N=57, likely complete)
#2: calc from Mamajek+08 (10pc, N=16, likely complete)
#3: calc from Kirkpatrick+12 (8pc, N=8, complete)
Note: del Pav (6.1pc) classified G8IV, but within 0.8 mag of MS (so "dwarf")
K dwarfs
0.0105(±0.0016) [#1]
0.0135(±0.0025) [#2]
0.0153(±0.0054) [#3]
0.0083(±0.0007) [#4]
0.129
(1 in 7.8)
EEM
#1: calc from RECONS (10pc, N=44, likely complete)
#2: calc from Kirkpatrick+12 (8pc, N=29, likely complete)
#3: calc from Kirkpatrick+12 (5pc, N=8, likely complete)
#4: all K stars: calc from SIMBAD (16pc, N=143, 7 are evolved; looks incomplete for dwarfs)
M dwarfs
0.0676(±0.0040) [#1]
0.0859(±0.0086) [#2]
0.0917(±0.0132) [#3]
0.0917(±0.0132) [#4]
0.725
(1 in 1.38)
EEM
#1: calc from RECONS (10pc, N=283, 2018.3)
#2: calc from Kirkpatrick+12 (6.527pc, N=100)
#3: calc from Kirkpatrick+12 (5pc, N=48, likely complete)
#4: calc from Winters+19 (5pc, N=48, likely complete)
white dwarfs
(e.g. DA, DB, DC, DQ, DZ, etc.)
0.0048(±0.0011)[#1]
0.0051(±0.0015)[#2]
0.0048(±0.0005)[#3]
0.0055(±0.0001)[#4]
0.00449(±0.00038)[#5]
0.059
(1 in 17)
EEM
#1: calc from RECONS 10 pc sample (N=20 as of 2012.0)
#2: calc from Kirkpatrick+2012 8 pc sample (N=11)
#3:
Holberg+ 2016
#4:
Munn+ 2017
#5:
Hollands+ 2018
"Evolved stars"
8.8e-4
0.011
(1 in 93)
EEM
includes stars just leaving main sequence, subgiants, giants, calc using HIP2 for Mv> 1 mag away from Wright 2004 main sequence, Mv < 4.5
(d < 35 pc; N=158)
"Red Giants"
2.7e-4(±4.9e-5)[#1]
3.3e-3
(1 in 300)
EEM
#1: G/K/M giants only, N=31 w/i d<30pc (using van Leeuwen 2007 HIP parallaxes)
all stars
OBAFGKM *s + WDs
ignoring NSs & BHs
0.0902(±0.0046)[#1]
0.0936(±0.0134)[#2]
0.0984(±0.0068)[#3]
1
EEM
#1: calc from RECONS 10 pc sample (N=378; 2018.3)
#2: calc from Kirkpatrick+2012 5 pc sample (N=49)
#3: calc from Kirkpatrick+2012 8 pc sample (N=211)
Star Type
# Density (pc^-3)
Fraction of stars
Reference
Comments
All of the densities should be interpreted as lower limits. HIP2 =
revised HIPPARCOS catalog (van Leeuwen 2007). Volume limits were
selected to ensure reasonable completeness in Hipparcos catalog,
taking into account the observed HR diagram for nearby stars
constructed
here. The
giants and evolved stars are assumed to be single (i.e. each HIP entry
is a single giant), so the number is a lower limit.
